Dose mapping: validation in 4D dosimetry with measurements and application in radiotherapy follow-up evaluation.

PubMed

Zhang, Geoffrey G; Huang, Tzung-Chi; Forster, Ken M; Lin, Kang-Ping; Stevens, Craig; Harris, Eleanor; Guerrero, Thomas

2008-04-01

The purpose of this paper is to validate a dose mapping program using optical flow method (OFM), and to demonstrate application of the program in radiotherapy follow-up evaluation. For the purpose of validation, the deformation matrices between four-dimensional (4D) CT data of different simulated respiration phases of a phantom were calculated using OFM. The matrices were then used to map doses of all phases to a single-phase image, and summed in equal time weighting. The calculated dose should closely represent the dose delivered to the moving phantom if the deformation matrices are accurately calculated. The measured point doses agreed with the OFM calculations better than 2% at isocenters, and dose distributions better than 1mm for the 50% isodose line. To demonstrate proof-of-concept for the use of deformable image registration in dose mapping for treatment evaluation, the treatment-planning CT was registered with the post-treatment CT image from the positron emission tomography (PET)/CT resulting in a deformation matrix. The dose distribution from the treatment plan was then mapped onto the restaging PET/CT using the deformation matrix. Two cases in which patients had thoracic malignancies are presented. Each patient had CT-based treatment planning for radiotherapy and restaging fluorodeoxy glucose (FDG)-PET/CT imaging 4-6 weeks after completion of treatments. Areas of pneumonitis and recurrence were identified radiographically on both PET and CT restaging images. Local dose and standard uptake values for pneumonitis and recurrence were studied as a demonstration of this method. By comparing the deformable mapped dose to measurement, the treatment evaluation method which is introduced in this manuscript proved to be accurate. It thus provides a more accurate analysis than other rigid or linear dose-image registration when used in studying treatment outcome versus dose.

How accurately can the peak skin dose in fluoroscopy be determined using indirect dose metrics?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, A. Kyle, E-mail: kyle.jones@mdanderson.org; Ensor, Joe E.; Pasciak, Alexander S.

Purpose: Skin dosimetry is important for fluoroscopically-guided interventions, as peak skin doses (PSD) that result in skin reactions can be reached during these procedures. There is no consensus as to whether or not indirect skin dosimetry is sufficiently accurate for fluoroscopically-guided interventions. However, measuring PSD with film is difficult and the decision to do so must be madea priori. The purpose of this study was to assess the accuracy of different types of indirect dose estimates and to determine if PSD can be calculated within ±50% using indirect dose metrics for embolization procedures. Methods: PSD were measured directly using radiochromicmore » film for 41 consecutive embolization procedures at two sites. Indirect dose metrics from the procedures were collected, including reference air kerma. Four different estimates of PSD were calculated from the indirect dose metrics and compared along with reference air kerma to the measured PSD for each case. The four indirect estimates included a standard calculation method, the use of detailed information from the radiation dose structured report, and two simplified calculation methods based on the standard method. Indirect dosimetry results were compared with direct measurements, including an analysis of uncertainty associated with film dosimetry. Factors affecting the accuracy of the different indirect estimates were examined. Results: When using the standard calculation method, calculated PSD were within ±35% for all 41 procedures studied. Calculated PSD were within ±50% for a simplified method using a single source-to-patient distance for all calculations. Reference air kerma was within ±50% for all but one procedure. Cases for which reference air kerma or calculated PSD exhibited large (±35%) differences from the measured PSD were analyzed, and two main causative factors were identified: unusually small or large source-to-patient distances and large contributions to reference air kerma from cone beam computed tomography or acquisition runs acquired at large primary gantry angles. When calculated uncertainty limits [−12.8%, 10%] were applied to directly measured PSD, most indirect PSD estimates remained within ±50% of the measured PSD. Conclusions: Using indirect dose metrics, PSD can be determined within ±35% for embolization procedures. Reference air kerma can be used without modification to set notification limits and substantial radiation dose levels, provided the displayed reference air kerma is accurate. These results can reasonably be extended to similar procedures, including vascular and interventional oncology. Considering these results, film dosimetry is likely an unnecessary effort for these types of procedures when indirect dose metrics are available.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Y; Liu, B; Liang, B

Purpose: Current CyberKnife treatment planning system (TPS) provided two dose calculation algorithms: Ray-tracing and Monte Carlo. Ray-tracing algorithm is fast, but less accurate, and also can’t handle irregular fields since a multi-leaf collimator system was recently introduced to CyberKnife M6 system. Monte Carlo method has well-known accuracy, but the current version still takes a long time to finish dose calculations. The purpose of this paper is to develop a GPU-based fast C/S dose engine for CyberKnife system to achieve both accuracy and efficiency. Methods: The TERMA distribution from a poly-energetic source was calculated based on beam’s eye view coordinate system,more » which is GPU friendly and has linear complexity. The dose distribution was then computed by inversely collecting the energy depositions from all TERMA points along 192 collapsed-cone directions. EGSnrc user code was used to pre-calculate energy deposition kernels (EDKs) for a series of mono-energy photons The energy spectrum was reconstructed based on measured tissue maximum ratio (TMR) curve, the TERMA averaged cumulative kernels was then calculated. Beam hardening parameters and intensity profiles were optimized based on measurement data from CyberKnife system. Results: The difference between measured and calculated TMR are less than 1% for all collimators except in the build-up regions. The calculated profiles also showed good agreements with the measured doses within 1% except in the penumbra regions. The developed C/S dose engine was also used to evaluate four clinical CyberKnife treatment plans, the results showed a better dose calculation accuracy than Ray-tracing algorithm compared with Monte Carlo method for heterogeneous cases. For the dose calculation time, it takes about several seconds for one beam depends on collimator size and dose calculation grids. Conclusion: A GPU-based C/S dose engine has been developed for CyberKnife system, which was proven to be efficient and accurate for clinical purpose, and can be easily implemented in TPS.« less

Dose calculation algorithm of fast fine-heterogeneity correction for heavy charged particle radiotherapy.

PubMed

Kanematsu, Nobuyuki

2011-04-01

This work addresses computing techniques for dose calculations in treatment planning with proton and ion beams, based on an efficient kernel-convolution method referred to as grid-dose spreading (GDS) and accurate heterogeneity-correction method referred to as Gaussian beam splitting. The original GDS algorithm suffered from distortion of dose distribution for beams tilted with respect to the dose-grid axes. Use of intermediate grids normal to the beam field has solved the beam-tilting distortion. Interplay of arrangement between beams and grids was found as another intrinsic source of artifact. Inclusion of rectangular-kernel convolution in beam transport, to share the beam contribution among the nearest grids in a regulatory manner, has solved the interplay problem. This algorithmic framework was applied to a tilted proton pencil beam and a broad carbon-ion beam. In these cases, while the elementary pencil beams individually split into several tens, the calculation time increased only by several times with the GDS algorithm. The GDS and beam-splitting methods will complementarily enable accurate and efficient dose calculations for radiotherapy with protons and ions. Copyright © 2010 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

An Approach in Radiation Therapy Treatment Planning: A Fast, GPU-Based Monte Carlo Method.

PubMed

Karbalaee, Mojtaba; Shahbazi-Gahrouei, Daryoush; Tavakoli, Mohammad B

2017-01-01

An accurate and fast radiation dose calculation is essential for successful radiation radiotherapy. The aim of this study was to implement a new graphic processing unit (GPU) based radiation therapy treatment planning for accurate and fast dose calculation in radiotherapy centers. A program was written for parallel running based on GPU. The code validation was performed by EGSnrc/DOSXYZnrc. Moreover, a semi-automatic, rotary, asymmetric phantom was designed and produced using a bone, the lung, and the soft tissue equivalent materials. All measurements were performed using a Mapcheck dosimeter. The accuracy of the code was validated using the experimental data, which was obtained from the anthropomorphic phantom as the gold standard. The findings showed that, compared with those of DOSXYZnrc in the virtual phantom and for most of the voxels (>95%), <3% dose-difference or 3 mm distance-to-agreement (DTA) was found. Moreover, considering the anthropomorphic phantom, compared to the Mapcheck dose measurements, <5% dose-difference or 5 mm DTA was observed. Fast calculation speed and high accuracy of GPU-based Monte Carlo method in dose calculation may be useful in routine radiation therapy centers as the core and main component of a treatment planning verification system.

SU-E-J-100: The Combination of Deformable Image Registration and Regions-Of-Interest Mapping Technique to Accomplish Accurate Dose Calculation On Cone Beam Computed Tomography for Esophageal Cancer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, B-T; Lu, J-Y

Purpose: We introduce a new method combined with the deformable image registration (DIR) and regions-of-interest mapping (ROIM) technique to accurately calculate dose on daily CBCT for esophageal cancer. Methods: Patients suffered from esophageal cancer were enrolled in the study. Prescription was set to 66 Gy/30 F and 54 Gy/30 F to the primary tumor (PTV66) and subclinical disease (PTV54) . Planning CT (pCT) were segmented into 8 substructures in terms of their differences in physical density, such as gross target volume (GTV), venae cava superior (SVC), aorta, heart, spinal cord, lung, muscle and bones. The pCT and its substructures weremore » transferred to the MIM software to readout their mean HU values. Afterwards, a deformable planning CT to daily KV-CBCT image registration method was then utilized to acquire a new structure set on CBCT. The newly generated structures on CBCT were then transferred back to the treatment planning system (TPS) and its HU information were overridden manually with mean HU values obtained from pCT. Finally, the treatment plan was projected onto the CBCT images with the same beam arrangements and monitor units (MUs) to accomplish dose calculation. Planning target volume (PTV) and organs at risk (OARs) from both of the pCT and CBCT were compared to evaluate the dose calculation accuracy. Results: It was found that the dose distribution in the CBCT showed little differences compared to the pCT, regardless of whether PTV or OARs were concerned. Specifically, dose variation in GTV, PTV54, PTV66, SVC, lung and heart were within 0.1%. The maximum dose variation was presented in the spinal cord, which was up to 2.7% dose difference. Conclusion: The proposed method combined with DIR and ROIM technique to accurately calculate dose distribution on CBCT for esophageal cancer is feasible.« less

A methodological approach to a realistic evaluation of skin absorbed doses during manipulation of radioactive sources by means of GAMOS Monte Carlo simulations

NASA Astrophysics Data System (ADS)

Italiano, Antonio; Amato, Ernesto; Auditore, Lucrezia; Baldari, Sergio

2018-05-01

The accurate evaluation of the radiation burden associated with radiation absorbed doses to the skin of the extremities during the manipulation of radioactive sources is a critical issue in operational radiological protection, deserving the most accurate calculation approaches available. Monte Carlo simulation of the radiation transport and interaction is the gold standard for the calculation of dose distributions in complex geometries and in presence of extended spectra of multi-radiation sources. We propose the use of Monte Carlo simulations in GAMOS, in order to accurately estimate the dose to the extremities during manipulation of radioactive sources. We report the results of these simulations for 90Y, 131I, 18F and 111In nuclides in water solutions enclosed in glass or plastic receptacles, such as vials or syringes. Skin equivalent doses at 70 μm of depth and dose-depth profiles are reported for different configurations, highlighting the importance of adopting a realistic geometrical configuration in order to get accurate dosimetric estimations. Due to the easiness of implementation of GAMOS simulations, case-specific geometries and nuclides can be adopted and results can be obtained in less than about ten minutes of computation time with a common workstation.

An accurate derivation of the air dose-rate and the deposition concentration distribution by aerial monitoring in a low level contaminated area

NASA Astrophysics Data System (ADS)

Nishizawa, Yukiyasu; Sugita, Takeshi; Sanada, Yukihisa; Torii, Tatsuo

2015-04-01

Since 2011, MEXT (Ministry of Education, Culture, Sports, Science and Technology, Japan) have been conducting aerial monitoring to investigate the distribution of radioactive cesium dispersed into the atmosphere after the accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), Tokyo Electric Power Company. Distribution maps of the air dose-rate at 1 m above the ground and the radioactive cesium deposition concentration on the ground are prepared using spectrum obtained by aerial monitoring. The radioactive cesium deposition is derived from its dose rate, which is calculated by excluding the dose rate of the background radiation due to natural radionuclides from the air dose-rate at 1 m above the ground. The first step of the current method of calculating the dose rate due to natural radionuclides is calculate the ratio of the total count rate of areas where no radioactive cesium is detected and the count rate of regions with energy levels of 1,400 keV or higher (BG-Index). Next, calculate the air dose rate of radioactive cesium by multiplying the BG-Index and the integrated count rate of 1,400 keV or higher for the area where the radioactive cesium is distributed. In high dose-rate areas, however, the count rate of the 1,365-keV peak of Cs-134, though small, is included in the integrated count rate of 1,400 keV or higher, which could cause an overestimation of the air dose rate of natural radionuclides. We developed a method for accurately evaluating the distribution maps of natural air dose-rate by excluding the effect of radioactive cesium, even in contaminated areas, and obtained the accurate air dose-rate map attributed the radioactive cesium deposition on the ground. Furthermore, the natural dose-rate distribution throughout Japan has been obtained by this method.

Monte Carlo dose calculation in dental amalgam phantom

PubMed Central

Aziz, Mohd. Zahri Abdul; Yusoff, A. L.; Osman, N. D.; Abdullah, R.; Rabaie, N. A.; Salikin, M. S.

2015-01-01

It has become a great challenge in the modern radiation treatment to ensure the accuracy of treatment delivery in electron beam therapy. Tissue inhomogeneity has become one of the factors for accurate dose calculation, and this requires complex algorithm calculation like Monte Carlo (MC). On the other hand, computed tomography (CT) images used in treatment planning system need to be trustful as they are the input in radiotherapy treatment. However, with the presence of metal amalgam in treatment volume, the CT images input showed prominent streak artefact, thus, contributed sources of error. Hence, metal amalgam phantom often creates streak artifacts, which cause an error in the dose calculation. Thus, a streak artifact reduction technique was applied to correct the images, and as a result, better images were observed in terms of structure delineation and density assigning. Furthermore, the amalgam density data were corrected to provide amalgam voxel with accurate density value. As for the errors of dose uncertainties due to metal amalgam, they were reduced from 46% to as low as 2% at d80 (depth of the 80% dose beyond Zmax) using the presented strategies. Considering the number of vital and radiosensitive organs in the head and the neck regions, this correction strategy is suggested in reducing calculation uncertainties through MC calculation. PMID:26500401

Implementation of Monte Carlo Dose calculation for CyberKnife treatment planning

NASA Astrophysics Data System (ADS)

Ma, C.-M.; Li, J. S.; Deng, J.; Fan, J.

2008-02-01

Accurate dose calculation is essential to advanced stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) especially for treatment planning involving heterogeneous patient anatomy. This paper describes the implementation of a fast Monte Carlo dose calculation algorithm in SRS/SRT treatment planning for the CyberKnife® SRS/SRT system. A superposition Monte Carlo algorithm is developed for this application. Photon mean free paths and interaction types for different materials and energies as well as the tracks of secondary electrons are pre-simulated using the MCSIM system. Photon interaction forcing and splitting are applied to the source photons in the patient calculation and the pre-simulated electron tracks are repeated with proper corrections based on the tissue density and electron stopping powers. Electron energy is deposited along the tracks and accumulated in the simulation geometry. Scattered and bremsstrahlung photons are transported, after applying the Russian roulette technique, in the same way as the primary photons. Dose calculations are compared with full Monte Carlo simulations performed using EGS4/MCSIM and the CyberKnife treatment planning system (TPS) for lung, head & neck and liver treatments. Comparisons with full Monte Carlo simulations show excellent agreement (within 0.5%). More than 10% differences in the target dose are found between Monte Carlo simulations and the CyberKnife TPS for SRS/SRT lung treatment while negligible differences are shown in head and neck and liver for the cases investigated. The calculation time using our superposition Monte Carlo algorithm is reduced up to 62 times (46 times on average for 10 typical clinical cases) compared to full Monte Carlo simulations. SRS/SRT dose distributions calculated by simple dose algorithms may be significantly overestimated for small lung target volumes, which can be improved by accurate Monte Carlo dose calculations.

Dose specification for radiation therapy: dose to water or dose to medium?

NASA Astrophysics Data System (ADS)

Ma, C.-M.; Li, Jinsheng

2011-05-01

The Monte Carlo method enables accurate dose calculation for radiation therapy treatment planning and has been implemented in some commercial treatment planning systems. Unlike conventional dose calculation algorithms that provide patient dose information in terms of dose to water with variable electron density, the Monte Carlo method calculates the energy deposition in different media and expresses dose to a medium. This paper discusses the differences in dose calculated using water with different electron densities and that calculated for different biological media and the clinical issues on dose specification including dose prescription and plan evaluation using dose to water and dose to medium. We will demonstrate that conventional photon dose calculation algorithms compute doses similar to those simulated by Monte Carlo using water with different electron densities, which are close (<4% differences) to doses to media but significantly different (up to 11%) from doses to water converted from doses to media following American Association of Physicists in Medicine (AAPM) Task Group 105 recommendations. Our results suggest that for consistency with previous radiation therapy experience Monte Carlo photon algorithms report dose to medium for radiotherapy dose prescription, treatment plan evaluation and treatment outcome analysis.

SU-E-T-632: Preliminary Study On Treating Nose Skin Using Energy and Intensity Modulated Electron Beams with Monte Carlo Based Dose Calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, L; Eldib, A; Li, J

Purpose: Uneven nose surfaces and air cavities underneath and the use of bolus present complexity and dose uncertainty when using a single electron energy beam to plan treatments of nose skin with a pencil beam-based planning system. This work demonstrates more accurate dose calculation and more optimal planning using energy and intensity modulated electron radiotherapy (MERT) delivered with a pMLC. Methods: An in-house developed Monte Carlo (MC)-based dose calculation/optimization planning system was employed for treatment planning. Phase space data (6, 9, 12 and 15 MeV) were used as an input source for MC dose calculations for the linac. To reducemore » the scatter-caused penumbra, a short SSD (61 cm) was used. Our previous work demonstrates good agreement in percentage depth dose and off-axis dose between calculations and film measurement for various field sizes. A MERT plan was generated for treating the nose skin using a patient geometry and a dose volume histogram (DVH) was obtained. The work also shows the comparison of 2D dose distributions between a clinically used conventional single electron energy plan and the MERT plan. Results: The MERT plan resulted in improved target dose coverage as compared to the conventional plan, which demonstrated a target dose deficit at the field edge. The conventional plan showed higher dose normal tissue irradiation underneath the nose skin while the MERT plan resulted in improved conformity and thus reduces normal tissue dose. Conclusion: This preliminary work illustrates that MC-based MERT planning is a promising technique in treating nose skin, not only providing more accurate dose calculation, but also offering an improved target dose coverage and conformity. In addition, this technique may eliminate the necessity of bolus, which often produces dose delivery uncertainty due to the air gaps that may exist between the bolus and skin.« less

Practical applications of internal dose calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carbaugh, E.H.

1994-06-01

Accurate estimates of intake magnitude and internal dose are the goal for any assessment of an actual intake of radioactivity. When only one datum is available on which to base estimates, the choices for internal dose assessment become straight-forward: apply the appropriate retention or excretion function, calculate the intake, and calculate the dose. The difficulty comes when multiple data and different types of data become available. Then practical decisions must be made on how to interpret conflicting data, or how to adjust the assumptions and techniques underlying internal dose assessments to give results consistent with the data. This article describesmore » nine types of adjustments which can be incorporated into calculations of intake and internal dose, and then offers several practical insights to dealing with some real-world internal dose puzzles.« less

The influence of the dose calculation resolution of VMAT plans on the calculated dose for eye lens and optic pathway.

PubMed

Park, Jong Min; Park, So-Yeon; Kim, Jung-In; Carlson, Joel; Kim, Jin Ho

2017-03-01

To investigate the effect of dose calculation grid on calculated dose-volumetric parameters for eye lenses and optic pathways. A total of 30 patients treated using the volumetric modulated arc therapy (VMAT) technique, were retrospectively selected. For each patient, dose distributions were calculated with calculation grids ranging from 1 to 5 mm at 1 mm intervals. Identical structures were used for VMAT planning. The changes in dose-volumetric parameters according to the size of the calculation grid were investigated. Compared to dose calculation with 1 mm grid, the maximum doses to the eye lens with calculation grids of 2, 3, 4 and 5 mm increased by 0.2 ± 0.2 Gy, 0.5 ± 0.5 Gy, 0.9 ± 0.8 Gy and 1.7 ± 1.5 Gy on average, respectively. The Spearman's correlation coefficient between dose gradients near structures vs. the differences between the calculated doses with 1 mm grid and those with 5 mm grid, were 0.380 (p < 0.001). For the accurate calculation of dose distributions, as well as efficiency, using a grid size of 2 mm appears to be the most appropriate choice.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cebe, M; Pacaci, P; Mabhouti, H

Purpose: In this study, the two available calculation algorithms of the Varian Eclipse treatment planning system(TPS), the electron Monte Carlo(eMC) and General Gaussian Pencil Beam(GGPB) algorithms were used to compare measured and calculated peripheral dose distribution of electron beams. Methods: Peripheral dose measurements were carried out for 6, 9, 12, 15, 18 and 22 MeV electron beams of Varian Triology machine using parallel plate ionization chamber and EBT3 films in the slab phantom. Measurements were performed for 6×6, 10×10 and 25×25cm{sup 2} cone sizes at dmax of each energy up to 20cm beyond the field edges. Using the same filmmore » batch, the net OD to dose calibration curve was obtained for each energy. Films were scanned 48 hours after irradiation using an Epson 1000XL flatbed scanner. Dose distribution measured using parallel plate ionization chamber and EBT3 film and calculated by eMC and GGPB algorithms were compared. The measured and calculated data were then compared to find which algorithm calculates peripheral dose distribution more accurately. Results: The agreement between measurement and eMC was better than GGPB. The TPS underestimated the out of field doses. The difference between measured and calculated doses increase with the cone size. The largest deviation between calculated and parallel plate ionization chamber measured dose is less than 4.93% for eMC, but it can increase up to 7.51% for GGPB. For film measurement, the minimum gamma analysis passing rates between measured and calculated dose distributions were 98.2% and 92.7% for eMC and GGPB respectively for all field sizes and energies. Conclusion: Our results show that the Monte Carlo algorithm for electron planning in Eclipse is more accurate than previous algorithms for peripheral dose distributions. It must be emphasized that the use of GGPB for planning large field treatments with 6 MeV could lead to inaccuracies of clinical significance.« less

An accurate model for the computation of the dose of protons in water.

PubMed

Embriaco, A; Bellinzona, V E; Fontana, A; Rotondi, A

2017-06-01

The accurate and fast calculation of the dose in proton radiation therapy is an essential ingredient for successful treatments. We propose a novel approach with a minimal number of parameters. The approach is based on the exact calculation of the electromagnetic part of the interaction, namely the Molière theory of the multiple Coulomb scattering for the transversal 1D projection and the Bethe-Bloch formula for the longitudinal stopping power profile, including a gaussian energy straggling. To this e.m. contribution the nuclear proton-nucleus interaction is added with a simple two-parameter model. Then, the non gaussian lateral profile is used to calculate the radial dose distribution with a method that assumes the cylindrical symmetry of the distribution. The results, obtained with a fast C++ based computational code called MONET (MOdel of ioN dosE for Therapy), are in very good agreement with the FLUKA MC code, within a few percent in the worst case. This study provides a new tool for fast dose calculation or verification, possibly for clinical use. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

DICOM organ dose does not accurately represent calculated dose in mammography

NASA Astrophysics Data System (ADS)

Suleiman, Moayyad E.; Brennan, Patrick C.; McEntee, Mark F.

2016-03-01

This study aims to analyze the agreement between the mean glandular dose estimated by the mammography unit (organ dose) and mean glandular dose calculated using Dance et al published method (calculated dose). Anonymised digital mammograms from 50 BreastScreen NSW centers were downloaded and exposure information required for the calculation of dose was extracted from the DICOM header along with the organ dose estimated by the system. Data from quality assurance annual tests for the included centers were collected and used to calculate the mean glandular dose for each mammogram. Bland-Altman analysis and a two-tailed paired t-test were used to study the agreement between calculated and organ dose and the significance of any differences. A total of 27,869 dose points from 40 centers were included in the study, mean calculated dose and mean organ dose (+/- standard deviation) were 1.47 (+/-0.66) and 1.38 (+/-0.56) mGy respectively. A statistically significant 0.09 mGy bias (t = 69.25; p<0.0001) with 95% limits of agreement between calculated and organ doses ranging from -0.34 and 0.52 were shown by Bland-Altman analysis, which indicates a small yet highly significant difference between the two means. The use of organ dose for dose audits is done at the risk of over or underestimating the calculated dose, hence, further work is needed to identify the causal agents for differences between organ and calculated doses and to generate a correction factor for organ dose.

Radial secondary electron dose profiles and biological effects in light-ion beams based on analytical and Monte Carlo calculations using distorted wave cross sections.

PubMed

Wiklund, Kristin; Olivera, Gustavo H; Brahme, Anders; Lind, Bengt K

2008-07-01

To speed up dose calculation, an analytical pencil-beam method has been developed to calculate the mean radial dose distributions due to secondary electrons that are set in motion by light ions in water. For comparison, radial dose profiles calculated using a Monte Carlo technique have also been determined. An accurate comparison of the resulting radial dose profiles of the Bragg peak for (1)H(+), (4)He(2+) and (6)Li(3+) ions has been performed. The double differential cross sections for secondary electron production were calculated using the continuous distorted wave-eikonal initial state method (CDW-EIS). For the secondary electrons that are generated, the radial dose distribution for the analytical case is based on the generalized Gaussian pencil-beam method and the central axis depth-dose distributions are calculated using the Monte Carlo code PENELOPE. In the Monte Carlo case, the PENELOPE code was used to calculate the whole radial dose profile based on CDW data. The present pencil-beam and Monte Carlo calculations agree well at all radii. A radial dose profile that is shallower at small radii and steeper at large radii than the conventional 1/r(2) is clearly seen with both the Monte Carlo and pencil-beam methods. As expected, since the projectile velocities are the same, the dose profiles of Bragg-peak ions of 0.5 MeV (1)H(+), 2 MeV (4)He(2+) and 3 MeV (6)Li(3+) are almost the same, with about 30% more delta electrons in the sub keV range from (4)He(2+)and (6)Li(3+) compared to (1)H(+). A similar behavior is also seen for 1 MeV (1)H(+), 4 MeV (4)He(2+) and 6 MeV (6)Li(3+), all classically expected to have the same secondary electron cross sections. The results are promising and indicate a fast and accurate way of calculating the mean radial dose profile.

SU-E-T-800: Verification of Acurose XB Dose Calculation Algorithm at Air Cavity-Tissue Interface Using Film Measurement for Small Fields of 6-MV Flattening Filter-Free Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, S; Suh, T; Chung, J

2015-06-15

Purpose: To verify the dose accuracy of Acuros XB (AXB) dose calculation algorithm at air-tissue interface using inhomogeneous phantom for 6-MV flattening filter-free (FFF) beams. Methods: An inhomogeneous phantom included air cavity was manufactured for verifying dose accuracy at the air-tissue interface. The phantom was composed with 1 and 3 cm thickness of air cavity. To evaluate the central axis doses (CAD) and dose profiles of the interface, the dose calculations were performed for 3 × 3 and 4 × 4 cm{sup 2} fields of 6 MV FFF beams with AAA and AXB in Eclipse treatment plainning system. Measurements inmore » this region were performed with Gafchromic film. The root mean square errors (RMSE) were analyzed with calculated and measured dose profile. Dose profiles were divided into inner-dose profile (>80%) and penumbra (20% to 80%) region for evaluating RMSE. To quantify the distribution difference, gamma evaluation was used and determined the agreement with 3%/3mm criteria. Results: The percentage differences (%Diffs) between measured and calculated CAD in the interface, AXB shows more agreement than AAA. The %Diffs were increased with increasing the thickness of air cavity size and it is similar for both algorithms. In RMSEs of inner-profile, AXB was more accurate than AAA. The difference was up to 6 times due to overestimation by AAA. RMSEs of penumbra appeared to high difference for increasing the measurement depth. Gamma agreement also presented that the passing rates decreased in penumbra. Conclusion: This study demonstrated that the dose calculation with AXB shows more accurate than with AAA for the air-tissue interface. The 2D dose distributions with AXB for both inner-profile and penumbra showed better agreement than with AAA relative to variation of the measurement depths and air cavity sizes.« less

A medical image-based graphical platform -- features, applications and relevance for brachytherapy.

PubMed

Fonseca, Gabriel P; Reniers, Brigitte; Landry, Guillaume; White, Shane; Bellezzo, Murillo; Antunes, Paula C G; de Sales, Camila P; Welteman, Eduardo; Yoriyaz, Hélio; Verhaegen, Frank

2014-01-01

Brachytherapy dose calculation is commonly performed using the Task Group-No 43 Report-Updated protocol (TG-43U1) formalism. Recently, a more accurate approach has been proposed that can handle tissue composition, tissue density, body shape, applicator geometry, and dose reporting either in media or water. Some model-based dose calculation algorithms are based on Monte Carlo (MC) simulations. This work presents a software platform capable of processing medical images and treatment plans, and preparing the required input data for MC simulations. The A Medical Image-based Graphical platfOrm-Brachytherapy module (AMIGOBrachy) is a user interface, coupled to the MCNP6 MC code, for absorbed dose calculations. The AMIGOBrachy was first validated in water for a high-dose-rate (192)Ir source. Next, dose distributions were validated in uniform phantoms consisting of different materials. Finally, dose distributions were obtained in patient geometries. Results were compared against a treatment planning system including a linear Boltzmann transport equation (LBTE) solver capable of handling nonwater heterogeneities. The TG-43U1 source parameters are in good agreement with literature with more than 90% of anisotropy values within 1%. No significant dependence on the tissue composition was observed comparing MC results against an LBTE solver. Clinical cases showed differences up to 25%, when comparing MC results against TG-43U1. About 92% of the voxels exhibited dose differences lower than 2% when comparing MC results against an LBTE solver. The AMIGOBrachy can improve the accuracy of the TG-43U1 dose calculation by using a more accurate MC dose calculation algorithm. The AMIGOBrachy can be incorporated in clinical practice via a user-friendly graphical interface. Copyright © 2014 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.

[Benchmark experiment to verify radiation transport calculations for dosimetry in radiation therapy].

PubMed

Renner, Franziska

2016-09-01

Monte Carlo simulations are regarded as the most accurate method of solving complex problems in the field of dosimetry and radiation transport. In (external) radiation therapy they are increasingly used for the calculation of dose distributions during treatment planning. In comparison to other algorithms for the calculation of dose distributions, Monte Carlo methods have the capability of improving the accuracy of dose calculations - especially under complex circumstances (e.g. consideration of inhomogeneities). However, there is a lack of knowledge of how accurate the results of Monte Carlo calculations are on an absolute basis. A practical verification of the calculations can be performed by direct comparison with the results of a benchmark experiment. This work presents such a benchmark experiment and compares its results (with detailed consideration of measurement uncertainty) with the results of Monte Carlo calculations using the well-established Monte Carlo code EGSnrc. The experiment was designed to have parallels to external beam radiation therapy with respect to the type and energy of the radiation, the materials used and the kind of dose measurement. Because the properties of the beam have to be well known in order to compare the results of the experiment and the simulation on an absolute basis, the benchmark experiment was performed using the research electron accelerator of the Physikalisch-Technische Bundesanstalt (PTB), whose beam was accurately characterized in advance. The benchmark experiment and the corresponding Monte Carlo simulations were carried out for two different types of ionization chambers and the results were compared. Considering the uncertainty, which is about 0.7 % for the experimental values and about 1.0 % for the Monte Carlo simulation, the results of the simulation and the experiment coincide. Copyright © 2015. Published by Elsevier GmbH.

SU-F-SPS-11: The Dosimetric Comparison of Truebeam 2.0 and Cyberknife M6 Treatment Plans for Brain SRS Treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mabhouti, H; Sanli, E; Cebe, M

Purpose: Brain stereotactic radiosurgery involves the use of precisely directed, single session radiation to create a desired radiobiologic response within the brain target with acceptable minimal effects on surrounding structures or tissues. In this study, the dosimetric comparison of Truebeam 2.0 and Cyberknife M6 treatment plans were made. Methods: For Truebeam 2.0 machine, treatment planning were done using 2 full arc VMAT technique with 6 FFF beam on the CT scan of Randophantom simulating the treatment of sterotactic treatments for one brain metastasis. The dose distribution were calculated using Eclipse treatment planning system with Acuros XB algorithm. The treatment planningmore » of the same target were also done for Cyberknife M6 machine with Multiplan treatment planning system using Monte Carlo algorithm. Using the same film batch, the net OD to dose calibration curve was obtained using both machine by delivering 0- 800 cGy. Films were scanned 48 hours after irradiation using an Epson 1000XL flatbed scanner. Dose distribution were measured using EBT3 film dosimeter. The measured and calculated doses were compared. Results: The dose distribution in the target and 2 cm beyond the target edge were calculated on TPSs and measured using EBT3 film. For cyberknife plans, the gamma analysis passing rates between measured and calculated dose distributions were 99.2% and 96.7% for target and peripheral region of target respectively. For Truebeam plans, the gamma analysis passing rates were 99.1% and 95.5% for target and peripheral region of target respectively. Conclusion: Although, target dose distribution calculated accurately by Acuros XB and Monte Carlo algorithms, Monte carlo calculation algorithm predicts dose distribution around the peripheral region of target more accurately than Acuros algorithm.« less

Dose calculation accuracy of different image value to density tables for cone-beam CT planning in head & neck and pelvic localizations.

PubMed

Barateau, Anaïs; Garlopeau, Christopher; Cugny, Audrey; De Figueiredo, Bénédicte Henriques; Dupin, Charles; Caron, Jérôme; Antoine, Mikaël

2015-03-01

We aimed to identify the most accurate combination of phantom and protocol for image value to density table (IVDT) on volume-modulated arc therapy (VMAT) dose calculation based on kV-Cone-beam CT imaging, for head and neck (H&N) and pelvic localizations. Three phantoms (Catphan(®)600, CIRS(®)062M (inner phantom for head and outer phantom for body), and TomoTherapy(®) "Cheese" phantom) were used to create IVDT curves of CBCT systems with two different CBCT protocols (Standard-dose Head and Standard Pelvis). Hounsfield Unit (HU) time stability and repeatability for a single On-Board-Imager (OBI) and compatibility of two distinct devices were assessed with Catphan(®)600. Images from the anthropomorphic phantom CIRS ATOM(®) for both CT and CBCT modalities were used for VMAT dose calculation from different IVDT curves. Dosimetric indices from CT and CBCT imaging were compared. IVDT curves from CBCT images were highly different depending on phantom used (up to 1000 HU for high densities) and protocol applied (up to 200 HU for high densities). HU time stability was verified over seven weeks. A maximum difference of 3% on the dose calculation indices studied was found between CT and CBCT VMAT dose calculation across the two localizations using appropriate IVDT curves. One IVDT curve per localization can be established with a bi-monthly verification of IVDT-CBCT. The IVDT-CBCTCIRS-Head phantom with the Standard-dose Head protocol was the most accurate combination for dose calculation on H&N CBCT images. For pelvic localizations, the IVDT-CBCTCheese established with the Standard Pelvis protocol provided the best accuracy. Copyright © 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heintz, P; Heintz, B; Sandoval, D

Purpose: Computerized radiation therapy treatment planning is performed on almost all patients today. However it is seldom used for laboratory irradiations. The first objective is to assess whether modern radiation therapy treatment planning (RTP) systems accurately predict the subject dose by comparing in vivo and decedent dose measurements to calculated doses. The other objective is determine the importance of using a RTP system for laboratory irradiations. Methods: 5 MOSFET radiation dosimeters were placed enterically in each subject (2 sedated Rhesus Macaques) to measure the absorbed dose at 5 levels (carina, lung, heart, liver and rectum) during whole body irradiation. Themore » subjects were treated with large opposed lateral fields and extended distances to cover the entire subject using a Varian 600C linac. CT simulation was performed ante-mortem (AM) and post-mortem (PM). To compare AM and PM doses, calculation points were placed at the location of each dosimeter in the treatment plan. The measured results were compared to the results using Varian Eclipse and Prowess Panther RTP systems. Results: The Varian and Prowess treatment planning system agreed to within in +1.5% for both subjects. However there were significant differences between the measured and calculated doses. For both animals the calculated central axis dose was higher than prescribed by 3–5%. This was caused in part by inaccurate measurement of animal thickness at the time of irradiation. For one subject the doses ranged from 4% to 7% high and the other subject the doses ranged 7% to 14% high when compared to the RTP doses. Conclusions: Our results suggest that using proper CT RTP system can more accurately deliver the prescribed dose to laboratory subjects. It also shows that there is significant dose variation in such subjects when inhomogeneities are not considered in the planning process.« less

SU-F-T-569: Implementation of a Patient Specific QA Method Using EBT-XD for CyberKnife SRS/SBRT Plans

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zerouali, K; Aubry, J; Doucet, R

2016-06-15

Purpose: To implement the new EBT-XD Gafchromic films for accurate dosimetric and geometric validation of stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) CyberKnife (CK) patient specific QA. Methods: Film calibration was performed using a triplechannel film analysis on an Epson 10000XL scanner. Calibration films were irradiated using a Varian Clinac 21EX flattened beam (0 to 20 Gy), to ensure sufficient dose homogeneity. Films were scanned to a resolution of 0.3 mm, 24 hours post irradiation following a well-defined protocol. A set of 12 QA was performed for several types of CK plans: trigeminal neuralgia, brain metastasis, prostate andmore » lung tumors. A custom made insert for the CK head phantom has been manufactured to yield an accurate measured to calculated dose registration. When the high dose region was large enough, absolute dose was also measured with an ionization chamber. Dose calculation is performed using MultiPlan Ray-tracing algorithm for all cases since the phantom is mostly made from near water-equivalent plastic. Results: Good agreement (<2%) was found between the dose to the chamber and the film, when a chamber measurement was possible The average dose difference and standard deviations between film measurements and TPS calculations were respectively 1.75% and 3%. The geometric accuracy has been estimated to be <1 mm, combining robot positioning uncertainty and film registration to calculated dose. Conclusion: Patient specific QA measurements using EBT-XD films yielded a full 2D dose plane with high spatial resolution and acceptable dose accuracy. This method is particularly promising for trigeminal neuralgia plan QA, where the positioning of the spatial dose distribution is equally or more important than the absolute delivered dose to achieve clinical goals.« less

Gamma-ray spectra and doses from the Little Boy replica

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moss, C.E.; Lucas, M.C.; Tisinger, E.W.

1984-01-01

Most radiation safety guidelines in the nuclear industry are based on the data concerning the survivors of the nuclear explosions at Hiroshima and Nagasaki. Crucial to determining these guidelines is the radiation from the explosions. We have measured gamma-ray pulse-height distributions from an accurate replica of the Little Boy device used at Hiroshima, operated at low power levels near critical. The device was placed outdoors on a stand 4 m from the ground to minimize environmental effects. The power levels were based on a monitor detector calibrated very carefully in independent experiments. High-resolution pulse-height distributions were acquired with a germaniummore » detector to identify the lines and to obtain line intensities. The 7631 to 7645 keV doublet from neutron capture in the heavy steel case was dominant. Low-resolution pulse-height distributions were acquired with bismuth-germanate detectors. We calculated flux spectra from these distributions using accurately measured detector response functions and efficiency curves. We then calculated dose-rate spectra from the flux spectra using a flux-to-dose-rate conversion procedure. The integral of each dose-rate spectrum gave an integral dose rate. The integral doses at 2 m ranged from 0.46 to 1.03 mrem per 10/sup 13/ fissions. The output of the Little Boy replica can be calculated with Monte Carlo codes. Comparison of our experimental spectra, line intensities, and integral doses can be used to verify these calculations at low power levels and give increased confidence to the calculated values from the explosion at Hiroshima. These calculations then can be used to establish better radiation safety guidelines. 7 references, 7 figures, 2 tables.« less

Temporal resolution required for accurate evaluation of the interplay effect in spot scanning proton therapy

NASA Astrophysics Data System (ADS)

Seo, Jeongmin; Han, Min Cheol; Yeom, Yeon Soo; Lee, Hyun Su; Kim, Chan Hyeong; Jeong, Jong Hwi; Kim, SeongHoon

2017-04-01

In proton therapy, the spot scanning method is known to suffer from the interplay effect induced from the independent movements of the proton beam and the organs in the patient during the treatment. To study the interplay effect, several investigators have performed four-dimensional (4D) dose calculations with some limited temporal resolutions (4 or 10 phases per respiratory cycle) by using the 4D computed tomography (CT) images of the patient; however, the validity of the limited temporal resolutions has not been confirmed. The aim of the present study is to determine whether the previous temporal resolutions (4 or 10 phases per respiratory cycle) are really high enough for adequate study of the interplay effect in spot scanning proton therapy. For this study, a series of 4D dose calculations were performed with a virtual water phantom moving in the vertical direction during dose delivery. The dose distributions were calculated for different temporal resolutions (4, 10, 25, 50, and 100 phases per respiratory cycle), and the calculated dose distributions were compared with the reference dose distribution, which was calculated using an almost continuously-moving water phantom ( i.e., 1000 phases per respiratory cycle). The results of the present study show that the temporal resolutions of 4 and 10 phases per respiratory cycle are not high enough for an accurate evaluation of the interplay effect for spot scanning proton therapy. The temporal resolution should be at least 14 and 17 phases per respiratory cycle for 10-mm and 20-mm movement amplitudes, respectively, even for rigid movement ( i.e., without deformation) of the homogeneous water phantom considered in the present study. We believe that even higher temporal resolutions are needed for an accurate evaluation of the interplay effect in the human body, in which the organs are inhomogeneous and deform during movement.

TU-AB-BRC-12: Optimized Parallel MonteCarlo Dose Calculations for Secondary MU Checks

DOE Office of Scientific and Technical Information (OSTI.GOV)

French, S; Nazareth, D; Bellor, M

Purpose: Secondary MU checks are an important tool used during a physics review of a treatment plan. Commercial software packages offer varying degrees of theoretical dose calculation accuracy, depending on the modality involved. Dose calculations of VMAT plans are especially prone to error due to the large approximations involved. Monte Carlo (MC) methods are not commonly used due to their long run times. We investigated two methods to increase the computational efficiency of MC dose simulations with the BEAMnrc code. Distributed computing resources, along with optimized code compilation, will allow for accurate and efficient VMAT dose calculations. Methods: The BEAMnrcmore » package was installed on a high performance computing cluster accessible to our clinic. MATLAB and PYTHON scripts were developed to convert a clinical VMAT DICOM plan into BEAMnrc input files. The BEAMnrc installation was optimized by running the VMAT simulations through profiling tools which indicated the behavior of the constituent routines in the code, e.g. the bremsstrahlung splitting routine, and the specified random number generator. This information aided in determining the most efficient compiling parallel configuration for the specific CPU’s available on our cluster, resulting in the fastest VMAT simulation times. Our method was evaluated with calculations involving 10{sup 8} – 10{sup 9} particle histories which are sufficient to verify patient dose using VMAT. Results: Parallelization allowed the calculation of patient dose on the order of 10 – 15 hours with 100 parallel jobs. Due to the compiler optimization process, further speed increases of 23% were achieved when compared with the open-source compiler BEAMnrc packages. Conclusion: Analysis of the BEAMnrc code allowed us to optimize the compiler configuration for VMAT dose calculations. In future work, the optimized MC code, in conjunction with the parallel processing capabilities of BEAMnrc, will be applied to provide accurate and efficient secondary MU checks.« less

Effect of age-dependent bone electron density on the calculated dose distribution from kilovoltage and megavoltage photon and electron radiotherapy in paediatric MRI-only treatment planning.

PubMed

Zeinali-Rafsanjani, B; Faghihi, R; Mosleh-Shirazi, M A; Saeedi-Moghadam, M; Jalli, R; Sina, S

2018-01-01

MRI-only treatment planning (TP) can be advantageous in paediatric radiotherapy. However, electron density extraction is necessary for dose calculation. Normally, after bone segmentation, a bulk density is assigned. However, the variation of bone bulk density in patients makes the creation of pseudo CTs challenging. This study aims to assess the effects of bone density variations in children on radiation attenuation and dose calculation for MRI-only TP. Bone contents of <15-year-old children were calculated, and substituted in the Oak Ridge National Laboratory paediatric phantoms. The percentage depth dose and beam profile of 150 kVp and 6 MV photon and 6 MeV electron beams were then calculated using Xcom, MCNPX (Monte Carlo N-particle version X) and ORLN phantoms. Using 150 kVp X-rays, the difference in attenuation coefficient was almost 5% between an 11-year-old child and a newborn, and ~8% between an adult and a newborn. With megavoltage radiation, the differences were smaller but still important. For an 18 MV photon beam, the difference of radiation attenuation between an 11-year-old child and a newborn was 4% and ~7.4% between an adult and a newborn. For 6 MeV electrons, dose differences were observed up to the 2 cm depth. The percentage depth dose difference between 1 and 10-year-olds was 18.5%, and between 10 and 15-year-olds was 24%. The results suggest that for MRI-only TP of photon- or electron-beam radiotherapy, the bone densities of each age group should be defined separately for accurate dose calculation. Advances in knowledge: This study highlights the need for more age-specific determination of bone electron density for accurate dose calculations in paediatric MRI-only radiotherapy TP.

Dosimetric verification and clinical evaluation of a new commercially available Monte Carlo-based dose algorithm for application in stereotactic body radiation therapy (SBRT) treatment planning

NASA Astrophysics Data System (ADS)

Fragoso, Margarida; Wen, Ning; Kumar, Sanath; Liu, Dezhi; Ryu, Samuel; Movsas, Benjamin; Munther, Ajlouni; Chetty, Indrin J.

2010-08-01

Modern cancer treatment techniques, such as intensity-modulated radiation therapy (IMRT) and stereotactic body radiation therapy (SBRT), have greatly increased the demand for more accurate treatment planning (structure definition, dose calculation, etc) and dose delivery. The ability to use fast and accurate Monte Carlo (MC)-based dose calculations within a commercial treatment planning system (TPS) in the clinical setting is now becoming more of a reality. This study describes the dosimetric verification and initial clinical evaluation of a new commercial MC-based photon beam dose calculation algorithm, within the iPlan v.4.1 TPS (BrainLAB AG, Feldkirchen, Germany). Experimental verification of the MC photon beam model was performed with film and ionization chambers in water phantoms and in heterogeneous solid-water slabs containing bone and lung-equivalent materials for a 6 MV photon beam from a Novalis (BrainLAB) linear accelerator (linac) with a micro-multileaf collimator (m3 MLC). The agreement between calculated and measured dose distributions in the water phantom verification tests was, on average, within 2%/1 mm (high dose/high gradient) and was within ±4%/2 mm in the heterogeneous slab geometries. Example treatment plans in the lung show significant differences between the MC and one-dimensional pencil beam (PB) algorithms within iPlan, especially for small lesions in the lung, where electronic disequilibrium effects are emphasized. Other user-specific features in the iPlan system, such as options to select dose to water or dose to medium, and the mean variance level, have been investigated. Timing results for typical lung treatment plans show the total computation time (including that for processing and I/O) to be less than 10 min for 1-2% mean variance (running on a single PC with 8 Intel Xeon X5355 CPUs, 2.66 GHz). Overall, the iPlan MC algorithm is demonstrated to be an accurate and efficient dose algorithm, incorporating robust tools for MC-based SBRT treatment planning in the routine clinical setting.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Y M; Bush, K; Han, B

Purpose: Accurate and fast dose calculation is a prerequisite of precision radiation therapy in modern photon and particle therapy. While Monte Carlo (MC) dose calculation provides high dosimetric accuracy, the drastically increased computational time hinders its routine use. Deterministic dose calculation methods are fast, but problematic in the presence of tissue density inhomogeneity. We leverage the useful features of deterministic methods and MC to develop a hybrid dose calculation platform with autonomous utilization of MC and deterministic calculation depending on the local geometry, for optimal accuracy and speed. Methods: Our platform utilizes a Geant4 based “localized Monte Carlo” (LMC) methodmore » that isolates MC dose calculations only to volumes that have potential for dosimetric inaccuracy. In our approach, additional structures are created encompassing heterogeneous volumes. Deterministic methods calculate dose and energy fluence up to the volume surfaces, where the energy fluence distribution is sampled into discrete histories and transported using MC. Histories exiting the volume are converted back into energy fluence, and transported deterministically. By matching boundary conditions at both interfaces, deterministic dose calculation account for dose perturbations “downstream” of localized heterogeneities. Hybrid dose calculation was performed for water and anthropomorphic phantoms. Results: We achieved <1% agreement between deterministic and MC calculations in the water benchmark for photon and proton beams, and dose differences of 2%–15% could be observed in heterogeneous phantoms. The saving in computational time (a factor ∼4–7 compared to a full Monte Carlo dose calculation) was found to be approximately proportional to the volume of the heterogeneous region. Conclusion: Our hybrid dose calculation approach takes advantage of the computational efficiency of deterministic method and accuracy of MC, providing a practical tool for high performance dose calculation in modern RT. The approach is generalizable to all modalities where heterogeneities play a large role, notably particle therapy.« less

Calculation of Organ Doses for a Large Number of Patients Undergoing CT Examinations.

PubMed

Bahadori, Amir; Miglioretti, Diana; Kruger, Randell; Flynn, Michael; Weinmann, Sheila; Smith-Bindman, Rebecca; Lee, Choonsik

2015-10-01

The objective of our study was to develop an automated calculation method to provide organ dose assessment for a large cohort of pediatric and adult patients undergoing CT examinations. We adopted two dose libraries that were previously published: the volume CT dose index-normalized organ dose library and the tube current-exposure time product (100 mAs)-normalized weighted CT dose index library. We developed an algorithm to calculate organ doses using the two dose libraries and the CT parameters available from DICOM data. We calculated organ doses for pediatric (n = 2499) and adult (n = 2043) CT examinations randomly selected from four health care systems in the United States and compared the adult organ doses with the values calculated from the ImPACT calculator. The median brain dose was 20 mGy (pediatric) and 24 mGy (adult), and the brain dose was greater than 40 mGy for 11% (pediatric) and 18% (adult) of the head CT studies. Both the National Cancer Institute (NCI) and ImPACT methods provided similar organ doses (median discrepancy < 20%) for all organs except the organs located close to the scanning boundaries. The visual comparisons of scanning coverage and phantom anatomies revealed that the NCI method, which is based on realistic computational phantoms, provides more accurate organ doses than the ImPACT method. The automated organ dose calculation method developed in this study reduces the time needed to calculate doses for a large number of patients. We have successfully used this method for a variety of CT-related studies including retrospective epidemiologic studies and CT dose trend analysis studies.

SU-E-T-138: Dosimetric Verification For Volumetric Modulated Arc Therapy Cranio-Spinal Irradiation Technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goksel, E; Bilge, H; Yildiz, Yarar

2014-06-01

Purpose: Dosimetric feasibility of cranio-spinal irradiation with volumetric modulated arc therapy (VMAT-CSI) technique in terms of dose distribution accuracy was investigated using a humanlike phantom. Methods: The OARs and PTV volumes for the Rando phantom were generated on supine CT images. Eclipse (version 8.6) TPS with AAA algorithm was used to create the treatment plan with VMAT-CSI technique. RapidArc plan consisted of cranial, upper spinal (US) and lower spinal (LS) regions that were optimized in the same plan. US field was overlapped by 3cm with cranial and LS fields. Three partial arcs for cranium and 1 full arc for eachmore » US and LS region were used. The VMAT-CSI dose distribution inside the Rando phantom was measured with thermoluminescent detectors (TLD) and film dosimetry, and was compared to the calculated doses of field junctions, target and OARs. TLDs were placed at 24 positions throughout the phantom. The measured TLD doses were compared to the calculated point doses. Planar doses for field junctions were verified with Gafchromic films. Films were analyzed in PTW Verisoft application software using gamma analysis method with the 4 mm distance to agreement (DTA) and 4% dose agreement criteria. Results: TLD readings demonstrated accurate dose delivery, with a median dose difference of -0.3% (range: -8% and 12%) when compared with calculated doses for the areas inside the treatment portal. The maximum dose difference was 12% higher in testicals that are outside the treatment region and 8% lower in lungs where the heterogeinity was higher. All planar dose verifications for field junctions passed the gamma analysis and measured planar dose distributions demonstrated average 97% agreement with calculated doses. Conclusion: The dosimetric data verified with TLD and film dosimetry shows that VMAT-CSI technique provides accurate dose distribution and can be delivered safely.« less

The Effects of Metal on Size Specific Dose Estimation (SSDE) in CT: A Phantom Study

NASA Astrophysics Data System (ADS)

Alsanea, Maram M.

Over the past number of years there has been a significant increase in the awareness of radiation dose from use of computed tomography (CT). Efforts have been made to reduce radiation dose from CT and to better quantify dose being delivered. However, unfortunately, these dose metrics such as CTDI vol are not a specific patient dose. In 2011, the size-specific dose estimation (SSDE) was introduced by AAPM TG-204 which accounts for the physical size of the patient. However, the approach presented in TG-204 ignores the importance of the attenuation differences in the body. In 2014, a newer methodology that accounted for tissue attenuation was introduced by the AAPM TG-220 based on the concept of water equivalent diameter, Dw. One of the limitation of TG-220 is that there is no estimation of the dose while highly attenuating objects such as metal is present in the body. The purpose of this research is to evaluate the accuracy of size-specific dose estimates in CT in the presence of simulated metal prostheses using a conventional PMMA CTDI phantom at different phantom diameter (body and head) and beam energy. Titanium, Cobalt- chromium and stainless steel alloys rods were used in the study. Two approaches were used as introduced by AAPM TG-204 and 220 utilizing the effective diameter and the Dw calculations. From these calculations, conversion factors have been derived that could be applied to the measured CTDIvol to convert it to specific patient dose, or size specific dose estimate, (SSDE). Radiation dose in tissue (f-factor = 0.94) was measured at various chamber positions with the presence of metal. Following, an average weighted tissue dose (AWTD) was calculated in a manner similar to the weighted CTDI (CTDIw). In general, for the 32 cm body phantom SSDE220 provided more accurate estimates of AWTD than did SSDE204. For smaller patient size, represented by the 16 cm head phantom, the SSDE204 was a more accurate estimate of AWTD that that of SSDE220. However, as the quantity of metal increased it was shown that SSDE220 became more accurate where the percentage error was within +/-4% of the AWTD. In addition, the acquired axial CT images were reconstructed both with and without a single energy metal artifact reduction algorithm (SEMAR), to study the effect on Dw. The Dw calculations used to determine SSDE220 varied by less than 0.2% between the images reconstructed with and without the metal artifact reduction algorithm. For the majority of the scans percentage error observed with 100 kVp is less than that with 120 kVp for SSDE204. Finally, a comparison of the manually calculated SSDE220 and that calculated by the Radimetrics software, showed an overestimation of SSDE values reported by the software compared to the manually calculated measurements which is due to an underestimation of Dw values calculated by the software. This underestimation resulted from including the slices effected by the cone beam artifact in SSDE calculations.

SU-E-T-36: A GPU-Accelerated Monte-Carlo Dose Calculation Platform and Its Application Toward Validating a ViewRay Beam Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Y; Mazur, T; Green, O

Purpose: To build a fast, accurate and easily-deployable research platform for Monte-Carlo dose calculations. We port the dose calculation engine PENELOPE to C++, and accelerate calculations using GPU acceleration. Simulations of a Co-60 beam model provided by ViewRay demonstrate the capabilities of the platform. Methods: We built software that incorporates a beam model interface, CT-phantom model, GPU-accelerated PENELOPE engine, and GUI front-end. We rewrote the PENELOPE kernel in C++ (from Fortran) and accelerated the code on a GPU. We seamlessly integrated a Co-60 beam model (obtained from ViewRay) into our platform. Simulations of various field sizes and SSDs using amore » homogeneous water phantom generated PDDs, dose profiles, and output factors that were compared to experiment data. Results: With GPU acceleration using a dated graphics card (Nvidia Tesla C2050), a highly accurate simulation – including 100*100*100 grid, 3×3×3 mm3 voxels, <1% uncertainty, and 4.2×4.2 cm2 field size – runs 24 times faster (20 minutes versus 8 hours) than when parallelizing on 8 threads across a new CPU (Intel i7-4770). Simulated PDDs, profiles and output ratios for the commercial system agree well with experiment data measured using radiographic film or ionization chamber. Based on our analysis, this beam model is precise enough for general applications. Conclusions: Using a beam model for a Co-60 system provided by ViewRay, we evaluate a dose calculation platform that we developed. Comparison to measurements demonstrates the promise of our software for use as a research platform for dose calculations, with applications including quality assurance and treatment plan verification.« less

Dosimetric impact of a CT metal artefact suppression algorithm for proton, electron and photon therapies

NASA Astrophysics Data System (ADS)

Wei, Jikun; Sandison, George A.; Hsi, Wen-Chien; Ringor, Michael; Lu, Xiaoyi

2006-10-01

Accurate dose calculation is essential to precision radiation treatment planning and this accuracy depends upon anatomic and tissue electron density information. Modern treatment planning inhomogeneity corrections use x-ray CT images and calibrated scales of tissue CT number to electron density to provide this information. The presence of metal in the volume scanned by an x-ray CT scanner causes metal induced image artefacts that influence CT numbers and thereby introduce errors in the radiation dose distribution calculated. This paper investigates the dosimetric improvement achieved by a previously proposed x-ray CT metal artefact suppression technique when the suppressed images of a patient with bilateral hip prostheses are used in commercial treatment planning systems for proton, electron or photon therapies. For all these beam types, this clinical image and treatment planning study reveals that the target may be severely underdosed if a metal artefact-contaminated image is used for dose calculations instead of the artefact suppressed one. Of the three beam types studied, the metal artefact suppression is most important for proton therapy dose calculations, intermediate for electron therapy and least important for x-ray therapy but still significant. The study of a water phantom having a metal rod simulating a hip prosthesis indicates that CT numbers generated after image processing for metal artefact suppression are accurate and thus dose calculations based on the metal artefact suppressed images will be of high fidelity.

Characterization of differences in calculated and actual measured skin doses to canine limbs during stereotactic radiosurgery using Gafchromic film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walters, Jerri; Colorado State University, Fort Collins, CO; Ryan, Stewart

Accurate calculation of absorbed dose to the skin, especially the superficial and radiosensitive basal cell layer, is difficult for many reasons including, but not limited to, the build-up effect of megavoltage photons, tangential beam effects, mixed energy scatter from support devices, and dose interpolation caused by a finite resolution calculation matrix. Stereotactic body radiotherapy (SBRT) has been developed as an alternative limb salvage treatment option at Colorado State University Veterinary Teaching Hospital for dogs with extremity bone tumors. Optimal dose delivery to the tumor during SBRT treatment can be limited by uncertainty in skin dose calculation. The aim of thismore » study was to characterize the difference between measured and calculated radiation dose by the Varian Eclipse (Varian Medical Systems, Palo Alto, CA) AAA treatment planning algorithm (for 1-mm, 2-mm, and 5-mm calculation voxel dimensions) as a function of distance from the skin surface. The study used Gafchromic EBT film (International Specialty Products, Wayne, NJ), FilmQA analysis software, a limb phantom constructed from plastic water Trade-Mark-Sign (fluke Biomedical, Everett, WA) and a canine cadaver forelimb. The limb phantom was exposed to 6-MV treatments consisting of a single-beam, a pair of parallel opposed beams, and a 7-beam coplanar treatment plan. The canine forelimb was exposed to the 7-beam coplanar plan. Radiation dose to the forelimb skin at the surface and at depths of 1.65 mm and 1.35 mm below the skin surface were also measured with the Gafchromic film. The calculation algorithm estimated the dose well at depths beyond buildup for all calculation voxel sizes. The calculation algorithm underestimated the dose in portions of the buildup region of tissue for all comparisons, with the most significant differences observed in the 5-mm calculation voxel and the least difference in the 1-mm voxel. Results indicate a significant difference between measured and calculated data extending to average depths of 2.5 mm, 3.4 mm, and 10 mm for the 1-mm, 2-mm, and 5-mm dimension calculation matrices, respectively. These results emphasize the importance of selecting as small a treatment planning software calculation matrix dimension as is practically possible and of taking a conservative approach for skin treatment planning objectives. One suggested conservative approach is accomplished by defining the skin organ as the outermost 2-3 mm of the body such that the high dose tail of the skin organ dose-volume histogram curve represents dose on the deep side of the skin where the algorithm is more accurate.« less

Monte Carlo dose calculations of beta-emitting sources for intravascular brachytherapy: a comparison between EGS4, EGSnrc, and MCNP.

PubMed

Wang, R; Li, X A

2001-02-01

The dose parameters for the beta-particle emitting 90Sr/90Y source for intravascular brachytherapy (IVBT) have been calculated by different investigators. At a distant distance from the source, noticeable differences are seen in these parameters calculated using different Monte Carlo codes. The purpose of this work is to quantify as well as to understand these differences. We have compared a series of calculations using an EGS4, an EGSnrc, and the MCNP Monte Carlo codes. Data calculated and compared include the depth dose curve for a broad parallel beam of electrons, and radial dose distributions for point electron sources (monoenergetic or polyenergetic) and for a real 90Sr/90Y source. For the 90Sr/90Y source, the doses at the reference position (2 mm radial distance) calculated by the three code agree within 2%. However, the differences between the dose calculated by the three codes can be over 20% in the radial distance range interested in IVBT. The difference increases with radial distance from source, and reaches 30% at the tail of dose curve. These differences may be partially attributed to the different multiple scattering theories and Monte Carlo models for electron transport adopted in these three codes. Doses calculated by the EGSnrc code are more accurate than those by the EGS4. The two calculations agree within 5% for radial distance <6 mm.

SU-F-BRF-14: Increasing the Accuracy of Dose Calculation On Cone-Beam Imaging Using Deformable Image Registration in the Case of Prostate Translation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fillion, O; Gingras, L; Departement de physique, de genie physique et d'optique, Universite Laval, Quebec, Quebec

2014-06-15

Purpose: Artifacts can reduce the quality of dose re-calculations on CBCT scans during a treatment. The aim of this project is to correct the CBCT images in order to allow for more accurate and exact dose calculations in the case of a translation of the tumor in prostate cancer. Methods: Our approach is to develop strategies based on deformable image registration algorithms using the elastix software (Klein et al., 2010) to register the treatment planning CT on a daily CBCT scan taken during treatment. Sets of images are provided by a 3D deformable phantom and comprise two CT and twomore » CBCT scans: one of both with the reference anatomy and the others with known deformations (i.e. translations of the prostate). The reference CT is registered onto the deformed CBCT and the deformed CT serves as the control for dose calculation accuracy. The planned treatment used for the evaluation of dose calculation is a 2-Gy fraction prescribed at the location of the reference prostate and assigned to 7 rectangular fields. Results: For a realistic 0.5-cm translation of the prostate, the relative dose discrepancy between the CBCT and the CT control scan at the prostate's centroid is 8.9 ± 0.8 % while dose discrepancy between the registered CT and the control scan lessens to −2.4 ± 0.8 %. For a 2-cm translation, clinical indices like the V90 and the D100 are more accurate by 0.7 ± 0.3 % and 8.0 ± 0.5 cGy respectively when using registered CT than when using CBCT for dose calculation. Conclusion: The results show that this strategy gives doses in agreement within a few percents with those from calculations on actual CT scans. In the future, various deformations of the phantom anatomy will allow a thorough characterization of the registration strategies needed for more complex anatomies.« less

Statistical analysis of radiation dose derived from ingestion of foods

NASA Astrophysics Data System (ADS)

Dougherty, Ward L.

2001-09-01

This analysis undertook the task of designing and implementing a methodology to determine an individual's probabilistic radiation dose from ingestion of foods utilizing Crystal Ball. A dietary intake model was determined by comparing previous existing models. Two principal radionuclides were considered-Lead210 (Pb-210) and Radium 226 (Ra-226). Samples from three different local grocery stores-Publix, Winn Dixie, and Albertsons-were counted on a gamma spectroscopy system with a GeLi detector. The same food samples were considered as those in the original FIPR database. A statistical analysis, utilizing the Crystal Ball program, was performed on the data to assess the most accurate distribution to use for these data. This allowed a determination of a radiation dose to an individual based on the above-information collected. Based on the analyses performed, radiation dose for grocery store samples was lower for Radium-226 than FIPR debris analyses, 2.7 vs. 5.91 mrem/yr. Lead-210 had a higher dose in the grocery store sample than the FIPR debris analyses, 21.4 vs. 518 mrem/yr. The output radiation dose was higher for all evaluations when an accurate estimation of distributions for each value was considered. Radium-226 radiation dose for FIPR and grocery rose to 9.56 and 4.38 mrem/yr. Radiation dose from ingestion of Pb-210 rose to 34.7 and 854 mrem/yr for FIPR and grocery data, respectively. Lead-210 was higher than initial doses for many reasons: Different peak examined, lower edge of detection limit, and minimum detectable concentration was considered. FIPR did not utilize grocery samples as a control because they calculated radiation dose that appeared unreasonably high. Consideration of distributions with the initial values allowed reevaluation of radiation does and showed a significant difference to original deterministic values. This work shows the value and importance of considering distributions to ensure that a person's radiation dose is accurately calculated. Probabilistic dose methodology was proved to be a more accurate and realistic method of radiation dose determination. This type of methodology provides a visual presentation of dose distribution that can be a vital aid in risk methodology.

SU-E-T-357: Electronic Compensation Technique to Deliver Total Body Dose

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lakeman, T; Wang, I; Podgorsak, M

Purpose: Total body irradiation (TBI) uses large parallel-opposed radiation fields to suppress the patient’s immune system and eradicate the residual cancer cells in preparation of recipient for bone marrow transplant. The manual placement of lead compensators has conventionally been used to compensate for the varying thickness through the entire body in large-field TBI. The goal of this study is to pursue utilizing the modern electronic compensation technique to more accurately and efficiently deliver dose to patients in need of TBI. Methods: Treatment plans utilizing electronic compensation to deliver a total body dose were created retrospectively for patients for whom CTmore » data had been previously acquired. Each treatment plan includes two, specifically weighted, pair of opposed fields. One pair of open, large fields (collimator=45°), to encompass the patient’s entire anatomy, and one pair of smaller fields (collimator=0°) focused only on the thicker midsection of the patient. The optimal fluence for each one of the smaller fields was calculated at a patient specific penetration depth. Irregular surface compensators provide a more uniform dose distribution within the smaller opposed fields. Results: Dose-volume histograms (DVH) were calculated for the evaluating the electronic compensation technique. In one case, the maximum body doses calculated from the DVH were reduced from the non-compensated 195.8% to 165.3% in the electronically compensated plans, indicating a more uniform dose with the region of electronic compensation. The mean body doses calculated from the DVH were also reduced from the non-compensated 120.6% to 112.7% in the electronically compensated plans, indicating a more accurate delivery of the prescription dose. All calculated monitor units were well within clinically acceptable limits. Conclusion: Electronic compensation technique for TBI will not substantially increase the beam on time while it can significantly reduce the compensator setup time and the potential risk of errors in manually placing lead compensators.« less

Calculations of dose distributions using a neural network model

NASA Astrophysics Data System (ADS)

Mathieu, R.; Martin, E.; Gschwind, R.; Makovicka, L.; Contassot-Vivier, S.; Bahi, J.

2005-03-01

The main goal of external beam radiotherapy is the treatment of tumours, while sparing, as much as possible, surrounding healthy tissues. In order to master and optimize the dose distribution within the patient, dosimetric planning has to be carried out. Thus, for determining the most accurate dose distribution during treatment planning, a compromise must be found between the precision and the speed of calculation. Current techniques, using analytic methods, models and databases, are rapid but lack precision. Enhanced precision can be achieved by using calculation codes based, for example, on Monte Carlo methods. However, in spite of all efforts to optimize speed (methods and computer improvements), Monte Carlo based methods remain painfully slow. A newer way to handle all of these problems is to use a new approach in dosimetric calculation by employing neural networks. Neural networks (Wu and Zhu 2000 Phys. Med. Biol. 45 913-22) provide the advantages of those various approaches while avoiding their main inconveniences, i.e., time-consumption calculations. This permits us to obtain quick and accurate results during clinical treatment planning. Currently, results obtained for a single depth-dose calculation using a Monte Carlo based code (such as BEAM (Rogers et al 2003 NRCC Report PIRS-0509(A) rev G)) require hours of computing. By contrast, the practical use of neural networks (Mathieu et al 2003 Proceedings Journées Scientifiques Francophones, SFRP) provides almost instant results and quite low errors (less than 2%) for a two-dimensional dosimetric map.

Calculations of dose distributions using a neural network model.

PubMed

Mathieu, R; Martin, E; Gschwind, R; Makovicka, L; Contassot-Vivier, S; Bahi, J

2005-03-07

The main goal of external beam radiotherapy is the treatment of tumours, while sparing, as much as possible, surrounding healthy tissues. In order to master and optimize the dose distribution within the patient, dosimetric planning has to be carried out. Thus, for determining the most accurate dose distribution during treatment planning, a compromise must be found between the precision and the speed of calculation. Current techniques, using analytic methods, models and databases, are rapid but lack precision. Enhanced precision can be achieved by using calculation codes based, for example, on Monte Carlo methods. However, in spite of all efforts to optimize speed (methods and computer improvements), Monte Carlo based methods remain painfully slow. A newer way to handle all of these problems is to use a new approach in dosimetric calculation by employing neural networks. Neural networks (Wu and Zhu 2000 Phys. Med. Biol. 45 913-22) provide the advantages of those various approaches while avoiding their main inconveniences, i.e., time-consumption calculations. This permits us to obtain quick and accurate results during clinical treatment planning. Currently, results obtained for a single depth-dose calculation using a Monte Carlo based code (such as BEAM (Rogers et al 2003 NRCC Report PIRS-0509(A) rev G)) require hours of computing. By contrast, the practical use of neural networks (Mathieu et al 2003 Proceedings Journees Scientifiques Francophones, SFRP) provides almost instant results and quite low errors (less than 2%) for a two-dimensional dosimetric map.

Fast CPU-based Monte Carlo simulation for radiotherapy dose calculation.

PubMed

Ziegenhein, Peter; Pirner, Sven; Ph Kamerling, Cornelis; Oelfke, Uwe

2015-08-07

Monte-Carlo (MC) simulations are considered to be the most accurate method for calculating dose distributions in radiotherapy. Its clinical application, however, still is limited by the long runtimes conventional implementations of MC algorithms require to deliver sufficiently accurate results on high resolution imaging data. In order to overcome this obstacle we developed the software-package PhiMC, which is capable of computing precise dose distributions in a sub-minute time-frame by leveraging the potential of modern many- and multi-core CPU-based computers. PhiMC is based on the well verified dose planning method (DPM). We could demonstrate that PhiMC delivers dose distributions which are in excellent agreement to DPM. The multi-core implementation of PhiMC scales well between different computer architectures and achieves a speed-up of up to 37[Formula: see text] compared to the original DPM code executed on a modern system. Furthermore, we could show that our CPU-based implementation on a modern workstation is between 1.25[Formula: see text] and 1.95[Formula: see text] faster than a well-known GPU implementation of the same simulation method on a NVIDIA Tesla C2050. Since CPUs work on several hundreds of GB RAM the typical GPU memory limitation does not apply for our implementation and high resolution clinical plans can be calculated.

An Eye Model for Computational Dosimetry Using A Multi-Scale Voxel Phantom

NASA Astrophysics Data System (ADS)

Caracappa, Peter F.; Rhodes, Ashley; Fiedler, Derek

2014-06-01

The lens of the eye is a radiosensitive tissue with cataract formation being the major concern. Recently reduced recommended dose limits to the lens of the eye have made understanding the dose to this tissue of increased importance. Due to memory limitations, the voxel resolution of computational phantoms used for radiation dose calculations is too large to accurately represent the dimensions of the eye. A revised eye model is constructed using physiological data for the dimensions of radiosensitive tissues, and is then transformed into a high-resolution voxel model. This eye model is combined with an existing set of whole body models to form a multi-scale voxel phantom, which is used with the MCNPX code to calculate radiation dose from various exposure types. This phantom provides an accurate representation of the radiation transport through the structures of the eye. Two alternate methods of including a high-resolution eye model within an existing whole body model are developed. The accuracy and performance of each method is compared against existing computational phantoms.

Validation of a track repeating algorithm for intensity modulated proton therapy: clinical cases study

NASA Astrophysics Data System (ADS)

Yepes, Pablo P.; Eley, John G.; Liu, Amy; Mirkovic, Dragan; Randeniya, Sharmalee; Titt, Uwe; Mohan, Radhe

2016-04-01

Monte Carlo (MC) methods are acknowledged as the most accurate technique to calculate dose distributions. However, due its lengthy calculation times, they are difficult to utilize in the clinic or for large retrospective studies. Track-repeating algorithms, based on MC-generated particle track data in water, accelerate dose calculations substantially, while essentially preserving the accuracy of MC. In this study, we present the validation of an efficient dose calculation algorithm for intensity modulated proton therapy, the fast dose calculator (FDC), based on a track-repeating technique. We validated the FDC algorithm for 23 patients, which included 7 brain, 6 head-and-neck, 5 lung, 1 spine, 1 pelvis and 3 prostate cases. For validation, we compared FDC-generated dose distributions with those from a full-fledged Monte Carlo based on GEANT4 (G4). We compared dose-volume-histograms, 3D-gamma-indices and analyzed a series of dosimetric indices. More than 99% of the voxels in the voxelized phantoms describing the patients have a gamma-index smaller than unity for the 2%/2 mm criteria. In addition the difference relative to the prescribed dose between the dosimetric indices calculated with FDC and G4 is less than 1%. FDC reduces the calculation times from 5 ms per proton to around 5 μs.

Dose calculations at high altitudes and in deep space with GEANT4 using BIC and JQMD models for nucleus nucleus reactions

NASA Astrophysics Data System (ADS)

Sihver, L.; Matthiä, D.; Koi, T.; Mancusi, D.

2008-10-01

Radiation exposure of aircrew is more and more recognized as an occupational hazard. The ionizing environment at standard commercial aircraft flight altitudes consists mainly of secondary particles, of which the neutrons give a major contribution to the dose equivalent. Accurate estimations of neutron spectra in the atmosphere are therefore essential for correct calculations of aircrew doses. Energetic solar particle events (SPE) could also lead to significantly increased dose rates, especially at routes close to the North Pole, e.g. for flights between Europe and USA. It is also well known that the radiation environment encountered by personnel aboard low Earth orbit (LEO) spacecraft or aboard a spacecraft traveling outside the Earth's protective magnetosphere is much harsher compared with that within the atmosphere since the personnel are exposed to radiation from both galactic cosmic rays (GCR) and SPE. The relative contribution to the dose from GCR when traveling outside the Earth's magnetosphere, e.g. to the Moon or Mars, is even greater, and reliable and accurate particle and heavy ion transport codes are essential to calculate the radiation risks for both aircrew and personnel on spacecraft. We have therefore performed calculations of neutron distributions in the atmosphere, total dose equivalents, and quality factors at different depths in a water sphere in an imaginary spacecraft during solar minimum in a geosynchronous orbit. The calculations were performed with the GEANT4 Monte Carlo (MC) code using both the binary cascade (BIC) model, which is part of the standard GEANT4 package, and the JQMD model, which is used in the particle and heavy ion transport code PHITS GEANT4.

Fast dose kernel interpolation using Fourier transform with application to permanent prostate brachytherapy dosimetry.

PubMed

Liu, Derek; Sloboda, Ron S

2014-05-01

Boyer and Mok proposed a fast calculation method employing the Fourier transform (FT), for which calculation time is independent of the number of seeds but seed placement is restricted to calculation grid points. Here an interpolation method is described enabling unrestricted seed placement while preserving the computational efficiency of the original method. The Iodine-125 seed dose kernel was sampled and selected values were modified to optimize interpolation accuracy for clinically relevant doses. For each seed, the kernel was shifted to the nearest grid point via convolution with a unit impulse, implemented in the Fourier domain. The remaining fractional shift was performed using a piecewise third-order Lagrange filter. Implementation of the interpolation method greatly improved FT-based dose calculation accuracy. The dose distribution was accurate to within 2% beyond 3 mm from each seed. Isodose contours were indistinguishable from explicit TG-43 calculation. Dose-volume metric errors were negligible. Computation time for the FT interpolation method was essentially the same as Boyer's method. A FT interpolation method for permanent prostate brachytherapy TG-43 dose calculation was developed which expands upon Boyer's original method and enables unrestricted seed placement. The proposed method substantially improves the clinically relevant dose accuracy with negligible additional computation cost, preserving the efficiency of the original method.

In vivo dose perturbation effects of metallic dental alloys during head and neck irradiation with intensity modulated radiation therapy.

PubMed

Fuller, Clifton D; Diaz, Irma; Cavanaugh, Sean X; Eng, Tony Y

2004-07-01

A patient with base of tongue squamous sell carcinoma, with significant CT artifact-inducing metallic alloy, non-removable dental restorations in both the mandible and maxilla was identified. Simultaneous with IMRT treatment, thermoluminescent dosimeters (TLDs) were placed in the oral cavity. After a series of three treatments, the data from the TLDs and software calculations were analyzed. Analysis of mean in vivo TLD dosimetry reveals differentials from software predicted dose calculation that fall within acceptable dose variation limits. IMRT dose calculation software is a relatively accurate predictor of dose attenuation and augmentation due to dental alloys within the treatment volume, as measured by intra-oral thermoluminescent dosimetry. IMRT represents a safe and effective methodology to treat patients with non-removable metallic dental work who have head and neck cancer.

SU-F-J-217: Accurate Dose Volume Parameters Calculation for Revealing Rectum Dose-Toxicity Effect Using Deformable Registration in Cervical Cancer Brachytherapy: A Pilot Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhen, X; Chen, H; Liao, Y

Purpose: To study the feasibility of employing deformable registration methods for accurate rectum dose volume parameters calculation and their potentials in revealing rectum dose-toxicity between complication and non-complication cervical cancer patients with brachytherapy treatment. Method and Materials: Data from 60 patients treated with BT including planning images, treatment plans, and follow-up clinical exam were retrospectively collected. Among them, 12 patients complained about hematochezia were further examined with colonoscopy and scored as Grade 1–3 complication (CP). Meanwhile, another 12 non-complication (NCP) patients were selected as a reference group. To seek for potential gains in rectum toxicity prediction when fractional anatomical deformationsmore » are account for, the rectum dose volume parameters D0.1/1/2cc of the selected patients were retrospectively computed by three different approaches: the simple “worstcase scenario” (WS) addition method, an intensity-based deformable image registration (DIR) algorithm-Demons, and a more accurate, recent developed local topology preserved non-rigid point matching algorithm (TOP). Statistical significance of the differences between rectum doses of the CP group and the NCP group were tested by a two-tailed t-test and results were considered to be statistically significant if p < 0.05. Results: For the D0.1cc, no statistical differences are found between the CP and NCP group in all three methods. For the D1cc, dose difference is not detected by the WS method, however, statistical differences between the two groups are observed by both Demons and TOP, and more evident in TOP. For the D2cc, the CP and NCP cases are statistically significance of the difference for all three methods but more pronounced with TOP. Conclusion: In this study, we calculated the rectum D0.1/1/2cc by simple WS addition and two DIR methods and seek for gains in rectum toxicity prediction. The results favor the claim that accurate dose deformation and summation tend to be more sensitive in unveiling the dose-toxicity relationship. This work is supported in part by grant from VARIAN MEDICAL SYSTEMS INC, the National Natural Science Foundation of China (no 81428019 and no 81301940), the Guangdong Natural Science Foundation (2015A030313302)and the 2015 Pearl River S&T Nova Program of Guangzhou (201506010096).« less

Investigation of Advanced Dose Verification Techniques for External Beam Radiation Treatment

NASA Astrophysics Data System (ADS)

Asuni, Ganiyu Adeniyi

Intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) have been introduced in radiation therapy to achieve highly conformal dose distributions around the tumour while minimizing dose to surrounding normal tissues. These techniques have increased the need for comprehensive quality assurance tests, to verify that customized patient treatment plans are accurately delivered during treatment. in vivo dose verification, performed during treatment delivery, confirms that the actual dose delivered is the same as the prescribed dose, helping to reduce treatment delivery errors. in vivo measurements may be accomplished using entrance or exit detectors. The objective of this project is to investigate a novel entrance detector designed for in vivo dose verification. This thesis is separated into three main investigations, focusing on a prototype entrance transmission detector (TRD) developed by IBA Dosimetry, Germany. First contaminant electrons generated by the TRD in a 6 MV photon beam were investigated using Monte Carlo (MC) simulation. This study demonstrates that modification of the contaminant electron model in the treatment planning system is required for accurate patient dose calculation in buildup regions when using the device. Second, the ability of the TRD to accurately measure dose from IMRT and VMAT was investigated by characterising the spatial resolution of the device. This was accomplished by measuring the point spread function with further validation provided by MC simulation. Comparisons of measured and calculated doses show that the spatial resolution of the TRD allows for measurement of clinical IMRT fields within acceptable tolerance. Finally, a new general research tool was developed to perform MC simulations for VMAT and IMRT treatments, simultaneously tracking dose deposition in both the patient CT geometry and an arbitrary planar detector system, generalized to handle either entrance or exit orientations. It was demonstrated that the tool accurately simulates dose to the patient CT and planar detector geometries. The tool has been made freely available to the medical physics research community to help advance the development of in vivo planar detectors. In conclusion, this thesis presents several investigations that improve the understanding of a novel entrance detector designed for patient in vivo dosimetry.

Comparison of a 3-D multi-group SN particle transport code with Monte Carlo for intracavitary brachytherapy of the cervix uteri.

PubMed

Gifford, Kent A; Wareing, Todd A; Failla, Gregory; Horton, John L; Eifel, Patricia J; Mourtada, Firas

2009-12-03

A patient dose distribution was calculated by a 3D multi-group S N particle transport code for intracavitary brachytherapy of the cervix uteri and compared to previously published Monte Carlo results. A Cs-137 LDR intracavitary brachytherapy CT data set was chosen from our clinical database. MCNPX version 2.5.c, was used to calculate the dose distribution. A 3D multi-group S N particle transport code, Attila version 6.1.1 was used to simulate the same patient. Each patient applicator was built in SolidWorks, a mechanical design package, and then assembled with a coordinate transformation and rotation for the patient. The SolidWorks exported applicator geometry was imported into Attila for calculation. Dose matrices were overlaid on the patient CT data set. Dose volume histograms and point doses were compared. The MCNPX calculation required 14.8 hours, whereas the Attila calculation required 22.2 minutes on a 1.8 GHz AMD Opteron CPU. Agreement between Attila and MCNPX dose calculations at the ICRU 38 points was within +/- 3%. Calculated doses to the 2 cc and 5 cc volumes of highest dose differed by not more than +/- 1.1% between the two codes. Dose and DVH overlays agreed well qualitatively. Attila can calculate dose accurately and efficiently for this Cs-137 CT-based patient geometry. Our data showed that a three-group cross-section set is adequate for Cs-137 computations. Future work is aimed at implementing an optimized version of Attila for radiotherapy calculations.

Comparison of a 3D multi‐group SN particle transport code with Monte Carlo for intercavitary brachytherapy of the cervix uteri

PubMed Central

Wareing, Todd A.; Failla, Gregory; Horton, John L.; Eifel, Patricia J.; Mourtada, Firas

2009-01-01

A patient dose distribution was calculated by a 3D multi‐group SN particle transport code for intracavitary brachytherapy of the cervix uteri and compared to previously published Monte Carlo results. A Cs‐137 LDR intracavitary brachytherapy CT data set was chosen from our clinical database. MCNPX version 2.5.c, was used to calculate the dose distribution. A 3D multi‐group SN particle transport code, Attila version 6.1.1 was used to simulate the same patient. Each patient applicator was built in SolidWorks, a mechanical design package, and then assembled with a coordinate transformation and rotation for the patient. The SolidWorks exported applicator geometry was imported into Attila for calculation. Dose matrices were overlaid on the patient CT data set. Dose volume histograms and point doses were compared. The MCNPX calculation required 14.8 hours, whereas the Attila calculation required 22.2 minutes on a 1.8 GHz AMD Opteron CPU. Agreement between Attila and MCNPX dose calculations at the ICRU 38 points was within ±3%. Calculated doses to the 2 cc and 5 cc volumes of highest dose differed by not more than ±1.1% between the two codes. Dose and DVH overlays agreed well qualitatively. Attila can calculate dose accurately and efficiently for this Cs‐137 CT‐based patient geometry. Our data showed that a three‐group cross‐section set is adequate for Cs‐137 computations. Future work is aimed at implementing an optimized version of Attila for radiotherapy calculations. PACS number: 87.53.Jw

A photon source model based on particle transport in a parameterized accelerator structure for Monte Carlo dose calculations.

PubMed

Ishizawa, Yoshiki; Dobashi, Suguru; Kadoya, Noriyuki; Ito, Kengo; Chiba, Takahito; Takayama, Yoshiki; Sato, Kiyokazu; Takeda, Ken

2018-05-17

An accurate source model of a medical linear accelerator is essential for Monte Carlo (MC) dose calculations. This study aims to propose an analytical photon source model based on particle transport in parameterized accelerator structures, focusing on a more realistic determination of linac photon spectra compared to existing approaches. We designed the primary and secondary photon sources based on the photons attenuated and scattered by a parameterized flattening filter. The primary photons were derived by attenuating bremsstrahlung photons based on the path length in the filter. Conversely, the secondary photons were derived from the decrement of the primary photons in the attenuation process. This design facilitates these sources to share the free parameters of the filter shape and be related to each other through the photon interaction in the filter. We introduced two other parameters of the primary photon source to describe the particle fluence in penumbral regions. All the parameters are optimized based on calculated dose curves in water using the pencil-beam-based algorithm. To verify the modeling accuracy, we compared the proposed model with the phase space data (PSD) of the Varian TrueBeam 6 and 15 MV accelerators in terms of the beam characteristics and the dose distributions. The EGS5 Monte Carlo code was used to calculate the dose distributions associated with the optimized model and reference PSD in a homogeneous water phantom and a heterogeneous lung phantom. We calculated the percentage of points passing 1D and 2D gamma analysis with 1%/1 mm criteria for the dose curves and lateral dose distributions, respectively. The optimized model accurately reproduced the spectral curves of the reference PSD both on- and off-axis. The depth dose and lateral dose profiles of the optimized model also showed good agreement with those of the reference PSD. The passing rates of the 1D gamma analysis with 1%/1 mm criteria between the model and PSD were 100% for 4 × 4, 10 × 10, and 20 × 20 cm 2 fields at multiple depths. For the 2D dose distributions calculated in the heterogeneous lung phantom, the 2D gamma pass rate was 100% for 6 and 15 MV beams. The model optimization time was less than 4 min. The proposed source model optimization process accurately produces photon fluence spectra from a linac using valid physical properties, without detailed knowledge of the geometry of the linac head, and with minimal optimization time. © 2018 American Association of Physicists in Medicine.

SU-E-CAMPUS-I-05: Internal Dosimetric Calculations for Several Imaging Radiopharmaceuticals in Preclinical Studies and Quantitative Assessment of the Mouse Size Impact On Them. Realistic Monte Carlo Simulations Based On the 4D-MOBY Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kostou, T; Papadimitroulas, P; Kagadis, GC

2014-06-15

Purpose: Commonly used radiopharmaceuticals were tested to define the most important dosimetric factors in preclinical studies. Dosimetric calculations were applied in two different whole-body mouse models, with varying organ size, so as to determine their impact on absorbed doses and S-values. Organ mass influence was evaluated with computational models and Monte Carlo(MC) simulations. Methods: MC simulations were executed on GATE to determine dose distribution in the 4D digital MOBY mouse phantom. Two mouse models, 28 and 34 g respectively, were constructed based on realistic preclinical exams to calculate the absorbed doses and S-values of five commonly used radionuclides in SPECT/PETmore » studies (18F, 68Ga, 177Lu, 111In and 99mTc).Radionuclide biodistributions were obtained from literature. Realistic statistics (uncertainty lower than 4.5%) were acquired using the standard physical model in Geant4. Comparisons of the dosimetric calculations on the two different phantoms for each radiopharmaceutical are presented. Results: Dose per organ in mGy was calculated for all radiopharmaceuticals. The two models introduced a difference of 0.69% in their brain masses, while the largest differences were observed in the marrow 18.98% and in the thyroid 18.65% masses.Furthermore, S-values of the most important target-organs were calculated for each isotope. Source-organ was selected to be the whole mouse body.Differences on the S-factors were observed in the 6.0–30.0% range. Tables with all the calculations as reference dosimetric data were developed. Conclusion: Accurate dose per organ and the most appropriate S-values are derived for specific preclinical studies. The impact of the mouse model size is rather high (up to 30% for a 17.65% difference in the total mass), and thus accurate definition of the organ mass is a crucial parameter for self-absorbed S values calculation.Our goal is to extent the study for accurate estimations in small animal imaging, whereas it is known that there is a large variety in the anatomy of the organs.« less

Optimization of Monte Carlo dose calculations: The interface problem

NASA Astrophysics Data System (ADS)

Soudentas, Edward

1998-05-01

High energy photon beams are widely used for radiation treatment of deep-seated tumors. The human body contains many types of interfaces between dissimilar materials that affect dose distribution in radiation therapy. Experimentally, significant radiation dose perturbations has been observed at such interfaces. The EGS4 Monte Carlo code was used to calculate dose perturbations at boundaries between dissimilar materials (such as bone/water) for 60Co and 6 MeV linear accelerator beams using a UNIX workstation. A simple test of the reliability of a random number generator was also developed. A systematic study of the adjustable parameters in EGS4 was performed in order to minimize calculational artifacts at boundaries. Calculations of dose perturbations at boundaries between different materials showed that there is a 12% increase in dose at water/bone interface, and a 44% increase in dose at water/copper interface. with the increase mainly due to electrons produced in water and backscattered from the high atomic number material. The dependence of the dose increase on the atomic number was also investigated. The clinically important case of using two parallel opposed beams for radiation therapy was investigated where increased doses at boundaries has been observed. The Monte Carlo calculations can provide accurate dosimetry data under conditions of electronic non-equilibrium at tissue interfaces.

New approach based on tetrahedral-mesh geometry for accurate 4D Monte Carlo patient-dose calculation

NASA Astrophysics Data System (ADS)

Han, Min Cheol; Yeom, Yeon Soo; Kim, Chan Hyeong; Kim, Seonghoon; Sohn, Jason W.

2015-02-01

In the present study, to achieve accurate 4D Monte Carlo dose calculation in radiation therapy, we devised a new approach that combines (1) modeling of the patient body using tetrahedral-mesh geometry based on the patient’s 4D CT data, (2) continuous movement/deformation of the tetrahedral patient model by interpolation of deformation vector fields acquired through deformable image registration, and (3) direct transportation of radiation particles during the movement and deformation of the tetrahedral patient model. The results of our feasibility study show that it is certainly possible to construct 4D patient models (= phantoms) with sufficient accuracy using the tetrahedral-mesh geometry and to directly transport radiation particles during continuous movement and deformation of the tetrahedral patient model. This new approach not only produces more accurate dose distribution in the patient but also replaces the current practice of using multiple 3D voxel phantoms and combining multiple dose distributions after Monte Carlo simulations. For routine clinical application of our new approach, the use of fast automatic segmentation algorithms is a must. In order to achieve, simultaneously, both dose accuracy and computation speed, the number of tetrahedrons for the lungs should be optimized. Although the current computation speed of our new 4D Monte Carlo simulation approach is slow (i.e. ~40 times slower than that of the conventional dose accumulation approach), this problem is resolvable by developing, in Geant4, a dedicated navigation class optimized for particle transportation in tetrahedral-mesh geometry.

Dosimetric verification of radiation therapy including intensity modulated treatments, using an amorphous-silicon electronic portal imaging device

NASA Astrophysics Data System (ADS)

Chytyk-Praznik, Krista Joy

Radiation therapy is continuously increasing in complexity due to technological innovation in delivery techniques, necessitating thorough dosimetric verification. Comparing accurately predicted portal dose images to measured images obtained during patient treatment can determine if a particular treatment was delivered correctly. The goal of this thesis was to create a method to predict portal dose images that was versatile and accurate enough to use in a clinical setting. All measured images in this work were obtained with an amorphous silicon electronic portal imaging device (a-Si EPID), but the technique is applicable to any planar imager. A detailed, physics-motivated fluence model was developed to characterize fluence exiting the linear accelerator head. The model was further refined using results from Monte Carlo simulations and schematics of the linear accelerator. The fluence incident on the EPID was converted to a portal dose image through a superposition of Monte Carlo-generated, monoenergetic dose kernels specific to the a-Si EPID. Predictions of clinical IMRT fields with no patient present agreed with measured portal dose images within 3% and 3 mm. The dose kernels were applied ignoring the geometrically divergent nature of incident fluence on the EPID. A computational investigation into this parallel dose kernel assumption determined its validity under clinically relevant situations. Introducing a patient or phantom into the beam required the portal image prediction algorithm to account for patient scatter and attenuation. Primary fluence was calculated by attenuating raylines cast through the patient CT dataset, while scatter fluence was determined through the superposition of pre-calculated scatter fluence kernels. Total dose in the EPID was calculated by convolving the total predicted incident fluence with the EPID-specific dose kernels. The algorithm was tested on water slabs with square fields, agreeing with measurement within 3% and 3 mm. The method was then applied to five prostate and six head-and-neck IMRT treatment courses (˜1900 clinical images). Deviations between the predicted and measured images were quantified. The portal dose image prediction model developed in this thesis work has been shown to be accurate, and it was demonstrated to be able to verify patients' delivered radiation treatments.

Benchmarking and validation of a Geant4-SHADOW Monte Carlo simulation for dose calculations in microbeam radiation therapy.

PubMed

Cornelius, Iwan; Guatelli, Susanna; Fournier, Pauline; Crosbie, Jeffrey C; Sanchez Del Rio, Manuel; Bräuer-Krisch, Elke; Rosenfeld, Anatoly; Lerch, Michael

2014-05-01

Microbeam radiation therapy (MRT) is a synchrotron-based radiotherapy modality that uses high-intensity beams of spatially fractionated radiation to treat tumours. The rapid evolution of MRT towards clinical trials demands accurate treatment planning systems (TPS), as well as independent tools for the verification of TPS calculated dose distributions in order to ensure patient safety and treatment efficacy. Monte Carlo computer simulation represents the most accurate method of dose calculation in patient geometries and is best suited for the purpose of TPS verification. A Monte Carlo model of the ID17 biomedical beamline at the European Synchrotron Radiation Facility has been developed, including recent modifications, using the Geant4 Monte Carlo toolkit interfaced with the SHADOW X-ray optics and ray-tracing libraries. The code was benchmarked by simulating dose profiles in water-equivalent phantoms subject to irradiation by broad-beam (without spatial fractionation) and microbeam (with spatial fractionation) fields, and comparing against those calculated with a previous model of the beamline developed using the PENELOPE code. Validation against additional experimental dose profiles in water-equivalent phantoms subject to broad-beam irradiation was also performed. Good agreement between codes was observed, with the exception of out-of-field doses and toward the field edge for larger field sizes. Microbeam results showed good agreement between both codes and experimental results within uncertainties. Results of the experimental validation showed agreement for different beamline configurations. The asymmetry in the out-of-field dose profiles due to polarization effects was also investigated, yielding important information for the treatment planning process in MRT. This work represents an important step in the development of a Monte Carlo-based independent verification tool for treatment planning in MRT.

SU-E-J-58: Dosimetric Verification of Metal Artifact Effects: Comparison of Dose Distributions Affected by Patient Teeth and Implants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, M; Kang, S; Lee, S

Purpose: Implant-supported dentures seem particularly appropriate for the predicament of becoming edentulous and cancer patients are no exceptions. As the number of people having dental implants increased in different ages, critical dosimetric verification of metal artifact effects are required for the more accurate head and neck radiation therapy. The purpose of this study is to verify the theoretical analysis of the metal(streak and dark) artifact, and to evaluate dosimetric effect which cause by dental implants in CT images of patients with the patient teeth and implants inserted humanoid phantom. Methods: The phantom comprises cylinder which is shaped to simulate themore » anatomical structures of a human head and neck. Through applying various clinical cases, made phantom which is closely allied to human. Developed phantom can verify two classes: (i)closed mouth (ii)opened mouth. RapidArc plans of 4 cases were created in the Eclipse planning system. Total dose of 2000 cGy in 10 fractions is prescribed to the whole planning target volume (PTV) using 6MV photon beams. Acuros XB (AXB) advanced dose calculation algorithm, Analytical Anisotropic Algorithm (AAA) and progressive resolution optimizer were used in dose optimization and calculation. Results: In closed and opened mouth phantom, because dark artifacts formed extensively around the metal implants, dose variation was relatively higher than that of streak artifacts. As the PTV was delineated on the dark regions or large streak artifact regions, maximum 7.8% dose error and average 3.2% difference was observed. The averaged minimum dose to the PTV predicted by AAA was about 5.6% higher and OARs doses are also 5.2% higher compared to AXB. Conclusion: The results of this study showed that AXB dose calculation involving high-density materials is more accurate than AAA calculation, and AXB was superior to AAA in dose predictions beyond dark artifact/air cavity portion when compared against the measurements.« less

Beyond Gaussians: a study of single spot modeling for scanning proton dose calculation

PubMed Central

Li, Yupeng; Zhu, Ronald X.; Sahoo, Narayan; Anand, Aman; Zhang, Xiaodong

2013-01-01

Active spot scanning proton therapy is becoming increasingly adopted by proton therapy centers worldwide. Unlike passive-scattering proton therapy, active spot scanning proton therapy, especially intensity-modulated proton therapy, requires proper modeling of each scanning spot to ensure accurate computation of the total dose distribution contributed from a large number of spots. During commissioning of the spot scanning gantry at the Proton Therapy Center in Houston, it was observed that the long-range scattering protons in a medium may have been inadequately modeled for high-energy beams by a commercial treatment planning system, which could lead to incorrect prediction of field-size effects on dose output. In the present study, we developed a pencil-beam algorithm for scanning-proton dose calculation by focusing on properly modeling individual scanning spots. All modeling parameters required by the pencil-beam algorithm can be generated based solely on a few sets of measured data. We demonstrated that low-dose halos in single-spot profiles in the medium could be adequately modeled with the addition of a modified Cauchy-Lorentz distribution function to a double-Gaussian function. The field-size effects were accurately computed at all depths and field sizes for all energies, and good dose accuracy was also achieved for patient dose verification. The implementation of the proposed pencil beam algorithm also enabled us to study the importance of different modeling components and parameters at various beam energies. The results of this study may be helpful in improving dose calculation accuracy and simplifying beam commissioning and treatment planning processes for spot scanning proton therapy. PMID:22297324

Commissioning of a Varian Clinac iX 6 MV photon beam using Monte Carlo simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dirgayussa, I Gde Eka, E-mail: ekadirgayussa@gmail.com; Yani, Sitti; Haryanto, Freddy, E-mail: freddy@fi.itb.ac.id

2015-09-30

Monte Carlo modelling of a linear accelerator is the first and most important step in Monte Carlo dose calculations in radiotherapy. Monte Carlo is considered today to be the most accurate and detailed calculation method in different fields of medical physics. In this research, we developed a photon beam model for Varian Clinac iX 6 MV equipped with MilleniumMLC120 for dose calculation purposes using BEAMnrc/DOSXYZnrc Monte Carlo system based on the underlying EGSnrc particle transport code. Monte Carlo simulation for this commissioning head LINAC divided in two stages are design head Linac model using BEAMnrc, characterize this model using BEAMDPmore » and analyze the difference between simulation and measurement data using DOSXYZnrc. In the first step, to reduce simulation time, a virtual treatment head LINAC was built in two parts (patient-dependent component and patient-independent component). The incident electron energy varied 6.1 MeV, 6.2 MeV and 6.3 MeV, 6.4 MeV, and 6.6 MeV and the FWHM (full width at half maximum) of source is 1 mm. Phase-space file from the virtual model characterized using BEAMDP. The results of MC calculations using DOSXYZnrc in water phantom are percent depth doses (PDDs) and beam profiles at depths 10 cm were compared with measurements. This process has been completed if the dose difference of measured and calculated relative depth-dose data along the central-axis and dose profile at depths 10 cm is ≤ 5%. The effect of beam width on percentage depth doses and beam profiles was studied. Results of the virtual model were in close agreement with measurements in incident energy electron 6.4 MeV. Our results showed that photon beam width could be tuned using large field beam profile at the depth of maximum dose. The Monte Carlo model developed in this study accurately represents the Varian Clinac iX with millennium MLC 120 leaf and can be used for reliable patient dose calculations. In this commissioning process, the good criteria of dose difference in PDD and dose profiles were achieve using incident electron energy 6.4 MeV.« less

Use of convolution/superposition-based treatment planning system for dose calculations in the kilovoltage energy range

NASA Astrophysics Data System (ADS)

Alaei, Parham

2000-11-01

A number of procedures in diagnostic radiology and cardiology make use of long exposures to x rays from fluoroscopy units. Adverse effects of these long exposure times on the patients' skin have been documented in recent years. These include epilation, erythema, and, in severe cases, moist desquamation and tissue necrosis. Potential biological effects from these exposures to other organs include radiation-induced cataracts and pneumonitis. Although there have been numerous studies to measure or calculate the dose to skin from these procedures, there have only been a handful of studies to determine the dose to other organs. Therefore, there is a need for accurate methods to measure the dose in tissues and organs other than the skin. This research was concentrated in devising a method to determine accurately the radiation dose to these tissues and organs. The work was performed in several stages: First, a three dimensional (3D) treatment planning system used in radiation oncology was modified and complemented to make it usable with the low energies of x rays used in diagnostic radiology. Using the system for low energies required generation of energy deposition kernels using Monte Carlo methods. These kernels were generated using the EGS4 Monte Carlo system of codes and added to the treatment planning system. Following modification, the treatment planning system was evaluated for its accuracy of calculations in low energies within homogeneous and heterogeneous media. A study of the effects of lungs and bones on the dose distribution was also performed. The next step was the calculation of dose distributions in humanoid phantoms using this modified system. The system was used to calculate organ doses in these phantoms and the results were compared to those obtained from other methods. These dose distributions can subsequently be used to create dose-volume histograms (DVHs) for internal organs irradiated by these beams. Using this data and the concept of normal tissue complication probability (NTCP) developed for radiation oncology, the risk of future complications in a particular organ can be estimated.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Badkul, R; Nicolai, W; Pokhrel, D

Purpose: To compare the impact of Pencil Beam(PB) and Anisotropic Analytic Algorithm(AAA) dose calculation algorithms on OARs and planning target volume (PTV) in thoracic spine stereotactic body radiation therapy (SBRT). Methods: Ten Spine SBRT patients were planned on Brainlab iPlan system using hybrid plan consisting of 1–2 non-coplanar conformal-dynamic arcs and few IMRT beams treated on NovalisTx with 6MV photon. Dose prescription varied from 20Gy to 30Gy in 5 fractions depending on the situation of the patient. PB plans were retrospectively recalculated using the Varian Eclipse with AAA algorithm using same MUs, MLC pattern and grid size(3mm).Differences in dose volumemore » parameters for PTV, spinal cord, lung, and esophagus were analyzed and compared for PB and AAA algorithms. OAR constrains were followed per RTOG-0631. Results: Since patients were treated using PB calculation, we compared all the AAA DVH values with respect to PB plan values as standard, although AAA predicts the dose more accurately than PB. PTV(min), PTV(Max), PTV(mean), PTV(D99%), PTV(D90%) were overestimated with AAA calculation on average by 3.5%, 1.84%, 0.95%, 3.98% and 1.55% respectively as compared to PB. All lung DVH parameters were underestimated with AAA algorithm mean deviation of lung V20, V10, V5, and 1000cc were 42.81%,19.83%, 18.79%, and 18.35% respectively. AAA overestimated Cord(0.35cc) by mean of 17.3%; cord (0.03cc) by 12.19% and cord(max) by 10.5% as compared to PB. Esophagus max dose were overestimated by 4.4% and 5cc by 3.26% for AAA algorithm as compared to PB. Conclusion: AAA overestimated the PTV dose values by up to 4%.The lung DVH had the greatest underestimation of dose by AAA versus PB. Spinal cord dose was overestimated by AAA versus PB. Given the critical importance of accuracy of OAR and PTV dose calculation for SBRT spine, more accurate algorithms and validation of calculated doses in phantom models are indicated.« less

SU-C-BRC-04: Efficient Dose Calculation Algorithm for FFF IMRT with a Simplified Bivariate Gaussian Source Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, F; Park, J; Barraclough, B

2016-06-15

Purpose: To develop an efficient and accurate independent dose calculation algorithm with a simplified analytical source model for the quality assurance and safe delivery of Flattening Filter Free (FFF)-IMRT on an Elekta Versa HD. Methods: The source model consisted of a point source and a 2D bivariate Gaussian source, respectively modeling the primary photons and the combined effect of head scatter, monitor chamber backscatter and collimator exchange effect. The in-air fluence was firstly calculated by back-projecting the edges of beam defining devices onto the source plane and integrating the visible source distribution. The effect of the rounded MLC leaf end,more » tongue-and-groove and interleaf transmission was taken into account in the back-projection. The in-air fluence was then modified with a fourth degree polynomial modeling the cone-shaped dose distribution of FFF beams. Planar dose distribution was obtained by convolving the in-air fluence with a dose deposition kernel (DDK) consisting of the sum of three 2D Gaussian functions. The parameters of the source model and the DDK were commissioned using measured in-air output factors (Sc) and cross beam profiles, respectively. A novel method was used to eliminate the volume averaging effect of ion chambers in determining the DDK. Planar dose distributions of five head-and-neck FFF-IMRT plans were calculated and compared against measurements performed with a 2D diode array (MapCHECK™) to validate the accuracy of the algorithm. Results: The proposed source model predicted Sc for both 6MV and 10MV with an accuracy better than 0.1%. With a stringent gamma criterion (2%/2mm/local difference), the passing rate of the FFF-IMRT dose calculation was 97.2±2.6%. Conclusion: The removal of the flattening filter represents a simplification of the head structure which allows the use of a simpler source model for very accurate dose calculation. The proposed algorithm offers an effective way to ensure the safe delivery of FFF-IMRT.« less

SU-E-T-481: Dosimetric Effects of Tissue Heterogeneity in Proton Therapy: Monte Carlo Simulation and Experimental Study Using Animal Tissue Phantoms.

PubMed

Liu, Y; Zheng, Y

2012-06-01

Accurate determination of proton dosimetric effect for tissue heterogeneity is critical in proton therapy. Proton beams have finite range and consequently tissue heterogeneity plays a more critical role in proton therapy. The purpose of this study is to investigate the tissue heterogeneity effect in proton dosimetry based on anatomical-based Monte Carlo simulation using animal tissues. Animal tissues including a pig head and beef bulk were used in this study. Both pig head and beef were scanned using a GE CT scanner with 1.25 mm slice thickness. A treatment plan was created, using the CMS XiO treatment planning system (TPS) with a single proton spread-out-Bragg-peak beam (SOBP). Radiochromic films were placed at the distal falloff region. Image guidance was used to align the phantom before proton beams were delivered according to the treatment plan. The same two CT sets were converted to Monte Carlo simulation model. The Monte Carlo simulated dose calculations with/without tissue omposition were compared to TPS calculations and measurements. Based on the preliminary comparison, at the center of SOBP plane, the Monte Carlo simulation dose without tissue composition agreed generally well with TPS calculation. In the distal falloff region, the dose difference was large, and about 2 mm isodose line shift was observed with the consideration of tissue composition. The detailed comparison of dose distributions between Monte Carlo simulation, TPS calculations and measurements is underway. Accurate proton dose calculations are challenging in proton treatment planning for heterogeneous tissues. Tissue heterogeneity and tissue composition may lead to isodose line shifts up to a few millimeters in the distal falloff region. By simulating detailed particle transport and energy deposition, Monte Carlo simulations provide a verification method in proton dose calculation where inhomogeneous tissues are present. © 2012 American Association of Physicists in Medicine.

TH-E-BRE-05: Analysis of Dosimetric Characteristics in Two Leaf Motion Calculator Algorithms for Sliding Window IMRT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, L; Huang, B; Rowedder, B

Purpose: The Smart leaf motion calculator (SLMC) in Eclipse treatment planning system is an advanced fluence delivery modeling algorithm as it takes into account fine MLC features including inter-leaf leakage, rounded leaf tips, non-uniform leaf thickness, and the spindle cavity etc. In this study, SLMC and traditional Varian LMC (VLMC) algorithms were investigated, for the first time, in dosimetric characteristics and delivery accuracy of sliding window (SW) IMRT. Methods: The SW IMRT plans of 51 cancer cases were included to evaluate dosimetric characteristics and dose delivery accuracy from leaf motion calculated by SLMC and VLMC, respectively. All plans were deliveredmore » using a Varian TrueBeam Linac. The DVH and MUs of the plans were analyzed. Three patient specific QA tools - independent dose calculation software IMSure, Delta4 phantom, and EPID portal dosimetry were also used to measure the delivered dose distribution. Results: Significant differences in the MUs were observed between the two LMCs (p≤0.001).Gamma analysis shows an excellent agreement between the planned dose distribution calculated by both LMC algorithms and delivered dose distribution measured by three QA tools in all plans at 3%/3 mm, leading to a mean pass rate exceeding 97%. The mean fraction of pixels with gamma < 1 of SLMC is slightly lower than that of VLMC in the IMSure and Delta4 results, but higher in portal dosimetry (the highest spatial resolution), especially in complex cases such as nasopharynx. Conclusion: The study suggests that the two LMCs generates the similar target coverage and sparing patterns of critical structures. However, SLMC is modestly more accurate than VLMC in modeling advanced MLC features, which may lead to a more accurate dose delivery in SW IMRT. Current clinical QA tools might not be specific enough to differentiate the dosimetric discrepancies at the millimeter level calculated by these two LMC algorithms. NIH/NIGMS grant U54 GM104944, Lincy Endowed Assistant Professorship.« less

Validation of OSLD and a treatment planning system for surface dose determination in IMRT treatments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhuang, Audrey H., E-mail: hzhuang@usc.edu; Olch, Arthur J.

2014-08-15

Purpose: To evaluate the accuracy of skin dose determination for composite multibeam 3D conformal radiation therapy (3DCRT) and intensity modulated radiation therapy (IMRT) treatments using optically stimulated luminescent dosimeters (OSLDs) and Eclipse treatment planning system. Methods: Surface doses measured by OSLDs in the buildup region for open field 6 MV beams, either perpendicular or oblique to the surface, were evaluated by comparing against dose measured by Markus Parallel Plate (PP) chamber, surface diodes, and calculated by Monte Carlo simulations. The accuracy of percent depth dose (PDD) calculation in the buildup region from the authors’ Eclipse system (Version 10), which wasmore » precisely commissioned in the buildup region and was used with 1 mm calculation grid, was also evaluated by comparing to PP chamber measurements and Monte Carlo simulations. Finally, an anthropomorphic pelvic phantom was CT scanned with OSLDs in place at three locations. A planning target volume (PTV) was defined that extended close to the surface. Both an 8 beam 3DCRT and IMRT plan were generated in Eclipse. OSLDs were placed at the CT scanned reference locations to measure the skin doses and were compared to diode measurements and Eclipse calculations. Efforts were made to ensure that the dose comparison was done at the effective measurement points of each detector and corresponding locations in CT images. Results: The depth of the effective measurement point is 0.8 mm for OSLD when used in the buildup region in a 6 MV beam and is 0.7 mm for the authors’ surface diode. OSLDs and Eclipse system both agree well with Monte Carlo and/or Markus PP ion chamber and/or diode in buildup regions in 6 MV beams with normal or oblique incidence and across different field sizes. For the multiple beam 3DCRT plan and IMRT plans, the differences between OSLDs and Eclipse calculations on the surface of the anthropomorphic phantom were within 3% and distance-to-agreement less than 0.3 mm. Conclusions: The authors’ experiment showed that OSLD is an accurate dosimeter for skin dose measurements in complex 3DCRT or IMRT plans. It also showed that an Eclipse system with accurate commissioning of the data in the buildup region and 1 mm calculation grid can calculate surface doses with high accuracy and has a potential to replacein vivo measurements.« less

Prediction of Exposure Level of Energetic Solar Particle Events

NASA Astrophysics Data System (ADS)

Kim, M. H. Y.; Blattnig, S.

2016-12-01

The potential for exposure to large solar particle events (SPEs) with fluxes that extend to high energies is a major concern during interplanetary transfer and extravehicular activities (EVAs) on the lunar and Martian surfaces. Prediction of sporadic occurrence of SPEs is not accurate for near or long-term scales, while the expected frequency of such events is strongly influenced by solar cycle activity. In the development of NASA's operational strategies real-time estimation of exposure to SPEs has been considered so that adequate responses can be applied in a timely manner to reduce exposures to well below the exposure limits. Previously, the organ doses of large historical SPEs had been calculated by using the complete energy spectra of each event and then developing a prediction model for blood-forming organ (BFO) dose based solely on an assumed value of integrated fluence above 30 MeV (Φ30) for an otherwise unspecified future SPE. While BFO dose is determined primarily by solar protons with high energies, it was reasoned that more accurate BFO dose prediction models could be developed using integrated fluence above 60 MeV (Φ60) and above 100 MeV (Φ100) as predictors instead of Φ30. In the current study, re-analysis of major SPEs (in which the proton spectra of the ground level enhancement [GLE] events since 1956 are correctly described by Band functions) has been used in evaluation of exposure levels. More accurate prediction models for BFO dose and NASA effective dose are then developed using integrated fluence above 200 MeV (Φ200), which by far have the most weight in the calculation of doses for deep-seated organs from exposure to extreme SPEs (GLEs or sub-GLEs). The unconditional probability of a BFO dose exceeding a pre-specified BFO dose limit is simultaneously calculated by taking into account the distribution of the predictor (Φ30, Φ60, Φ100, or Φ200) as estimated from historical SPEs. These results can be applied to the development of approaches to improve radiation protection of astronauts and the optimization of mission planning for future space missions.

Electronic compensation technique to deliver a total body dose

NASA Astrophysics Data System (ADS)

Lakeman, Tara E.

Purpose: Total body irradiation (TBI) uses large parallel-opposed radiation fields to suppress the patient's immune system and eradicate the residual cancer cells in preparation of recipient for bone marrow transplant. The manual placement of lead compensators has been conventionally used to compensate for the varying thickness throughout the body in large-field TBI. The goal of this study is to pursue utilizing the modern electronic compensation technique to more accurately and efficiently deliver dose to patients in need of TBI. Method: Treatment plans utilizing the electronic compensation to deliver a total body dose were created retrospectively for patients for whom CT data had been previously acquired. Each treatment plan includes two pair of parallel opposed fields. One pair of large fields is used to encompass the majority of the patient's anatomy. The other pair are very small open fields focused only on the thin bottom portion of the patient's anatomy, which requires much less radiation than the rest of the body to reach 100% of the prescribed dose. A desirable fluence pattern was manually painted within each of the larger fields for each patient to provide a more uniform distribution. Results: Dose-volume histograms (DVH) were calculated for evaluating the electronic compensation technique. In the electronically compensated plans, the maximum body doses calculated from the DVH were reduced from the conventionally-compensated plans by an average of 15%, indicating a more uniform dose. The mean body doses calculated from the electronically compensated DVH remained comparable to that of the conventionally-compensated plans, indicating an accurate delivery of the prescription dose using electronic compensation. All calculated monitor units were within clinically acceptable limits. Conclusion: Electronic compensation technique for TBI will not increase the beam on time beyond clinically acceptable limits while it can substantially reduce the compensator setup time and the potential risk of errors in manually placing lead compensators.

An end-to-end assessment of range uncertainty in proton therapy using animal tissues.

PubMed

Zheng, Yuanshui; Kang, Yixiu; Zeidan, Omar; Schreuder, Niek

2016-11-21

Accurate assessment of range uncertainty is critical in proton therapy. However, there is a lack of data and consensus on how to evaluate the appropriate amount of uncertainty. The purpose of this study is to quantify the range uncertainty in various treatment conditions in proton therapy, using transmission measurements through various animal tissues. Animal tissues, including a pig head, beef steak, and lamb leg, were used in this study. For each tissue, an end-to-end test closely imitating patient treatments was performed. This included CT scan simulation, treatment planning, image-guided alignment, and beam delivery. Radio-chromic films were placed at various depths in the distal dose falloff region to measure depth dose. Comparisons between measured and calculated doses were used to evaluate range differences. The dose difference at the distal falloff between measurement and calculation depends on tissue type and treatment conditions. The estimated range difference was up to 5, 6 and 4 mm for the pig head, beef steak, and lamb leg irradiation, respectively. Our study shows that the TPS was able to calculate proton range within about 1.5% plus 1.5 mm. Accurate assessment of range uncertainty in treatment planning would allow better optimization of proton beam treatment, thus fully achieving proton beams' superior dose advantage over conventional photon-based radiation therapy.

Comparison of selected dose calculation algorithms in radiotherapy treatment planning for tissues with inhomogeneities

NASA Astrophysics Data System (ADS)

Woon, Y. L.; Heng, S. P.; Wong, J. H. D.; Ung, N. M.

2016-03-01

Inhomogeneity correction is recommended for accurate dose calculation in radiotherapy treatment planning since human body are highly inhomogeneous with the presence of bones and air cavities. However, each dose calculation algorithm has its own limitations. This study is to assess the accuracy of five algorithms that are currently implemented for treatment planning, including pencil beam convolution (PBC), superposition (SP), anisotropic analytical algorithm (AAA), Monte Carlo (MC) and Acuros XB (AXB). The calculated dose was compared with the measured dose using radiochromic film (Gafchromic EBT2) in inhomogeneous phantoms. In addition, the dosimetric impact of different algorithms on intensity modulated radiotherapy (IMRT) was studied for head and neck region. MC had the best agreement with the measured percentage depth dose (PDD) within the inhomogeneous region. This was followed by AXB, AAA, SP and PBC. For IMRT planning, MC algorithm is recommended for treatment planning in preference to PBC and SP. The MC and AXB algorithms were found to have better accuracy in terms of inhomogeneity correction and should be used for tumour volume within the proximity of inhomogeneous structures.

SU-F-T-415: Differences in Lung Sparing in Deep Inspiration Breath-Hold and Free Breathing Breast Plans Calculated in Pinnacle and Monaco

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saenz, D; Stathakis, S

Purpose: Deep inspiration breath-hold (DIBH) is used for left-sided breast radiotherapy to spare the heart and lung. The magnitude of sparing has been shown to be significant. Monte Carlo, furthermore, has the potential to calculate most accurately the dose in the heterogeneous lung medium at the interface with the lung wall. The lung dose was investigated in Monaco to determine the level of sparing relative to that calculated in Pinnacle{sup 3}. Methods: Five patients undergoing DIBH radiotherapy on an Elekta Versa HD linear accelerator in conjunction with the Catalyst C-RAD surface imaging system were planned using Phillips Pinnacle{sup 3}. Freemore » breathing plans were also created to clinically assure a benefit. Both plans were re-calculated in Monaco to determine if there were any significant differences. The mean heart dose, mean left lung, and mean total lung dose were compared in addition to the V20 for left and both lungs. Dose was calculated as dose to medium as well as dose to water with a statistical precision of 0.7%. Results: Mean lung dose was significantly different (p < 0.003) between the two calculations for both DIBH (11.6% higher in Monaco) and free breathing (14.2% higher in Monaco). V20 was also higher in Monaco (p < 0.05) for DIBH (5.7% higher) and free breathing (4.9% higher). The mean heart dose was not significantly different between the dose calculations for either DIBH or free breathing. Results were no more than 0.1% different when calculated as dose to water. Conclusion: The use of Monte Carlo can provide insight on the lung dose for both free breathing and DIBH techniques for whole breast irradiation. While the sparing (dose reductions with DIBH as compared to free breathing) is equivalent for either planning system, the lung doses themselves are higher when calculated with Monaco.« less

A simplified approach to characterizing a kilovoltage source spectrum for accurate dose computation.

PubMed

Poirier, Yannick; Kouznetsov, Alexei; Tambasco, Mauro

2012-06-01

To investigate and validate the clinical feasibility of using half-value layer (HVL) and peak tube potential (kVp) for characterizing a kilovoltage (kV) source spectrum for the purpose of computing kV x-ray dose accrued from imaging procedures. To use this approach to characterize a Varian® On-Board Imager® (OBI) source and perform experimental validation of a novel in-house hybrid dose computation algorithm for kV x-rays. We characterized the spectrum of an imaging kV x-ray source using the HVL and the kVp as the sole beam quality identifiers using third-party freeware Spektr to generate the spectra. We studied the sensitivity of our dose computation algorithm to uncertainties in the beam's HVL and kVp by systematically varying these spectral parameters. To validate our approach experimentally, we characterized the spectrum of a Varian® OBI system by measuring the HVL using a Farmer-type Capintec ion chamber (0.06 cc) in air and compared dose calculations using our computationally validated in-house kV dose calculation code to measured percent depth-dose and transverse dose profiles for 80, 100, and 125 kVp open beams in a homogeneous phantom and a heterogeneous phantom comprising tissue, lung, and bone equivalent materials. The sensitivity analysis of the beam quality parameters (i.e., HVL, kVp, and field size) on dose computation accuracy shows that typical measurement uncertainties in the HVL and kVp (±0.2 mm Al and ±2 kVp, respectively) source characterization parameters lead to dose computation errors of less than 2%. Furthermore, for an open beam with no added filtration, HVL variations affect dose computation accuracy by less than 1% for a 125 kVp beam when field size is varied from 5 × 5 cm(2) to 40 × 40 cm(2). The central axis depth dose calculations and experimental measurements for the 80, 100, and 125 kVp energies agreed within 2% for the homogeneous and heterogeneous block phantoms, and agreement for the transverse dose profiles was within 6%. The HVL and kVp are sufficient for characterizing a kV x-ray source spectrum for accurate dose computation. As these parameters can be easily and accurately measured, they provide for a clinically feasible approach to characterizing a kV energy spectrum to be used for patient specific x-ray dose computations. Furthermore, these results provide experimental validation of our novel hybrid dose computation algorithm. © 2012 American Association of Physicists in Medicine.

Monte Carlo calculations for reporting patient organ doses from interventional radiology

NASA Astrophysics Data System (ADS)

Huo, Wanli; Feng, Mang; Pi, Yifei; Chen, Zhi; Gao, Yiming; Xu, X. George

2017-09-01

This paper describes a project to generate organ dose data for the purposes of extending VirtualDose software from CT imaging to interventional radiology (IR) applications. A library of 23 mesh-based anthropometric patient phantoms were involved in Monte Carlo simulations for database calculations. Organ doses and effective doses of IR procedures with specific beam projection, filed of view (FOV) and beam quality for all parts of body were obtained. Comparing organ doses for different beam qualities, beam projections, patients' ages and patient's body mass indexes (BMIs) which generated by VirtualDose-IR, significant discrepancies were observed. For relatively long time exposure, IR doses depend on beam quality, beam direction and patient size. Therefore, VirtualDose-IR, which is based on the latest anatomically realistic patient phantoms, can generate accurate doses for IR treatment. It is suitable to apply this software in clinical IR dose management as an effective tool to estimate patient doses and optimize IR treatment plans.

Shading correction for cone-beam CT in radiotherapy: validation of dose calculation accuracy using clinical images

NASA Astrophysics Data System (ADS)

Marchant, T. E.; Joshi, K. D.; Moore, C. J.

2017-03-01

Cone-beam CT (CBCT) images are routinely acquired to verify patient position in radiotherapy (RT), but are typically not calibrated in Hounsfield Units (HU) and feature non-uniformity due to X-ray scatter and detector persistence effects. This prevents direct use of CBCT for re-calculation of RT delivered dose. We previously developed a prior-image based correction method to restore HU values and improve uniformity of CBCT images. Here we validate the accuracy with which corrected CBCT can be used for dosimetric assessment of RT delivery, using CBCT images and RT plans for 45 patients including pelvis, lung and head sites. Dose distributions were calculated based on each patient's original RT plan and using CBCT image values for tissue heterogeneity correction. Clinically relevant dose metrics were calculated (e.g. median and minimum target dose, maximum organ at risk dose). Accuracy of CBCT based dose metrics was determined using an "override ratio" method where the ratio of the dose metric to that calculated on a bulk-density assigned version of the image is assumed to be constant for each patient, allowing comparison to "gold standard" CT. For pelvis and head images the proportion of dose errors >2% was reduced from 40% to 1.3% after applying shading correction. For lung images the proportion of dose errors >3% was reduced from 66% to 2.2%. Application of shading correction to CBCT images greatly improves their utility for dosimetric assessment of RT delivery, allowing high confidence that CBCT dose calculations are accurate within 2-3%.

The dosimetric effects of tissue heterogeneities in intensity-modulated radiation therapy (IMRT) of the head and neck

NASA Astrophysics Data System (ADS)

Al-Hallaq, H. A.; Reft, C. S.; Roeske, J. C.

2006-03-01

The dosimetric effects of bone and air heterogeneities in head and neck IMRT treatments were quantified. An anthropomorphic RANDO phantom was CT-scanned with 16 thermoluminescent dosimeter (TLD) chips placed in and around the target volume. A standard IMRT plan generated with CORVUS was used to irradiate the phantom five times. On average, measured dose was 5.1% higher than calculated dose. Measurements were higher by 7.1% near the heterogeneities and by 2.6% in tissue. The dose difference between measurement and calculation was outside the 95% measurement confidence interval for six TLDs. Using CORVUS' heterogeneity correction algorithm, the average difference between measured and calculated doses decreased by 1.8% near the heterogeneities and by 0.7% in tissue. Furthermore, dose differences lying outside the 95% confidence interval were eliminated for five of the six TLDs. TLD doses recalculated by Pinnacle3's convolution/superposition algorithm were consistently higher than CORVUS doses, a trend that matched our measured results. These results indicate that the dosimetric effects of air cavities are larger than those of bone heterogeneities, thereby leading to a higher delivered dose compared to CORVUS calculations. More sophisticated algorithms such as convolution/superposition or Monte Carlo should be used for accurate tailoring of IMRT dose in head and neck tumours.

Ionization chamber-based reference dosimetry of intensity modulated radiation beams.

PubMed

Bouchard, Hugo; Seuntjens, Jan

2004-09-01

The present paper addresses reference dose measurements using thimble ionization chambers for quality assurance in IMRT fields. In these radiation fields, detector fluence perturbation effects invalidate the application of open-field dosimetry protocol data for the derivation of absorbed dose to water from ionization chamber measurements. We define a correction factor C(Q)IMRT to correct the absorbed dose to water calibration coefficient N(D, w)Q for fluence perturbation effects in individual segments of an IMRT delivery and developed a calculation method to evaluate the factor. The method consists of precalculating, using accurate Monte Carlo techniques, ionization chamber, type-dependent cavity air dose, and in-phantom dose to water at the reference point for zero-width pencil beams as a function of position of the pencil beams impinging on the phantom surface. These precalculated kernels are convolved with the IMRT fluence distribution to arrive at the dose-to-water-dose-to-cavity air ratio [D(a)w (IMRT)] for IMRT fields and with a 10x10 cm2 open-field fluence to arrive at the same ratio D(a)w (Q) for the 10x10 cm2 reference field. The correction factor C(Q)IMRT is then calculated as the ratio of D(a)w (IMRT) and D(a)w (Q). The calculation method was experimentally validated and the magnitude of chamber correction factors in reference dose measurements in single static and dynamic IMRT fields was studied. The results show that, for thimble-type ionization chambers the correction factor in a single, realistic dynamic IMRT field can be of the order of 10% or more. We therefore propose that for accurate reference dosimetry of complete n-beam IMRT deliveries, ionization chamber fluence perturbation correction factors must explicitly be taken into account.

SU-E-T-512: Evaluation of Treatment Planning Dose Calculation Accuracy at the Interface of Prosthetic Devices.

PubMed

Paulu, D; Alaei, P

2012-06-01

To evaluate the ability of treatment planning algorithm to accurately predict dose delivered at the interface of high density implanted devices. A high density (7.6 g/cc) Cobalt-Chromium-Molybdenum hip prosthesis was molded into an epoxy-based cylindrical leg phantom. The phantom was designed to be separated in half to access the prosthesis and to place the TLDs. Using MVCT to image the apparatus, a simple treatment plan was developed using the Philips Pinnacle treatment planning system. Wires were placed in the molded epoxy to allow for accurate definition of measurement sites (TLD positions) along the surface of the prosthesis. Micro-cube TLDs (1 mm 3 ) were placed at six measurement locations for which the dose had been calculated by the treatment planning system. An Elekta Synergy linear accelerator was used to deliver a 400 cGy plan to the phantom with 6 MV photons in a single fraction. A total of four 10 cm × 21 cm fields were used at 0, 90, 180, and 270 degree gantry rotations. Initial results indicate that the measured dose is 7-17% lower than the dose calculated by the treatment planning system. Further study using high energy beams are also in progress. Initial results indicate that the treatment planning system does predict the dose near a high density prosthetic device within 10-15% but underestimates the dose. The results of this study could help in designing treatment plans which would reduce the uncertainty of the dose delivered in the vicinity of prosthetic hip implants and similar devices. © 2012 American Association of Physicists in Medicine.

TH-A-19A-06: Site-Specific Comparison of Analytical and Monte Carlo Based Dose Calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schuemann, J; Grassberger, C; Paganetti, H

2014-06-15

Purpose: To investigate the impact of complex patient geometries on the capability of analytical dose calculation algorithms to accurately predict dose distributions and to verify currently used uncertainty margins in proton therapy. Methods: Dose distributions predicted by an analytical pencilbeam algorithm were compared with Monte Carlo simulations (MCS) using TOPAS. 79 complete patient treatment plans were investigated for 7 disease sites (liver, prostate, breast, medulloblastoma spine and whole brain, lung and head and neck). A total of 508 individual passively scattered treatment fields were analyzed for field specific properties. Comparisons based on target coverage indices (EUD, D95, D90 and D50)more » were performed. Range differences were estimated for the distal position of the 90% dose level (R90) and the 50% dose level (R50). Two-dimensional distal dose surfaces were calculated and the root mean square differences (RMSD), average range difference (ARD) and average distal dose degradation (ADD), the distance between the distal position of the 80% and 20% dose levels (R80- R20), were analyzed. Results: We found target coverage indices calculated by TOPAS to generally be around 1–2% lower than predicted by the analytical algorithm. Differences in R90 predicted by TOPAS and the planning system can be larger than currently applied range margins in proton therapy for small regions distal to the target volume. We estimate new site-specific range margins (R90) for analytical dose calculations considering total range uncertainties and uncertainties from dose calculation alone based on the RMSD. Our results demonstrate that a reduction of currently used uncertainty margins is feasible for liver, prostate and whole brain fields even without introducing MC dose calculations. Conclusion: Analytical dose calculation algorithms predict dose distributions within clinical limits for more homogeneous patients sites (liver, prostate, whole brain). However, we recommend treatment plan verification using Monte Carlo simulations for patients with complex geometries.« less

SU-F-BRF-13: Investigating the Feasibility of Accurate Dose Measurement in a Deforming Radiochromic Dosimeter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Juang, T; Adamovics, J; Oldham, M

Purpose: Presage-Def, a deformable radiochromic 3D dosimeter, has been previously shown to have potential for validating deformable image registration algorithms. This work extends this effort to investigate the feasibility of using Presage-Def to validate dose-accumulation algorithms in deforming structures. Methods: Two cylindrical Presage-Def dosimeters (8cm diameter, 4.5cm length) were irradiated in a water-bath with a simple 4-field box treatment. Isocentric dose was 20Gy. One dosimeter served as control (no deformation) while the other was laterally compressed during irradiation by 21%. Both dosimeters were imaged before and after irradiation with a fast (∼10 minutes for 1mm isotropic resolution), broad beam, highmore » resolution optical-CT scanner. Measured dose distributions were compared to corresponding distributions calculated by a commissioned Eclipse planning system. Accuracy in the control was evaluated with 3D gamma (3%/3mm). The dose distribution calculated for the compressed dosimeter in the irradiation geometry cannot be directly compared via profiles or 3D gamma to the measured distribution, which deforms with release from compression. Thus, accuracy under deformation was determined by comparing integral dose within the high dose region of the deformed dosimeter distribution versus calculated dose. Dose profiles were used to study temporal stability of measured dose distributions. Results: Good dose agreement was demonstrated in the control with a 3D gamma passing rate of 96.6%. For the dosimeter irradiated under compression, the measured integral dose in the high dose region (518.0Gy*cm3) was within 6% of the Eclipse-calculated integral dose (549.4Gy*cm3). Elevated signal was noted on the dosimeter edge in the direction of compression. Change in dosimeter signal over 1.5 hours was ≤2.7%, and the relative dose distribution remained stable over this period of time. Conclusion: Presage-Def is promising as a 3D dosimeter capable of accurately measuring dose in a deforming structure, and warrants further study to quantify comprehensive accuracy at different levels of deformation. This work was supported by NIH R01CA100835. John Adamovics is the president of Heuris Inc., which commercializes PRESAGE.« less

Dose calculation of dynamic trajectory radiotherapy using Monte Carlo.

PubMed

Manser, P; Frauchiger, D; Frei, D; Volken, W; Terribilini, D; Fix, M K

2018-04-06

Using volumetric modulated arc therapy (VMAT) delivery technique gantry position, multi-leaf collimator (MLC) as well as dose rate change dynamically during the application. However, additional components can be dynamically altered throughout the dose delivery such as the collimator or the couch. Thus, the degrees of freedom increase allowing almost arbitrary dynamic trajectories for the beam. While the dose delivery of such dynamic trajectories for linear accelerators is technically possible, there is currently no dose calculation and validation tool available. Thus, the aim of this work is to develop a dose calculation and verification tool for dynamic trajectories using Monte Carlo (MC) methods. The dose calculation for dynamic trajectories is implemented in the previously developed Swiss Monte Carlo Plan (SMCP). SMCP interfaces the treatment planning system Eclipse with a MC dose calculation algorithm and is already able to handle dynamic MLC and gantry rotations. Hence, the additional dynamic components, namely the collimator and the couch, are described similarly to the dynamic MLC by defining data pairs of positions of the dynamic component and the corresponding MU-fractions. For validation purposes, measurements are performed with the Delta4 phantom and film measurements using the developer mode on a TrueBeam linear accelerator. These measured dose distributions are then compared with the corresponding calculations using SMCP. First, simple academic cases applying one-dimensional movements are investigated and second, more complex dynamic trajectories with several simultaneously moving components are compared considering academic cases as well as a clinically motivated prostate case. The dose calculation for dynamic trajectories is successfully implemented into SMCP. The comparisons between the measured and calculated dose distributions for the simple as well as for the more complex situations show an agreement which is generally within 3% of the maximum dose or 3mm. The required computation time for the dose calculation remains the same when the additional dynamic moving components are included. The results obtained for the dose comparisons for simple and complex situations suggest that the extended SMCP is an accurate dose calculation and efficient verification tool for dynamic trajectory radiotherapy. This work was supported by Varian Medical Systems. Copyright © 2018. Published by Elsevier GmbH.

TU-AB-BRC-09: Fast Dose-Averaged LET and Biological Dose Calculations for Proton Therapy Using Graphics Cards

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wan, H; Tseung, Chan; Beltran, C

Purpose: To demonstrate fast and accurate Monte Carlo (MC) calculations of proton dose-averaged linear energy transfer (LETd) and biological dose (BD) on a Graphics Processing Unit (GPU) card. Methods: A previously validated GPU-based MC simulation of proton transport was used to rapidly generate LETd distributions for proton treatment plans. Since this MC handles proton-nuclei interactions on an event-by-event using a Bertini intranuclear cascade-evaporation model, secondary protons were taken into account. The smaller contributions of secondary neutrons and recoil nuclei were ignored. Recent work has shown that LETd values are sensitive to the scoring method. The GPU-based LETd calculations were verifiedmore » by comparing with a TOPAS custom scorer that uses tabulated stopping powers, following recommendations by other authors. Comparisons were made for prostate and head-and-neck patients. A python script is used to convert the MC-generated LETd distributions to BD using a variety of published linear quadratic models, and to export the BD in DICOM format for subsequent evaluation. Results: Very good agreement is obtained between TOPAS and our GPU MC. Given a complex head-and-neck plan with 1 mm voxel spacing, the physical dose, LETd and BD calculations for 10{sup 8} proton histories can be completed in ∼5 minutes using a NVIDIA Titan X card. The rapid turnover means that MC feedback can be obtained on dosimetric plan accuracy as well as BD hotspot locations, particularly in regards to their proximity to critical structures. In our institution the GPU MC-generated dose, LETd and BD maps are used to assess plan quality for all patients undergoing treatment. Conclusion: Fast and accurate MC-based LETd calculations can be performed on the GPU. The resulting BD maps provide valuable feedback during treatment plan review. Partially funded by Varian Medical Systems.« less

Monte Carlo characterization of materials for prosthetic implants and dosimetric validation of Pinnacle 3 TPS

NASA Astrophysics Data System (ADS)

Palleri, Francesca; Baruffaldi, Fabio; Angelini, Anna Lisa; Ferri, Andrea; Spezi, Emiliano

2008-12-01

In external beam radiotherapy the calculation of dose distribution for patients with hip prostheses is critical. Metallic implants not only degrade the image quality but also perturb the dose distribution. Conventional treatment planning systems do not accurately account for high-Z prosthetic implants heterogeneities, especially at interfaces. The materials studied in this work have been chosen on the basis of a statistical investigation on the hip prostheses implanted in 70 medical centres. The first aim of this study is a systematic characterization of materials used for hip prostheses, and it has been provided by BEAMnrc Monte Carlo code. The second aim is to evaluate the capabilities of a specific treatment planning system, Pinnacle 3, when dealing with dose calculations in presence of metals, also close to the regions of high-Z gradients. In both cases it has been carried out an accurate comparison versus experimental measurements for two clinical photon beam energies (6 MV and 18 MV) and for two experimental sets-up: metallic cylinders inserted in a water phantom and in a specifically built PMMA slab. Our results show an agreement within 2% between experiments and MC simulations. TPS calculations agree with experiments within 3%.

Patient-specific IMRT verification using independent fluence-based dose calculation software: experimental benchmarking and initial clinical experience.

PubMed

Georg, Dietmar; Stock, Markus; Kroupa, Bernhard; Olofsson, Jörgen; Nyholm, Tufve; Ahnesjö, Anders; Karlsson, Mikael

2007-08-21

Experimental methods are commonly used for patient-specific intensity-modulated radiotherapy (IMRT) verification. The purpose of this study was to investigate the accuracy and performance of independent dose calculation software (denoted as 'MUV' (monitor unit verification)) for patient-specific quality assurance (QA). 52 patients receiving step-and-shoot IMRT were considered. IMRT plans were recalculated by the treatment planning systems (TPS) in a dedicated QA phantom, in which an experimental 1D and 2D verification (0.3 cm(3) ionization chamber; films) was performed. Additionally, an independent dose calculation was performed. The fluence-based algorithm of MUV accounts for collimator transmission, rounded leaf ends, tongue-and-groove effect, backscatter to the monitor chamber and scatter from the flattening filter. The dose calculation utilizes a pencil beam model based on a beam quality index. DICOM RT files from patient plans, exported from the TPS, were directly used as patient-specific input data in MUV. For composite IMRT plans, average deviations in the high dose region between ionization chamber measurements and point dose calculations performed with the TPS and MUV were 1.6 +/- 1.2% and 0.5 +/- 1.1% (1 S.D.). The dose deviations between MUV and TPS slightly depended on the distance from the isocentre position. For individual intensity-modulated beams (total 367), an average deviation of 1.1 +/- 2.9% was determined between calculations performed with the TPS and with MUV, with maximum deviations up to 14%. However, absolute dose deviations were mostly less than 3 cGy. Based on the current results, we aim to apply a confidence limit of 3% (with respect to the prescribed dose) or 6 cGy for routine IMRT verification. For off-axis points at distances larger than 5 cm and for low dose regions, we consider 5% dose deviation or 10 cGy acceptable. The time needed for an independent calculation compares very favourably with the net time for an experimental approach. The physical effects modelled in the dose calculation software MUV allow accurate dose calculations in individual verification points. Independent calculations may be used to replace experimental dose verification once the IMRT programme is mature.

Calculation of dose contributions of electron and charged heavy particles inside phantoms irradiated by monoenergetic neutron.

PubMed

Satoh, Daiki; Takahashi, Fumiaki; Endo, Akira; Ohmachi, Yasushi; Miyahara, Nobuyuki

2008-09-01

The radiation-transport code PHITS with an event generator mode has been applied to analyze energy depositions of electrons and charged heavy particles in two spherical phantoms and a voxel-based mouse phantom upon neutron irradiation. The calculations using the spherical phantoms quantitatively clarified the type and energy of charged particles which are released through interactions of neutrons with the phantom elements and contribute to the radiation dose. The relative contribution of electrons increased with an increase in the size of the phantom and with a decrease in the energy of the incident neutrons. Calculations with the voxel-based mouse phantom for 2.0-MeV neutron irradiation revealed that the doses to different locations inside the body are uniform, and that the energy is mainly deposited by recoil protons. The present study has demonstrated that analysis using PHITS can yield dose distributions that are accurate enough for RBE evaluation.

A simplified analytical random walk model for proton dose calculation

NASA Astrophysics Data System (ADS)

Yao, Weiguang; Merchant, Thomas E.; Farr, Jonathan B.

2016-10-01

We propose an analytical random walk model for proton dose calculation in a laterally homogeneous medium. A formula for the spatial fluence distribution of primary protons is derived. The variance of the spatial distribution is in the form of a distance-squared law of the angular distribution. To improve the accuracy of dose calculation in the Bragg peak region, the energy spectrum of the protons is used. The accuracy is validated against Monte Carlo simulation in water phantoms with either air gaps or a slab of bone inserted. The algorithm accurately reflects the dose dependence on the depth of the bone and can deal with small-field dosimetry. We further applied the algorithm to patients’ cases in the highly heterogeneous head and pelvis sites and used a gamma test to show the reasonable accuracy of the algorithm in these sites. Our algorithm is fast for clinical use.

Cellular dosimetry of (111)In using monte carlo N-particle computer code: comparison with analytic methods and correlation with in vitro cytotoxicity.

PubMed

Cai, Zhongli; Pignol, Jean-Philippe; Chan, Conrad; Reilly, Raymond M

2010-03-01

Our objective was to compare Monte Carlo N-particle (MCNP) self- and cross-doses from (111)In to the nucleus of breast cancer cells with doses calculated by reported analytic methods (Goddu et al. and Farragi et al.). A further objective was to determine whether the MCNP-predicted surviving fraction (SF) of breast cancer cells exposed in vitro to (111)In-labeled diethylenetriaminepentaacetic acid human epidermal growth factor ((111)In-DTPA-hEGF) could accurately predict the experimentally determined values. MCNP was used to simulate the transport of electrons emitted by (111)In from the cell surface, cytoplasm, or nucleus. The doses to the nucleus per decay (S values) were calculated for single cells, closely packed monolayer cells, or cell clusters. The cell and nucleus dimensions of 6 breast cancer cell lines were measured, and cell line-specific S values were calculated. For self-doses, MCNP S values of nucleus to nucleus agreed very well with those of Goddu et al. (ratio of S values using analytic methods vs. MCNP = 0.962-0.995) and Faraggi et al. (ratio = 1.011-1.024). MCNP S values of cytoplasm and cell surface to nucleus compared fairly well with the reported values (ratio = 0.662-1.534 for Goddu et al.; 0.944-1.129 for Faraggi et al.). For cross doses, the S values to the nucleus were independent of (111)In subcellular distribution but increased with cluster size. S values for monolayer cells were significantly different from those of single cells and cell clusters. The MCNP-predicted SF for monolayer MDA-MB-468, MDA-MB-231, and MCF-7 cells agreed with the experimental data (relative error of 3.1%, -1.0%, and 1.7%). The single-cell and cell cluster models were less accurate in predicting the SF. For MDA-MB-468 cells, relative error was 8.1% using the single-cell model and -54% to -67% using the cell cluster model. Individual cell-line dimensions had large effects on S values and were needed to estimate doses and SF accurately. MCNP simulation compared well with the reported analytic methods in the calculation of subcellular S values for single cells and cell clusters. Application of a monolayer model was most accurate in predicting the SF of breast cancer cells exposed in vitro to (111)In-DTPA-hEGF.

Skin-sparing Helical Tomotherapy vs 3D-conformal Radiotherapy for Adjuvant Breast Radiotherapy: In Vivo Skin Dosimetry Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Capelle, Lisa; Warkentin, Heather; MacKenzie, Marc

Purpose: We investigated whether treatment-planning system (TPS)-calculated dose accurately reflects skin dose received for patients receiving adjuvant breast radiotherapy (RT) with standard three-dimensional conformal RT (3D-CRT) or skin-sparing helical tomotherapy (HT). Methods and Materials: Fifty patients enrolled in a randomized controlled trial investigating acute skin toxicity from adjuvant breast RT with 3D-CRT compared to skin-sparing HT, where a 5-mm strip of ipsilateral breast skin was spared. Thermoluminescent dosimetry or optically stimulated luminescence measurements were made in multiple locations and were compared to TPS-calculated doses. Skin dosimetric parameters and acute skin toxicity were recorded in these patients. Results: With HT theremore » was a significant correlation between calculated and measured dose in the medial and lateral ipsilateral breast (r = 0.67, P<.001; r = 0.44, P=.03, respectively) and the medial and central contralateral breast (r = 0.73, P<.001; r = 0.88, P<.001, respectively). With 3D-CRT there was a significant correlation in the medial and lateral ipsilateral breast (r = 0.45, P=.03; r = 0.68, P<.001, respectively); the medial and central contralateral breast (r = 0.62, P=.001; r = 0.86, P<.001, respectively); and the mid neck (r = 0.42, P=.04, respectively). On average, HT-calculated dose overestimated the measured dose by 14%; 3D-CRT underestimated the dose by 0.4%. There was a borderline association between highest measured skin dose and moist desquamation (P=.05). Skin-sparing HT had greater skin homogeneity (homogeneity index of 1.39 vs 1.65, respectively; P=.005) than 3D-CRT plans. HT plans had a lower skin{sub V50} (1.4% vs 5.9%, respectively; P=.001) but higher skin{sub V40} and skin{sub V30} (71.7% vs 64.0%, P=.02; and 99.0% vs 93.8%, P=.001, respectively) than 3D-CRT plans. Conclusion: The 3D-CRT TPS more accurately reflected skin dose than the HT TPS, which tended to overestimate dose received by 14% in patients receiving adjuvant breast RT.« less

SU-F-P-21: Study of Dosimetry Accuracy of Small Passively Scattered Proton Beam Fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Y; Gautam, A; Kerr, M

2016-06-15

Purpose: To study the accuracy of the dose distribution of very small irregular fields of passively scattered proton beams calculated by the analytical pencil beam model of the Eclipse treatment planning system (TPS). Methods: An irregular field with a narrow region (width < 1 cm) that was used for the treatment of a small volume adjacent to a previously treated area were chosen for this investigation. Point doses at different locations inside the field were measured with a small volume ion chamber (A26, Standard Imaging). 2-D dose distributions were measured using a 2-D ion chamber array (MatriXX, IBA). All themore » measurements were done in plastic water phantom. The measured dose distributions were compared with the verification plan dose calculated in a water like phantom for the patient treatment field without the use of the compensator. Results: Point doses measured with the ion chamber in the narrowest section of the field were found to differ as much as 10% from the Eclipse calculated dose at some of the points. The 2-D dose distribution measured with the MatriXX which was validated by comparison with limited film measurement, at the proximal 95%, center of the spread out Bragg Peak and distal 90% depths agreed reasonably well with the TPS calculated dose distribution with more than 92% of the pixels passing the 2% / 2 mm dose distance agreement. Conclusion: The dose calculated by the pencil beam model of the Eclipse TPS for narrow irregular fields may not be accurate within 5% at some locations of the field, especially at the points close to the field edge due to the limitation of the dose calculation model. Overall accuracy of the calculated 2-D dose distribution was found to be acceptable for the 2%/2 mm dose/distance agreement with the measurement.« less

Dose rate calculations around 192Ir brachytherapy sources using a Sievert integration model

NASA Astrophysics Data System (ADS)

Karaiskos, P.; Angelopoulos, A.; Baras, P.; Rozaki-Mavrouli, H.; Sandilos, P.; Vlachos, L.; Sakelliou, L.

2000-02-01

The classical Sievert integral method is a valuable tool for dose rate calculations around brachytherapy sources, combining simplicity with reasonable computational times. However, its accuracy in predicting dose rate anisotropy around 192 Ir brachytherapy sources has been repeatedly put into question. In this work, we used a primary and scatter separation technique to improve an existing modification of the Sievert integral (Williamson's isotropic scatter model) that determines dose rate anisotropy around commercially available 192 Ir brachytherapy sources. The proposed Sievert formalism provides increased accuracy while maintaining the simplicity and computational time efficiency of the Sievert integral method. To describe transmission within the materials encountered, the formalism makes use of narrow beam attenuation coefficients which can be directly and easily calculated from the initially emitted 192 Ir spectrum. The other numerical parameters required for its implementation, once calculated with the aid of our home-made Monte Carlo simulation code, can be used for any 192 Ir source design. Calculations of dose rate and anisotropy functions with the proposed Sievert expression, around commonly used 192 Ir high dose rate sources and other 192 Ir elongated source designs, are in good agreement with corresponding accurate Monte Carlo results which have been reported by our group and other authors.

The Multi-Step CADIS method for shutdown dose rate calculations and uncertainty propagation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ibrahim, Ahmad M.; Peplow, Douglas E.; Grove, Robert E.

2015-12-01

Shutdown dose rate (SDDR) analysis requires (a) a neutron transport calculation to estimate neutron flux fields, (b) an activation calculation to compute radionuclide inventories and associated photon sources, and (c) a photon transport calculation to estimate final SDDR. In some applications, accurate full-scale Monte Carlo (MC) SDDR simulations are needed for very large systems with massive amounts of shielding materials. However, these simulations are impractical because calculation of space- and energy-dependent neutron fluxes throughout the structural materials is needed to estimate distribution of radioisotopes causing the SDDR. Biasing the neutron MC calculation using an importance function is not simple becausemore » it is difficult to explicitly express the response function, which depends on subsequent computational steps. Furthermore, the typical SDDR calculations do not consider how uncertainties in MC neutron calculation impact SDDR uncertainty, even though MC neutron calculation uncertainties usually dominate SDDR uncertainty.« less

A new tissue segmentation method to calculate 3D dose in small animal radiation therapy.

PubMed

Noblet, C; Delpon, G; Supiot, S; Potiron, V; Paris, F; Chiavassa, S

2018-02-26

In pre-clinical animal experiments, radiation delivery is usually delivered with kV photon beams, in contrast to the MV beams used in clinical irradiation, because of the small size of the animals. At this medium energy range, however, the contribution of the photoelectric effect to absorbed dose is significant. Accurate dose calculation therefore requires a more detailed tissue definition because both density (ρ) and elemental composition (Z eff ) affect the dose distribution. Moreover, when applied to cone beam CT (CBCT) acquisitions, the stoichiometric calibration of HU becomes inefficient as it is designed for highly collimated fan beam CT acquisitions. In this study, we propose an automatic tissue segmentation method of CBCT imaging that assigns both density (ρ) and elemental composition (Z eff ) in small animal dose calculation. The method is based on the relationship found between CBCT number and ρ*Z eff product computed from known materials. Monte Carlo calculations were performed to evaluate the impact of ρZ eff variation on the absorbed dose in tissues. These results led to the creation of a tissue database composed of artificial tissues interpolated from tissue values published by the ICRU. The ρZ eff method was validated by measuring transmitted doses through tissue substitute cylinders and a mouse with EBT3 film. Measurements were compared to the results of the Monte Carlo calculations. The study of the impact of ρZ eff variation over the range of materials, from ρZ eff  = 2 g.cm - 3 (lung) to 27 g.cm - 3 (cortical bone) led to the creation of 125 artificial tissues. For tissue substitute cylinders, the use of ρZ eff method led to maximal and average relative differences between the Monte Carlo results and the EBT3 measurements of 3.6% and 1.6%. Equivalent comparison for the mouse gave maximal and average relative differences of 4.4% and 1.2%, inside the 80% isodose area. Gamma analysis led to a 94.9% success rate in the 10% isodose area with 4% and 0.3 mm criteria in dose and distance. Our new tissue segmentation method was developed for 40kVp CBCT images. Both density and elemental composition are assigned to each voxel by using a relationship between HU and the product ρZ eff . The method, validated by comparing measurements and calculations, enables more accurate small animal dose distribution calculated on low energy CBCT images.

Brachytherapy dosimetry of 125I and 103Pd sources using an updated cross section library for the MCNP Monte Carlo transport code.

PubMed

Bohm, Tim D; DeLuca, Paul M; DeWerd, Larry A

2003-04-01

Permanent implantation of low energy (20-40 keV) photon emitting radioactive seeds to treat prostate cancer is an important treatment option for patients. In order to produce accurate implant brachytherapy treatment plans, the dosimetry of a single source must be well characterized. Monte Carlo based transport calculations can be used for source characterization, but must have up to date cross section libraries to produce accurate dosimetry results. This work benchmarks the MCNP code and its photon cross section library for low energy photon brachytherapy applications. In particular, we calculate the emitted photon spectrum, air kerma, depth dose in water, and radial dose function for both 125I and 103Pd based seeds and compare to other published results. Our results show that MCNP's cross section library differs from recent data primarily in the photoelectric cross section for low energies and low atomic number materials. In water, differences as large as 10% in the photoelectric cross section and 6% in the total cross section occur at 125I and 103Pd photon energies. This leads to differences in the dose rate constant of 3% and 5%, and differences as large as 18% and 20% in the radial dose function for the 125I and 103Pd based seeds, respectively. Using a partially updated photon library, calculations of the dose rate constant and radial dose function agree with other published results. Further, the use of the updated photon library allows us to verify air kerma and depth dose in water calculations performed using MCNP's perturbation feature to simulate updated cross sections. We conclude that in order to most effectively use MCNP for low energy photon brachytherapy applications, we must update its cross section library. Following this update, the MCNP code system will be a very effective tool for low energy photon brachytherapy dosimetry applications.

Preliminary skyshine calculations for the Poloidal Diverter Tokamak Experiment

NASA Astrophysics Data System (ADS)

Nigg, D. W.; Wheeler, F. J.

1981-01-01

A calculational model is presented to estimate the radiation dose, due to the skyshine effect, in the control room and at the site boundary of the Poloidal Diverter Experiment (PDX) facility at Princeton University which requires substantial radiation shielding. The required composition and thickness of a water-filled roof shield that would reduce this effect to an acceptable level is computed, using an efficient one-dimensional model with an Sn calculation in slab geometry. The actual neutron skyshine dose is computed using a Monte Carlo model with the neutron source at the roof surface obtained from the slab Sn calculation, and the capture gamma dose is computed using a simple point-kernel single-scatter method. It is maintained that the slab model provides the exact probability of leakage out the top surface of the roof and that it is nearly as accurate as and much less costly than multi-dimensional techniques.

Preliminary skyshine calculations for the Poloidal Diverter Tokamak Experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nigg, D.W.; Wheeler, F.J.

1981-01-01

A calculational model is presented to estimate the radiation dose, due to the skyshine effect, in the control room and at the site boundary of the Poloidal Diverter Experiment (PDX) facility at Princeton University which requires substantial radiation shielding. The required composition and thickness of a water-filled roof shield that would reduce this effect to an acceptable level is computed, using an efficient one-dimensional model with an Sn calculation in slab geometry. The actual neutron skyshine dose is computed using a Monte Carlo model with the neutron source at the roof surface obtained from the slab Sn calculation, and themore » capture gamma dose is computed using a simple point-kernel single-scatter method. It is maintained that the slab model provides the exact probability of leakage out the top surface of the roof and that it is nearly as accurate as and much less costly than multi-dimensional techniques.« less

Neon-20 depth-dose relations in water

NASA Technical Reports Server (NTRS)

Wilson, J. W.; Townsend, L. W.; Bidasaria, H. B.; Schimmerling, W.; Wong, M.; Howard, J.

1984-01-01

The dose from heavy ion beams has been calculated using a one-dimensional transport theory and evaluated for 670 MeV/amu 20 Ne beams in water. The result is presented so as to be applicable to arbitrary ions for which the necessary interaction data are known. The present evaluation is based on thar Silberg-Tsao fragmentation parameters augmented with light fragment production from intranuclear cascades, recently calculated nuclear absorption cross sections, and evaluated stopping power data. Comparison with recent experimental data obtained at the Lawrence Berkeley Laboratory reveals the need for more accurate fragmentation data.

Neon-20 depth-dose relations in water

NASA Astrophysics Data System (ADS)

Wilson, J. W.; Townsend, L. W.; Bidasaria, H. B.; Schimmerling, W.; Wong, M.; Howard, J.

1984-05-01

The dose from heavy ion beams has been calculated using a one-dimensional transport theory and evaluated for 670 MeV/amu 20 Ne beams in water. The result is presented so as to be applicable to arbitrary ions for which the necessary interaction data are known. The present evaluation is based on thar Silberg-Tsao fragmentation parameters augmented with light fragment production from intranuclear cascades, recently calculated nuclear absorption cross sections, and evaluated stopping power data. Comparison with recent experimental data obtained at the Lawrence Berkeley Laboratory reveals the need for more accurate fragmentation data.

SU-E-T-22: A Deterministic Solver of the Boltzmann-Fokker-Planck Equation for Dose Calculation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, X; Gao, H; Paganetti, H

2015-06-15

Purpose: The Boltzmann-Fokker-Planck equation (BFPE) accurately models the migration of photons/charged particles in tissues. While the Monte Carlo (MC) method is popular for solving BFPE in a statistical manner, we aim to develop a deterministic BFPE solver based on various state-of-art numerical acceleration techniques for rapid and accurate dose calculation. Methods: Our BFPE solver is based on the structured grid that is maximally parallelizable, with the discretization in energy, angle and space, and its cross section coefficients are derived or directly imported from the Geant4 database. The physical processes that are taken into account are Compton scattering, photoelectric effect, pairmore » production for photons, and elastic scattering, ionization and bremsstrahlung for charged particles.While the spatial discretization is based on the diamond scheme, the angular discretization synergizes finite element method (FEM) and spherical harmonics (SH). Thus, SH is used to globally expand the scattering kernel and FFM is used to locally discretize the angular sphere. As a Result, this hybrid method (FEM-SH) is both accurate in dealing with forward-peaking scattering via FEM, and efficient for multi-energy-group computation via SH. In addition, FEM-SH enables the analytical integration in energy variable of delta scattering kernel for elastic scattering with reduced truncation error from the numerical integration based on the classic SH-based multi-energy-group method. Results: The accuracy of the proposed BFPE solver was benchmarked against Geant4 for photon dose calculation. In particular, FEM-SH had improved accuracy compared to FEM, while both were within 2% of the results obtained with Geant4. Conclusion: A deterministic solver of the Boltzmann-Fokker-Planck equation is developed for dose calculation, and benchmarked against Geant4. Xiang Hong and Hao Gao were partially supported by the NSFC (#11405105), the 973 Program (#2015CB856000) and the Shanghai Pujiang Talent Program (#14PJ1404500)« less

The scenario-based generalization of radiation therapy margins.

PubMed

Fredriksson, Albin; Bokrantz, Rasmus

2016-03-07

We give a scenario-based treatment plan optimization formulation that is equivalent to planning with geometric margins if the scenario doses are calculated using the static dose cloud approximation. If the scenario doses are instead calculated more accurately, then our formulation provides a novel robust planning method that overcomes many of the difficulties associated with previous scenario-based robust planning methods. In particular, our method protects only against uncertainties that can occur in practice, it gives a sharp dose fall-off outside high dose regions, and it avoids underdosage of the target in 'easy' scenarios. The method shares the benefits of the previous scenario-based robust planning methods over geometric margins for applications where the static dose cloud approximation is inaccurate, such as irradiation with few fields and irradiation with ion beams. These properties are demonstrated on a suite of phantom cases planned for treatment with scanned proton beams subject to systematic setup uncertainty.

Towards real-time photon Monte Carlo dose calculation in the cloud

NASA Astrophysics Data System (ADS)

Ziegenhein, Peter; Kozin, Igor N.; Kamerling, Cornelis Ph; Oelfke, Uwe

2017-06-01

Near real-time application of Monte Carlo (MC) dose calculation in clinic and research is hindered by the long computational runtimes of established software. Currently, fast MC software solutions are available utilising accelerators such as graphical processing units (GPUs) or clusters based on central processing units (CPUs). Both platforms are expensive in terms of purchase costs and maintenance and, in case of the GPU, provide only limited scalability. In this work we propose a cloud-based MC solution, which offers high scalability of accurate photon dose calculations. The MC simulations run on a private virtual supercomputer that is formed in the cloud. Computational resources can be provisioned dynamically at low cost without upfront investment in expensive hardware. A client-server software solution has been developed which controls the simulations and transports data to and from the cloud efficiently and securely. The client application integrates seamlessly into a treatment planning system. It runs the MC simulation workflow automatically and securely exchanges simulation data with the server side application that controls the virtual supercomputer. Advanced encryption standards were used to add an additional security layer, which encrypts and decrypts patient data on-the-fly at the processor register level. We could show that our cloud-based MC framework enables near real-time dose computation. It delivers excellent linear scaling for high-resolution datasets with absolute runtimes of 1.1 seconds to 10.9 seconds for simulating a clinical prostate and liver case up to 1% statistical uncertainty. The computation runtimes include the transportation of data to and from the cloud as well as process scheduling and synchronisation overhead. Cloud-based MC simulations offer a fast, affordable and easily accessible alternative for near real-time accurate dose calculations to currently used GPU or cluster solutions.

Towards real-time photon Monte Carlo dose calculation in the cloud.

PubMed

Ziegenhein, Peter; Kozin, Igor N; Kamerling, Cornelis Ph; Oelfke, Uwe

2017-06-07

Near real-time application of Monte Carlo (MC) dose calculation in clinic and research is hindered by the long computational runtimes of established software. Currently, fast MC software solutions are available utilising accelerators such as graphical processing units (GPUs) or clusters based on central processing units (CPUs). Both platforms are expensive in terms of purchase costs and maintenance and, in case of the GPU, provide only limited scalability. In this work we propose a cloud-based MC solution, which offers high scalability of accurate photon dose calculations. The MC simulations run on a private virtual supercomputer that is formed in the cloud. Computational resources can be provisioned dynamically at low cost without upfront investment in expensive hardware. A client-server software solution has been developed which controls the simulations and transports data to and from the cloud efficiently and securely. The client application integrates seamlessly into a treatment planning system. It runs the MC simulation workflow automatically and securely exchanges simulation data with the server side application that controls the virtual supercomputer. Advanced encryption standards were used to add an additional security layer, which encrypts and decrypts patient data on-the-fly at the processor register level. We could show that our cloud-based MC framework enables near real-time dose computation. It delivers excellent linear scaling for high-resolution datasets with absolute runtimes of 1.1 seconds to 10.9 seconds for simulating a clinical prostate and liver case up to 1% statistical uncertainty. The computation runtimes include the transportation of data to and from the cloud as well as process scheduling and synchronisation overhead. Cloud-based MC simulations offer a fast, affordable and easily accessible alternative for near real-time accurate dose calculations to currently used GPU or cluster solutions.

Comparison of depth-dose distributions of proton therapeutic beams calculated by means of logical detectors and ionization chamber modeled in Monte Carlo codes

NASA Astrophysics Data System (ADS)

Pietrzak, Robert; Konefał, Adam; Sokół, Maria; Orlef, Andrzej

2016-08-01

The success of proton therapy depends strongly on the precision of treatment planning. Dose distribution in biological tissue may be obtained from Monte Carlo simulations using various scientific codes making it possible to perform very accurate calculations. However, there are many factors affecting the accuracy of modeling. One of them is a structure of objects called bins registering a dose. In this work the influence of bin structure on the dose distributions was examined. The MCNPX code calculations of Bragg curve for the 60 MeV proton beam were done in two ways: using simple logical detectors being the volumes determined in water, and using a precise model of ionization chamber used in clinical dosimetry. The results of the simulations were verified experimentally in the water phantom with Marcus ionization chamber. The average local dose difference between the measured relative doses in the water phantom and those calculated by means of the logical detectors was 1.4% at first 25 mm, whereas in the full depth range this difference was 1.6% for the maximum uncertainty in the calculations less than 2.4% and for the maximum measuring error of 1%. In case of the relative doses calculated with the use of the ionization chamber model this average difference was somewhat greater, being 2.3% at depths up to 25 mm and 2.4% in the full range of depths for the maximum uncertainty in the calculations of 3%. In the dose calculations the ionization chamber model does not offer any additional advantages over the logical detectors. The results provided by both models are similar and in good agreement with the measurements, however, the logical detector approach is a more time-effective method.

SU-E-T-538: Evaluation of IMRT Dose Calculation Based on Pencil-Beam and AAA Algorithms.

PubMed

Yuan, Y; Duan, J; Popple, R; Brezovich, I

2012-06-01

To evaluate the accuracy of dose calculation for intensity modulated radiation therapy (IMRT) based on Pencil Beam (PB) and Analytical Anisotropic Algorithm (AAA) computation algorithms. IMRT plans of twelve patients with different treatment sites, including head/neck, lung and pelvis, were investigated. For each patient, dose calculation with PB and AAA algorithms using dose grid sizes of 0.5 mm, 0.25 mm, and 0.125 mm, were compared with composite-beam ion chamber and film measurements in patient specific QA. Discrepancies between the calculation and the measurement were evaluated by percentage error for ion chamber dose and γ〉l failure rate in gamma analysis (3%/3mm) for film dosimetry. For 9 patients, ion chamber dose calculated with AAA-algorithms is closer to ion chamber measurement than that calculated with PB algorithm with grid size of 2.5 mm, though all calculated ion chamber doses are within 3% of the measurements. For head/neck patients and other patients with large treatment volumes, γ〉l failure rate is significantly reduced (within 5%) with AAA-based treatment planning compared to generally more than 10% with PB-based treatment planning (grid size=2.5 mm). For lung and brain cancer patients with medium and small treatment volumes, γ〉l failure rates are typically within 5% for both AAA and PB-based treatment planning (grid size=2.5 mm). For both PB and AAA-based treatment planning, improvements of dose calculation accuracy with finer dose grids were observed in film dosimetry of 11 patients and in ion chamber measurements for 3 patients. AAA-based treatment planning provides more accurate dose calculation for head/neck patients and other patients with large treatment volumes. Compared with film dosimetry, a γ〉l failure rate within 5% can be achieved for AAA-based treatment planning. © 2012 American Association of Physicists in Medicine.

A new concept of pencil beam dose calculation for 40-200 keV photons using analytical dose kernels.

PubMed

Bartzsch, Stefan; Oelfke, Uwe

2013-11-01

The advent of widespread kV-cone beam computer tomography in image guided radiation therapy and special therapeutic application of keV photons, e.g., in microbeam radiation therapy (MRT) require accurate and fast dose calculations for photon beams with energies between 40 and 200 keV. Multiple photon scattering originating from Compton scattering and the strong dependence of the photoelectric cross section on the atomic number of the interacting tissue render these dose calculations by far more challenging than the ones established for corresponding MeV beams. That is why so far developed analytical models of kV photon dose calculations fail to provide the required accuracy and one has to rely on time consuming Monte Carlo simulation techniques. In this paper, the authors introduce a novel analytical approach for kV photon dose calculations with an accuracy that is almost comparable to the one of Monte Carlo simulations. First, analytical point dose and pencil beam kernels are derived for homogeneous media and compared to Monte Carlo simulations performed with the Geant4 toolkit. The dose contributions are systematically separated into contributions from the relevant orders of multiple photon scattering. Moreover, approximate scaling laws for the extension of the algorithm to inhomogeneous media are derived. The comparison of the analytically derived dose kernels in water showed an excellent agreement with the Monte Carlo method. Calculated values deviate less than 5% from Monte Carlo derived dose values, for doses above 1% of the maximum dose. The analytical structure of the kernels allows adaption to arbitrary materials and photon spectra in the given energy range of 40-200 keV. The presented analytical methods can be employed in a fast treatment planning system for MRT. In convolution based algorithms dose calculation times can be reduced to a few minutes.

Accuracy of the dose-shift approximation in estimating the delivered dose in SBRT of lung tumors considering setup errors and breathing motions.

PubMed

Karlsson, Kristin; Lax, Ingmar; Lindbäck, Elias; Poludniowski, Gavin

2017-09-01

Geometrical uncertainties can result in a delivered dose to the tumor different from that estimated in the static treatment plan. The purpose of this project was to investigate the accuracy of the dose calculated to the clinical target volume (CTV) with the dose-shift approximation, in stereotactic body radiation therapy (SBRT) of lung tumors considering setup errors and breathing motion. The dose-shift method was compared with a beam-shift method with dose recalculation. Included were 10 patients (10 tumors) selected to represent a variety of SBRT-treated lung tumors in terms of tumor location, CTV volume, and tumor density. An in-house developed toolkit within a treatment planning system allowed the shift of either the dose matrix or a shift of the beam isocenter with dose recalculation, to simulate setup errors and breathing motion. Setup shifts of different magnitudes (up to 10 mm) and directions as well as breathing with different peak-to-peak amplitudes (up to 10:5:5 mm) were modeled. The resulting dose-volume histograms (DVHs) were recorded and dose statistics were extracted. Generally, both the dose-shift and beam-shift methods resulted in calculated doses lower than the static planned dose, although the minimum (D 98% ) dose exceeded the prescribed dose in all cases, for setup shifts up to 5 mm. The dose-shift method also generally underestimated the dose compared with the beam-shift method. For clinically realistic systematic displacements of less than 5 mm, the results demonstrated that in the minimum dose region within the CTV, the dose-shift method was accurate to 2% (root-mean-square error). Breathing motion only marginally degraded the dose distributions. Averaged over the patients and shift directions, the dose-shift approximation was determined to be accurate to approximately 2% (RMS) within the CTV, for clinically relevant geometrical uncertainties for SBRT of lung tumors.

Comparison of normal tissue dose calculation methods for epidemiological studies of radiotherapy patients.

PubMed

Mille, Matthew M; Jung, Jae Won; Lee, Choonik; Kuzmin, Gleb A; Lee, Choonsik

2018-06-01

Radiation dosimetry is an essential input for epidemiological studies of radiotherapy patients aimed at quantifying the dose-response relationship of late-term morbidity and mortality. Individualised organ dose must be estimated for all tissues of interest located in-field, near-field, or out-of-field. Whereas conventional measurement approaches are limited to points in water or anthropomorphic phantoms, computational approaches using patient images or human phantoms offer greater flexibility and can provide more detailed three-dimensional dose information. In the current study, we systematically compared four different dose calculation algorithms so that dosimetrists and epidemiologists can better understand the advantages and limitations of the various approaches at their disposal. The four dose calculations algorithms considered were as follows: the (1) Analytical Anisotropic Algorithm (AAA) and (2) Acuros XB algorithm (Acuros XB), as implemented in the Eclipse treatment planning system (TPS); (3) a Monte Carlo radiation transport code, EGSnrc; and (4) an accelerated Monte Carlo code, the x-ray Voxel Monte Carlo (XVMC). The four algorithms were compared in terms of their accuracy and appropriateness in the context of dose reconstruction for epidemiological investigations. Accuracy in peripheral dose was evaluated first by benchmarking the calculated dose profiles against measurements in a homogeneous water phantom. Additional simulations in a heterogeneous cylinder phantom evaluated the performance of the algorithms in the presence of tissue heterogeneity. In general, we found that the algorithms contained within the commercial TPS (AAA and Acuros XB) were fast and accurate in-field or near-field, but not acceptable out-of-field. Therefore, the TPS is best suited for epidemiological studies involving large cohorts and where the organs of interest are located in-field or partially in-field. The EGSnrc and XVMC codes showed excellent agreement with measurements both in-field and out-of-field. The EGSnrc code was the most accurate dosimetry approach, but was too slow to be used for large-scale epidemiological cohorts. The XVMC code showed similar accuracy to EGSnrc, but was significantly faster, and thus epidemiological applications seem feasible, especially when the organs of interest reside far away from the field edge.

Comparison of Monte Carlo and analytical dose computations for intensity modulated proton therapy

NASA Astrophysics Data System (ADS)

Yepes, Pablo; Adair, Antony; Grosshans, David; Mirkovic, Dragan; Poenisch, Falk; Titt, Uwe; Wang, Qianxia; Mohan, Radhe

2018-02-01

To evaluate the effect of approximations in clinical analytical calculations performed by a treatment planning system (TPS) on dosimetric indices in intensity modulated proton therapy. TPS calculated dose distributions were compared with dose distributions as estimated by Monte Carlo (MC) simulations, calculated with the fast dose calculator (FDC) a system previously benchmarked to full MC. This study analyzed a total of 525 patients for four treatment sites (brain, head-and-neck, thorax and prostate). Dosimetric indices (D02, D05, D20, D50, D95, D98, EUD and Mean Dose) and a gamma-index analysis were utilized to evaluate the differences. The gamma-index passing rates for a 3%/3 mm criterion for voxels with a dose larger than 10% of the maximum dose had a median larger than 98% for all sites. The median difference for all dosimetric indices for target volumes was less than 2% for all cases. However, differences for target volumes as large as 10% were found for 2% of the thoracic patients. For organs at risk (OARs), the median absolute dose difference was smaller than 2 Gy for all indices and cohorts. However, absolute dose differences as large as 10 Gy were found for some small volume organs in brain and head-and-neck patients. This analysis concludes that for a fraction of the patients studied, TPS may overestimate the dose in the target by as much as 10%, while for some OARs the dose could be underestimated by as much as 10 Gy. Monte Carlo dose calculations may be needed to ensure more accurate dose computations to improve target coverage and sparing of OARs in proton therapy.

Poster — Thur Eve — 30: 4D VMAT dose calculation methodology to investigate the interplay effect: experimental validation using TrueBeam Developer Mode and Gafchromic film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teke, T; Milette, MP; Huang, V

2014-08-15

The interplay effect between the tumor motion and the radiation beam modulation during a VMAT treatment delivery alters the delivered dose distribution from the planned one. This work present and validate a method to accurately calculate the dose distribution in 4D taking into account the tumor motion, the field modulation and the treatment starting phase. A QUASAR™ respiratory motion phantom was 4D scanned with motion amplitude of 3 cm and with a 3 second period. A static scan was also acquired with the lung insert and the tumor contained in it centered. A VMAT plan with a 6XFFF beam wasmore » created on the averaged CT and delivered on a Varian TrueBeam and the trajectory log file was saved. From the trajectory log file 10 VMAT plans (one for each breathing phase) and a developer mode XML file were created. For the 10 VMAT plans, the tumor motion was modeled by moving the isocentre on the static scan, the plans were re-calculated and summed in the treatment planning system. In the developer mode, the tumor motion was simulated by moving the couch dynamically during the treatment. Gafchromic films were placed in the QUASAR phantom static and irradiated using the developer mode. Different treatment starting phase were investigated (no phase shift, maximum inhalation and maximum exhalation). Calculated and measured isodose lines and profiles are in very good agreement. For each starting phase, the dose distribution exhibit significant differences but are accurately calculated with the methodology presented in this work.« less

Evaluation of the Eclipse eMC algorithm for bolus electron conformal therapy using a standard verification dataset.

PubMed

Carver, Robert L; Sprunger, Conrad P; Hogstrom, Kenneth R; Popple, Richard A; Antolak, John A

2016-05-08

The purpose of this study was to evaluate the accuracy and calculation speed of electron dose distributions calculated by the Eclipse electron Monte Carlo (eMC) algorithm for use with bolus electron conformal therapy (ECT). The recent com-mercial availability of bolus ECT technology requires further validation of the eMC dose calculation algorithm. eMC-calculated electron dose distributions for bolus ECT have been compared to previously measured TLD-dose points throughout patient-based cylindrical phantoms (retromolar trigone and nose), whose axial cross sections were based on the mid-PTV (planning treatment volume) CT anatomy. The phantoms consisted of SR4 muscle substitute, SR4 bone substitute, and air. The treatment plans were imported into the Eclipse treatment planning system, and electron dose distributions calculated using 1% and < 0.2% statistical uncertainties. The accuracy of the dose calculations using moderate smoothing and no smooth-ing were evaluated. Dose differences (eMC-calculated less measured dose) were evaluated in terms of absolute dose difference, where 100% equals the given dose, as well as distance to agreement (DTA). Dose calculations were also evaluated for calculation speed. Results from the eMC for the retromolar trigone phantom using 1% statistical uncertainty without smoothing showed calculated dose at 89% (41/46) of the measured TLD-dose points was within 3% dose difference or 3 mm DTA of the measured value. The average dose difference was -0.21%, and the net standard deviation was 2.32%. Differences as large as 3.7% occurred immediately distal to the mandible bone. Results for the nose phantom, using 1% statistical uncertainty without smoothing, showed calculated dose at 93% (53/57) of the measured TLD-dose points within 3% dose difference or 3 mm DTA. The average dose difference was 1.08%, and the net standard deviation was 3.17%. Differences as large as 10% occurred lateral to the nasal air cavities. Including smoothing had insignificant effects on the accuracy of the retromolar trigone phantom calculations, but reduced the accuracy of the nose phantom calculations in the high-gradient dose areas. Dose calculation times with 1% statistical uncertainty for the retromolar trigone and nose treatment plans were 30 s and 24 s, respectively, using 16 processors (Intel Xeon E5-2690, 2.9 GHz) on a framework agent server (FAS). In comparison, the eMC was significantly more accurate than the pencil beam algorithm (PBA). The eMC has comparable accuracy to the pencil beam redefinition algorithm (PBRA) used for bolus ECT planning and has acceptably low dose calculation times. The eMC accuracy decreased when smoothing was used in high-gradient dose regions. The eMC accuracy was consistent with that previously reported for accuracy of the eMC electron dose algorithm and shows that the algorithm is suitable for clinical implementation of bolus ECT.

Quantitative assessment of the accuracy of dose calculation using pencil beam and Monte Carlo algorithms and requirements for clinical quality assurance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ali, Imad, E-mail: iali@ouhsc.edu; Ahmad, Salahuddin

2013-10-01

To compare the doses calculated using the BrainLAB pencil beam (PB) and Monte Carlo (MC) algorithms for tumors located in various sites including the lung and evaluate quality assurance procedures required for the verification of the accuracy of dose calculation. The dose-calculation accuracy of PB and MC was also assessed quantitatively with measurement using ionization chamber and Gafchromic films placed in solid water and heterogeneous phantoms. The dose was calculated using PB convolution and MC algorithms in the iPlan treatment planning system from BrainLAB. The dose calculation was performed on the patient's computed tomography images with lesions in various treatmentmore » sites including 5 lungs, 5 prostates, 4 brains, 2 head and necks, and 2 paraspinal tissues. A combination of conventional, conformal, and intensity-modulated radiation therapy plans was used in dose calculation. The leaf sequence from intensity-modulated radiation therapy plans or beam shapes from conformal plans and monitor units and other planning parameters calculated by the PB were identical for calculating dose with MC. Heterogeneity correction was considered in both PB and MC dose calculations. Dose-volume parameters such as V95 (volume covered by 95% of prescription dose), dose distributions, and gamma analysis were used to evaluate the calculated dose by PB and MC. The measured doses by ionization chamber and EBT GAFCHROMIC film in solid water and heterogeneous phantoms were used to quantitatively asses the accuracy of dose calculated by PB and MC. The dose-volume histograms and dose distributions calculated by PB and MC in the brain, prostate, paraspinal, and head and neck were in good agreement with one another (within 5%) and provided acceptable planning target volume coverage. However, dose distributions of the patients with lung cancer had large discrepancies. For a plan optimized with PB, the dose coverage was shown as clinically acceptable, whereas in reality, the MC showed a systematic lack of dose coverage. The dose calculated by PB for lung tumors was overestimated by up to 40%. An interesting feature that was observed is that despite large discrepancies in dose-volume histogram coverage of the planning target volume between PB and MC, the point doses at the isocenter (center of the lesions) calculated by both algorithms were within 7% even for lung cases. The dose distributions measured with EBT GAFCHROMIC films in heterogeneous phantoms showed large discrepancies of nearly 15% lower than PB at interfaces between heterogeneous media, where these lower doses measured by the film were in agreement with those by MC. The doses (V95) calculated by MC and PB agreed within 5% for treatment sites with small tissue heterogeneities such as the prostate, brain, head and neck, and paraspinal tumors. Considerable discrepancies, up to 40%, were observed in the dose-volume coverage between MC and PB in lung tumors, which may affect clinical outcomes. The discrepancies between MC and PB increased for 15 MV compared with 6 MV indicating the importance of implementation of accurate clinical treatment planning such as MC. The comparison of point doses is not representative of the discrepancies in dose coverage and might be misleading in evaluating the accuracy of dose calculation between PB and MC. Thus, the clinical quality assurance procedures required to verify the accuracy of dose calculation using PB and MC need to consider measurements of 2- and 3-dimensional dose distributions rather than a single point measurement using heterogeneous phantoms instead of homogenous water-equivalent phantoms.« less

Comparison of different approaches of estimating effective dose from reported exposure data in 3D imaging with interventional fluoroscopy systems

NASA Astrophysics Data System (ADS)

Svalkvist, Angelica; Hansson, Jonny; Bâth, Magnus

2014-03-01

Three-dimensional (3D) imaging with interventional fluoroscopy systems is today a common examination. The examination includes acquisition of two-dimensional projection images, used to reconstruct section images of the patient. The aim of the present study was to investigate the difference in resulting effective dose obtained using different levels of complexity in calculations of effective doses from these examinations. In the study the Siemens Artis Zeego interventional fluoroscopy system (Siemens Medical Solutions, Erlangen, Germany) was used. Images of anthropomorphic chest and pelvis phantoms were acquired. The exposure values obtained were used to calculate the resulting effective doses from the examinations, using the computer software PCXMC (STUK, Helsinki, Finland). The dose calculations were performed using three different methods: 1. using individual exposure values for each projection image, 2. using the mean tube voltage and the total DAP value, evenly distributed over the projection images, and 3. using the mean kV and the total DAP value, evenly distributed over smaller selection of projection images. The results revealed that the difference in resulting effective dose between the first two methods was smaller than 5%. When only a selection of projection images were used in the dose calculations the difference increased to over 10%. Given the uncertainties associated with the effective dose concept, the results indicate that dose calculations based on average exposure values distributed over a smaller selection of projection angles can provide reasonably accurate estimations of the radiation doses from 3D imaging using interventional fluoroscopy systems.

SU-E-T-423: Fast Photon Convolution Calculation with a 3D-Ideal Kernel On the GPU

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moriya, S; Sato, M; Tachibana, H

Purpose: The calculation time is a trade-off for improving the accuracy of convolution dose calculation with fine calculation spacing of the KERMA kernel. We investigated to accelerate the convolution calculation using an ideal kernel on the Graphic Processing Units (GPU). Methods: The calculation was performed on the AMD graphics hardware of Dual FirePro D700 and our algorithm was implemented using the Aparapi that convert Java bytecode to OpenCL. The process of dose calculation was separated with the TERMA and KERMA steps. The dose deposited at the coordinate (x, y, z) was determined in the process. In the dose calculation runningmore » on the central processing unit (CPU) of Intel Xeon E5, the calculation loops were performed for all calculation points. On the GPU computation, all of the calculation processes for the points were sent to the GPU and the multi-thread computation was done. In this study, the dose calculation was performed in a water equivalent homogeneous phantom with 150{sup 3} voxels (2 mm calculation grid) and the calculation speed on the GPU to that on the CPU and the accuracy of PDD were compared. Results: The calculation time for the GPU and the CPU were 3.3 sec and 4.4 hour, respectively. The calculation speed for the GPU was 4800 times faster than that for the CPU. The PDD curve for the GPU was perfectly matched to that for the CPU. Conclusion: The convolution calculation with the ideal kernel on the GPU was clinically acceptable for time and may be more accurate in an inhomogeneous region. Intensity modulated arc therapy needs dose calculations for different gantry angles at many control points. Thus, it would be more practical that the kernel uses a coarse spacing technique if the calculation is faster while keeping the similar accuracy to a current treatment planning system.« less

SU-F-T-587: Quality Assurance of Stereotactic Radiosurgery (SRS) and Stereotactic Body Radiation Therapy (SBRT) for Patient Specific Plans: A Comparison Between MATRIXX and Delta4 QA Devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsai, YC; Lu, SH; Chen, LH

2016-06-15

Purpose: Patient-specific quality assurance (QA) is necessary to accurately deliver high dose radiation to the target, especially for stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT). Unlike previous 2 dimensional (D) array QA devices, Delta{sup 4} can verify the dose delivery in 3D. In this study, the difference between calculated and measured dose distribution was compared with two QA devices (MATRIXX and Delta{sup 4}) to evaluate the delivery accuracy. Methods: Twenty-seven SRS/SBRT plans with VMAT were verified with point-dose and dose-map analysis. We use an ion chamber (A1SL, 0.053cc) for point-dose measurement. For verification of the dose map, themore » differences between the calculated and measured doses were analyzed with a gamma index using MATRIXX and Delta{sup 4} devices. The passing criteria for gamma evaluation were set at 3 mm for distance-to-agreement (DTA) and 3% for dose-difference. A gamma index less than 1 was defined as the verification passing the criteria and satisfying at least 95% of the points. Results: The mean prescribed dose and fraction was 40 ± 14.41 Gy (range: 16–60) and 10 ± 2.35 fractions (range: 1–8), respectively. In point dose analysis, the differences between the calculated and measured doses were all less than 5% (mean: 2.12 ± 1.13%; range: −0.55% to 4.45%). In dose-map analysis, the average passing rates were 99.38 ± 0.96% (range: 95.31–100%) and 100 ± 0.12% (range: 99.5%–100%) for MATRIXX and Delta{sup 4}, respectively. Even using criteria of 2%/2 mm, the passing rate of Delta{sup 4} was still more than 95% (mean: 99 ± 1.08%; range: 95.6%–100%). Conclusion: Both MATRIXX and Delta{sup 4} offer accurate and efficient verification for SRS/SBRT plans. The results measured by MATRIXX and Delta{sup 4} dosimetry systems are similar for SRS/SBRT performed with the VMAT technique.« less

A clinical study of lung cancer dose calculation accuracy with Monte Carlo simulation.

PubMed

Zhao, Yanqun; Qi, Guohai; Yin, Gang; Wang, Xianliang; Wang, Pei; Li, Jian; Xiao, Mingyong; Li, Jie; Kang, Shengwei; Liao, Xiongfei

2014-12-16

The accuracy of dose calculation is crucial to the quality of treatment planning and, consequently, to the dose delivered to patients undergoing radiation therapy. Current general calculation algorithms such as Pencil Beam Convolution (PBC) and Collapsed Cone Convolution (CCC) have shortcomings in regard to severe inhomogeneities, particularly in those regions where charged particle equilibrium does not hold. The aim of this study was to evaluate the accuracy of the PBC and CCC algorithms in lung cancer radiotherapy using Monte Carlo (MC) technology. Four treatment plans were designed using Oncentra Masterplan TPS for each patient. Two intensity-modulated radiation therapy (IMRT) plans were developed using the PBC and CCC algorithms, and two three-dimensional conformal therapy (3DCRT) plans were developed using the PBC and CCC algorithms. The DICOM-RT files of the treatment plans were exported to the Monte Carlo system to recalculate. The dose distributions of GTV, PTV and ipsilateral lung calculated by the TPS and MC were compared. For 3DCRT and IMRT plans, the mean dose differences for GTV between the CCC and MC increased with decreasing of the GTV volume. For IMRT, the mean dose differences were found to be higher than that of 3DCRT. The CCC algorithm overestimated the GTV mean dose by approximately 3% for IMRT. For 3DCRT plans, when the volume of the GTV was greater than 100 cm(3), the mean doses calculated by CCC and MC almost have no difference. PBC shows large deviations from the MC algorithm. For the dose to the ipsilateral lung, the CCC algorithm overestimated the dose to the entire lung, and the PBC algorithm overestimated V20 but underestimated V5; the difference in V10 was not statistically significant. PBC substantially overestimates the dose to the tumour, but the CCC is similar to the MC simulation. It is recommended that the treatment plans for lung cancer be developed using an advanced dose calculation algorithm other than PBC. MC can accurately calculate the dose distribution in lung cancer and can provide a notably effective tool for benchmarking the performance of other dose calculation algorithms within patients.

A method for photon beam Monte Carlo multileaf collimator particle transport

NASA Astrophysics Data System (ADS)

Siebers, Jeffrey V.; Keall, Paul J.; Kim, Jong Oh; Mohan, Radhe

2002-09-01

Monte Carlo (MC) algorithms are recognized as the most accurate methodology for patient dose assessment. For intensity-modulated radiation therapy (IMRT) delivered with dynamic multileaf collimators (DMLCs), accurate dose calculation, even with MC, is challenging. Accurate IMRT MC dose calculations require inclusion of the moving MLC in the MC simulation. Due to its complex geometry, full transport through the MLC can be time consuming. The aim of this work was to develop an MLC model for photon beam MC IMRT dose computations. The basis of the MC MLC model is that the complex MLC geometry can be separated into simple geometric regions, each of which readily lends itself to simplified radiation transport. For photons, only attenuation and first Compton scatter interactions are considered. The amount of attenuation material an individual particle encounters while traversing the entire MLC is determined by adding the individual amounts from each of the simplified geometric regions. Compton scatter is sampled based upon the total thickness traversed. Pair production and electron interactions (scattering and bremsstrahlung) within the MLC are ignored. The MLC model was tested for 6 MV and 18 MV photon beams by comparing it with measurements and MC simulations that incorporate the full physics and geometry for fields blocked by the MLC and with measurements for fields with the maximum possible tongue-and-groove and tongue-or-groove effects, for static test cases and for sliding windows of various widths. The MLC model predicts the field size dependence of the MLC leakage radiation within 0.1% of the open-field dose. The entrance dose and beam hardening behind a closed MLC are predicted within +/-1% or 1 mm. Dose undulations due to differences in inter- and intra-leaf leakage are also correctly predicted. The MC MLC model predicts leaf-edge tongue-and-groove dose effect within +/-1% or 1 mm for 95% of the points compared at 6 MV and 88% of the points compared at 18 MV. The dose through a static leaf tip is also predicted generally within +/-1% or 1 mm. Tests with sliding windows of various widths confirm the accuracy of the MLC model for dynamic delivery and indicate that accounting for a slight leaf position error (0.008 cm for our MLC) will improve the accuracy of the model. The MLC model developed is applicable to both dynamic MLC and segmental MLC IMRT beam delivery and will be useful for patient IMRT dose calculations, pre-treatment verification of IMRT delivery and IMRT portal dose transmission dosimetry.

Agreement between gamma passing rates using computed tomography in radiotherapy and secondary cancer risk prediction from more advanced dose calculated models

PubMed Central

Balosso, Jacques

2017-01-01

Background During the past decades, in radiotherapy, the dose distributions were calculated using density correction methods with pencil beam as type ‘a’ algorithm. The objectives of this study are to assess and evaluate the impact of dose distribution shift on the predicted secondary cancer risk (SCR), using modern advanced dose calculation algorithms, point kernel, as type ‘b’, which consider change in lateral electrons transport. Methods Clinical examples of pediatric cranio-spinal irradiation patients were evaluated. For each case, two radiotherapy treatment plans with were generated using the same prescribed dose to the target resulting in different number of monitor units (MUs) per field. The dose distributions were calculated, respectively, using both algorithms types. A gamma index (γ) analysis was used to compare dose distribution in the lung. The organ equivalent dose (OED) has been calculated with three different models, the linear, the linear-exponential and the plateau dose response curves. The excess absolute risk ratio (EAR) was also evaluated as (EAR = OED type ‘b’ / OED type ‘a’). Results The γ analysis results indicated an acceptable dose distribution agreement of 95% with 3%/3 mm. Although, the γ-maps displayed dose displacement >1 mm around the healthy lungs. Compared to type ‘a’, the OED values from type ‘b’ dose distributions’ were about 8% to 16% higher, leading to an EAR ratio >1, ranged from 1.08 to 1.13 depending on SCR models. Conclusions The shift of dose calculation in radiotherapy, according to the algorithm, can significantly influence the SCR prediction and the plan optimization, since OEDs are calculated from DVH for a specific treatment. The agreement between dose distribution and SCR prediction depends on dose response models and epidemiological data. In addition, the γ passing rates of 3%/3 mm does not translate the difference, up to 15%, in the predictions of SCR resulting from alternative algorithms. Considering that modern algorithms are more accurate, showing more precisely the dose distributions, but that the prediction of absolute SCR is still very imprecise, only the EAR ratio could be used to rank radiotherapy plans. PMID:28811995

Monte Carlo dose calculations for high-dose-rate brachytherapy using GPU-accelerated processing.

PubMed

Tian, Z; Zhang, M; Hrycushko, B; Albuquerque, K; Jiang, S B; Jia, X

2016-01-01

Current clinical brachytherapy dose calculations are typically based on the Association of American Physicists in Medicine Task Group report 43 (TG-43) guidelines, which approximate patient geometry as an infinitely large water phantom. This ignores patient and applicator geometries and heterogeneities, causing dosimetric errors. Although Monte Carlo (MC) dose calculation is commonly recognized as the most accurate method, its associated long computational time is a major bottleneck for routine clinical applications. This article presents our recent developments of a fast MC dose calculation package for high-dose-rate (HDR) brachytherapy, gBMC, built on a graphics processing unit (GPU) platform. gBMC-simulated photon transport in voxelized geometry with physics in (192)Ir HDR brachytherapy energy range considered. A phase-space file was used as a source model. GPU-based parallel computation was used to simultaneously transport multiple photons, one on a GPU thread. We validated gBMC by comparing the dose calculation results in water with that computed TG-43. We also studied heterogeneous phantom cases and a patient case and compared gBMC results with Acuros BV results. Radial dose function in water calculated by gBMC showed <0.6% relative difference from that of the TG-43 data. Difference in anisotropy function was <1%. In two heterogeneous slab phantoms and one shielded cylinder applicator case, average dose discrepancy between gBMC and Acuros BV was <0.87%. For a tandem and ovoid patient case, good agreement between gBMC and Acruos BV results was observed in both isodose lines and dose-volume histograms. In terms of the efficiency, it took ∼47.5 seconds for gBMC to reach 0.15% statistical uncertainty within the 5% isodose line for the patient case. The accuracy and efficiency of a new GPU-based MC dose calculation package, gBMC, for HDR brachytherapy make it attractive for clinical applications. Copyright © 2016 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.

Monte Carlo Investigation on the Effect of Heterogeneities on Strut Adjusted Volume Implant (SAVI) Dosimetry

NASA Astrophysics Data System (ADS)

Koontz, Craig

Breast cancer is the most prevalent cancer for women with more than 225,000 new cases diagnosed in the United States in 2012 (ACS, 2012). With the high prevalence, comes an increased emphasis on researching new techniques to treat this disease. Accelerated partial breast irradiation (APBI) has been used as an alternative to whole breast irradiation (WBI) in order to treat occult disease after lumpectomy. Similar recurrence rates have been found using ABPI after lumpectomy as with mastectomy alone, but with the added benefit of improved cosmetic and psychological results. Intracavitary brachytherapy devices have been used to deliver the APBI prescription. However, inability to produce asymmetric dose distributions in order to avoid overdosing skin and chest wall has been an issue with these devices. Multi-lumen devices were introduced to overcome this problem. Of these, the Strut-Adjusted Volume Implant (SAVI) has demonstrated the greatest ability to produce an asymmetric dose distribution, which would have greater ability to avoid skin and chest wall dose, and thus allow more women to receive this type of treatment. However, SAVI treatments come with inherent heterogeneities including variable backscatter due to the proximity to the tissue-air and tissue-lung interfaces and variable contents within the cavity created by the SAVI. The dose calculation protocol based on TG-43 does not account for heterogeneities and thus will not produce accurate dosimetry; however Acuros, a model-based dose calculation algorithm manufactured by Varian Medical Systems, claims to accurately account for heterogeneities. Monte Carlo simulation can calculate the dosimetry with high accuracy. In this thesis, a model of the SAVI will be created for Monte Carlo, specifically using MCNP code, in order to explore the affects of heterogeneities on the dose distribution. This data will be compared to TG-43 and Acuros calculated dosimetry to explore their accuracy.

The use of tetrahedral mesh geometries in Monte Carlo simulation of applicator based brachytherapy dose distributions

NASA Astrophysics Data System (ADS)

Paiva Fonseca, Gabriel; Landry, Guillaume; White, Shane; D'Amours, Michel; Yoriyaz, Hélio; Beaulieu, Luc; Reniers, Brigitte; Verhaegen, Frank

2014-10-01

Accounting for brachytherapy applicator attenuation is part of the recommendations from the recent report of AAPM Task Group 186. To do so, model based dose calculation algorithms require accurate modelling of the applicator geometry. This can be non-trivial in the case of irregularly shaped applicators such as the Fletcher Williamson gynaecological applicator or balloon applicators with possibly irregular shapes employed in accelerated partial breast irradiation (APBI) performed using electronic brachytherapy sources (EBS). While many of these applicators can be modelled using constructive solid geometry (CSG), the latter may be difficult and time-consuming. Alternatively, these complex geometries can be modelled using tessellated geometries such as tetrahedral meshes (mesh geometries (MG)). Recent versions of Monte Carlo (MC) codes Geant4 and MCNP6 allow for the use of MG. The goal of this work was to model a series of applicators relevant to brachytherapy using MG. Applicators designed for 192Ir sources and 50 kV EBS were studied; a shielded vaginal applicator, a shielded Fletcher Williamson applicator and an APBI balloon applicator. All applicators were modelled in Geant4 and MCNP6 using MG and CSG for dose calculations. CSG derived dose distributions were considered as reference and used to validate MG models by comparing dose distribution ratios. In general agreement within 1% for the dose calculations was observed for all applicators between MG and CSG and between codes when considering volumes inside the 25% isodose surface. When compared to CSG, MG required longer computation times by a factor of at least 2 for MC simulations using the same code. MCNP6 calculation times were more than ten times shorter than Geant4 in some cases. In conclusion we presented methods allowing for high fidelity modelling with results equivalent to CSG. To the best of our knowledge MG offers the most accurate representation of an irregular APBI balloon applicator.

SU-E-T-430: Modeling MLC Leaf End in 2D for Sliding Window IMRT and Arc Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, X; Zhu, T

2014-06-01

Purpose: To develop a 2D geometric model for MLC accounting for leaf end dose leakage for dynamic IMRT and Rapidarc therapy. Methods: Leaf-end dose leakage is one of the problems for MLC dose calculation and modeling. Dosimetric leaf gap used to model the MLC and to count for leakage in dose calculation, but may not be accurate for smaller leaf gaps. We propose another geometric modeling method to compensate for the MLC round-shape leaf ends dose leakage, and improve the accuracy of dose calculation and dose verification. A triangular function is used to geometrically model the MLC leaf end leakagemore » in the leaf motion direction, and a step function is used in the perpendicular direction. Dose measurements with different leaf gap, different window width, and different window height were conducted, and the results were used to fit the analytical model to get the model parameters. Results: Analytical models have been obtained for stop-and-shoot and dynamic modes for MLC motion. Parameters a=0.4, lw'=5.0 mm for 6X and a=0.54, lw'=4.1 mm for 15x were obtained from the fitting process. The proposed MLC leaf end model improves the dose profile at the two ends of the sliding window opening. This improvement is especially significant for smaller sliding window openings, which are commonly used for highly modulated IMRT plans and arc therapy plans. Conclusion: This work models the MLC round leaf end shape and movement pattern for IMRT dose calculation. The theory, as well as the results in this work provides a useful tool for photon beam IMRT dose calculation and verification.« less

Pencil-beam redefinition algorithm dose calculations for electron therapy treatment planning

NASA Astrophysics Data System (ADS)

Boyd, Robert Arthur

2001-08-01

The electron pencil-beam redefinition algorithm (PBRA) of Shiu and Hogstrom has been developed for use in radiotherapy treatment planning (RTP). Earlier studies of Boyd and Hogstrom showed that the PBRA lacked an adequate incident beam model, that PBRA might require improved electron physics, and that no data existed which allowed adequate assessment of the PBRA-calculated dose accuracy in a heterogeneous medium such as one presented by patient anatomy. The hypothesis of this research was that by addressing the above issues the PBRA-calculated dose would be accurate to within 4% or 2 mm in regions of high dose gradients. A secondary electron source was added to the PBRA to account for collimation-scattered electrons in the incident beam. Parameters of the dual-source model were determined from a minimal data set to allow ease of beam commissioning. Comparisons with measured data showed 3% or better dose accuracy in water within the field for cases where 4% accuracy was not previously achievable. A measured data set was developed that allowed an evaluation of PBRA in regions distal to localized heterogeneities. Geometries in the data set included irregular surfaces and high- and low-density internal heterogeneities. The data was estimated to have 1% precision and 2% agreement with accurate, benchmarked Monte Carlo (MC) code. PBRA electron transport was enhanced by modeling local pencil beam divergence. This required fundamental changes to the mathematics of electron transport (divPBRA). Evaluation of divPBRA with the measured data set showed marginal improvement in dose accuracy when compared to PBRA; however, 4% or 2mm accuracy was not achieved by either PBRA version for all data points. Finally, PBRA was evaluated clinically by comparing PBRA- and MC-calculated dose distributions using site-specific patient RTP data. Results show PBRA did not agree with MC to within 4% or 2mm in a small fraction (<3%) of the irradiated volume. Although the hypothesis of the research was shown to be false, the minor dose inaccuracies should have little or no impact on RTP decisions or patient outcome. Therefore, given ease of beam commissioning, documentation of accuracy, and calculational speed, the PBRA should be considered a practical tool for clinical use.

Monte Carlo modeling of a 6 and 18 MV Varian Clinac medical accelerator for in-field and out-of-field dose calculations: development and validation

PubMed Central

Bednarz, Bryan; Xu, X George

2012-01-01

There is a serious and growing concern about the increased risk of radiation-induced second cancers and late tissue injuries associated with radiation treatment. To better understand and to more accurately quantify non-target organ doses due to scatter and leakage radiation from medical accelerators, a detailed Monte Carlo model of the medical linear accelerator is needed. This paper describes the development and validation of a detailed accelerator model of the Varian Clinac operating at 6 and 18 MV beam energies. Over 100 accelerator components have been defined and integrated using the Monte Carlo code MCNPX. A series of in-field and out-of-field dose validation studies were performed. In-field dose distributions calculated using the accelerator models were tuned to match measurement data that are considered the de facto ‘gold standard’ for the Varian Clinac accelerator provided by the manufacturer. Field sizes of 4 cm × 4 cm, 10 cm × 10 cm, 20 cm × 20 cm and 40 cm × 40 cm were considered. The local difference between calculated and measured dose on the percent depth dose curve was less than 2% for all locations. The local difference between calculated and measured dose on the dose profile curve was less than 2% in the plateau region and less than 2 mm in the penumbra region for all locations. Out-of-field dose profiles were calculated and compared to measurement data for both beam energies for field sizes of 4 cm × 4 cm, 10 cm × 10 cm and 20 cm × 20 cm. For all field sizes considered in this study, the average local difference between calculated and measured dose for the 6 and 18 MV beams was 14 and 16%, respectively. In addition, a method for determining neutron contamination in the 18 MV operating model was validated by comparing calculated in-air neutron fluence with reported calculations and measurements. The average difference between calculated and measured neutron fluence was 20%. As one of the most detailed accelerator models for both in-field and out-of-field dose calculations, the model will be combined with anatomically realistic computational patient phantoms into a computational framework to calculate non-target organ doses to patients from various radiation treatment plans. PMID:19141879

SU-E-T-339: Dosimetric Verification of Acuros XB Dose Calculation Algorithm On An Air Cavity for 6-MV Flattening Filter-Free Beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, S; Suh, T; Chung, J

Purpose: This study was to verify the accuracy of Acuros XB (AXB) dose calculation algorithm on an air cavity for a single radiation field using 6-MV flattening filter-free (FFF) beam. Methods: A rectangular slab phantom containing an air cavity was made for this study. The CT images of the phantom for dose calculation were scanned with and without film at measurement depths (4.5, 5.5, 6.5 and 7.5 cm). The central axis doses (CADs) and the off-axis doses (OADs) were measured by film and calculated with Analytical Anisotropic Algorithm (AAA) and AXB for field sizes ranging from 2 Χ 2 tomore » 5 Χ 5 cm{sup 2} of 6-MV FFF beams. Both algorithms were divided into AXB-w and AAA -w when included the film in phantom for dose calculation, and AXB-w/o and AAA-w/o in calculation without film. The calculated OADs for both algorithms were compared with the measured OADs and difference values were determined using root means squares error (RMSE) and gamma evaluation. Results: The percentage differences (%Diffs) between the measured and calculated CAD for AXB-w was most agreement than others. Compared to the %Diff with and without film, the %Diffs with film were decreased than without within both algorithms. The %Diffs for both algorithms were reduced with increasing field size and increased relative to the depth increment. RMSEs of CAD for AXB-w were within 10.32% for both inner-profile and penumbra, while the corresponding values of AAA-w appeared to 96.50%. Conclusion: This study demonstrated that the dose calculation with AXB within air cavity shows more accurate than with AAA compared to the measured dose. Furthermore, we found that the AXB-w was superior to AXB-w/o in this region when compared against the measurements.« less

SU-E-T-465: Dose Calculation Method for Dynamic Tumor Tracking Using a Gimbal-Mounted Linac

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sugimoto, S; Inoue, T; Kurokawa, C

Purpose: Dynamic tumor tracking using the gimbal-mounted linac (Vero4DRT, Mitsubishi Heavy Industries, Ltd., Japan) has been available when respiratory motion is significant. The irradiation accuracy of the dynamic tumor tracking has been reported to be excellent. In addition to the irradiation accuracy, a fast and accurate dose calculation algorithm is needed to validate the dose distribution in the presence of respiratory motion because the multiple phases of it have to be considered. A modification of dose calculation algorithm is necessary for the gimbal-mounted linac due to the degrees of freedom of gimbal swing. The dose calculation algorithm for the gimbalmore » motion was implemented using the linear transformation between coordinate systems. Methods: The linear transformation matrices between the coordinate systems with and without gimbal swings were constructed using the combination of translation and rotation matrices. The coordinate system where the radiation source is at the origin and the beam axis along the z axis was adopted. The transformation can be divided into the translation from the radiation source to the gimbal rotation center, the two rotations around the center relating to the gimbal swings, and the translation from the gimbal center to the radiation source. After operating the transformation matrix to the phantom or patient image, the dose calculation can be performed as the no gimbal swing. The algorithm was implemented in the treatment planning system, PlanUNC (University of North Carolina, NC). The convolution/superposition algorithm was used. The dose calculations with and without gimbal swings were performed for the 3 × 3 cm{sup 2} field with the grid size of 5 mm. Results: The calculation time was about 3 minutes per beam. No significant additional time due to the gimbal swing was observed. Conclusions: The dose calculation algorithm for the finite gimbal swing was implemented. The calculation time was moderate.« less

SU-E-T-454: Impact of Calculation Grid Size On Dosimetry and Radiobiological Parameters for Head and Neck IMRT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Srivastava, S; Das, I; Indiana University Health Methodist Hospital, Indianapolis, IN

2014-06-01

Purpose: IMRT has become standard of care for complex treatments to optimize dose to target and spare normal tissues. However, the impact of calculation grid size is not widely known especially dose distribution, tumor control probability (TCP) and normal tissue complication probability (NTCP) which is investigated in this study. Methods: Ten head and neck IMRT patients treated with 6 MV photons were chosen for this study. Using Eclipse TPS, treatment plans were generated for different grid sizes in the range 1–5 mm for the same optimization criterion with specific dose-volume constraints. The dose volume histogram (DVH) was calculated for allmore » IMRT plans and dosimetric data were compared. ICRU-83 dose points such as D2%, D50%, D98%, as well as the homogeneity and conformity indices (HI, CI) were calculated. In addition, TCP and NTCP were calculated from DVH data. Results: The PTV mean dose and TCP decreases with increasing grid size with an average decrease in mean dose by 2% and TCP by 3% respectively. Increasing grid size from 1–5 mm grid size, the average mean dose and NTCP for left parotid was increased by 6.0% and 8.0% respectively. Similar patterns were observed for other OARs such as cochlea, parotids and spinal cord. The HI increases up to 60% and CI decreases on average by 3.5% between 1 and 5 mm grid that resulted in decreased TCP and increased NTCP values. The number of points meeting the gamma criteria of ±3% dose difference and ±3mm DTA was higher with a 1 mm on average (97.2%) than with a 5 mm grid (91.3%). Conclusion: A smaller calculation grid provides superior dosimetry with improved TCP and reduced NTCP values. The effect is more pronounced for smaller OARs. Thus, the smallest possible grid size should be used for accurate dose calculation especially in H and N planning.« less

A rule of unity for human intestinal absorption 3: Application to pharmaceuticals.

PubMed

Patel, Raj B; Yalkowsky, Samuel H

2018-02-01

The rule of unity is based on a simple absorption parameter, Π, that can accurately predict whether or not an orally administered drug will be well absorbed or poorly absorbed. The intrinsic aqueous solubility and octanol-water partition coefficient, along with the drug dose are used to calculate Π. We show that a single delineator value for Π exist that can distinguish whether a drug is likely to be well absorbed (FA ≥ 0.5) or poorly absorbed (FA < 0.5) at any specified dose. The model is shown to give 82.5% correct predictions for over 938 pharmaceuticals. The maximum well-absorbed dose (i.e. the maximum dose that will be more than 50% absorbed) calculated using this model can be utilized as a guideline for drug design and synthesis. Copyright © 2017 John Wiley & Sons, Ltd.

SU-E-T-169: Evaluation of Oncentra TPS for Nasopharynx Brachy Using Patient Specific Voxel Phantom and EGSnrc

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hadad, K; Zoherhvand, M; Faghihi, R

2014-06-01

Purpose: Nasopharnx carcinoma (NPC) treatment is being carried out using Ir-192 HDR seeds in Mehdieh Hospital in Hamadan, Iran. The Oncentra™ TPS is based on optimized TG-43 formalism which disregards heterogeneity in the treatment area. Due to abundant heterogeneity in head and neck, comparison of the Oncentra™ TPS dose evaluation and an accurate dose calculation method in NPC brachytherapy is the objective of this study. Methods: CT DICOMs of a patient with NPC obtained from Mehdieh Hospital used to create 3D voxel phantom with CTCREATE utility of EGSnrc code package. The voxel phantom together with Ir-192 HDR brachytherapy source weremore » the input to DOSXYZnrc to calculate the 3D dose distribution. The sources were incorporate with type 6 source in DOSXYZnrc and their dwell times were taken into account in final dose calculations. Results: The direct comparison between isodoses as well as DVHs for the GTV, PTV and CTV obtained by Oncentra™ and EGSnrc Monte Carlo code are made. EGSnrc results are obtained using 5×10{sup 9} histories to reduce the statistical error below 1% in GTV and 5% in 5% dose areas. The standard ICRP700 cross section library is employed in DOSXYZnrc dose calculation. Conclusion: A direct relationship between increased dose differences and increased material density (hence heterogeneity) is observed when isodoses contours of the TPS and DOSXYZnrc are compared. Regarding the point dose calculations, the differences range from 1.2% in PTV to 5.6% for cavity region and 7.8% for bone regions. While Oncentra™ TPS overestimates the dose in cavities, it tends to underestimate dose depositions within bones.« less

SU-E-T-373: Evaluation and Reduction of Contralateral Skin /subcutaneous Dose for Tangential Breast Irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Butson, M; Carroll, S; Whitaker, M

2015-06-15

Purpose: Tangential breast irradiation is a standard treatment technique for breast cancer therapy. One aspect of dose delivery includes dose delivered to the skin caused by electron contamination. This effect is especially important for highly oblique beams used on the medical tangent where the electron contamination deposits dose on the contralateral breast side. This work aims to investigate and predict as well as define a method to reduce this dose during tangential breast radiotherapy. Methods: Analysis and calculation of breast skin and subcutaneous dose is performed using a Varian Eclipse planning system, AAA algorithm for 6MV x-ray treatments. Measurements weremore » made using EBT3 Gafchromic film to verify the accuracy of planning data. Various materials were tested to assess their ability to remove electron contamination on the contralateral breast. Results: Results showed that the Varian Eclipse AAA algorithm could accurately estimate contralateral breast dose in the build-up region at depths of 2mm or deeper. Surface dose was underestimated by the AAA algorithm. Doses up to 12% of applied dose were seen on the contralateral breast surface and up to 9 % at 2mm depth. Due to the nature of this radiation, being mainly low energy electron contamination, a bolus material could be used to reduce this dose to less than 3%. This is accomplished by 10 mm of superflab bolus or by 1 mm of lead. Conclusion: Contralateral breast skin and subcutaneous dose is present for tangential breast treatment and has been measured to be up to 12% of applied dose from the medial tangent beam. This dose is deposited at shallow depths and is accurately calculated by the Eclipse AAA algorithm at depths of 2mm or greater. Bolus material placed over the contralateral can be used to effectively reduce this skin dose.« less

Modification and validation of an analytical source model for external beam radiotherapy Monte Carlo dose calculations.

PubMed

Davidson, Scott E; Cui, Jing; Kry, Stephen; Deasy, Joseph O; Ibbott, Geoffrey S; Vicic, Milos; White, R Allen; Followill, David S

2016-08-01

A dose calculation tool, which combines the accuracy of the dose planning method (DPM) Monte Carlo code and the versatility of a practical analytical multisource model, which was previously reported has been improved and validated for the Varian 6 and 10 MV linear accelerators (linacs). The calculation tool can be used to calculate doses in advanced clinical application studies. One shortcoming of current clinical trials that report dose from patient plans is the lack of a standardized dose calculation methodology. Because commercial treatment planning systems (TPSs) have their own dose calculation algorithms and the clinical trial participant who uses these systems is responsible for commissioning the beam model, variation exists in the reported calculated dose distributions. Today's modern linac is manufactured to tight specifications so that variability within a linac model is quite low. The expectation is that a single dose calculation tool for a specific linac model can be used to accurately recalculate dose from patient plans that have been submitted to the clinical trial community from any institution. The calculation tool would provide for a more meaningful outcome analysis. The analytical source model was described by a primary point source, a secondary extra-focal source, and a contaminant electron source. Off-axis energy softening and fluence effects were also included. The additions of hyperbolic functions have been incorporated into the model to correct for the changes in output and in electron contamination with field size. A multileaf collimator (MLC) model is included to facilitate phantom and patient dose calculations. An offset to the MLC leaf positions was used to correct for the rudimentary assumed primary point source. Dose calculations of the depth dose and profiles for field sizes 4 × 4 to 40 × 40 cm agree with measurement within 2% of the maximum dose or 2 mm distance to agreement (DTA) for 95% of the data points tested. The model was capable of predicting the depth of the maximum dose within 1 mm. Anthropomorphic phantom benchmark testing of modulated and patterned MLCs treatment plans showed agreement to measurement within 3% in target regions using thermoluminescent dosimeters (TLD). Using radiochromic film normalized to TLD, a gamma criteria of 3% of maximum dose and 2 mm DTA was applied with a pass rate of least 85% in the high dose, high gradient, and low dose regions. Finally, recalculations of patient plans using DPM showed good agreement relative to a commercial TPS when comparing dose volume histograms and 2D dose distributions. A unique analytical source model coupled to the dose planning method Monte Carlo dose calculation code has been modified and validated using basic beam data and anthropomorphic phantom measurement. While this tool can be applied in general use for a particular linac model, specifically it was developed to provide a singular methodology to independently assess treatment plan dose distributions from those clinical institutions participating in National Cancer Institute trials.

Effectiveness of the training material in drug-dose calculation skills.

PubMed

Basak, Tulay; Aslan, Ozlem; Unver, Vesile; Yildiz, Dilek

2016-07-01

The aim of study was to evaluate the effectiveness of the training material based on low-level environmental fidelity simulation in drug-dose calculation skills in senior nursing students. A quasi-experimental design with one group. The sample included senior nursing students attending a nursing school in Turkey in the period December 2012-January 2013. Eighty-two senior nursing students were included in the sample. Data were obtained using a data collection form which was developed by the researchers. A paired-sample t-test was used to compare the pretest and post-test scores. The difference between the mean pretest score and the mean post-test score was statistically significant (P < 0.05). This study revealed that the training material based on low-level environmental fidelity simulation positively impacted accurate drug-dose calculation skills in senior nursing students. © 2016 Japan Academy of Nursing Science.

Comparative Study between Measurement Data and Treatment Planning System (TPS) in Small Fields for High Energy Photon Beams.

PubMed

El Shahat, Khaled; El Saeid, Aziza; Attalla, Ehab; Yassin, Adel

2014-01-01

To achieve tumor control for radiotherapy, a dose distribution is planned which has a good chance of sterilizing all cancer cells without causing unacceptable normal tissue complications. The aim of the present study was to achieve an accurate calculation of dose for small field dimensions and perform this by evaluating the accuracy of planning system calculation. This will be compared with real measurement of dose for the same small field dimensions using different detectors. Practical work was performed in two steps: (i) determination of the physical factors required for dose estimation measured by three ionization chambers and calculated by treatment planning system (TPS) based on the latest technical report series (IAEATRS-398) and (ii) comparison of the calculated and measured data. Our data analysis for small field is irradiated by photon energy matched with the data obtained from the ionization chambers and the treatment planning system. Radiographic films were used as an additional detector for the obtained data and showed matching with TPS calculation. It can be concluded that studied small field dimensions were averaged 6% and 4% for 6 MV and 15 MV, respectively. Radiographic film measurements showed a variation in results within ±2% than TPS calculation.

Limitations of current dosimetry for intracavitary accelerated partial breast irradiation with high dose rate iridium-192 and electronic brachytherapy sources

NASA Astrophysics Data System (ADS)

Raffi, Julie A.

Intracavitary accelerated partial breast irradiation (APBI) is a method of treating early stage breast cancer using a high dose rate (HDR) brachytherapy source positioned within the lumpectomy cavity. An expandable applicator stretches the surrounding tissue into a roughly spherical or elliptical shape and the dose is prescribed to 1 cm beyond the edge of the cavity. Currently, dosimetry for these treatments is most often performed using the American Association of Physicists in Medicine Task Group No. 43 (TG-43) formalism. The TG-43 dose-rate equation determines the dose delivered to a homogeneous water medium by scaling the measured source strength with standardized parameters that describe the radial and angular features of the dose distribution. Since TG-43 parameters for each source model are measured or calculated in a homogeneous water medium, the dosimetric effects of the patient's dimensions and composition are not accounted for. Therefore, the accuracy of TG-43 calculations for intracavitary APBI is limited by the presence of inhomogeneities in and around the target volume. Specifically, the breast is smaller than the phantoms used to determine TG-43 parameters and is surrounded by air, ribs, and lung tissue. Also, the composition of the breast tissue itself can affect the dose distribution. This dissertation is focused on investigating the limitations of TG-43 dosimetry for intracavitary APBI for two HDR brachytherapy sources: the VariSource TM VS2000 192Ir source and the AxxentRTM miniature x-ray source. The dose for various conditions was determined using thermoluminescent dosimeters (TLDs) and Monte Carlo (MC) calculations. Accurate measurements and calculations were achieved through the implementation of new measurement and simulation techniques and a novel breast phantom was developed to enable anthropomorphic phantom measurements. Measured and calculated doses for phantom and patient geometries were compared with TG-43 calculated doses to illustrate the limitations of TG-43 dosimetry for intracavitary APBI. TG-43 dose calculations overestimate the dose for regions approaching the lung and breast surface and underestimate the dose for regions in and beyond less-attenuating media such as lung tissue, and for lower energies, breast tissue as well.

SU-E-T-482: In Vivo Dosimetry of An Anthropomorphic Phantom by Using the RADPOS System for Proton Beam Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kohno, R; Motegi, K; Hotta, K

Purpose: Delivered doses in an anthropomorphic phantom were evaluated by using the RADPOS system for proton beam therapy. Methods: The RADPOS in vivo dosimetry system combines an electromagnetic positioning sensor with MOSFET dosimetry, allowing simultaneous online measurements of dose and spatial position. Through the RADPOS system, dose evaluation points can be determined. In vivo proton dosimetry was evaluated by using the RADPOS system and anthropomorphic head and neck phantom. MOSFET doses measured at 3D positions obtained with the RADPOS were compared to the treatment plan values that were calculated by a simplified Monte Carlo (SMC) method. Although the MOSFET responsemore » depends strongly on the linear energy transfer (LET) of proton beam, the MOSFET responses to proton beams were corrected with the SMC. Here, the SMC calculated only dose deposition determined by the experimental depth–dose distribution and lateral displacement of protons due to both multiple scattering effect in materials and incident angle. As a Result, the SMC could quickly calculate accurate doses in even heterogeneities. Results: In vivo dosimetry by using the RADPOS, as well as the MOSFET doses agreed in comparison with calculations by the SMC in the range of −3.0% to 8.3%. Most measurement errors occurred because of the uncertainties of dose calculations due to the position error of 1 mm. Conclusion: We evaluated the delivered doses in the anthropomorphic phantom by using the RADPOS system for proton beam therapy. The MOSFET doses agreed in comparison with calculations by the SMC within the measurement error. Therefore, we could successfully control the uncertainties of the measurement positions by using the RADPOS system within 1 mm in in vivo proton dosimetry. We aim for the clinical application of in vivo proton dosimetry with this RADPOS system.« less

SU-E-T-477: An Efficient Dose Correction Algorithm Accounting for Tissue Heterogeneities in LDR Brachytherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mashouf, S; Lai, P; Karotki, A

2014-06-01

Purpose: Seed brachytherapy is currently used for adjuvant radiotherapy of early stage prostate and breast cancer patients. The current standard for calculation of dose surrounding the brachytherapy seeds is based on American Association of Physicist in Medicine Task Group No. 43 (TG-43 formalism) which generates the dose in homogeneous water medium. Recently, AAPM Task Group No. 186 emphasized the importance of accounting for tissue heterogeneities. This can be done using Monte Carlo (MC) methods, but it requires knowing the source structure and tissue atomic composition accurately. In this work we describe an efficient analytical dose inhomogeneity correction algorithm implemented usingmore » MIM Symphony treatment planning platform to calculate dose distributions in heterogeneous media. Methods: An Inhomogeneity Correction Factor (ICF) is introduced as the ratio of absorbed dose in tissue to that in water medium. ICF is a function of tissue properties and independent of source structure. The ICF is extracted using CT images and the absorbed dose in tissue can then be calculated by multiplying the dose as calculated by the TG-43 formalism times ICF. To evaluate the methodology, we compared our results with Monte Carlo simulations as well as experiments in phantoms with known density and atomic compositions. Results: The dose distributions obtained through applying ICF to TG-43 protocol agreed very well with those of Monte Carlo simulations as well as experiments in all phantoms. In all cases, the mean relative error was reduced by at least 50% when ICF correction factor was applied to the TG-43 protocol. Conclusion: We have developed a new analytical dose calculation method which enables personalized dose calculations in heterogeneous media. The advantages over stochastic methods are computational efficiency and the ease of integration into clinical setting as detailed source structure and tissue segmentation are not needed. University of Toronto, Natural Sciences and Engineering Research Council of Canada.« less

Quantification of confounding factors in MRI-based dose calculations as applied to prostate IMRT

NASA Astrophysics Data System (ADS)

Maspero, Matteo; Seevinck, Peter R.; Schubert, Gerald; Hoesl, Michaela A. U.; van Asselen, Bram; Viergever, Max A.; Lagendijk, Jan J. W.; Meijer, Gert J.; van den Berg, Cornelis A. T.

2017-02-01

Magnetic resonance (MR)-only radiotherapy treatment planning requires pseudo-CT (pCT) images to enable MR-based dose calculations. To verify the accuracy of MR-based dose calculations, institutions interested in introducing MR-only planning will have to compare pCT-based and computer tomography (CT)-based dose calculations. However, interpreting such comparison studies may be challenging, since potential differences arise from a range of confounding factors which are not necessarily specific to MR-only planning. Therefore, the aim of this study is to identify and quantify the contribution of factors confounding dosimetric accuracy estimation in comparison studies between CT and pCT. The following factors were distinguished: set-up and positioning differences between imaging sessions, MR-related geometric inaccuracy, pCT generation, use of specific calibration curves to convert pCT into electron density information, and registration errors. The study comprised fourteen prostate cancer patients who underwent CT/MRI-based treatment planning. To enable pCT generation, a commercial solution (MRCAT, Philips Healthcare, Vantaa, Finland) was adopted. IMRT plans were calculated on CT (gold standard) and pCTs. Dose difference maps in a high dose region (CTV) and in the body volume were evaluated, and the contribution to dose errors of possible confounding factors was individually quantified. We found that the largest confounding factor leading to dose difference was the use of different calibration curves to convert pCT and CT into electron density (0.7%). The second largest factor was the pCT generation which resulted in pCT stratified into a fixed number of tissue classes (0.16%). Inter-scan differences due to patient repositioning, MR-related geometric inaccuracy, and registration errors did not significantly contribute to dose differences (0.01%). The proposed approach successfully identified and quantified the factors confounding accurate MRI-based dose calculation in the prostate. This study will be valuable for institutions interested in introducing MR-only dose planning in their clinical practice.

SU-F-J-109: Generate Synthetic CT From Cone Beam CT for CBCT-Based Dose Calculation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, H; Barbee, D; Wang, W

Purpose: The use of CBCT for dose calculation is limited by its HU inaccuracy from increased scatter. This study presents a method to generate synthetic CT images from CBCT data by a probabilistic classification that may be robust to CBCT noise. The feasibility of using the synthetic CT for dose calculation is evaluated in IMRT for unilateral H&N cancer. Methods: In the training phase, a fuzzy c-means classification was performed on HU vectors (CBCT, CT) of planning CT and registered day-1 CBCT image pair. Using the resulting centroid CBCT and CT values for five classified “tissue” types, a synthetic CTmore » for a daily CBCT was created by classifying each CBCT voxel to obtain its probability belonging to each tissue class, then assigning a CT HU with a probability-weighted summation of the classes’ CT centroids. Two synthetic CTs from a CBCT were generated: s-CT using the centroids from classification of individual patient CBCT/CT data; s2-CT using the same centroids for all patients to investigate the applicability of group-based centroids. IMRT dose calculations for five patients were performed on the synthetic CTs and compared with CT-planning doses by dose-volume statistics. Results: DVH curves of PTVs and critical organs calculated on s-CT and s2-CT agree with those from planning-CT within 3%, while doses calculated with heterogeneity off or on raw CBCT show DVH differences up to 15%. The differences in PTV D95% and spinal cord max are 0.6±0.6% and 0.6±0.3% for s-CT, and 1.6±1.7% and 1.9±1.7% for s2-CT. Gamma analysis (2%/2mm) shows 97.5±1.6% and 97.6±1.6% pass rates for using s-CTs and s2-CTs compared with CT-based doses, respectively. Conclusion: CBCT-synthesized CTs using individual or group-based centroids resulted in dose calculations that are comparable to CT-planning dose for unilateral H&N cancer. The method may provide a tool for accurate dose calculation based on daily CBCT.« less

Three-Dimensional Electron Beam Dose Calculations.

NASA Astrophysics Data System (ADS)

Shiu, Almon Sowchee

The MDAH pencil-beam algorithm developed by Hogstrom et al (1981) has been widely used in clinics for electron beam dose calculations for radiotherapy treatment planning. The primary objective of this research was to address several deficiencies of that algorithm and to develop an enhanced version. Two enhancements have been incorporated into the pencil-beam algorithm; one models fluence rather than planar fluence, and the other models the bremsstrahlung dose using measured beam data. Comparisons of the resulting calculated dose distributions with measured dose distributions for several test phantoms have been made. From these results it is concluded (1) that the fluence-based algorithm is more accurate to use for the dose calculation in an inhomogeneous slab phantom, and (2) the fluence-based calculation provides only a limited improvement to the accuracy the calculated dose in the region just downstream of the lateral edge of an inhomogeneity. The source of the latter inaccuracy is believed primarily due to assumptions made in the pencil beam's modeling of the complex phantom or patient geometry. A pencil-beam redefinition model was developed for the calculation of electron beam dose distributions in three dimensions. The primary aim of this redefinition model was to solve the dosimetry problem presented by deep inhomogeneities, which was the major deficiency of the enhanced version of the MDAH pencil-beam algorithm. The pencil-beam redefinition model is based on the theory of electron transport by redefining the pencil beams at each layer of the medium. The unique approach of this model is that all the physical parameters of a given pencil beam are characterized for multiple energy bins. Comparisons of the calculated dose distributions with measured dose distributions for a homogeneous water phantom and for phantoms with deep inhomogeneities have been made. From these results it is concluded that the redefinition algorithm is superior to the conventional, fluence-based, pencil-beam algorithm, especially in predicting the dose distribution downstream of a local inhomogeneity. The accuracy of this algorithm appears sufficient for clinical use, and the algorithm is structured for future expansion of the physical model if required for site specific treatment planning problems.

SU-E-T-470: Importance of HU-Mass Density Calibration Technique in Proton Pencil Beam Dose Calculation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Penfold, S; Miller, A

2015-06-15

Purpose: Stoichiometric calibration of Hounsfield Units (HUs) for conversion to proton relative stopping powers (RStPs) is vital for accurate dose calculation in proton therapy. However proton dose distributions are not only dependent on RStP, but also on relative scattering power (RScP) of patient tissues. RScP is approximated from material density but a stoichiometric calibration of HU-density tables is commonly neglected. The purpose of this work was to quantify the difference in calculated dose of a commercial TPS when using HU-density tables based on tissue substitute materials and stoichiometric calibrated ICRU tissues. Methods: Two HU-density calibration tables were generated based onmore » scans of the CIRS electron density phantom. The first table was based directly on measured HU and manufacturer quoted density of tissue substitute materials. The second was based on the same CT scan of the CIRS phantom followed by a stoichiometric calibration of ICRU44 tissue materials. The research version of Pinnacle{sup 3} proton therapy was used to compute dose in a patient CT data set utilizing both HU-density tables. Results: The two HU-density tables showed significant differences for bone tissues; the difference increasing with increasing HU. Differences in density calibration table translated to a difference in calculated RScP of −2.5% for ICRU skeletal muscle and 9.2% for ICRU femur. Dose-volume histogram analysis of a parallel opposed proton therapy prostate plan showed that the difference in calculated dose was negligible when using the two different HU-density calibration tables. Conclusion: The impact of HU-density calibration technique on proton therapy dose calculation was assessed. While differences were found in the calculated RScP of bony tissues, the difference in dose distribution for realistic treatment scenarios was found to be insignificant.« less

Initial experience of ArcCHECK and 3DVH software for RapidArc treatment plan verification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Infusino, Erminia; Mameli, Alessandra, E-mail: e.infusino@unicampus.it; Conti, Roberto

2014-10-01

The purpose of this study was to perform delivery quality assurance with ArcCHECK and 3DVH system (Sun Nuclear, FL) and to evaluate the suitability of this system for volumetric-modulated arc therapy (VMAT) (RapidArc [RA]) verification. This software calculates the delivered dose distributions in patients by perturbing the calculated dose using errors detected in fluence or planar dose measurements. The device is tested to correlate the gamma passing rate (%GP) and the composite dose predicted by 3DVH software. A total of 28 patients with prostate cancer who were treated with RA were analyzed. RA treatments were delivered to a diode arraymore » phantom (ArcCHECK), which was used to create a planned dose perturbation (PDP) file. The 3DVH analysis used the dose differences derived from comparing the measured dose with the treatment planning system (TPS)-calculated doses to perturb the initial TPS-calculated dose. The 3DVH then overlays the resultant dose on the patient's structures using the resultant “PDP” beams. Measured dose distributions were compared with the calculated ones using the gamma index (GI) method by applying the global (Van Dyk) normalization and acceptance criteria, i.e., 3%/3 mm. Paired differences tests were used to estimate statistical significance of the differences between the composite dose calculated using 3DVH and %GP. Also, statistical correlation by means of logistic regression analysis has been analyzed. Dose-volume histogram (DVH) analysis for patient plans revealed small differences between treatment plan calculations and 3DVH results for organ at risk (OAR), whereas planning target volume (PTV) of the measured plan was systematically higher than that predicted by the TPS. The t-test results between the planned and the estimated DVH values showed that mean values were incomparable (p < 0.05). The quality assurance (QA) gamma analysis 3%/3 mm showed that in all cases there were only weak-to-moderate correlations (Pearson r: 0.12 to 0.74). Moreover, clinically relevant differences increased with increasing QA passing rate, indicating that some of the largest dose differences occurred in the cases of high QA passing rates, which may be called “false negatives.” The clinical importance of any disagreement between the measured and the calculated dose is often difficult to interpret; however, beam errors (either in delivery or in TPS calculation) can affect the effectiveness of the patient dose. Further research is needed to determinate the role of a PDP-type algorithm to accurately estimate patient dose effect.« less

Experimental and Monte Carlo evaluation of Eclipse treatment planning system for effects on dose distribution of the hip prostheses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Çatlı, Serap, E-mail: serapcatli@hotmail.com; Tanır, Güneş

2013-10-01

The present study aimed to investigate the effects of titanium, titanium alloy, and stainless steel hip prostheses on dose distribution based on the Monte Carlo simulation method, as well as the accuracy of the Eclipse treatment planning system (TPS) at 6 and 18 MV photon energies. In the present study the pencil beam convolution (PBC) method implemented in the Eclipse TPS was compared to the Monte Carlo method and ionization chamber measurements. The present findings show that if high-Z material is used in prosthesis, large dose changes can occur due to scattering. The variance in dose observed in the presentmore » study was dependent on material type, density, and atomic number, as well as photon energy; as photon energy increased back scattering decreased. The dose perturbation effect of hip prostheses was significant and could not be predicted accurately by the PBC method for hip prostheses. The findings show that for accurate dose calculation the Monte Carlo-based TPS should be used in patients with hip prostheses.« less

On the parametrization of lateral dose profiles in proton radiation therapy.

PubMed

Bellinzona, V E; Ciocca, M; Embriaco, A; Fontana, A; Mairani, A; Mori, M; Parodi, K

2015-07-01

The accurate evaluation of the lateral dose profile is an important issue in the field of proton radiation therapy. The beam spread, due to Multiple Coulomb Scattering (MCS), is described by the Molière's theory. To take into account also the contribution of nuclear interactions, modern Treatment Planning Systems (TPSs) generally approximate the dose profiles by a sum of Gaussian functions. In this paper we have compared different parametrizations for the lateral dose profile of protons in water for therapeutical energies: the goal is to improve the performances of the actual treatment planning. We have simulated typical dose profiles at the CNAO (Centro Nazionale di Adroterapia Oncologica) beamline with the FLUKA code and validated them with data taken at CNAO considering different energies and depths. We then performed best fits of the lateral dose profiles for different functions using ROOT and MINUIT. The accuracy of the best fits was analyzed by evaluating the reduced χ(2), the number of free parameters of the functions and the calculation time. The best results were obtained with the triple Gaussian and double Gaussian Lorentz-Cauchy functions which have 6 parameters, but good results were also obtained with the so called Gauss-Rutherford function which has only 4 parameters. The comparison of the studied functions with accurate and validated Monte Carlo calculations and with experimental data from CNAO lead us to propose an original parametrization, the Gauss-Rutherford function, to describe the lateral dose profiles of proton beams. Copyright © 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Commissioning of the tongue-and-groove modelling in treatment planning systems: from static fields to VMAT treatments

NASA Astrophysics Data System (ADS)

Hernandez, Victor; Vera-Sánchez, Juan Antonio; Vieillevigne, Laure; Saez, Jordi

2017-08-01

Adequate modelling of the multi-leaf collimator (MLC) by treatment planning systems (TPS) is essential for accurate dose calculations in intensity-modulated radiation-therapy. For this reason modern TPSs incorporate MLC characteristics such as the leaf end curvature, MLC transmission and the tongue-and-groove. However, the modelling of the tongue-and-groove is often neglected during TPS commissioning and it is not known how accurate it is. This study evaluates the dosimetric consequences of the tongue-and-groove effect for two different MLC models using both film dosimetry and ionisation chambers. A set of comprehensive tests are presented that evaluate the ability of TPSs to accurately model this effect in (a) static fields, (b) sliding window beams and (c) VMAT arcs. The tests proposed are useful for the commissioning of TPSs and for the validation of major upgrades. With the ECLIPSE TPS, relevant differences were found between calculations and measurements for beams with dynamic MLCs in the presence of the TG effect, especially for the High Definition MLC, small gap sizes and the 1 mm calculation grid. For this combination, dose differences as high as 10% and 7% were obtained for dynamic MLC gaps of 5 mm and 10 mm, respectively. These differences indicate inadequate modelling of the tongue-and-groove effect, which might not be identified without the proposed tests. In particular, the TPS tended to underestimate the calculated dose, which may require tuning of other configuration parameters in the TPS (such as the dosimetric leaf gap) in order to maximise the agreement between calculations and measurements in clinical plans. In conclusion, a need for better modelling of the MLC by TPSs is demonstrated, one of the relevant aspects being the tongue-and-groove effect. This would improve the accuracy of TPS calculations, especially for plans using small MLC gaps, such as plans with small target volumes or high complexities. Improved modelling of the MLC would also reduce the need for tuning parameters in the TPS, facilitating a more comprehensive configuration and commissioning of TPSs.

Determination of MLC model parameters for Monaco using commercial diode arrays.

PubMed

Kinsella, Paul; Shields, Laura; McCavana, Patrick; McClean, Brendan; Langan, Brian

2016-07-08

Multileaf collimators (MLCs) need to be characterized accurately in treatment planning systems to facilitate accurate intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT). The aim of this study was to examine the use of MapCHECK 2 and ArcCHECK diode arrays for optimizing MLC parameters in Monaco X-ray voxel Monte Carlo (XVMC) dose calculation algorithm. A series of radiation test beams designed to evaluate MLC model parameters were delivered to MapCHECK 2, ArcCHECK, and EBT3 Gafchromic film for comparison. Initial comparison of the calculated and ArcCHECK-measured dose distributions revealed it was unclear how to change the MLC parameters to gain agreement. This ambiguity arose due to an insufficient sampling of the test field dose distributions and unexpected discrepancies in the open parts of some test fields. Consequently, the XVMC MLC parameters were optimized based on MapCHECK 2 measurements. Gafchromic EBT3 film was used to verify the accuracy of MapCHECK 2 measured dose distributions. It was found that adjustment of the MLC parameters from their default values resulted in improved global gamma analysis pass rates for MapCHECK 2 measurements versus calculated dose. The lowest pass rate of any MLC-modulated test beam improved from 68.5% to 93.5% with 3% and 2 mm gamma criteria. Given the close agreement of the optimized model to both MapCHECK 2 and film, the optimized model was used as a benchmark to highlight the relatively large discrepancies in some of the test field dose distributions found with ArcCHECK. Comparison between the optimized model-calculated dose and ArcCHECK-measured dose resulted in global gamma pass rates which ranged from 70.0%-97.9% for gamma criteria of 3% and 2 mm. The simple square fields yielded high pass rates. The lower gamma pass rates were attributed to the ArcCHECK overestimating the dose in-field for the rectangular test fields whose long axis was parallel to the long axis of the ArcCHECK. Considering ArcCHECK measurement issues and the lower gamma pass rates for the MLC-modulated test beams, it was concluded that MapCHECK 2 was a more suitable detector than ArcCHECK for the optimization process. © 2016 The Authors

A general model for stray dose calculation of static and intensity-modulated photon radiation.

PubMed

Hauri, Pascal; Hälg, Roger A; Besserer, Jürgen; Schneider, Uwe

2016-04-01

There is an increasing number of cancer survivors who are at risk of developing late effects caused by ionizing radiation such as induction of second tumors. Hence, the determination of out-of-field dose for a particular treatment plan in the patient's anatomy is of great importance. The purpose of this study was to analytically model the stray dose according to its three major components. For patient scatter, a mechanistic model was developed. For collimator scatter and head leakage, an empirical approach was used. The models utilize a nominal beam energy of 6 MeV to describe two linear accelerator types of a single vendor. The parameters of the models were adjusted using ionization chamber measurements registering total absorbed dose in simple geometries. Whole-body dose measurements using thermoluminescent dosimeters in an anthropomorphic phantom for static and intensity-modulated treatment plans were compared to the 3D out-of-field dose distributions calculated by a combined model. The absolute mean difference between the whole-body predicted and the measured out-of-field dose of four different plans was 11% with a maximum difference below 44%. Computation time of 36 000 dose points for one field was around 30 s. By combining the model-calculated stray dose with the treatment planning system dose, the whole-body dose distribution can be viewed in the treatment planning system. The results suggest that the model is accurate, fast and can be used for a wide range of treatment modalities to calculate the whole-body dose distribution for clinical analysis. For similar energy spectra, the mechanistic patient scatter model can be used independently of treatment machine or beam orientation.

Dose evaluation of organs at risk (OAR) cervical cancer using dose volume histogram (DVH) on brachytherapy

NASA Astrophysics Data System (ADS)

Arif Wibowo, R.; Haris, Bambang; Inganatul Islamiyah, dan

2017-05-01

Brachytherapy is one way to cure cervical cancer. It works by placing a radioactive source near the tumor. However, there are some healthy tissues or organs at risk (OAR) such as bladder and rectum which received radiation also. This study aims to evaluate the radiation dose of the bladder and rectum. There were 12 total radiation dose data of the bladder and rectum obtained from patients’ brachytherapy. The dose of cervix for all patients was 6 Gy. Two-dimensional calculation of the radiation dose was based on the International Commission on Radiation Units and Measurements (ICRU) points or called DICRU while the 3-dimensional calculation derived from Dose Volume Histogram (DVH) on a volume of 2 cc (D2cc). The radiation dose of bladder and rectum from both methods were analysed using independent t test. The mean DICRU of bladder was 4.33730 Gy and its D2cc was4.78090 Gy. DICRU and D2cc bladder did not differ significantly (p = 0.144). The mean DICRU of rectum was 3.57980 Gy and 4.58670 Gy for D2cc. The mean DICRU of rectum differed significantly from D2cc of rectum (p = 0.000). The three-dimensional method radiation dose of the bladder and rectum was higher than the two-dimensional method with ratios 1.10227 for bladder and 1.28127 for rectum. The radiation dose of the bladder and rectum was still below the tolerance dose. Two-dimensional calculation of the bladder and rectum dose was lower than three-dimension which was more accurate due to its calculation at the whole volume of the organs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mandapaka, A; Ghebremedhin, A; Patyal, B

Purpose: Patients who undergo n-BCA glue embolization as part of treatment for AVMs are later referred for proton therapy. Knowing the relative stopping power of the glue accurately allows us to perform accurate dose calculations. In this study we experimentally determine the relative stopping power of an n-BCA mixture in a 126 MeV and 149.6 MeV proton beams. Methods: One unit of the TRUFILL™ n-BCA liquid embolic system consists of 1g unit of n-BCA, 1g unit of Tantalum powder and one 10mL vial of Ethiodized oil. The physician mixed 3:1 Ethiodized oil to n-BCA. Five units (20cc) of the n-BCAmore » liquid embolic glue were prepared and placed in a 6cm x 3cm x3cm Lucite container. The container was placed in front of a water tank in the proton beam path. A diamond detector (active volume 0.004mm3) was used to measure distal edge of depth dose of a modulated 126 MeV proton beam collimated using a 3cm brass aperture. The procedure was repeated with a container carrying the same amount of water placed in front of the water tank. The difference in the depth dose measured with glue and with water was used to determine the relative stopping power of the glue. The same determination was done earlier at 149.6 MeV using a different smaller sample (4cc) of n-BCA. Results: The relative stopping power of this particular n-BCA mixture was determined to be 1.06 at both 126 MeV and 149.6 MeV. We are working on obtaining the composition data of the n-BCA glue so we can perform Monte Carlo calculations. Conclusion: Accurate value of the stopping power of the n-BCA glue in the proton beam was determined to be 1.06. It will improve the accuracy of dose calculations in proton radiosurgery procedures on AVM patients with n-BCA embolization.« less

Dose computation for therapeutic electron beams

NASA Astrophysics Data System (ADS)

Glegg, Martin Mackenzie

The accuracy of electron dose calculations performed by two commercially available treatment planning computers, Varian Cadplan and Helax TMS, has been assessed. Measured values of absorbed dose delivered by a Varian 2100C linear accelerator, under a wide variety of irradiation conditions, were compared with doses calculated by the treatment planning computers. Much of the motivation for this work was provided by a requirement to verify the accuracy of calculated electron dose distributions in situations encountered clinically at Glasgow's Beatson Oncology Centre. Calculated dose distributions are required in a significant minority of electron treatments, usually in cases involving treatment to the head and neck. Here, therapeutic electron beams are subject to factors which may cause non-uniformity in the distribution of dose, and which may complicate the calculation of dose. The beam shape is often irregular, the beam may enter the patient at an oblique angle or at an extended source to skin distance (SSD), tissue inhomogeneities can alter the dose distribution, and tissue equivalent material (such as wax) may be added to reduce dose to critical organs. Technological advances have allowed the current generation of treatment planning computers to implement dose calculation algorithms with the ability to model electron beams in these complex situations. These calculations have, however, yet to be verified by measurement. This work has assessed the accuracy of calculations in a number of specific instances. Chapter two contains a comparison of measured and calculated planar electron isodose distributions. Three situations were considered: oblique incidence, incidence on an irregular surface (such as that which would be arise from the use of wax to reduce dose to spinal cord), and incidence on a phantom containing a small air cavity. Calculations were compared with measurements made by thermoluminescent dosimetry (TLD) in a WTe electron solid water phantom. Chapter three assesses the planning computers' ability to model electron beam penumbra at extended SSD. Calculations were compared with diode measurements in a water phantom. Further measurements assessed doses in the junction region produced by abutting an extended SSD electron field with opposed photon fields. Chapter four describes an investigation of the size and shape of the region enclosed by the 90% isodose line when produced by limiting the electron beam with square and elliptical apertures. The 90% isodose line was chosen because clinical treatments are often prescribed such that a given volume receives at least 90% dose. Calculated and measured dose distributions were compared in a plane normal to the beam central axis. Measurements were made by film dosimetry. While chapters two to four examine relative doses, chapter five assesses the accuracy of absolute dose (or output) calculations performed by the planning computers. Output variation with SSD and field size was examined. Two further situations already assessed for the distribution of relative dose were also considered: an obliquely incident field, and a field incident on an irregular surface. The accuracy of calculations was assessed against criteria stipulated by the International Commission on Radiation Units and Measurement (ICRU). The Varian Cadplan and Helax TMS treatment planning systems produce acceptable accuracy in the calculation of relative dose from therapeutic electron beams in most commonly encountered situations. When interpreting clinical dose distributions, however, knowledge of the limitations of the calculation algorithm employed by each system is required in order to identify the minority of situations where results are not accurate. The calculation of absolute dose is too inaccurate to implement in a clinical environment. (Abstract shortened by ProQuest.).

An empirical model for calculation of the collimator contamination dose in therapeutic proton beams

NASA Astrophysics Data System (ADS)

Vidal, M.; De Marzi, L.; Szymanowski, H.; Guinement, L.; Nauraye, C.; Hierso, E.; Freud, N.; Ferrand, R.; François, P.; Sarrut, D.

2016-02-01

Collimators are used as lateral beam shaping devices in proton therapy with passive scattering beam lines. The dose contamination due to collimator scattering can be as high as 10% of the maximum dose and influences calculation of the output factor or monitor units (MU). To date, commercial treatment planning systems generally use a zero-thickness collimator approximation ignoring edge scattering in the aperture collimator and few analytical models have been proposed to take scattering effects into account, mainly limited to the inner collimator face component. The aim of this study was to characterize and model aperture contamination by means of a fast and accurate analytical model. The entrance face collimator scatter distribution was modeled as a 3D secondary dose source. Predicted dose contaminations were compared to measurements and Monte Carlo simulations. Measurements were performed on two different proton beam lines (a fixed horizontal beam line and a gantry beam line) with divergent apertures and for several field sizes and energies. Discrepancies between analytical algorithm dose prediction and measurements were decreased from 10% to 2% using the proposed model. Gamma-index (2%/1 mm) was respected for more than 90% of pixels. The proposed analytical algorithm increases the accuracy of analytical dose calculations with reasonable computation times.

Neutron track length estimator for GATE Monte Carlo dose calculation in radiotherapy.

PubMed

Elazhar, H; Deschler, T; Létang, J M; Nourreddine, A; Arbor, N

2018-06-20

The out-of-field dose in radiation therapy is a growing concern in regards to the late side-effects and secondary cancer induction. In high-energy x-ray therapy, the secondary neutrons generated through photonuclear reactions in the accelerator are part of this secondary dose. The neutron dose is currently not estimated by the treatment planning system while it appears to be preponderant for distances greater than 50 cm from the isocenter. Monte Carlo simulation has become the gold standard for accurately calculating the neutron dose under specific treatment conditions but the method is also known for having a slow statistical convergence, which makes it difficult to be used on a clinical basis. The neutron track length estimator, a neutron variance reduction technique inspired by the track length estimator method has thus been developped for the first time in the Monte Carlo code GATE to allow a fast computation of the neutron dose in radiotherapy. The details of its implementation, as well as the comparison of its performances against the analog MC method, are presented here. A gain of time from 15 to 400 can be obtained by our method, with a mean difference in the dose calculation of about 1% in comparison with the analog MC method.

Statistic and dosimetric criteria to assess the shift of the prescribed dose for lung radiotherapy plans when integrating point kernel models in medical physics: are we ready?

PubMed

Chaikh, Abdulhamid; Balosso, Jacques

2016-12-01

To apply the statistical bootstrap analysis and dosimetric criteria's to assess the change of prescribed dose (PD) for lung cancer to maintain the same clinical results when using new generations of dose calculation algorithms. Nine lung cancer cases were studied. For each patient, three treatment plans were generated using exactly the same beams arrangements. In plan 1, the dose was calculated using pencil beam convolution (PBC) algorithm turning on heterogeneity correction with modified batho (PBC-MB). In plan 2, the dose was calculated using anisotropic analytical algorithm (AAA) and the same PD, as plan 1. In plan 3, the dose was calculated using AAA with monitor units (MUs) obtained from PBC-MB, as input. The dosimetric criteria's include MUs, delivered dose at isocentre (Diso) and calculated dose to 95% of the target volume (D95). The bootstrap method was used to assess the significance of the dose differences and to accurately estimate the 95% confidence interval (95% CI). Wilcoxon and Spearman's rank tests were used to calculate P values and the correlation coefficient (ρ). Statistically significant for dose difference was found using point kernel model. A good correlation was observed between both algorithms types, with ρ>0.9. Using AAA instead of PBC-MB, an adjustment of the PD in the isocentre is suggested. For a given set of patients, we assessed the need to readjust the PD for lung cancer using dosimetric indices and bootstrap statistical method. Thus, if the goal is to keep on with the same clinical results, the PD for lung tumors has to be adjusted with AAA. According to our simulation we suggest to readjust the PD by 5% and an optimization for beam arrangements to better protect the organs at risks (OARs).

A flexible Monte Carlo tool for patient or phantom specific calculations: comparison with preliminary validation measurements

NASA Astrophysics Data System (ADS)

Davidson, S.; Cui, J.; Followill, D.; Ibbott, G.; Deasy, J.

2008-02-01

The Dose Planning Method (DPM) is one of several 'fast' Monte Carlo (MC) computer codes designed to produce an accurate dose calculation for advanced clinical applications. We have developed a flexible machine modeling process and validation tests for open-field and IMRT calculations. To complement the DPM code, a practical and versatile source model has been developed, whose parameters are derived from a standard set of planning system commissioning measurements. The primary photon spectrum and the spectrum resulting from the flattening filter are modeled by a Fatigue function, cut-off by a multiplying Fermi function, which effectively regularizes the difficult energy spectrum determination process. Commonly-used functions are applied to represent the off-axis softening, increasing primary fluence with increasing angle ('the horn effect'), and electron contamination. The patient dependent aspect of the MC dose calculation utilizes the multi-leaf collimator (MLC) leaf sequence file exported from the treatment planning system DICOM output, coupled with the source model, to derive the particle transport. This model has been commissioned for Varian 2100C 6 MV and 18 MV photon beams using percent depth dose, dose profiles, and output factors. A 3-D conformal plan and an IMRT plan delivered to an anthropomorphic thorax phantom were used to benchmark the model. The calculated results were compared to Pinnacle v7.6c results and measurements made using radiochromic film and thermoluminescent detectors (TLD).

SU-E-T-329: Dosimetric Impact of Implementing Metal Artifact Reduction Methods and Metal Energy Deposition Kernels for Photon Dose Calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, J; Followill, D; Howell, R

2015-06-15

Purpose: To investigate two strategies for reducing dose calculation errors near metal implants: use of CT metal artifact reduction methods and implementation of metal-based energy deposition kernels in the convolution/superposition (C/S) method. Methods: Radiochromic film was used to measure the dose upstream and downstream of titanium and Cerrobend implants. To assess the dosimetric impact of metal artifact reduction methods, dose calculations were performed using baseline, uncorrected images and metal artifact reduction Methods: Philips O-MAR, GE’s monochromatic gemstone spectral imaging (GSI) using dual-energy CT, and GSI imaging with metal artifact reduction software applied (MARs).To assess the impact of metal kernels, titaniummore » and silver kernels were implemented into a commercial collapsed cone C/S algorithm. Results: The CT artifact reduction methods were more successful for titanium than Cerrobend. Interestingly, for beams traversing the metal implant, we found that errors in the dimensions of the metal in the CT images were more important for dose calculation accuracy than reduction of imaging artifacts. The MARs algorithm caused a distortion in the shape of the titanium implant that substantially worsened the calculation accuracy. In comparison to water kernel dose calculations, metal kernels resulted in better modeling of the increased backscatter dose at the upstream interface but decreased accuracy directly downstream of the metal. We also found that the success of metal kernels was dependent on dose grid size, with smaller calculation voxels giving better accuracy. Conclusion: Our study yielded mixed results, with neither the metal artifact reduction methods nor the metal kernels being globally effective at improving dose calculation accuracy. However, some successes were observed. The MARs algorithm decreased errors downstream of Cerrobend by a factor of two, and metal kernels resulted in more accurate backscatter dose upstream of metals. Thus, these two strategies do have the potential to improve accuracy for patients with metal implants in certain scenarios. This work was supported by Public Health Service grants CA 180803 and CA 10953 awarded by the National Cancer Institute, United States of Health and Human Services, and in part by Mobius Medical Systems.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schnell, E; Ferreira, C; Ahmad, S

Purpose: Accuracy of a RSP-HU calibration curve produced for proton treatment planning is tested by comparing the treatment planning system dose grid to physical doses delivered on film by a Mevion S250 double-scattering proton unit. Methods: A single batch of EBT3 Gafchromic film was used for calibration and measurements. The film calibration curve was obtained using Mevion proton beam reference option 20 (15cm range, 10cm modulation). Paired films were positioned at the center of the spread out Bragg peak (SOBP) in solid water. The calibration doses were verified with an ion chamber, including background and doses from 20cGy to 350cGy.more » Films were scanned in a flatbed Epson-Expression 10000-XL scanner, and analyzed using the red channel. A Rando phantom was scanned with a GE LightSpeed CT Simulator. A single-field proton plan (Eclipse, Varian) was calculated to deliver 171cGy to the pelvis section (heterogeneous region), using a standard 4×4cm aperture without compensator, 7.89cm beam range, and 5.36cm SOBP. Varied depths of the calculated distal 90% isodose-line were recorded and compared. The dose distribution from film irradiated between Rando slices was compared with the calculated plans using RIT v.6.2. Results: Distal 90% isodose-line depth variation between CT scans was 2mm on average, and 4mm at maximum. Fine calculation of this variation was restricted by the dose calculation grid, as well as the slice thickness. Dose differences between calibrated film measurements and calculated doses were on average 5.93cGy (3.5%), with the large majority of differences forming a normal distribution around 3.5cGy (2%). Calculated doses were almost entirely greater than those measured. Conclusion: RSP to HU calibration curve is shown to produce distal depth variation within the margin of tolerance (±4.3mm) across all potential scan energies and protocols. Dose distribution calculation is accurate to 2–4% within the SOBP, including areas of high tissue heterogeneity.« less

Predictive model accuracy in estimating last Δ9-tetrahydrocannabinol (THC) intake from plasma and whole blood cannabinoid concentrations in chronic, daily cannabis smokers administered subchronic oral THC.

PubMed

Karschner, Erin L; Schwope, David M; Schwilke, Eugene W; Goodwin, Robert S; Kelly, Deanna L; Gorelick, David A; Huestis, Marilyn A

2012-10-01

Determining time since last cannabis/Δ9-tetrahydrocannabinol (THC) exposure is important in clinical, workplace, and forensic settings. Mathematical models calculating time of last exposure from whole blood concentrations typically employ a theoretical 0.5 whole blood-to-plasma (WB/P) ratio. No studies previously evaluated predictive models utilizing empirically-derived WB/P ratios, or whole blood cannabinoid pharmacokinetics after subchronic THC dosing. Ten male chronic, daily cannabis smokers received escalating around-the-clock oral THC (40-120 mg daily) for 8 days. Cannabinoids were quantified in whole blood and plasma by two-dimensional gas chromatography-mass spectrometry. Maximum whole blood THC occurred 3.0 h after the first oral THC dose and 103.5h (4.3 days) during multiple THC dosing. Median WB/P ratios were THC 0.63 (n=196), 11-hydroxy-THC 0.60 (n=189), and 11-nor-9-carboxy-THC (THCCOOH) 0.55 (n=200). Predictive models utilizing these WB/P ratios accurately estimated last cannabis exposure in 96% and 100% of specimens collected within 1-5h after a single oral THC dose and throughout multiple dosing, respectively. Models were only 60% and 12.5% accurate 12.5 and 22.5h after the last THC dose, respectively. Predictive models estimating time since last cannabis intake from whole blood and plasma cannabinoid concentrations were inaccurate during abstinence, but highly accurate during active THC dosing. THC redistribution from large cannabinoid body stores and high circulating THCCOOH concentrations create different pharmacokinetic profiles than those in less than daily cannabis smokers that were used to derive the models. Thus, the models do not accurately predict time of last THC intake in individuals consuming THC daily. Published by Elsevier Ireland Ltd.

Experimental pencil beam kernels derivation for 3D dose calculation in flattening filter free modulated fields

NASA Astrophysics Data System (ADS)

Diego Azcona, Juan; Barbés, Benigno; Wang, Lilie; Burguete, Javier

2016-01-01

This paper presents a method to obtain the pencil-beam kernels that characterize a megavoltage photon beam generated in a flattening filter free (FFF) linear accelerator (linac) by deconvolution from experimental measurements at different depths. The formalism is applied to perform independent dose calculations in modulated fields. In our previous work a formalism was developed for ideal flat fluences exiting the linac’s head. That framework could not deal with spatially varying energy fluences, so any deviation from the ideal flat fluence was treated as a perturbation. The present work addresses the necessity of implementing an exact analysis where any spatially varying fluence can be used such as those encountered in FFF beams. A major improvement introduced here is to handle the actual fluence in the deconvolution procedure. We studied the uncertainties associated to the kernel derivation with this method. Several Kodak EDR2 radiographic films were irradiated with a 10 MV FFF photon beam from two linacs from different vendors, at the depths of 5, 10, 15, and 20cm in polystyrene (RW3 water-equivalent phantom, PTW Freiburg, Germany). The irradiation field was a 50mm diameter circular field, collimated with a lead block. The 3D kernel for a FFF beam was obtained by deconvolution using the Hankel transform. A correction on the low dose part of the kernel was performed to reproduce accurately the experimental output factors. Error uncertainty in the kernel derivation procedure was estimated to be within 0.2%. Eighteen modulated fields used clinically in different treatment localizations were irradiated at four measurement depths (total of fifty-four film measurements). Comparison through the gamma-index to their corresponding calculated absolute dose distributions showed a number of passing points (3%, 3mm) mostly above 99%. This new procedure is more reliable and robust than the previous one. Its ability to perform accurate independent dose calculations was demonstrated.

High and low energy gamma beam dump designs for the gamma beam delivery system at ELI-NP

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yasin, Zafar, E-mail: zafar.yasin@eli-np.ro; Matei, Catalin; Ur, Calin A.

The Extreme Light Infrastructure - Nuclear Physics (ELI-NP) is under construction in Magurele, Bucharest, Romania. The facility will use two 10 PW lasers and a high intensity, narrow bandwidth gamma beam for stand-alone and combined laser-gamma experiments. The accurate estimation of particle doses and their restriction within the limits for both personel and general public is very important in the design phase of any nuclear facility. In the present work, Monte Carlo simulations are performed using FLUKA and MCNPX to design 19.4 and 4 MeV gamma beam dumps along with shielding of experimental areas. Dose rate contour plots from both FLUKAmore » and MCNPX along with numerical values of doses in experimental area E8 of the facility are performed. The calculated doses are within the permissible limits. Furthermore, a reasonable agreement between both codes enhances our confidence in using one or both of them for future calculations in beam dump designs, radiation shielding, radioactive inventory, and other calculations releated to radiation protection. Residual dose rates and residual activity calculations are also performed for high-energy beam dump and their effect is negligible in comparison to contributions from prompt radiation.« less

SU-G-201-17: Verification of Dose Distributions From High-Dose-Rate Brachytherapy Ir-192 Source Using a Multiple-Array-Diode-Detector (MapCheck2)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harpool, K; De La Fuente Herman, T; Ahmad, S

Purpose: To investigate quantitatively the accuracy of dose distributions for the Ir-192 high-dose-rate (HDR) brachytherapy source calculated by the Brachytherapy-Planning system (BPS) and measured using a multiple-array-diode-detector in a heterogeneous medium. Methods: A two-dimensional diode-array-detector system (MapCheck2) was scanned with a catheter and the CT-images were loaded into the Varian-Brachytherapy-Planning which uses TG-43-formalism for dose calculation. Treatment plans were calculated for different combinations of one dwell-position and varying irradiation times and different-dwell positions and fixed irradiation time with the source placed 12mm from the diode-array plane. The calculated dose distributions were compared to the measured doses with MapCheck2 delivered bymore » an Ir-192-source from a Nucletron-Microselectron-V2-remote-after-loader. The linearity of MapCheck2 was tested for a range of dwell-times (2–600 seconds). The angular effect was tested with 30 seconds irradiation delivered to the central-diode and then moving the source away in increments of 10mm. Results: Large differences were found between calculated and measured dose distributions. These differences are mainly due to absence of heterogeneity in the dose calculation and diode-artifacts in the measurements. The dose differences between measured and calculated due to heterogeneity ranged from 5%–12% depending on the position of the source relative to the diodes in MapCheck2 and different heterogeneities in the beam path. The linearity test of the diode-detector showed 3.98%, 2.61%, and 2.27% over-response at short irradiation times of 2, 5, and 10 seconds, respectively, and within 2% for 20 to 600 seconds (p-value=0.05) which depends strongly on MapCheck2 noise. The angular dependency was more pronounced at acute angles ranging up to 34% at 5.7 degrees. Conclusion: Large deviations between measured and calculated dose distributions for HDR-brachytherapy with Ir-192 may be improved when considering medium heterogeneity and dose-artifact of the diodes. This study demonstrates that multiple-array-diode-detectors provide practical and accurate dosimeter to verify doses delivered from the brachytherapy Ir-192-source.« less

Modification and validation of an analytical source model for external beam radiotherapy Monte Carlo dose calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davidson, Scott E., E-mail: sedavids@utmb.edu

Purpose: A dose calculation tool, which combines the accuracy of the dose planning method (DPM) Monte Carlo code and the versatility of a practical analytical multisource model, which was previously reported has been improved and validated for the Varian 6 and 10 MV linear accelerators (linacs). The calculation tool can be used to calculate doses in advanced clinical application studies. One shortcoming of current clinical trials that report dose from patient plans is the lack of a standardized dose calculation methodology. Because commercial treatment planning systems (TPSs) have their own dose calculation algorithms and the clinical trial participant who usesmore » these systems is responsible for commissioning the beam model, variation exists in the reported calculated dose distributions. Today’s modern linac is manufactured to tight specifications so that variability within a linac model is quite low. The expectation is that a single dose calculation tool for a specific linac model can be used to accurately recalculate dose from patient plans that have been submitted to the clinical trial community from any institution. The calculation tool would provide for a more meaningful outcome analysis. Methods: The analytical source model was described by a primary point source, a secondary extra-focal source, and a contaminant electron source. Off-axis energy softening and fluence effects were also included. The additions of hyperbolic functions have been incorporated into the model to correct for the changes in output and in electron contamination with field size. A multileaf collimator (MLC) model is included to facilitate phantom and patient dose calculations. An offset to the MLC leaf positions was used to correct for the rudimentary assumed primary point source. Results: Dose calculations of the depth dose and profiles for field sizes 4 × 4 to 40 × 40 cm agree with measurement within 2% of the maximum dose or 2 mm distance to agreement (DTA) for 95% of the data points tested. The model was capable of predicting the depth of the maximum dose within 1 mm. Anthropomorphic phantom benchmark testing of modulated and patterned MLCs treatment plans showed agreement to measurement within 3% in target regions using thermoluminescent dosimeters (TLD). Using radiochromic film normalized to TLD, a gamma criteria of 3% of maximum dose and 2 mm DTA was applied with a pass rate of least 85% in the high dose, high gradient, and low dose regions. Finally, recalculations of patient plans using DPM showed good agreement relative to a commercial TPS when comparing dose volume histograms and 2D dose distributions. Conclusions: A unique analytical source model coupled to the dose planning method Monte Carlo dose calculation code has been modified and validated using basic beam data and anthropomorphic phantom measurement. While this tool can be applied in general use for a particular linac model, specifically it was developed to provide a singular methodology to independently assess treatment plan dose distributions from those clinical institutions participating in National Cancer Institute trials.« less

Monte Carlo calculation of dose rate conversion factors for external exposure to photon emitters in soil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clovas, A.; Zanthos, S.; Antonopoulos-Domis, M.

2000-03-01

The dose rate conversion factors {dot D}{sub CF} (absorbed dose rate in air per unit activity per unit of soil mass, nGy h{sup {minus}1} per Bq kg{sup {minus}1}) are calculated 1 m above ground for photon emitters of natural radionuclides uniformly distributed in the soil. Three Monte Carlo codes are used: (1) The MCNP code of Los Alamos; (2) The GEANT code of CERN; and (3) a Monte Carlo code developed in the Nuclear Technology Laboratory of the Aristotle University of Thessaloniki. The accuracy of the Monte Carlo results is tested by the comparison of the unscattered flux obtained bymore » the three Monte Carlo codes with an independent straightforward calculation. All codes and particularly the MCNP calculate accurately the absorbed dose rate in air due to the unscattered radiation. For the total radiation (unscattered plus scattered) the {dot D}{sub CF} values calculated from the three codes are in very good agreement between them. The comparison between these results and the results deduced previously by other authors indicates a good agreement (less than 15% of difference) for photon energies above 1,500 keV. Antithetically, the agreement is not as good (difference of 20--30%) for the low energy photons.« less

Calculating tumor trajectory and dose-of-the-day using cone-beam CT projections

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, Bernard L., E-mail: bernard.jones@ucdenver.edu; Westerly, David; Miften, Moyed

2015-02-15

Purpose: Cone-beam CT (CBCT) projection images provide anatomical data in real-time over several respiratory cycles, forming a comprehensive picture of tumor movement. The authors developed and validated a method which uses these projections to determine the trajectory of and dose to highly mobile tumors during each fraction of treatment. Methods: CBCT images of a respiration phantom were acquired, the trajectory of which mimicked a lung tumor with high amplitude (up to 2.5 cm) and hysteresis. A template-matching algorithm was used to identify the location of a steel BB in each CBCT projection, and a Gaussian probability density function for themore » absolute BB position was calculated which best fit the observed trajectory of the BB in the imager geometry. Two modifications of the trajectory reconstruction were investigated: first, using respiratory phase information to refine the trajectory estimation (Phase), and second, using the Monte Carlo (MC) method to sample the estimated Gaussian tumor position distribution. The accuracies of the proposed methods were evaluated by comparing the known and calculated BB trajectories in phantom-simulated clinical scenarios using abdominal tumor volumes. Results: With all methods, the mean position of the BB was determined with accuracy better than 0.1 mm, and root-mean-square trajectory errors averaged 3.8% ± 1.1% of the marker amplitude. Dosimetric calculations using Phase methods were more accurate, with mean absolute error less than 0.5%, and with error less than 1% in the highest-noise trajectory. MC-based trajectories prevent the overestimation of dose, but when viewed in an absolute sense, add a small amount of dosimetric error (<0.1%). Conclusions: Marker trajectory and target dose-of-the-day were accurately calculated using CBCT projections. This technique provides a method to evaluate highly mobile tumors using ordinary CBCT data, and could facilitate better strategies to mitigate or compensate for motion during stereotactic body radiotherapy.« less

SU-E-T-626: Accuracy of Dose Calculation Algorithms in MultiPlan Treatment Planning System in Presence of Heterogeneities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moignier, C; Huet, C; Barraux, V

Purpose: Advanced stereotactic radiotherapy (SRT) treatments require accurate dose calculation for treatment planning especially for treatment sites involving heterogeneous patient anatomy. The purpose of this study was to evaluate the accuracy of dose calculation algorithms, Raytracing and Monte Carlo (MC), implemented in the MultiPlan treatment planning system (TPS) in presence of heterogeneities. Methods: First, the LINAC of a CyberKnife radiotherapy facility was modeled with the PENELOPE MC code. A protocol for the measurement of dose distributions with EBT3 films was established and validated thanks to comparison between experimental dose distributions and calculated dose distributions obtained with MultiPlan Raytracing and MCmore » algorithms as well as with the PENELOPE MC model for treatments planned with the homogenous Easycube phantom. Finally, bones and lungs inserts were used to set up a heterogeneous Easycube phantom. Treatment plans with the 10, 7.5 or the 5 mm field sizes were generated in Multiplan TPS with different tumor localizations (in the lung and at the lung/bone/soft tissue interface). Experimental dose distributions were compared to the PENELOPE MC and Multiplan calculations using the gamma index method. Results: Regarding the experiment in the homogenous phantom, 100% of the points passed for the 3%/3mm tolerance criteria. These criteria include the global error of the method (CT-scan resolution, EBT3 dosimetry, LINAC positionning …), and were used afterwards to estimate the accuracy of the MultiPlan algorithms in heterogeneous media. Comparison of the dose distributions obtained in the heterogeneous phantom is in progress. Conclusion: This work has led to the development of numerical and experimental dosimetric tools for small beam dosimetry. Raytracing and MC algorithms implemented in MultiPlan TPS were evaluated in heterogeneous media.« less

Accurate tissue characterization in low-dose CT imaging with pure iterative reconstruction.

PubMed

Murphy, Kevin P; McLaughlin, Patrick D; Twomey, Maria; Chan, Vincent E; Moloney, Fiachra; Fung, Adrian J; Chan, Faimee E; Kao, Tafline; O'Neill, Siobhan B; Watson, Benjamin; O'Connor, Owen J; Maher, Michael M

2017-04-01

We assess the ability of low-dose hybrid iterative reconstruction (IR) and 'pure' model-based IR (MBIR) images to maintain accurate Hounsfield unit (HU)-determined tissue characterization. Standard-protocol (SP) and low-dose modified-protocol (MP) CTs were contemporaneously acquired in 34 Crohn's disease patients referred for CT. SP image reconstruction was via the manufacturer's recommendations (60% FBP, filtered back projection; 40% ASiR, Adaptive Statistical iterative Reconstruction; SP-ASiR40). MP data sets underwent four reconstructions (100% FBP; 40% ASiR; 70% ASiR; MBIR). Three observers measured tissue volumes using HU thresholds for fat, soft tissue and bone/contrast on each data set. Analysis was via SPSS. Inter-observer agreement was strong for 1530 datapoints (rs > 0.9). MP-MBIR tissue volume measurement was superior to other MP reconstructions and closely correlated with the reference SP-ASiR40 images for all tissue types. MP-MBIR superiority was most marked for fat volume calculation - close SP-ASiR40 and MP-MBIR Bland-Altman plot correlation was seen with the lowest average difference (336 cm 3 ) when compared with other MP reconstructions. Hounsfield unit-determined tissue volume calculations from MP-MBIR images resulted in values comparable to SP-ASiR40 calculations and values that are superior to MP-ASiR images. Accuracy of estimation of volume of tissues (e.g. fat) using segmentation software on low-dose CT images appears optimal when reconstructed with pure IR. © 2016 The Royal Australian and New Zealand College of Radiologists.

WE-E-18A-03: How Accurately Can the Peak Skin Dose in Fluoroscopy Be Determined Using Indirect Dose Metrics?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, A; Pasciak, A

Purpose: Skin dosimetry is important for fluoroscopically-guided interventions, as peak skin doses (PSD) that Result in skin reactions can be reached during these procedures. The purpose of this study was to assess the accuracy of different indirect dose estimates and to determine if PSD can be calculated within ±50% for embolization procedures. Methods: PSD were measured directly using radiochromic film for 41 consecutive embolization procedures. Indirect dose metrics from procedures were collected, including reference air kerma (RAK). Four different estimates of PSD were calculated and compared along with RAK to the measured PSD. The indirect estimates included a standard method,more » use of detailed information from the RDSR, and two simplified calculation methods. Indirect dosimetry was compared with direct measurements, including an analysis of uncertainty associated with film dosimetry. Factors affecting the accuracy of the indirect estimates were examined. Results: PSD calculated with the standard calculation method were within ±50% for all 41 procedures. This was also true for a simplified method using a single source-to-patient distance (SPD) for all calculations. RAK was within ±50% for all but one procedure. Cases for which RAK or calculated PSD exhibited large differences from the measured PSD were analyzed, and two causative factors were identified: ‘extreme’ SPD and large contributions to RAK from rotational angiography or runs acquired at large gantry angles. When calculated uncertainty limits [−12.8%, 10%] were applied to directly measured PSD, most indirect PSD estimates remained within ±50% of the measured PSD. Conclusions: Using indirect dose metrics, PSD can be determined within ±50% for embolization procedures, and usually to within ±35%. RAK can be used without modification to set notification limits and substantial radiation dose levels. These results can be extended to similar procedures, including vascular and interventional oncology. Film dosimetry is likely an unnecessary effort for these types of procedures.« less

In vivo dose verification of IMRT treated head and neck cancer patients.

PubMed

Engström, Per E; Haraldsson, Pia; Landberg, Torsten; Sand Hansen, Hanne; Aage Engelholm, Svend; Nyström, Håkan

2005-01-01

An independent in vivo dose verification procedure for IMRT treatments of head and neck cancers was developed. Results of 177 intracavitary TLD measurements from 10 patients are presented. The study includes data from 10 patients with cancer of the rhinopharynx or the thyroid treated with dynamic IMRT. Dose verification was performed by insertion of a flexible naso-oesophageal tube containing TLD rods and markers for EPID and simulator image detection. Part of the study focussed on investigating the accuracy of the TPS calculations in the presence of inhomogeneities. Phantom measurements and Monte Carlo simulations were performed for a number of geometries involving lateral electronic disequilibrium and steep density shifts. The in vivo TLD measurements correlated well with the predictions of the treatment planning system with a measured/calculated dose ratio of 1.002+/-0.051 (1 SD, N=177). The measurements were easily performed and well tolerated by the patients. We conclude that in vivo intracavitary dosimetry with TLD is suitable and accurate for dose determination in intensity-modulated beams.

Calculated organ doses for Mayak production association central hall using ICRP and MCNP.

PubMed

Choe, Dong-Ok; Shelkey, Brenda N; Wilde, Justin L; Walk, Heidi A; Slaughter, David M

2003-03-01

As part of an ongoing dose reconstruction project, equivalent organ dose rates from photons and neutrons were estimated using the energy spectra measured in the central hall above the graphite reactor core located in the Russian Mayak Production Association facility. Reconstruction of the work environment was necessary due to the lack of personal dosimeter data for neutrons in the time period prior to 1987. A typical worker scenario for the central hall was developed for the Monte Carlo Neutron Photon-4B (MCNP) code. The resultant equivalent dose rates for neutrons and photons were compared with the equivalent dose rates derived from calculations using the conversion coefficients in the International Commission on Radiological Protection Publications 51 and 74 in order to validate the model scenario for this Russian facility. The MCNP results were in good agreement with the results of the ICRP publications indicating the modeling scenario was consistent with actual work conditions given the spectra provided. The MCNP code will allow for additional orientations to accurately reflect source locations.

TU-F-17A-08: The Relative Accuracy of 4D Dose Accumulation for Lung Radiotherapy Using Rigid Dose Projection Versus Dose Recalculation On Every Breathing Phase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lamb, J; Lee, C; Tee, S

2014-06-15

Purpose: To investigate the accuracy of 4D dose accumulation using projection of dose calculated on the end-exhalation, mid-ventilation, or average intensity breathing phase CT scan, versus dose accumulation performed using full Monte Carlo dose recalculation on every breathing phase. Methods: Radiotherapy plans were analyzed for 10 patients with stage I-II lung cancer planned using 4D-CT. SBRT plans were optimized using the dose calculated by a commercially-available Monte Carlo algorithm on the end-exhalation 4D-CT phase. 4D dose accumulations using deformable registration were performed with a commercially available tool that projected the planned dose onto every breathing phase without recalculation, as wellmore » as with a Monte Carlo recalculation of the dose on all breathing phases. The 3D planned dose (3D-EX), the 3D dose calculated on the average intensity image (3D-AVE), and the 4D accumulations of the dose calculated on the end-exhalation phase CT (4D-PR-EX), the mid-ventilation phase CT (4D-PR-MID), and the average intensity image (4D-PR-AVE), respectively, were compared against the accumulation of the Monte Carlo dose recalculated on every phase. Plan evaluation metrics relating to target volumes and critical structures relevant for lung SBRT were analyzed. Results: Plan evaluation metrics tabulated using 4D-PR-EX, 4D-PR-MID, and 4D-PR-AVE differed from those tabulated using Monte Carlo recalculation on every phase by an average of 0.14±0.70 Gy, - 0.11±0.51 Gy, and 0.00±0.62 Gy, respectively. Deviations of between 8 and 13 Gy were observed between the 4D-MC calculations and both 3D methods for the proximal bronchial trees of 3 patients. Conclusions: 4D dose accumulation using projection without re-calculation may be sufficiently accurate compared to 4D dose accumulated from Monte Carlo recalculation on every phase, depending on institutional protocols. Use of 4D dose accumulation should be considered when evaluating normal tissue complication probabilities as well as in clinical situations where target volumes are directly inferior to mobile critical structures.« less

Monte Carlo evaluation of Acuros XB dose calculation Algorithm for intensity modulated radiation therapy of nasopharyngeal carcinoma

NASA Astrophysics Data System (ADS)

Yeh, Peter C. Y.; Lee, C. C.; Chao, T. C.; Tung, C. J.

2017-11-01

Intensity-modulated radiation therapy is an effective treatment modality for the nasopharyngeal carcinoma. One important aspect of this cancer treatment is the need to have an accurate dose algorithm dealing with the complex air/bone/tissue interface in the head-neck region to achieve the cure without radiation-induced toxicities. The Acuros XB algorithm explicitly solves the linear Boltzmann transport equation in voxelized volumes to account for the tissue heterogeneities such as lungs, bone, air, and soft tissues in the treatment field receiving radiotherapy. With the single beam setup in phantoms, this algorithm has already been demonstrated to achieve the comparable accuracy with Monte Carlo simulations. In the present study, five nasopharyngeal carcinoma patients treated with the intensity-modulated radiation therapy were examined for their dose distributions calculated using the Acuros XB in the planning target volume and the organ-at-risk. Corresponding results of Monte Carlo simulations were computed from the electronic portal image data and the BEAMnrc/DOSXYZnrc code. Analysis of dose distributions in terms of the clinical indices indicated that the Acuros XB was in comparable accuracy with Monte Carlo simulations and better than the anisotropic analytical algorithm for dose calculations in real patients.

SU-F-BRD-07: Fast Monte Carlo-Based Biological Optimization of Proton Therapy Treatment Plans for Thyroid Tumors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wan Chan Tseung, H; Ma, J; Ma, D

2015-06-15

Purpose: To demonstrate the feasibility of fast Monte Carlo (MC) based biological planning for the treatment of thyroid tumors in spot-scanning proton therapy. Methods: Recently, we developed a fast and accurate GPU-based MC simulation of proton transport that was benchmarked against Geant4.9.6 and used as the dose calculation engine in a clinically-applicable GPU-accelerated IMPT optimizer. Besides dose, it can simultaneously score the dose-averaged LET (LETd), which makes fast biological dose (BD) estimates possible. To convert from LETd to BD, we used a linear relation based on cellular irradiation data. Given a thyroid patient with a 93cc tumor volume, we createdmore » a 2-field IMPT plan in Eclipse (Varian Medical Systems). This plan was re-calculated with our MC to obtain the BD distribution. A second 5-field plan was made with our in-house optimizer, using pre-generated MC dose and LETd maps. Constraints were placed to maintain the target dose to within 25% of the prescription, while maximizing the BD. The plan optimization and calculation of dose and LETd maps were performed on a GPU cluster. The conventional IMPT and biologically-optimized plans were compared. Results: The mean target physical and biological doses from our biologically-optimized plan were, respectively, 5% and 14% higher than those from the MC re-calculation of the IMPT plan. Dose sparing to critical structures in our plan was also improved. The biological optimization, including the initial dose and LETd map calculations, can be completed in a clinically viable time (∼30 minutes) on a cluster of 25 GPUs. Conclusion: Taking advantage of GPU acceleration, we created a MC-based, biologically optimized treatment plan for a thyroid patient. Compared to a standard IMPT plan, a 5% increase in the target’s physical dose resulted in ∼3 times as much increase in the BD. Biological planning was thus effective in escalating the target BD.« less

In vivo diode dosimetry vs. computerized tomography and digitally reconstructed radiographs for critical organ dose calculation in high-dose-rate brachytherapy of cervical cancer.

PubMed

Hassouna, Ashraf H; Bahadur, Yasir A; Constantinescu, Camelia; El Sayed, Mohamed E; Naseem, Hussain; Naga, Adly F

2011-01-01

To investigate the correlation between the dose predicted by the treatment planning system using digitally reconstructed radiographs or three-dimensional (3D)-reconstructed CT images and the dose measured by semiconductor detectors, under clinical conditions of high-dose-rate brachytherapy of the cervix uteri. Thirty-two intracavitary brachytherapy applications were performed for 12 patients with cancer of the cervix uteri. The prescribed dose to Point A was 7 Gy. Dose was calculated for both International Commissioning on Radiation Units and Measurements (ICRU) bladder and rectal points based on digitally reconstructed radiographs and for 3D CT images-based volumetric calculation of the bladder and rectum. In vivo diode dosimetry was performed for the bladder and rectum. The ICRU reference point and the volumes of 1, 2, and 5cm(3) received 3.6±0.9, 5.6±2.0, 5.1±1.7, 4.3±1.4 and 5.0±1.2, 5.3±1.3, 4.9±1.1, and 4.2±0.9 Gy for the bladder and rectum, respectively. The ratio of the 1cm(3) and the ICRU reference point dose to the diode dose was 1.8±0.7 and 1.2±0.5 for the bladder and 1.9±0.6 and 1.7±0.5 for the rectum, respectively. 3D image-based dose calculation is the most accurate and reliable method to evaluate the dose given to critical organs. In vivo diode dosimetry is an important method of quality assurance, but clinical decisions should be made based on 3D-reconstructed CT image calculations. Copyright © 2011 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.

Electron dose distributions caused by the contact-type metallic eye shield: Studies using Monte Carlo and pencil beam algorithms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, Sei-Kwon; Yoon, Jai-Woong; Hwang, Taejin

A metallic contact eye shield has sometimes been used for eyelid treatment, but dose distribution has never been reported for a patient case. This study aimed to show the shield-incorporated CT-based dose distribution using the Pinnacle system and Monte Carlo (MC) calculation for 3 patient cases. For the artifact-free CT scan, an acrylic shield machined as the same size as that of the tungsten shield was used. For the MC calculation, BEAMnrc and DOSXYZnrc were used for the 6-MeV electron beam of the Varian 21EX, in which information for the tungsten, stainless steel, and aluminum material for the eye shieldmore » was used. The same plan was generated on the Pinnacle system and both were compared. The use of the acrylic shield produced clear CT images, enabling delineation of the regions of interest, and yielded CT-based dose calculation for the metallic shield. Both the MC and the Pinnacle systems showed a similar dose distribution downstream of the eye shield, reflecting the blocking effect of the metallic eye shield. The major difference between the MC and the Pinnacle results was the target eyelid dose upstream of the shield such that the Pinnacle system underestimated the dose by 19 to 28% and 11 to 18% for the maximum and the mean doses, respectively. The pattern of dose difference between the MC and the Pinnacle systems was similar to that in the previous phantom study. In conclusion, the metallic eye shield was successfully incorporated into the CT-based planning, and the accurate dose calculation requires MC simulation.« less

A GPU-accelerated Monte Carlo dose calculation platform and its application toward validating an MRI-guided radiation therapy beam model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Yuhe; Mazur, Thomas R.; Green, Olga

Purpose: The clinical commissioning of IMRT subject to a magnetic field is challenging. The purpose of this work is to develop a GPU-accelerated Monte Carlo dose calculation platform based on PENELOPE and then use the platform to validate a vendor-provided MRIdian head model toward quality assurance of clinical IMRT treatment plans subject to a 0.35 T magnetic field. Methods: PENELOPE was first translated from FORTRAN to C++ and the result was confirmed to produce equivalent results to the original code. The C++ code was then adapted to CUDA in a workflow optimized for GPU architecture. The original code was expandedmore » to include voxelized transport with Woodcock tracking, faster electron/positron propagation in a magnetic field, and several features that make gPENELOPE highly user-friendly. Moreover, the vendor-provided MRIdian head model was incorporated into the code in an effort to apply gPENELOPE as both an accurate and rapid dose validation system. A set of experimental measurements were performed on the MRIdian system to examine the accuracy of both the head model and gPENELOPE. Ultimately, gPENELOPE was applied toward independent validation of patient doses calculated by MRIdian’s KMC. Results: An acceleration factor of 152 was achieved in comparison to the original single-thread FORTRAN implementation with the original accuracy being preserved. For 16 treatment plans including stomach (4), lung (2), liver (3), adrenal gland (2), pancreas (2), spleen(1), mediastinum (1), and breast (1), the MRIdian dose calculation engine agrees with gPENELOPE with a mean gamma passing rate of 99.1% ± 0.6% (2%/2 mm). Conclusions: A Monte Carlo simulation platform was developed based on a GPU- accelerated version of PENELOPE. This platform was used to validate that both the vendor-provided head model and fast Monte Carlo engine used by the MRIdian system are accurate in modeling radiation transport in a patient using 2%/2 mm gamma criteria. Future applications of this platform will include dose validation and accumulation, IMRT optimization, and dosimetry system modeling for next generation MR-IGRT systems.« less

A GPU-accelerated Monte Carlo dose calculation platform and its application toward validating an MRI-guided radiation therapy beam model

PubMed Central

Wang, Yuhe; Mazur, Thomas R.; Green, Olga; Hu, Yanle; Li, Hua; Rodriguez, Vivian; Wooten, H. Omar; Yang, Deshan; Zhao, Tianyu; Mutic, Sasa; Li, H. Harold

2016-01-01

Purpose: The clinical commissioning of IMRT subject to a magnetic field is challenging. The purpose of this work is to develop a GPU-accelerated Monte Carlo dose calculation platform based on penelope and then use the platform to validate a vendor-provided MRIdian head model toward quality assurance of clinical IMRT treatment plans subject to a 0.35 T magnetic field. Methods: penelope was first translated from fortran to c++ and the result was confirmed to produce equivalent results to the original code. The c++ code was then adapted to cuda in a workflow optimized for GPU architecture. The original code was expanded to include voxelized transport with Woodcock tracking, faster electron/positron propagation in a magnetic field, and several features that make gpenelope highly user-friendly. Moreover, the vendor-provided MRIdian head model was incorporated into the code in an effort to apply gpenelope as both an accurate and rapid dose validation system. A set of experimental measurements were performed on the MRIdian system to examine the accuracy of both the head model and gpenelope. Ultimately, gpenelope was applied toward independent validation of patient doses calculated by MRIdian’s kmc. Results: An acceleration factor of 152 was achieved in comparison to the original single-thread fortran implementation with the original accuracy being preserved. For 16 treatment plans including stomach (4), lung (2), liver (3), adrenal gland (2), pancreas (2), spleen(1), mediastinum (1), and breast (1), the MRIdian dose calculation engine agrees with gpenelope with a mean gamma passing rate of 99.1% ± 0.6% (2%/2 mm). Conclusions: A Monte Carlo simulation platform was developed based on a GPU- accelerated version of penelope. This platform was used to validate that both the vendor-provided head model and fast Monte Carlo engine used by the MRIdian system are accurate in modeling radiation transport in a patient using 2%/2 mm gamma criteria. Future applications of this platform will include dose validation and accumulation, IMRT optimization, and dosimetry system modeling for next generation MR-IGRT systems. PMID:27370123

A GPU-accelerated Monte Carlo dose calculation platform and its application toward validating an MRI-guided radiation therapy beam model.

PubMed

Wang, Yuhe; Mazur, Thomas R; Green, Olga; Hu, Yanle; Li, Hua; Rodriguez, Vivian; Wooten, H Omar; Yang, Deshan; Zhao, Tianyu; Mutic, Sasa; Li, H Harold

2016-07-01

The clinical commissioning of IMRT subject to a magnetic field is challenging. The purpose of this work is to develop a GPU-accelerated Monte Carlo dose calculation platform based on penelope and then use the platform to validate a vendor-provided MRIdian head model toward quality assurance of clinical IMRT treatment plans subject to a 0.35 T magnetic field. penelope was first translated from fortran to c++ and the result was confirmed to produce equivalent results to the original code. The c++ code was then adapted to cuda in a workflow optimized for GPU architecture. The original code was expanded to include voxelized transport with Woodcock tracking, faster electron/positron propagation in a magnetic field, and several features that make gpenelope highly user-friendly. Moreover, the vendor-provided MRIdian head model was incorporated into the code in an effort to apply gpenelope as both an accurate and rapid dose validation system. A set of experimental measurements were performed on the MRIdian system to examine the accuracy of both the head model and gpenelope. Ultimately, gpenelope was applied toward independent validation of patient doses calculated by MRIdian's kmc. An acceleration factor of 152 was achieved in comparison to the original single-thread fortran implementation with the original accuracy being preserved. For 16 treatment plans including stomach (4), lung (2), liver (3), adrenal gland (2), pancreas (2), spleen(1), mediastinum (1), and breast (1), the MRIdian dose calculation engine agrees with gpenelope with a mean gamma passing rate of 99.1% ± 0.6% (2%/2 mm). A Monte Carlo simulation platform was developed based on a GPU- accelerated version of penelope. This platform was used to validate that both the vendor-provided head model and fast Monte Carlo engine used by the MRIdian system are accurate in modeling radiation transport in a patient using 2%/2 mm gamma criteria. Future applications of this platform will include dose validation and accumulation, IMRT optimization, and dosimetry system modeling for next generation MR-IGRT systems.

Report of the AAPM Task Group No. 105: Issues associated with clinical implementation of Monte Carlo-based photon and electron external beam treatment planning.

PubMed

Chetty, Indrin J; Curran, Bruce; Cygler, Joanna E; DeMarco, John J; Ezzell, Gary; Faddegon, Bruce A; Kawrakow, Iwan; Keall, Paul J; Liu, Helen; Ma, C M Charlie; Rogers, D W O; Seuntjens, Jan; Sheikh-Bagheri, Daryoush; Siebers, Jeffrey V

2007-12-01

The Monte Carlo (MC) method has been shown through many research studies to calculate accurate dose distributions for clinical radiotherapy, particularly in heterogeneous patient tissues where the effects of electron transport cannot be accurately handled with conventional, deterministic dose algorithms. Despite its proven accuracy and the potential for improved dose distributions to influence treatment outcomes, the long calculation times previously associated with MC simulation rendered this method impractical for routine clinical treatment planning. However, the development of faster codes optimized for radiotherapy calculations and improvements in computer processor technology have substantially reduced calculation times to, in some instances, within minutes on a single processor. These advances have motivated several major treatment planning system vendors to embark upon the path of MC techniques. Several commercial vendors have already released or are currently in the process of releasing MC algorithms for photon and/or electron beam treatment planning. Consequently, the accessibility and use of MC treatment planning algorithms may well become widespread in the radiotherapy community. With MC simulation, dose is computed stochastically using first principles; this method is therefore quite different from conventional dose algorithms. Issues such as statistical uncertainties, the use of variance reduction techniques, the ability to account for geometric details in the accelerator treatment head simulation, and other features, are all unique components of a MC treatment planning algorithm. Successful implementation by the clinical physicist of such a system will require an understanding of the basic principles of MC techniques. The purpose of this report, while providing education and review on the use of MC simulation in radiotherapy planning, is to set out, for both users and developers, the salient issues associated with clinical implementation and experimental verification of MC dose algorithms. As the MC method is an emerging technology, this report is not meant to be prescriptive. Rather, it is intended as a preliminary report to review the tenets of the MC method and to provide the framework upon which to build a comprehensive program for commissioning and routine quality assurance of MC-based treatment planning systems.

An MCNP-based model for the evaluation of the photoneutron dose in high energy medical electron accelerators.

PubMed

Carinou, Eleutheria; Stamatelatos, Ion Evangelos; Kamenopoulou, Vassiliki; Georgolopoulou, Paraskevi; Sandilos, Panayotis

The development of a computational model for the treatment head of a medical electron accelerator (Elekta/Philips SL-18) by the Monte Carlo code mcnp-4C2 is discussed. The model includes the major components of the accelerator head and a pmma phantom representing the patient body. Calculations were performed for a 14 MeV electron beam impinging on the accelerator target and a 10 cmx10 cm beam area at the isocentre. The model was used in order to predict the neutron ambient dose equivalent at the isocentre level and moreover the neutron absorbed dose distribution within the phantom. Calculations were validated against experimental measurements performed by gold foil activation detectors. The results of this study indicated that the equivalent dose at tissues or organs adjacent to the treatment field due to photoneutrons could be up to 10% of the total peripheral dose, for the specific accelerator characteristics examined. Therefore, photoneutrons should be taken into account when accurate dose calculations are required to sensitive tissues that are adjacent to the therapeutic X-ray beam. The method described can be extended to other accelerators and collimation configurations as well, upon specification of treatment head component dimensions, composition and nominal accelerating potential.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Papadimitroulas, P; Kagadis, GC; Loudos, G

Purpose: Our purpose is to evaluate the administered absorbed dose in pediatric, nuclear imaging studies. Monte Carlo simulations with the incorporation of pediatric computational models can serve as reference for the accurate determination of absorbed dose. The procedure of the calculated dosimetric factors is described, while a dataset of reference doses is created. Methods: Realistic simulations were executed using the GATE toolkit and a series of pediatric computational models, developed by the “IT'IS Foundation”. The series of the phantoms used in our work includes 6 models in the range of 5–14 years old (3 boys and 3 girls). Pre-processing techniquesmore » were applied to the images, to incorporate the phantoms in GATE simulations. The resolution of the phantoms was set to 2 mm3. The most important organ densities were simulated according to the GATE “Materials Database”. Several used radiopharmaceuticals in SPECT and PET applications are being tested, following the EANM pediatric dosage protocol. The biodistributions of the several isotopes used as activity maps in the simulations, were derived by the literature. Results: Initial results of absorbed dose per organ (mGy) are presented in a 5 years old girl from the whole body exposure to 99mTc - SestaMIBI, 30 minutes after administration. Heart, kidney, liver, ovary, pancreas and brain are the most critical organs, in which the S-factors are calculated. The statistical uncertainty in the simulation procedure was kept lower than 5%. The Sfactors for each target organ are calculated in Gy/(MBq*sec) with highest dose being absorbed in kidneys and pancreas (9.29*10{sup 10} and 0.15*10{sup 10} respectively). Conclusion: An approach for the accurate dosimetry on pediatric models is presented, creating a reference dosage dataset for several radionuclides in children computational models with the advantages of MC techniques. Our study is ongoing, extending our investigation to other reference models and evaluating the results with clinical estimated doses.« less

PROPOSAL FOR A SIMPLE AND EFFICIENT MONTHLY QUALITY MANAGEMENT PROGRAM ASSESSING THE CONSISTENCY OF ROBOTIC IMAGE-GUIDED SMALL ANIMAL RADIATION SYSTEMS

PubMed Central

Brodin, N. Patrik; Guha, Chandan; Tomé, Wolfgang A.

2015-01-01

Modern pre-clinical radiation therapy (RT) research requires high precision and accurate dosimetry to facilitate the translation of research findings into clinical practice. Several systems are available that provide precise delivery and on-board imaging capabilities, highlighting the need for a quality management program (QMP) to ensure consistent and accurate radiation dose delivery. An ongoing, simple, and efficient QMP for image-guided robotic small animal irradiators used in pre-clinical RT research is described. Protocols were developed and implemented to assess the dose output constancy (based on the AAPM TG-61 protocol), cone-beam computed tomography (CBCT) image quality and object representation accuracy (using a custom-designed imaging phantom), CBCT-guided target localization accuracy and consistency of the CBCT-based dose calculation. To facilitate an efficient read-out and limit the user dependence of the QMP data analysis, a semi-automatic image analysis and data representation program was developed using the technical computing software MATLAB. The results of the first six months experience using the suggested QMP for a Small Animal Radiation Research Platform (SARRP) are presented, with data collected on a bi-monthly basis. The dosimetric output constancy was established to be within ±1 %, the consistency of the image resolution was within ±0.2 mm, the accuracy of CBCT-guided target localization was within ±0.5 mm, and dose calculation consistency was within ±2 s (± 3 %) per treatment beam. Based on these results, this simple quality assurance program allows for the detection of inconsistencies in dosimetric or imaging parameters that are beyond the acceptable variability for a reliable and accurate pre-clinical RT system, on a monthly or bi-monthly basis. PMID:26425981

Proposal for a Simple and Efficient Monthly Quality Management Program Assessing the Consistency of Robotic Image-Guided Small Animal Radiation Systems.

PubMed

Brodin, N Patrik; Guha, Chandan; Tomé, Wolfgang A

2015-11-01

Modern pre-clinical radiation therapy (RT) research requires high precision and accurate dosimetry to facilitate the translation of research findings into clinical practice. Several systems are available that provide precise delivery and on-board imaging capabilities, highlighting the need for a quality management program (QMP) to ensure consistent and accurate radiation dose delivery. An ongoing, simple, and efficient QMP for image-guided robotic small animal irradiators used in pre-clinical RT research is described. Protocols were developed and implemented to assess the dose output constancy (based on the AAPM TG-61 protocol), cone-beam computed tomography (CBCT) image quality and object representation accuracy (using a custom-designed imaging phantom), CBCT-guided target localization accuracy and consistency of the CBCT-based dose calculation. To facilitate an efficient read-out and limit the user dependence of the QMP data analysis, a semi-automatic image analysis and data representation program was developed using the technical computing software MATLAB. The results of the first 6-mo experience using the suggested QMP for a Small Animal Radiation Research Platform (SARRP) are presented, with data collected on a bi-monthly basis. The dosimetric output constancy was established to be within ±1 %, the consistency of the image resolution was within ±0.2 mm, the accuracy of CBCT-guided target localization was within ±0.5 mm, and dose calculation consistency was within ±2 s (±3%) per treatment beam. Based on these results, this simple quality assurance program allows for the detection of inconsistencies in dosimetric or imaging parameters that are beyond the acceptable variability for a reliable and accurate pre-clinical RT system, on a monthly or bi-monthly basis.

MO-FG-202-08: Real-Time Monte Carlo-Based Treatment Dose Reconstruction and Monitoring for Radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Z; Shi, F; Gu, X

2016-06-15

Purpose: This proof-of-concept study is to develop a real-time Monte Carlo (MC) based treatment-dose reconstruction and monitoring system for radiotherapy, especially for the treatments with complicated delivery, to catch treatment delivery errors at the earliest possible opportunity and interrupt the treatment only when an unacceptable dosimetric deviation from our expectation occurs. Methods: First an offline scheme is launched to pre-calculate the expected dose from the treatment plan, used as ground truth for real-time monitoring later. Then an online scheme with three concurrent threads is launched while treatment delivering, to reconstruct and monitor the patient dose in a temporally resolved fashionmore » in real-time. Thread T1 acquires machine status every 20 ms to calculate and accumulate fluence map (FM). Once our accumulation threshold is reached, T1 transfers the FM to T2 for dose reconstruction ad starts to accumulate a new FM. A GPU-based MC dose calculation is performed on T2 when MC dose engine is ready and a new FM is available. The reconstructed instantaneous dose is directed to T3 for dose accumulation and real-time visualization. Multiple dose metrics (e.g. maximum and mean dose for targets and organs) are calculated from the current accumulated dose and compared with the pre-calculated expected values. Once the discrepancies go beyond our tolerance, an error message will be send to interrupt the treatment delivery. Results: A VMAT Head-and-neck patient case was used to test the performance of our system. Real-time machine status acquisition was simulated here. The differences between the actual dose metrics and the expected ones were 0.06%–0.36%, indicating an accurate delivery. ∼10Hz frequency of dose reconstruction and monitoring was achieved, with 287.94s online computation time compared to 287.84s treatment delivery time. Conclusion: Our study has demonstrated the feasibility of computing a dose distribution in a temporally resolved fashion in real-time and quantitatively and dosimetrically monitoring the treatment delivery.« less

Superficial dose evaluation of four dose calculation algorithms

NASA Astrophysics Data System (ADS)

Cao, Ying; Yang, Xiaoyu; Yang, Zhen; Qiu, Xiaoping; Lv, Zhiping; Lei, Mingjun; Liu, Gui; Zhang, Zijian; Hu, Yongmei

2017-08-01

Accurate superficial dose calculation is of major importance because of the skin toxicity in radiotherapy, especially within the initial 2 mm depth being considered more clinically relevant. The aim of this study is to evaluate superficial dose calculation accuracy of four commonly used algorithms in commercially available treatment planning systems (TPS) by Monte Carlo (MC) simulation and film measurements. The superficial dose in a simple geometrical phantom with size of 30 cm×30 cm×30 cm was calculated by PBC (Pencil Beam Convolution), AAA (Analytical Anisotropic Algorithm), AXB (Acuros XB) in Eclipse system and CCC (Collapsed Cone Convolution) in Raystation system under the conditions of source to surface distance (SSD) of 100 cm and field size (FS) of 10×10 cm2. EGSnrc (BEAMnrc/DOSXYZnrc) program was performed to simulate the central axis dose distribution of Varian Trilogy accelerator, combined with measurements of superficial dose distribution by an extrapolation method of multilayer radiochromic films, to estimate the dose calculation accuracy of four algorithms in the superficial region which was recommended in detail by the ICRU (International Commission on Radiation Units and Measurement) and the ICRP (International Commission on Radiological Protection). In superficial region, good agreement was achieved between MC simulation and film extrapolation method, with the mean differences less than 1%, 2% and 5% for 0°, 30° and 60°, respectively. The relative skin dose errors were 0.84%, 1.88% and 3.90%; the mean dose discrepancies (0°, 30° and 60°) between each of four algorithms and MC simulation were (2.41±1.55%, 3.11±2.40%, and 1.53±1.05%), (3.09±3.00%, 3.10±3.01%, and 3.77±3.59%), (3.16±1.50%, 8.70±2.84%, and 18.20±4.10%) and (14.45±4.66%, 10.74±4.54%, and 3.34±3.26%) for AXB, CCC, AAA and PBC respectively. Monte Carlo simulation verified the feasibility of the superficial dose measurements by multilayer Gafchromic films. And the rank of superficial dose calculation accuracy of four algorithms was AXB>CCC>AAA>PBC. Care should be taken when using the AAA and PBC algorithms in the superficial dose calculation.

SU-C-17A-07: The Development of An MR Accelerator-Enabled Planning-To-Delivery Technique for Stereotactic Palliative Radiotherapy Treatment of Spinal Metastases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoogcarspel, S J; Kontaxis, C; Velden, J M van der

2014-06-01

Purpose: To develop an MR accelerator-enabled online planning-todelivery technique for stereotactic palliative radiotherapy treatment of spinal metastases. The technical challenges include; automated stereotactic treatment planning, online MR-based dose calculation and MR guidance during treatment. Methods: Using the CT data of 20 patients previously treated at our institution, a class solution for automated treatment planning for spinal bone metastases was created. For accurate dose simulation right before treatment, we fused geometrically correct online MR data with pretreatment CT data of the target volume (TV). For target tracking during treatment, a dynamic T2-weighted TSE MR sequence was developed. An in house developedmore » GPU based IMRT optimization and dose calculation algorithm was used for fast treatment planning and simulation. An automatically generated treatment plan developed with this treatment planning system was irradiated on a clinical 6 MV linear accelerator and evaluated using a Delta4 dosimeter. Results: The automated treatment planning method yielded clinically viable plans for all patients. The MR-CT fusion based dose calculation accuracy was within 2% as compared to calculations performed with original CT data. The dynamic T2-weighted TSE MR Sequence was able to provide an update of the anatomical location of the TV every 10 seconds. Dose calculation and optimization of the automatically generated treatment plans using only one GPU took on average 8 minutes. The Delta4 measurement of the irradiated plan agreed with the dose calculation with a 3%/3mm gamma pass rate of 86.4%. Conclusions: The development of an MR accelerator-enabled planning-todelivery technique for stereotactic palliative radiotherapy treatment of spinal metastases was presented. Future work will involve developing an intrafraction motion adaptation strategy, MR-only dose calculation, radiotherapy quality-assurance in a magnetic field, and streamlining the entire treatment process on an MR accelerator.« less

Modeling of the metallic port in breast tissue expanders for photon radiotherapy.

PubMed

Yoon, Jihyung; Xie, Yibo; Heins, David; Zhang, Rui

2018-03-30

The purpose of this study was to model the metallic port in breast tissue expanders and to improve the accuracy of dose calculations in a commercial photon treatment planning system (TPS). The density of the model was determined by comparing TPS calculations and ion chamber (IC) measurements. The model was further validated and compared with two widely used clinical models by using a simplified anthropomorphic phantom and thermoluminescent dosimeters (TLD) measurements. Dose perturbations and target coverage for a single postmastectomy radiotherapy (PMRT) patient were also evaluated. The dimensions of the metallic port model were determined to be 1.75 cm in diameter and 5 mm in thickness. The density of the port was adjusted to be 7.5 g/cm 3 which minimized the differences between IC measurements and TPS calculations. Using the simplified anthropomorphic phantom, we found the TPS calculated point doses based on the new model were in agreement with TLD measurements within 5.0% and were more accurate than doses calculated based on the clinical models. Based on the photon treatment plans for a real patient, we found that the metallic port has a negligible dosimetric impact on chest wall, while the port introduced significant dose shadow in skin area. The current clinical port models either overestimate or underestimate the attenuation from the metallic port, and the dose perturbation depends on the plan and the model in a complex way. TPS calculations based on our model of the metallic port showed good agreement with measurements for all cases. This new model could improve the accuracy of dose calculations for PMRT patients who have temporary tissue expanders implanted during radiotherapy and could potentially reduce the risk of complications after the treatment. © 2018 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pokharel, S; Rana, S

Purpose: purpose of this study is to evaluate the effect of grid size in Eclipse AcurosXB dose calculation algorithm for SBRT lung. Methods: Five cases of SBRT lung previously treated have been chosen for present study. Four of the plans were 5 fields conventional IMRT and one was Rapid Arc plan. All five cases have been calculated with five grid sizes (1, 1.5, 2, 2.5 and 3mm) available for AXB algorithm with same plan normalization. Dosimetric indices relevant to SBRT along with MUs and time have been recorded for different grid sizes. The maximum difference was calculated as a percentagemore » of mean of all five values. All the plans were IMRT QAed with portal dosimetry. Results: The maximum difference of MUs was within 2%. The time increased was as high as 7 times from highest 3mm to lowest 1mm grid size. The largest difference of PTV minimum, maximum and mean dose were 7.7%, 1.5% and 1.6% respectively. The highest D2-Max difference was 6.1%. The highest difference in ipsilateral lung mean, V5Gy, V10Gy and V20Gy were 2.6%, 2.4%, 1.9% and 3.8% respectively. The maximum difference of heart, cord and esophagus dose were 6.5%, 7.8% and 4.02% respectively. The IMRT Gamma passing rate at 2%/2mm remains within 1.5% with at least 98% points passing with all grid sizes. Conclusion: This work indicates the lowest grid size of 1mm available in AXB is not necessarily required for accurate dose calculation. The IMRT passing rate was insignificant or not observed with the reduction of grid size less than 2mm. Although the maximum percentage difference of some of the dosimetric indices appear large, most of them are clinically insignificant in absolute dose values. So we conclude that 2mm grid size calculation is best compromise in light of dose calculation accuracy and time it takes to calculate dose.« less

A computational method for estimating the dosimetric effect of intra-fraction motion on step-and-shoot IMRT and compensator plans

NASA Astrophysics Data System (ADS)

Waghorn, Ben J.; Shah, Amish P.; Ngwa, Wilfred; Meeks, Sanford L.; Moore, Joseph A.; Siebers, Jeffrey V.; Langen, Katja M.

2010-07-01

Intra-fraction organ motion during intensity-modulated radiation therapy (IMRT) treatment can cause differences between the planned and the delivered dose distribution. To investigate the extent of these dosimetric changes, a computational model was developed and validated. The computational method allows for calculation of the rigid motion perturbed three-dimensional dose distribution in the CT volume and therefore a dose volume histogram-based assessment of the dosimetric impact of intra-fraction motion on a rigidly moving body. The method was developed and validated for both step-and-shoot IMRT and solid compensator IMRT treatment plans. For each segment (or beam), fluence maps were exported from the treatment planning system. Fluence maps were shifted according to the target position deduced from a motion track. These shifted, motion-encoded fluence maps were then re-imported into the treatment planning system and were used to calculate the motion-encoded dose distribution. To validate the accuracy of the motion-encoded dose distribution the treatment plan was delivered to a moving cylindrical phantom using a programmed four-dimensional motion phantom. Extended dose response (EDR-2) film was used to measure a planar dose distribution for comparison with the calculated motion-encoded distribution using a gamma index analysis (3% dose difference, 3 mm distance-to-agreement). A series of motion tracks incorporating both inter-beam step-function shifts and continuous sinusoidal motion were tested. The method was shown to accurately predict the film's dose distribution for all of the tested motion tracks, both for the step-and-shoot IMRT and compensator plans. The average gamma analysis pass rate for the measured dose distribution with respect to the calculated motion-encoded distribution was 98.3 ± 0.7%. For static delivery the average film-to-calculation pass rate was 98.7 ± 0.2%. In summary, a computational technique has been developed to calculate the dosimetric effect of intra-fraction motion. This technique has the potential to evaluate a given plan's sensitivity to anticipated organ motion. With knowledge of the organ's motion it can also be used as a tool to assess the impact of measured intra-fraction motion after dose delivery.

Comparison of the excretion of sodium and meglumine diatrizoate at urography with simulated compression: an experimental study in the rat.

PubMed

Owman, T

1981-07-01

In the experimental model in the rabbit the excretion of sodium and meglumine diatrizoate, respectively, have been compared. Urographic density which was estimated through renal pelvic volume as calculated according to previous experiments (Owman 1978; Owman & Olin 1980) and urinary iodine concentration, is suggested to be more accurate than mere determination of urine iodine concentration and diuresis when evaluating and comparing urographic contrast media experimentally. More reliable dose optima are probably found when calculating density rather than determining urine concentrations. Of the examined media in this investigation, the sodium salt of diatrizoate was not superior to the meglumine salt in dose ranges up to 320 mg I/kg body weight, while at higher doses sodium diatrizoate gave higher urinary iodine concentrations and higher estimated density.

SU-E-T-385: 4D Radiobiology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fourkal, E; Hossain, M; Veltchev, I

2014-06-01

Purpose: The linear-quadratic model is the most prevalent model for planning dose fractionation in radiation therapy in the low dose per fraction regimens. However for high-dose fractions, used in SRS/SBRT/HDR treatments the LQ model does not yield accurate predictions, due to neglecting the reduction in the number of sublethal lesions as a result of their conversion to lethal lesions with subsequent irradiation. Proper accounting for this reduction in the number of sublethally damaged lesions leads to the dependence of the survival fraction on the temporal structure of the dose. The main objective of this work is to show that themore » functional dependence of the dose rate on time in each voxel is an important additional factor that can significantly influence the TCP. Methods: Two SBRT lung plans have been used to calculate the TCPs for the same patient. One plan is a 3D conformal plan and the other is an IMRT plan. Both plans are normalized so that 99.5% of PTV volume receives the same prescription dose of 50 Gy in 5 fractions. The dose rate in each individual voxel is calculated as a function of treatment time and subsequently used in the calculation of TCP. Results: The calculated TCPs show that shorter delivery times lead to greater TCP, despite all delivery times being short compared to the repair half-time for sublethal lesions. Furthermore, calculated TCP(IMRT) =0.308 for the IMRT plan is smaller than TCP(3D) =0.425 for 3D conformal, even though it shows greater tumor hot spots and equal PTV coverage. The calculated TCPs are considerably lower compared to those based on the LQ model for which TCP=1 for both plans. Conclusion: The functional dependence of the voxel-by-voxel dose rate on time may be an important factor in predicting the treatment outcome and cannot be neglected in radiobiological modeling.« less

Poster - 07: Investigations of the Advanced Collapsed-cone Engine for HDR Brachytherapy Scalp Treatments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cawston-Grant, Brie; Morrison, Hali; Sloboda, Ron

Purpose: To present an investigation of the Advanced Collapsed-cone Engine (ACE) in Oncentraê Brachy (OcB) v4.5 using a tissue equivalent phantom modeling scalp brachytherapy (BT) treatments. Methods: A slab phantom modeling the skin, skull, brain and mold was used. A dose of 400cGy was prescribed to just above the skull layer using TG-43 and was delivered using an HDR afterloader. Measurements were made using Gafchromic™ EBT3 film at four depths within the phantom. The TG-43 planned and film measured doses were compared to the standard (sACE) and high (hACE) accuracy ACE options in OcB between the surface and below themore » skull. Results: The average difference between the TG-43 calculated and film measured doses was −11.25±3.38% when there was no air gap between the mold and skin; sACE and hACE doses were on average lower than TG-43 calculated doses by 3.41±0.03% and 2.45±0.03%, respectively. With a 3mm air gap between the mold and skin, the difference between the TG-43 calculated and measured doses was −8.28±5.76%; sACE and hACE calculations yielded average doses 1.87±0.03% and 1.78±0.04% greater than TG-43, respectively. Conclusions: TG-43, sACE, and hACE were found to overestimate doses below the skull layer compared to film. With a 3mm air gap between the mold and skin, sACE and hACE more accurately predicted the film dose to the skin surface than TG-43. More clinical variations and their implications are currently being investigated.« less

MO-C-17A-11: A Segmentation and Point Matching Enhanced Deformable Image Registration Method for Dose Accumulation Between HDR CT Images

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhen, X; Chen, H; Zhou, L

2014-06-15

Purpose: To propose and validate a novel and accurate deformable image registration (DIR) scheme to facilitate dose accumulation among treatment fractions of high-dose-rate (HDR) gynecological brachytherapy. Method: We have developed a method to adapt DIR algorithms to gynecologic anatomies with HDR applicators by incorporating a segmentation step and a point-matching step into an existing DIR framework. In the segmentation step, random walks algorithm is used to accurately segment and remove the applicator region (AR) in the HDR CT image. A semi-automatic seed point generation approach is developed to obtain the incremented foreground and background point sets to feed the randommore » walks algorithm. In the subsequent point-matching step, a feature-based thin-plate spline-robust point matching (TPS-RPM) algorithm is employed for AR surface point matching. With the resulting mapping, a DVF characteristic of the deformation between the two AR surfaces is generated by B-spline approximation, which serves as the initial DVF for the following Demons DIR between the two AR-free HDR CT images. Finally, the calculated DVF via Demons combined with the initial one serve as the final DVF to map doses between HDR fractions. Results: The segmentation and registration accuracy are quantitatively assessed by nine clinical HDR cases from three gynecological cancer patients. The quantitative results as well as the visual inspection of the DIR indicate that our proposed method can suppress the interference of the applicator with the DIR algorithm, and accurately register HDR CT images as well as deform and add interfractional HDR doses. Conclusions: We have developed a novel and robust DIR scheme that can perform registration between HDR gynecological CT images and yield accurate registration results. This new DIR scheme has potential for accurate interfractional HDR dose accumulation. This work is supported in part by the National Natural ScienceFoundation of China (no 30970866 and no 81301940)« less

Optimization of light source parameters in the photodynamic therapy of heterogeneous prostate

NASA Astrophysics Data System (ADS)

Li, Jun; Altschuler, Martin D.; Hahn, Stephen M.; Zhu, Timothy C.

2008-08-01

The three-dimensional (3D) heterogeneous distributions of optical properties in a patient prostate can now be measured in vivo. Such data can be used to obtain a more accurate light-fluence kernel. (For specified sources and points, the kernel gives the fluence delivered to a point by a source of unit strength.) In turn, the kernel can be used to solve the inverse problem that determines the source strengths needed to deliver a prescribed photodynamic therapy (PDT) dose (or light-fluence) distribution within the prostate (assuming uniform drug concentration). We have developed and tested computational procedures to use the new heterogeneous data to optimize delivered light-fluence. New problems arise, however, in quickly obtaining an accurate kernel following the insertion of interstitial light sources and data acquisition. (1) The light-fluence kernel must be calculated in 3D and separately for each light source, which increases kernel size. (2) An accurate kernel for light scattering in a heterogeneous medium requires ray tracing and volume partitioning, thus significant calculation time. To address these problems, two different kernels were examined and compared for speed of creation and accuracy of dose. Kernels derived more quickly involve simpler algorithms. Our goal is to achieve optimal dose planning with patient-specific heterogeneous optical data applied through accurate kernels, all within clinical times. The optimization process is restricted to accepting the given (interstitially inserted) sources, and determining the best source strengths with which to obtain a prescribed dose. The Cimmino feasibility algorithm is used for this purpose. The dose distribution and source weights obtained for each kernel are analyzed. In clinical use, optimization will also be performed prior to source insertion to obtain initial source positions, source lengths and source weights, but with the assumption of homogeneous optical properties. For this reason, we compare the results from heterogeneous optical data with those obtained from average homogeneous optical properties. The optimized treatment plans are also compared with the reference clinical plan, defined as the plan with sources of equal strength, distributed regularly in space, which delivers a mean value of prescribed fluence at detector locations within the treatment region. The study suggests that comprehensive optimization of source parameters (i.e. strengths, lengths and locations) is feasible, thus allowing acceptable dose coverage in a heterogeneous prostate PDT within the time constraints of the PDT procedure.

SU-E-T-802: Verification of Implanted Cardiac Pacemaker Doses in Intensity-Modulated Radiation Therapy: Dose Prediction Accuracy and Reduction Effect of a Lead Sheet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, J; Chung, J

2015-06-15

Purpose: To verify delivered doses on the implanted cardiac pacemaker, predicted doses with and without dose reduction method were verified using the MOSFET detectors in terms of beam delivery and dose calculation techniques in intensity-modulated radiation therapy (IMRT). Methods: The pacemaker doses for a patient with a tongue cancer were predicted according to the beam delivery methods [step-and-shoot (SS) and sliding window (SW)], intensity levels for dose optimization, and dose calculation algorithms. Dosimetric effects on the pacemaker were calculated three dose engines: pencil-beam convolution (PBC), analytical anisotropic algorithm (AAA), and Acuros-XB. A lead shield of 2 mm thickness was designedmore » for minimizing irradiated doses to the pacemaker. Dose variations affected by the heterogeneous material properties of the pacemaker and effectiveness of the lead shield were predicted by the Acuros-XB. Dose prediction accuracy and the feasibility of the dose reduction strategy were verified based on the measured skin doses right above the pacemaker using mosfet detectors during the radiation treatment. Results: The Acuros-XB showed underestimated skin doses and overestimated doses by the lead-shield effect, even though the lower dose disagreement was observed. It led to improved dose prediction with higher intensity level of dose optimization in IMRT. The dedicated tertiary lead sheet effectively achieved reduction of pacemaker dose up to 60%. Conclusion: The current SS technique could deliver lower scattered doses than recommendation criteria, however, use of the lead sheet contributed to reduce scattered doses.Thin lead plate can be a useful tertiary shielder and it could not acuse malfunction or electrical damage of the implanted pacemaker in IMRT. It is required to estimate more accurate scattered doses of the patient with medical device to design proper dose reduction strategy.« less

Automatic mesh adaptivity for hybrid Monte Carlo/deterministic neutronics modeling of difficult shielding problems

DOE PAGES

Ibrahim, Ahmad M.; Wilson, Paul P.H.; Sawan, Mohamed E.; ...

2015-06-30

The CADIS and FW-CADIS hybrid Monte Carlo/deterministic techniques dramatically increase the efficiency of neutronics modeling, but their use in the accurate design analysis of very large and geometrically complex nuclear systems has been limited by the large number of processors and memory requirements for their preliminary deterministic calculations and final Monte Carlo calculation. Three mesh adaptivity algorithms were developed to reduce the memory requirements of CADIS and FW-CADIS without sacrificing their efficiency improvement. First, a macromaterial approach enhances the fidelity of the deterministic models without changing the mesh. Second, a deterministic mesh refinement algorithm generates meshes that capture as muchmore » geometric detail as possible without exceeding a specified maximum number of mesh elements. Finally, a weight window coarsening algorithm decouples the weight window mesh and energy bins from the mesh and energy group structure of the deterministic calculations in order to remove the memory constraint of the weight window map from the deterministic mesh resolution. The three algorithms were used to enhance an FW-CADIS calculation of the prompt dose rate throughout the ITER experimental facility. Using these algorithms resulted in a 23.3% increase in the number of mesh tally elements in which the dose rates were calculated in a 10-day Monte Carlo calculation and, additionally, increased the efficiency of the Monte Carlo simulation by a factor of at least 3.4. The three algorithms enabled this difficult calculation to be accurately solved using an FW-CADIS simulation on a regular computer cluster, eliminating the need for a world-class super computer.« less

Activation calculation for the dismantling and decommissioning of a light water reactor using MCNP™ with ADVANTG and ORIGEN-S

NASA Astrophysics Data System (ADS)

Schlömer, Luc; Phlippen, Peter-W.; Lukas, Bernard

2017-09-01

The decommissioning of a light water reactor (LWR), which is licensed under § 7 of the German Atomic Energy Act, following the post-operational phase requires a comprehensive licensing procedure including in particular radiation protection aspects and possible impacts to the environment. Decommissioning includes essential changes in requirements for the systems and components and will mainly lead to the direct dismantling. In this context, neutron induced activation calculations for the structural components have to be carried out to predict activities in structures and to estimate future costs for conditioning and packaging. To avoid an overestimation of the radioactive inventory and to calculate the expenses for decommissioning as accurate as possible, modern state-of-the-art Monte-Carlo-Techniques (MCNP™) are applied and coupled with present-day activation and decay codes (ORIGEN-S). In this context ADVANTG is used as weight window generator for MCNP™ i. e. as variance reduction tool to speed up the calculation in deep penetration problems. In this paper the calculation procedure is described and the obtained results are presented with a validation along with measured activities and photon dose rates measured in the post-operational phase. The validation shows that the applied calculation procedure is suitable for the determination of the radioactive inventory of a nuclear power plant. Even the measured gamma dose rates in the post-operational phase at different positions in the reactor building agree within a factor of 2 to 3 with the calculation results. The obtained results are accurate and suitable to support effectively the decommissioning planning process.

SU-C-204-06: Monte Carlo Dose Calculation for Kilovoltage X-Ray-Psoralen Activated Cancer Therapy (X-PACT): Preliminary Results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mein, S; Gunasingha, R; Nolan, M

Purpose: X-PACT is an experimental cancer therapy where kV x-rays are used to photo-activate anti-cancer therapeutics through phosphor intermediaries (phosphors that absorb x-rays and re-radiate as UV light). Clinical trials in pet dogs are currently underway (NC State College of Veterinary Medicine) and an essential component is the ability to model the kV dose in these dogs. Here we report the commissioning and characterization of a Monte Carlo (MC) treatment planning simulation tool to calculate X-PACT radiation doses in canine trials. Methods: FLUKA multi-particle MC simulation package was used to simulate a standard X-PACT radiation treatment beam of 80kVp withmore » the Varian OBI x-ray source geometry. The beam quality was verified by comparing measured and simulated attenuation of the beam by various thicknesses of aluminum (2–4.6 mm) under narrow beam conditions (HVL). The beam parameters at commissioning were then corroborated using MC, characterized and verified with empirically collected commissioning data, including: percent depth dose curves (PDD), back-scatter factors (BSF), collimator scatter factor(s), and heel effect, etc. All simulations were conducted for N=30M histories at M=100 iterations. Results: HVL and PDD simulation data agreed with an average percent error of 2.42%±0.33 and 6.03%±1.58, respectively. The mean square error (MSE) values for HVL and PDD (0.07% and 0.50%) were low, as expected; however, longer simulations are required to validate convergence to the expected values. Qualitatively, pre- and post-filtration source spectra matched well with 80kVp references generated via SPEKTR software. Further validation of commissioning data simulation is underway in preparation for first-time 3D dose calculations with canine CBCT data. Conclusion: We have prepared a Monte Carlo simulation capable of accurate dose calculation for use with ongoing X-PACT canine clinical trials. Preliminary results show good agreement with measured data and hold promise for accurate quantification of dose for this novel psoralen X-ray therapy. Funding Support, Disclosures, & Conflict of Interest: The Monte Carlo simulation work was not funded; Drs. Adamson & Oldham have received funding from Immunolight LLC for X-PACT research.« less

Commissioning and Validation of the First Monte Carlo Based Dose Calculation Algorithm Commercial Treatment Planning System in Mexico

DOE Office of Scientific and Technical Information (OSTI.GOV)

Larraga-Gutierrez, J. M.; Garcia-Garduno, O. A.; Hernandez-Bojorquez, M.

2010-12-07

This work presents the beam data commissioning and dose calculation validation of the first Monte Carlo (MC) based treatment planning system (TPS) installed in Mexico. According to the manufacturer specifications, the beam data commissioning needed for this model includes: several in-air and water profiles, depth dose curves, head-scatter factors and output factors (6x6, 12x12, 18x18, 24x24, 42x42, 60x60, 80x80 and 100x100 mm{sup 2}). Radiographic and radiochromic films, diode and ionization chambers were used for data acquisition. MC dose calculations in a water phantom were used to validate the MC simulations using comparisons with measured data. Gamma index criteria 2%/2 mmmore » were used to evaluate the accuracy of MC calculations. MC calculated data show an excellent agreement for field sizes from 18x18 to 100x100 mm{sup 2}. Gamma analysis shows that in average, 95% and 100% of the data passes the gamma index criteria for these fields, respectively. For smaller fields (12x12 and 6x6 mm{sup 2}) only 92% of the data meet the criteria. Total scatter factors show a good agreement (<2.6%) between MC calculated and measured data, except for the smaller fields (12x12 and 6x6 mm{sup 2}) that show a error of 4.7%. MC dose calculations are accurate and precise for clinical treatment planning up to a field size of 18x18 mm{sup 2}. Special care must be taken for smaller fields.« less

SU-F-T-568: QA of a Multi-Target Multi-Dose VMAT SRS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roa, D; Kuo, J; Gonzales, A

2016-06-15

Purpose: To, experimentally, corroborated the prescribed doses utilizing dosimeters (e.g. films and TLDs) that can provide high spatial resolution, allow dose measurement of multiple targets at once, and provide accurate dosimetric results. Methods: A single-isocenter 6FFF SRS VMAT plan consisting of one 358° arc at 0° couch angle and four 179° arcs at 30°, 60°, 330° and 300° couch angles respectively, was generated in ECLIPSE v.11 using a Rando-Alderson anthropomorphic head phantom CT study. This plan was a reproduction of a clinical plan generated for a stage-IV melanoma patient diagnosed with 19 intracranial lesions. The phantom was loaded with axiallymore » mounted (between phantom slabs) Gafchromic EBT3 film and TLDs strategically positioned within various target volumes. Film and TLDS were calibrated according to established protocols. Target prescription doses were 16 Gy (3cc≤, 3 lesions), 18 Gy (∼1–3cc, 10 lesions) and 20 Gy (≤1cc, 6 lesions). Phantom setup was verified through CBCT imaging prior to irradiation. Gafchromic films were scanned in transmission mode and TLDs were read, respectively, ∼24 hrs after irradiation. Results: Dose calibrated Gafchromic film data were compared to the ECLIPSE calculated data using a 3% / 3mm gamma function analysis. Results for the gamma values were 96–99% in agreement with the calculated data and with 84–90% of the film pixels within the 3% dose difference. TLD data showed a dose difference of 0.4–8% while the film data for those same locations yielded a difference of 0.4–4%. It was observed that the highest dose discrepancies correlated with the location of the small volume targets. Conclusion: Overall this study corroborated that a VMAT SRS treatment, employing various treatment table rotations and arcs, to multiple intracranial lesions with multiple dose prescriptions can be delivered accurately with the existing radiotherapy technology.« less

GTV-based prescription in SBRT for lung lesions using advanced dose calculation algorithms.

PubMed

Lacornerie, Thomas; Lisbona, Albert; Mirabel, Xavier; Lartigau, Eric; Reynaert, Nick

2014-10-16

The aim of current study was to investigate the way dose is prescribed to lung lesions during SBRT using advanced dose calculation algorithms that take into account electron transport (type B algorithms). As type A algorithms do not take into account secondary electron transport, they overestimate the dose to lung lesions. Type B algorithms are more accurate but still no consensus is reached regarding dose prescription. The positive clinical results obtained using type A algorithms should be used as a starting point. In current work a dose-calculation experiment is performed, presenting different prescription methods. Three cases with three different sizes of peripheral lung lesions were planned using three different treatment platforms. For each individual case 60 Gy to the PTV was prescribed using a type A algorithm and the dose distribution was recalculated using a type B algorithm in order to evaluate the impact of the secondary electron transport. Secondly, for each case a type B algorithm was used to prescribe 48 Gy to the PTV, and the resulting doses to the GTV were analyzed. Finally, prescriptions based on specific GTV dose volumes were evaluated. When using a type A algorithm to prescribe the same dose to the PTV, the differences regarding median GTV doses among platforms and cases were always less than 10% of the prescription dose. The prescription to the PTV based on type B algorithms, leads to a more important variability of the median GTV dose among cases and among platforms, (respectively 24%, and 28%). However, when 54 Gy was prescribed as median GTV dose, using a type B algorithm, the variability observed was minimal. Normalizing the prescription dose to the median GTV dose for lung lesions avoids variability among different cases and treatment platforms of SBRT when type B algorithms are used to calculate the dose. The combination of using a type A algorithm to optimize a homogeneous dose in the PTV and using a type B algorithm to prescribe the median GTV dose provides a very robust method for treating lung lesions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wong, M; Lee, V; Leung, R

Purpose: Investigating the relative sensitivity of Monte Carlo (MC) and Pencil Beam (PB) dose calculation algorithms to low-Z (titanium) metallic artifacts is important for accurate and consistent dose reporting in post¬operative spinal RS. Methods: Sensitivity analysis of MC and PB dose calculation algorithms on the Monaco v.3.3 treatment planning system (Elekta CMS, Maryland Heights, MO, USA) was performed using CT images reconstructed without (plain) and with Orthopedic Metal Artifact Reduction (OMAR; Philips Healthcare system, Cleveland, OH, USA). 6MV and 10MV volumetric-modulated arc (VMAT) RS plans were obtained for MC and PB on the plain and OMAR images (MC-plain/OMAR and PB-plain/OMAR).more » Results: Maximum differences in dose to 0.2cc (D0.2cc) of spinal cord and cord +2mm for 6MV and 10MV VMAT plans were 0.1Gy between MC-OMAR and MC-plain, and between PB-OMAR and PB-plain. Planning target volume (PTV) dose coverage changed by 0.1±0.7% and 0.2±0.3% for 6MV and 10MV from MC-OMAR to MC-plain, and by 0.1±0.1% for both 6MV and 10 MV from PB-OMAR to PB-plain, respectively. In no case for both MC and PB the D0.2cc to spinal cord was found to exceed the planned tolerance changing from OMAR to plain CT in dose calculations. Conclusion: Dosimetric impacts of metallic artifacts caused by low-Z metallic spinal hardware (mainly titanium alloy) are not clinically important in VMAT-based spine RS, without significant dependence on dose calculation methods (MC and PB) and photon energy ≥ 6MV. There is no need to use one algorithm instead of the other to reduce uncertainty for dose reporting. The dose calculation method that should be used in spine RS shall be consistent with the usual clinical practice.« less

SU-F-T-273: Using a Diode Array to Explore the Weakness of TPS DoseCalculation Algorithm for VMAT and Sliding Window Techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, J; Lu, B; Yan, G

Purpose: To identify the weakness of dose calculation algorithm in a treatment planning system for volumetric modulated arc therapy (VMAT) and sliding window (SW) techniques using a two-dimensional diode array. Methods: The VMAT quality assurance(QA) was implemented with a diode array using multiple partial arcs that divided from a VMAT plan; each partial arc has the same segments and the original monitor units. Arc angles were less than ± 30°. Multiple arcs delivered through consecutive and repetitive gantry operating clockwise and counterclockwise. The source-toaxis distance setup with the effective depths of 10 and 20 cm were used for a diodemore » array. To figure out dose errors caused in delivery of VMAT fields, the numerous fields having the same segments with the VMAT field irradiated using different delivery techniques of static and step-and-shoot. The dose distributions of the SW technique were evaluated by creating split fields having fine moving steps of multi-leaf collimator leaves. Calculated doses using the adaptive convolution algorithm were analyzed with measured ones with distance-to-agreement and dose difference of 3 mm and 3%.. Results: While the beam delivery through static and step-and-shoot techniques showed the passing rate of 97 ± 2%, partial arc delivery of the VMAT fields brought out passing rate of 85%. However, when leaf motion was restricted less than 4.6 mm/°, passing rate was improved up to 95 ± 2%. Similar passing rate were obtained for both 10 and 20 cm effective depth setup. The calculated doses using the SW technique showed the dose difference over 7% at the final arrival point of moving leaves. Conclusion: Error components in dynamic delivery of modulated beams were distinguished by using the suggested QA method. This partial arc method can be used for routine VMAT QA. Improved SW calculation algorithm is required to provide accurate estimated doses.« less

SU-F-T-74: Experimental Validation of Monaco Electron Monte Carlo Dose Calculation for Small Fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Varadhan; Way, S; Arentsen, L

2016-06-15

Purpose: To verify experimentally the accuracy of Monaco (Elekta) electron Monte Carlo (eMC) algorithm to calculate small field size depth doses, monitor units and isodose distributions. Methods: Beam modeling of eMC algorithm was performed for electron energies of 6, 9, 12 15 and 18 Mev for a Elekta Infinity Linac and all available ( 6, 10, 14 20 and 25 cone) applicator sizes. Electron cutouts of incrementally smaller field sizes (20, 40, 60 and 80% blocked from open cone) were fabricated. Dose calculation was performed using a grid size smaller than one-tenth of the R{sub 80–20} electron distal falloff distancemore » and number of particle histories was set at 500,000 per cm{sup 2}. Percent depth dose scans and beam profiles at dmax, d{sub 90} and d{sub 80} depths were measured for each cutout and energy with Wellhoffer (IBA) Blue Phantom{sup 2} scanning system and compared against eMC calculated doses. Results: The measured dose and output factors of incrementally reduced cutout sizes (to 3cm diameter) agreed with eMC calculated doses within ± 2.5%. The profile comparisons at dmax, d{sub 90} and d{sub 80} depths and percent depth doses at reduced field sizes agreed within 2.5% or 2mm. Conclusion: Our results indicate that the Monaco eMC algorithm can accurately predict depth doses, isodose distributions, and monitor units in homogeneous water phantom for field sizes as small as 3.0 cm diameter for energies in the 6 to 18 MeV range at 100 cm SSD. Consequently, the old rule of thumb to approximate limiting cutout size for an electron field determined by the lateral scatter equilibrium (E (MeV)/2.5 in centimeters of water) does not apply to Monaco eMC algorithm.« less

Validation of a method for in vivo 3D dose reconstruction for IMRT and VMAT treatments using on-treatment EPID images and a model-based forward-calculation algorithm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Uytven, Eric, E-mail: eric.vanuytven@cancercare.mb.ca; Van Beek, Timothy; McCowan, Peter M.

2015-12-15

Purpose: Radiation treatments are trending toward delivering higher doses per fraction under stereotactic radiosurgery and hypofractionated treatment regimens. There is a need for accurate 3D in vivo patient dose verification using electronic portal imaging device (EPID) measurements. This work presents a model-based technique to compute full three-dimensional patient dose reconstructed from on-treatment EPID portal images (i.e., transmission images). Methods: EPID dose is converted to incident fluence entering the patient using a series of steps which include converting measured EPID dose to fluence at the detector plane and then back-projecting the primary source component of the EPID fluence upstream of themore » patient. Incident fluence is then recombined with predicted extra-focal fluence and used to calculate 3D patient dose via a collapsed-cone convolution method. This method is implemented in an iterative manner, although in practice it provides accurate results in a single iteration. The robustness of the dose reconstruction technique is demonstrated with several simple slab phantom and nine anthropomorphic phantom cases. Prostate, head and neck, and lung treatments are all included as well as a range of delivery techniques including VMAT and dynamic intensity modulated radiation therapy (IMRT). Results: Results indicate that the patient dose reconstruction algorithm compares well with treatment planning system computed doses for controlled test situations. For simple phantom and square field tests, agreement was excellent with a 2%/2 mm 3D chi pass rate ≥98.9%. On anthropomorphic phantoms, the 2%/2 mm 3D chi pass rates ranged from 79.9% to 99.9% in the planning target volume (PTV) region and 96.5% to 100% in the low dose region (>20% of prescription, excluding PTV and skin build-up region). Conclusions: An algorithm to reconstruct delivered patient 3D doses from EPID exit dosimetry measurements was presented. The method was applied to phantom and patient data sets, as well as for dynamic IMRT and VMAT delivery techniques. Results indicate that the EPID dose reconstruction algorithm presented in this work is suitable for clinical implementation.« less

Calibration of an x-ray cabinet unit for radiobiology use

NASA Astrophysics Data System (ADS)

McKerracher, Carolyn; Thwaites, David I.

2006-07-01

A Faxitron sealed x-ray cabinet, operated at 100 kV, was modified to irradiate monkey testicles, to a uniform, accurately calibrated dose, for work aimed at investigating spermatogenesis in children undergoing radiotherapy. An aluminium filter was added to increase the beam quality and a lead collimating system manufactured to reduce the beam size to between 1 and 4 cm diameter. Percentage depth doses and profiles were analysed and relative in-air outputs measured with a selection of small (0.2 cc, 0.015 cc) ion chambers. The absolute calibration of the unit was carried out in a 10 × 10 cm2 beam with a 0.6 cc chamber. Backscatter factors were based on standard tables, but then modified according to experimental results with thermoluminescent dosimeters (TLD) in a phantom to account for reduced scatter in the irradiation situations. A suitable irradiation set-up was devised for the monkeys, to ensure accuracy of delivered dose to the target volume and minimize the dose to the surrounding healthy tissue. The homogeneity throughout the testes was calculated to be well within ±5%, using a parallel-opposed irradiation technique. The TLD measured doses to the testes on three monkeys were lower than the calculated doses by 3 to 6%. Following modifications to the standard percentage depth doses to account for changes in scatter conditions, these differences became ±3%. The uncertainties on both calculated and measured dose were estimated to be approximately ±3.2% at 1 SD.

SU-F-T-51: Investigating the Effect of Eye Size and Eccentricity On Normal Tissue Doses From Eye Plaque Brachytherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Polsdofer, E; Crilly, R

Purpose: This study investigates the effect of eye size and eccentricity on doses to critical tissues by simulating doses in the Plaque Simulator (v. 6.3.1) software. Present OHSU plaque brachytherapy treatment focuses on delivering radiation to the tumor measured with ocular ultrasound plus a small margin and assumes the orbit has the dimensions of a “standard eye.” Accurately modeling the dimensions of the orbit requires a high resolution ocular CT. This study quantifies how standard differences in equatorial diameters and eccentricity affect calculated doses to critical structures in order to query the justification of the additional CT scan to themore » treatment planning process. Methods: Tumors of 10 mm × 10 mm × 5 mm were modeled at the 12:00:00 hour with a latitude of 45 degrees. Right eyes were modeled at a number of equatorial diameters from 17.5 to 28 mm for each of the standard non-notched COMS plaques with silastic inserts. The COMS plaques were fully loaded with uniform activity, centered on the tumor, and prescribed to a common tumor dose (85 Gy/100 hours). Variations in the calculated doses to normal structures were examined to see if the changes were significant. Results: The calculated dose to normal structures show a marked dependence on eye geometry. This is exemplified by fovea dose which more than doubled in the smaller eyes and nearly halved in the larger model. Additional significant dependence was found in plaque size on the calculated dose in spite of all plaques giving the same dose to the prescription point. Conclusion: The variation in dose with eye dimension fully justifies the addition of a high resolution ocular CT to the planning technique. Additional attention must be made to plaque size beyond simply covering the tumor when considering normal tissue dose.« less

Estimation of extremely small field radiation dose for brain stereotactic radiotherapy using the Vero4DRT system.

PubMed

Nakayama, Shinichi; Monzen, Hajime; Onishi, Yuichi; Kaneshige, Soichiro; Kanno, Ikuo

2018-06-01

The purpose of this study was a dosimetric validation of the Vero4DRT for brain stereotactic radiotherapy (SRT) with extremely small fields calculated by the treatment planning system (TPS) iPlan (Ver.4.5.1; algorithm XVMC). Measured and calculated data (e.g. percentage depth dose [PDD], dose profile, and point dose) were compared for small square fields of 30 × 30, 20 × 20, 10 × 10 and 5 × 5 mm 2 using ionization chambers of 0.01 or 0.04 cm 3 and a diamond detector. Dose verifications were performed using an ionization chamber and radiochromic film (EBT3; the equivalent field sizes used were 8.2, 8.7, 8.9, 9.5, and 12.9 mm 2 ) for five brain SRT cases irradiated with dynamic conformal arcs. The PDDs and dose profiles for the measured and calculated data were in good agreement for fields larger than or equal to 10 × 10 mm 2 when an appropriate detector was chosen. The dose differences for point doses in fields of 30 × 30, 20 × 20, 10 × 10 and 5 × 5 mm 2 were +0.48%, +0.56%, -0.52%, and +11.2% respectively. In the dose verifications for the brain SRT plans, the mean dose difference between the calculated and measured doses were -0.35% (range, -0.94% to +0.47%), with the average pass rates for the gamma index under the 3%/2 mm criterion being 96.71%, 93.37%, and 97.58% for coronal, sagittal, and axial planes respectively. The Vero4DRT system provides accurate delivery of radiation dose for small fields larger than or equal to 10 × 10 mm 2 . Copyright © 2018 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

SU-F-T-667: Development and Validation of Dose Calculation for An Open-Source KV Treatment Planning System for Small Animal Radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prajapati, S; Mo, X; Bednarz, B

Purpose: An open-source, convolution/superposition based kV-treatment planning system(TPS) was developed for small animal radiotherapy from previously existed in-house MV-TPS. It is flexible and applicable to both step and shoot and helical tomotherapy treatment delivery. For initial commissioning process, the dose calculation from kV-TPS was compared with measurements and Monte Carlo(MC) simulations. Methods: High resolution, low energy kernels were simulated using EGSnrc user code EDKnrc, which was used as an input in kV-TPS together with MC-simulated x-ray beam spectrum. The Blue Water™ homogeneous phantom (with film inserts) and heterogeneous phantom (with film and TLD inserts) were fabricated. Phantom was placed atmore » 100cm SSD, and was irradiated with 250 kVp beam for 10mins with 1.1cm × 1.1cm open field (at 100cm) created by newly designed binary micro-MLC assembly positioned at 90cm SSD. Gafchromic™ EBT3 film was calibrated in-phantom following AAPM TG-61 guidelines, and were used for measurement at 5 different depths in phantom. Calibrated TLD-100s were obtained from ADCL. EGS and MNCP5 simulation were used to model experimental irradiation set up calculation of dose in phantom. Results: Using the homogeneous phantom, dose difference between film and kV-TPS was calculated: mean(x)=0.9%; maximum difference(MD)=3.1%; standard deviation(σ)=1.1%. Dose difference between MCNP5 and kV-TPS was: x=1.5%; MD=4.6%; σ=1.9%. Dose difference between EGS and kV-TPS was: x=0.8%; MD=1.9%; σ=0.8%. Using the heterogeneous phantom, dose difference between film and kV-TPS was: x=2.6%; MD=3%; σ=1.1%; and dose difference between TLD and kV-TPS was: x=2.9%; MD=6.4%; σ=2.5%. Conclusion: The inhouse, open-source kV-TPS dose calculation system was comparable within 5% of measurements and MC simulations in both homogeneous and heterogeneous phantoms. The dose calculation system of the kV-TPS is validated as a part of initial commissioning process for small animal radiotherapy. The kV-TPS has the potential for accurate dose calculation for any kV treatment or imaging modalities.« less

Site-specific range uncertainties caused by dose calculation algorithms for proton therapy

NASA Astrophysics Data System (ADS)

Schuemann, J.; Dowdell, S.; Grassberger, C.; Min, C. H.; Paganetti, H.

2014-08-01

The purpose of this study was to assess the possibility of introducing site-specific range margins to replace current generic margins in proton therapy. Further, the goal was to study the potential of reducing margins with current analytical dose calculations methods. For this purpose we investigate the impact of complex patient geometries on the capability of analytical dose calculation algorithms to accurately predict the range of proton fields. Dose distributions predicted by an analytical pencil-beam algorithm were compared with those obtained using Monte Carlo (MC) simulations (TOPAS). A total of 508 passively scattered treatment fields were analyzed for seven disease sites (liver, prostate, breast, medulloblastoma-spine, medulloblastoma-whole brain, lung and head and neck). Voxel-by-voxel comparisons were performed on two-dimensional distal dose surfaces calculated by pencil-beam and MC algorithms to obtain the average range differences and root mean square deviation for each field for the distal position of the 90% dose level (R90) and the 50% dose level (R50). The average dose degradation of the distal falloff region, defined as the distance between the distal position of the 80% and 20% dose levels (R80-R20), was also analyzed. All ranges were calculated in water-equivalent distances. Considering total range uncertainties and uncertainties from dose calculation alone, we were able to deduce site-specific estimations. For liver, prostate and whole brain fields our results demonstrate that a reduction of currently used uncertainty margins is feasible even without introducing MC dose calculations. We recommend range margins of 2.8% + 1.2 mm for liver and prostate treatments and 3.1% + 1.2 mm for whole brain treatments, respectively. On the other hand, current margins seem to be insufficient for some breast, lung and head and neck patients, at least if used generically. If no case specific adjustments are applied, a generic margin of 6.3% + 1.2 mm would be needed for breast, lung and head and neck treatments. We conclude that the currently used generic range uncertainty margins in proton therapy should be redefined site specific and that complex geometries may require a field specific adjustment. Routine verifications of treatment plans using MC simulations are recommended for patients with heterogeneous geometries.

Sci-Sat AM: Radiation Dosimetry and Practical Therapy Solutions - 04: On 3D Fabrication of Phantoms and Experimental Verification of Patient Dose Computation Algorithms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khan, Rao; Zavan, Rodolfo; McGeachy, Philip

2016-08-15

Purpose: Transport based dose calculation algorithm Acuros XB (AXB) has been shown to accurately account for heterogeneities mostly through comparisons with Monte Carlo simulations. This study aims at providing additional experimental verification for AXB for flattened and unflattened clinical energies in low density phantoms of the same material. Materials and Methods: Polystyrene slabs were created using a bench-top 3D printer. Six slabs were printed at varying densities from 0.23 g/cm{sup 3} to 0.68 g/cm{sup 3}, corresponding to different density humanoid tissues. The slabs were used to form different single and multilayer geometries. Dose was calculated with AXB 11.0.31 for 6MV,more » 15MV flattened and 6FFF (flattening filter free) energies for field sizes of 2×2 cm{sup 2} and 5×5 cm{sup 2}. The phantoms containing radiochromic EBT3 films were irradiated. Absolute dose profiles and 2D gamma analyses were performed for 96 dose planes. Results: For all single slab, multislab configurations and energies, absolute dose differences between the AXB calculation and film measurements remained <3% for both fields, with slightly poor disagreement in penumbra. The gamma index at 2% / 2mm averaged 98% in all combinations of fields, phantoms and photon energies. Conclusions: The transport based dose algorithm AXB is in good agreement with the experimental measurements for small field sizes using 6MV, 6FFF and 15MV beams adjacent to low density heterogeneous media. This work provides sufficient experimental ground to support the use of AXB for heterogeneous dose calculation purposes.« less

The net fractional depth dose: a basis for a unified analytical description of FDD, TAR, TMR, and TPR.

PubMed

van de Geijn, J; Fraass, B A

1984-01-01

The net fractional depth dose (NFD) is defined as the fractional depth dose (FDD) corrected for inverse square law. Analysis of its behavior as a function of depth, field size, and source-surface distance has led to an analytical description with only seven model parameters related to straightforward physical properties. The determination of the characteristic parameter values requires only seven experimentally determined FDDs. The validity of the description has been tested for beam qualities ranging from 60Co gamma rays to 18-MV x rays, using published data from several different sources as well as locally measured data sets. The small number of model parameters is attractive for computer or hand-held calculator applications. The small amount of required measured data is important in view of practical data acquisition for implementation of a computer-based dose calculation system. The generating function allows easy and accurate generation of FDD, tissue-air ratio, tissue-maximum ratio, and tissue-phantom ratio tables.

Net fractional depth dose: a basis for a unified analytical description of FDD, TAR, TMR, and TPR

DOE Office of Scientific and Technical Information (OSTI.GOV)

van de Geijn, J.; Fraass, B.A.

The net fractional depth dose (NFD) is defined as the fractional depth dose (FDD) corrected for inverse square law. Analysis of its behavior as a function of depth, field size, and source-surface distance has led to an analytical description with only seven model parameters related to straightforward physical properties. The determination of the characteristic parameter values requires only seven experimentally determined FDDs. The validity of the description has been tested for beam qualities ranging from /sup 60/Co gamma rays to 18-MV x rays, using published data from several different sources as well as locally measured data sets. The small numbermore » of model parameters is attractive for computer or hand-held calculator applications. The small amount of required measured data is important in view of practical data acquisition for implementation of a computer-based dose calculation system. The generating function allows easy and accurate generation of FDD, tissue-air ratio, tissue-maximum ratio, and tissue-phantom ratio tables.« less

Implementation of IMRT and VMAT using Delta4 phantom and portal dosimetry as dosimetry verification tools

DOE Office of Scientific and Technical Information (OSTI.GOV)

Daci, Lulzime, E-mail: lulzime.daci@nodlandssykehuset.no; Malkaj, Partizan, E-mail: malkaj-p@hotmail.com

2016-03-25

In this study we analyzed and compared the dose distribution of different IMRT and VMAT plans with the intent to provide pre-treatment quality assurance using two different tools. Materials/Methods: We have used the electronic portal imaging device EPID after calibration to dose and correction for the background offset signal and also the Delta4 phantom after en evaluation of angular sensitivity. The Delta4 phantom has a two-dimensional array with ionization chambers. We analyzed three plans for each anatomical site calculated by Eclipse treatment planning system. The measurements were analyzed using γ-evaluation method with passing criteria 3% absolute dose and 3 mm distancemore » to agreement (DTA). For all the plans the range of score has been from 97% to 99% for gantry fixed at 0° while for rotational planes there was a slightly decreased pass rates and above 95%. Point measurement with a ionization chamber were done in additional to see the accuracy of portal dosimetry and to evaluate the Delta4 device to various dose rates. Conclusions: Both Delt4 and Portal dosimetry shows good results between the measured and calculated doses. While Delta4 is more accurate in measurements EPID is more time efficient. We have decided to use both methods in the first steps of IMRT and VMAT implementation and later on to decide which of the tools to use depending on the complexity of plans, how much accurate we want to be and the time we have on the machine.« less

Impact of a commercially available model-based dose calculation algorithm on treatment planning of high-dose-rate brachytherapy in patients with cervical cancer.

PubMed

Abe, Kota; Kadoya, Noriyuki; Sato, Shinya; Hashimoto, Shimpei; Nakajima, Yujiro; Miyasaka, Yuya; Ito, Kengo; Umezawa, Rei; Yamamoto, Takaya; Takahashi, Noriyoshi; Takeda, Ken; Jingu, Keiichi

2018-03-01

We evaluated the impact of model-based dose calculation algorithms (MBDCAs) on high-dose-rate brachytherapy (HDR-BT) treatment planning for patients with cervical cancer. Seven patients with cervical cancer treated using HDR-BT were studied. Tandem and ovoid applicators were used in four patients, a vaginal cylinder in one, and interstitial needles in the remaining two patients. MBDCAs were applied to the Advanced Collapsed cone Engine (ACE; Elekta, Stockholm, Sweden). All plans, which were originally calculated using TG-43, were re-calculated using both ACE and Monte Carlo (MC) simulations. Air was used as the rectal material. The mean difference in the rectum D2cm3 between ACErec-air and MCrec-air was 8.60 ± 4.64%, whereas that in the bladder D2cm3 was -2.80 ± 1.21%. Conversely, in the small group analysis (n = 4) using water instead of air as the rectal material, the mean difference in the rectum D2cm3 between TG-43 and ACErec-air was 11.87 ± 2.65%, whereas that between TG-43 and ACErec-water was 0.81 ± 2.04%, indicating that the use of water as the rectal material reduced the difference in D2cm3 between TG-43 and ACE. Our results suggested that the differences in the dose-volume histogram (DVH) parameters of TG-43 and ACE were large for the rectum when considerable air (gas) volume was present in it, and that this difference was reduced when the air (gas) volume was reduced. Also, ACE exhibited better dose calculation accuracy than that of TG-43 in this situation. Thus, ACE may be able to calculate the dose more accurately than TG-43 for HDR-BT in treating cervical cancers, particularly for patients with considerable air (gas) volume in the rectum.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Epstein, D; Shekel, E; Levin, D

Purpose: The purpose of this work was to verify the accuracy of the dose distribution along the field junction in a half beam irradiation technique for breast cancer patients receiving radiation to the breast or chest wall (CW) and the supraclavicular LN region for both free breathing and deep inspiration breath hold (DIBH) technique. Methods: We performed in vivo measurements for nine breast cancer patients receiving radiation to the breast/CW and to the supraclavicular LN region. Six patients were treated to the left breast/CW using DIBH technique and three patients were treated to the right breast/CW in free breath. Wemore » used five microMOSFET dosimeters: three located along the field junction, one located 1 cm above the junction and the fifth microMOSFET located 1 cm below the junction. We performed consecutive measurements over several days for each patient and compared the measurements to the TPS calculation (Eclipse, Varian™). Results: The calculated and measured doses along the junction were 0.97±0.08 Gy and 1.02±0.14 Gy, respectively. Above the junction calculated and measured doses were 0.91±0.08 Gy and 0.98±0.09 Gy respectively, and below the junction calculated and measured doses were 1.70±0.15 Gy and 1.61±0.09 Gy, respectively. All differences were not statistically significant. When comparing calculated and measured doses for DIBH patients only, there was still no statistically significant difference between values for all dosimeter locations. Analysis was done using the Mann-Whitney Rank-Sum Test. Conclusion: We found excellent correlation between calculated doses from the TPS and measured skin doses at the junction of several half beam fields. Even for the DIBH technique, where there is more potential for variance due to depth of breath, there is no over or underdose along the field junction. This correlation validates the TPS, as well an accurate, reproducible patient setup.« less

CT image electron density quantification in regions with metal implants: implications for radiotherapy treatment planning

NASA Astrophysics Data System (ADS)

Jechel, Christopher Alexander

In radiotherapy planning, computed tomography (CT) images are used to quantify the electron density of tissues and provide spatial anatomical information. Treatment planning systems use these data to calculate the expected spatial distribution of absorbed dose in a patient. CT imaging is complicated by the presence of metal implants which cause increased image noise, produce artifacts throughout the image and can exceed the available range of CT number values within the implant, perturbing electron density estimates in the image. Furthermore, current dose calculation algorithms do not accurately model radiation transport at metal-tissue interfaces. Combined, these issues adversely affect the accuracy of dose calculations in the vicinity of metal implants. As the number of patients with orthopedic and dental implants grows, so does the need to deliver safe and effective radiotherapy treatments in the presence of implants. The Medical Physics group at the Cancer Centre of Southeastern Ontario and Queen's University has developed a Cobalt-60 CT system that is relatively insensitive to metal artifacts due to the high energy, nearly monoenergetic Cobalt-60 photon beam. Kilovoltage CT (kVCT) images, including images corrected using a commercial metal artifact reduction tool, were compared to Cobalt-60 CT images throughout the treatment planning process, from initial imaging through to dose calculation. An effective metal artifact reduction algorithm was also implemented for the Cobalt-60 CT system. Electron density maps derived from the same kVCT and Cobalt-60 CT images indicated the impact of image artifacts on estimates of photon attenuation for treatment planning applications. Measurements showed that truncation of CT number data in kVCT images produced significant mischaracterization of the electron density of metals. Dose measurements downstream of metal inserts in a water phantom were compared to dose data calculated using CT images from kVCT and Cobalt-60 systems with and without artifact correction. The superior accuracy of electron density data derived from Cobalt-60 images compared to kVCT images produced calculated dose with far better agreement with measured results. These results indicated that dose calculation errors from metal image artifacts are primarily due to misrepresentation of electron density within metals rather than artifacts surrounding the implants.

Predictive model accuracy in estimating last Δ9-tetrahydrocannabinol (THC) intake from plasma and whole blood cannabinoid concentrations in chronic, daily cannabis smokers administered subchronic oral THC*

PubMed Central

Karschner, Erin L.; Schwope, David M.; Schwilke, Eugene W.; Goodwin, Robert S.; Kelly, Deanna L.; Gorelick, David A.; Huestis, Marilyn A.

2012-01-01

Background Determining time since last cannabis/Δ9-tetrahydrocannabinol (THC) exposure is important in clinical, workplace, and forensic settings. Mathematical models calculating time of last exposure from whole blood concentrations typically employ a theoretical 0.5 whole blood-to-plasma (WB/P) ratio. No studies previously evaluated predictive models utilizing empirically-derived WB/P ratios, or whole blood cannabinoid pharmacokinetics after subchronic THC dosing. Methods Ten male chronic, daily cannabis smokers received escalating around-the-clock oral THC (40-120 mg daily) for 8 days. Cannabinoids were quantified in whole blood and plasma by two-dimensional gas chromatography-mass spectrometry. Results Maximum whole blood THC occurred 3.0 h after the first oral THC dose and 103.5 h (4.3 days) during multiple THC dosing. Median WB/P ratios were THC 0.63 (n=196), 11-hydroxy-THC 0.60 (n=189), and 11-nor-9-carboxy-THC (THCCOOH) 0.55 (n=200). Predictive models utilizing these WB/P ratios accurately estimated last cannabis exposure in 96% and 100% of specimens collected within 1-5 h after a single oral THC dose and throughout multiple dosing, respectively. Models were only 60% and 12.5% accurate 12.5 and 22.5 h after the last THC dose, respectively. Conclusions Predictive models estimating time since last cannabis intake from whole blood and plasma cannabinoid concentrations were inaccurate during abstinence, but highly accurate during active THC dosing. THC redistribution from large cannabinoid body stores and high circulating THCCOOH concentrations create different pharmacokinetic profiles than those in less than daily cannabis smokers that were used to derive the models. Thus, the models do not accurately predict time of last THC intake in individuals consuming THC daily. PMID:22464363

SU-F-T-323: A Post-Mastectomy Radiation Therapy Dose Distribution Study Using Nanodots and Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qian, X; Vaidya, K; Puckett, L

Purpose: In post-mastectomy radiation therapy (RT), skin dose must be accurately estimated to assess skin reactions such as erythema, desquamation and necrosis. Planning systems cannot always provide accurate dosimetry for target volumes distal to skin. Therefore, in-vivo dosimetry is necessary. A female anthropomorphic phantom was used with optically stimulated luminescence dosimeters (nanoDots) to measure dose to chest wall skin. In addition, EBT2 films was employed to measure dose to left lung and heart in post-mastectomy RT. Methods: Films and nanoDots were calibrated under full buildup conditions at 100cm SAD for 6MV photons. Five pieces of films were placed between slabsmore » of Rando phantom to assess dose to left lung and heart. Two layers of 0.5cm thick bolus were used to cover the whole left chest. Six pairs of nanoDots were placed at medical and lateral aspects on the bolus surface, between the 0.5cm bolus layers, and under the bolus. Three control nanoDots were placed on chest wall to quantify imaging dose. The phantom was CT scanned with all dosimeters in place, and treatment planning was performed with tangential fields (200cGy). All dosimeters were contoured on CT and dose was extracted. NanoDots were read using nanoDot reader and films were scanned using film scanner. The measured and calculated doses were tabulated. Results: Dose to 12 nanoDots were evaluated. Dose variance for surface nanoDots were +3.8%, +2.7%, −5% and −9.8%. Those at lateral positions, with greater beam obliquity had larger variance than the medial positions. A similar trend was observed for other nanoDots (Table1). Point doses from films for heart and the left lung were 112.7cGy and 108.7cGy, with +10.2% and +9.04% deviation from calculated values, respectively. Conclusion: Dosimetry provided by the advanced planning system was verified using NanoDots and films. Both nanoDots and films provided good estimation of dose distribution in post-mastectomy RT.« less

SU-E-T-516: Dosimetric Validation of AcurosXB Algorithm in Comparison with AAA & CCC Algorithms for VMAT Technique.

PubMed

Kathirvel, M; Subramanian, V Sai; Arun, G; Thirumalaiswamy, S; Ramalingam, K; Kumar, S Ashok; Jagadeesh, K

2012-06-01

To dosimetrically validate AcurosXB algorithm for Volumetric Modulated Arc Therapy (VMAT) in comparison with standard clinical Anisotropic Analytic Algorithm(AAA) and Collapsed Cone Convolution(CCC) dose calculation algorithms. AcurosXB dose calculation algorithm is available with Varian Eclipse treatment planning system (V10). It uses grid-based Boltzmann equation solver to predict dose precisely in lesser time. This study was made to realize algorithms ability to predict dose accurately as its delivery for which five clinical cases each of Brain, Head&Neck, Thoracic, Pelvic and SBRT were taken. Verification plans were created on multicube phantom with iMatrixx-2D detector array and then dose prediction was done with AcurosXB, AAA & CCC (COMPASS System) algorithm and the same were delivered onto CLINAC-iX treatment machine. Delivered dose was captured in iMatrixx plane for all 25 plans. Measured dose was taken as reference to quantify the agreement between AcurosXB calculation algorithm against previously validated AAA and CCC algorithm. Gamma evaluation was performed with clinical criteria distance-to-agreement 3&2mm and dose difference 3&2% in omnipro-I'MRT software. Plans were evaluated in terms of correlation coefficient, quantitative area gamma and average gamma. Study shows good agreement between mean correlation 0.9979±0.0012, 0.9984±0.0009 & 0.9979±0.0011 for AAA, CCC & Acuros respectively. Mean area gamma for criteria 3mm/3% was found to be 98.80±1.04, 98.14±2.31, 98.08±2.01 and 2mm/2% was found to be 93.94±3.83, 87.17±10.54 & 92.36±5.46 for AAA, CCC & Acuros respectively. Mean average gamma for 3mm/3% was 0.26±0.07, 0.42±0.08, 0.28±0.09 and 2mm/2% was found to be 0.39±0.10, 0.64±0.11, 0.42±0.13 for AAA, CCC & Acuros respectively. This study demonstrated that the AcurosXB algorithm had a good agreement with the AAA & CCC in terms of dose prediction. In conclusion AcurosXB algorithm provides a valid, accurate and speedy alternative to AAA and CCC algorithms in a busy clinical environment. © 2012 American Association of Physicists in Medicine.

Verification measurements and clinical evaluation of the iPlan RT Monte Carlo dose algorithm for 6 MV photon energy

NASA Astrophysics Data System (ADS)

Petoukhova, A. L.; van Wingerden, K.; Wiggenraad, R. G. J.; van de Vaart, P. J. M.; van Egmond, J.; Franken, E. M.; van Santvoort, J. P. C.

2010-08-01

This study presents data for verification of the iPlan RT Monte Carlo (MC) dose algorithm (BrainLAB, Feldkirchen, Germany). MC calculations were compared with pencil beam (PB) calculations and verification measurements in phantoms with lung-equivalent material, air cavities or bone-equivalent material to mimic head and neck and thorax and in an Alderson anthropomorphic phantom. Dosimetric accuracy of MC for the micro-multileaf collimator (MLC) simulation was tested in a homogeneous phantom. All measurements were performed using an ionization chamber and Kodak EDR2 films with Novalis 6 MV photon beams. Dose distributions measured with film and calculated with MC in the homogeneous phantom are in excellent agreement for oval, C and squiggle-shaped fields and for a clinical IMRT plan. For a field with completely closed MLC, MC is much closer to the experimental result than the PB calculations. For fields larger than the dimensions of the inhomogeneities the MC calculations show excellent agreement (within 3%/1 mm) with the experimental data. MC calculations in the anthropomorphic phantom show good agreement with measurements for conformal beam plans and reasonable agreement for dynamic conformal arc and IMRT plans. For 6 head and neck and 15 lung patients a comparison of the MC plan with the PB plan was performed. Our results demonstrate that MC is able to accurately predict the dose in the presence of inhomogeneities typical for head and neck and thorax regions with reasonable calculation times (5-20 min). Lateral electron transport was well reproduced in MC calculations. We are planning to implement MC calculations for head and neck and lung cancer patients.

Monte Carlo calculations of the impact of a hip prosthesis on the dose distribution

NASA Astrophysics Data System (ADS)

Buffard, Edwige; Gschwind, Régine; Makovicka, Libor; David, Céline

2006-09-01

Because of the ageing of the population, an increasing number of patients with hip prostheses are undergoing pelvic irradiation. Treatment planning systems (TPS) currently available are not always able to accurately predict the dose distribution around such implants. In fact, only Monte Carlo simulation has the ability to precisely calculate the impact of a hip prosthesis during radiotherapeutic treatment. Monte Carlo phantoms were developed to evaluate the dose perturbations during pelvic irradiation. A first model, constructed with the DOSXYZnrc usercode, was elaborated to determine the dose increase at the tissue-metal interface as well as the impact of the material coating the prosthesis. Next, CT-based phantoms were prepared, using the usercode CTCreate, to estimate the influence of the geometry and the composition of such implants on the beam attenuation. Thanks to a program that we developed, the study was carried out with CT-based phantoms containing a hip prosthesis without metal artefacts. Therefore, anthropomorphic phantoms allowed better definition of both patient anatomy and the hip prosthesis in order to better reproduce the clinical conditions of pelvic irradiation. The Monte Carlo results revealed the impact of certain coatings such as PMMA on dose enhancement at the tissue-metal interface. Monte Carlo calculations in CT-based phantoms highlighted the marked influence of the implant's composition, its geometry as well as its position within the beam on dose distribution.

Comparison of GATE/GEANT4 with EGSnrc and MCNP for electron dose calculations at energies between 15 keV and 20 MeV.

PubMed

Maigne, L; Perrot, Y; Schaart, D R; Donnarieix, D; Breton, V

2011-02-07

The GATE Monte Carlo simulation platform based on the GEANT4 toolkit has come into widespread use for simulating positron emission tomography (PET) and single photon emission computed tomography (SPECT) imaging devices. Here, we explore its use for calculating electron dose distributions in water. Mono-energetic electron dose point kernels and pencil beam kernels in water are calculated for different energies between 15 keV and 20 MeV by means of GATE 6.0, which makes use of the GEANT4 version 9.2 Standard Electromagnetic Physics Package. The results are compared to the well-validated codes EGSnrc and MCNP4C. It is shown that recent improvements made to the GEANT4/GATE software result in significantly better agreement with the other codes. We furthermore illustrate several issues of general interest to GATE and GEANT4 users who wish to perform accurate simulations involving electrons. Provided that the electron step size is sufficiently restricted, GATE 6.0 and EGSnrc dose point kernels are shown to agree to within less than 3% of the maximum dose between 50 keV and 4 MeV, while pencil beam kernels are found to agree to within less than 4% of the maximum dose between 15 keV and 20 MeV.

Reconstruction of organ dose for external radiotherapy patients in retrospective epidemiologic studies

NASA Astrophysics Data System (ADS)

Lee, Choonik; Jung, Jae Won; Pelletier, Christopher; Pyakuryal, Anil; Lamart, Stephanie; Kim, Jong Oh; Lee, Choonsik

2015-03-01

Organ dose estimation for retrospective epidemiological studies of late effects in radiotherapy patients involves two challenges: radiological images to represent patient anatomy are not usually available for patient cohorts who were treated years ago, and efficient dose reconstruction methods for large-scale patient cohorts are not well established. In the current study, we developed methods to reconstruct organ doses for radiotherapy patients by using a series of computational human phantoms coupled with a commercial treatment planning system (TPS) and a radiotherapy-dedicated Monte Carlo transport code, and performed illustrative dose calculations. First, we developed methods to convert the anatomy and organ contours of the pediatric and adult hybrid computational phantom series to Digital Imaging and Communications in Medicine (DICOM)-image and DICOM-structure files, respectively. The resulting DICOM files were imported to a commercial TPS for simulating radiotherapy and dose calculation for in-field organs. The conversion process was validated by comparing electron densities relative to water and organ volumes between the hybrid phantoms and the DICOM files imported in TPS, which showed agreements within 0.1 and 2%, respectively. Second, we developed a procedure to transfer DICOM-RT files generated from the TPS directly to a Monte Carlo transport code, x-ray Voxel Monte Carlo (XVMC) for more accurate dose calculations. Third, to illustrate the performance of the established methods, we simulated a whole brain treatment for the 10 year-old male phantom and a prostate treatment for the adult male phantom. Radiation doses to selected organs were calculated using the TPS and XVMC, and compared to each other. Organ average doses from the two methods matched within 7%, whereas maximum and minimum point doses differed up to 45%. The dosimetry methods and procedures established in this study will be useful for the reconstruction of organ dose to support retrospective epidemiological studies of late effects in radiotherapy patients.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Serin, E.; Codel, G.; Mabhouti, H.

Purpose: In small field geometries, the electronic equilibrium can be lost, making it challenging for the dose-calculation algorithm to accurately predict the dose, especially in the presence of tissue heterogeneities. In this study, dosimetric accuracy of Monte Carlo (MC) advanced dose calculation and sequential algorithms of Multiplan treatment planning system were investigated for small radiation fields incident on homogeneous and heterogeneous geometries. Methods: Small open fields of fixed cones of Cyberknife M6 unit 100 to 500 mm2 were used for this study. The fields were incident on in house phantom containing lung, air, and bone inhomogeneities and also homogeneous phantom.more » Using the same film batch, the net OD to dose calibration curve was obtained using CK with the 60 mm fixed cone by delivering 0- 800 cGy. Films were scanned 48 hours after irradiation using an Epson 1000XL flatbed scanner. The dosimetric accuracy of MC and sequential algorithms in the presence of the inhomogeneities was compared against EBT3 film dosimetry Results: Open field tests in a homogeneous phantom showed good agreement between two algorithms and film measurement For MC algorithm, the minimum gamma analysis passing rates between measured and calculated dose distributions were 99.7% and 98.3% for homogeneous and inhomogeneous fields in the case of lung and bone respectively. For sequential algorithm, the minimum gamma analysis passing rates were 98.9% and 92.5% for for homogeneous and inhomogeneous fields respectively for used all cone sizes. In the case of the air heterogeneity, the differences were larger for both calculation algorithms. Overall, when compared to measurement, the MC had better agreement than sequential algorithm. Conclusion: The Monte Carlo calculation algorithm in the Multiplan treatment planning system is an improvement over the existing sequential algorithm. Dose discrepancies were observed for in the presence of air inhomogeneities.« less

SU-F-SPS-09: Parallel MC Kernel Calculations for VMAT Plan Improvement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chamberlain, S; Roswell Park Cancer Institute, Buffalo, NY; French, S

Purpose: Adding kernels (small perturbations in leaf positions) to the existing apertures of VMAT control points may improve plan quality. We investigate the calculation of kernel doses using a parallelized Monte Carlo (MC) method. Methods: A clinical prostate VMAT DICOM plan was exported from Eclipse. An arbitrary control point and leaf were chosen, and a modified MLC file was created, corresponding to the leaf position offset by 0.5cm. The additional dose produced by this 0.5 cm × 0.5 cm kernel was calculated using the DOSXYZnrc component module of BEAMnrc. A range of particle history counts were run (varying from 3more » × 10{sup 6} to 3 × 10{sup 7}); each job was split among 1, 10, or 100 parallel processes. A particle count of 3 × 10{sup 6} was established as the lower range because it provided the minimal accuracy level. Results: As expected, an increase in particle counts linearly increases run time. For the lowest particle count, the time varied from 30 hours for the single-processor run, to 0.30 hours for the 100-processor run. Conclusion: Parallel processing of MC calculations in the EGS framework significantly decreases time necessary for each kernel dose calculation. Particle counts lower than 1 × 10{sup 6} have too large of an error to output accurate dose for a Monte Carlo kernel calculation. Future work will investigate increasing the number of parallel processes and optimizing run times for multiple kernel calculations.« less

Multi-resolution voxel phantom modeling: a high-resolution eye model for computational dosimetry

NASA Astrophysics Data System (ADS)

Caracappa, Peter F.; Rhodes, Ashley; Fiedler, Derek

2014-09-01

Voxel models of the human body are commonly used for simulating radiation dose with a Monte Carlo radiation transport code. Due to memory limitations, the voxel resolution of these computational phantoms is typically too large to accurately represent the dimensions of small features such as the eye. Recently reduced recommended dose limits to the lens of the eye, which is a radiosensitive tissue with a significant concern for cataract formation, has lent increased importance to understanding the dose to this tissue. A high-resolution eye model is constructed using physiological data for the dimensions of radiosensitive tissues, and combined with an existing set of whole-body models to form a multi-resolution voxel phantom, which is used with the MCNPX code to calculate radiation dose from various exposure types. This phantom provides an accurate representation of the radiation transport through the structures of the eye. Two alternate methods of including a high-resolution eye model within an existing whole-body model are developed. The accuracy and performance of each method is compared against existing computational phantoms.

Numerical Analysis of Organ Doses Delivered During Computed Tomography Examinations Using Japanese Adult Phantoms with the WAZA-ARI Dosimetry System.

PubMed

Takahashi, Fumiaki; Sato, Kaoru; Endo, Akira; Ono, Koji; Ban, Nobuhiko; Hasegawa, Takayuki; Katsunuma, Yasushi; Yoshitake, Takayasu; Kai, Michiaki

2015-08-01

A dosimetry system for computed tomography (CT) examinations, named WAZA-ARI, is being developed to accurately assess radiation doses to patients in Japan. For dose calculations in WAZA-ARI, organ doses were numerically analyzed using average adult Japanese male (JM) and female (JF) phantoms with the Particle and Heavy Ion Transport code System (PHITS). Experimental studies clarified the photon energy distribution of emitted photons and dose profiles on the table for some multi-detector row CT (MDCT) devices. Numerical analyses using a source model in PHITS could specifically take into account emissions of x rays from the tube to the table with attenuation of photons through a beam-shaping filter for each MDCT device based on the experiment results. The source model was validated by measuring the CT dose index (CTDI). Numerical analyses with PHITS revealed a concordance of organ doses with body sizes of the JM and JF phantoms. The organ doses in the JM phantoms were compared with data obtained using previously developed systems. In addition, the dose calculations in WAZA-ARI were verified with previously reported results by realistic NUBAS phantoms and radiation dose measurement using a physical Japanese model (THRA1 phantom). The results imply that numerical analyses using the Japanese phantoms and specified source models can give reasonable estimates of dose for MDCT devices for typical Japanese adults.

A comparison of two dose calculation algorithms-anisotropic analytical algorithm and Acuros XB-for radiation therapy planning of canine intranasal tumors.

PubMed

Nagata, Koichi; Pethel, Timothy D

2017-07-01

Although anisotropic analytical algorithm (AAA) and Acuros XB (AXB) are both radiation dose calculation algorithms that take into account the heterogeneity within the radiation field, Acuros XB is inherently more accurate. The purpose of this retrospective method comparison study was to compare them and evaluate the dose discrepancy within the planning target volume (PTV). Radiation therapy (RT) plans of 11 dogs with intranasal tumors treated by radiation therapy at the University of Georgia were evaluated. All dogs were planned for intensity-modulated radiation therapy using nine coplanar X-ray beams that were equally spaced, then dose calculated with anisotropic analytical algorithm. The same plan with the same monitor units was then recalculated using Acuros XB for comparisons. Each dog's planning target volume was separated into air, bone, and tissue and evaluated. The mean dose to the planning target volume estimated by Acuros XB was 1.3% lower. It was 1.4% higher for air, 3.7% lower for bone, and 0.9% lower for tissue. The volume of planning target volume covered by the prescribed dose decreased by 21% when Acuros XB was used due to increased dose heterogeneity within the planning target volume. Anisotropic analytical algorithm relatively underestimates the dose heterogeneity and relatively overestimates the dose to the bone and tissue within the planning target volume for the radiation therapy planning of canine intranasal tumors. This can be clinically significant especially if the tumor cells are present within the bone, because it may result in relative underdosing of the tumor. © 2017 American College of Veterinary Radiology.

SU-F-T-111: Investigation of the Attila Deterministic Solver as a Supplement to Monte Carlo for Calculating Out-Of-Field Radiotherapy Dose

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mille, M; Lee, C; Failla, G

Purpose: To use the Attila deterministic solver as a supplement to Monte Carlo for calculating out-of-field organ dose in support of epidemiological studies looking at the risks of second cancers. Supplemental dosimetry tools are needed to speed up dose calculations for studies involving large-scale patient cohorts. Methods: Attila is a multi-group discrete ordinates code which can solve the 3D photon-electron coupled linear Boltzmann radiation transport equation on a finite-element mesh. Dose is computed by multiplying the calculated particle flux in each mesh element by a medium-specific energy deposition cross-section. The out-of-field dosimetry capability of Attila is investigated by comparing averagemore » organ dose to that which is calculated by Monte Carlo simulation. The test scenario consists of a 6 MV external beam treatment of a female patient with a tumor in the left breast. The patient is simulated by a whole-body adult reference female computational phantom. Monte Carlo simulations were performed using MCNP6 and XVMC. Attila can export a tetrahedral mesh for MCNP6, allowing for a direct comparison between the two codes. The Attila and Monte Carlo methods were also compared in terms of calculation speed and complexity of simulation setup. A key perquisite for this work was the modeling of a Varian Clinac 2100 linear accelerator. Results: The solid mesh of the torso part of the adult female phantom for the Attila calculation was prepared using the CAD software SpaceClaim. Preliminary calculations suggest that Attila is a user-friendly software which shows great promise for our intended application. Computational performance is related to the number of tetrahedral elements included in the Attila calculation. Conclusion: Attila is being explored as a supplement to the conventional Monte Carlo radiation transport approach for performing retrospective patient dosimetry. The goal is for the dosimetry to be sufficiently accurate for use in retrospective epidemiological investigations.« less

SU-E-T-425: Spherical Dose Distributions for Radiosurgery Using a Standardized MLC Plan

DOE Office of Scientific and Technical Information (OSTI.GOV)

Popple, R; Brezovich, I; Wu, X

2014-06-01

Purpose: To investigate a standardized MLC treatment plan to generate small spherical dose distributions. Methods: The static virtual cone plan comprised six table positions with clockwise and counterclockwise arcs having collimator angles 45 and 135 degrees, respectively, at each position. The central two leaves of a 2.5 mm leaf width MLC were set to a constant gap. Control points were weighted proportional to the sine of the gantry angle. Plans were created for the 10 MV flattening-filter-free beam of a TrueBeam STx (Varian Medical Systems) with gaps of 1, 1.5, 2, and 3 mm and were delivered to a phantommore » containing radiochromic film. Dose was calculated using the Eclipse AAA (Varian Medical Systems). A dynamic plan in which the table and gantry moved simultaneously with 1.5 mm gap was also created and delivered using the TrueBeam developer mode. Results: The full-width-half-max (FWHM) varied with leaf gap, ranging from 5.2 to 6.2 mm. Calculated FWHM was smaller than measured by 0.7 mm for the 1 mm gap and ≤ 0.4 mm for the larger gaps. The measured-to-calculated dose ratio was 0.93, 0.96, 1.01, and 0.99 for 1 mm, 1.5 mm, 2 mm, and 3 mm gaps, respectively. The dynamic results were the same as the static. The position deviations between the phantom target position and the center of the dose distribution were < 0.4 mm. Conclusion: The virtual cone can deliver spherical dose distributions suitable for radio surgery of small targets such as the trigeminal nerve. The Eclipse AAA accurately calculates the expected dose, particularly for leaf gap ≥ 1.5 mm. The measured dose distribution is slightly larger than the calculation, which is likely due to systematic leaf position error, isocenter variation due to gantry sag and table eccentricity, and inaccuracy in MLC leaf end modeling.« less

Estimation of the radiation dose from radiotherapy for skin haemangiomas in childhood: the ICTA software for epidemiology

NASA Astrophysics Data System (ADS)

Shamsaldin, A.; Lundell, M.; Diallo, I.; Ligot, L.; Chavaudra, J.; de Vathaire, F.

2000-12-01

Radium applicators and pure beta emitters have been widely used in the past to treat skin haemangioma in early childhood. A well defined relationship between the low doses received from these applicators and radiation-induced cancers requires accurate dosimetry. A human-based CT scan phantom has been used to simulate every patient and treatment condition and then to calculate the source-target distance when radium and pure beta applicators were used. The effective transmission factor ϕ(r) for the gamma spectrum emitted by the radium sources applied on the skin surface was modelled using Monte Carlo simulations. The well-known quantization approach was used to calculate gamma doses delivered from radium applicators to various anatomical points. For 32P, 90Sr/90Y applicators and 90Y needles we have used the apparent exponential attenuation equation. The dose calculation algorithm was integrated into the ICTA software (standing for a model that constructs an Individualized phantom based on CT slices and Auxological data), which has been developed for epidemiological studies of cohorts of patients who received radium and beta-treatments for skin haemangioma. The ϕ(r) values obtained for radium skin applicators are in good agreement with the available values in the first 10 cm but higher at greater distances. Gamma doses can be calculated with this algorithm at 165 anatomical points throughout the body of patients treated with radium applicators. Lung heterogeneity and air crossed by the gamma rays are considered. Comparison of absorbed doses in water from a 10 mg equivalent radium source simulated by ICTA with those measured at the Radiumhemmet, Karolinska Hospital (RAH) showed good agreement, but ICTA estimation of organ doses did not always correspond those estimated at the RAH. Beta doses from 32P, 90Sr/90Y applicators and 90Y needles are calculated up to the maximum beta range (11 mm).

Quantification of the kV X-ray imaging dose during real-time tumor tracking and from three- and four-dimensional cone-beam computed tomography in lung cancer patients using a Monte Carlo simulation.

PubMed

Nakamura, Mitsuhiro; Ishihara, Yoshitomo; Matsuo, Yukinori; Iizuka, Yusuke; Ueki, Nami; Iramina, Hiraku; Hirashima, Hideaki; Mizowaki, Takashi

2018-03-01

Knowledge of the imaging doses delivered to patients and accurate dosimetry of the radiation to organs from various imaging procedures is becoming increasingly important for clinicians. The purposes of this study were to calculate imaging doses delivered to the organs of lung cancer patients during real-time tumor tracking (RTTT) with three-dimensional (3D), and four-dimensional (4D) cone-beam computed tomography (CBCT), using Monte Carlo techniques to simulate kV X-ray dose distributions delivered using the Vero4DRT. Imaging doses from RTTT, 3D-CBCT and 4D-CBCT were calculated with the planning CT images for nine lung cancer patients who underwent stereotactic body radiotherapy (SBRT) with RTTT. With RTTT, imaging doses from correlation modeling and from monitoring of imaging during beam delivery were calculated. With CBCT, doses from 3D-CBCT and 4D-CBCT were also simulated. The doses covering 2-cc volumes (D2cc) in correlation modeling were up to 9.3 cGy for soft tissues and 48.4 cGy for bone. The values from correlation modeling and monitoring were up to 11.0 cGy for soft tissues and 59.8 cGy for bone. Imaging doses in correlation modeling were larger with RTTT. On a single 4D-CBCT, the skin and bone D2cc values were in the ranges of 7.4-10.5 cGy and 33.5-58.1 cGy, respectively. The D2cc from 4D-CBCT was approximately double that from 3D-CBCT. Clinicians should Figure that the imaging dose increases the cumulative doses to organs.

Quantification of the kV X-ray imaging dose during real-time tumor tracking and from three- and four-dimensional cone-beam computed tomography in lung cancer patients using a Monte Carlo simulation

PubMed Central

Nakamura, Mitsuhiro; Ishihara, Yoshitomo; Matsuo, Yukinori; Iizuka, Yusuke; Ueki, Nami; Iramina, Hiraku; Hirashima, Hideaki; Mizowaki, Takashi

2018-01-01

Abstract Knowledge of the imaging doses delivered to patients and accurate dosimetry of the radiation to organs from various imaging procedures is becoming increasingly important for clinicians. The purposes of this study were to calculate imaging doses delivered to the organs of lung cancer patients during real-time tumor tracking (RTTT) with three-dimensional (3D), and four-dimensional (4D) cone-beam computed tomography (CBCT), using Monte Carlo techniques to simulate kV X-ray dose distributions delivered using the Vero4DRT. Imaging doses from RTTT, 3D-CBCT and 4D-CBCT were calculated with the planning CT images for nine lung cancer patients who underwent stereotactic body radiotherapy (SBRT) with RTTT. With RTTT, imaging doses from correlation modeling and from monitoring of imaging during beam delivery were calculated. With CBCT, doses from 3D-CBCT and 4D-CBCT were also simulated. The doses covering 2-cc volumes (D2cc) in correlation modeling were up to 9.3 cGy for soft tissues and 48.4 cGy for bone. The values from correlation modeling and monitoring were up to 11.0 cGy for soft tissues and 59.8 cGy for bone. Imaging doses in correlation modeling were larger with RTTT. On a single 4D-CBCT, the skin and bone D2cc values were in the ranges of 7.4–10.5 cGy and 33.5–58.1 cGy, respectively. The D2cc from 4D-CBCT was approximately double that from 3D-CBCT. Clinicians should Figure that the imaging dose increases the cumulative doses to organs. PMID:29385514

Evaluation of an analytic linear Boltzmann transport equation solver for high-density inhomogeneities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lloyd, S. A. M.; Ansbacher, W.; Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia V8W 3P6

2013-01-15

Purpose: Acuros external beam (Acuros XB) is a novel dose calculation algorithm implemented through the ECLIPSE treatment planning system. The algorithm finds a deterministic solution to the linear Boltzmann transport equation, the same equation commonly solved stochastically by Monte Carlo methods. This work is an evaluation of Acuros XB, by comparison with Monte Carlo, for dose calculation applications involving high-density materials. Existing non-Monte Carlo clinical dose calculation algorithms, such as the analytic anisotropic algorithm (AAA), do not accurately model dose perturbations due to increased electron scatter within high-density volumes. Methods: Acuros XB, AAA, and EGSnrc based Monte Carlo are usedmore » to calculate dose distributions from 18 MV and 6 MV photon beams delivered to a cubic water phantom containing a rectangular high density (4.0-8.0 g/cm{sup 3}) volume at its center. The algorithms are also used to recalculate a clinical prostate treatment plan involving a unilateral hip prosthesis, originally evaluated using AAA. These results are compared graphically and numerically using gamma-index analysis. Radio-chromic film measurements are presented to augment Monte Carlo and Acuros XB dose perturbation data. Results: Using a 2% and 1 mm gamma-analysis, between 91.3% and 96.8% of Acuros XB dose voxels containing greater than 50% the normalized dose were in agreement with Monte Carlo data for virtual phantoms involving 18 MV and 6 MV photons, stainless steel and titanium alloy implants and for on-axis and oblique field delivery. A similar gamma-analysis of AAA against Monte Carlo data showed between 80.8% and 87.3% agreement. Comparing Acuros XB and AAA evaluations of a clinical prostate patient plan involving a unilateral hip prosthesis, Acuros XB showed good overall agreement with Monte Carlo while AAA underestimated dose on the upstream medial surface of the prosthesis due to electron scatter from the high-density material. Film measurements support the dose perturbations demonstrated by Monte Carlo and Acuros XB data. Conclusions: Acuros XB is shown to perform as well as Monte Carlo methods and better than existing clinical algorithms for dose calculations involving high-density volumes.« less

SU-E-T-280: Reconstructed Rectal Wall Dose Map-Based Verification of Rectal Dose Sparing Effect According to Rectum Definition Methods and Dose Perturbation by Air Cavity in Endo-Rectal Balloon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, J; Research Institute of Biomedical Engineering, The Catholic University of Korea, Seoul; Park, H

Purpose: Dosimetric effect and discrepancy according to the rectum definition methods and dose perturbation by air cavity in an endo-rectal balloon (ERB) were verified using rectal-wall (Rwall) dose maps considering systematic errors in dose optimization and calculation accuracy in intensity-modulated radiation treatment (IMRT) for prostate cancer patients. Methods: When the inflated ERB having average diameter of 4.5 cm and air volume of 100 cc is used for patient, Rwall doses were predicted by pencil-beam convolution (PBC), anisotropic analytic algorithm (AAA), and AcurosXB (AXB) with material assignment function. The errors of dose optimization and calculation by separating air cavity from themore » whole rectum (Rwhole) were verified with measured rectal doses. The Rwall doses affected by the dose perturbation of air cavity were evaluated using a featured rectal phantom allowing insert of rolled-up gafchromic films and glass rod detectors placed along the rectum perimeter. Inner and outer Rwall doses were verified with reconstructed predicted rectal wall dose maps. Dose errors and extent at dose levels were evaluated with estimated rectal toxicity. Results: While AXB showed insignificant difference of target dose coverage, Rwall doses underestimated by up to 20% in dose optimization for the Rwhole than Rwall at all dose range except for the maximum dose. As dose optimization for Rwall was applied, the Rwall doses presented dose error less than 3% between dose calculation algorithm except for overestimation of maximum rectal dose up to 5% in PBC. Dose optimization for Rwhole caused dose difference of Rwall especially at intermediate doses. Conclusion: Dose optimization for Rwall could be suggested for more accurate prediction of rectal wall dose prediction and dose perturbation effect by air cavity in IMRT for prostate cancer. This research was supported by the Leading Foreign Research Institute Recruitment Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (MSIP) (Grant No. 200900420)« less

Dose perturbations by two carbon fiber treatment couches and the ability of a commercial treatment planning system to predict these effects.

PubMed

Gerig, L H; Niedbala, M; Nyiri, B J

2010-01-01

To measure the effect of the treatment couch on dose distributions and to investigate the ability of a modern planning system to accurately model these effects. This work measured the dose perturbation at depth and in the dose buildup region when one of two treatment couches, CIVCO (formerly MED-TEC) or Medical Intelligence, was placed between a photon beam source (6, 10, and 18 MV) and the phantom. Beam attenuation was measured in the center of a cylindrical acrylic phantom with a Farmer type ion chamber at multiple gantry angles. Dose buildup was measured in Solid Water with plane parallel ion chambers (NACP-02 and PTW Markus) with the beam normal to both the phantom and couch surfaces. The effective point of measurement method as described [M. R. McEwen et al. "The effective point of measurement of ionization chambers and the build-up anomaly in MV x-ray beams," Med. Phys. 35(3), 950-958 (2008)] was employed to calculate dose in the buildup region. Both experiments were modeled in XiO. Images of the treatment couches were merged with images of the phantoms such that they were included as part of the "patient" image. Dose distributions calculated with superposition and fast superposition algorithms were compared to measurement. The two treatment couches have different radiological signatures and dissimilar water equivalent thicknesses (4.2 vs 6.3 mm.) Maximum attenuation was 7%. Both couches caused significant loss of skin sparing, the worst case showing an increase in surface dose from 17% (no couch) to 88% (with couch). The TPS accurately predicted the surface dose (+/-3%) and the attenuation at depth when the phantom was in contact with the couch. For the open beam the TPS was less successful in the buildup region. The treatment couch is not radio-transparent. Its presence between the patient and beam source significantly alters dose in the patient. For the most part, a modern treatment planning system can adequately predict the altered dose distribution.

Technical Note: Construction of heterogeneous head phantom for quality control in stereotactic radiosurgery.

PubMed

Najafi, Mohsen; Teimouri, Javad; Shirazi, Alireza; Geraily, Ghazale; Esfahani, Mahbod; Shafaei, Mostafa

2017-10-01

Stereotactic radiosurgery is a high precision modality for conformally delivering high doses of radiation to the brain lesion with a large dose volume. Several studies for the quality control of this technique were performed to measure the dose delivered to the target with a homogenous head phantom and some dosimeters. Some studies were also performed with one or two instances of heterogeneity in the head phantom to measure the dose delivered to the target. But these studies assumed the head as a sphere and simple shape heterogeneity. The construction of an adult human head phantom with the same size, shape, and real inhomogeneity as an adult human head is needed. Only then is measuring the accurate dose delivered to the area of interest and comparison with the calculated dose possible. According to the ICRU Report 44, polytetrafluoroethylene (PTFE) and methyl methacrylate were selected as a bone and soft tissue, respectively. A set of computed tomography (CT) scans from a standard human head were taken, and simplification of the CT images was used to design the layers of the phantom. The parts of each slice were cut and attached together. Tests of density and CT number were done to compare the material of the phantom with tissues of the head. The dose delivered to the target was measured with an EBT3 film. The density of the PTFE and Plexiglas that were inserted in the phantom are in good agreement with bone and soft tissue. Also, the CT numbers of these materials have a low difference. The dose distribution from the EBT3 film and the treatment planning system is similar. The constructed phantom with a size and inhomogeneity like an adult human head is suitable to measure the dose delivered to the area of interest. It also helps make an accurate comparison with the calculated dose by the treatment planning system. By using this phantom, the actual dose delivered to the target was obtained. This anthropomorphic head phantom can be used in other modalities of radiosurgery as well. © 2017 American Association of Physicists in Medicine.

A simple and fast physics-based analytical method to calculate therapeutic and stray doses from external beam, megavoltage x-ray therapy

PubMed Central

Wilson, Lydia J; Newhauser, Wayne D

2015-01-01

State-of-the-art radiotherapy treatment planning systems provide reliable estimates of the therapeutic radiation but are known to underestimate or neglect the stray radiation exposures. Most commonly, stray radiation exposures are reconstructed using empirical formulas or lookup tables. The purpose of this study was to develop the basic physics of a model capable of calculating the total absorbed dose both inside and outside of the therapeutic radiation beam for external beam photon therapy. The model was developed using measurements of total absorbed dose in a water-box phantom from a 6 MV medical linear accelerator to calculate dose profiles in both the in-plane and cross-plane direction for a variety of square field sizes and depths in water. The water-box phantom facilitated development of the basic physical aspects of the model. RMS discrepancies between measured and calculated total absorbed dose values in water were less than 9.3% for all fields studied. Computation times for 10 million dose points within a homogeneous phantom were approximately 4 minutes. These results suggest that the basic physics of the model are sufficiently simple, fast, and accurate to serve as a foundation for a variety of clinical and research applications, some of which may require that the model be extended or simplified based on the needs of the user. A potentially important advantage of a physics-based approach is that the model is more readily adaptable to a wide variety of treatment units and treatment techniques than with empirical models. PMID:26040833

A simple and fast physics-based analytical method to calculate therapeutic and stray doses from external beam, megavoltage x-ray therapy.

PubMed

Jagetic, Lydia J; Newhauser, Wayne D

2015-06-21

State-of-the-art radiotherapy treatment planning systems provide reliable estimates of the therapeutic radiation but are known to underestimate or neglect the stray radiation exposures. Most commonly, stray radiation exposures are reconstructed using empirical formulas or lookup tables. The purpose of this study was to develop the basic physics of a model capable of calculating the total absorbed dose both inside and outside of the therapeutic radiation beam for external beam photon therapy. The model was developed using measurements of total absorbed dose in a water-box phantom from a 6 MV medical linear accelerator to calculate dose profiles in both the in-plane and cross-plane direction for a variety of square field sizes and depths in water. The water-box phantom facilitated development of the basic physical aspects of the model. RMS discrepancies between measured and calculated total absorbed dose values in water were less than 9.3% for all fields studied. Computation times for 10 million dose points within a homogeneous phantom were approximately 4 min. These results suggest that the basic physics of the model are sufficiently simple, fast, and accurate to serve as a foundation for a variety of clinical and research applications, some of which may require that the model be extended or simplified based on the needs of the user. A potentially important advantage of a physics-based approach is that the model is more readily adaptable to a wide variety of treatment units and treatment techniques than with empirical models.

Re-186 and Sm-153 dosimetry based on scintigraphic imaging data in skeletal metastasis palliative treatment and Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Andreou, M.; Lagopati, N.; Lyra, M.

2011-09-01

Optimum treatment planning of patients suffering from painful skeletal metastases requires accurate calculations concerning absorbed dose in metastatic lesions and critical organs, such as red marrow. Delivering high doses to tumor cells while limiting radiation dose to normal tissue, is the key for successful palliation treatment. The aim of this study is to compare the dosimetric calculations, obtained by Monte Carlo (MC) simulation and the MIRDOSE model, in therapeutic schemes of skeleton metastatic lesions, with Rhenium-186 (Sn) -HEDP and Samarium-153 -EDTMP. A bolus injection of 1295 MBq (35mCi) Re-186- HEDP was infused in 11 patients with multiple skeletal metastases. The administered dose for the 8 patients who received Sm-153 was 1 mCi /kg. Planar scintigraphic images for the two groups of patients were obtained, 24 h, 48 h and 72 h post injection, by an Elscint Apex SPX gamma camera. The images were processed, utilizing ROI quantitative methods, to determine residence times and radionuclide uptakes. Dosimetric calculations were performed using the patient specific scintigraphic data by the MIRDOSE3 code of MIRD. Also, MCNPX was employed, simulating the distribution of the radioisotope in the ROI and calculating the absorbed doses in the metastatic lesion, and in critical organs. Summarizing, there is a good agreement between the results, derived from the two pathways, the patient specific and the mathematical, with a deviation of less than 9% for planar scintigraphic data compared to MC, for both radiopharmaceuticals.

Development of a Monte Carlo multiple source model for inclusion in a dose calculation auditing tool.

PubMed

Faught, Austin M; Davidson, Scott E; Fontenot, Jonas; Kry, Stephen F; Etzel, Carol; Ibbott, Geoffrey S; Followill, David S

2017-09-01

The Imaging and Radiation Oncology Core Houston (IROC-H) (formerly the Radiological Physics Center) has reported varying levels of agreement in their anthropomorphic phantom audits. There is reason to believe one source of error in this observed disagreement is the accuracy of the dose calculation algorithms and heterogeneity corrections used. To audit this component of the radiotherapy treatment process, an independent dose calculation tool is needed. Monte Carlo multiple source models for Elekta 6 MV and 10 MV therapeutic x-ray beams were commissioned based on measurement of central axis depth dose data for a 10 × 10 cm 2 field size and dose profiles for a 40 × 40 cm 2 field size. The models were validated against open field measurements consisting of depth dose data and dose profiles for field sizes ranging from 3 × 3 cm 2 to 30 × 30 cm 2 . The models were then benchmarked against measurements in IROC-H's anthropomorphic head and neck and lung phantoms. Validation results showed 97.9% and 96.8% of depth dose data passed a ±2% Van Dyk criterion for 6 MV and 10 MV models respectively. Dose profile comparisons showed an average agreement using a ±2%/2 mm criterion of 98.0% and 99.0% for 6 MV and 10 MV models respectively. Phantom plan comparisons were evaluated using ±3%/2 mm gamma criterion, and averaged passing rates between Monte Carlo and measurements were 87.4% and 89.9% for 6 MV and 10 MV models respectively. Accurate multiple source models for Elekta 6 MV and 10 MV x-ray beams have been developed for inclusion in an independent dose calculation tool for use in clinical trial audits. © 2017 American Association of Physicists in Medicine.

Portal dosimetry for VMAT using integrated images obtained during treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bedford, James L., E-mail: James.Bedford@icr.ac.uk; Hanson, Ian M.; Hansen, Vibeke Nordmark

2014-02-15

Purpose: Portal dosimetry provides an accurate and convenient means of verifying dose delivered to the patient. A simple method for carrying out portal dosimetry for volumetric modulated arc therapy (VMAT) is described, together with phantom measurements demonstrating the validity of the approach. Methods: Portal images were predicted by projecting dose in the isocentric plane through to the portal image plane, with exponential attenuation and convolution with a double-Gaussian scatter function. Appropriate parameters for the projection were selected by fitting the calculation model to portal images measured on an iViewGT portal imager (Elekta AB, Stockholm, Sweden) for a variety of phantommore » thicknesses and field sizes. This model was then used to predict the portal image resulting from each control point of a VMAT arc. Finally, all these control point images were summed to predict the overall integrated portal image for the whole arc. The calculated and measured integrated portal images were compared for three lung and three esophagus plans delivered to a thorax phantom, and three prostate plans delivered to a homogeneous phantom, using a gamma index for 3% and 3 mm. A 0.6 cm{sup 3} ionization chamber was used to verify the planned isocentric dose. The sensitivity of this method to errors in monitor units, field shaping, gantry angle, and phantom position was also evaluated by means of computer simulations. Results: The calculation model for portal dose prediction was able to accurately compute the portal images due to simple square fields delivered to solid water phantoms. The integrated images of VMAT treatments delivered to phantoms were also correctly predicted by the method. The proportion of the images with a gamma index of less than unity was 93.7% ± 3.0% (1SD) and the difference between isocenter dose calculated by the planning system and measured by the ionization chamber was 0.8% ± 1.0%. The method was highly sensitive to errors in monitor units and field shape, but less sensitive to errors in gantry angle or phantom position. Conclusions: This method of predicting integrated portal images provides a convenient means of verifying dose delivered using VMAT, with minimal image acquisition and data processing requirements.« less

[Radiation protective quality of spacesuit "Orlan-M" during extravehicular activities on the International Space Station].

PubMed

Shurshakov, V A; Kartashov, D A; Kolomenskiĭ, A V; Petrov, V M; Red'ko, V I; Abramov, I P; Letkova, L I; Tikhomirov, E P

2006-01-01

Sampling irradiation of spacesuit "Orlan-M" allowed construction of a simulation model of the spacesuit shielding function for critical body organs. The critical organs self-shielding model is a Russian standard anthropomorphic phantom. Radiation protective quality of the spacesuit was assessed by calculating the dose attenuation rates for several critical body organs of an ISS crewmember implementing EVA. These calculations are intended for more accurate assessment of radiation risk to the ISS crews donning "Orlan-M" in near-Earth orbits.

Evaluation of 3D Gamma index calculation implemented in two commercial dosimetry systems

NASA Astrophysics Data System (ADS)

Xing, Aitang; Arumugam, Sankar; Deshpande, Shrikant; George, Armia; Vial, Philip; Holloway, Lois; Goozee, Gary

2015-01-01

3D Gamma index is one of the metrics which have been widely used for clinical routine patient specific quality assurance for IMRT, Tomotherapy and VMAT. The algorithms for calculating the 3D Gamma index using global and local methods implemented in two software tools: PTW- VeriSoft® as a part of OCTIVIUS 4D dosimeter systems and 3DVHTM from Sun Nuclear were assessed. The Gamma index calculated by the two systems was compared with manual calculated for one data set. The Gamma pass rate calculated by the two systems was compared using 3%/3mm, 2%/2mm, 3%/2mm and 2%/3mm for two additional data sets. The Gamma indexes calculated by the two systems were accurate, but Gamma pass rates calculated by the two software tools for same data set with the same dose threshold were different due to the different interpolation of raw dose data by the two systems and different implementation of Gamma index calculation and other modules in the two software tools. The mean difference was -1.3%±3.38 (1SD) with a maximum difference of 11.7%.

Estimation of absorbed doses from paediatric cone-beam CT scans: MOSFET measurements and Monte Carlo simulations.

PubMed

Kim, Sangroh; Yoshizumi, Terry T; Toncheva, Greta; Frush, Donald P; Yin, Fang-Fang

2010-03-01

The purpose of this study was to establish a dose estimation tool with Monte Carlo (MC) simulations. A 5-y-old paediatric anthropomorphic phantom was computed tomography (CT) scanned to create a voxelised phantom and used as an input for the abdominal cone-beam CT in a BEAMnrc/EGSnrc MC system. An X-ray tube model of the Varian On-Board Imager((R)) was built in the MC system. To validate the model, the absorbed doses at each organ location for standard-dose and low-dose modes were measured in the physical phantom with MOSFET detectors; effective doses were also calculated. In the results, the MC simulations were comparable to the MOSFET measurements. This voxelised phantom approach could produce a more accurate dose estimation than the stylised phantom method. This model can be easily applied to multi-detector CT dosimetry.

HDRK-Man: a whole-body voxel model based on high-resolution color slice images of a Korean adult male cadaver

NASA Astrophysics Data System (ADS)

Kim, Chan Hyeong; Hyoun Choi, Sang; Jeong, Jong Hwi; Lee, Choonsik; Chung, Min Suk

2008-08-01

A Korean voxel model, named 'High-Definition Reference Korean-Man (HDRK-Man)', was constructed using high-resolution color photographic images that were obtained by serially sectioning the cadaver of a 33-year-old Korean adult male. The body height and weight, the skeletal mass and the dimensions of the individual organs and tissues were adjusted to the reference Korean data. The resulting model was then implemented into a Monte Carlo particle transport code, MCNPX, to calculate the dose conversion coefficients for the internal organs and tissues. The calculated values, overall, were reasonable in comparison with the values from other adult voxel models. HDRK-Man showed higher dose conversion coefficients than other models, due to the facts that HDRK-Man has a smaller torso and that the arms of HDRK-Man are shifted backward. The developed model is believed to adequately represent average Korean radiation workers and thus can be used for more accurate calculation of dose conversion coefficients for Korean radiation workers in the future.

Validation of GPU-accelerated superposition-convolution dose computations for the Small Animal Radiation Research Platform.

PubMed

Cho, Nathan; Tsiamas, Panagiotis; Velarde, Esteban; Tryggestad, Erik; Jacques, Robert; Berbeco, Ross; McNutt, Todd; Kazanzides, Peter; Wong, John

2018-05-01

The Small Animal Radiation Research Platform (SARRP) has been developed for conformal microirradiation with on-board cone beam CT (CBCT) guidance. The graphics processing unit (GPU)-accelerated Superposition-Convolution (SC) method for dose computation has been integrated into the treatment planning system (TPS) for SARRP. This paper describes the validation of the SC method for the kilovoltage energy by comparing with EBT2 film measurements and Monte Carlo (MC) simulations. MC data were simulated by EGSnrc code with 3 × 10 8 -1.5 × 10 9 histories, while 21 photon energy bins were used to model the 220 kVp x-rays in the SC method. Various types of phantoms including plastic water, cork, graphite, and aluminum were used to encompass the range of densities of mouse organs. For the comparison, percentage depth dose (PDD) of SC, MC, and film measurements were analyzed. Cross beam (x,y) dosimetric profiles of SC and film measurements are also presented. Correction factors (CFz) to convert SC to MC dose-to-medium are derived from the SC and MC simulations in homogeneous phantoms of aluminum and graphite to improve the estimation. The SC method produces dose values that are within 5% of film measurements and MC simulations in the flat regions of the profile. The dose is less accurate at the edges, due to factors such as geometric uncertainties of film placement and difference in dose calculation grids. The GPU-accelerated Superposition-Convolution dose computation method was successfully validated with EBT2 film measurements and MC calculations. The SC method offers much faster computation speed than MC and provides calculations of both dose-to-water in medium and dose-to-medium in medium. © 2018 American Association of Physicists in Medicine.

The effect of voxel size on dose distribution in Varian Clinac iX 6 MV photon beam using Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Yani, Sitti; Dirgayussa, I. Gde E.; Rhani, Moh. Fadhillah; Haryanto, Freddy; Arif, Idam

2015-09-01

Recently, Monte Carlo (MC) calculation method has reported as the most accurate method of predicting dose distributions in radiotherapy. The MC code system (especially DOSXYZnrc) has been used to investigate the different voxel (volume elements) sizes effect on the accuracy of dose distributions. To investigate this effect on dosimetry parameters, calculations were made with three different voxel sizes. The effects were investigated with dose distribution calculations for seven voxel sizes: 1 × 1 × 0.1 cm3, 1 × 1 × 0.5 cm3, and 1 × 1 × 0.8 cm3. The 1 × 109 histories were simulated in order to get statistical uncertainties of 2%. This simulation takes about 9-10 hours to complete. Measurements are made with field sizes 10 × 10 cm2 for the 6 MV photon beams with Gaussian intensity distribution FWHM 0.1 cm and SSD 100.1 cm. MC simulated and measured dose distributions in a water phantom. The output of this simulation i.e. the percent depth dose and dose profile in dmax from the three sets of calculations are presented and comparisons are made with the experiment data from TTSH (Tan Tock Seng Hospital, Singapore) in 0-5 cm depth. Dose that scored in voxels is a volume averaged estimate of the dose at the center of a voxel. The results in this study show that the difference between Monte Carlo simulation and experiment data depend on the voxel size both for percent depth dose (PDD) and profile dose. PDD scan on Z axis (depth) of water phantom, the big difference obtain in the voxel size 1 × 1 × 0.8 cm3 about 17%. In this study, the profile dose focused on high gradient dose area. Profile dose scan on Y axis and the big difference get in the voxel size 1 × 1 × 0.1 cm3 about 12%. This study demonstrated that the arrange voxel in Monte Carlo simulation becomes important.

SU-F-T-672: A Novel Kernel-Based Dose Engine for KeV Photon Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reinhart, M; Fast, M F; Nill, S

2016-06-15

Purpose: Mimicking state-of-the-art patient radiotherapy with high precision irradiators for small animals allows advanced dose-effect studies and radiobiological investigations. One example is the implementation of pre-clinical IMRT-like irradiations, which requires the development of inverse planning for keV photon beams. As a first step, we present a novel kernel-based dose calculation engine for keV x-rays with explicit consideration of energy and material dependencies. Methods: We follow a superposition-convolution approach adapted to keV x-rays, based on previously published work on micro-beam therapy. In small animal radiotherapy, we assume local energy deposition at the photon interaction point, since the electron ranges in tissuemore » are of the same order of magnitude as the voxel size. This allows us to use photon-only kernel sets generated by MC simulations, which are pre-calculated for six energy windows and ten base materials. We validate our stand-alone dose engine against Geant4 MC simulations for various beam configurations in water, slab phantoms with bone and lung inserts, and on a mouse CT with (0.275mm)3 voxels. Results: We observe good agreement for all cases. For field sizes of 1mm{sup 2} to 1cm{sup 2} in water, the depth dose curves agree within 1% (mean), with the largest deviations in the first voxel (4%) and at depths>5cm (<2.5%). The out-of-field doses at 1cm depth agree within 8% (mean) for all but the smallest field size. In slab geometries, the mean agreement was within 3%, with maximum deviations of 8% at water-bone interfaces. The γ-index (1mm/1%) passing rate for a single-field mouse irradiation is 71%. Conclusion: The presented dose engine yields an accurate representation of keV-photon doses suitable for inverse treatment planning for IMRT. It has the potential to become a significantly faster yet sufficiently accurate alternative to full MC simulations. Further investigations will focus on energy sampling as well as calculation times. Research at ICR is also supported by Cancer Research UK under Programme C33589/A19727 and NHS funding to the NIHR Biomedical Research Centre at RMH and ICR. MFF is supported by Cancer Research UK under Programme C33589/A19908.« less

Estimating age-based antiretroviral therapy costs for HIV-infected children in resource-limited settings based on World Health Organization weight-based dosing recommendations.

PubMed

Doherty, Kathleen; Essajee, Shaffiq; Penazzato, Martina; Holmes, Charles; Resch, Stephen; Ciaranello, Andrea

2014-05-02

Pediatric antiretroviral therapy (ART) has been shown to substantially reduce morbidity and mortality in HIV-infected infants and children. To accurately project program costs, analysts need accurate estimations of antiretroviral drug (ARV) costs for children. However, the costing of pediatric antiretroviral therapy is complicated by weight-based dosing recommendations which change as children grow. We developed a step-by-step methodology for estimating the cost of pediatric ARV regimens for children ages 0-13 years old. The costing approach incorporates weight-based dosing recommendations to provide estimated ARV doses throughout childhood development. Published unit drug costs are then used to calculate average monthly drug costs. We compared our derived monthly ARV costs to published estimates to assess the accuracy of our methodology. The estimates of monthly ARV costs are provided for six commonly used first-line pediatric ARV regimens, considering three possible care scenarios. The costs derived in our analysis for children were fairly comparable to or slightly higher than available published ARV drug or regimen estimates. The methodology described here can be used to provide an accurate estimation of pediatric ARV regimen costs for cost-effectiveness analysts to project the optimum packages of care for HIV-infected children, as well as for program administrators and budget analysts who wish to assess the feasibility of increasing pediatric ART availability in constrained budget environments.

Dose conversion coefficients for photon exposure of the human eye lens.

PubMed

Behrens, R; Dietze, G

2011-01-21

In recent years, several papers dealing with the eye lens dose have been published, because epidemiological studies implied that the induction of cataracts occurs even at eye lens doses of less than 500 mGy. Different questions were addressed: Which personal dose equivalent quantity is appropriate for monitoring the dose to the eye lens? Is a new definition of the dose quantity H(p)(3) based on a cylinder phantom to represent the human head necessary? Are current conversion coefficients from fluence to equivalent dose to the lens sufficiently accurate? To investigate the latter question, a realistic model of the eye including the inner structure of the lens was developed. Using this eye model, conversion coefficients for electrons have already been presented. In this paper, the same eye model-with the addition of the whole body-was used to calculate conversion coefficients from fluence (and air kerma) to equivalent dose to the lens for photon radiation from 5 keV to 10 MeV. Compared to the values adopted in 1996 by the International Commission on Radiological Protection (ICRP), the new values are similar between 40 keV and 1 MeV and lower by up to a factor of 5 and 7 for photon energies at about 10 keV and 10 MeV, respectively. Above 1 MeV, the new values (calculated without kerma approximation) should be applied in pure photon radiation fields, while the values adopted by the ICRP in 1996 (calculated with kerma approximation) should be applied in case a significant contribution from secondary electrons originating outside the body is present.

Dose conversion coefficients for photon exposure of the human eye lens

NASA Astrophysics Data System (ADS)

Behrens, R.; Dietze, G.

2011-01-01

In recent years, several papers dealing with the eye lens dose have been published, because epidemiological studies implied that the induction of cataracts occurs even at eye lens doses of less than 500 mGy. Different questions were addressed: Which personal dose equivalent quantity is appropriate for monitoring the dose to the eye lens? Is a new definition of the dose quantity Hp(3) based on a cylinder phantom to represent the human head necessary? Are current conversion coefficients from fluence to equivalent dose to the lens sufficiently accurate? To investigate the latter question, a realistic model of the eye including the inner structure of the lens was developed. Using this eye model, conversion coefficients for electrons have already been presented. In this paper, the same eye model—with the addition of the whole body—was used to calculate conversion coefficients from fluence (and air kerma) to equivalent dose to the lens for photon radiation from 5 keV to 10 MeV. Compared to the values adopted in 1996 by the International Commission on Radiological Protection (ICRP), the new values are similar between 40 keV and 1 MeV and lower by up to a factor of 5 and 7 for photon energies at about 10 keV and 10 MeV, respectively. Above 1 MeV, the new values (calculated without kerma approximation) should be applied in pure photon radiation fields, while the values adopted by the ICRP in 1996 (calculated with kerma approximation) should be applied in case a significant contribution from secondary electrons originating outside the body is present.

A comparison of simple and realistic eye models for calculation of fluence to dose conversion coefficients in a broad parallel beam incident of protons

NASA Astrophysics Data System (ADS)

Sakhaee, Mahmoud; Vejdani-Noghreiyan, Alireza; Ebrahimi-Khankook, Atiyeh

2015-01-01

Radiation induced cataract has been demonstrated among people who are exposed to ionizing radiation. To evaluate the deterministic effects of ionizing radiation on the eye lens, several papers dealing with the eye lens dose have been published. ICRP Publication 103 states that the lens of the eye may be more radiosensitive than previously considered. Detailed investigation of the response of the lens showed that there are strong differences in sensitivity to ionizing radiation exposure with respect to cataract induction among the tissues of the lens of the eye. This motivated several groups to look deeper into issue of the dose to a sensitive cell population within the lens, especially for radiations with low energy penetrability that have steep dose gradients inside the lens. Two sophisticated mathematical models of the eye including the inner structure have been designed for the accurate dose estimation in recent years. This study focuses on the calculations of the absorbed doses of different parts of the eye using the stylized models located in UF-ORNL phantom and comparison with the data calculated with the reference computational phantom in a broad parallel beam incident of protons with energies between 20 MeV and 10 GeV. The obtained results indicate that the total lens absorbed doses of reference phantom has good compliance with those of the more sensitive regions of stylized models. However, total eye absorbed dose of these models greatly differ with each other for lower energies.

Effect of photon energy spectrum on dosimetric parameters of brachytherapy sources.

PubMed

Ghorbani, Mahdi; Mehrpouyan, Mohammad; Davenport, David; Ahmadi Moghaddas, Toktam

2016-06-01

The aim of this study is to quantify the influence of the photon energy spectrum of brachytherapy sources on task group No. 43 (TG-43) dosimetric parameters. Different photon spectra are used for a specific radionuclide in Monte Carlo simulations of brachytherapy sources. MCNPX code was used to simulate 125I, 103Pd, 169Yb, and 192Ir brachytherapy sources. Air kerma strength per activity, dose rate constant, radial dose function, and two dimensional (2D) anisotropy functions were calculated and isodose curves were plotted for three different photon energy spectra. The references for photon energy spectra were: published papers, Lawrence Berkeley National Laboratory (LBNL), and National Nuclear Data Center (NNDC). The data calculated by these photon energy spectra were compared. Dose rate constant values showed a maximum difference of 24.07% for 103Pd source with different photon energy spectra. Radial dose function values based on different spectra were relatively the same. 2D anisotropy function values showed minor differences in most of distances and angles. There was not any detectable difference between the isodose contours. Dosimetric parameters obtained with different photon spectra were relatively the same, however it is suggested that more accurate and updated photon energy spectra be used in Monte Carlo simulations. This would allow for calculation of reliable dosimetric data for source modeling and calculation in brachytherapy treatment planning systems.

Effect of photon energy spectrum on dosimetric parameters of brachytherapy sources

PubMed Central

Ghorbani, Mahdi; Davenport, David

2016-01-01

Abstract Aim The aim of this study is to quantify the influence of the photon energy spectrum of brachytherapy sources on task group No. 43 (TG-43) dosimetric parameters. Background Different photon spectra are used for a specific radionuclide in Monte Carlo simulations of brachytherapy sources. Materials and methods MCNPX code was used to simulate 125I, 103Pd, 169Yb, and 192Ir brachytherapy sources. Air kerma strength per activity, dose rate constant, radial dose function, and two dimensional (2D) anisotropy functions were calculated and isodose curves were plotted for three different photon energy spectra. The references for photon energy spectra were: published papers, Lawrence Berkeley National Laboratory (LBNL), and National Nuclear Data Center (NNDC). The data calculated by these photon energy spectra were compared. Results Dose rate constant values showed a maximum difference of 24.07% for 103Pd source with different photon energy spectra. Radial dose function values based on different spectra were relatively the same. 2D anisotropy function values showed minor differences in most of distances and angles. There was not any detectable difference between the isodose contours. Conclusions Dosimetric parameters obtained with different photon spectra were relatively the same, however it is suggested that more accurate and updated photon energy spectra be used in Monte Carlo simulations. This would allow for calculation of reliable dosimetric data for source modeling and calculation in brachytherapy treatment planning systems. PMID:27247558

Methodology comparison for gamma-heating calculations in material-testing reactors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lemaire, M.; Vaglio-Gaudard, C.; Lyoussi, A.

2015-07-01

The Jules Horowitz Reactor (JHR) is a Material-Testing Reactor (MTR) under construction in the south of France at CEA Cadarache (French Alternative Energies and Atomic Energy Commission). It will typically host about 20 simultaneous irradiation experiments in the core and in the beryllium reflector. These experiments will help us better understand the complex phenomena occurring during the accelerated ageing of materials and the irradiation of nuclear fuels. Gamma heating, i.e. photon energy deposition, is mainly responsible for temperature rise in non-fuelled zones of nuclear reactors, including JHR internal structures and irradiation devices. As temperature is a key parameter for physicalmore » models describing the behavior of material, accurate control of temperature, and hence gamma heating, is required in irradiation devices and samples in order to perform an advanced suitable analysis of future experimental results. From a broader point of view, JHR global attractiveness as a MTR depends on its ability to monitor experimental parameters with high accuracy, including gamma heating. Strict control of temperature levels is also necessary in terms of safety. As JHR structures are warmed up by gamma heating, they must be appropriately cooled down to prevent creep deformation or melting. Cooling-power sizing is based on calculated levels of gamma heating in the JHR. Due to these safety concerns, accurate calculation of gamma heating with well-controlled bias and associated uncertainty as low as possible is all the more important. There are two main kinds of calculation bias: bias coming from nuclear data on the one hand and bias coming from physical approximations assumed by computer codes and by general calculation route on the other hand. The former must be determined by comparison between calculation and experimental data; the latter by calculation comparisons between codes and between methodologies. In this presentation, we focus on this latter kind of bias. Nuclear heating is represented by the physical quantity called absorbed dose (energy deposition induced by particle-matter interactions, divided by mass). Its calculation with Monte Carlo codes is possible but computationally expensive as it requires transport simulation of charged particles, along with neutrons and photons. For that reason, the calculation of another physical quantity, called KERMA, is often preferred, as KERMA calculation with Monte Carlo codes only requires transport of neutral particles. However, KERMA is only an estimator of the absorbed dose and many conditions must be fulfilled for KERMA to be equal to absorbed dose, including so-called condition of electronic equilibrium. Also, Monte Carlo computations of absorbed dose still present some physical approximations, even though there is only a limited number of them. Some of these approximations are linked to the way how Monte Carlo codes apprehend the transport simulation of charged particles and the productive and destructive interactions between photons, electrons and positrons. There exists a huge variety of electromagnetic shower models which tackle this topic. Differences in the implementation of these models can lead to discrepancies in calculated values of absorbed dose between different Monte Carlo codes. The magnitude of order of such potential discrepancies should be quantified for JHR gamma-heating calculations. We consequently present a two-pronged plan. In a first phase, we intend to perform compared absorbed dose / KERMA Monte Carlo calculations in the JHR. This way, we will study the presence or absence of electronic equilibrium in the different JHR structures and experimental devices and we will give recommendations for the choice of KERMA or absorbed dose when calculating gamma heating in the JHR. In a second phase, we intend to perform compared TRIPOLI4 / MCNP absorbed dose calculations in a simplified JHR-representative geometry. For this comparison, we will use the same nuclear data library for both codes (the European library JEFF3.1.1 and photon library EPDL97) so as to isolate the effects from electromagnetic shower models on absorbed dose calculation. This way, we hope to get insightful feedback on these models and their implementation in Monte Carlo codes. (authors)« less

Advanced Collapsed cone Engine dose calculations in tissue media for COMS eye plaques loaded with I-125 seeds.

PubMed

Morrison, Hali; Menon, Geetha; Larocque, Matthew P; van Veelen, Bob; Niatsetski, Yury; Weis, Ezekiel; Sloboda, Ron S

2018-05-04

To investigate the dose calculation accuracy of the Advanced Collapsed cone Engine (ACE) algorithm for ocular brachytherapy using a COMS plaque loaded with I-125 seeds for two heterogeneous patient tissue scenarios. The Oncura model 6711 I-125 seed and 16 mm COMS plaque were added to a research version (v4.6) of the Oncentra ® Brachy (OcB) treatment planning system (TPS) for dose calculations using ACE. Treatment plans were created for two heterogeneous cases: (a) a voxelized eye phantom comprising realistic eye materials and densities and (b) a patient CT dataset with variable densities throughout the dataset. ACE dose calculations were performed using a high accuracy mode, high-resolution calculation grid matching the imported CT datasets (0.5 × 0.5 × 0.5 mm 3 ), and a user-defined CT calibration curve. The accuracy of ACE was evaluated by replicating the plan geometries and comparing to Monte Carlo (MC) calculated doses obtained using MCNP6. The effects of the heterogeneous patient tissues on the dose distributions were also evaluated by performing the ACE and MCNP6 calculations for the same scenarios but setting all tissues and air to water. Average local percent dose differences between ACE and MC within contoured structures and at points of interest for both scenarios ranged from 1.2% to 20.9%, and along the plaque central axis (CAX) from 0.7% to 7.8%. The largest differences occurred in the plaque penumbra (up to 17%), and at contoured structure interfaces (up to 20%). Other regions in the eye agreed more closely, within the uncertainties of ACE dose calculations (~5%). Compared to that, dose differences between water-based and fully heterogeneous tissue simulations were up to 27%. Overall, ACE dosimetry agreed well with MC in the tumor volume and along the plaque CAX for the two heterogeneous tissue scenarios, indicating that ACE could potentially be used for clinical ocular brachytherapy dosimetry. In general, ACE data matched the fully heterogeneous MC data more closely than water-based data, even in regions where the ACE accuracy was relatively low. However, depending on the plaque position, doses to critical structures near the plaque penumbra or at tissue interfaces were less accurate, indicating that improvements may be necessary. More extensive knowledge of eye tissue compositions is still required. © 2018 American Association of Physicists in Medicine.

Patient-specific dose calculations for pediatric CT of the chest, abdomen and pelvis

PubMed Central

Fraser, Nicholas D.; Carver, Diana E.; Pickens, David R.; Price, Ronald R.; Hernanz-Schulman, Marta; Stabin, Michael G.

2015-01-01

Background Organ dose is essential for accurate estimates of patient dose from CT. Objective To determine organ doses from a broad range of pediatric patients undergoing diagnostic chest–abdomen–pelvis CT and investigate how these relate to patient size. Materials and methods We used a previously validated Monte Carlo simulation model of a Philips Brilliance 64 multi-detector CT scanner (Philips Healthcare, Best, The Netherlands) to calculate organ doses for 40 pediatric patients (M:F=21:19; range 0.6–17 years). Organ volumes and positions were determined from the images using standard segmentation techniques. Non-linear regression was performed to determine the relationship between volume CT dose index (CTDIvol)-normalized organ doses and abdominopelvic diameter. We then compared results with values obtained from independent studies. Results We found that CTDIvol-normalized organ dose correlated strongly with exponentially decreasing abdominopelvic diameter (R2>0.8 for most organs). A similar relationship was determined for effective dose when normalized by dose-length product (R2=0.95). Our results agreed with previous studies within 12% using similar scan parameters (i.e. bowtie filter size, beam collimation); however results varied up to 25% when compared to studies using different bowtie filters. Conclusion Our study determined that organ doses can be estimated from measurements of patient size, namely body diameter, and CTDIvol prior to CT examination. This information provides an improved method for patient dose estimation. PMID:26142256

Simulation of computed tomography dose based on voxel phantom

NASA Astrophysics Data System (ADS)

Liu, Chunyu; Lv, Xiangbo; Li, Zhaojun

2017-01-01

Computed Tomography (CT) is one of the preferred and the most valuable imaging tool used in diagnostic radiology, which provides a high-quality cross-sectional image of the body. It still causes higher doses of radiation to patients comparing to the other radiological procedures. The Monte-Carlo method is appropriate for estimation of the radiation dose during the CT examinations. The simulation of the Computed Tomography Dose Index (CTDI) phantom was developed in this paper. Under a similar conditions used in physical measurements, dose profiles were calculated and compared against the measured values that were reported. The results demonstrate a good agreement between the calculated and the measured doses. From different CT exam simulations using the voxel phantom, the highest absorbed dose was recorded for the lung, the brain, the bone surface. A comparison between the different scan type shows that the effective dose for a chest scan is the highest one, whereas the effective dose values during abdomen and pelvis scan are very close, respectively. The lowest effective dose resulted from the head scan. Although, the dose in CT is related to various parameters, such as the tube current, exposure time, beam energy, slice thickness and patient size, this study demonstrates that the MC simulation is a useful tool to accurately estimate the dose delivered to any specific organs for patients undergoing the CT exams and can be also a valuable technique for the design and the optimization of the CT x-ray source.

Impact of a commercially available model-based dose calculation algorithm on treatment planning of high-dose-rate brachytherapy in patients with cervical cancer

PubMed Central

Abe, Kota; Kadoya, Noriyuki; Sato, Shinya; Hashimoto, Shimpei; Nakajima, Yujiro; Miyasaka, Yuya; Ito, Kengo; Umezawa, Rei; Yamamoto, Takaya; Takahashi, Noriyoshi; Takeda, Ken; Jingu, Keiichi

2018-01-01

Abstract We evaluated the impact of model-based dose calculation algorithms (MBDCAs) on high-dose-rate brachytherapy (HDR-BT) treatment planning for patients with cervical cancer. Seven patients with cervical cancer treated using HDR-BT were studied. Tandem and ovoid applicators were used in four patients, a vaginal cylinder in one, and interstitial needles in the remaining two patients. MBDCAs were applied to the Advanced Collapsed cone Engine (ACE; Elekta, Stockholm, Sweden). All plans, which were originally calculated using TG-43, were re-calculated using both ACE and Monte Carlo (MC) simulations. Air was used as the rectal material. The mean difference in the rectum D2cm3 between ACErec-air and MCrec-air was 8.60 ± 4.64%, whereas that in the bladder D2cm3 was −2.80 ± 1.21%. Conversely, in the small group analysis (n = 4) using water instead of air as the rectal material, the mean difference in the rectum D2cm3 between TG-43 and ACErec-air was 11.87 ± 2.65%, whereas that between TG-43 and ACErec-water was 0.81 ± 2.04%, indicating that the use of water as the rectal material reduced the difference in D2cm3 between TG-43 and ACE. Our results suggested that the differences in the dose–volume histogram (DVH) parameters of TG-43 and ACE were large for the rectum when considerable air (gas) volume was present in it, and that this difference was reduced when the air (gas) volume was reduced. Also, ACE exhibited better dose calculation accuracy than that of TG-43 in this situation. Thus, ACE may be able to calculate the dose more accurately than TG-43 for HDR-BT in treating cervical cancers, particularly for patients with considerable air (gas) volume in the rectum. PMID:29378024

TU-F-CAMPUS-T-05: A Cloud-Based Monte Carlo Dose Calculation for Electron Cutout Factors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mitchell, T; Bush, K

Purpose: For electron cutouts of smaller sizes, it is necessary to verify electron cutout factors due to perturbations in electron scattering. Often, this requires a physical measurement using a small ion chamber, diode, or film. The purpose of this study is to develop a fast Monte Carlo based dose calculation framework that requires only a smart phone photograph of the cutout and specification of the SSD and energy to determine the electron cutout factor, with the ultimate goal of making this cloud-based calculation widely available to the medical physics community. Methods: The algorithm uses a pattern recognition technique to identifymore » the corners of the cutout in the photograph as shown in Figure 1. It then corrects for variations in perspective, scaling, and translation of the photograph introduced by the user’s positioning of the camera. Blob detection is used to identify the portions of the cutout which comprise the aperture and the portions which are cutout material. This information is then used define physical densities of the voxels used in the Monte Carlo dose calculation algorithm as shown in Figure 2, and select a particle source from a pre-computed library of phase-spaces scored above the cutout. The electron cutout factor is obtained by taking a ratio of the maximum dose delivered with the cutout in place to the dose delivered under calibration/reference conditions. Results: The algorithm has been shown to successfully identify all necessary features of the electron cutout to perform the calculation. Subsequent testing will be performed to compare the Monte Carlo results with a physical measurement. Conclusion: A simple, cloud-based method of calculating electron cutout factors could eliminate the need for physical measurements and substantially reduce the time required to properly assure accurate dose delivery.« less

Analytical model for out-of-field dose in photon craniospinal irradiation

NASA Astrophysics Data System (ADS)

Taddei, Phillip J.; Jalbout, Wassim; Howell, Rebecca M.; Khater, Nabil; Geara, Fady; Homann, Kenneth; Newhauser, Wayne D.

2013-11-01

The prediction of late effects after radiotherapy in organs outside a treatment field requires accurate estimations of out-of-field dose. However, out-of-field dose is not calculated accurately by commercial treatment planning systems (TPSs). The purpose of this study was to develop and test an analytical model for out-of-field dose during craniospinal irradiation (CSI) from photon beams produced by a linear accelerator. In two separate evaluations of the model, we measured absorbed dose for a 6 MV CSI using thermoluminescent dosimeters placed throughout an anthropomorphic phantom and fit the measured data to an analytical model of absorbed dose versus distance outside of the composite field edge. These measurements were performed in two separate clinics—the University of Texas MD Anderson Cancer Center (MD Anderson) and the American University of Beirut Medical Center (AUBMC)—using the same phantom but different linear accelerators and TPSs commissioned for patient treatments. The measurement at AUBMC also included in-field locations. Measured dose values were compared to those predicted by TPSs and parameters were fit to the model in each setting. In each clinic, 95% of the measured data were contained within a factor of 0.2 and one root mean square deviation of the model-based values. The root mean square deviations of the mathematical model were 0.91 cGy Gy-1 and 1.67 cGy Gy-1 in the MD Anderson and AUBMC clinics, respectively. The TPS predictions agreed poorly with measurements in regions of sharp dose gradient, e.g., near the field edge. At distances greater than 1 cm from the field edge, the TPS underestimated the dose by an average of 14% ± 24% and 44% ± 19% in the MD Anderson and AUBMC clinics, respectively. The in-field measured dose values of the measurement at AUBMC matched the dose values calculated by the TPS to within 2%. Dose algorithms in TPSs systematically underestimated the actual out-of-field dose. Therefore, it is important to use an improved model based on measurements when estimating out-of-field dose. The model proposed in this study performed well for this purpose in two clinics and may be applicable in other clinics with similar treatment field configurations.

SU-E-T-424: Dosimetric Verification of Modulated Electron Radiation Therapy Delivered Using An Electron Specific Multileaf Collimator for Treatment of Scalp Cases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eldib, A; Al-Azhar University Cairo; Jin, L

2014-06-01

Purpose: Modulated electron radiotherapy (MERT) has the potential to achieve better treatment outcome for shallow tumors such as those of breast and scalp. In a separate study with scalp lesions, MERT was compared to volumetric modulated arc therapy. Our results showed a reduction in the dose reaching the brain with MERT. However dose calculation accuracy and delivery efficiency challenges remain. Thus in the current study we proceed to add more cases to demonstrate MERT beneficial outcome and its delivery accuracy using an electron specific multileaf collimator (eMLC). Methods: We have used the MCBEAM code for treatment head simulation and formore » generating phase space files to be used as radiation source input for our Monte Carlo based treatment planning system (MC TPS). MCPLAN code is used for calculation of patient specific dose deposition coefficient and for final MERT plan dose calculation. An in-house developed optimization code is used for the optimization process. MERT plans were generated for real patients and head and neck phantom. Film was used for dosimetric verification. The film was cut following the contour of the curved phantom surface and then sealed with black masking tape. In the measurement, the sealed film packet was sandwiched between two adjacent slabs of the head and neck phantom. The measured 2D dose distribution was then compared with calculations. Results: The eMLC allows effective treatment of scalps with multi-lesions spreading around the patient head, which was usually difficult to plan or very time consuming with conventional applicators. MERT continues to show better reduction in the brain dose. The dosimetric measurements showed slight discrepancy, which was attributed to the film setup. Conclusion: MERT can improve treatment plan quality for patients with scalp cancers. Our in-house MC TPS is capable of performing treatment planning and accurate dose calculation for MERT using the eMLC.« less

Optimization of tomotherapy treatment planning for patients with bilateral hip prostheses.

PubMed

Chapman, David; Smith, Shaun; Barnett, Rob; Bauman, Glenn; Yartsev, Slav

2014-02-04

To determine the effect of different imaging options and the most efficient imaging strategy for treatment planning of patients with hip prostheses. The planning kilovoltage CT (kVCT) and daily megavoltage CT (MVCT) studies for three prostate cancer patients with bilateral hip prostheses were used for creating hybrid kVCT/MVCT image sets. Treatment plans were created for kVCT images alone, hybrid kVCT/MVCT images, and MVCT images alone using the same dose prescription and planning parameters. The resulting dose volume histograms were compared. The orthopedic metal artifact reduction (O-MAR) reconstruction tool for kVCT images and different MVCT options were investigated with a water tank fit with double hip prostheses. Treatment plans were created for all imaging options and calculated dose was compared with the one measured by a pin-point ion chamber. On average for three patients, the D35% for the bladder was 8% higher in plans based on MVCT images and 7% higher in plans based on hybrid images, compared to the plans based on kVCT images alone. Likewise, the D35% for the rectum was 3% higher than the kVCT based plan for both hybrid and MVCT plans. The average difference in planned D99% in the PTV compared to kVCT plans was 0.9% and 0.1% for MVCT and hybrid plans, respectively. For the water tank with hip prostheses phantom, the kVCT plan with O-MAR correction applied showed better agreement between the measured and calculated dose than the original image set, with a difference of -1.9% compared to 3.3%. The measured doses for the MVCT plans were lower than the calculated dose due to image size limitations. The best agreement was for the kVCT/MVCT hybrid plans with the difference between calculated and measured dose around 1%. MVCT image provides better visualization of patient anatomy and hybrid kVCT/MVCT study enables more accurate calculations using updated MVCT relative electron density calibration.

SU-F-BRF-12: Investigating Dosimetric Effects of Inter-Fraction Deformation in Lung Cancer Stereotactic Body Radiotherapy (SBRT)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jia, J; Tian, Z; Gu, X

2014-06-15

Purpose: We studied dosimetric effects of inter-fraction deformation in lung stereotactic body radiotherapy (SBRT), in order to investigate the necessity of adaptive re-planning for lung SBRT treatments. Methods: Six lung cancer patients with different treatment fractions were retrospectively investigated. All the patients were immobilized and localized with a stereotactic body frame and were treated under cone-beam CT (CBCT) image guidance at each fraction. We calculated the actual delivered dose of the treatment plan using the up-to-date patient geometry of each fraction, and compared the dose with the intended plan dose to investigate the dosimetric effects of the inter-fraction deformation. Deformablemore » registration was carried out between the treatment planning CT and the CBCT of each fraction to obtain deformed planning CT for more accurate dose calculations of the delivered dose. The extent of the inter-fraction deformation was also evaluated by calculating the dice similarity coefficient between the delineated structures on the planning CT and those on the deformed planning CT. Results: The average dice coefficients for PTV, spinal cord, esophagus were 0.87, 0.83 and 0.69, respectively. The volume of PTV covered by prescription dose was decreased by 23.78% on average for all fractions and all patients. For spinal cord and esophagus, the volumes covered by the constraint dose were increased by 4.57% and 3.83%. The maximum dose was also increased by 4.11% for spinal cord and 4.29% for esophagus. Conclusion: Due to inter-fraction deformation, large deterioration was found in both PTV coverage and OAR sparing, which demonstrated the needs for adaptive re-planning of lung SBRT cases to improve target coverage while reducing radiation dose to nearby normal tissues.« less

Biothermal modeling of transurethral ultrasound applicators for MR-guided prostate thermal therapy (Invited Paper)

NASA Astrophysics Data System (ADS)

Ross, Anthony B.; Diederich, Chris J.; Nau, William H.; Tyreus, Per D.; Gill, Harcharan; Bouley, Donna; Butts, R. K.; Rieke, Viola; Daniel, Bruce; Sommer, Graham

2005-04-01

Thermal ablation is a minimally-invasive treatment option for benign prostatic hyperplasia (BPH) and localized prostate cancer. Accurate spatial control of thermal dose delivery is paramount to improving thermal therapy efficacy and avoiding post-treatment complications. We have recently developed three types of transurethral ultrasound applicators, each with different degrees of heating selectivity. These applicators have been evaluated in vivo in coordination with magnetic resonance temperature imaging, and demonstrated to accurately ablate specific regions of the canine prostate. A finite difference biothermal model of the three types of transurethral ultrasound applicators (sectored tubular, planar, and curvilinear transducer sections) was developed and used to further study the performance and heating capabilities of each these devices. The biothermal model is based on the Pennes bioheat equation. The acoustic power deposition pattern corresponding to each applicator type was calculated using the rectangular radiator approximation to the Raleigh Sommerfield diffraction integral. In this study, temperature and thermal dose profiles were calculated for different treatment schemes and target volumes, including single shot and angular scanning procedures. This study also demonstrated the ability of the applicators to conform the cytotoxic thermal dose distribution to a predefined target area. Simulated thermal profiles corresponded well with MR temperature images from previous in vivo experiments. Biothermal simulations presented in this study reinforce the potential of improved efficacy of transurethral ultrasound thermal therapy of prostatic disease.

Calculation and mitigation of isotopic interferences in liquid chromatography-mass spectrometry/mass spectrometry assays and its application in supporting microdose absolute bioavailability studies.

PubMed

Gu, Huidong; Wang, Jian; Aubry, Anne-Françoise; Jiang, Hao; Zeng, Jianing; Easter, John; Wang, Jun-sheng; Dockens, Randy; Bifano, Marc; Burrell, Richard; Arnold, Mark E

2012-06-05

A methodology for the accurate calculation and mitigation of isotopic interferences in liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) assays and its application in supporting microdose absolute bioavailability studies are reported for the first time. For simplicity, this calculation methodology and the strategy to minimize the isotopic interference are demonstrated using a simple molecule entity, then applied to actual development drugs. The exact isotopic interferences calculated with this methodology were often much less than the traditionally used, overestimated isotopic interferences simply based on the molecular isotope abundance. One application of the methodology is the selection of a stable isotopically labeled internal standard (SIL-IS) for an LC-MS/MS bioanalytical assay. The second application is the selection of an SIL analogue for use in intravenous (i.v.) microdosing for the determination of absolute bioavailability. In the case of microdosing, the traditional approach of calculating isotopic interferences can result in selecting a labeling scheme that overlabels the i.v.-dosed drug or leads to incorrect conclusions on the feasibility of using an SIL drug and analysis by LC-MS/MS. The methodology presented here can guide the synthesis by accurately calculating the isotopic interferences when labeling at different positions, using different selective reaction monitoring (SRM) transitions or adding more labeling positions. This methodology has been successfully applied to the selection of the labeled i.v.-dosed drugs for use in two microdose absolute bioavailability studies, before initiating the chemical synthesis. With this methodology, significant time and cost saving can be achieved in supporting microdose absolute bioavailability studies with stable labeled drugs.

Improved dosimetry techniques for intravascular brachytherapy

NASA Astrophysics Data System (ADS)

Sehgal, Varun

Coronary artery disease leads to the accumulation of atheromatous plaque leading to coronary stenosis. Coronary intervention techniques such as balloon angioplasty and atherectomy are used to address coronary stenosis and establish a stable lumen thus enhancing blood flow to the myocardium. Restenosis or re-blockage of the arteries is a major limitation of the above mentioned interventional techniques. Neointimal hyperplasia or proliferation of cells in response to the vascular injury as a result of coronary intervention is considered to be one of the major causes of restenosis. Recent studies indicated that irradiation of the coronary lesion site, with radiation doses ranging from 15 to 30 Gy, leads to diminishing neointimal hyperplasia with subsequent reduction in restenosis. The radiation dose is given by catheter-based radiation delivery systems using beta-emitters 90Sr/90Y, 32P and gamma-emitting 192Ir among others. However the dose schema used for dose prescription for these sources are relatively simplistic, and are based on calculations using uniform homogenous water or tissue media and simple cylinder geometry. Stenotic coronary vessels are invariably lined with atheromatous plaque of heterogeneous composition, the radiation dose distribution obtained from such dosimetry data can cause significant variations in the actual dose received by a given patient. Such discrepancies in dose calculation can introduce relatively large uncertainties in the limits of dose window for effective and safe application of intravascular brachytherapy, and consequently in the clinical evaluation of the efficacy of this modality. In this research study we investigated the effect of different geometrical and material heterogeneities, including residual plaque, catheter non-centering, lesion eccentricity and cardiac motion on the radiation dose delivered at the lesion site. Correction factors including dose perturbation factors and dose variation factors have been calculated using Monte Carlo-based radiation transport code MCNP and tabulated for a range of different coronary geometries and different radionuclides. A new technique using imaging techniques such as intravascular ultrasound and angiography to assess dosimetry for realistic coronary arteries is also introduced. The results indicate the need for accurate assessment of post-intervention clinical measurements such as minimal lumen diameter and residual plaque burden and incorporating them into dose calculations.

Evaluation of the influence of double and triple Gaussian proton kernel models on accuracy of dose calculations for spot scanning technique.

PubMed

Hirayama, Shusuke; Takayanagi, Taisuke; Fujii, Yusuke; Fujimoto, Rintaro; Fujitaka, Shinichiro; Umezawa, Masumi; Nagamine, Yoshihiko; Hosaka, Masahiro; Yasui, Keisuke; Omachi, Chihiro; Toshito, Toshiyuki

2016-03-01

The main purpose in this study was to present the results of beam modeling and how the authors systematically investigated the influence of double and triple Gaussian proton kernel models on the accuracy of dose calculations for spot scanning technique. The accuracy of calculations was important for treatment planning software (TPS) because the energy, spot position, and absolute dose had to be determined by TPS for the spot scanning technique. The dose distribution was calculated by convolving in-air fluence with the dose kernel. The dose kernel was the in-water 3D dose distribution of an infinitesimal pencil beam and consisted of an integral depth dose (IDD) and a lateral distribution. Accurate modeling of the low-dose region was important for spot scanning technique because the dose distribution was formed by cumulating hundreds or thousands of delivered beams. The authors employed a double Gaussian function as the in-air fluence model of an individual beam. Double and triple Gaussian kernel models were also prepared for comparison. The parameters of the kernel lateral model were derived by fitting a simulated in-water lateral dose profile induced by an infinitesimal proton beam, whose emittance was zero, at various depths using Monte Carlo (MC) simulation. The fitted parameters were interpolated as a function of depth in water and stored as a separate look-up table. These stored parameters for each energy and depth in water were acquired from the look-up table when incorporating them into the TPS. The modeling process for the in-air fluence and IDD was based on the method proposed in the literature. These were derived using MC simulation and measured data. The authors compared the measured and calculated absolute doses at the center of the spread-out Bragg peak (SOBP) under various volumetric irradiation conditions to systematically investigate the influence of the two types of kernel models on the dose calculations. The authors investigated the difference between double and triple Gaussian kernel models. The authors found that the difference between the two studied kernel models appeared at mid-depths and the accuracy of predicting the double Gaussian model deteriorated at the low-dose bump that appeared at mid-depths. When the authors employed the double Gaussian kernel model, the accuracy of calculations for the absolute dose at the center of the SOBP varied with irradiation conditions and the maximum difference was 3.4%. In contrast, the results obtained from calculations with the triple Gaussian kernel model indicated good agreement with the measurements within ±1.1%, regardless of the irradiation conditions. The difference between the results obtained with the two types of studied kernel models was distinct in the high energy region. The accuracy of calculations with the double Gaussian kernel model varied with the field size and SOBP width because the accuracy of prediction with the double Gaussian model was insufficient at the low-dose bump. The evaluation was only qualitative under limited volumetric irradiation conditions. Further accumulation of measured data would be needed to quantitatively comprehend what influence the double and triple Gaussian kernel models had on the accuracy of dose calculations.

Proton dose distribution measurements using a MOSFET detector with a simple dose-weighted correction method for LET effects.

PubMed

Kohno, Ryosuke; Hotta, Kenji; Matsuura, Taeko; Matsubara, Kana; Nishioka, Shie; Nishio, Teiji; Kawashima, Mitsuhiko; Ogino, Takashi

2011-04-04

We experimentally evaluated the proton beam dose reproducibility, sensitivity, angular dependence and depth-dose relationships for a new Metal Oxide Semiconductor Field Effect Transistor (MOSFET) detector. The detector was fabricated with a thinner oxide layer and was operated at high-bias voltages. In order to accurately measure dose distributions, we developed a practical method for correcting the MOSFET response to proton beams. The detector was tested by examining lateral dose profiles formed by protons passing through an L-shaped bolus. The dose reproducibility, angular dependence and depth-dose response were evaluated using a 190 MeV proton beam. Depth-output curves produced using the MOSFET detectors were compared with results obtained using an ionization chamber (IC). Since accurate measurements of proton dose distribution require correction for LET effects, we developed a simple dose-weighted correction method. The correction factors were determined as a function of proton penetration depth, or residual range. The residual proton range at each measurement point was calculated using the pencil beam algorithm. Lateral measurements in a phantom were obtained for pristine and SOBP beams. The reproducibility of the MOSFET detector was within 2%, and the angular dependence was less than 9%. The detector exhibited a good response at the Bragg peak (0.74 relative to the IC detector). For dose distributions resulting from protons passing through an L-shaped bolus, the corrected MOSFET dose agreed well with the IC results. Absolute proton dosimetry can be performed using MOSFET detectors to a precision of about 3% (1 sigma). A thinner oxide layer thickness improved the LET in proton dosimetry. By employing correction methods for LET dependence, it is possible to measure absolute proton dose using MOSFET detectors.

SU-E-T-556: Monte Carlo Generated Dose Distributions for Orbital Irradiation Using a Single Anterior-Posterior Electron Beam and a Hanging Lens Shield

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duwel, D; Lamba, M; Elson, H

Purpose: Various cancers of the eye are successfully treated with radiotherapy utilizing one anterior-posterior (A/P) beam that encompasses the entire content of the orbit. In such cases, a hanging lens shield can be used to spare dose to the radiosensitive lens of the eye to prevent cataracts. Methods: This research focused on Monte Carlo characterization of dose distributions resulting from a single A-P field to the orbit with a hanging shield in place. Monte Carlo codes were developed which calculated dose distributions for various electron radiation energies, hanging lens shield radii, shield heights above the eye, and beam spoiler configurations.more » Film dosimetry was used to benchmark the coding to ensure it was calculating relative dose accurately. Results: The Monte Carlo dose calculations indicated that lateral and depth dose profiles are insensitive to changes in shield height and electron beam energy. Dose deposition was sensitive to shield radius and beam spoiler composition and height above the eye. Conclusion: The use of a single A/P electron beam to treat cancers of the eye while maintaining adequate lens sparing is feasible. Shield radius should be customized to have the same radius as the patient’s lens. A beam spoiler should be used if it is desired to substantially dose the eye tissues lying posterior to the lens in the shadow of the lens shield. The compromise between lens sparing and dose to diseased tissues surrounding the lens can be modulated by varying the beam spoiler thickness, spoiler material composition, and spoiler height above the eye. The sparing ratio is a metric that can be used to evaluate the compromise between lens sparing and dose to surrounding tissues. The higher the ratio, the more dose received by the tissues immediately posterior to the lens relative to the dose received by the lens.« less

Effect of inhomogeneity in a patient's body on the accuracy of the pencil beam algorithm in comparison to Monte Carlo

NASA Astrophysics Data System (ADS)

Yamashita, T.; Akagi, T.; Aso, T.; Kimura, A.; Sasaki, T.

2012-11-01

The pencil beam algorithm (PBA) is reasonably accurate and fast. It is, therefore, the primary method used in routine clinical treatment planning for proton radiotherapy; still, it needs to be validated for use in highly inhomogeneous regions. In our investigation of the effect of patient inhomogeneity, PBA was compared with Monte Carlo (MC). A software framework was developed for the MC simulation of radiotherapy based on Geant4. Anatomical sites selected for the comparison were the head/neck, liver, lung and pelvis region. The dose distributions calculated by the two methods in selected examples were compared, as well as a dose volume histogram (DVH) derived from the dose distributions. The comparison of the off-center ratio (OCR) at the iso-center showed good agreement between the PBA and MC, while discrepancies were seen around the distal fall-off regions. While MC showed a fine structure on the OCR in the distal fall-off region, the PBA showed smoother distribution. The fine structures in MC calculation appeared downstream of very low-density regions. Comparison of DVHs showed that most of the target volumes were similarly covered, while some OARs located around the distal region received a higher dose when calculated by MC than the PBA.

Calibration of CT Hounsfield units for proton therapy treatment planning: use of kilovoltage and megavoltage images and comparison of parameterized methods

NASA Astrophysics Data System (ADS)

De Marzi, L.; Lesven, C.; Ferrand, R.; Sage, J.; Boulé, T.; Mazal, A.

2013-06-01

Proton beam range is of major concern, in particular, when images used for dose computations are artifacted (for example in patients with surgically treated bone tumors). We investigated several conditions and methods for determination of computed tomography Hounsfield unit (CT-HU) calibration curves, using two different conversion schemes. A stoichiometric methodology was used on either kilovoltage (kV) or megavoltage (MV) CT images and the accuracy of the calibration methods was evaluated. We then studied the effects of metal artifacts on proton dose distributions using metallic implants in rigid phantom mimicking clinical conditions. MV-CT images were used to evaluate relative proton stopping power in certain high density implants, and a methodology is proposed for accurate delineation and dose calculation, using a combined set of kV- and MV-CT images. Our results show good agreement between measurements and dose calculations or relative proton stopping power determination (<5%). The results also show that range uncertainty increases when only kV-CT images are used or when no correction is made on artifacted images. However, differences between treatment plans calculated on corrected kV-CT data and MV-CT data remained insignificant in the investigated patient case, even with streak artifacts and volume effects that reduce the accuracy of manual corrections.

Solid state TL detectors for in vivo dosimetry in brachytherapy.

PubMed

Gambarini, G; Borroni, M; Grisotto, S; Maucione, A; Cerrotta, A; Fallai, C; Carrara, M

2012-12-01

In vivo dosimetry provides information about the actual dose delivered to the patient treated with radiotherapy and can be adopted within a routinary treatment quality assurance protocol. Aim of this study was to evaluate the feasibility of performing in vivo rectal dosimetry by placing thermoluminescence detectors directly on the transrectal ultrasound probe adopted for on-line treatment planning of high dose rate brachytherapy boosts of prostate cancer patients. A suitable protocol for TLD calibration has been set up. In vivo measurements resulted to be in good agreement with the calculated doses, showing that the proposed method is feasible and returns accurate results. Copyright © 2012 Elsevier Ltd. All rights reserved.

Improved-resolution real-time skin-dose mapping for interventional fluoroscopic procedures

NASA Astrophysics Data System (ADS)

Rana, Vijay K.; Rudin, Stephen; Bednarek, Daniel R.

2014-03-01

We have developed a dose-tracking system (DTS) that provides a real-time display of the skin-dose distribution on a 3D patient graphic during fluoroscopic procedures. Radiation dose to individual points on the skin is calculated using exposure and geometry parameters from the digital bus on a Toshiba C-arm unit. To accurately define the distribution of dose, it is necessary to use a high-resolution patient graphic consisting of a large number of elements. In the original DTS version, the patient graphics were obtained from a library of population body scans which consisted of larger-sized triangular elements resulting in poor congruence between the graphic points and the x-ray beam boundary. To improve the resolution without impacting real-time performance, the number of calculations must be reduced and so we created software-designed human models and modified the DTS to read the graphic as a list of vertices of the triangular elements such that common vertices of adjacent triangles are listed once. Dose is calculated for each vertex point once instead of the number of times that a given vertex appears in multiple triangles. By reformatting the graphic file, we were able to subdivide the triangular elements by a factor of 64 times with an increase in the file size of only 1.3 times. This allows a much greater number of smaller triangular elements and improves resolution of the patient graphic without compromising the real-time performance of the DTS and also gives a smoother graphic display for better visualization of the dose distribution.

NOTE: MCDE: a new Monte Carlo dose engine for IMRT

NASA Astrophysics Data System (ADS)

Reynaert, N.; DeSmedt, B.; Coghe, M.; Paelinck, L.; Van Duyse, B.; DeGersem, W.; DeWagter, C.; DeNeve, W.; Thierens, H.

2004-07-01

A new accurate Monte Carlo code for IMRT dose computations, MCDE (Monte Carlo dose engine), is introduced. MCDE is based on BEAMnrc/DOSXYZnrc and consequently the accurate EGSnrc electron transport. DOSXYZnrc is reprogrammed as a component module for BEAMnrc. In this way both codes are interconnected elegantly, while maintaining the BEAM structure and only minimal changes to BEAMnrc.mortran are necessary. The treatment head of the Elekta SLiplus linear accelerator is modelled in detail. CT grids consisting of up to 200 slices of 512 × 512 voxels can be introduced and up to 100 beams can be handled simultaneously. The beams and CT data are imported from the treatment planning system GRATIS via a DICOM interface. To enable the handling of up to 50 × 106 voxels the system was programmed in Fortran95 to enable dynamic memory management. All region-dependent arrays (dose, statistics, transport arrays) were redefined. A scoring grid was introduced and superimposed on the geometry grid, to be able to limit the number of scoring voxels. The whole system uses approximately 200 MB of RAM and runs on a PC cluster consisting of 38 1.0 GHz processors. A set of in-house made scripts handle the parallellization and the centralization of the Monte Carlo calculations on a server. As an illustration of MCDE, a clinical example is discussed and compared with collapsed cone convolution calculations. At present, the system is still rather slow and is intended to be a tool for reliable verification of IMRT treatment planning in the case of the presence of tissue inhomogeneities such as air cavities.

SU-F-T-50: Evaluation of Monte Carlo Simulations Performance for Pediatric Brachytherapy Dosimetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chatzipapas, C; Kagadis, G; Papadimitroulas, P

Purpose: Pediatric tumors are generally treated with multi-modal procedures. Brachytherapy can be used with pediatric tumors, especially given that in this patient population low toxicity on normal tissues is critical as is the suppression of the probability for late malignancies. Our goal is to validate the GATE toolkit on realistic brachytherapy applications, and evaluate brachytherapy plans on pediatrics for accurate dosimetry on sensitive and critical organs of interest. Methods: The GATE Monte Carlo (MC) toolkit was used. Two High Dose Rate (HDR) 192Ir brachytherapy sources were simulated (Nucletron mHDR-v1 and Varian VS2000), and fully validated using the AAPM and ESTROmore » protocols. A realistic brachytherapy plan was also simulated using the XCAT anthropomorphic computational model .The simulated data were compared to the clinical dose points. Finally, a 14 years old girl with vaginal rhabdomyosarcoma was modelled based on clinical procedures for the calculation of the absorbed dose per organ. Results: The MC simulations resulted in accurate dosimetry in terms of dose rate constant (Λ), radial dose gL(r) and anisotropy function F(r,θ) for both sources.The simulations were executed using ∼1010 number of primaries resulting in statistical uncertainties lower than 2%.The differences between the theoretical values and the simulated ones ranged from 0.01% up to 3.3%, with the largest discrepancy (6%) being observed in the dose rate constant calculation.The simulated DVH using an adult female XCAT model was also compared to a clinical one resulting in differences smaller than 5%. Finally, a realistic pediatric brachytherapy simulation was performed to evaluate the absorbed dose per organ and to calculate DVH with respect to heterogeneities of the human anatomy. Conclusion: GATE is a reliable tool for brachytherapy simulations both for source modeling and for dosimetry in anthropomorphic voxelized models. Our project aims to evaluate a variety of pediatric brachytherapy schemes using a population of pediatric phantoms for several pathological cases. This study is part of a project that has received funding from the European Union Horizon2020 research and innovation programme under the MarieSklodowska-Curiegrantagreement.No691203.The results published in this study reflect only the authors view and the Research Executive Agency (REA) and the European Commission is not responsible for any use that may be madeof the information it contains.« less

The energy-dependent electron loss model: backscattering and application to heterogeneous slab media.

PubMed

Lee, Tae Kyu; Sandison, George A

2003-01-21

Electron backscattering has been incorporated into the energy-dependent electron loss (EL) model and the resulting algorithm is applied to predict dose deposition in slab heterogeneous media. This algorithm utilizes a reflection coefficient from the interface that is computed on the basis of Goudsmit-Saunderson theory and an average energy for the backscattered electrons based on Everhart's theory. Predictions of dose deposition in slab heterogeneous media are compared to the Monte Carlo based dose planning method (DPM) and a numerical discrete ordinates method (DOM). The slab media studied comprised water/Pb, water/Al, water/bone, water/bone/water, and water/lung/water, and incident electron beam energies of 10 MeV and 18 MeV. The predicted dose enhancement due to backscattering is accurate to within 3% of dose maximum even for lead as the backscattering medium. Dose discrepancies at large depths beyond the interface were as high as 5% of dose maximum and we speculate that this error may be attributed to the EL model assuming a Gaussian energy distribution for the electrons at depth. The computational cost is low compared to Monte Carlo simulations making the EL model attractive as a fast dose engine for dose optimization algorithms. The predictive power of the algorithm demonstrates that the small angle scattering restriction on the EL model can be overcome while retaining dose calculation accuracy and requiring only one free variable, chi, in the algorithm to be determined in advance of calculation.

The energy-dependent electron loss model: backscattering and application to heterogeneous slab media

NASA Astrophysics Data System (ADS)

Lee, Tae Kyu; Sandison, George A.

2003-01-01

Electron backscattering has been incorporated into the energy-dependent electron loss (EL) model and the resulting algorithm is applied to predict dose deposition in slab heterogeneous media. This algorithm utilizes a reflection coefficient from the interface that is computed on the basis of Goudsmit-Saunderson theory and an average energy for the backscattered electrons based on Everhart's theory. Predictions of dose deposition in slab heterogeneous media are compared to the Monte Carlo based dose planning method (DPM) and a numerical discrete ordinates method (DOM). The slab media studied comprised water/Pb, water/Al, water/bone, water/bone/water, and water/lung/water, and incident electron beam energies of 10 MeV and 18 MeV. The predicted dose enhancement due to backscattering is accurate to within 3% of dose maximum even for lead as the backscattering medium. Dose discrepancies at large depths beyond the interface were as high as 5% of dose maximum and we speculate that this error may be attributed to the EL model assuming a Gaussian energy distribution for the electrons at depth. The computational cost is low compared to Monte Carlo simulations making the EL model attractive as a fast dose engine for dose optimization algorithms. The predictive power of the algorithm demonstrates that the small angle scattering restriction on the EL model can be overcome while retaining dose calculation accuracy and requiring only one free variable, χ, in the algorithm to be determined in advance of calculation.

TH-EF-BRB-10: Dosimetric Validation of a Trajectory Based Cranial SRS Treatment Technique On a Varian TrueBeam Linac

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilson, B; Vancouver Cancer Centre, Vancouver, BC; Gete, E

2016-06-15

Purpose: This work investigates the dosimetric accuracy of a trajectory based delivery technique in which an optimized radiation beam is delivered along a Couch-Gantry trajectory that is formed by simultaneous rotation of the linac gantry and the treatment couch. Methods: Nine trajectory based cranial SRS treatment plans were created using in-house optimization software. The plans were calculated for delivery on the TrueBeam STx linac with 6MV photon beam. Dose optimization was performed along a user-defined trajectory using MLC modulation, dose rate modulation and jaw tracking. The pre-defined trajectory chosen for this study is formed by a couch rotation through itsmore » full range of 180 degrees while the gantry makes four partial arc sweeps which are 170 degrees each. For final dose calculation, the trajectory based plans were exported to the Varian Eclipse Treatment Planning System. The plans were calculated on a homogeneous cube phantom measuring 18.2×18.2×18.2 cm3 with the analytical anisotropic algorithm (AAA) using a 1mm3 calculation voxel. The plans were delivered on the TrueBeam linac via the developer’s mode. Point dose measurements were performed on 9 patients with the IBA CC01 mini-chamber with a sensitive volume of 0.01 cc. Gafchromic film measurements along the sagittal and coronal planes were performed on three of the 9 treatment plans. Point dose values were compared with ion chamber measurements. Gamma analysis comparing film measurement and AAA calculations was performed using FilmQA Pro. Results: The AAA calculations and measurements were in good agreement. The point dose difference between AAA and ion chamber measurements were within 2.2%. Gamma analysis test pass rates (2%, 2mm passing criteria) for the Gafchromic film measurements were >95%. Conclusion: We have successfully tested TrueBeam’s ability to deliver accurate trajectory based treatments involving simultaneous gantry and couch rotation with MLC and dose rate modulation along the trajectory.« less

SU-D-206-05: A Critical Look at CBCT-Based Dose Calculation Accuracy as It Is Applied to Adaptive Radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bejarano Buele, A; Sperling, N; Parsai, E

2016-06-15

Purpose: Cone-beam CTs (CBCT) obtained from On-Board Imaging Devices (OBI) are increasingly being used for dose calculation purposes in adaptive radiotherapy. Patient and target morphology are monitored and the treatment plan is updated using CBCT. Due to the difference in image acquisition parameters, dose calculated in a CBCT can differ from planned dose. We evaluate the difference between dose calculation in kV CBCT and simulation CT, and the effect of HU-density tables in dose discrepancies Methods: HU values for various materials were obtained using a Catphan 504 phantom for a simulator CT (CTSIM) and two different OBI systems using threemore » imaging protocols: Head, Thorax and Pelvis. HU-density tables were created in the TPS for each OBI image protocol. Treatment plans were made on each Catphan 504 dataset and on the head, thorax and pelvis sections of an anthropomorphic phantom, with and without the respective HU-density table. DVH information was compared among OBI systems and planning CT. Results: Dose calculations carried on the Catphan 504 CBCTs, with and without the respective CT-density table, had a maximum difference of −0.65% from the values on the planning CT. The use of the respective HU-density table decreased the percent differences from planned values by half in most of the protocols. For the anthropomorphic phantom datasets, the use of the correct HU-density table reduced differences by 0.89% on OBI1 and 0.59% on OBI2 for the head, 0.49% on OBI1 for the thorax, and 0.25% on OBI2 for the pelvis. Differences from planned values without HU-density correction ranged from 3.13% (OBI1, thorax) to 0.30% (OBI2, thorax). Conclusion: CT-density tables in the TPS yield acceptable differences when used in partly homogeneous medium. Further corrections are needed when the medium contains pronounced density differences for accurate CBCT calculation. Current difference range (1–3%) can be clinically acceptable.« less

SU-G-BRC-16: Theory and Clinical Implications of the Constant Dosimetric Leaf Gap (DLG) Approximation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumaraswamy, L; Xu, Z; Podgorsak, M

Purpose: Commercial dose calculation algorithms incorporate a single DLG value for a given beam energy that is applied across an entire treatment field. However, the physical processes associated with beam generation and dose delivery suggest that the DLG is not constant. The aim of this study is to evaluate the variation of DLG among all leaf pairs, to quantify how this variation impacts delivered dose, and to establish a novel method to correct dose distributions calculated using the approximation of constant DLG. Methods: A 2D diode array was used to measure the DLG for all 60 leaf pairs at severalmore » points along each leaf pair travel direction. This approach was validated by comparison to DLG values measured at select points using a 0.6 cc ion chamber with the standard formalism. In-house software was developed to enable incorporation of position dependent DLG values into dose distribution optimization and calculation. The accuracy of beam delivery of both the corrected and uncorrected treatment plans was studied through gamma pass rate evaluation. A comparison of DVH statistics in corrected and uncorrected treatment plans was made. Results: The outer 20 MLC leaf pairs (1.0 cm width) have DLG values that are 0.32 mm (mean) to 0.65 mm (maximum) lower than the central leaf-pair. VMAT plans using a large number of 1 cm wide leaves were more accurately delivered (gamma pass rate increased by 5%) and dose coverage was higher (D100 increased by 3%) when the 2D DLG was modeled. Conclusion: Using a constant DLG value for a given beam energy will result in dose optimization, dose calculation and treatment delivery inaccuracies that become significant for treatment plans with high modulation complexity scores delivered with 1 cm wide leaves.« less

Developing a Treatment Planning Software Based on TG-43U1 Formalism for Cs-137 LDR Brachytherapy.

PubMed

Sina, Sedigheh; Faghihi, Reza; Soleimani Meigooni, Ali; Siavashpour, Zahra; Mosleh-Shirazi, Mohammad Amin

2013-08-01

The old Treatment Planning Systems (TPSs) used for intracavitary brachytherapy with Cs-137 Selectron source utilize traditional dose calculation methods, considering each source as a point source. Using such methods introduces significant errors in dose estimation. As of 1995, TG-43 is used as the main dose calculation formalism in treatment TPSs. The purpose of this study is to design and establish a treatment planning software for Cs-137 Solectron brachytherapy source, based on TG-43U1 formalism by applying the effects of the applicator and dummy spacers. Two softwares used for treatment planning of Cs-137 sources in Iran (STPS and PLATO), are based on old formalisms. The purpose of this work is to establish and develop a TPS for Selectron source based on TG-43 formalism. In this planning system, the dosimetry parameters of each pellet in different places inside applicators were obtained by MCNP4c code. Then the dose distribution around every combination of active and inactive pellets was obtained by summing the doses. The accuracy of this algorithm was checked by comparing its results for special combination of active and inactive pellets with MC simulations. Finally, the uncertainty of old dose calculation formalism was investigated by comparing the results of STPS and PLATO softwares with those obtained by the new algorithm. For a typical arrangement of 10 active pellets in the applicator, the percentage difference between doses obtained by the new algorithm at 1cm distance from the tip of the applicator and those obtained by old formalisms is about 30%, while the difference between the results of MCNP and the new algorithm is less than 5%. According to the results, the old dosimetry formalisms, overestimate the dose especially towards the applicator's tip. While the TG-43U1 based software perform the calculations more accurately.

SU-F-T-81: Treating Nose Skin Using Energy and Intensity Modulated Electron Beams with Monte Carlo Based Dose Calculation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, L; Fan, J; Eldib, A

Purpose: Treating nose skin with an electron beam is of a substantial challenge due to uneven nose surfaces and tissue heterogeneity, and consequently could have a great uncertainty of dose accuracy on the target. This work explored the method using Monte Carlo (MC)-based energy and intensity modulated electron radiotherapy (MERT), which would be delivered with a photon MLC in a standard medical linac (Artiste). Methods: The traditional treatment on the nose skin involves the usage of a bolus, often with a single energy electron beam. This work avoided using the bolus, and utilized mixed energies of electron beams. An in-housemore » developed Monte Carlo (MC)-based dose calculation/optimization planning system was employed for treatment planning. Phase space data (6, 9, 12 and 15 MeV) were used as an input source for MC dose calculations for the linac. To reduce the scatter-caused penumbra, a short SSD (61 cm) was used. A clinical case of the nose skin, which was previously treated with a single 9 MeV electron beam, was replanned with the MERT method. The resultant dose distributions were compared with the plan previously clinically used. The dose volume histogram of the MERT plan is calculated to examine the coverage of the planning target volume (PTV) and critical structure doses. Results: The target coverage and conformality in the MERT plan are improved as compared to the conventional plan. The MERT can provide more sufficient target coverage and less normal tissue dose underneath the nose skin. Conclusion: Compared to the conventional treatment technique, using MERT for the nose skin treatment has shown the dosimetric advantages in the PTV coverage and conformality. In addition, this technique eliminates the necessity of the cutout and bolus, which makes the treatment more efficient and accurate.« less

SU-D-BRC-01: An Automatic Beam Model Commissioning Method for Monte Carlo Simulations in Pencil-Beam Scanning Proton Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qin, N; Shen, C; Tian, Z

Purpose: Monte Carlo (MC) simulation is typically regarded as the most accurate dose calculation method for proton therapy. Yet for real clinical cases, the overall accuracy also depends on that of the MC beam model. Commissioning a beam model to faithfully represent a real beam requires finely tuning a set of model parameters, which could be tedious given the large number of pencil beams to commmission. This abstract reports an automatic beam-model commissioning method for pencil-beam scanning proton therapy via an optimization approach. Methods: We modeled a real pencil beam with energy and spatial spread following Gaussian distributions. Mean energy,more » and energy and spatial spread are model parameters. To commission against a real beam, we first performed MC simulations to calculate dose distributions of a set of ideal (monoenergetic, zero-size) pencil beams. Dose distribution for a real pencil beam is hence linear superposition of doses for those ideal pencil beams with weights in the Gaussian form. We formulated the commissioning task as an optimization problem, such that the calculated central axis depth dose and lateral profiles at several depths match corresponding measurements. An iterative algorithm combining conjugate gradient method and parameter fitting was employed to solve the optimization problem. We validated our method in simulation studies. Results: We calculated dose distributions for three real pencil beams with nominal energies 83, 147 and 199 MeV using realistic beam parameters. These data were regarded as measurements and used for commission. After commissioning, average difference in energy and beam spread between determined values and ground truth were 4.6% and 0.2%. With the commissioned model, we recomputed dose. Mean dose differences from measurements were 0.64%, 0.20% and 0.25%. Conclusion: The developed automatic MC beam-model commissioning method for pencil-beam scanning proton therapy can determine beam model parameters with satisfactory accuracy.« less

Development of 1-year-old computational phantom and calculation of organ doses during CT scans using Monte Carlo simulation.

PubMed

Pan, Yuxi; Qiu, Rui; Gao, Linfeng; Ge, Chaoyong; Zheng, Junzheng; Xie, Wenzhang; Li, Junli

2014-09-21

With the rapidly growing number of CT examinations, the consequential radiation risk has aroused more and more attention. The average dose in each organ during CT scans can only be obtained by using Monte Carlo simulation with computational phantoms. Since children tend to have higher radiation sensitivity than adults, the radiation dose of pediatric CT examinations requires special attention and needs to be assessed accurately. So far, studies on organ doses from CT exposures for pediatric patients are still limited. In this work, a 1-year-old computational phantom was constructed. The body contour was obtained from the CT images of a 1-year-old physical phantom and the internal organs were deformed from an existing Chinese reference adult phantom. To ensure the organ locations in the 1-year-old computational phantom were consistent with those of the physical phantom, the organ locations in 1-year-old computational phantom were manually adjusted one by one, and the organ masses were adjusted to the corresponding Chinese reference values. Moreover, a CT scanner model was developed using the Monte Carlo technique and the 1-year-old computational phantom was applied to estimate organ doses derived from simulated CT exposures. As a result, a database including doses to 36 organs and tissues from 47 single axial scans was built. It has been verified by calculation that doses of axial scans are close to those of helical scans; therefore, this database could be applied to helical scans as well. Organ doses were calculated using the database and compared with those obtained from the measurements made in the physical phantom for helical scans. The differences between simulation and measurement were less than 25% for all organs. The result shows that the 1-year-old phantom developed in this work can be used to calculate organ doses in CT exposures, and the dose database provides a method for the estimation of 1-year-old patient doses in a variety of CT examinations.

Development of 1-year-old computational phantom and calculation of organ doses during CT scans using Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Pan, Yuxi; Qiu, Rui; Gao, Linfeng; Ge, Chaoyong; Zheng, Junzheng; Xie, Wenzhang; Li, Junli

2014-09-01

With the rapidly growing number of CT examinations, the consequential radiation risk has aroused more and more attention. The average dose in each organ during CT scans can only be obtained by using Monte Carlo simulation with computational phantoms. Since children tend to have higher radiation sensitivity than adults, the radiation dose of pediatric CT examinations requires special attention and needs to be assessed accurately. So far, studies on organ doses from CT exposures for pediatric patients are still limited. In this work, a 1-year-old computational phantom was constructed. The body contour was obtained from the CT images of a 1-year-old physical phantom and the internal organs were deformed from an existing Chinese reference adult phantom. To ensure the organ locations in the 1-year-old computational phantom were consistent with those of the physical phantom, the organ locations in 1-year-old computational phantom were manually adjusted one by one, and the organ masses were adjusted to the corresponding Chinese reference values. Moreover, a CT scanner model was developed using the Monte Carlo technique and the 1-year-old computational phantom was applied to estimate organ doses derived from simulated CT exposures. As a result, a database including doses to 36 organs and tissues from 47 single axial scans was built. It has been verified by calculation that doses of axial scans are close to those of helical scans; therefore, this database could be applied to helical scans as well. Organ doses were calculated using the database and compared with those obtained from the measurements made in the physical phantom for helical scans. The differences between simulation and measurement were less than 25% for all organs. The result shows that the 1-year-old phantom developed in this work can be used to calculate organ doses in CT exposures, and the dose database provides a method for the estimation of 1-year-old patient doses in a variety of CT examinations.

Range-Finding Risk Assessment of Inhalation Exposure to Nanodiamonds in a Laboratory Environment

PubMed Central

Koivisto, Antti J.; Palomäki, Jaana E.; Viitanen, Anna-Kaisa; Siivola, Kirsi M.; Koponen, Ismo K.; Yu, Mingzhou; Kanerva, Tomi S.; Norppa, Hannu; Alenius, Harri T.; Hussein, Tareq; Savolainen, Kai M.; Hämeri, Kaarle J.

2014-01-01

This study considers fundamental methods in occupational risk assessment of exposure to airborne engineered nanomaterials. We discuss characterization of particle emissions, exposure assessment, hazard assessment with in vitro studies, and risk range characterization using calculated inhaled doses and dose-response translated to humans from in vitro studies. Here, the methods were utilized to assess workers’ risk range of inhalation exposure to nanodiamonds (NDs) during handling and sieving of ND powder. NDs were agglomerated to over 500 nm particles, and mean exposure levels of different work tasks varied from 0.24 to 4.96 µg·m−3 (0.08 to 0.74 cm−3). In vitro-experiments suggested that ND exposure may cause a risk for activation of inflammatory cascade. However, risk range characterization based on in vitro dose-response was not performed because accurate assessment of delivered (settled) dose on the cells was not possible. Comparison of ND exposure with common pollutants revealed that ND exposure was below 5 μg·m−3, which is one of the proposed exposure limits for diesel particulate matter, and the workers’ calculated dose of NDs during the measurement day was 74 ng which corresponded to 0.02% of the modeled daily (24 h) dose of submicrometer urban air particles. PMID:24840353

Direct dose mapping versus energy/mass transfer mapping for 4D dose accumulation: fundamental differences and dosimetric consequences.

PubMed

Li, Haisen S; Zhong, Hualiang; Kim, Jinkoo; Glide-Hurst, Carri; Gulam, Misbah; Nurushev, Teamour S; Chetty, Indrin J

2014-01-06

The direct dose mapping (DDM) and energy/mass transfer (EMT) mapping are two essential algorithms for accumulating the dose from different anatomic phases to the reference phase when there is organ motion or tumor/tissue deformation during the delivery of radiation therapy. DDM is based on interpolation of the dose values from one dose grid to another and thus lacks rigor in defining the dose when there are multiple dose values mapped to one dose voxel in the reference phase due to tissue/tumor deformation. On the other hand, EMT counts the total energy and mass transferred to each voxel in the reference phase and calculates the dose by dividing the energy by mass. Therefore it is based on fundamentally sound physics principles. In this study, we implemented the two algorithms and integrated them within the Eclipse treatment planning system. We then compared the clinical dosimetric difference between the two algorithms for ten lung cancer patients receiving stereotactic radiosurgery treatment, by accumulating the delivered dose to the end-of-exhale (EE) phase. Specifically, the respiratory period was divided into ten phases and the dose to each phase was calculated and mapped to the EE phase and then accumulated. The displacement vector field generated by Demons-based registration of the source and reference images was used to transfer the dose and energy. The DDM and EMT algorithms produced noticeably different cumulative dose in the regions with sharp mass density variations and/or high dose gradients. For the planning target volume (PTV) and internal target volume (ITV) minimum dose, the difference was up to 11% and 4% respectively. This suggests that DDM might not be adequate for obtaining an accurate dose distribution of the cumulative plan, instead, EMT should be considered.

Direct dose mapping versus energy/mass transfer mapping for 4D dose accumulation: fundamental differences and dosimetric consequences

NASA Astrophysics Data System (ADS)

Li, Haisen S.; Zhong, Hualiang; Kim, Jinkoo; Glide-Hurst, Carri; Gulam, Misbah; Nurushev, Teamour S.; Chetty, Indrin J.

2014-01-01

The direct dose mapping (DDM) and energy/mass transfer (EMT) mapping are two essential algorithms for accumulating the dose from different anatomic phases to the reference phase when there is organ motion or tumor/tissue deformation during the delivery of radiation therapy. DDM is based on interpolation of the dose values from one dose grid to another and thus lacks rigor in defining the dose when there are multiple dose values mapped to one dose voxel in the reference phase due to tissue/tumor deformation. On the other hand, EMT counts the total energy and mass transferred to each voxel in the reference phase and calculates the dose by dividing the energy by mass. Therefore it is based on fundamentally sound physics principles. In this study, we implemented the two algorithms and integrated them within the Eclipse treatment planning system. We then compared the clinical dosimetric difference between the two algorithms for ten lung cancer patients receiving stereotactic radiosurgery treatment, by accumulating the delivered dose to the end-of-exhale (EE) phase. Specifically, the respiratory period was divided into ten phases and the dose to each phase was calculated and mapped to the EE phase and then accumulated. The displacement vector field generated by Demons-based registration of the source and reference images was used to transfer the dose and energy. The DDM and EMT algorithms produced noticeably different cumulative dose in the regions with sharp mass density variations and/or high dose gradients. For the planning target volume (PTV) and internal target volume (ITV) minimum dose, the difference was up to 11% and 4% respectively. This suggests that DDM might not be adequate for obtaining an accurate dose distribution of the cumulative plan, instead, EMT should be considered.

TK Modeler version 1.0, a Microsoft® Excel®-based modeling software for the prediction of diurnal blood/plasma concentration for toxicokinetic use.

PubMed

McCoy, Alene T; Bartels, Michael J; Rick, David L; Saghir, Shakil A

2012-07-01

TK Modeler 1.0 is a Microsoft® Excel®-based pharmacokinetic (PK) modeling program created to aid in the design of toxicokinetic (TK) studies. TK Modeler 1.0 predicts the diurnal blood/plasma concentrations of a test material after single, multiple bolus or dietary dosing using known PK information. Fluctuations in blood/plasma concentrations based on test material kinetics are calculated using one- or two-compartment PK model equations and the principle of superposition. This information can be utilized for the determination of appropriate dosing regimens based on reaching a specific desired C(max), maintaining steady-state blood/plasma concentrations, or other exposure target. This program can also aid in the selection of sampling times for accurate calculation of AUC(24h) (diurnal area under the blood concentration time curve) using sparse-sampling methodologies (one, two or three samples). This paper describes the construction, use and validation of TK Modeler. TK Modeler accurately predicted blood/plasma concentrations of test materials and provided optimal sampling times for the calculation of AUC(24h) with improved accuracy using sparse-sampling methods. TK Modeler is therefore a validated, unique and simple modeling program that can aid in the design of toxicokinetic studies. Copyright © 2012 Elsevier Inc. All rights reserved.

Absorbed dose in target cell nuclei and dose conversion coefficient of radon progeny in the human lung.

PubMed

Nikezic, D; Lau, B M F; Stevanovic, N; Yu, K N

2006-01-01

To calculate the absorbed dose in the human lung due to inhaled radon progeny, ICRP focussed on the layers containing the target cells, i.e., the basal and secretory cells. Such an approach did not consider details of the sensitive cells in the layers. The present work uses the microdosimetric approach and determines the absorbed alpha-particle energy in non-spherical nuclei of target cells (basal and secretory cells). The absorbed energy for alpha particles emitted by radon progeny in the human respiratory tract was calculated in basal- and secretory-cell nuclei, assuming conical and ellipsoidal forms for these cells. Distributions of specific energy for different combinations of alpha-particle sources, energies and targets are calculated and shown. The dose conversion coefficient for radon progeny is reduced for about 2mSv/WLM when conical and ellipsoidal cell nuclei are considered instead of the layers. While changes in the geometry of secretory-cell nuclei do not have significant effects on their absorbed dose, changes from spherical to conical basal-cell nuclei have significantly reduced their absorbed dose from approximately 4 to approximately 3mGy/WLM. This is expected because basal cells are situated close to the end of the range of 6MeV alpha particles. This also underlines the significance of better and more precise information on targets in the T-B tree. A further change in the dose conversion coefficient can be achieved if a different weighting scheme is adopted for the doses for the cells. The results demonstrate the necessity for better information on the target cells for more accurate dosimetry for radon progeny.

A preliminary study of in-house Monte Carlo simulations: an integrated Monte Carlo verification system.

PubMed

Mukumoto, Nobutaka; Tsujii, Katsutomo; Saito, Susumu; Yasunaga, Masayoshi; Takegawa, Hideki; Yamamoto, Tokihiro; Numasaki, Hodaka; Teshima, Teruki

2009-10-01

To develop an infrastructure for the integrated Monte Carlo verification system (MCVS) to verify the accuracy of conventional dose calculations, which often fail to accurately predict dose distributions, mainly due to inhomogeneities in the patient's anatomy, for example, in lung and bone. The MCVS consists of the graphical user interface (GUI) based on a computational environment for radiotherapy research (CERR) with MATLAB language. The MCVS GUI acts as an interface between the MCVS and a commercial treatment planning system to import the treatment plan, create MC input files, and analyze MC output dose files. The MCVS consists of the EGSnrc MC codes, which include EGSnrc/BEAMnrc to simulate the treatment head and EGSnrc/DOSXYZnrc to calculate the dose distributions in the patient/phantom. In order to improve computation time without approximations, an in-house cluster system was constructed. The phase-space data of a 6-MV photon beam from a Varian Clinac unit was developed and used to establish several benchmarks under homogeneous conditions. The MC results agreed with the ionization chamber measurements to within 1%. The MCVS GUI could import and display the radiotherapy treatment plan created by the MC method and various treatment planning systems, such as RTOG and DICOM-RT formats. Dose distributions could be analyzed by using dose profiles and dose volume histograms and compared on the same platform. With the cluster system, calculation time was improved in line with the increase in the number of central processing units (CPUs) at a computation efficiency of more than 98%. Development of the MCVS was successful for performing MC simulations and analyzing dose distributions.

Dosimetric and radiobiological comparison of TG-43 and Monte Carlo calculations in 192Ir breast brachytherapy applications.

PubMed

Peppa, V; Pappas, E P; Karaiskos, P; Major, T; Polgár, C; Papagiannis, P

2016-10-01

To investigate the clinical significance of introducing model based dose calculation algorithms (MBDCAs) as an alternative to TG-43 in 192 Ir interstitial breast brachytherapy. A 57 patient cohort was used in a retrospective comparison between TG-43 based dosimetry data exported from a treatment planning system and Monte Carlo (MC) dosimetry performed using MCNP v. 6.1 with plan and anatomy information in DICOM-RT format. Comparison was performed for the target, ipsilateral lung, heart, skin, breast and ribs, using dose distributions, dose-volume histograms (DVH) and plan quality indices clinically used for plan evaluation, as well as radiobiological parameters. TG-43 overestimation of target DVH parameters is statistically significant but small (less than 2% for the target coverage indices and 4% for homogeneity indices, on average). Significant dose differences (>5%) were observed close to the skin and at relatively large distances from the implant leading to a TG-43 dose overestimation for the organs at risk. These differences correspond to low dose regions (<50% of the prescribed dose), being less than 2% of the prescribed dose. Detected dosimetric differences did not induce clinically significant differences in calculated tumor control probabilities (mean absolute difference <0.2%) and normal tissue complication probabilities. While TG-43 shows a statistically significant overestimation of most indices used for plan evaluation, differences are small and therefore not clinically significant. Improved MBDCA dosimetry could be important for re-irradiation, technique inter-comparison and/or the assessment of secondary cancer induction risk, where accurate dosimetry in the whole patient anatomy is of the essence. Copyright © 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Poster — Thur Eve — 33: The Influence of a Modeled Treatment Couch on Dose Distributions During IMRT and RapidArc Treatment Delivery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aldosary, Ghada; Nobah, Ahmad; Al-Zorkani, Faisal

2014-08-15

Treatment couches have been known to perturb dose delivery in patients. This effect is most pronounced in techniques such as IMRT and RapidArc. Although modern treatment planning systems (TPS) include data for a “default” treatment couch, actual couches are not manufactured identically. Thus, variations in their Hounsfield Unit (HU) values may exist. This study demonstrates a practical and simple method of acquiring reliable HU data for any treatment couch. We also investigate the effects of both the default and modeled treatment couches on absorbed dose. Experimental verifications show that by neglecting to incorporate the treatment couch in the TPS, dosemore » differences of up to 9.5% and 7.3% were present for 4 MV and 10 MV photon beams, respectively. Furthermore, a clinical study based on a cohort of 20 RapidArc and IMRT (brain, pelvis and abdominal) cases is performed. 2D dose distributions show that without the couch in the planning phase, differences ≤ 4.6% and 5.9% for RapidArc and IMRT cases are present for the same cases that the default couch was added to. Additionally, in comparison to the default couch, employing the modeled couch in the calculation process influences dose distributions by ≤ 2.7% and 8% for RapidArc and IMRT cases, respectively. This result was found to be site specific; where an accurate couch proves to be preferable for IMRT brain plans. As such, adding the couch during dose calculation decreases dose calculation errors, and a precisely modeled treatment couch offers higher dose delivery accuracy for brain treatment using IMRT.« less

A Review of the “Bolus Guide,” A New Insulin Bolus Dosing Support Tool Based on Selection of Carbohydrate Ranges

PubMed Central

Pańkowska, Ewa

2010-01-01

In this issue of Journal of Diabetes Science and Technology, Shapira and colleagues present new concepts of carbohydrate load estimation in intensive insulin therapy. By using a mathematical model, they attempt to establish how accurately carbohydrate food content should be maintained in order to keep postprandial blood glucose levels in the recommended range. Their mathematical formula, the “bolus guide” (BG), is verified by simulating prandial insulin dosing and responding to proper blood glucose levels. Different variants such as insulin sensitivity factor, insulin-to-carbohydrate ratio, and target blood glucose were taken into this formula in establishing the calculated proper insulin dose. The new approach presented here estimates the carbohydrate content by rearranging the carbohydrate load instead of the simple point estimation that the current bolus calculators (BCs) use. Computerized estimations show that the BG directives, as compared to a BC, result in more glucose levels above 200 mg/dl and thus indicate less hypoglycemia readings. PMID:20663454

Computation of Cosmic Ray Ionization and Dose at Mars: a Comparison of HZETRN and Planetocosmics for Proton and Alpha Particles

NASA Technical Reports Server (NTRS)

Gronoff, Guillaume; Norman, Ryan B.; Mertens, Christopher J.

2014-01-01

The ability to evaluate the cosmic ray environment at Mars is of interest for future manned exploration. To support exploration, tools must be developed to accurately access the radiation environment in both free space and on planetary surfaces. The primary tool NASA uses to quantify radiation exposure behind shielding materials is the space radiation transport code, HZETRN. In order to build confidence in HZETRN, code benchmarking against Monte Carlo radiation transport codes is often used. This work compares the dose calculations at Mars by HZETRN and the Geant4 application Planetocosmics. The dose at ground and the energy deposited in the atmosphere by galactic cosmic ray protons and alpha particles has been calculated for the Curiosity landing conditions. In addition, this work has considered Solar Energetic Particle events, allowing for the comparison of varying input radiation environments. The results for protons and alpha particles show very good agreement between HZETRN and Planetocosmics.

SU-E-T-252: Developing a Pencil Beam Dose Calculation Algorithm for CyberKnife System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, B; Duke University Medical Center, Durham, NC; Liu, B

2015-06-15

Purpose: Currently there are two dose calculation algorithms available in the Cyberknife planning system: ray-tracing and Monte Carlo, which is either not accurate or time-consuming for irregular field shaped by the MLC that was recently introduced. The purpose of this study is to develop a fast and accurate pencil beam dose calculation algorithm which can handle irregular field. Methods: A pencil beam dose calculation algorithm widely used in Linac system is modified. The algorithm models both primary (short range) and scatter (long range) components with a single input parameter: TPR{sub 20}/{sub 10}. The TPR{sub 20}/{sub 20}/{sub 10} value was firstmore » estimated to derive an initial set of pencil beam model parameters (PBMP). The agreement between predicted and measured TPRs for all cones were evaluated using the root mean square of the difference (RMSTPR), which was then minimized by adjusting PBMPs. PBMPs are further tuned to minimize OCR RMS (RMSocr) by focusing at the outfield region. Finally, an arbitrary intensity profile is optimized by minimizing RMSocr difference at infield region. To test model validity, the PBMPs were obtained by fitting to only a subset of cones (4) and applied to all cones (12) for evaluation. Results: With RMS values normalized to the dmax and all cones combined, the average RMSTPR at build-up and descending region is 2.3% and 0.4%, respectively. The RMSocr at infield, penumbra and outfield region is 1.5%, 7.8% and 0.6%, respectively. Average DTA in penumbra region is 0.5mm. There is no trend found in TPR or OCR agreement among cones or depths. Conclusion: We have developed a pencil beam algorithm for Cyberknife system. The prediction agrees well with commissioning data. Only a subset of measurements is needed to derive the model. Further improvements are needed for TPR buildup region and OCR penumbra. Experimental validations on MLC shaped irregular field needs to be performed. This work was partially supported by the National Natural Science Foundation of China (61171005) and the China Scholarship Council (CSC)« less

MO-FG-CAMPUS-TeP3-03: Calculation of Proton Pencil Beam Properties with Full Beamline Model in TOPAS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wulff, J; Abel, E

2016-06-15

Purpose: Introducing Monte Carlo based dose calculation algorithms into proton therapy planning systems (TPS) leads to improved accuracy. However accurate modelling of the proton pencil beam impinging the patient is necessary. Current approaches rely on measurement-driven reconstruction of phase-space and spectrum properties, typically constrained to analytical model functions. In this study a detailed Monte Carlo model of the complete cyclotron-based delivery system was created with the aim of providing more representative beam properties at treatment position. Methods: A model of the Varian Probeam proton system from the cyclotron exit to isocenter was constructed in the TOPAS Monte Carlo framework. Themore » beam evolution through apertures and magnetic elements was validated using Transport/Turtle calculations and additionally against measurements from the Probeam™ system at Scripps Proton Therapy Center (SPTC) in San Diego, CA. A voxelized water phantom at isocenter allowed for comparison of the dose-depth curve from the Probeam model with that of a corresponding Gaussian beam over the entire energy range (70–240 MeV). Measurements of relative beam fluence cross-profiles and depth-dose curves at and around isocenter were also compared to the MC results. Results: The simulated TOPAS beam envelope was found to agree with both the Transport/Turtle and measurements to within 5% for most of the beamline. The MC predicted energy spectrum at isocenter was found to deviate increasingly from Gaussian at energies below 160 MeV. The corresponding effects on the depth dose curve agreed well with measurements. Conclusion: Given the flexibility of TOPAS and available details of the delivery system, an accurate characterization of a proton pencil beam at isocenter is possible. Incorporation of the MC derived properties of the proton pencil beam can eliminate analytical approximations and ultimately increase treatment plan accuracy and quality. Both authors are employees of Varian Medical Systems.« less

Organ Doses Associated with Partial-Body Irradiation with 2.5% Bone Marrow Sparing of the Non-Human Primate: A Retrospective Study.

PubMed

Prado, C; MacVittie, T J; Bennett, A W; Kazi, A; Farese, A M; Prado, K

2017-12-01

A partial-body irradiation model with approximately 2.5% bone marrow sparing (PBI/BM2.5) was established to determine the radiation dose-response relationships for the prolonged and delayed multi-organ effects of acute radiation exposure. Historically, doses reported to the entire body were assumed to be equal to the prescribed dose at some defined calculation point, and the dose-response relationship for multi-organ injury has been defined relative to the prescribed dose being delivered at this point, e.g., to a point at mid-depth at the level of the xiphoid of the non-human primate (NHP). In this retrospective-dose study, the true distribution of dose within the major organs of the NHP was evaluated, and these doses were related to that at the traditional dose-prescription point. Male rhesus macaques were exposed using the PBI/BM2.5 protocol to a prescribed dose of 10 Gy using 6-MV linear accelerator photons at a rate of 0.80 Gy/min. Point and organ doses were calculated for each NHP from computed tomography (CT) scans using heterogeneous density data. The prescribed dose of 10.0 Gy to a point at midline tissue assuming homogeneous media resulted in 10.28 Gy delivered to the prescription point when calculated using the heterogeneous CT volume of the NHP. Respective mean organ doses to the volumes of nine organs, including the heart, lung, bowel and kidney, were computed. With modern treatment planning systems, utilizing a three-dimensional reconstruction of the NHP's CT images to account for the variations in body shape and size, and using density corrections for each of the tissue types, bone, water, muscle and air, accurate determination of the differences in dose to the NHP can be achieved. Dose and volume statistics can be ascertained for any body structure or organ that has been defined using contouring tools in the planning system. Analysis of the dose delivered to critical organs relative to the total-body target dose will permit a more definitive analysis of organ-specific effects and their respective influence in multiple organ injury.

A novel method for interactive multi-objective dose-guided patient positioning

NASA Astrophysics Data System (ADS)

Haehnle, Jonas; Süss, Philipp; Landry, Guillaume; Teichert, Katrin; Hille, Lucas; Hofmaier, Jan; Nowak, Dimitri; Kamp, Florian; Reiner, Michael; Thieke, Christian; Ganswindt, Ute; Belka, Claus; Parodi, Katia; Küfer, Karl-Heinz; Kurz, Christopher

2017-01-01

In intensity-modulated radiation therapy (IMRT), 3D in-room imaging data is typically utilized for accurate patient alignment on the basis of anatomical landmarks. In the presence of non-rigid anatomical changes, it is often not obvious which patient position is most suitable. Thus, dose-guided patient alignment is an interesting approach to use available in-room imaging data for up-to-date dose calculation, aimed at finding the position that yields the optimal dose distribution. This contribution presents the first implementation of dose-guided patient alignment as multi-criteria optimization problem. User-defined clinical objectives are employed for setting up a multi-objective problem. Using pre-calculated dose distributions at a limited number of patient shifts and dose interpolation, a continuous space of Pareto-efficient patient shifts becomes accessible. Pareto sliders facilitate interactive browsing of the possible shifts with real-time dose display to the user. Dose interpolation accuracy is validated and the potential of multi-objective dose-guided positioning demonstrated for three head and neck (H&N) and three prostate cancer patients. Dose-guided positioning is compared to replanning for all cases. A delineated replanning CT served as surrogate for in-room imaging data. Dose interpolation accuracy was high. Using a 2 % dose difference criterion, a median pass-rate of 95.7% for H&N and 99.6% for prostate cases was determined in a comparison to exact dose calculations. For all patients, dose-guided positioning allowed to find a clinically preferable dose distribution compared to bony anatomy based alignment. For all H&N cases, mean dose to the spared parotid glands was below 26~\\text{Gy} (up to 27.5~\\text{Gy} with bony alignment) and clinical target volume (CTV) {{V}95 % } above 99.1% (compared to 95.1%). For all prostate patients, CTV {{V}95 % } was above 98.9% (compared to 88.5%) and {{V}50~\\text{Gy}} to the rectum below 50 % (compared to 56.1%). Replanning yielded improved results for the H&N cases. For the prostate cases, differences to dose-guided positioning were minor.

Monte Carlo dose distribution calculation at nuclear level for Auger-emitting radionuclide energies.

PubMed

Di Maria, S; Belchior, A; Romanets, Y; Paulo, A; Vaz, P

2018-05-01

The distribution of radiopharmaceuticals in tumor cells represents a fundamental aspect for a successful molecular targeted radiotherapy. It was largely demonstrated at microscopic level that only a fraction of cells in tumoral tissues incorporate the radiolabel. In addition, the distribution of the radionuclides at sub-cellular level, namely inside each nucleus, should also be investigated for accurate dosimetry estimation. The most used method to perform cellular dosimetry is the MIRD one, where S-values are able to estimate cellular absorbed doses for several electron energies, nucleus diameters, and considering homogeneous source distributions. However the radionuclide distribution inside nuclei can be also highly non-homogeneous. The aim of this study is to show in what extent a non-accurate cellular dosimetry could lead to misinterpretations of surviving cell fraction vs dose relationship; in this context, a dosimetric case study with 99m Tc is also presented. The state-of-art MCNP6 Monte Carlo simulation was used in order to model cell structures both in MIRD geometry (MG) and MIRD modified geometries (MMG), where also entire mitotic chromosome volumes were considered (each structure was modeled as liquid water material). In order to simulate a wide energy range of Auger emitting radionuclides, four mono energetic electron emissions were considered, namely 213eV, 6keV, 11keV and 20keV. A dosimetric calculation for 99m Tc undergoing inhomogeneous nuclear internalization was also performed. After a successful validation step between MIRD and our computed S-values for three Auger-emitting radionuclides ( 99m Tc, 125 I and 64 Cu), absorbed dose results showed that the standard MG could differ from the MMG from one to three orders of magnitude. These results were also confirmed by considering the 99m Tc spectrum emission (Auger and internal conversion electrons). Moreover, considering an inhomogeneous radionuclide distribution, the average electron energy that maximizes the absorbed dose was found to be different for MG and MMG. The modeling of realistic radionuclide localization inside cells, including a inhomogeneous nuclear distribution, revealed that i) a strong bias in surviving cell fraction vs dose relationships (taking to different radiobiological models) can arise; ii) the alternative models might contribute to a more accurate prediction of the radiobiological effects inherent to more specific molecular targeted radiotherapy strategies. Copyright © 2018 Elsevier Ltd. All rights reserved.

TU-H-CAMPUS-IeP1-03: Comparison of Monte Carlo Simulation and Conversion Factor Based Method On Estimation of Effective Dose in Pediatric Patients Undergoing Interventional Cardiac Procedures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leung, K; Wong, M; Ng, Y

Purpose: Interventional cardiac procedures utilize frequent fluoroscopy and cineangiography, which impose considerable radiation risk to patients, especially pediatric patients. Accurate calculation of effective dose is important in order to estimate cancer risk over the rest of their lifetime. This study evaluates the difference in effective dose calculated by Monte Carlo simulation with those estimated by locally-derived conversion factors (CF-local) and by commonly quoted conversion factors from Karambatsakidou et al (CF-K). Methods: Effective dose (E),of 12 pediatric patients, age between 2.5–19 years old, who had undergone interventional cardiac procedures, were calculated using PCXMC-2.0 software. Tube spectrum, irradiation geometry, exposure parameters andmore » dose-area product (DAP) of each projection were included in the software calculation. Effective doses for each patient were also estimated by two Methods: 1) CF-local: conversion factor derived locally by generalizing results of 12 patients, multiplied by DAP of each patient gives E-local. 2) CF-K: selected factor from above-mentioned literature, multiplied by DAP of each patient gives E-K. Results: Mean of E, E-local and E-K were 16.01 mSv, 16.80 mSv and 22.25 mSv respectively. A deviation of −29.35% to +34.85% between E and E-local, while a greater deviation of −28.96% to +60.86% between E and EK were observed. E-K overestimated the effective dose for patients at age 7.5–19. Conclusion: Effective dose obtained by conversion factors is simple and quick to estimate radiation risk of pediatric patients. This study showed that estimation by CF-local may bear an error of 35% when compared with Monte Carlo calculation. If using conversion factors derived by other studies may result in an even greater error, of up to 60%, due to factors that are not catered for in the estimation, including patient size, projection angles, exposure parameters, tube filtration, etc. Users must be aware of these potential inaccuracies when simple conversion method is employed.« less

SU-E-T-371: Evaluating the Convolution Algorithm of a Commercially Available Radiosurgery Irradiator Using a Novel Phantom

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cates, J; Drzymala, R

2015-06-15

Purpose: The purpose of this study was to develop and use a novel phantom to evaluate the accuracy and usefulness of the Leskell Gamma Plan convolution-based dose calculation algorithm compared with the current TMR10 algorithm. Methods: A novel phantom was designed to fit the Leskell Gamma Knife G Frame which could accommodate various materials in the form of one inch diameter, cylindrical plugs. The plugs were split axially to allow EBT2 film placement. Film measurements were made during two experiments. The first utilized plans generated on a homogeneous acrylic phantom setup using the TMR10 algorithm, with various materials inserted intomore » the phantom during film irradiation to assess the effect on delivered dose due to unplanned heterogeneities upstream in the beam path. The second experiment utilized plans made on CT scans of different heterogeneous setups, with one plan using the TMR10 dose calculation algorithm and the second using the convolution-based algorithm. Materials used to introduce heterogeneities included air, LDPE, polystyrene, Delrin, Teflon, and aluminum. Results: The data shows that, as would be expected, having heterogeneities in the beam path does induce dose delivery error when using the TMR10 algorithm, with the largest errors being due to the heterogeneities with electron densities most different from that of water, i.e. air, Teflon, and aluminum. Additionally, the Convolution algorithm did account for the heterogeneous material and provided a more accurate predicted dose, in extreme cases up to a 7–12% improvement over the TMR10 algorithm. The convolution algorithm expected dose was accurate to within 3% in all cases. Conclusion: This study proves that the convolution algorithm is an improvement over the TMR10 algorithm when heterogeneities are present. More work is needed to determine what the heterogeneity size/volume limits are where this improvement exists, and in what clinical and/or research cases this would be relevant.« less

Estimating age-based antiretroviral therapy costs for HIV-infected children in resource-limited settings based on World Health Organization weight-based dosing recommendations

PubMed Central

2014-01-01

Background Pediatric antiretroviral therapy (ART) has been shown to substantially reduce morbidity and mortality in HIV-infected infants and children. To accurately project program costs, analysts need accurate estimations of antiretroviral drug (ARV) costs for children. However, the costing of pediatric antiretroviral therapy is complicated by weight-based dosing recommendations which change as children grow. Methods We developed a step-by-step methodology for estimating the cost of pediatric ARV regimens for children ages 0–13 years old. The costing approach incorporates weight-based dosing recommendations to provide estimated ARV doses throughout childhood development. Published unit drug costs are then used to calculate average monthly drug costs. We compared our derived monthly ARV costs to published estimates to assess the accuracy of our methodology. Results The estimates of monthly ARV costs are provided for six commonly used first-line pediatric ARV regimens, considering three possible care scenarios. The costs derived in our analysis for children were fairly comparable to or slightly higher than available published ARV drug or regimen estimates. Conclusions The methodology described here can be used to provide an accurate estimation of pediatric ARV regimen costs for cost-effectiveness analysts to project the optimum packages of care for HIV-infected children, as well as for program administrators and budget analysts who wish to assess the feasibility of increasing pediatric ART availability in constrained budget environments. PMID:24885453

Investigation of photon beam models in heterogeneous media of modern radiotherapy.

PubMed

Ding, W; Johnston, P N; Wong, T P Y; Bubb, I F

2004-06-01

This study investigates the performance of photon beam models in dose calculations involving heterogeneous media in modern radiotherapy. Three dose calculation algorithms implemented in the CMS FOCUS treatment planning system have been assessed and validated using ionization chambers, thermoluminescent dosimeters (TLDs) and film. The algorithms include the multigrid superposition (MGS) algorithm, fast Fourier Transform Convolution (FFTC) algorithm and Clarkson algorithm. Heterogeneous phantoms used in the study consist of air cavities, lung analogue and an anthropomorphic phantom. Depth dose distributions along the central beam axis for 6 MV and 10 MV photon beams with field sizes of 5 cm x 5 cm and 10 cm x 10 cm were measured in the air cavity phantoms and lung analogue phantom. Point dose measurements were performed in the anthropomorphic phantom. Calculated results with three dose calculation algorithms were compared with measured results. In the air cavity phantoms, the maximum dose differences between the algorithms and the measurements were found at the distal surface of the air cavity with a 10 MV photon beam and a 5 cm x 5 cm field size. The differences were 3.8%. 24.9% and 27.7% for the MGS. FFTC and Clarkson algorithms. respectively. Experimental measurements of secondary electron build-up range beyond the air cavity showed an increase with decreasing field size, increasing energy and increasing air cavity thickness. The maximum dose differences in the lung analogue with 5 cm x 5 cm field size were found to be 0.3%. 4.9% and 6.9% for the MGS. FFTC and Clarkson algorithms with a 6 MV photon beam and 0.4%. 6.3% and 9.1% with a 10 MV photon beam, respectively. In the anthropomorphic phantom, the dose differences between calculations using the MGS algorithm and measurements with TLD rods were less than +/-4.5% for 6 MV and 10 MV photon beams with 10 cm x 10 cm field size and 6 MV photon beam with 5 cm x 5 cm field size, and within +/-7.5% for 10 MV with 5 cm x 5 cm field size, respectively. The FFTC and Clarkson algorithms overestimate doses at all dose points in the lung of the anthropomorphic phantom. In conclusion, the MGS is the most accurate dose calculation algorithm of investigated photon beam models. It is strongly recommended for implementation in modern radiotherapy with multiple small fields when heterogeneous media are in the treatment fields.

TH-E-BRE-07: Development of Dose Calculation Error Predictors for a Widely Implemented Clinical Algorithm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Egan, A; Laub, W

2014-06-15

Purpose: Several shortcomings of the current implementation of the analytic anisotropic algorithm (AAA) may lead to dose calculation errors in highly modulated treatments delivered to highly heterogeneous geometries. Here we introduce a set of dosimetric error predictors that can be applied to a clinical treatment plan and patient geometry in order to identify high risk plans. Once a problematic plan is identified, the treatment can be recalculated with more accurate algorithm in order to better assess its viability. Methods: Here we focus on three distinct sources dosimetric error in the AAA algorithm. First, due to a combination of discrepancies inmore » smallfield beam modeling as well as volume averaging effects, dose calculated through small MLC apertures can be underestimated, while that behind small MLC blocks can overestimated. Second, due the rectilinear scaling of the Monte Carlo generated pencil beam kernel, energy is not properly transported through heterogeneities near, but not impeding, the central axis of the beamlet. And third, AAA overestimates dose in regions very low density (< 0.2 g/cm{sup 3}). We have developed an algorithm to detect the location and magnitude of each scenario within the patient geometry, namely the field-size index (FSI), the heterogeneous scatter index (HSI), and the lowdensity index (LDI) respectively. Results: Error indices successfully identify deviations between AAA and Monte Carlo dose distributions in simple phantom geometries. Algorithms are currently implemented in the MATLAB computing environment and are able to run on a typical RapidArc head and neck geometry in less than an hour. Conclusion: Because these error indices successfully identify each type of error in contrived cases, with sufficient benchmarking, this method can be developed into a clinical tool that may be able to help estimate AAA dose calculation errors and when it might be advisable to use Monte Carlo calculations.« less

Calculated and TLD-based absorbed dose estimates for I-131-labeled 3F8 monoclonal antibody in a human neuroblastoma xenograft nude mouse model.

PubMed

Ugur, O; Scott, A M; Kostakoglu, L; Hui, T E; Masterson, M E; Febo, R; Sgouros, G; Rosa, E; Mehta, B M; Fisher, D R

1995-01-01

Preclinical evaluation of the therapeutic potential of radiolabeled antibodies is commonly performed in a xenografted nude mouse model. To assess therapeutic efficacy it is important to estimate the absorbed dose to the tumor and normal tissues of the nude mouse. The current study was designed to accurately measure radiation does to human neuroblastoma xenografts and normal organs in nude mice treated with I-131-labeled 3F8 monoclonal antibody (MoAb) against disialoganglioside GD2 antigen. Absorbed dose estimates were obtained using two different approaches: (1) measurement with teflon-imbedded CaSO4:Dy mini-thermoluminescent dosimeters (TLDs) and (2) calculations using mouse S-factors. The calculated total dose to tumor one week after i.v. injection of the 50 microCi I-131-3F8 MoAb was 604 cGy. The corresponding decay corrected and not corrected TLD measurements were 109 +/- 9 and 48.7 +/- 3.4 cGy respectively. The calculated to TLD-derived dose ratios for tumor ranged from 6.1 at 24 h to 5.5 at 1 week. The light output fading rate was found to depend upon the tissue type within which the TLDs were implanted. The decay rate in tumor, muscle, subcutaneous tissue and in vitro, were 9.5, 5.0, 3.7 and 0.67% per day, respectively. We have demonstrated that the type of tissue in which the TLD was implanted strongly influenced the in vivo decay of light output. Even with decay correction, a significant discrepancy was observed between MIRD-based calculated and CaSO4:Dy mini-TLD measured absorbed doses. Batch dependence, pH of the tumor or other variables associated with TLDs which are not as yet well known may account for this discrepancy.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sudhyadhom, A; McGuinness, C; Descovich, M

Purpose: To develop a methodology for validation of a Monte-Carlo dose calculation model for robotic small field SRS/SBRT deliveries. Methods: In a robotic treatment planning system, a Monte-Carlo model was iteratively optimized to match with beam data. A two-part analysis was developed to verify this model. 1) The Monte-Carlo model was validated in a simulated water phantom versus a Ray-Tracing calculation on a single beam collimator-by-collimator calculation. 2) The Monte-Carlo model was validated to be accurate in the most challenging situation, lung, by acquiring in-phantom measurements. A plan was created and delivered in a CIRS lung phantom with film insert.more » Separately, plans were delivered in an in-house created lung phantom with a PinPoint chamber insert within a lung simulating material. For medium to large collimator sizes, a single beam was delivered to the phantom. For small size collimators (10, 12.5, and 15mm), a robotically delivered plan was created to generate a uniform dose field of irradiation over a 2×2cm{sup 2} area. Results: Dose differences in simulated water between Ray-Tracing and Monte-Carlo were all within 1% at dmax and deeper. Maximum dose differences occurred prior to dmax but were all within 3%. Film measurements in a lung phantom show high correspondence of over 95% gamma at the 2%/2mm level for Monte-Carlo. Ion chamber measurements for collimator sizes of 12.5mm and above were within 3% of Monte-Carlo calculated values. Uniform irradiation involving the 10mm collimator resulted in a dose difference of ∼8% for both Monte-Carlo and Ray-Tracing indicating that there may be limitations with the dose calculation. Conclusion: We have developed a methodology to validate a Monte-Carlo model by verifying that it matches in water and, separately, that it corresponds well in lung simulating materials. The Monte-Carlo model and algorithm tested may have more limited accuracy for 10mm fields and smaller.« less

Proton dose distribution measurements using a MOSFET detector with a simple dose‐weighted correction method for LET effects

PubMed Central

Hotta, Kenji; Matsuura, Taeko; Matsubara, Kana; Nishioka, Shie; Nishio, Teiji; Kawashima, Mitsuhiko; Ogino, Takashi

2011-01-01

We experimentally evaluated the proton beam dose reproducibility, sensitivity, angular dependence and depth‐dose relationships for a new Metal Oxide Semiconductor Field Effect Transistor (MOSFET) detector. The detector was fabricated with a thinner oxide layer and was operated at high‐bias voltages. In order to accurately measure dose distributions, we developed a practical method for correcting the MOSFET response to proton beams. The detector was tested by examining lateral dose profiles formed by protons passing through an L‐shaped bolus. The dose reproducibility, angular dependence and depth‐dose response were evaluated using a 190 MeV proton beam. Depth‐output curves produced using the MOSFET detectors were compared with results obtained using an ionization chamber (IC). Since accurate measurements of proton dose distribution require correction for LET effects, we developed a simple dose‐weighted correction method. The correction factors were determined as a function of proton penetration depth, or residual range. The residual proton range at each measurement point was calculated using the pencil beam algorithm. Lateral measurements in a phantom were obtained for pristine and SOBP beams. The reproducibility of the MOSFET detector was within 2%, and the angular dependence was less than 9%. The detector exhibited a good response at the Bragg peak (0.74 relative to the IC detector). For dose distributions resulting from protons passing through an L‐shaped bolus, the corrected MOSFET dose agreed well with the IC results. Absolute proton dosimetry can be performed using MOSFET detectors to a precision of about 3% (1 sigma). A thinner oxide layer thickness improved the LET in proton dosimetry. By employing correction methods for LET dependence, it is possible to measure absolute proton dose using MOSFET detectors. PACS number: 87.56.‐v

Delivery confirmation of bolus electron conformal therapy combined with intensity modulated x-ray therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kavanaugh, James A.; Hogstrom, Kenneth R.; Fontenot, Jonas P.

2013-02-15

Purpose: The purpose of this study was to demonstrate that a bolus electron conformal therapy (ECT) dose plan and a mixed beam plan, composed of an intensity modulated x-ray therapy (IMXT) dose plan optimized on top of the bolus ECT plan, can be accurately delivered. Methods: Calculated dose distributions were compared with measured dose distributions for parotid and chest wall (CW) bolus ECT and mixed beam plans, each simulated in a cylindrical polystyrene phantom that allowed film dose measurements. Bolus ECT plans were created for both parotid and CW PTVs (planning target volumes) using 20 and 16 MeV beams, respectively,more » whose 90% dose surface conformed to the PTV. Mixed beam plans consisted of an IMXT dose plan optimized on top of the bolus ECT dose plan. The bolus ECT, IMXT, and mixed beam dose distributions were measured using radiographic films in five transverse and one sagittal planes for a total of 36 measurement conditions. Corrections for film dose response, effects of edge-on photon irradiation, and effects of irregular phantom optical properties on the Cerenkov component of the film signal resulted in high precision measurements. Data set consistency was verified by agreement of depth dose at the intersections of the sagittal plane with the five measured transverse planes. For these same depth doses, results for the mixed beam plan agreed with the sum of the individual depth doses for the bolus ECT and IMXT plans. The six mean measured planar dose distributions were compared with those calculated by the treatment planning system for all modalities. Dose agreement was assessed using the 4% dose difference and 0.2 cm distance to agreement. Results: For the combined high-dose region and low-dose region, pass rates for the parotid and CW plans were 98.7% and 96.2%, respectively, for the bolus ECT plans and 97.9% and 97.4%, respectively, for the mixed beam plans. For the high-dose gradient region, pass rates for the parotid and CW plans were 93.1% and 94.62%, respectively, for the bolus ECT plans and 89.2% and 95.1%, respectively, for the mixed beam plans. For all regions, pass rates for the parotid and CW plans were 98.8% and 97.3%, respectively, for the bolus ECT plans and 97.5% and 95.9%, respectively, for the mixed beam plans. For the IMXT component of the mixed beam plans, pass rates for the parotid and CW plans were 93.7% and 95.8%. Conclusions: Bolus ECT and mixed beam therapy dose delivery to the phantom were more accurate than IMXT delivery, adding confidence to the use of planning, fabrication, and delivery for bolus ECT tools either alone or as part of mixed beam therapy. The methodology reported in this work could serve as a basis for future standardization of the commissioning of bolus ECT or mixed beam therapy. When applying this technology to patients, it is recommended that an electron dose algorithm more accurate than the pencil beam algorithm, e.g., a Monte Carlo algorithm or analytical transport such as the pencil beam redefinition algorithm, be used for planning to ensure the desired accuracy.« less

Oncentra brachytherapy planning system.

PubMed

Yang, Jack

2018-03-27

In modern cancer management, treatment planning has progressed as a contemporary tool with all the advances in computing power in recent years. One of the advanced planning tools uses 3-dimensional (3D) data sets for accurate dose distributions in patient prescription. Among these planning processes, brachytherapy has been a very important part of a successful cancer management program, offering clinical benefits with specific or combined treatments with external beam therapy. In this chapter, we mainly discussed the Elekta Oncentra planning system, which is the main treatment planning tool for high-dose rate (HDR) modality in our facility and in many other facilities in the United States. HDR is a technically advanced form of brachytherapy; a high-intensity radiation source (3.6 mm in length) is delivered with step motor in submillimeter precision under computer guidance directly into the tumor areas while minimizing injury to surrounding normal healthy tissue. Oncentra planning is the key component to generate a deliverable brachytherapy procedure, which is executed on the microSelectron V3 remote afterloader treatment system. Creating a highly conformal plan can be a time-consuming task. The development of Oncentra software (version 4.5.3) offers a variety of useful tools that facilitate many of the clinical challenging tasks for planning, such as contouring and image reconstruction, as well as rapid planning calculations with dose and dose volume histogram analysis. Oncentra Brachy module creates workflow and optimizes the planning accuracy for wide varieties of clinical HDR treatments, such as skin, gynecologic (GYN), breast, prostate, and many other applications. The treatment file can also be transferred to the afterloader control station for speedy delivery. The design concept, calculation algorithms, and optimization modules presented some key characteristics to plan and treat the patients effectively and accurately. The dose distribution and accuracy of several clinical sample cases were discussed to illustrate the effectiveness and clinical efficacy. The American Association of Physicists in Medicine brachytherapy reports of TG-43 and TG-186 were also described and compared in evaluations of fundamental calculation methodologies. Copyright © 2018 American Association of Medical Dosimetrists. Published by Elsevier Inc. All rights reserved.

Fast, high-resolution 3D dosimetry utilizing a novel optical-CT scanner incorporating tertiary telecentric collimation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sakhalkar, H. S.; Oldham, M.

2008-01-15

This study introduces a charge coupled device (CCD) area detector based optical-computed tomography (optical-CT) scanner for comprehensive verification of radiation dose distributions recorded in nonscattering radiochromic dosimeters. Defining characteristics include: (i) a very fast scanning time of {approx}5 min to acquire a complete three-dimensional (3D) dataset, (ii) improved image formation through the use of custom telecentric optics, which ensures accurate projection images and minimizes artifacts from scattered and stray-light sources, and (iii) high resolution (potentially 50 {mu}m) isotropic 3D dose readout. The performance of the CCD scanner for 3D dose readout was evaluated by comparison with independent 3D readout frommore » the single laser beam OCTOPUS-scanner for the same PRESAGE dosimeters. The OCTOPUS scanner was considered the 'gold standard' technique in light of prior studies demonstrating its accuracy. Additional comparisons were made against calculated dose distributions from the ECLIPSE treatment-planning system. Dose readout for the following treatments were investigated: (i) a single rectangular beam irradiation to investigate small field and very steep dose gradient dosimetry away from edge effects, (ii) a 2-field open beam parallel-opposed irradiation to investigate dosimetry along steep dose gradients, and (iii) a 7-field intensity modulated radiation therapy (IMRT) irradiation to investigate dosimetry for complex treatment delivery involving modulation of fluence and for dosimetry along moderate dose gradients. Dose profiles, dose-difference plots, and gamma maps were employed to evaluate quantitative estimates of agreement between independently measured and calculated dose distributions. Results indicated that dose readout from the CCD scanner was in agreement with independent gold-standard readout from the OCTOPUS-scanner as well as the calculated ECLIPSE dose distribution for all treatments, except in regions within a few millimeters of the edge of the dosimeter, where edge artifact is predominant. Agreement of line profiles was observed, even along steep dose gradients. Dose difference plots indicated that the CCD scanner dose readout differed from the OCTOPUSscanner readout and ECLIPSE calculations by {approx}10% along steep dose gradients and by {approx}5% along moderate dose gradients. Gamma maps (3% dose-difference and 3 mm distance-to-agreement acceptance criteria) revealed agreement, except for regions within 5 mm of the edge of the dosimeter where the edge artifact occurs. In summary, the data demonstrate feasibility of using the fast, high-resolution CCD scanner for comprehensive 3D dosimetry in all applications, except where dose readout is required close to the edges of the dosimeter. Further work is ongoing to reduce this artifact.« less

Three-Dimensional Dose Calculation for Total Body Irradiation

NASA Astrophysics Data System (ADS)

Ito, Akira

Bone Marrow Transplant (BMT) therapy has been a big success in the treatment of leukemia and other haematopoietic diseases 1 . Prior to BMT, total body irradiation (TBI) is given to the patient for the purpose of (1) killing leukemia cells in bone marrow, as well as in the whole body, and (2) producing immuno-suppressive status in the patient so that the donor's marrow cells will be transplanted without rejection. TBI employs a very large field photon beam to irradiate the whole body of the patient. A uniform dose distribution over the entire body is the treatment goal. To prevent the occurrence of a serious side effect (interstitial pneumonia), the lung dose should not exceed a certain level. This novel technique poses various new radiological physics problems. The accurate assessment of dose and dose distribution in the patient is essential. Physical and dosimetric problems associated with TBI are reviewed elsewhere 2,3 .

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shrotriya, D., E-mail: shrotriya2007@gmail.com; Srivastava, R. N. L.; Kumar, S.

The accurate dose delivery to the clinical target volume in radiotherapy can be affected by various pelvic tissues heterogeneities. An in-house heterogeneous woman pelvic phantom was designed and used to verify the consistency and computational capability of treatment planning system of radiation dose delivery in the treatment of cancer cervix. Oncentra 3D-TPS with collapsed cone convolution (CCC) dose calculation algorithm was used to generate AP/PA and box field technique plan. the radiation dose was delivered by Primus Linac (Siemens make) employing high energy 15 MV photon beam by isocenter technique. A PTW make, 0.125cc ionization chamber was used for directmore » measurements at various reference points in cervix, bladder and rectum. The study revealed that maximum variation between computed and measured dose at cervix reference point was 1% in both the techniques and 3% and 4% variation in AP/PA field and 5% and 4.5% in box technique at bladder and rectum points respectively.« less

Developing of an automation for therapy dosimetry systems by using labview software

NASA Astrophysics Data System (ADS)

Aydin, Selim; Kam, Erol

2018-06-01

Traceability, accuracy and consistency of radiation measurements are essential in radiation dosimetry, particularly in radiotherapy, where the outcome of treatments is highly dependent on the radiation dose delivered to patients. Therefore it is very important to provide reliable, accurate and fast calibration services for therapy dosimeters since the radiation dose delivered to a radiotherapy patient is directly related to accuracy and reliability of these devices. In this study, we report the performance of in-house developed computer controlled data acquisition and monitoring software for the commercially available radiation therapy electrometers. LabVIEW® software suite is used to provide reliable, fast and accurate calibration services. The software also collects environmental data such as temperature, pressure and humidity in order to use to use these them in correction factor calculations. By using this software tool, a better control over the calibration process is achieved and the need for human intervention is reduced. This is the first software that can control frequently used dosimeter systems, in radiation thereapy field at hospitals, such as Unidos Webline, Unidos E, Dose-1 and PC Electrometers.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vikraman, S; Ramu, M; Karrthick, Kp

Purpose: The purpose of this study was to validate the advent of COMPASS 3D dosimetry as a routine pre treatment verification tool with commercially available CMS Monaco and Oncentra Masterplan planning system. Methods: Twenty esophagus patients were selected for this study. All these patients underwent radical VMAT treatment in Elekta Linac and plans were generated in Monaco v5.0 with MonteCarlo(MC) dose calculation algorithm. COMPASS 3D dosimetry comprises an advanced dose calculation algorithm of collapsed cone convolution(CCC). To validate CCC algorithm in COMPASS, The DICOM RT Plans generated using Monaco MC algorithm were transferred to Oncentra Masterplan v4.3 TPS. Only finalmore » dose calculations were performed using CCC algorithm with out optimization in Masterplan planning system. It is proven that MC algorithm is an accurate algorithm and obvious that there will be a difference with MC and CCC algorithms. Hence CCC in COMPASS should be validated with other commercially available CCC algorithm. To use the CCC as pretreatment verification tool with reference to MC generated treatment plans, CCC in OMP and CCC in COMPASS were validated using dose volume based indices such as D98, D95 for target volumes and OAR doses. Results: The point doses for open beams were observed <1% with reference to Monaco MC algorithms. Comparisons of CCC(OMP) Vs CCC(COMPASS) showed a mean difference of 1.82%±1.12SD and 1.65%±0.67SD for D98 and D95 respectively for Target coverage. Maximum point dose of −2.15%±0.60SD difference was observed in target volume. The mean lung dose of −2.68%±1.67SD was noticed between OMP and COMPASS. The maximum point doses for spinal cord were −1.82%±0.287SD. Conclusion: In this study, the accuracy of CCC algorithm in COMPASS 3D dosimetry was validated by compared with CCC algorithm in OMP TPS. Dose calculation in COMPASS is feasible within < 2% in comparison with commercially available TPS algorithms.« less

WE-H-207A-07: Image-Based Versus Atlas-Based Internal Dosimetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fallahpoor, M; Abbasi, M; Parach, A

Purpose: Monte Carlo (MC) simulation is known as the gold standard method for internal dosimetry. It requires radionuclide distribution from PET or SPECT and body structure from CT for accurate dose calculation. The manual or semi-automatic segmentation of organs from CT images is a major obstacle. The aim of this study is to compare the dosimetry results based on patient’s own CT and a digital humanoid phantom as an atlas with pre-specified organs. Methods: SPECT-CT images of a 50 year old woman who underwent bone pain palliation with Samarium-153 EDTMP for osseous metastases from breast cancer were used. The anatomicalmore » date and attenuation map were extracted from SPECT/CT and three XCAT digital phantoms with different BMIs (i.e. matched (38.8) and unmatched (35.5 and 36.7) with patient’s BMI that was 38.3). Segmentation of patient’s organs in CT image was performed using itk-SNAP software. GATE MC Simulator was used for dose calculation. Specific absorbed fractions (SAFs) and S-values were calculated for the segmented organs. Results: The differences between SAFs and S-values are high using different anatomical data and range from −13% to 39% for SAF values and −109% to 79% for S-values in different organs. In the spine, the clinically important target organ for Samarium Therapy, the differences in the S-values and SAF values are higher between XCAT phantom and CT when the phantom with identical BMI is employed (53.8% relative difference in S-value and 26.8% difference in SAF). However, the whole body dose values were the same between the calculations based on the CT and XCAT with different BMIs. Conclusion: The results indicated that atlas-based dosimetry using XCAT phantom even with matched BMI for patient leads to considerable errors as compared to image-based dosimetry that uses the patient’s own CT Patient-specific dosimetry using CT image is essential for accurate results.« less

Charged particle transport in magnetic fields in EGSnrc.

PubMed

Malkov, V N; Rogers, D W O

2016-07-01

To accurately and efficiently implement charged particle transport in a magnetic field in EGSnrc and validate the code for the use in phantom and ion chamber simulations. The effect of the magnetic field on the particle motion and position is determined using one- and three-point numerical integrations of the Lorentz force on the charged particle and is added to the condensed history calculation performed by the EGSnrc PRESTA-II algorithm. The code is tested with a Fano test adapted for the presence of magnetic fields. The code is compatible with all EGSnrc based applications, including egs++. Ion chamber calculations are compared to experimental measurements and the effect of the code on the efficiency and timing is determined. Agreement with the Fano test's theoretical value is obtained at the 0.1% level for large step-sizes and in magnetic fields as strong as 5 T. The NE2571 dose calculations achieve agreement with the experiment within 0.5% up to 1 T beyond which deviations up to 1.2% are observed. Uniform air gaps of 0.5 and 1 mm and a misalignment of the incoming photon beam with the magnetic field are found to produce variations in the normalized dose on the order of 1%. These findings necessitate a clear definition of all experimental conditions to allow for accurate Monte Carlo simulations. It is found that ion chamber simulation times are increased by only 38%, and a 10 × 10 × 6 cm(3) water phantom with (3 mm)(3) voxels experiences a 48% increase in simulation time as compared to the default EGSnrc with no magnetic field. The incorporation of the effect of the magnetic fields in EGSnrc provides the capability to calculate high accuracy ion chamber and phantom doses for the use in MRI-radiation systems. Further, the effect of apparently insignificant experimental details is found to be accentuated by the presence of the magnetic field.

A Monte Carlo investigation of contaminant electrons due to a novel in vivo transmission detector.

PubMed

Asuni, G; Jensen, J M; McCurdy, B M C

2011-02-21

A novel transmission detector (IBA Dosimetry, Germany) developed as an IMRT quality assurance tool, intended for in vivo patient dose measurements, is studied here. The goal of this investigation is to use Monte Carlo techniques to characterize treatment beam parameters in the presence of the detector and to compare to those of a plastic block tray (a frequently used clinical device). Particular attention is paid to the impact of the detector on electron contamination model parameters of two commercial dose calculation algorithms. The linac head together with the COMPASS transmission detector (TRD) was modeled using BEAMnrc code. To understand the effect of the TRD on treatment beams, the contaminant electron fluence, energy spectra, and angular distributions at different SSDs were analyzed for open and non-open (i.e. TRD and block tray) fields. Contaminant electrons in the BEAMnrc simulations were separated according to where they were created. Calculation of surface dose and the evaluation of contributions from contaminant electrons were performed using the DOSXYZnrc user code. The effect of the TRD on contaminant electrons model parameters in Eclipse AAA and Pinnacle(3) dose calculation algorithms was investigated. Comparisons of the fluence of contaminant electrons produced in the non-open fields versus open field show that electrons created in the non-open fields increase at shorter SSD, but most of the electrons at shorter SSD are of low energy with large angular spread. These electrons are out-scattered or absorbed in air and contribute less to surface dose at larger SSD. Calculated surface doses with the block tray are higher than those with the TRD. Contribution of contaminant electrons to dose in the buildup region increases with increasing field size. The additional contribution of electrons to surface dose increases with field size for TRD and block tray. The introduction of the TRD results in a 12% and 15% increase in the Gaussian widths used in the contaminant electron source model of the Eclipse AAA dose algorithm. The off-axis coefficient in the Pinnacle(3) dose calculation algorithm decreases in the presence of TRD compared to without the device. The electron model parameters were modified to reflect the increase in electron contamination with the TRD, a necessary step for accurate beam modeling when using the device.

SU-F-T-325: On the Use of Bolus in Dosimetry and Dose Reduction for Pacemaker and Defibrillator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, W; Kenneth, R; Higgins, S

Purpose: Special attention is required in planning and administering radiation therapy to patients with cardiac implantable electronic devices (CIEDs), such as pacemaker and defibrillator. The range of dose to CIEDs that can induce malfunction is very large among CIEDs. Significant defects have been reported at dose as low as 0.15Gy. Failures causing discomfort have been reported at dose as low as 0.05Gy. Therefore, accurate estimation of dose to CIED and dose reduction are both important even if the dose is expected to be less than the often-used 2Gy limit. We investigate the use of bolus in in vivo dosimetry formore » CIEDs. Methods: In our clinic, high-energy beams (>10MV) are not used for patients with CIED due to neutron production. Solid water phantom measurements of out-of-field dose for a 6MV beam were performed using parallel plate chamber at different depth with and without 2cm bolus covering the chamber. In vivo dosimetry at skin surface above the pacemaker was performed with and without bolus for 3 patients with pacemaker <5cm from the field edge. Results: Chamber measured dose at depth ∼1 to 1.5cm below the skin surface, where the CIED is normally located, was reduced by ∼6% – 20% with bolus. The dose reduction became smaller at deeper depth. In vivo dosimetry at skin surface also yielded ∼20% – 60% lower dose when using bolus for the 3 patients. In general, TPS calculation underestimated the dose. The dose measured with bolus is closer to the dose at the depth of the pacemaker and less affected by contaminant electrons and linac head leakage. Conclusion: In vivo CIED dose measurements should be performed with 1 to 2cm bolus covering the dosimeter on the skin above the CIED for more accurate CIED dose estimation. The use of bolus also reduces the dose delivered to CIED.« less

SU-E-T-561: Monte Carlo-Based Organ Dose Reconstruction Using Pre-Contoured Human Model for Hodgkins Lymphoma Patients Treated by Cobalt-60 External Beam Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jung, J; Pelletier, C; Lee, C

Purpose: Organ doses for the Hodgkin’s lymphoma patients treated with cobalt-60 radiation were estimated using an anthropomorphic model and Monte Carlo modeling. Methods: A cobalt-60 treatment unit modeled in the BEAMnrc Monte Carlo code was used to produce phase space data. The Monte Carlo simulation was verified with percent depth dose measurement in water at various field sizes. Radiation transport through the lung blocks were modeled by adjusting the weights of phase space data. We imported a precontoured adult female hybrid model and generated a treatment plan. The adjusted phase space data and the human model were imported to themore » XVMC Monte Carlo code for dose calculation. The organ mean doses were estimated and dose volume histograms were plotted. Results: The percent depth dose agreement between measurement and calculation in water phantom was within 2% for all field sizes. The mean organ doses of heart, left breast, right breast, and spleen for the selected case were 44.3, 24.1, 14.6 and 3.4 Gy, respectively with the midline prescription dose of 40.0 Gy. Conclusion: Organ doses were estimated for the patient group whose threedimensional images are not available. This development may open the door to more accurate dose reconstruction and estimates of uncertainties in secondary cancer risk for Hodgkin’s lymphoma patients. This work was partially supported by the intramural research program of the National Institutes of Health, National Cancer Institute, Division of Cancer Epidemiology and Genetics.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brualla, Lorenzo, E-mail: lorenzo.brualla@uni-due.de; Zaragoza, Francisco J.; Sempau, Josep

Purpose: External beam radiotherapy is the only conservative curative approach for Stage I non-Hodgkin lymphomas of the conjunctiva. The target volume is geometrically complex because it includes the eyeball and lid conjunctiva. Furthermore, the target volume is adjacent to radiosensitive structures, including the lens, lacrimal glands, cornea, retina, and papilla. The radiotherapy planning and optimization requires accurate calculation of the dose in these anatomical structures that are much smaller than the structures traditionally considered in radiotherapy. Neither conventional treatment planning systems nor dosimetric measurements can reliably determine the dose distribution in these small irradiated volumes. Methods and Materials: The Montemore » Carlo simulations of a Varian Clinac 2100 C/D and human eye were performed using the PENELOPE and PENEASYLINAC codes. Dose distributions and dose volume histograms were calculated for the bulbar conjunctiva, cornea, lens, retina, papilla, lacrimal gland, and anterior and posterior hemispheres. Results: The simulated results allow choosing the most adequate treatment setup configuration, which is an electron beam energy of 6 MeV with additional bolus and collimation by a cerrobend block with a central cylindrical hole of 3.0 cm diameter and central cylindrical rod of 1.0 cm diameter. Conclusions: Monte Carlo simulation is a useful method to calculate the minute dose distribution in ocular tissue and to optimize the electron irradiation technique in highly critical structures. Using a voxelized eye phantom based on patient computed tomography images, the dose distribution can be estimated with a standard statistical uncertainty of less than 2.4% in 3 min using a computing cluster with 30 cores, which makes this planning technique clinically relevant.« less

An analytic linear accelerator source model for GPU-based Monte Carlo dose calculations.

PubMed

Tian, Zhen; Li, Yongbao; Folkerts, Michael; Shi, Feng; Jiang, Steve B; Jia, Xun

2015-10-21

Recently, there has been a lot of research interest in developing fast Monte Carlo (MC) dose calculation methods on graphics processing unit (GPU) platforms. A good linear accelerator (linac) source model is critical for both accuracy and efficiency considerations. In principle, an analytical source model should be more preferred for GPU-based MC dose engines than a phase-space file-based model, in that data loading and CPU-GPU data transfer can be avoided. In this paper, we presented an analytical field-independent source model specifically developed for GPU-based MC dose calculations, associated with a GPU-friendly sampling scheme. A key concept called phase-space-ring (PSR) was proposed. Each PSR contained a group of particles that were of the same type, close in energy and reside in a narrow ring on the phase-space plane located just above the upper jaws. The model parameterized the probability densities of particle location, direction and energy for each primary photon PSR, scattered photon PSR and electron PSR. Models of one 2D Gaussian distribution or multiple Gaussian components were employed to represent the particle direction distributions of these PSRs. A method was developed to analyze a reference phase-space file and derive corresponding model parameters. To efficiently use our model in MC dose calculations on GPU, we proposed a GPU-friendly sampling strategy, which ensured that the particles sampled and transported simultaneously are of the same type and close in energy to alleviate GPU thread divergences. To test the accuracy of our model, dose distributions of a set of open fields in a water phantom were calculated using our source model and compared to those calculated using the reference phase-space files. For the high dose gradient regions, the average distance-to-agreement (DTA) was within 1 mm and the maximum DTA within 2 mm. For relatively low dose gradient regions, the root-mean-square (RMS) dose difference was within 1.1% and the maximum dose difference within 1.7%. The maximum relative difference of output factors was within 0.5%. Over 98.5% passing rate was achieved in 3D gamma-index tests with 2%/2 mm criteria in both an IMRT prostate patient case and a head-and-neck case. These results demonstrated the efficacy of our model in terms of accurately representing a reference phase-space file. We have also tested the efficiency gain of our source model over our previously developed phase-space-let file source model. The overall efficiency of dose calculation was found to be improved by ~1.3-2.2 times in water and patient cases using our analytical model.

A modified microdosimetric kinetic model for relative biological effectiveness calculation

NASA Astrophysics Data System (ADS)

Chen, Yizheng; Li, Junli; Li, Chunyan; Qiu, Rui; Wu, Zhen

2018-01-01

In the heavy ion therapy, not only the distribution of physical absorbed dose, but also the relative biological effectiveness (RBE) weighted dose needs to be taken into account. The microdosimetric kinetic model (MKM) can predict the RBE value of heavy ions with saturation-corrected dose-mean specific energy, which has been used in clinical treatment planning at the National Institute of Radiological Sciences. In the theoretical assumption of the MKM, the yield of the primary lesion is independent of the radiation quality, while the experimental data shows that DNA double strand break (DSB) yield, considered as the main primary lesion, depends on the LET of the particle. Besides, the β parameter of the MKM is constant with LET resulting from this assumption, which also differs from the experimental conclusion. In this study, a modified MKM was developed, named MMKM. Based on the experimental DSB yield of mammalian cells under the irradiation of ions with different LETs, a RBEDSB (RBE for the induction of DSB)-LET curve was fitted as the correction factor to modify the primary lesion yield in the MKM, and the variation of the primary lesion yield with LET is considered in the MMKM. Compared with the present the MKM, not only the α parameter of the MMKM for mono-energetic ions agree with the experimental data, but also the β parameter varies with LET and the variation trend of the experimental result can be reproduced on the whole. Then a spread-out Bragg peaks (SOBP) distribution of physical dose was simulated with Geant4 Monte Carlo code, and the biological and clinical dose distributions were calculated, under the irradiation of carbon ions. The results show that the distribution of clinical dose calculated with the MMKM is closed to the distribution with the MKM in the SOBP, while the discrepancy before and after the SOBP are both within 10%. Moreover, the MKM might overestimate the clinical dose at the distal end of the SOBP more than 5% because of its constant β value, while a minimal value of β is calculated with the MMKM at this position. Besides, the discrepancy of the averaged cell survival fraction in the SOBP calculated with the two models is more than 15% at the high dose level. The MMKM may provide a reference for the accurate calculation of the RBE value in heavy ion therapy.

SU-E-T-515: Field-In-Field Compensation Technique Using Multi-Leaf Collimator to Deliver Total Body Irradiation (TBI) Dose

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lakeman, T; Wang, IZ; Roswell Park Cancer Institute, Buffalo, NY

Purpose: Total body irradiation (TBI) uses large parallel-opposed radiation fields to suppress the patient's immune system and eradicate the residual cancer cells in preparation of recipient for bone marrow transplant. The manual placement of lead compensators has been used conventionally to compensate for the varying thickness through the entire body in large-field TBI. The goal of this study is to pursue utilizing the modern field-in-field (FIF) technique with the multi-leaf collimator (MLC) to more accurately and efficiently deliver dose to patients in need of TBI. Method: Treatment plans utilizing the FIF technique to deliver a total body dose were createdmore » retrospectively for patients for whom CT data had been previously acquired. Treatment fields include one pair of opposed open large fields (collimator=45°) with a specific weighting and a succession of smaller fields (collimator=90°) each with their own weighting. The smaller fields are shaped by moving MLC to block the sections of the patient which have already received close to 100% of the prescribed dose. The weighting factors for each of these fields were calculated using the attenuation coefficient of the initial lead compensators and the separation of the patient in different positions in the axial plane. Results: Dose-volume histograms (DVH) were calculated for evaluating the FIF compensation technique. The maximum body doses calculated from the DVH were reduced from the non-compensated 179.3% to 148.2% in the FIF plans, indicating a more uniform dose with the FIF compensation. All calculated monitor units were well within clinically acceptable limits and exceeded those of the original lead compensation plan by less than 50 MU (only ~1.1% increase). Conclusion: MLC FIF technique for TBI will not significantly increase the beam on time while it can substantially reduce the compensator setup time and the potential risk of errors in manually placing lead compensators.« less

Dosimetry in small-animal CT using Monte Carlo simulations

NASA Astrophysics Data System (ADS)

Lee, C.-L.; Park, S.-J.; Jeon, P.-H.; Jo, B.-D.; Kim, H.-J.

2016-01-01

Small-animal computed tomography (micro-CT) imaging devices are increasingly being used in biological research. While investigators are mainly interested in high-contrast, low-noise, and high-resolution anatomical images, relatively large radiation doses are required, and there is also growing concern over the radiological risk from preclinical experiments. This study was conducted to determine the radiation dose in a mouse model for dosimetric estimates using the GEANT4 application for tomographic emission simulations (GATE) and to extend its techniques to various small-animal CT applications. Radiation dose simulations were performed with the same parameters as those for the measured micro-CT data, using the MOBY phantom, a pencil ion chamber and an electrometer with a CT detector. For physical validation of radiation dose, absorbed dose of brain and liver in mouse were evaluated to compare simulated results with physically measured data using thermoluminescent dosimeters (TLDs). The mean difference between simulated and measured data was less than 2.9% at 50 kVp X-ray source. The absorbed doses of 37 brain tissues and major organs of the mouse were evaluated according to kVp changes. The absorbed dose over all of the measurements in the brain (37 types of tissues) consistently increased and ranged from 42.4 to 104.0 mGy. Among the brain tissues, the absorbed dose of the hypothalamus (157.8-414.30 mGy) was the highest for the beams at 50-80 kVp, and that of the corpus callosum (11.2-26.6 mGy) was the lowest. These results can be used as a dosimetric database to control mouse doses and preclinical targeted radiotherapy experiments. In addition, to accurately calculate the mouse-absorbed dose, the X-ray spectrum, detector alignment, and uncertainty in the elemental composition of the simulated materials must be accurately modeled.

A GPU OpenCL based cross-platform Monte Carlo dose calculation engine (goMC)

NASA Astrophysics Data System (ADS)

Tian, Zhen; Shi, Feng; Folkerts, Michael; Qin, Nan; Jiang, Steve B.; Jia, Xun

2015-09-01

Monte Carlo (MC) simulation has been recognized as the most accurate dose calculation method for radiotherapy. However, the extremely long computation time impedes its clinical application. Recently, a lot of effort has been made to realize fast MC dose calculation on graphic processing units (GPUs). However, most of the GPU-based MC dose engines have been developed under NVidia’s CUDA environment. This limits the code portability to other platforms, hindering the introduction of GPU-based MC simulations to clinical practice. The objective of this paper is to develop a GPU OpenCL based cross-platform MC dose engine named goMC with coupled photon-electron simulation for external photon and electron radiotherapy in the MeV energy range. Compared to our previously developed GPU-based MC code named gDPM (Jia et al 2012 Phys. Med. Biol. 57 7783-97), goMC has two major differences. First, it was developed under the OpenCL environment for high code portability and hence could be run not only on different GPU cards but also on CPU platforms. Second, we adopted the electron transport model used in EGSnrc MC package and PENELOPE’s random hinge method in our new dose engine, instead of the dose planning method employed in gDPM. Dose distributions were calculated for a 15 MeV electron beam and a 6 MV photon beam in a homogenous water phantom, a water-bone-lung-water slab phantom and a half-slab phantom. Satisfactory agreement between the two MC dose engines goMC and gDPM was observed in all cases. The average dose differences in the regions that received a dose higher than 10% of the maximum dose were 0.48-0.53% for the electron beam cases and 0.15-0.17% for the photon beam cases. In terms of efficiency, goMC was ~4-16% slower than gDPM when running on the same NVidia TITAN card for all the cases we tested, due to both the different electron transport models and the different development environments. The code portability of our new dose engine goMC was validated by successfully running it on a variety of different computing devices including an NVidia GPU card, two AMD GPU cards and an Intel CPU processor. Computational efficiency among these platforms was compared.

A GPU OpenCL based cross-platform Monte Carlo dose calculation engine (goMC).

PubMed

Tian, Zhen; Shi, Feng; Folkerts, Michael; Qin, Nan; Jiang, Steve B; Jia, Xun

2015-10-07

Monte Carlo (MC) simulation has been recognized as the most accurate dose calculation method for radiotherapy. However, the extremely long computation time impedes its clinical application. Recently, a lot of effort has been made to realize fast MC dose calculation on graphic processing units (GPUs). However, most of the GPU-based MC dose engines have been developed under NVidia's CUDA environment. This limits the code portability to other platforms, hindering the introduction of GPU-based MC simulations to clinical practice. The objective of this paper is to develop a GPU OpenCL based cross-platform MC dose engine named goMC with coupled photon-electron simulation for external photon and electron radiotherapy in the MeV energy range. Compared to our previously developed GPU-based MC code named gDPM (Jia et al 2012 Phys. Med. Biol. 57 7783-97), goMC has two major differences. First, it was developed under the OpenCL environment for high code portability and hence could be run not only on different GPU cards but also on CPU platforms. Second, we adopted the electron transport model used in EGSnrc MC package and PENELOPE's random hinge method in our new dose engine, instead of the dose planning method employed in gDPM. Dose distributions were calculated for a 15 MeV electron beam and a 6 MV photon beam in a homogenous water phantom, a water-bone-lung-water slab phantom and a half-slab phantom. Satisfactory agreement between the two MC dose engines goMC and gDPM was observed in all cases. The average dose differences in the regions that received a dose higher than 10% of the maximum dose were 0.48-0.53% for the electron beam cases and 0.15-0.17% for the photon beam cases. In terms of efficiency, goMC was ~4-16% slower than gDPM when running on the same NVidia TITAN card for all the cases we tested, due to both the different electron transport models and the different development environments. The code portability of our new dose engine goMC was validated by successfully running it on a variety of different computing devices including an NVidia GPU card, two AMD GPU cards and an Intel CPU processor. Computational efficiency among these platforms was compared.

Use of a graphics processing unit (GPU) to facilitate real-time 3D graphic presentation of the patient skin-dose distribution during fluoroscopic interventional procedures

PubMed Central

Rana, Vijay; Rudin, Stephen; Bednarek, Daniel R.

2012-01-01

We have developed a dose-tracking system (DTS) that calculates the radiation dose to the patient’s skin in real-time by acquiring exposure parameters and imaging-system-geometry from the digital bus on a Toshiba Infinix C-arm unit. The cumulative dose values are then displayed as a color map on an OpenGL-based 3D graphic of the patient for immediate feedback to the interventionalist. Determination of those elements on the surface of the patient 3D-graphic that intersect the beam and calculation of the dose for these elements in real time demands fast computation. Reducing the size of the elements results in more computation load on the computer processor and therefore a tradeoff occurs between the resolution of the patient graphic and the real-time performance of the DTS. The speed of the DTS for calculating dose to the skin is limited by the central processing unit (CPU) and can be improved by using the parallel processing power of a graphics processing unit (GPU). Here, we compare the performance speed of GPU-based DTS software to that of the current CPU-based software as a function of the resolution of the patient graphics. Results show a tremendous improvement in speed using the GPU. While an increase in the spatial resolution of the patient graphics resulted in slowing down the computational speed of the DTS on the CPU, the speed of the GPU-based DTS was hardly affected. This GPU-based DTS can be a powerful tool for providing accurate, real-time feedback about patient skin-dose to physicians while performing interventional procedures. PMID:24027616

Use of a graphics processing unit (GPU) to facilitate real-time 3D graphic presentation of the patient skin-dose distribution during fluoroscopic interventional procedures.

PubMed

Rana, Vijay; Rudin, Stephen; Bednarek, Daniel R

2012-02-23

We have developed a dose-tracking system (DTS) that calculates the radiation dose to the patient's skin in real-time by acquiring exposure parameters and imaging-system-geometry from the digital bus on a Toshiba Infinix C-arm unit. The cumulative dose values are then displayed as a color map on an OpenGL-based 3D graphic of the patient for immediate feedback to the interventionalist. Determination of those elements on the surface of the patient 3D-graphic that intersect the beam and calculation of the dose for these elements in real time demands fast computation. Reducing the size of the elements results in more computation load on the computer processor and therefore a tradeoff occurs between the resolution of the patient graphic and the real-time performance of the DTS. The speed of the DTS for calculating dose to the skin is limited by the central processing unit (CPU) and can be improved by using the parallel processing power of a graphics processing unit (GPU). Here, we compare the performance speed of GPU-based DTS software to that of the current CPU-based software as a function of the resolution of the patient graphics. Results show a tremendous improvement in speed using the GPU. While an increase in the spatial resolution of the patient graphics resulted in slowing down the computational speed of the DTS on the CPU, the speed of the GPU-based DTS was hardly affected. This GPU-based DTS can be a powerful tool for providing accurate, real-time feedback about patient skin-dose to physicians while performing interventional procedures.

SU-E-T-175: Clinical Evaluations of Monte Carlo-Based Inverse Treatment Plan Optimization for Intensity Modulated Radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chi, Y; Li, Y; Tian, Z

2015-06-15

Purpose: Pencil-beam or superposition-convolution type dose calculation algorithms are routinely used in inverse plan optimization for intensity modulated radiation therapy (IMRT). However, due to their limited accuracy in some challenging cases, e.g. lung, the resulting dose may lose its optimality after being recomputed using an accurate algorithm, e.g. Monte Carlo (MC). It is the objective of this study to evaluate the feasibility and advantages of a new method to include MC in the treatment planning process. Methods: We developed a scheme to iteratively perform MC-based beamlet dose calculations and plan optimization. In the MC stage, a GPU-based dose engine wasmore » used and the particle number sampled from a beamlet was proportional to its optimized fluence from the previous step. We tested this scheme in four lung cancer IMRT cases. For each case, the original plan dose, plan dose re-computed by MC, and dose optimized by our scheme were obtained. Clinically relevant dosimetric quantities in these three plans were compared. Results: Although the original plan achieved a satisfactory PDV dose coverage, after re-computing doses using MC method, it was found that the PTV D95% were reduced by 4.60%–6.67%. After re-optimizing these cases with our scheme, the PTV coverage was improved to the same level as in the original plan, while the critical OAR coverages were maintained to clinically acceptable levels. Regarding the computation time, it took on average 144 sec per case using only one GPU card, including both MC-based beamlet dose calculation and treatment plan optimization. Conclusion: The achieved dosimetric gains and high computational efficiency indicate the feasibility and advantages of the proposed MC-based IMRT optimization method. Comprehensive validations in more patient cases are in progress.« less

Clinical evaluation of the iterative metal artifact reduction algorithm for CT simulation in radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Axente, Marian; Von Eyben, Rie; Hristov, Dimitre, E-mail: dimitre.hristov@stanford.edu

2015-03-15

Purpose: To clinically evaluate an iterative metal artifact reduction (IMAR) algorithm prototype in the radiation oncology clinic setting by testing for accuracy in CT number retrieval, relative dosimetric changes in regions affected by artifacts, and improvements in anatomical and shape conspicuity of corrected images. Methods: A phantom with known material inserts was scanned in the presence/absence of metal with different configurations of placement and sizes. The relative change in CT numbers from the reference data (CT with no metal) was analyzed. The CT studies were also used for dosimetric tests where dose distributions from both photon and proton beams weremore » calculated. Dose differences and gamma analysis were calculated to quantify the relative changes between doses calculated on the different CT studies. Data from eight patients (all different treatment sites) were also used to quantify the differences between dose distributions before and after correction with IMAR, with no reference standard. A ranking experiment was also conducted to analyze the relative confidence of physicians delineating anatomy in the near vicinity of the metal implants. Results: IMAR corrected images proved to accurately retrieve CT numbers in the phantom study, independent of metal insert configuration, size of the metal, and acquisition energy. For plastic water, the mean difference between corrected images and reference images was −1.3 HU across all scenarios (N = 37) with a 90% confidence interval of [−2.4, −0.2] HU. While deviations were relatively higher in images with more metal content, IMAR was able to effectively correct the CT numbers independent of the quantity of metal. Residual errors in the CT numbers as well as some induced by the correction algorithm were found in the IMAR corrected images. However, the dose distributions calculated on IMAR corrected images were closer to the reference data in phantom studies. Relative spatial difference in the dose distributions in the regions affected by the metal artifacts was also observed in patient data. However, in absence of a reference ground truth (CT set without metal inserts), these differences should not be interpreted as improvement/deterioration of the accuracy of calculated dose. With limited data presented, it was observed that proton dosimetry was affected more than photons as expected. Physicians were significantly more confident contouring anatomy in the regions affected by artifacts. While site specific preferences were detected, all indicated that they would consistently use IMAR corrected images. Conclusions: IMAR correction algorithm could be readily implemented in an existing clinical workflow upon commercial release. While residual errors still exist in IMAR corrected images, these images present with better overall conspicuity of the patient/phantom geometry and offer more accurate CT numbers for improved local dosimetry. The variety of different scenarios included herein attest to the utility of the evaluated IMAR for a wide range of radiotherapy clinical scenarios.« less

The evaluation of a 2D diode array in "magic phantom" for use in high dose rate brachytherapy pretreatment quality assurance.

PubMed

Espinoza, A; Petasecca, M; Fuduli, I; Howie, A; Bucci, J; Corde, S; Jackson, M; Lerch, M L F; Rosenfeld, A B

2015-02-01

High dose rate (HDR) brachytherapy is a treatment method that is used increasingly worldwide. The development of a sound quality assurance program for the verification of treatment deliveries can be challenging due to the high source activity utilized and the need for precise measurements of dwell positions and times. This paper describes the application of a novel phantom, based on a 2D 11 × 11 diode array detection system, named "magic phantom" (MPh), to accurately measure plan dwell positions and times, compare them directly to the treatment plan, determine errors in treatment delivery, and calculate absorbed dose. The magic phantom system was CT scanned and a 20 catheter plan was generated to simulate a nonspecific treatment scenario. This plan was delivered to the MPh and, using a custom developed software suite, the dwell positions and times were measured and compared to the plan. The original plan was also modified, with changes not disclosed to the primary authors, and measured again using the device and software to determine the modifications. A new metric, the "position-time gamma index," was developed to quantify the quality of a treatment delivery when compared to the treatment plan. The MPh was evaluated to determine the minimum measurable dwell time and step size. The incorporation of the TG-43U1 formalism directly into the software allows for dose calculations to be made based on the measured plan. The estimated dose distributions calculated by the software were compared to the treatment plan and to calibrated EBT3 film, using the 2D gamma analysis method. For the original plan, the magic phantom system was capable of measuring all dwell points and dwell times and the majority were found to be within 0.93 mm and 0.25 s, respectively, from the plan. By measuring the altered plan and comparing it to the unmodified treatment plan, the use of the position-time gamma index showed that all modifications made could be readily detected. The MPh was able to measure dwell times down to 0.067 ± 0.001 s and planned dwell positions separated by 1 mm. The dose calculation carried out by the MPh software was found to be in agreement with values calculated by the treatment planning system within 0.75%. Using the 2D gamma index, the dose map of the MPh plane and measured EBT3 were found to have a pass rate of over 95% when compared to the original plan. The application of this magic phantom quality assurance system to HDR brachytherapy has demonstrated promising ability to perform the verification of treatment plans, based upon the measured dwell positions and times. The introduction of the quantitative position-time gamma index allows for direct comparison of measured parameters against the plan and could be used prior to patient treatment to ensure accurate delivery. © 2015 American Association of Physicists in Medicine.

Assessment of the point-source method for estimating dose rates to members of the public from exposure to patients with 131I thyroid treatment

DOE PAGES

Dewji, Shaheen Azim; Bellamy, Michael B.; Hertel, Nolan E.; ...

2015-09-01

The U.S. Nuclear Regulatory Commission (USNRC) initiated a contract with Oak Ridge National Laboratory (ORNL) to calculate radiation dose rates to members of the public that may result from exposure to patients recently administered iodine-131 ( 131I) as part of medical therapy. The main purpose was to compare dose rate estimates based on a point source and target with values derived from more realistic simulations that considered the time-dependent distribution of 131I in the patient and attenuation of emitted photons by the patient’s tissues. The external dose rate estimates were derived using Monte Carlo methods and two representations of themore » Phantom with Movable Arms and Legs, previously developed by ORNL and the USNRC, to model the patient and a nearby member of the public. Dose rates to tissues and effective dose rates were calculated for distances ranging from 10 to 300 cm between the phantoms and compared to estimates based on the point-source method, as well as to results of previous studies that estimated exposure from 131I patients. The point-source method overestimates dose rates to members of the public in very close proximity to an 131I patient but is a broadly accurate method of dose rate estimation at separation distances of 300 cm or more at times closer to administration.« less

Verification of dosimetric accuracy on the TrueBeam STx: rounded leaf effect of the high definition MLC.

PubMed

Kielar, Kayla N; Mok, Ed; Hsu, Annie; Wang, Lei; Luxton, Gary

2012-10-01

The dosimetric leaf gap (DLG) in the Varian Eclipse treatment planning system is determined during commissioning and is used to model the effect of the rounded leaf-end of the multileaf collimator (MLC). This parameter attempts to model the physical difference between the radiation and light field and account for inherent leakage between leaf tips. With the increased use of single fraction high dose treatments requiring larger monitor units comes an enhanced concern in the accuracy of leakage calculations, as it accounts for much of the patient dose. This study serves to verify the dosimetric accuracy of the algorithm used to model the rounded leaf effect for the TrueBeam STx, and describes a methodology for determining best-practice parameter values, given the novel capabilities of the linear accelerator such as flattening filter free (FFF) treatments and a high definition MLC (HDMLC). During commissioning, the nominal MLC position was verified and the DLG parameter was determined using MLC-defined field sizes and moving gap tests, as is common in clinical testing. Treatment plans were created, and the DLG was optimized to achieve less than 1% difference between measured and calculated dose. The DLG value found was tested on treatment plans for all energies (6 MV, 10 MV, 15 MV, 6 MV FFF, 10 MV FFF) and modalities (3D conventional, IMRT, conformal arc, VMAT) available on the TrueBeam STx. The DLG parameter found during the initial MLC testing did not match the leaf gap modeling parameter that provided the most accurate dose delivery in clinical treatment plans. Using the physical leaf gap size as the DLG for the HDMLC can lead to 5% differences in measured and calculated doses. Separate optimization of the DLG parameter using end-to-end tests must be performed to ensure dosimetric accuracy in the modeling of the rounded leaf ends for the Eclipse treatment planning system. The difference in leaf gap modeling versus physical leaf gap dimensions is more pronounced in the more recent versions of Eclipse for both the HDMLC and the Millennium MLC. Once properly commissioned and tested using a methodology based on treatment plan verification, Eclipse is able to accurately model radiation dose delivered for SBRT treatments using the TrueBeam STx.

GGEMS-Brachy: GPU GEant4-based Monte Carlo simulation for brachytherapy applications

NASA Astrophysics Data System (ADS)

Lemaréchal, Yannick; Bert, Julien; Falconnet, Claire; Després, Philippe; Valeri, Antoine; Schick, Ulrike; Pradier, Olivier; Garcia, Marie-Paule; Boussion, Nicolas; Visvikis, Dimitris

2015-07-01

In brachytherapy, plans are routinely calculated using the AAPM TG43 formalism which considers the patient as a simple water object. An accurate modeling of the physical processes considering patient heterogeneity using Monte Carlo simulation (MCS) methods is currently too time-consuming and computationally demanding to be routinely used. In this work we implemented and evaluated an accurate and fast MCS on Graphics Processing Units (GPU) for brachytherapy low dose rate (LDR) applications. A previously proposed Geant4 based MCS framework implemented on GPU (GGEMS) was extended to include a hybrid GPU navigator, allowing navigation within voxelized patient specific images and analytically modeled 125I seeds used in LDR brachytherapy. In addition, dose scoring based on track length estimator including uncertainty calculations was incorporated. The implemented GGEMS-brachy platform was validated using a comparison with Geant4 simulations and reference datasets. Finally, a comparative dosimetry study based on the current clinical standard (TG43) and the proposed platform was performed on twelve prostate cancer patients undergoing LDR brachytherapy. Considering patient 3D CT volumes of 400  × 250  × 65 voxels and an average of 58 implanted seeds, the mean patient dosimetry study run time for a 2% dose uncertainty was 9.35 s (≈500 ms 10-6 simulated particles) and 2.5 s when using one and four GPUs, respectively. The performance of the proposed GGEMS-brachy platform allows envisaging the use of Monte Carlo simulation based dosimetry studies in brachytherapy compatible with clinical practice. Although the proposed platform was evaluated for prostate cancer, it is equally applicable to other LDR brachytherapy clinical applications. Future extensions will allow its application in high dose rate brachytherapy applications.

Sci—Thur PM: Planning and Delivery — 03: Automated delivery and quality assurance of a modulated electron radiation therapy plan

DOE Office of Scientific and Technical Information (OSTI.GOV)

Connell, T; Papaconstadopoulos, P; Alexander, A

2014-08-15

Modulated electron radiation therapy (MERT) offers the potential to improve healthy tissue sparing through increased dose conformity. Challenges remain, however, in accurate beamlet dose calculation, plan optimization, collimation method and delivery accuracy. In this work, we investigate the accuracy and efficiency of an end-to-end MERT plan and automated-delivery workflow for the electron boost portion of a previously treated whole breast irradiation case. Dose calculations were performed using Monte Carlo methods and beam weights were determined using a research-based treatment planning system capable of inverse optimization. The plan was delivered to radiochromic film placed in a water equivalent phantom for verification,more » using an automated motorized tertiary collimator. The automated delivery, which covered 4 electron energies, 196 subfields and 6183 total MU was completed in 25.8 minutes, including 6.2 minutes of beam-on time with the remainder of the delivery time spent on collimator leaf motion and the automated interfacing with the accelerator in service mode. The delivery time could be reduced by 5.3 minutes with minor electron collimator modifications and the beam-on time could be reduced by and estimated factor of 2–3 through redesign of the scattering foils. Comparison of the planned and delivered film dose gave 3%/3 mm gamma pass rates of 62.1, 99.8, 97.8, 98.3, and 98.7 percent for the 9, 12, 16, 20 MeV, and combined energy deliveries respectively. Good results were also seen in the delivery verification performed with a MapCHECK 2 device. The results showed that accurate and efficient MERT delivery is possible with current technologies.« less

Monte Carlo-based QA for IMRT of head and neck cancers

NASA Astrophysics Data System (ADS)

Tang, F.; Sham, J.; Ma, C.-M.; Li, J.-S.

2007-06-01

It is well-known that the presence of large air cavity in a dense medium (or patient) introduces significant electronic disequilibrium when irradiated with megavoltage X-ray field. This condition may worsen by the possible use of tiny beamlets in intensity-modulated radiation therapy (IMRT). Commercial treatment planning systems (TPSs), in particular those based on the pencil-beam method, do not provide accurate dose computation for the lungs and other cavity-laden body sites such as the head and neck. In this paper we present the use of Monte Carlo (MC) technique for dose re-calculation of IMRT of head and neck cancers. In our clinic, a turn-key software system is set up for MC calculation and comparison with TPS-calculated treatment plans as part of the quality assurance (QA) programme for IMRT delivery. A set of 10 off-the-self PCs is employed as the MC calculation engine with treatment plan parameters imported from the TPS via a graphical user interface (GUI) which also provides a platform for launching remote MC simulation and subsequent dose comparison with the TPS. The TPS-segmented intensity maps are used as input for the simulation hence skipping the time-consuming simulation of the multi-leaf collimator (MLC). The primary objective of this approach is to assess the accuracy of the TPS calculations in the presence of air cavities in the head and neck whereas the accuracy of leaf segmentation is verified by fluence measurement using a fluoroscopic camera-based imaging device. This measurement can also validate the correct transfer of intensity maps to the record and verify system. Comparisons between TPS and MC calculations of 6 MV IMRT for typical head and neck treatments review regional consistency in dose distribution except at and around the sinuses where our pencil-beam-based TPS sometimes over-predicts the dose by up to 10%, depending on the size of the cavities. In addition, dose re-buildup of up to 4% is observed at the posterior nasopharyngeal mucosa for some treatments with heavily-weighted anterior fields.

Reducing the number of CTs performed to monitor personalized dosimetry during peptide receptor radionuclide therapy (PRRT).

PubMed

Chicheportiche, Alexandre; Artoul, Faozi; Schwartz, Arnon; Grozinsky-Glasberg, Simona; Meirovitz, Amichay; Gross, David J; Godefroy, Jeremy

2018-06-19

Peptide receptor radionuclide therapy (PRRT) with [ 177 Lu]-DOTA-TATE is an effective treatment of neuroendocrine tumors (NETs). After each cycle of treatment, patient dosimetry evaluates the radiation dose to the risk organs, kidneys, and bone marrow, the most radiosensitive tissues. Absorbed doses are calculated from the radioactivity in the blood and from single photon emission computed tomography (SPECT) images corrected by computed tomography (CT) acquired after each course of treatment. The aim of this work is to assess whether the dosimetry along all treatment cycles can be calculated using a single CT. We hypothesize that the absorbed doses to the risk organs calculated with a single CT will be accurate enough to correctly manage the patients, i.e., whether or not to continue PRRT. Twenty-four patients diagnosed with metastatic NETs undergoing PRRT with [ 177 Lu]-DOTA-TATE were retrospectively included in this study. We compared radiation doses to the kidneys and bone marrow using two protocols. In the "classical" one, dosimetry is calculated based on a SPECT and a CT after each treatment cycle. In the new protocol, dosimetry is calculated based on a SPECT study after each cycle but with the first acquired CT for all cycles. The decision whether or not to stop PRRT because of unsafe absorbed dose to the risk organs would have been the same had the classical or the new protocol been used. The agreement between the cumulative doses to the kidneys and bone marrow obtained from the two protocols was excellent with Pearson's correlation coefficients r = 0.95 and r = 0.99 (P < 0.0001) and mean relative differences of 5.30 ± 6.20% and 0.48 ± 4.88%, respectively. Dosimetry calculations for a given patient can be done using a single CT registered to serial SPECTs. This new protocol reduces the need for a hybrid camera in the follow-up of patients receiving [ 177 Lu]-DOTA-TATE.

Monte Carlo calculated microdosimetric spread for cell nucleus-sized targets exposed to brachytherapy 125I and 192Ir sources and 60Co cell irradiation.

PubMed

Villegas, Fernanda; Tilly, Nina; Ahnesjö, Anders

2013-09-07

The stochastic nature of ionizing radiation interactions causes a microdosimetric spread in energy depositions for cell or cell nucleus-sized volumes. The magnitude of the spread may be a confounding factor in dose response analysis. The aim of this work is to give values for the microdosimetric spread for a range of doses imparted by (125)I and (192)Ir brachytherapy radionuclides, and for a (60)Co source. An upgraded version of the Monte Carlo code PENELOPE was used to obtain frequency distributions of specific energy for each of these radiation qualities and for four different cell nucleus-sized volumes. The results demonstrate that the magnitude of the microdosimetric spread increases when the target size decreases or when the energy of the radiation quality is reduced. Frequency distributions calculated according to the formalism of Kellerer and Chmelevsky using full convolution of the Monte Carlo calculated single track frequency distributions confirm that at doses exceeding 0.08 Gy for (125)I, 0.1 Gy for (192)Ir, and 0.2 Gy for (60)Co, the resulting distribution can be accurately approximated with a normal distribution. A parameterization of the width of the distribution as a function of dose and target volume of interest is presented as a convenient form for the use in response modelling or similar contexts.

Improved tissue assignment using dual-energy computed tomography in low-dose rate prostate brachytherapy for Monte Carlo dose calculation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Côté, Nicolas; Bedwani, Stéphane; Carrier, Jean-François, E-mail: jean-francois.carrier.chum@ssss.gouv.qc.ca

Purpose: An improvement in tissue assignment for low-dose rate brachytherapy (LDRB) patients using more accurate Monte Carlo (MC) dose calculation was accomplished with a metallic artifact reduction (MAR) method specific to dual-energy computed tomography (DECT). Methods: The proposed MAR algorithm followed a four-step procedure. The first step involved applying a weighted blend of both DECT scans (I {sub H/L}) to generate a new image (I {sub Mix}). This action minimized Hounsfield unit (HU) variations surrounding the brachytherapy seeds. In the second step, the mean HU of the prostate in I {sub Mix} was calculated and shifted toward the mean HUmore » of the two original DECT images (I {sub H/L}). The third step involved smoothing the newly shifted I {sub Mix} and the two original I {sub H/L}, followed by a subtraction of both, generating an image that represented the metallic artifact (I {sub A,(H/L)}) of reduced noise levels. The final step consisted of subtracting the original I {sub H/L} from the newly generated I {sub A,(H/L)} and obtaining a final image corrected for metallic artifacts. Following the completion of the algorithm, a DECT stoichiometric method was used to extract the relative electronic density (ρ{sub e}) and effective atomic number (Z {sub eff}) at each voxel of the corrected scans. Tissue assignment could then be determined with these two newly acquired physical parameters. Each voxel was assigned the tissue bearing the closest resemblance in terms of ρ{sub e} and Z {sub eff}, comparing with values from the ICRU 42 database. A MC study was then performed to compare the dosimetric impacts of alternative MAR algorithms. Results: An improvement in tissue assignment was observed with the DECT MAR algorithm, compared to the single-energy computed tomography (SECT) approach. In a phantom study, tissue misassignment was found to reach 0.05% of voxels using the DECT approach, compared with 0.40% using the SECT method. Comparison of the DECT and SECT D {sub 90} dose parameter (volume receiving 90% of the dose) indicated that D {sub 90} could be underestimated by up to 2.3% using the SECT method. Conclusions: The DECT MAR approach is a simple alternative to reduce metallic artifacts found in LDRB patient scans. Images can be processed quickly and do not require the determination of x-ray spectra. Substantial information on density and atomic number can also be obtained. Furthermore, calcifications within the prostate are detected by the tissue assignment algorithm. This enables more accurate, patient-specific MC dose calculations.« less

Metallic artifact mitigation and organ-constrained tissue assignment for Monte Carlo calculations of permanent implant lung brachytherapy.

PubMed

Sutherland, J G H; Miksys, N; Furutani, K M; Thomson, R M

2014-01-01

To investigate methods of generating accurate patient-specific computational phantoms for the Monte Carlo calculation of lung brachytherapy patient dose distributions. Four metallic artifact mitigation methods are applied to six lung brachytherapy patient computed tomography (CT) images: simple threshold replacement (STR) identifies high CT values in the vicinity of the seeds and replaces them with estimated true values; fan beam virtual sinogram replaces artifact-affected values in a virtual sinogram and performs a filtered back-projection to generate a corrected image; 3D median filter replaces voxel values that differ from the median value in a region of interest surrounding the voxel and then applies a second filter to reduce noise; and a combination of fan beam virtual sinogram and STR. Computational phantoms are generated from artifact-corrected and uncorrected images using several tissue assignment schemes: both lung-contour constrained and unconstrained global schemes are considered. Voxel mass densities are assigned based on voxel CT number or using the nominal tissue mass densities. Dose distributions are calculated using the EGSnrc user-code BrachyDose for (125)I, (103)Pd, and (131)Cs seeds and are compared directly as well as through dose volume histograms and dose metrics for target volumes surrounding surgical sutures. Metallic artifact mitigation techniques vary in ability to reduce artifacts while preserving tissue detail. Notably, images corrected with the fan beam virtual sinogram have reduced artifacts but residual artifacts near sources remain requiring additional use of STR; the 3D median filter removes artifacts but simultaneously removes detail in lung and bone. Doses vary considerably between computational phantoms with the largest differences arising from artifact-affected voxels assigned to bone in the vicinity of the seeds. Consequently, when metallic artifact reduction and constrained tissue assignment within lung contours are employed in generated phantoms, this erroneous assignment is reduced, generally resulting in higher doses. Lung-constrained tissue assignment also results in increased doses in regions of interest due to a reduction in the erroneous assignment of adipose to voxels within lung contours. Differences in dose metrics calculated for different computational phantoms are sensitive to radionuclide photon spectra with the largest differences for (103)Pd seeds and smallest but still considerable differences for (131)Cs seeds. Despite producing differences in CT images, dose metrics calculated using the STR, fan beam + STR, and 3D median filter techniques produce similar dose metrics. Results suggest that the accuracy of dose distributions for permanent implant lung brachytherapy is improved by applying lung-constrained tissue assignment schemes to metallic artifact corrected images.

SU-E-T-287: Patterns of Patient Specific Dosimetry in Total Body Irradiation.

PubMed

Akino, Y; McMullen, K; Das, I

2012-06-01

Total body irradiation (TBI) is commonly used for conditioning prior to transplant in hematologic and immunologic diseases. Due to variability in body thickness, achieving dose uniformity across body within ±10% of the prescribed dose is challenging. The dose uniformity is further complicated by, techniques and beam energy used, lung shielding and selection of detector. The translational table technique for TBI could compensate for estimated delivered dose to whole body by adjusting couch speed during treatment. However, it is difficult to accurately estimate the dose by calculation and hence in vivo dosimetry (IVD) is routinely performed for TBI. The patterns of patient specific dosimetry, IVD are presented in this study. Under IRB exempt status, 161 patients who received TBI treatment between 2006 and 2011 were retrospectively analyzed using the treatment records from Cobalt-60 teletherapy unit and translational treatment couch. During treatment, IVD detectors (TLD, diode, or MOSFET) were placed on patient surface; both entrance and exit dose were recorded at the patient's head, neck, mediastinum, umbilicus, and knee. When large differences between prescribed and measured dose were observed, the dose delivery was corrected for subsequent fractions by adjustment in couch speed and/or bolus placement. Across the entire cohort, the mean (range) percent variance between calculated and measured dose were -2.3% (-66.2 - 35.3), 1.1% (-62.2 - 40.3), -1.9% (-66.4 - 46.6), -1.1% (-35.2 - 42.9), and 3.4% (-47.9 - 108.5) for head, neck, mediastinum, umbilicus, and knee, respectively. When the dose differences for multiple fractions were averaged, the compliance (±10%) between prescription and measured dose was improved as at umbilicus from 83.9% to 98.5%. Actual dose measurement analysis of TBI patients reveals a potentially wide variance from calculated dose. Dose uniformity can be significantly improved with immediate feedback after the first fraction prior to subsequent treatments. This work was supported by the JSPS Core-to-Core Program No. 23003. © 2012 American Association of Physicists in Medicine.

SU-F-T-430: Validation of IBEAM Evo Couch Top for Different Relative Electron Density (RED) Combination During Photon Beam Dose Calculation in Monaco− Treatment Planning System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manigandan, D; Kumar, M; Mohandas, P

Purpose: Validation of iBEAM™ evo couch-top for different relative electron density (RED) combination during photon beam dose calculation in Monaco− TPS. Methods: The iBEAM™ evo couch-top has two layers:outer carbon fiber (CF) and inner foam core (FC). To study the beam intensity attenuation of couch-top, measured doses were compared with doses calculated for different REDs. Measurements were performed in solid water phantom with PTW-0.125cc ion-chamber positioned at center of the phantom with 5.3cm thickness slabs placed above and below the chamber. Similarly, in TPS, iBEAM™ evo couch-top was simulated and doses were calculated for different RED combinations (0.2CF-0.2FC, 0.4CF-0.2FC, 0.6CF-0.2FC,more » 0.8CF-0.2FC, and 1.0CF-0.2FC) by using Monte Carlo dose calculation algorithm in Monaco TPS (V5.1). Doses were measured for every 10 degree gantry angle separation, 10×10cm{sup 2} field size and 6MV photons. Then, attenuation is defined as the ratio of output at posterior gantry angle to output of its opposed anterior gantry angle (e.g.225°/45°). output fluctuation with different gantry angle was within ±0.21%. To confirm above results, dose-planes were measured for five pelvic VMAT plans (360°arc) in PTW two-dimensional array and compared with different calculated dose-planes of above-mentioned couch REDs. Gamma pass rates<1.00) were analyzed for 3%/2mm criteria. Results: Measured and calculated attenuation was in good agreement for the RED combination of 0.2CF-0.2FC and difference was within ±0.515%. However, other density combination showed difference of ±0.9841%, ±1.667%, ±2.9241% and ±2.8832% for 0.4CF-0.2FC, 0.6CF-0.2FC, 0.8CF-0.2FC, and 1.0CF-0.2FC, respectively. Maximum couch-top attenuation was observed at 110°–120° and 240°–250° and decreases linearly as the gantry angle approaches 180°. Moreover, gamma pass rate confirmed the above results and showed maximum pass rate of 96.23% for 0.2CF-0.2FC, whereas others were 95.72%, 95.12%, 94.31% and 93.24%. Conclusion: RED value of 0.2CF-0.2FC was found to be suitable for accurate couch-top modeling for 6MV photon beam Monte Carlo calculations in Monaco TPS.« less

The influence of Monte Carlo source parameters on detector design and dose perturbation in small field dosimetry

NASA Astrophysics Data System (ADS)

Charles, P. H.; Crowe, S. B.; Kairn, T.; Knight, R.; Hill, B.; Kenny, J.; Langton, C. M.; Trapp, J. V.

2014-03-01

To obtain accurate Monte Carlo simulations of small radiation fields, it is important model the initial source parameters (electron energy and spot size) accurately. However recent studies have shown that small field dosimetry correction factors are insensitive to these parameters. The aim of this work is to extend this concept to test if these parameters affect dose perturbations in general, which is important for detector design and calculating perturbation correction factors. The EGSnrc C++ user code cavity was used for all simulations. Varying amounts of air between 0 and 2 mm were deliberately introduced upstream to a diode and the dose perturbation caused by the air was quantified. These simulations were then repeated using a range of initial electron energies (5.5 to 7.0 MeV) and electron spot sizes (0.7 to 2.2 FWHM). The resultant dose perturbations were large. For example 2 mm of air caused a dose reduction of up to 31% when simulated with a 6 mm field size. However these values did not vary by more than 2 % when simulated across the full range of source parameters tested. If a detector is modified by the introduction of air, one can be confident that the response of the detector will be the same across all similar linear accelerators and the Monte Carlo modelling of each machine is not required.

Tumor and red bone marrow dosimetry: comparison of methods for prospective treatment planning in pretargeted radioimmunotherapy.

PubMed

Woliner-van der Weg, Wietske; Schoffelen, Rafke; Hobbs, Robert F; Gotthardt, Martin; Goldenberg, David M; Sharkey, Robert M; Slump, Cornelis H; van der Graaf, Winette Ta; Oyen, Wim Jg; Boerman, Otto C; Sgouros, George; Visser, Eric P

2015-12-01

Red bone marrow (RBM) toxicity is dose-limiting in (pretargeted) radioimmunotherapy (RIT). Previous blood-based and two-dimensional (2D) image-based methods have failed to show a clear dose-response relationship. We developed a three-dimensional (3D) image-based RBM dosimetry approach using the Monte Carlo-based 3D radiobiological dosimetry (3D-RD) software and determined its additional value for predicting RBM toxicity. RBM doses were calculated for 13 colorectal cancer patients after pretargeted RIT with the two-step administration of an anti-CEA × anti-HSG bispecific monoclonal antibody and a (177)Lu-labeled di-HSG-peptide. 3D-RD RBM dosimetry was based on the lumbar vertebrae, delineated on single photon emission computed tomography (SPECT) scans acquired directly, 3, 24, and 72 h after (177)Lu administration. RBM doses were correlated to hematologic effects, according to NCI-CTC v3 and compared with conventional 2D cranium-based and blood-based dosimetry results. Tumor doses were calculated with 3D-RD, which has not been possible with 2D dosimetry. Tumor-to-RBM dose ratios were calculated and compared for (177)Lu-based pretargeted RIT and simulated pretargeted RIT with (90)Y. 3D-RD RBM doses of all seven patients who developed thrombocytopenia were higher (range 0.43 to 0.97 Gy) than that of the six patients without thrombocytopenia (range 0.12 to 0.39 Gy), except in one patient (0.47 Gy) without thrombocytopenia but with grade 2 leucopenia. Blood and 2D image-based RBM doses for patients with grade 1 to 2 thrombocytopenia were in the same range as in patients without thrombocytopenia (0.14 to 0.29 and 0.11 to 0.26 Gy, respectively). Blood-based RBM doses for two grade 3 to 4 patients were higher (0.66 and 0.51 Gy, respectively) than the others, and the cranium-based dose of only the grade 4 patient was higher (0.34 Gy). Tumor-to-RBM dose ratios would increase by 25% on average when treating with (90)Y instead of (177)Lu. 3D dosimetry identifies patients at risk of developing any grade of RBM toxicity more accurately than blood- or 2D image-based methods. It has the added value to enable calculation of tumor-to-RBM dose ratios.

Assessment of the unattached fraction of indoor radon progeny and its contribution to dose: a pilot study in China.

PubMed

Guo, Qiuju; Zhang, Lei; Guo, Lu

2012-12-01

The unattached fraction of radon progeny (f(p)) is one of the most important factors for accurate evaluation of the effective dose from a unit of radon exposure, and it may vary greatly in different environments. For precise evaluation of the indoor radon exposure dose and the influence of unattached radon progeny, a pilot survey of f(p) in different environments was carried out in China with a portable and integrating monitor. The dose conversion factors for radon progeny are calculated with LUDEP(®) code, and the dose contributions from the unattached and the attached radon progenies were simultaneously evaluated based on the results of field measurements. The results show that even though the concentrations of radon progeny vary significantly among different indoor environments, the variations of f(p) seem relatively small (9.3-16.9%). The dose contribution from unattached radon progeny is generally larger (30.2-46.2%) in an indoor environment.

Radiation dose delivery verification in the treatment of carcinoma-cervix

NASA Astrophysics Data System (ADS)

Shrotriya, D.; Kumar, S.; Srivastava, R. N. L.

2015-06-01

The accurate dose delivery to the clinical target volume in radiotherapy can be affected by various pelvic tissues heterogeneities. An in-house heterogeneous woman pelvic phantom was designed and used to verify the consistency and computational capability of treatment planning system of radiation dose delivery in the treatment of cancer cervix. Oncentra 3D-TPS with collapsed cone convolution (CCC) dose calculation algorithm was used to generate AP/PA and box field technique plan. the radiation dose was delivered by Primus Linac (Siemens make) employing high energy 15 MV photon beam by isocenter technique. A PTW make, 0.125cc ionization chamber was used for direct measurements at various reference points in cervix, bladder and rectum. The study revealed that maximum variation between computed and measured dose at cervix reference point was 1% in both the techniques and 3% and 4% variation in AP/PA field and 5% and 4.5% in box technique at bladder and rectum points respectively.

Comparison of Martian Meteorites and Martian Regolith as Shield Materials for Galactic Cosmic Rays

NASA Technical Reports Server (NTRS)

Kim, Myung-Hee Y.; Thibeault, Sheila A.; Simonsen, Lisa C.; Wilson, John W.

1998-01-01

Theoretical calculations of radiation attenuation due to energetic galactic cosmic rays behind Martian rock and Martian regolith material have been made to compare their utilization as shields for advanced manned missions to Mars because the detailed chemical signature of Mars is distinctly different from Earth. The modified radiation fields behind the Martian rocks and the soil model were generated by solving the Boltzmann equation using a HZETRN system with the 1977 Solar Minimum environmental model. For the comparison of the attenuation characteristics, dose and dose equivalent are calculated for the five different subgroups of Martian rocks and the Martian regolith. The results indicate that changes in composition of subgroups of Martian rocks have negligible effects on the overall shielding properties because of the similarity of their constituents. The differences for dose and dose equivalent of these materials relative to those of Martian regolith are within 0.5 and 1 percent, respectively. Therefore, the analysis of Martian habitat construction options using in situ materials according to the Martian regolith model composition is reasonably accurate. Adding an epoxy to Martian regolith, which changes the major constituents of the material, enhances shielding properties because of the added hydrogenous constituents.

MRI-Only Based Radiotherapy Treatment Planning for the Rat Brain on a Small Animal Radiation Research Platform (SARRP).

PubMed

Gutierrez, Shandra; Descamps, Benedicte; Vanhove, Christian

2015-01-01

Computed tomography (CT) is the standard imaging modality in radiation therapy treatment planning (RTP). However, magnetic resonance (MR) imaging provides superior soft tissue contrast, increasing the precision of target volume selection. We present MR-only based RTP for a rat brain on a small animal radiation research platform (SARRP) using probabilistic voxel classification with multiple MR sequences. Six rat heads were imaged, each with one CT and five MR sequences. The MR sequences were: T1-weighted, T2-weighted, zero-echo time (ZTE), and two ultra-short echo time sequences with 20 μs (UTE1) and 2 ms (UTE2) echo times. CT data were manually segmented into air, soft tissue, and bone to obtain the RTP reference. Bias field corrected MR images were automatically segmented into the same tissue classes using a fuzzy c-means segmentation algorithm with multiple images as input. Similarities between segmented CT and automatic segmented MR (ASMR) images were evaluated using Dice coefficient. Three ASMR images with high similarity index were used for further RTP. Three beam arrangements were investigated. Dose distributions were compared by analysing dose volume histograms. The highest Dice coefficients were obtained for the ZTE-UTE2 combination and for the T1-UTE1-T2 combination when ZTE was unavailable. Both combinations, along with UTE1-UTE2, often used to generate ASMR images, were used for further RTP. Using 1 beam, MR based RTP underestimated the dose to be delivered to the target (range: 1.4%-7.6%). When more complex beam configurations were used, the calculated dose using the ZTE-UTE2 combination was the most accurate, with 0.7% deviation from CT, compared to 0.8% for T1-UTE1-T2 and 1.7% for UTE1-UTE2. The presented MR-only based workflow for RTP on a SARRP enables both accurate organ delineation and dose calculations using multiple MR sequences. This method can be useful in longitudinal studies where CT's cumulative radiation dose might contribute to the total dose.

MRI-Only Based Radiotherapy Treatment Planning for the Rat Brain on a Small Animal Radiation Research Platform (SARRP)

PubMed Central

Gutierrez, Shandra; Descamps, Benedicte; Vanhove, Christian

2015-01-01

Computed tomography (CT) is the standard imaging modality in radiation therapy treatment planning (RTP). However, magnetic resonance (MR) imaging provides superior soft tissue contrast, increasing the precision of target volume selection. We present MR-only based RTP for a rat brain on a small animal radiation research platform (SARRP) using probabilistic voxel classification with multiple MR sequences. Six rat heads were imaged, each with one CT and five MR sequences. The MR sequences were: T1-weighted, T2-weighted, zero-echo time (ZTE), and two ultra-short echo time sequences with 20 μs (UTE1) and 2 ms (UTE2) echo times. CT data were manually segmented into air, soft tissue, and bone to obtain the RTP reference. Bias field corrected MR images were automatically segmented into the same tissue classes using a fuzzy c-means segmentation algorithm with multiple images as input. Similarities between segmented CT and automatic segmented MR (ASMR) images were evaluated using Dice coefficient. Three ASMR images with high similarity index were used for further RTP. Three beam arrangements were investigated. Dose distributions were compared by analysing dose volume histograms. The highest Dice coefficients were obtained for the ZTE-UTE2 combination and for the T1-UTE1-T2 combination when ZTE was unavailable. Both combinations, along with UTE1-UTE2, often used to generate ASMR images, were used for further RTP. Using 1 beam, MR based RTP underestimated the dose to be delivered to the target (range: 1.4%-7.6%). When more complex beam configurations were used, the calculated dose using the ZTE-UTE2 combination was the most accurate, with 0.7% deviation from CT, compared to 0.8% for T1-UTE1-T2 and 1.7% for UTE1-UTE2. The presented MR-only based workflow for RTP on a SARRP enables both accurate organ delineation and dose calculations using multiple MR sequences. This method can be useful in longitudinal studies where CT’s cumulative radiation dose might contribute to the total dose. PMID:26633302

The future of dental amalgam: a review of the literature. Part 3: Mercury exposure from amalgam restorations in dental patients.

PubMed

Eley, B M

1997-05-10

This is the third article in a series of seven on the future of dental amalgam and covers mercury exposure from functioning dental amalgam restorations in patients. It firstly discusses the evidence for mercury release from amalgam fillings by considering the mechanisms of mercury release and its measurement in the expired air and the intra-oral air. In this connection it also discusses the various factors involved in the accurate measurement and calculation of mercury levels in these situations. It finally describes the various attempts to calculate the daily mercury dose from dental amalgam fillings and considers the likely accuracy of these calculations.

Patient-specific FDG dosimetry for adult males, adult females, and very low birth weight infants

NASA Astrophysics Data System (ADS)

Niven, Erin

Fluorodeoxyglucose is the most commonly used radiopharmaceutical in Positron Emission Tomography, with applications in neurology, cardiology, and oncology. Despite its routine use worldwide, the radiation absorbed dose estimates from FDG have been based primarily on data obtained from two dogs studied in 1977 and 11 adults (most likely males) studied in 1982. In addition, the dose estimates calculated for FDG have been centered on the adult male, with little or no mention of variations in the dose estimates due to sex, age, height, weight, nationality, diet, or pathological condition. Through an extensive investigation into the Medical Internal Radiation Dose schema for calculating absorbed doses, I have developed a simple patient-specific equation; this equation incorporates the parameters necessary for alterations to the mathematical values of the human model to produce an estimate more representative of the individual under consideration. I have used this method to determine the range of absorbed doses to FDG from the collection of a large quantity of biological data obtained in adult males, adult females, and very low birth weight infants. Therefore, a more accurate quantification of the dose to humans from FDG has been completed. My results show that per unit administered activity, the absorbed dose from FDG is higher for infants compared to adults, and the dose for adult women is higher than for adult men. Given an injected activity of approximately 3.7 MBq kg-1, the doses for adult men, adult women, and full-term newborns would be on the order of 5.5, 7.1, and 2.8 mSv, respectively. These absorbed doses are comparable to the doses received from other nuclear medicine procedures.

I-125 ROPES eye plaque dosimetry: Validation of a commercial 3D ophthalmic brachytherapy treatment planning system and independent dose calculation software with GafChromic{sup ®} EBT3 films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poder, Joel; Corde, Stéphanie

Purpose: The purpose of this study was to measure the dose distributions for different Radiation Oncology Physics and Engineering Services, Australia (ROPES) type eye plaques loaded with I-125 (model 6711) seeds using GafChromic{sup ®} EBT3 films, in order to verify the dose distributions in the Plaque Simulator™ (PS) ophthalmic 3D treatment planning system. The brachytherapy module of RADCALC{sup ®} was used to independently check the dose distributions calculated by PS. Correction factors were derived from the measured data to be used in PS to account for the effect of the stainless steel ROPES plaque backing on the 3D dose distribution.Methods:more » Using GafChromic{sup ®} EBT3 films inserted in a specially designed Solid Water™ eye ball phantom, dose distributions were measured three-dimensionally both along and perpendicular to I-125 (model 6711) loaded ROPES eye plaque's central axis (CAX) with 2 mm depth increments. Each measurement was performed in full scatter conditions both with and without the stainless steel plaque backing attached to the eye plaque, to assess its effect on the dose distributions. Results were compared to the dose distributions calculated by Plaque Simulator™ and checked independently with RADCALC{sup ®}.Results: The EBT3 film measurements without the stainless steel backing were found to agree with PS and RADCALC{sup ®} to within 2% and 4%, respectively, on the plaque CAX. Also, RADCALC{sup ®} was found to agree with PS to within 2%. The CAX depth doses measured using EBT3 film with the stainless steel backing were observed to result in a 4% decrease relative to when the backing was not present. Within experimental uncertainty, the 4% decrease was found to be constant with depth and independent of plaque size. Using a constant dose correction factor of T= 0.96 in PS, where the calculated dose for the full water scattering medium is reduced by 4% in every voxel in the dose grid, the effect of the plaque backing was accurately modeled in the planning system. Off-axis profiles were also modeled in PS by taking into account the three-dimensional model of the plaque backing.Conclusions: The doses calculated by PS and RADCALC{sup ®} for uniformly loaded ROPES plaques in full and uniform scattering conditions were validated by the EBT3 film measurements. The stainless steel plaque backing was observed to decrease the measured dose by 4%. Through the introduction of a scalar correction factor (0.96) in PS, the dose homogeneity effect of the stainless steel plaque backing was found to agree with the measured EBT3 film measurements.« less

I-125 ROPES eye plaque dosimetry: validation of a commercial 3D ophthalmic brachytherapy treatment planning system and independent dose calculation software with GafChromic® EBT3 films.

PubMed

Poder, Joel; Corde, Stéphanie

2013-12-01

The purpose of this study was to measure the dose distributions for different Radiation Oncology Physics and Engineering Services, Australia (ROPES) type eye plaques loaded with I-125 (model 6711) seeds using GafChromic(®) EBT3 films, in order to verify the dose distributions in the Plaque Simulator™ (PS) ophthalmic 3D treatment planning system. The brachytherapy module of RADCALC(®) was used to independently check the dose distributions calculated by PS. Correction factors were derived from the measured data to be used in PS to account for the effect of the stainless steel ROPES plaque backing on the 3D dose distribution. Using GafChromic(®) EBT3 films inserted in a specially designed Solid Water™ eye ball phantom, dose distributions were measured three-dimensionally both along and perpendicular to I-125 (model 6711) loaded ROPES eye plaque's central axis (CAX) with 2 mm depth increments. Each measurement was performed in full scatter conditions both with and without the stainless steel plaque backing attached to the eye plaque, to assess its effect on the dose distributions. Results were compared to the dose distributions calculated by Plaque Simulator™ and checked independently with RADCALC(®). The EBT3 film measurements without the stainless steel backing were found to agree with PS and RADCALC(®) to within 2% and 4%, respectively, on the plaque CAX. Also, RADCALC(®) was found to agree with PS to within 2%. The CAX depth doses measured using EBT3 film with the stainless steel backing were observed to result in a 4% decrease relative to when the backing was not present. Within experimental uncertainty, the 4% decrease was found to be constant with depth and independent of plaque size. Using a constant dose correction factor of T = 0.96 in PS, where the calculated dose for the full water scattering medium is reduced by 4% in every voxel in the dose grid, the effect of the plaque backing was accurately modeled in the planning system. Off-axis profiles were also modeled in PS by taking into account the three-dimensional model of the plaque backing. The doses calculated by PS and RADCALC(®) for uniformly loaded ROPES plaques in full and uniform scattering conditions were validated by the EBT3 film measurements. The stainless steel plaque backing was observed to decrease the measured dose by 4%. Through the introduction of a scalar correction factor (0.96) in PS, the dose homogeneity effect of the stainless steel plaque backing was found to agree with the measured EBT3 film measurements.

SU-F-T-53: Treatment Planning with Inhomogeneity Correction for Intraoperative Radiotherapy Using KV X-Ray Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Y; Ghaly, M; Souri, S

Purpose: The current standard in dose calculation for intraoperative radiotherapy (IORT) using the ZEISS Intrabeam 50 kV x-ray system is based on depth dose measurements in water and no heterogeneous tissue effect has been taken into account. We propose an algorithm for pre-treatment planning including inhomogeneity correction based on data of depth dose measurements in various tissue phantoms for kV x-rays. Methods: Direct depth dose measurements were made in air, water, inner bone and cortical bone phantoms for the Intrabeam 50 kV x-rays with a needle applicator. The data were modelled by a function of power law combining exponential withmore » different parameters. Those phantom slabs used in the measurements were scanned to obtain CT numbers. The x-ray beam initiated from the source isocenter is ray-traced through tissues. The corresponding doses will be deposited/assigned at different depths. On the boundary of tissue/organ changes, the x-ray beam will be re-traced in new tissue/organ starting at an equivalent depth with the same dose. In principle, a volumetric dose distribution can be generated if enough directional beams are traced. In practice, a several typical rays traced may be adequate in providing estimates of maximum dose to the organ at risk and minimum dose in the target volume. Results: Depth dose measurements and modeling are shown in Figure 1. The dose versus CT number is shown in Figure 2. A computer program has been written for Kypho-IORT planning using those data. A direct measurement through 2 mm solid water, 2 mm inner bone, and 1 mm solid water yields a dose rate of 7.7 Gy/min. Our calculation shows 8.1±0.4 Gy/min, consistent with the measurement within 5%. Conclusion: The proposed method can be used to more accurately calculate the dose by taking into account the heterogeneous effect. The further validation includes comparison with Monte Carlo simulation.« less

Monaco and film dosimetry of 3D CRT, IMRT and VMAT cases in a realistic pelvic prosthetic phantom

NASA Astrophysics Data System (ADS)

Ade, Nicholas; du Plessis, F. C. P.

2018-04-01

The dosimetry of patients with metallic hip implants during irradiation of pelvic lesions is challenging due to dose distortions caused by implants. This work presents a dosimetric comparison of various multi-field photon-beam dose distributions in the presence of unilateral hip titanium prosthesis (UHTiP) embedded in a unique pelvic phantom made out of water-equivalent nylon slices. The impact of the UHTiP on the accuracy of dose calculations from a Monaco TPS (treatment planning system) using the X-ray voxel Monte Carlo (XVMC) algorithm was benchmarked against measured dose data using Gafchromic EBT3 film. Multi-field beam arrangements including a 4-field box, 5-field 3DCRT (three-dimensional conformal radiation therapy), 6-field IMRT (intensity modulated radiation therapy) and a single-arc VMAT (volumetric modulated arc therapy) plan were set up for 6 MV and 15 MV beams. These plans were generated for the pelvic phantom that contains the prosthesis with film inserted. Compared to Monaco TPS dose calculations, film measurements showed enhanced dose in the prosthesis which was not predicted by Monaco due to its limitation in relative density assignment. The enhanced prosthesis dose increased with increase in beam energy and decreased with the complexity of the treatment plans, with VMAT giving the least escalated dose. The dose increased between 5% and 19% for 6 MV and between 6% and 21% for 15 MV. A gamma index analysis showed that 70-92% of dose points (excluding the prosthesis) were within 3% discrepancy. Increasing the number of treatment fields increases target dose coverage and improves the agreement between film and Monaco. When the relative electron density (RED) in the prosthesis was varied between 3.72 and 15 the dose discrepancy between film and Monaco increased from 30% to 57% for 6 MV and from 30% to 50% for 15 MV. The study indicates that beam weights for fields that pass through the prosthesis should be minimised and its RED must be correct for accurate dose calculation on Monaco.

Preliminary skyshine calculations for the Poloidal Diverter Tokamak Experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nigg, D.W.; Wheeler, F.J.

1981-01-01

The Poloidal Diverter Experiment (PDX) facility at Princeton University is the first operating tokamak to require substantial radiation shielding. A calculational model has been developed to estimate the radiation dose in the PDX control room and at the site boundary due to the skyshine effect. An efficient one-dimensional method is used to compute the neutron and capture gamma leakage currents at the top surface of the PDX roof shield. This method employs an S /SUB n/ calculation in slab geometry and, for the PDX, is superior to spherical models found in the literature. If certain conditions are met, the slabmore » model provides the exact probability of leakage out the top surface of the roof for fusion source neutrons and for capture gamma rays produced in the PDX floor and roof shield. The model also provides the correct neutron and capture gamma leakage current spectra and angular distributions, averaged over the top roof shield surface. For the PDX, this method is nearly as accurate as multidimensional techniques for computing the roof leakage and is much less costly. The actual neutron skyshine dose is computed using a Monte Carlo model with the neutron source at the roof surface obtained from the slab S /SUB n/ calculation. The capture gamma dose is computed using a simple point-kernel single-scatter method.« less

Practical aspects and uncertainty analysis of biological effective dose (BED) regarding its three-dimensional calculation in multiphase radiotherapy treatment plans

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kauweloa, Kevin I., E-mail: Kauweloa@livemail.uthscsa.edu; Gutierrez, Alonso N.; Bergamo, Angelo

2014-07-15

Purpose: There is a growing interest in the radiation oncology community to use the biological effective dose (BED) rather than the physical dose (PD) in treatment plan evaluation and optimization due to its stronger correlation with radiobiological effects. Radiotherapy patients may receive treatments involving a single only phase or multiple phases (e.g., primary and boost). Since most treatment planning systems cannot calculate the analytical BED distribution in multiphase treatments, an approximate multiphase BED expression, which is based on the total physical dose distribution, has been used. The purpose of this paper is to reveal the mathematical properties of the approximatemore » BED formulation, relative to the true BED. Methods: The mathematical properties of the approximate multiphase BED equation are analyzed and evaluated. In order to better understand the accuracy of the approximate multiphase BED equation, the true multiphase BED equation was derived and the mathematical differences between the true and approximate multiphase BED equations were determined. The magnitude of its inaccuracies under common clinical circumstances was also studied. All calculations were performed on a voxel-by-voxel basis using the three-dimensional dose matrices. Results: Results showed that the approximate multiphase BED equation is accurate only when the dose-per-fractions (DPFs) in both the first and second phases are equal, which occur when the dose distribution does not significantly change between the phases. In the case of heterogeneous dose distributions, which significantly vary between the phases, there are fewer occurrences of equal DPFs and hence the inaccuracy of the approximate multiphase BED is greater. These characteristics are usually seen in the dose distributions being delivered to organs at risk rather than to targets. Conclusions: The finding of this study indicates that the true multiphase BED equation should be implemented in the treatment planning systems due to the inconsistent accuracy of the approximate multiphase BED equation in most of the clinical situations.« less

TH-C-BRD-02: Analytical Modeling and Dose Calculation Method for Asymmetric Proton Pencil Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gelover, E; Wang, D; Hill, P

2014-06-15

Purpose: A dynamic collimation system (DCS), which consists of two pairs of orthogonal trimmer blades driven by linear motors has been proposed to decrease the lateral penumbra in pencil beam scanning proton therapy. The DCS reduces lateral penumbra by intercepting the proton pencil beam near the lateral boundary of the target in the beam's eye view. The resultant trimmed pencil beams are asymmetric and laterally shifted, and therefore existing pencil beam dose calculation algorithms are not capable of trimmed beam dose calculations. This work develops a method to model and compute dose from trimmed pencil beams when using the DCS.more » Methods: MCNPX simulations were used to determine the dose distributions expected from various trimmer configurations using the DCS. Using these data, the lateral distribution for individual beamlets was modeled with a 2D asymmetric Gaussian function. The integral depth dose (IDD) of each configuration was also modeled by combining the IDD of an untrimmed pencil beam with a linear correction factor. The convolution of these two terms, along with the Highland approximation to account for lateral growth of the beam along the depth direction, allows a trimmed pencil beam dose distribution to be analytically generated. The algorithm was validated by computing dose for a single energy layer 5×5 cm{sup 2} treatment field, defined by the trimmers, using both the proposed method and MCNPX beamlets. Results: The Gaussian modeled asymmetric lateral profiles along the principal axes match the MCNPX data very well (R{sup 2}≥0.95 at the depth of the Bragg peak). For the 5×5 cm{sup 2} treatment plan created with both the modeled and MCNPX pencil beams, the passing rate of the 3D gamma test was 98% using a standard threshold of 3%/3 mm. Conclusion: An analytical method capable of accurately computing asymmetric pencil beam dose when using the DCS has been developed.« less

Automated seed localization from CT datasets of the prostate.

PubMed

Brinkmann, D H; Kline, R W

1998-09-01

With the increasing utilization of permanent brachytherapy implants for treating carcinoma of the prostate, the importance of accurate post-treatment dose calculation also increases for assessing patient outcome and planning future treatments. An automatic method for seed localization of permanent brachytherapy implants, using CT datasets of the prostate, has been developed and tested on a phantom using an actual patient planned seed distribution. This method was also compared to results with the three-film technique for three patient datasets. The automatic method is as accurate or more accurate than the three film technique for 1 mm, 3 mm, and 5 mm contiguous CT slices, and eliminates the inter- and intra-observer variability of the manual methods. The automated method improves the localization of brachytherapy seeds while reducing the time required for the user to input information, and is demonstrated to be less operator dependent, less time consuming, and potentially more accurate than the three-film technique.

Alpha particle and proton relative thermoluminescence efficiencies in LiF:Mg,Cu,P:is track structure theory up to the task?

PubMed

Horowitz, Y S; Siboni, D; Oster, L; Livingstone, J; Guatelli, S; Rosenfeld, A; Emfietzoglou, D; Bilski, P; Obryk, B

2012-07-01

Low-energy alpha particle and proton heavy charged particle (HCP) relative thermoluminescence (TL) efficiencies are calculated for the major dosimetric glow peak in LiF:Mg,Cu,P (MCP-N) in the framework of track structure theory (TST). The calculations employ previously published TRIPOS-E Monte Carlo track segment values of the radial dose in condensed phase LiF calculated at the Instituto National de Investigaciones Nucleares (Mexico) and experimentally measured normalised (60)Co gamma-induced TL dose-response functions, f(D), carried out at the Institute of Nuclear Physics (Poland). The motivation for the calculations is to test the validity of TST in a TL system in which f(D) is not supralinear (f(D) >1) and is not significantly dependent on photon energy contrary to the behaviour of the dose-response of composite peak 5 in the glow curve of LiF:Mg,Ti (TLD-100). The calculated HCP relative efficiencies in LiF:MCP-N are 23-87% lower than the experimentally measured values, indicating a weakness in the major premise of TST which exclusively relates HCP effects to the radiation action of the secondary electrons liberated by the HCP slowing down. However, an analysis of the uncertainties involved in the TST calculations and experiments (i.e. experimental measurement of f(D) at high levels of dose, sample light self-absorption and accuracy in the estimation of D(r), especially towards the end of the HCP track) indicate that these may be too large to enable a definite conclusion. More accurate estimation of sample light self-absorption, improved measurements of f(D) and full-track Monte Carlo calculations of D(r) incorporating improvements of the low-energy electron transport are indicated in order to reduce uncertainties and enable a final conclusion.

Energy-based dosimetry of low-energy, photon-emitting brachytherapy sources

NASA Astrophysics Data System (ADS)

Malin, Martha J.

Model-based dose calculation algorithms (MBDCAs) for low-energy, photon-emitting brachytherapy sources have advanced to the point where the algorithms may be used in clinical practice. Before these algorithms can be used, a methodology must be established to verify the accuracy of the source models used by the algorithms. Additionally, the source strength metric for these algorithms must be established. This work explored the feasibility of verifying the source models used by MBDCAs by measuring the differential photon fluence emitted from the encapsulation of the source. The measured fluence could be compared to that modeled by the algorithm to validate the source model. This work examined how the differential photon fluence varied with position and angle of emission from the source, and the resolution that these measurements would require for dose computations to be accurate to within 1.5%. Both the spatial and angular resolution requirements were determined. The techniques used to determine the resolution required for measurements of the differential photon fluence were applied to determine why dose-rate constants determined using a spectroscopic technique disagreed with those computed using Monte Carlo techniques. The discrepancy between the two techniques had been previously published, but the cause of the discrepancy was not known. This work determined the impact that some of the assumptions used by the spectroscopic technique had on the accuracy of the calculation. The assumption of isotropic emission was found to cause the largest discrepancy in the spectroscopic dose-rate constant. Finally, this work improved the instrumentation used to measure the rate at which energy leaves the encapsulation of a brachytherapy source. This quantity is called emitted power (EP), and is presented as a possible source strength metric for MBDCAs. A calorimeter that measured EP was designed and built. The theoretical framework that the calorimeter relied upon to measure EP was established. Four clinically relevant 125I brachytherapy sources were measured with the instrument. The accuracy of the measured EP was compared to an air-kerma strength-derived EP to test the accuracy of the instrument. The instrument was accurate to within 10%, with three out of the four source measurements accurate to within 4%.

Benchmark solutions for the galactic ion transport equations: Energy and spatially dependent problems

NASA Technical Reports Server (NTRS)

Ganapol, Barry D.; Townsend, Lawrence W.; Wilson, John W.

1989-01-01

Nontrivial benchmark solutions are developed for the galactic ion transport (GIT) equations in the straight-ahead approximation. These equations are used to predict potential radiation hazards in the upper atmosphere and in space. Two levels of difficulty are considered: (1) energy independent, and (2) spatially independent. The analysis emphasizes analytical methods never before applied to the GIT equations. Most of the representations derived have been numerically implemented and compared to more approximate calculations. Accurate ion fluxes are obtained (3 to 5 digits) for nontrivial sources. For monoenergetic beams, both accurate doses and fluxes are found. The benchmarks presented are useful in assessing the accuracy of transport algorithms designed to accommodate more complex radiation protection problems. In addition, these solutions can provide fast and accurate assessments of relatively simple shield configurations.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pokhrel, D; Badkul, R; Jiang, H

Purpose: To compare dose distributions calculated using the iPlan XVMC algorithm and heterogeneities corrected/uncorrected Pencil Beam (PB-hete/PB-homo) algorithms for SBRT treatments of lung tumors. Methods: Ten patients with centrally located solitary lung tumors were treated using MC-based SBRT to 60Gy in 5 fractions for PTVV100%=95%. ITV was delineated on MIP-images based on 4D-CT scans. PTVs(ITV+5mm margins) ranged from 10.1–106.5cc(mean=48.6cc). MC-SBRT plans were generated with a combination of non-coplanar conformal arcs/beams using iPlan-XVMC-algorithm (BrainLABiPlan ver.4.1.2) for Novalis-TX consisting of HD-MLCs and 6MV-SRS(1000MU/min) mode, following RTOG 0813 dosimetric criteria. For comparison, PB-hete/PB-homo algorithms were used to re-calculate dose distributions using same beammore » configurations, MLCs/monitor units. Plans were evaluated with isocenter/maximal/mean doses to PTV. Normal lung doses were evaluated with V5/V10/V20 and mean-lung-dose(MLD), excluding PTV. Other OAR doses such as maximal spinal cord/2cc-esophagus/max bronchial tree (BT/maximal heart doses were tabulated. Results: Maximal/mean/isocenter doses to PTV calculated by PB-hete were uniformly larger than MC plans by a factors of 1.09/1.13/1.07, on average, whereas they were consistently lower by PB-homo by a factors of 0.9/0.84/0.9, respectively. The volume covered by 5Gy/10Gy/20Gy isodose-lines of the lung were comparable (average within±3%) when calculated by PB-hete compared to XVMC, but, consistently lower by PB-homo by a factors of 0.90/0.88/0.85, respectively. MLD was higher with PB-hete by 1.05, but, lower by PB-homo by 0.9, on average, compared to XVMC. XVMC max-cord/max-BT/max-heart and 2cc of esophagus doses were comparable to PB-hete; however, PB-homo underestimates by a factors of 0.82/0.89/0.88/0.86, on average, respectively. Conclusion: PB-hete significantly overestimates dose to PTV relative to XVMC -hence underdosing the target. MC is more complex and accurate with tissue-heterogeneities.The magnitude of variation significantly varies with ‘small-island-tumor’ surrounded by low-density lung tissues -PB algorithms lacks later electron scattering. Dose calculation with XVMC for lung SBRT is routinely performed in our clinic, its performance for head'neck/sinus cases will also be investigated.« less

SU-E-T-493: Accelerated Monte Carlo Methods for Photon Dosimetry Using a Dual-GPU System and CUDA.

PubMed

Liu, T; Ding, A; Xu, X

2012-06-01

To develop a Graphics Processing Unit (GPU) based Monte Carlo (MC) code that accelerates dose calculations on a dual-GPU system. We simulated a clinical case of prostate cancer treatment. A voxelized abdomen phantom derived from 120 CT slices was used containing 218×126×60 voxels, and a GE LightSpeed 16-MDCT scanner was modeled. A CPU version of the MC code was first developed in C++ and tested on Intel Xeon X5660 2.8GHz CPU, then it was translated into GPU version using CUDA C 4.1 and run on a dual Tesla m 2 090 GPU system. The code was featured with automatic assignment of simulation task to multiple GPUs, as well as accurate calculation of energy- and material- dependent cross-sections. Double-precision floating point format was used for accuracy. Doses to the rectum, prostate, bladder and femoral heads were calculated. When running on a single GPU, the MC GPU code was found to be ×19 times faster than the CPU code and ×42 times faster than MCNPX. These speedup factors were doubled on the dual-GPU system. The dose Result was benchmarked against MCNPX and a maximum difference of 1% was observed when the relative error is kept below 0.1%. A GPU-based MC code was developed for dose calculations using detailed patient and CT scanner models. Efficiency and accuracy were both guaranteed in this code. Scalability of the code was confirmed on the dual-GPU system. © 2012 American Association of Physicists in Medicine.

Investigation of real tissue water equivalent path lengths using an efficient dose extinction method

NASA Astrophysics Data System (ADS)

Zhang, Rongxiao; Baer, Esther; Jee, Kyung-Wook; Sharp, Gregory C.; Flanz, Jay; Lu, Hsiao-Ming

2017-07-01

For proton therapy, an accurate conversion of CT HU to relative stopping power (RSP) is essential. Validation of the conversion based on real tissue samples is more direct than the current practice solely based on tissue substitutes and can potentially address variations over the population. Based on a novel dose extinction method, we measured water equivalent path lengths (WEPL) on animal tissue samples to evaluate the accuracy of CT HU to RSP conversion and potential variations over a population. A broad proton beam delivered a spread out Bragg peak to the samples sandwiched between a water tank and a 2D ion-chamber detector. WEPLs of the samples were determined from the transmission dose profiles measured as a function of the water level in the tank. Tissue substitute inserts and Lucite blocks with known WEPLs were used to validate the accuracy. A large number of real tissue samples were measured. Variations of WEPL over different batches of tissue samples were also investigated. The measured WEPLs were compared with those computed from CT scans with the Stoichiometric calibration method. WEPLs were determined within  ±0.5% percentage deviation (% std/mean) and  ±0.5% error for most of the tissue surrogate inserts and the calibration blocks. For biological tissue samples, percentage deviations were within  ±0.3%. No considerable difference (<1%) in WEPL was observed for the same type of tissue from different sources. The differences between measured WEPLs and those calculated from CT were within 1%, except for some bony tissues. Depending on the sample size, each dose extinction measurement took around 5 min to produce ~1000 WEPL values to be compared with calculations. This dose extinction system measures WEPL efficiently and accurately, which allows the validation of CT HU to RSP conversions based on the WEPL measured for a large number of samples and real tissues.

Characterisation of mega-voltage electron pencil beam dose distributions: viability of a measurement-based approach.

PubMed

Barnes, M P; Ebert, M A

2008-03-01

The concept of electron pencil-beam dose distributions is central to pencil-beam algorithms used in electron beam radiotherapy treatment planning. The Hogstrom algorithm, which is a common algorithm for electron treatment planning, models large electron field dose distributions by the superposition of a series of pencil beam dose distributions. This means that the accurate characterisation of an electron pencil beam is essential for the accuracy of the dose algorithm. The aim of this study was to evaluate a measurement based approach for obtaining electron pencil-beam dose distributions. The primary incentive for the study was the accurate calculation of dose distributions for narrow fields as traditional electron algorithms are generally inaccurate for such geometries. Kodak X-Omat radiographic film was used in a solid water phantom to measure the dose distribution of circular 12 MeV beams from a Varian 21EX linear accelerator. Measurements were made for beams of diameter, 1.5, 2, 4, 8, 16 and 32 mm. A blocked-field technique was used to subtract photon contamination in the beam. The "error function" derived from Fermi-Eyges Multiple Coulomb Scattering (MCS) theory for corresponding square fields was used to fit resulting dose distributions so that extrapolation down to a pencil beam distribution could be made. The Monte Carlo codes, BEAM and EGSnrc were used to simulate the experimental arrangement. The 8 mm beam dose distribution was also measured with TLD-100 microcubes. Agreement between film, TLD and Monte Carlo simulation results were found to be consistent with the spatial resolution used. The study has shown that it is possible to extrapolate narrow electron beam dose distributions down to a pencil beam dose distribution using the error function. However, due to experimental uncertainties and measurement difficulties, Monte Carlo is recommended as the method of choice for characterising electron pencil-beam dose distributions.

Development of a golden beam data set for the commissioning of a proton double-scattering system in a pencil-beam dose calculation algorithm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Slopsema, R. L., E-mail: rslopsema@floridaproton.org; Flampouri, S.; Yeung, D.

2014-09-15

Purpose: The purpose of this investigation is to determine if a single set of beam data, described by a minimal set of equations and fitting variables, can be used to commission different installations of a proton double-scattering system in a commercial pencil-beam dose calculation algorithm. Methods: The beam model parameters required to commission the pencil-beam dose calculation algorithm (virtual and effective SAD, effective source size, and pristine-peak energy spread) are determined for a commercial double-scattering system. These parameters are measured in a first room and parameterized as function of proton energy and nozzle settings by fitting four analytical equations tomore » the measured data. The combination of these equations and fitting values constitutes the golden beam data (GBD). To determine the variation in dose delivery between installations, the same dosimetric properties are measured in two additional rooms at the same facility, as well as in a single room at another facility. The difference between the room-specific measurements and the GBD is evaluated against tolerances that guarantee the 3D dose distribution in each of the rooms matches the GBD-based dose distribution within clinically reasonable limits. The pencil-beam treatment-planning algorithm is commissioned with the GBD. The three-dimensional dose distribution in water is evaluated in the four treatment rooms and compared to the treatment-planning calculated dose distribution. Results: The virtual and effective SAD measurements fall between 226 and 257 cm. The effective source size varies between 2.4 and 6.2 cm for the large-field options, and 1.0 and 2.0 cm for the small-field options. The pristine-peak energy spread decreases from 1.05% at the lowest range to 0.6% at the highest. The virtual SAD as well as the effective source size can be accurately described by a linear relationship as function of the inverse of the residual energy. An additional linear correction term as function of RM-step thickness is required for accurate parameterization of the effective SAD. The GBD energy spread is given by a linear function of the exponential of the beam energy. Except for a few outliers, the measured parameters match the GBD within the specified tolerances in all of the four rooms investigated. For a SOBP field with a range of 15 g/cm{sup 2} and an air gap of 25 cm, the maximum difference in the 80%–20% lateral penumbra between the GBD-commissioned treatment-planning system and measurements in any of the four rooms is 0.5 mm. Conclusions: The beam model parameters of the double-scattering system can be parameterized with a limited set of equations and parameters. This GBD closely matches the measured dosimetric properties in four different rooms.« less

Handling Density Conversion in TPS.

PubMed

Isobe, Tomonori; Mori, Yutaro; Takei, Hideyuki; Sato, Eisuke; Tadano, Kiichi; Kobayashi, Daisuke; Tomita, Tetsuya; Sakae, Takeji

2016-01-01

Conversion from CT value to density is essential to a radiation treatment planning system. Generally CT value is converted to the electron density in photon therapy. In the energy range of therapeutic photon, interactions between photons and materials are dominated with Compton scattering which the cross-section depends on the electron density. The dose distribution is obtained by calculating TERMA and kernel using electron density where TERMA is the energy transferred from primary photons and kernel is a volume considering spread electrons. Recently, a new method was introduced which uses the physical density. This method is expected to be faster and more accurate than that using the electron density. As for particle therapy, dose can be calculated with CT-to-stopping power conversion since the stopping power depends on the electron density. CT-to-stopping power conversion table is also called as CT-to-water-equivalent range and is an essential concept for the particle therapy.

Generalized Fokker-Planck theory for electron and photon transport in biological tissues: application to radiotherapy.

PubMed

Olbrant, Edgar; Frank, Martin

2010-12-01

In this paper, we study a deterministic method for particle transport in biological tissues. The method is specifically developed for dose calculations in cancer therapy and for radiological imaging. Generalized Fokker-Planck (GFP) theory [Leakeas and Larsen, Nucl. Sci. Eng. 137 (2001), pp. 236-250] has been developed to improve the Fokker-Planck (FP) equation in cases where scattering is forward-peaked and where there is a sufficient amount of large-angle scattering. We compare grid-based numerical solutions to FP and GFP in realistic medical applications. First, electron dose calculations in heterogeneous parts of the human body are performed. Therefore, accurate electron scattering cross sections are included and their incorporation into our model is extensively described. Second, we solve GFP approximations of the radiative transport equation to investigate reflectance and transmittance of light in biological tissues. All results are compared with either Monte Carlo or discrete-ordinates transport solutions.

SU-E-J-14: A Novel Approach to Evaluate the Dosimetric Effect of Rectal Variation During Image Guided Prostate Radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murray, J; McQuaid, D; Dunlop, A

2014-06-01

Purpose: Deformable registration establishes the spatial correspondence back to the reference image in order to accumulate dose. However, in prostate radiotherapy the changing shape and volume of the rectum present a challenge to accurate deformable registration and consequently calculation of delivered dose. We explored an alternative approach to calculating accumulated dose to the rectum, independent of deformable registration. Methods: This study was performed on three patients who received online image-guided radiotherapy (IGRT) with daily CBCT (XVI-system,Elekta) and target localization using intraprostatic fiducials. On each CBCT, the rectum was manually contoured and bulk density assignments were made allowing dose to bemore » calculated for each fraction. Dose-surface maps (DSM) were generated (MATLAB,Mathworks,Natick,MA) by considering the rectum as a cylinder and sampling the dose at 21-equispaced points on each CT slice. The cylinder was “cut” at the posterior-most position on each CT and unfolded to generate a DSM. These were normalised in the longitudinal direction by interpolation creating maps of 21×21 pixels. A DSM was produced for each CBCT and the dose was accumulated. Results: The mean accumulated delivered rectal surface dose was on average 7.5(+/−3.5)% lower than the planned dose. The dose difference maps consistently show that the greatest variation in dose between planned and delivered dose is away from where the rectal surface is adjacent to the prostate. Conclusion: Estimation of dose accumulation using DSM provides an alternative method for determining actual delivered dose to the rectum. The dose difference is greatest in areas away from the region where the rectal surface abuts the prostate, the region where set-up is verified. The change in size and shape of the rectum was shown to resultin a change in the accumulated dose compared to the planned dose and this will have an impact on determining the relationships between dose delivered and toxicity. We acknowledge funding from CRUK and acknowledge NHS funding to the NIHR Biomedical Research Centre for Cancer. Patients were treated within the CHHiP IGRT sub-study (CRUK/06/016, ISRCTN:97182923) funded by CRUK. RayStation was used under an evaluation agreement with RaySearch Laboratories AB.« less

Accelerator shield design of KIPT neutron source facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhong, Z.; Gohar, Y.

Argonne National Laboratory (ANL) of the United States and Kharkov Institute of Physics and Technology (KIPT) of Ukraine have been collaborating on the design development of a neutron source facility at KIPT utilizing an electron-accelerator-driven subcritical assembly. Electron beam power is 100 kW, using 100 MeV electrons. The facility is designed to perform basic and applied nuclear research, produce medical isotopes, and train young nuclear specialists. The biological shield of the accelerator building is designed to reduce the biological dose to less than 0.5-mrem/hr during operation. The main source of the biological dose is the photons and the neutrons generatedmore » by interactions of leaked electrons from the electron gun and accelerator sections with the surrounding concrete and accelerator materials. The Monte Carlo code MCNPX serves as the calculation tool for the shield design, due to its capability to transport electrons, photons, and neutrons coupled problems. The direct photon dose can be tallied by MCNPX calculation, starting with the leaked electrons. However, it is difficult to accurately tally the neutron dose directly from the leaked electrons. The neutron yield per electron from the interactions with the surrounding components is less than 0.01 neutron per electron. This causes difficulties for Monte Carlo analyses and consumes tremendous computation time for tallying with acceptable statistics the neutron dose outside the shield boundary. To avoid these difficulties, the SOURCE and TALLYX user subroutines of MCNPX were developed for the study. The generated neutrons are banked, together with all related parameters, for a subsequent MCNPX calculation to obtain the neutron and secondary photon doses. The weight windows variance reduction technique is utilized for both neutron and photon dose calculations. Two shielding materials, i.e., heavy concrete and ordinary concrete, were considered for the shield design. The main goal is to maintain the total dose outside the shield boundary at less than 0.5-mrem/hr. The shield configuration and parameters of the accelerator building have been determined and are presented in this paper. (authors)« less

SU-C-BRB-06: Utilizing 3D Scanner and Printer for Dummy Eye-Shield: Artifact-Free CT Images of Tungsten Eye-Shield for Accurate Dose Calculation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, J; Lee, J; Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul

Purpose: To evaluate the effect of a tungsten eye-shield on the dose distribution of a patient. Methods: A 3D scanner was used to extract the dimension and shape of a tungsten eye-shield in the STL format. Scanned data was transferred into a 3D printer. A dummy eye shield was then produced using bio-resin (3D systems, VisiJet M3 Proplast). For a patient with mucinous carcinoma, the planning CT was obtained with the dummy eye-shield placed on the patient’s right eye. Field shaping of 6 MeV was performed using a patient-specific cerrobend block on the 15 x 15 cm{sup 2} applicator. Themore » gantry angle was 330° to cover the planning target volume near by the lens. EGS4/BEAMnrc was commissioned from our measurement data from a Varian 21EX. For the CT-based dose calculation using EGS4/DOSXYZnrc, the CT images were converted to a phantom file through the ctcreate program. The phantom file had the same resolution as the planning CT images. By assigning the CT numbers of the dummy eye-shield region to 17000, the real dose distributions below the tungsten eye-shield were calculated in EGS4/DOSXYZnrc. In the TPS, the CT number of the dummy eye-shield region was assigned to the maximum allowable CT number (3000). Results: As compared to the maximum dose, the MC dose on the right lens or below the eye shield area was less than 2%, while the corresponding RTP calculated dose was an unrealistic value of approximately 50%. Conclusion: Utilizing a 3D scanner and a 3D printer, a dummy eye-shield for electron treatment can be easily produced. The artifact-free CT images were successfully incorporated into the CT-based Monte Carlo simulations. The developed method was useful in predicting the realistic dose distributions around the lens blocked with the tungsten shield.« less

Dosimetric impact of dual-energy CT tissue segmentation for low-energy prostate brachytherapy: a Monte Carlo study

NASA Astrophysics Data System (ADS)

Remy, Charlotte; Lalonde, Arthur; Béliveau-Nadeau, Dominic; Carrier, Jean-François; Bouchard, Hugo

2018-01-01

The purpose of this study is to evaluate the impact of a novel tissue characterization method using dual-energy over single-energy computed tomography (DECT and SECT) on Monte Carlo (MC) dose calculations for low-dose rate (LDR) prostate brachytherapy performed in a patient like geometry. A virtual patient geometry is created using contours from a real patient pelvis CT scan, where known elemental compositions and varying densities are overwritten in each voxel. A second phantom is made with additional calcifications. Both phantoms are the ground truth with which all results are compared. Simulated CT images are generated from them using attenuation coefficients taken from the XCOM database with a 100 kVp spectrum for SECT and 80 and 140Sn kVp for DECT. Tissue segmentation for Monte Carlo dose calculation is made using a stoichiometric calibration method for the simulated SECT images. For the DECT images, Bayesian eigentissue decomposition is used. A LDR prostate brachytherapy plan is defined with 125I sources and then calculated using the EGSnrc user-code Brachydose for each case. Dose distributions and dose-volume histograms (DVH) are compared to ground truth to assess the accuracy of tissue segmentation. For noiseless images, DECT-based tissue segmentation outperforms the SECT procedure with a root mean square error (RMS) on relative errors on dose distributions respectively of 2.39% versus 7.77%, and provides DVHs closest to the reference DVHs for all tissues. For a medium level of CT noise, Bayesian eigentissue decomposition still performs better on the overall dose calculation as the RMS error is found to be of 7.83% compared to 9.15% for SECT. Both methods give a similar DVH for the prostate while the DECT segmentation remains more accurate for organs at risk and in presence of calcifications, with less than 5% of RMS errors within the calcifications versus up to 154% for SECT. In a patient-like geometry, DECT-based tissue segmentation provides dose distributions with the highest accuracy and the least bias compared to SECT. When imaging noise is considered, benefits of DECT are noticeable if important calcifications are found within the prostate.

PNNL Measurement Results for the 2016 Criticality Accident Dosimetry Exercise at the Nevada National Security Stite (IER-148)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rathbone, Bruce A.; Morley, Shannon M.; Stephens, John A.

The Pacific Northwest National Laboratory (PNNL) participated in a criticality accident dosimetry intercomparison exercise held at the Nevada National Security Site (NNSS) May 24-27, 2016. The exercise was administered by Lawrence Livermore National Laboratory (LLNL) and consisted of three exposures performed using the Godiva-IV critical assembly housed in the Device Assembly Facility (DAF) located on the NNSS site. The exercise allowed participants to test the ability of their nuclear accident dosimeters to meet the performance criteria in ANSI/HPS N13.3-2013, Dosimetry for Criticality Accidents and to obtain new measurement data for use in revising dose calculation methods and quick sort screeningmore » methods where appropriate. PNNL participated with new prototype Personal Nuclear Accident Dosimeter (PNAD) and Fixed Nuclear Accident Dosimeter (FNAD) designs as well as the existing historical PNAD design. The new prototype designs incorporate optically stimulated luminescence (OSL) dosimeters in place of thermoluminescence dosimeters (TLDs), among other design changes, while retaining the same set of activation foils historically used. The default dose calculation methodology established decades ago for use with activation foils in PNNL PNADs and FNADs was used to calculate neutron dose results for both the existing and prototype dosimeters tested in the exercise. The results indicate that the effective cross sections and/or dose conversion factors used historically need to be updated to accurately measure the operational quantities recommended for nuclear accident dosimetry in ANSI/HPS N13.3-2013 and to ensure PNAD and FNAD performance meets the ANSI/HPS N13.3-2013 performance criteria. The operational quantities recommended for nuclear accident dosimetry are personal absorbed dose, Dp(10), and ambient absorbed dose, D*(10).« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Foster, R; Ding, C; Jiang, S

Purpose Spine SRS/SAbR treatment plans typically require very steep dose gradients to meet spinal cord constraints and it is crucial that the dose distribution be accurate. However, these plans are typically calculated on helical free-breathing CT scans, which often contain motion artifacts. While the spine itself doesn’t exhibit very much intra-fraction motion, tissues around the spine, particularly the liver, do move with respiration. We investigated the dosimetric effect of liver motion on dose distributions calculated on helical free-breathing CT scans for spine SAbR delivered to the T and L spine. Methods We took 5 spine SAbR plans and used densitymore » overrides to simulate an average reconstruction CT image set, which would more closely represent the patient anatomy during treatment. The value used for the density override was 0.66 g/cc. All patients were planned using our standard beam arrangement, which consists of 13 coplanar step and shoot IMRT beams. The original plan was recalculated with the same MU on the “average” scan and target coverage and spinal cord dose were compared to the original plan. Results The average changes in minimum PTV dose, PTV coverage, max cord dose and volume of cord receiving 10 Gy were 0.6%, 0.8%, 0.3% and 4.4% (0.012 cc), respectively. Conclusion SAbR spine plans are surprisingly robust relative to surrounding organ motion due to respiration. Motion artifacts in helical planning CT scans do not cause clinically significant differences when these plans are re-calculated on pseudo-average CT reconstructions. This is likely due to the beam arrangement used because only three beams pass through the liver and only one beam passes completely through the density override. The effect of the respiratory motion on VMAT plans for spine SAbR is being evaluated.« less

SU-E-T-416: VMAT Dose Calculations Using Cone Beam CT Images: A Preliminary Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, S; Sehgal, V; Kuo, J

Purpose: Cone beam CT (CBCT) images have been used routinely for patient positioning throughout the treatment course. However, use of CBCT for dose calculation is still investigational. The purpose of this study is to assess the utility of CBCT images for Volumetric Modulated Arc Therapy (VMAT) plan dose calculation. Methods: A CATPHAN 504 phantom (The Phantom Laboratory, Salem, NY) was used to compare the dosimetric and geometric accuracy between conventional CT and CBCT (in both full and half fan modes). Hounsfield units (HU) profiles at different density areas were evaluated. A C shape target that surrounds a central avoidance structuremore » was created and a VMAT plan was generated on the CT images and copied to the CBCT phantom images. Patient studies included three brain patients, and one head and neck (H'N) patient. VMAT plans generated on the patients treatment planning CT was applied to CBCT images obtained during the first treatment. Isodose distributions and dosevolume- histograms (DVHs) were compared. Results: For the phantom study, the HU difference between CT and CBCT is within 100 (maximum 96 HU for Teflon CBCT images in full fan mode). The impact of these differences on the calculated dose distributions was clinically insignificant. In both phantom and patient studies, target DVHs based on CBCT images were in excellent agreement with those based on planning CT images. Mean, Median, near minimum (D98%), and near maximum (D2%) doses agreed within 0-2.5%. A slightly larger discrepancy is observed in the patient studies compared to that seen in the phantom study, (0-1% vs. 0 - 2.5%). Conclusion: CBCT images can be used to accurately predict dosimetric results, without any HU correction. It is feasible to use CBCT to evaluate the actual dose delivered at each fraction. The dosimetric consequences resulting from tumor response and patient geometry changes could be monitored.« less

Accurate condensed history Monte Carlo simulation of electron transport. II. Application to ion chamber response simulations.

PubMed

Kawrakow, I

2000-03-01

In this report the condensed history Monte Carlo simulation of electron transport and its application to the calculation of ion chamber response is discussed. It is shown that the strong step-size dependencies and lack of convergence to the correct answer previously observed are the combined effect of the following artifacts caused by the EGS4/PRESTA implementation of the condensed history technique: dose underprediction due to PRESTA'S pathlength correction and lateral correlation algorithm; dose overprediction due to the boundary crossing algorithm; dose overprediction due to the breakdown of the fictitious cross section method for sampling distances between discrete interaction and the inaccurate evaluation of energy-dependent quantities. These artifacts are now understood quantitatively and analytical expressions for their effect are given.

Gamma-H2AX-based dose estimation for whole and partial body radiation exposure.

PubMed

Horn, Simon; Barnard, Stephen; Rothkamm, Kai

2011-01-01

Most human exposures to ionising radiation are partial body exposures. However, to date only limited tools are available for rapid and accurate estimation of the dose distribution and the extent of the body spared from the exposure. These parameters are of great importance for emergency triage and clinical management of exposed individuals. Here, measurements of γ-H2AX immunofluorescence by microscopy and flow cytometry were compared as rapid biodosimetric tools for whole and partial body exposures. Ex vivo uniformly X-irradiated blood lymphocytes from one donor were used to generate a universal biexponential calibration function for γ-H2AX foci/intensity yields per unit dose for time points up to 96 hours post exposure. Foci--but not intensity--levels remained significantly above background for 96 hours for doses of 0.5 Gy or more. Foci-based dose estimates for ex vivo X-irradiated blood samples from 13 volunteers were in excellent agreement with the actual dose delivered to the targeted samples. Flow cytometric dose estimates for X-irradiated blood samples from 8 volunteers were in excellent agreement with the actual dose delivered at 1 hour post exposure but less so at 24 hours post exposure. In partial body exposures, simulated by mixing ex vivo irradiated and unirradiated lymphocytes, foci/intensity distributions were significantly over-dispersed compared to uniformly irradiated lymphocytes. For both methods and in all cases the estimated fraction of irradiated lymphocytes and dose to that fraction, calculated using the zero contaminated Poisson test and γ-H2AX calibration function, were in good agreement with the actual mixing ratios and doses delivered to the samples. In conclusion, γ-H2AX analysis of irradiated lymphocytes enables rapid and accurate assessment of whole body doses while dispersion analysis of foci or intensity distributions helps determine partial body doses and the irradiated fraction size in cases of partial body exposures.

The Radiological Physics Center's standard dataset for small field size output factors.

PubMed

Followill, David S; Kry, Stephen F; Qin, Lihong; Lowenstein, Jessica; Molineu, Andrea; Alvarez, Paola; Aguirre, Jose Francisco; Ibbott, Geoffrey S

2012-08-08

Delivery of accurate intensity-modulated radiation therapy (IMRT) or stereotactic radiotherapy depends on a multitude of steps in the treatment delivery process. These steps range from imaging of the patient to dose calculation to machine delivery of the treatment plan. Within the treatment planning system's (TPS) dose calculation algorithm, various unique small field dosimetry parameters are essential, such as multileaf collimator modeling and field size dependence of the output. One of the largest challenges in this process is determining accurate small field size output factors. The Radiological Physics Center (RPC), as part of its mission to ensure that institutions deliver comparable and consistent radiation doses to their patients, conducts on-site dosimetry review visits to institutions. As a part of the on-site audit, the RPC measures the small field size output factors as might be used in IMRT treatments, and compares the resulting field size dependent output factors to values calculated by the institution's treatment planning system (TPS). The RPC has gathered multiple small field size output factor datasets for X-ray energies ranging from 6 to 18 MV from Varian, Siemens and Elekta linear accelerators. These datasets were measured at 10 cm depth and ranged from 10 × 10 cm(2) to 2 × 2 cm(2). The field sizes were defined by the MLC and for the Varian machines the secondary jaws were maintained at a 10 × 10 cm(2). The RPC measurements were made with a micro-ion chamber whose volume was small enough to gather a full ionization reading even for the 2 × 2 cm(2) field size. The RPC-measured output factors are tabulated and are reproducible with standard deviations (SD) ranging from 0.1% to 1.5%, while the institutions' calculated values had a much larger SD range, ranging up to 7.9% [corrected].The absolute average percent differences were greater for the 2 × 2 cm(2) than for the other field sizes. The RPC's measured small field output factors provide institutions with a standard dataset against which to compare their TPS calculated values. Any discrepancies noted between the standard dataset and calculated values should be investigated with careful measurements and with attention to the specific beam model.

The linearized multistage model and the future of quantitative risk assessment.

PubMed

Crump, K S

1996-10-01

The linearized multistage (LMS) model has for over 15 years been the default dose-response model used by the U.S. Environmental Protection Agency (USEPA) and other federal and state regulatory agencies in the United States for calculating quantitative estimates of low-dose carcinogenic risks from animal data. The LMS model is in essence a flexible statistical model that can describe both linear and non-linear dose-response patterns, and that produces an upper confidence bound on the linear low-dose slope of the dose-response curve. Unlike its namesake, the Armitage-Doll multistage model, the parameters of the LMS do not correspond to actual physiological phenomena. Thus the LMS is 'biological' only to the extent that the true biological dose response is linear at low dose and that low-dose slope is reflected in the experimental data. If the true dose response is non-linear the LMS upper bound may overestimate the true risk by many orders of magnitude. However, competing low-dose extrapolation models, including those derived from 'biologically-based models' that are capable of incorporating additional biological information, have not shown evidence to date of being able to produce quantitative estimates of low-dose risks that are any more accurate than those obtained from the LMS model. Further, even if these attempts were successful, the extent to which more accurate estimates of low-dose risks in a test animal species would translate into improved estimates of human risk is questionable. Thus, it does not appear possible at present to develop a quantitative approach that would be generally applicable and that would offer significant improvements upon the crude bounding estimates of the type provided by the LMS model. Draft USEPA guidelines for cancer risk assessment incorporate an approach similar to the LMS for carcinogens having a linear mode of action. However, under these guidelines quantitative estimates of low-dose risks would not be developed for carcinogens having a non-linear mode of action; instead dose-response modelling would be used in the experimental range to calculate an LED10* (a statistical lower bound on the dose corresponding to a 10% increase in risk), and safety factors would be applied to the LED10* to determine acceptable exposure levels for humans. This approach is very similar to the one presently used by USEPA for non-carcinogens. Rather than using one approach for carcinogens believed to have a linear mode of action and a different approach for all other health effects, it is suggested herein that it would be more appropriate to use an approach conceptually similar to the 'LED10*-safety factor' approach for all health effects, and not to routinely develop quantitative risk estimates from animal data.

Estimating Effective Dose of Radiation From Pediatric Cardiac CT Angiography Using a 64-MDCT Scanner: New Conversion Factors Relating Dose-Length Product to Effective Dose.

PubMed

Trattner, Sigal; Chelliah, Anjali; Prinsen, Peter; Ruzal-Shapiro, Carrie B; Xu, Yanping; Jambawalikar, Sachin; Amurao, Maxwell; Einstein, Andrew J

2017-03-01

The purpose of this study is to determine the conversion factors that enable accurate estimation of the effective dose (ED) used for cardiac 64-MDCT angiography performed for children. Anthropomorphic phantoms representative of 1- and 10-year-old children, with 50 metal oxide semiconductor field-effect transistor dosimeters placed in organs, underwent scanning performed using a 64-MDCT scanner with different routine clinical cardiac scan modes and x-ray tube potentials. Organ doses were used to calculate the ED on the basis of weighting factors published in 1991 in International Commission on Radiological Protection (ICRP) publication 60 and in 2007 in ICRP publication 103. The EDs and the scanner-reported dose-length products were used to determine conversion factors for each scan mode. The effect of infant heart rate on the ED and the conversion factors was also assessed. The mean conversion factors calculated using the current definition of ED that appeared in ICRP publication 103 were as follows: 0.099 mSv · mGy -1 · cm -1 , for the 1-year-old phantom, and 0.049 mSv · mGy -1 · cm -1 , for the 10-year-old phantom. These conversion factors were a mean of 37% higher than the corresponding conversion factors calculated using the older definition of ED that appeared in ICRP publication 60. Varying the heart rate did not influence the ED or the conversion factors. Conversion factors determined using the definition of ED in ICRP publication 103 and cardiac, rather than chest, scan coverage suggest that the radiation doses that children receive from cardiac CT performed using a contemporary 64-MDCT scanner are higher than the radiation doses previously reported when older chest conversion factors were used. Additional up-to-date pediatric cardiac CT conversion factors are required for use with other contemporary CT scanners and patients of different age ranges.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, R; Bai, W

Purpose: Because of statistical noise in Monte Carlo dose calculations, effective point doses may not be accurate. Volume spheres are useful for evaluating dose in Monte Carlo plans, which have an inherent statistical uncertainty.We use a user-defined sphere volume instead of a point, take sphere sampling around effective point make the dose statistics to decrease the stochastic errors. Methods: Direct dose measurements were made using a 0.125cc Semiflex ion chamber (IC) 31010 isocentrically placed in the center of a homogeneous Cylindric sliced RW3 phantom (PTW, Germany).In the scanned CT phantom series the sensitive volume length of the IC (6.5mm) weremore » delineated and defined the isocenter as the simulation effective points. All beams were simulated in Monaco in accordance to the measured model. In our simulation using 2mm voxels calculation grid spacing and choose calculate dose to medium and request the relative standard deviation ≤0.5%. Taking three different assigned IC over densities (air electron density(ED) as 0.01g/cm3 default CT scanned ED and Esophageal lumen ED 0.21g/cm3) were tested at different sampling sphere radius (2.5, 2, 1.5 and 1 mm) statistics dose were compared with the measured does. Results: The results show that in the Monaco TPS for the IC using Esophageal lumen ED 0.21g/cm3 and sampling sphere radius 1.5mm the statistical value is the best accordance with the measured value, the absolute average percentage deviation is 0.49%. And when the IC using air electron density(ED) as 0.01g/cm3 and default CT scanned EDthe recommented statistical sampling sphere radius is 2.5mm, the percentage deviation are 0.61% and 0.70%, respectivly. Conclusion: In Monaco treatment planning system for the ionization chamber 31010 recommend air cavity using ED 0.21g/cm3 and sampling 1.5mm sphere volume instead of a point dose to decrease the stochastic errors. Funding Support No.C201505006.« less

Fast and accurate Monte Carlo modeling of a kilovoltage X-ray therapy unit using a photon-source approximation for treatment planning in complex media.

PubMed

Zeinali-Rafsanjani, B; Mosleh-Shirazi, M A; Faghihi, R; Karbasi, S; Mosalaei, A

2015-01-01

To accurately recompute dose distributions in chest-wall radiotherapy with 120 kVp kilovoltage X-rays, an MCNP4C Monte Carlo model is presented using a fast method that obviates the need to fully model the tube components. To validate the model, half-value layer (HVL), percentage depth doses (PDDs) and beam profiles were measured. Dose measurements were performed for a more complex situation using thermoluminescence dosimeters (TLDs) placed within a Rando phantom. The measured and computed first and second HVLs were 3.8, 10.3 mm Al and 3.8, 10.6 mm Al, respectively. The differences between measured and calculated PDDs and beam profiles in water were within 2 mm/2% for all data points. In the Rando phantom, differences for majority of data points were within 2%. The proposed model offered an approximately 9500-fold reduced run time compared to the conventional full simulation. The acceptable agreement, based on international criteria, between the simulations and the measurements validates the accuracy of the model for its use in treatment planning and radiobiological modeling studies of superficial therapies including chest-wall irradiation using kilovoltage beam.

A virtual photon energy fluence model for Monte Carlo dose calculation.

PubMed

Fippel, Matthias; Haryanto, Freddy; Dohm, Oliver; Nüsslin, Fridtjof; Kriesen, Stephan

2003-03-01

The presented virtual energy fluence (VEF) model of the patient-independent part of the medical linear accelerator heads, consists of two Gaussian-shaped photon sources and one uniform electron source. The planar photon sources are located close to the bremsstrahlung target (primary source) and to the flattening filter (secondary source), respectively. The electron contamination source is located in the plane defining the lower end of the filter. The standard deviations or widths and the relative weights of each source are free parameters. Five other parameters correct for fluence variations, i.e., the horn or central depression effect. If these parameters and the field widths in the X and Y directions are given, the corresponding energy fluence distribution can be calculated analytically and compared to measured dose distributions in air. This provides a method of fitting the free parameters using the measurements for various square and rectangular fields and a fixed number of monitor units. The next step in generating the whole set of base data is to calculate monoenergetic central axis depth dose distributions in water which are used to derive the energy spectrum by deconvolving the measured depth dose curves. This spectrum is also corrected to take the off-axis softening into account. The VEF model is implemented together with geometry modules for the patient specific part of the treatment head (jaws, multileaf collimator) into the XVMC dose calculation engine. The implementation into other Monte Carlo codes is possible based on the information in this paper. Experiments are performed to verify the model by comparing measured and calculated dose distributions and output factors in water. It is demonstrated that open photon beams of linear accelerators from two different vendors are accurately simulated using the VEF model. The commissioning procedure of the VEF model is clinically feasible because it is based on standard measurements in air and water. It is also useful for IMRT applications because a full Monte Carlo simulation of the treatment head would be too time-consuming for many small fields.

TU-F-17A-05: Calculating Tumor Trajectory and Dose-Of-The-Day for Highly Mobile Tumors Using Cone-Beam CT Projections

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, B; Miften, M

2014-06-15

Purpose: Cone-beam CT (CBCT) projection images provide anatomical data in real-time over several respiratory cycles, forming a comprehensive picture of tumor movement. We developed a method using these projections to determine the trajectory and dose of highly mobile tumors during each fraction of treatment. Methods: CBCT images of a respiration phantom were acquired, where the trajectory mimicked a lung tumor with high amplitude (2.4 cm) and hysteresis. A template-matching algorithm was used to identify the location of a steel BB in each projection. A Gaussian probability density function for tumor position was calculated which best fit the observed trajectory ofmore » the BB in the imager geometry. Two methods to improve the accuracy of tumor track reconstruction were investigated: first, using respiratory phase information to refine the trajectory estimation, and second, using the Monte Carlo method to sample the estimated Gaussian tumor position distribution. 15 clinically-drawn abdominal/lung CTV volumes were used to evaluate the accuracy of the proposed methods by comparing the known and calculated BB trajectories. Results: With all methods, the mean position of the BB was determined with accuracy better than 0.1 mm, and root-mean-square (RMS) trajectory errors were lower than 5% of marker amplitude. Use of respiratory phase information decreased RMS errors by 30%, and decreased the fraction of large errors (>3 mm) by half. Mean dose to the clinical volumes was calculated with an average error of 0.1% and average absolute error of 0.3%. Dosimetric parameters D90/D95 were determined within 0.5% of maximum dose. Monte-Carlo sampling increased RMS trajectory and dosimetric errors slightly, but prevented over-estimation of dose in trajectories with high noise. Conclusions: Tumor trajectory and dose-of-the-day were accurately calculated using CBCT projections. This technique provides a widely-available method to evaluate highly-mobile tumors, and could facilitate better strategies to mitigate or compensate for motion during SBRT.« less

SU-E-T-278: Realization of Dose Verification Tool for IMRT Plan Based On DPM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, Jinfeng; Cao, Ruifen; Dai, Yumei

Purpose: To build a Monte Carlo dose verification tool for IMRT Plan by implementing a irradiation source model into DPM code. Extend the ability of DPM to calculate any incident angles and irregular-inhomogeneous fields. Methods: With the virtual source and the energy spectrum which unfolded from the accelerator measurement data,combined with optimized intensity maps to calculate the dose distribution of the irradiation irregular-inhomogeneous field. The irradiation source model of accelerator was substituted by a grid-based surface source. The contour and the intensity distribution of the surface source were optimized by ARTS (Accurate/Advanced Radiotherapy System) optimization module based on the tumormore » configuration. The weight of the emitter was decided by the grid intensity. The direction of the emitter was decided by the combination of the virtual source and the emitter emitting position. The photon energy spectrum unfolded from the accelerator measurement data was adjusted by compensating the contaminated electron source. For verification, measured data and realistic clinical IMRT plan were compared with DPM dose calculation. Results: The regular field was verified by comparing with the measured data. It was illustrated that the differences were acceptable (<2% inside the field, 2–3mm in the penumbra). The dose calculation of irregular field by DPM simulation was also compared with that of FSPB (Finite Size Pencil Beam) and the passing rate of gamma analysis was 95.1% for peripheral lung cancer. The regular field and the irregular rotational field were all within the range of permitting error. The computing time of regular fields were less than 2h, and the test of peripheral lung cancer was 160min. Through parallel processing, the adapted DPM could complete the calculation of IMRT plan within half an hour. Conclusion: The adapted parallelized DPM code with irradiation source model is faster than classic Monte Carlo codes. Its computational accuracy and speed satisfy the clinical requirement, and it is expectable to be a Monte Carlo dose verification tool for IMRT Plan. Strategic Priority Research Program of the China Academy of Science(XDA03040000); National Natural Science Foundation of China (81101132)« less

SU-F-T-364: Monte Carlo-Dose Verification of Volumetric Modulated Arc Therapy Plans Using AAPM TG-119 Test Patterns

DOE Office of Scientific and Technical Information (OSTI.GOV)

Onizuka, R; Araki, F; Ohno, T

2016-06-15

Purpose: To investigate the Monte Carlo (MC)-based dose verification for VMAT plans by a treatment planning system (TPS). Methods: The AAPM TG-119 test structure set was used for VMAT plans by the Pinnacle3 (convolution/superposition), using a Synergy radiation head of a 6 MV beam with the Agility MLC. The Synergy was simulated with the EGSnrc/BEAMnrc code, and VMAT dose distributions were calculated with the EGSnrc/DOSXYZnrc code by the same irradiation conditions as TPS. VMAT dose distributions of TPS and MC were compared with those of EBT3 film, by 2-D gamma analysis of ±3%/3 mm criteria with a threshold of 30%more » of prescribed doses. VMAT dose distributions between TPS and MC were also compared by DVHs and 3-D gamma analysis of ±3%/3 mm criteria with a threshold of 10%, and 3-D passing rates for PTVs and OARs were analyzed. Results: TPS dose distributions differed from those of film, especially for Head & neck. The dose difference between TPS and film results from calculation accuracy for complex motion of MLCs like tongue and groove effect. In contrast, MC dose distributions were in good agreement with those of film. This is because MC can model fully the MLC configuration and accurately reproduce the MLC motion between control points in VMAT plans. D95 of PTV for Prostate, Head & neck, C-shaped, and Multi Target was 97.2%, 98.1%, 101.6%, and 99.7% for TPS and 95.7%, 96.0%, 100.6%, and 99.1% for MC, respectively. Similarly, 3-D gamma passing rates of each PTV for TPS vs. MC were 100%, 89.5%, 99.7%, and 100%, respectively. 3-D passing rates of TPS reduced for complex VMAT fields like Head & neck because MLCs are not modeled completely for TPS. Conclusion: MC-calculated VMAT dose distributions is useful for the 3-D dose verification of VMAT plans by TPS.« less

Accuracy of Monte Carlo simulations compared to in-vivo MDCT dosimetry.

PubMed

Bostani, Maryam; Mueller, Jonathon W; McMillan, Kyle; Cody, Dianna D; Cagnon, Chris H; DeMarco, John J; McNitt-Gray, Michael F

2015-02-01

The purpose of this study was to assess the accuracy of a Monte Carlo simulation-based method for estimating radiation dose from multidetector computed tomography (MDCT) by comparing simulated doses in ten patients to in-vivo dose measurements. MD Anderson Cancer Center Institutional Review Board approved the acquisition of in-vivo rectal dose measurements in a pilot study of ten patients undergoing virtual colonoscopy. The dose measurements were obtained by affixing TLD capsules to the inner lumen of rectal catheters. Voxelized patient models were generated from the MDCT images of the ten patients, and the dose to the TLD for all exposures was estimated using Monte Carlo based simulations. The Monte Carlo simulation results were compared to the in-vivo dose measurements to determine accuracy. The calculated mean percent difference between TLD measurements and Monte Carlo simulations was -4.9% with standard deviation of 8.7% and a range of -22.7% to 5.7%. The results of this study demonstrate very good agreement between simulated and measured doses in-vivo. Taken together with previous validation efforts, this work demonstrates that the Monte Carlo simulation methods can provide accurate estimates of radiation dose in patients undergoing CT examinations.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dolly, S; University of Missouri, Columbia, MO; Chen, H

Purpose: Local noise power spectrum (NPS) properties are significantly affected by calculation variables and CT acquisition and reconstruction parameters, but a thoughtful analysis of these effects is absent. In this study, we performed a complete analysis of the effects of calculation and imaging parameters on the NPS. Methods: The uniformity module of a Catphan phantom was scanned with a Philips Brilliance 64-slice CT simulator using various scanning protocols. Images were reconstructed using both FBP and iDose4 reconstruction algorithms. From these images, local NPS were calculated for regions of interest (ROI) of varying locations and sizes, using four image background removalmore » methods. Additionally, using a predetermined ground truth, NPS calculation accuracy for various calculation parameters was compared for computer simulated ROIs. A complete analysis of the effects of calculation, acquisition, and reconstruction parameters on the NPS was conducted. Results: The local NPS varied with ROI size and image background removal method, particularly at low spatial frequencies. The image subtraction method was the most accurate according to the computer simulation study, and was also the most effective at removing low frequency background components in the acquired data. However, first-order polynomial fitting using residual sum of squares and principle component analysis provided comparable accuracy under certain situations. Similar general trends were observed when comparing the NPS for FBP to that of iDose4 while varying other calculation and scanning parameters. However, while iDose4 reduces the noise magnitude compared to FBP, this reduction is spatial-frequency dependent, further affecting NPS variations at low spatial frequencies. Conclusion: The local NPS varies significantly depending on calculation parameters, image acquisition parameters, and reconstruction techniques. Appropriate local NPS calculation should be performed to capture spatial variations of noise; calculation methodology should be selected with consideration of image reconstruction effects and the desired purpose of CT simulation for radiotherapy tasks.« less

Dose conversion coefficients for electron exposure of the human eye lens

NASA Astrophysics Data System (ADS)

Behrens, R.; Dietze, G.; Zankl, M.

2009-07-01

Recent epidemiological studies suggest a rather low dose threshold (below 0.5 Gy) for the induction of a cataract of the eye lens. Some other studies even assume that there is no threshold at all. Therefore, protection measures have to be optimized and current dose limits for the eye lens may be reduced in the future. Two questions arise from this situation: first, which dose quantity is related to the risk of developing a cataract, and second, which personal dose equivalent quantity is appropriate for monitoring this dose quantity. While the dose equivalent quantity Hp(0.07) has often been seen as being sufficiently accurate for monitoring the dose to the lens of the eye, this would be questionable in the case when the dose limits were reduced and, thus, it may be necessary to generally use the dose equivalent quantity Hp(3) for this purpose. The basis for a decision, however, must be the knowledge of accurate conversion coefficients from fluence to equivalent dose to the lens. This is especially important for low-penetrating radiation, for example, electrons. Formerly published values of conversion coefficients are based on quite simple models of the eye. In this paper, quite a sophisticated model of the eye including the inner structure of the lens was used for the calculations and precise conversion coefficients for electrons with energies between 0.2 MeV and 12 MeV, and for angles of radiation incidence between 0° and 45° are presented. Compared to the values adopted in 1996 by the International Commission on Radiological Protection (ICRP), the new values are up to 1000 times smaller for electron energies below 1 MeV, nearly equal at 1 MeV and above 4 MeV, and by a factor of 1.5 larger at about 1.5 MeV electron energy.

Dose conversion coefficients for electron exposure of the human eye lens.

PubMed

Behrens, R; Dietze, G; Zankl, M

2009-07-07

Recent epidemiological studies suggest a rather low dose threshold (below 0.5 Gy) for the induction of a cataract of the eye lens. Some other studies even assume that there is no threshold at all. Therefore, protection measures have to be optimized and current dose limits for the eye lens may be reduced in the future. Two questions arise from this situation: first, which dose quantity is related to the risk of developing a cataract, and second, which personal dose equivalent quantity is appropriate for monitoring this dose quantity. While the dose equivalent quantity H(p)(0.07) has often been seen as being sufficiently accurate for monitoring the dose to the lens of the eye, this would be questionable in the case when the dose limits were reduced and, thus, it may be necessary to generally use the dose equivalent quantity H(p)(3) for this purpose. The basis for a decision, however, must be the knowledge of accurate conversion coefficients from fluence to equivalent dose to the lens. This is especially important for low-penetrating radiation, for example, electrons. Formerly published values of conversion coefficients are based on quite simple models of the eye. In this paper, quite a sophisticated model of the eye including the inner structure of the lens was used for the calculations and precise conversion coefficients for electrons with energies between 0.2 MeV and 12 MeV, and for angles of radiation incidence between 0 degrees and 45 degrees are presented. Compared to the values adopted in 1996 by the International Commission on Radiological Protection (ICRP), the new values are up to 1000 times smaller for electron energies below 1 MeV, nearly equal at 1 MeV and above 4 MeV, and by a factor of 1.5 larger at about 1.5 MeV electron energy.

Improving Dose Determination Accuracy in Nonstandard Fields of the Varian TrueBeam Accelerator

NASA Astrophysics Data System (ADS)

Hyun, Megan A.

In recent years, the use of flattening-filter-free (FFF) linear accelerators in radiation-based cancer therapy has gained popularity, especially for hypofractionated treatments (high doses of radiation given in few sessions). However, significant challenges to accurate radiation dose determination remain. If physicists cannot accurately determine radiation dose in a clinical setting, cancer patients treated with these new machines will not receive safe, accurate and effective treatment. In this study, an extensive characterization of two commonly used clinical radiation detectors (ionization chambers and diodes) and several potential reference detectors (thermoluminescent dosimeters, plastic scintillation detectors, and alanine pellets) has been performed to investigate their use in these challenging, nonstandard fields. From this characterization, reference detectors were identified for multiple beam sizes, and correction factors were determined to improve dosimetric accuracy for ionization chambers and diodes. A validated computational (Monte Carlo) model of the TrueBeam(TM) accelerator, including FFF beam modes, was also used to calculate these correction factors, which compared favorably to measured results. Small-field corrections of up to 18 % were shown to be necessary for clinical detectors such as microionization chambers. Because the impact of these large effects on treatment delivery is not well known, a treatment planning study was completed using actual hypofractionated brain, spine, and lung treatments that were delivered at the UW Carbone Cancer Center. This study demonstrated that improperly applying these detector correction factors can have a substantial impact on patient treatments. This thesis work has taken important steps toward improving the accuracy of FFF dosimetry through rigorous experimentally and Monte-Carlo-determined correction factors, the validation of an important published protocol (TG-51) for use with FFF reference fields, and a demonstration of the clinical significance of small-field correction factors. These results will facilitate the safe, accurate and effective use of this treatment modality in the clinic.

MO-FG-CAMPUS-TeP1-05: Rapid and Efficient 3D Dosimetry for End-To-End Patient-Specific QA of Rotational SBRT Deliveries Using a High-Resolution EPID

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Y M; Han, B; Xing, L

2016-06-15

Purpose: EPID-based patient-specific quality assurance provides verification of the planning setup and delivery process that phantomless QA and log-file based virtual dosimetry methods cannot achieve. We present a method for EPID-based QA utilizing spatially-variant EPID response kernels that allows for direct calculation of the entrance fluence and 3D phantom dose. Methods: An EPID dosimetry system was utilized for 3D dose reconstruction in a cylindrical phantom for the purposes of end-to-end QA. Monte Carlo (MC) methods were used to generate pixel-specific point-spread functions (PSFs) characterizing the spatially non-uniform EPID portal response in the presence of phantom scatter. The spatially-variant PSFs weremore » decomposed into spatially-invariant basis PSFs with the symmetric central-axis kernel as the primary basis kernel and off-axis representing orthogonal perturbations in pixel-space. This compact and accurate characterization enables the use of a modified Richardson-Lucy deconvolution algorithm to directly reconstruct entrance fluence from EPID images without iterative scatter subtraction. High-resolution phantom dose kernels were cogenerated in MC with the PSFs enabling direct recalculation of the resulting phantom dose by rapid forward convolution once the entrance fluence was calculated. A Delta4 QA phantom was used to validate the dose reconstructed in this approach. Results: The spatially-invariant representation of the EPID response accurately reproduced the entrance fluence with >99.5% fidelity with a simultaneous reduction of >60% in computational overhead. 3D dose for 10{sub 6} voxels was reconstructed for the entire phantom geometry. A 3D global gamma analysis demonstrated a >95% pass rate at 3%/3mm. Conclusion: Our approach demonstrates the capabilities of an EPID-based end-to-end QA methodology that is more efficient than traditional EPID dosimetry methods. Displacing the point of measurement external to the QA phantom reduces the necessary complexity of the phantom itself while offering a method that is highly scalable and inherently generalizable to rotational and trajectory based deliveries. This research was partially supported by Varian.« less

The evaluation of a 2D diode array in “magic phantom” for use in high dose rate brachytherapy pretreatment quality assurance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Espinoza, A.; Petasecca, M.; Fuduli, I.

2015-02-15

Purpose: High dose rate (HDR) brachytherapy is a treatment method that is used increasingly worldwide. The development of a sound quality assurance program for the verification of treatment deliveries can be challenging due to the high source activity utilized and the need for precise measurements of dwell positions and times. This paper describes the application of a novel phantom, based on a 2D 11 × 11 diode array detection system, named “magic phantom” (MPh), to accurately measure plan dwell positions and times, compare them directly to the treatment plan, determine errors in treatment delivery, and calculate absorbed dose. Methods: Themore » magic phantom system was CT scanned and a 20 catheter plan was generated to simulate a nonspecific treatment scenario. This plan was delivered to the MPh and, using a custom developed software suite, the dwell positions and times were measured and compared to the plan. The original plan was also modified, with changes not disclosed to the primary authors, and measured again using the device and software to determine the modifications. A new metric, the “position–time gamma index,” was developed to quantify the quality of a treatment delivery when compared to the treatment plan. The MPh was evaluated to determine the minimum measurable dwell time and step size. The incorporation of the TG-43U1 formalism directly into the software allows for dose calculations to be made based on the measured plan. The estimated dose distributions calculated by the software were compared to the treatment plan and to calibrated EBT3 film, using the 2D gamma analysis method. Results: For the original plan, the magic phantom system was capable of measuring all dwell points and dwell times and the majority were found to be within 0.93 mm and 0.25 s, respectively, from the plan. By measuring the altered plan and comparing it to the unmodified treatment plan, the use of the position–time gamma index showed that all modifications made could be readily detected. The MPh was able to measure dwell times down to 0.067 ± 0.001 s and planned dwell positions separated by 1 mm. The dose calculation carried out by the MPh software was found to be in agreement with values calculated by the treatment planning system within 0.75%. Using the 2D gamma index, the dose map of the MPh plane and measured EBT3 were found to have a pass rate of over 95% when compared to the original plan. Conclusions: The application of this magic phantom quality assurance system to HDR brachytherapy has demonstrated promising ability to perform the verification of treatment plans, based upon the measured dwell positions and times. The introduction of the quantitative position–time gamma index allows for direct comparison of measured parameters against the plan and could be used prior to patient treatment to ensure accurate delivery.« less

A comparison study of size-specific dose estimate calculation methods.

PubMed

Parikh, Roshni A; Wien, Michael A; Novak, Ronald D; Jordan, David W; Klahr, Paul; Soriano, Stephanie; Ciancibello, Leslie; Berlin, Sheila C

2018-01-01

The size-specific dose estimate (SSDE) has emerged as an improved metric for use by medical physicists and radiologists for estimating individual patient dose. Several methods of calculating SSDE have been described, ranging from patient thickness or attenuation-based (automated and manual) measurements to weight-based techniques. To compare the accuracy of thickness vs. weight measurement of body size to allow for the calculation of the size-specific dose estimate (SSDE) in pediatric body CT. We retrospectively identified 109 pediatric body CT examinations for SSDE calculation. We examined two automated methods measuring a series of level-specific diameters of the patient's body: method A used the effective diameter and method B used the water-equivalent diameter. Two manual methods measured patient diameter at two predetermined levels: the superior endplate of L2, where body width is typically most thin, and the superior femoral head or iliac crest (for scans that did not include the pelvis), where body width is typically most thick; method C averaged lateral measurements at these two levels from the CT projection scan, and method D averaged lateral and anteroposterior measurements at the same two levels from the axial CT images. Finally, we used body weight to characterize patient size, method E, and compared this with the various other measurement methods. Methods were compared across the entire population as well as by subgroup based on body width. Concordance correlation (ρ c ) between each of the SSDE calculation methods (methods A-E) was greater than 0.92 across the entire population, although the range was wider when analyzed by subgroup (0.42-0.99). When we compared each SSDE measurement method with CTDI vol, there was poor correlation, ρ c <0.77, with percentage differences between 20.8% and 51.0%. Automated computer algorithms are accurate and efficient in the calculation of SSDE. Manual methods based on patient thickness provide acceptable dose estimates for pediatric patients <30 cm in body width. Body weight provides a quick and practical method to identify conversion factors that can be used to estimate SSDE with reasonable accuracy in pediatric patients with body width ≥20 cm.

Metallic artifact mitigation and organ-constrained tissue assignment for Monte Carlo calculations of permanent implant lung brachytherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sutherland, J. G. H.; Miksys, N.; Thomson, R. M., E-mail: rthomson@physics.carleton.ca

2014-01-15

Purpose: To investigate methods of generating accurate patient-specific computational phantoms for the Monte Carlo calculation of lung brachytherapy patient dose distributions. Methods: Four metallic artifact mitigation methods are applied to six lung brachytherapy patient computed tomography (CT) images: simple threshold replacement (STR) identifies high CT values in the vicinity of the seeds and replaces them with estimated true values; fan beam virtual sinogram replaces artifact-affected values in a virtual sinogram and performs a filtered back-projection to generate a corrected image; 3D median filter replaces voxel values that differ from the median value in a region of interest surrounding the voxelmore » and then applies a second filter to reduce noise; and a combination of fan beam virtual sinogram and STR. Computational phantoms are generated from artifact-corrected and uncorrected images using several tissue assignment schemes: both lung-contour constrained and unconstrained global schemes are considered. Voxel mass densities are assigned based on voxel CT number or using the nominal tissue mass densities. Dose distributions are calculated using the EGSnrc user-code BrachyDose for{sup 125}I, {sup 103}Pd, and {sup 131}Cs seeds and are compared directly as well as through dose volume histograms and dose metrics for target volumes surrounding surgical sutures. Results: Metallic artifact mitigation techniques vary in ability to reduce artifacts while preserving tissue detail. Notably, images corrected with the fan beam virtual sinogram have reduced artifacts but residual artifacts near sources remain requiring additional use of STR; the 3D median filter removes artifacts but simultaneously removes detail in lung and bone. Doses vary considerably between computational phantoms with the largest differences arising from artifact-affected voxels assigned to bone in the vicinity of the seeds. Consequently, when metallic artifact reduction and constrained tissue assignment within lung contours are employed in generated phantoms, this erroneous assignment is reduced, generally resulting in higher doses. Lung-constrained tissue assignment also results in increased doses in regions of interest due to a reduction in the erroneous assignment of adipose to voxels within lung contours. Differences in dose metrics calculated for different computational phantoms are sensitive to radionuclide photon spectra with the largest differences for{sup 103}Pd seeds and smallest but still considerable differences for {sup 131}Cs seeds. Conclusions: Despite producing differences in CT images, dose metrics calculated using the STR, fan beam + STR, and 3D median filter techniques produce similar dose metrics. Results suggest that the accuracy of dose distributions for permanent implant lung brachytherapy is improved by applying lung-constrained tissue assignment schemes to metallic artifact corrected images.« less

SU-E-T-237: Deformable Image Registration and Deformed Dose Composite for Volumetric Evaluation of Multimodal Gynecological Cancer Treatments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Albani, D; Sherertz, T; Ellis, R

2015-06-15

Purpose: Radiotherapy plans for patients with cervical cancer treated with EBRT followed by HDR brachytherapy are optimized by constraining dose to organs at risk (OARs). Risk of treatment related toxicities is estimated based on the dose received to the hottest 2cc (D2cc) of the bladder, bowel, rectum, and sigmoid. To account for intrafractional variation in OAR volume and positioning, a dose deformation method is proposed for more accurate evaluation of dose distribution for these patients. Methods: Radiotherapy plans from five patients who received 50.4Gy pelvic EBRT followed by 30Gy in five fractions of HDR brachytherapy, using split-ring and tandem applicators,more » were retrospectively evaluated using MIM Software version 6.0. Dose accumulation workflows were used for initial deformation of EBRT and HDR planning CTs onto a common HDR planning CT. The Reg Refine tool was applied with user-specified local alignments to refine the deformation. Doses from the deformed images were transferred to the common planning CT. Deformed doses were scaled to the EQD2, following the linear-quadratic BED model (considered α/β ratio for tumor as 10, and 3 for rest of the tissues), and then combined to create the dose composite. MIM composite doses were compared to the clinically-reported plan assessments based upon the American Brachytherapy Society (ABS) guidelines for cervical HDR brachytherapy treatment. Results: Bladder D2cc exhibited significant reduction (−11.4%±3.85%, p< 0.02) when evaluated using MIM deformable dose composition. Differences observed for bowel, rectum, and sigmoid D2cc were not significant (−0.58±7.37%, −4.13%±13.7%, and 8.58%±4.71%, respectively and p>0.05 for all) relative to the calculated values used clinically. Conclusion: Application of deformable dose composite techniques may lead to more accurate total dose reporting and can allow for elevated dose to target structures with the assurance of not exceeding dose to OARs. Further study into deformable dose composition and correlation with clinical outcomes is warranted.« less

Dosimetry Formalism and Implementation of a Homogenous Irradiation Protocol to Improve the Accuracy of Small Animal Whole-Body Irradiation Using a Cesium-137 Irradiator

PubMed Central

Brodin, N. Patrik; Chen, Yong; Yaparpalvi, Ravindra; Guha, Chandan; Tomé, Wolfgang A.

2015-01-01

Shielded 137Cs irradiators are routinely used in pre-clinical radiation research to perform in vitro or in vivo investigations. Without appropriate dosimetry and irradiation protocols in place, there can be large uncertainty in the delivered dose of radiation between irradiated subjects that could lead to inaccurate and possibly misleading results. Here, a dosimetric evaluation of the JL Shepard Mark I-68A 137Cs irradiator and an irradiation technique for whole-body irradiation of small animals that allows one to limit the between subject variation in delivered dose to ±3% are provided. Mathematical simulation techniques and Gafchromic EBT film were used to describe the region within the irradiation cavity with homogeneous dose distribution (100% ±5%), the dosimetric impact of varying source-to-subject distance, and the variation in attenuation thickness due to turntable rotation. Furthermore, an irradiation protocol and dosimetry formalism that allows calculation of irradiation time for whole-body irradiation of small animals is proposed, that is designed to ensure a more consistent dose delivery between irradiated subjects. To compare this protocol with the conventional irradiation protocol suggested by the vendor, high-resolution film dosimetry measurements evaluating the dose difference between irradiation subjects and the dose distribution throughout subjects was performed, using phantoms resembling small animals. Based on these results, there can be considerable variation in the delivered dose of > ±5% using the conventional irradiation protocol for whole-body irradiation doses below 5 Gy. Using the proposed irradiation protocol this variability can be reduced to within ±3% and the dosimetry formalism allows for more accurate calculation of the irradiation time in relation to the intended prescription dose. PMID:26710162

Comparison between beta radiation dose distribution due to LDR and HDR ocular brachytherapy applicators using GATE Monte Carlo platform.

PubMed

Mostafa, Laoues; Rachid, Khelifi; Ahmed, Sidi Moussa

2016-08-01

Eye applicators with 90Sr/90Y and 106Ru/106Rh beta-ray sources are generally used in brachytherapy for the treatment of eye diseases as uveal melanoma. Whenever, radiation is used in treatment, dosimetry is essential. However, knowledge of the exact dose distribution is a critical decision-making to the outcome of the treatment. The Monte Carlo technique provides a powerful tool for calculation of the dose and dose distributions which helps to predict and determine the doses from different shapes of various types of eye applicators more accurately. The aim of this work consisted in using the Monte Carlo GATE platform to calculate the 3D dose distribution on a mathematical model of the human eye according to international recommendations. Mathematical models were developed for four ophthalmic applicators, two HDR 90Sr applicators SIA.20 and SIA.6, and two LDR 106Ru applicators, a concave CCB model and a flat CCB model. In present work, considering a heterogeneous eye phantom and the chosen tumor, obtained results with the use of GATE for mean doses distributions in a phantom and according to international recommendations show a discrepancy with respect to those specified by the manufacturers. The QC of dosimetric parameters shows that contrarily to the other applicators, the SIA.20 applicator is consistent with recommendations. The GATE platform show that the SIA.20 applicator present better results, namely the dose delivered to critical structures were lower compared to those obtained for the other applicators, and the SIA.6 applicator, simulated with MCNPX generates higher lens doses than those generated by GATE. Copyright © 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Precision IORT - Image guided intraoperative radiation therapy (igIORT) using online treatment planning including tissue heterogeneity correction.

PubMed

Schneider, Frank; Bludau, Frederic; Clausen, Sven; Fleckenstein, Jens; Obertacke, Udo; Wenz, Frederik

2017-05-01

To the present date, IORT has been eye and hand guided without treatment planning and tissue heterogeneity correction. This limits the precision of the application and the precise documentation of the location and the deposited dose in the tissue. Here we present a set-up where we use image guidance by intraoperative cone beam computed tomography (CBCT) for precise online Monte Carlo treatment planning including tissue heterogeneity correction. An IORT was performed during balloon kyphoplasty using a dedicated Needle Applicator. An intraoperative CBCT was registered with a pre-op CT. Treatment planning was performed in Radiance using a hybrid Monte Carlo algorithm simulating dose in homogeneous (MCwater) and heterogeneous medium (MChet). Dose distributions on CBCT and pre-op CT were compared with each other. Spinal cord and the metastasis doses were evaluated. The MCwater calculations showed a spherical dose distribution as expected. The minimum target dose for the MChet simulations on pre-op CT was increased by 40% while the maximum spinal cord dose was decreased by 35%. Due to the artefacts on the CBCT the comparison between MChet simulations on CBCT and pre-op CT showed differences up to 50% in dose. igIORT and online treatment planning improves the accuracy of IORT. However, the current set-up is limited by CT artefacts. Fusing an intraoperative CBCT with a pre-op CT allows the combination of an accurate dose calculation with the knowledge of the correct source/applicator position. This method can be also used for pre-operative treatment planning followed by image guided surgery. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Real-time simulator for designing electron dual scattering foil systems.

PubMed

Carver, Robert L; Hogstrom, Kenneth R; Price, Michael J; LeBlanc, Justin D; Pitcher, Garrett M

2014-11-08

The purpose of this work was to develop a user friendly, accurate, real-time com- puter simulator to facilitate the design of dual foil scattering systems for electron beams on radiotherapy accelerators. The simulator allows for a relatively quick, initial design that can be refined and verified with subsequent Monte Carlo (MC) calculations and measurements. The simulator also is a powerful educational tool. The simulator consists of an analytical algorithm for calculating electron fluence and X-ray dose and a graphical user interface (GUI) C++ program. The algorithm predicts electron fluence using Fermi-Eyges multiple Coulomb scattering theory with the reduced Gaussian formalism for scattering powers. The simulator also estimates central-axis and off-axis X-ray dose arising from the dual foil system. Once the geometry of the accelerator is specified, the simulator allows the user to continuously vary primary scattering foil material and thickness, secondary scat- tering foil material and Gaussian shape (thickness and sigma), and beam energy. The off-axis electron relative fluence or total dose profile and central-axis X-ray dose contamination are computed and displayed in real time. The simulator was validated by comparison of off-axis electron relative fluence and X-ray percent dose profiles with those calculated using EGSnrc MC. Over the energy range 7-20 MeV, using present foils on an Elekta radiotherapy accelerator, the simulator was able to reproduce MC profiles to within 2% out to 20 cm from the central axis. The central-axis X-ray percent dose predictions matched measured data to within 0.5%. The calculation time was approximately 100 ms using a single Intel 2.93 GHz processor, which allows for real-time variation of foil geometrical parameters using slider bars. This work demonstrates how the user-friendly GUI and real-time nature of the simulator make it an effective educational tool for gaining a better understanding of the effects that various system parameters have on a relative dose profile. This work also demonstrates a method for using the simulator as a design tool for creating custom dual scattering foil systems in the clinical range of beam energies (6-20 MeV). 

SU-F-T-301: Planar Dose Pass Rate Inflation Due to the MapCHECK Measurement Uncertainty Function

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bailey, D; Spaans, J; Kumaraswamy, L

Purpose: To quantify the effect of the Measurement Uncertainty function on planar dosimetry pass rates, as analyzed with Sun Nuclear Corporation analytic software (“MapCHECK” or “SNC Patient”). This optional function is toggled on by default upon software installation, and automatically increases the user-defined dose percent difference (%Diff) tolerance for each planar dose comparison. Methods: Dose planes from 109 IMRT fields and 40 VMAT arcs were measured with the MapCHECK 2 diode array, and compared to calculated planes from a commercial treatment planning system. Pass rates were calculated within the SNC analytic software using varying calculation parameters, including Measurement Uncertainty onmore » and off. By varying the %Diff criterion for each dose comparison performed with Measurement Uncertainty turned off, an effective %Diff criterion was defined for each field/arc corresponding to the pass rate achieved with MapCHECK Uncertainty turned on. Results: For 3%/3mm analysis, the Measurement Uncertainty function increases the user-defined %Diff by 0.8–1.1% average, depending on plan type and calculation technique, for an average pass rate increase of 1.0–3.5% (maximum +8.7%). For 2%, 2 mm analysis, the Measurement Uncertainty function increases the user-defined %Diff by 0.7–1.2% average, for an average pass rate increase of 3.5–8.1% (maximum +14.2%). The largest increases in pass rate are generally seen with poorly-matched planar dose comparisons; the MapCHECK Uncertainty effect is markedly smaller as pass rates approach 100%. Conclusion: The Measurement Uncertainty function may substantially inflate planar dose comparison pass rates for typical IMRT and VMAT planes. The types of uncertainties incorporated into the function (and their associated quantitative estimates) as described in the software user’s manual may not accurately estimate realistic measurement uncertainty for the user’s measurement conditions. Pass rates listed in published reports or otherwise compared to the results of other users or vendors should clearly indicate whether the Measurement Uncertainty function is used.« less

Adaptive intensity modulated radiotherapy for advanced prostate cancer

NASA Astrophysics Data System (ADS)

Ludlum, Erica Marie

The purpose of this research is to develop and evaluate improvements in intensity modulated radiotherapy (IMRT) for concurrent treatment of prostate and pelvic lymph nodes. The first objective is to decrease delivery time while maintaining treatment quality, and evaluate the effectiveness and efficiency of novel one-step optimization compared to conventional two-step optimization. Both planning methods are examined at multiple levels of complexity by comparing the number of beam apertures, or segments, the amount of radiation delivered as measured by monitor units (MUs), and delivery time. One-step optimization is demonstrated to simplify IMRT planning and reduce segments (from 160 to 40), MUs (from 911 to 746), and delivery time (from 22 to 7 min) with comparable plan quality. The second objective is to examine the capability of three commercial dose calculation engines employing different levels of accuracy and efficiency to handle high--Z materials, such as metallic hip prostheses, included in the treatment field. Pencil beam, convolution superposition, and Monte Carlo dose calculation engines are compared by examining the dose differences for patient plans with unilateral and bilateral hip prostheses, and for phantom plans with a metal insert for comparison with film measurements. Convolution superposition and Monte Carlo methods calculate doses that are 1.3% and 34.5% less than the pencil beam method, respectively. Film results demonstrate that Monte Carlo most closely represents actual radiation delivery, but none of the three engines accurately predict the dose distribution when high-Z heterogeneities exist in the treatment fields. The final objective is to improve the accuracy of IMRT delivery by accounting for independent organ motion during concurrent treatment of the prostate and pelvic lymph nodes. A leaf-shifting algorithm is developed to track daily prostate position without requiring online dose calculation. Compared to conventional methods of adjusting patient position, adjusting the multileaf collimator (MLC) leaves associated with the prostate in each segment significantly improves lymph node dose coverage (maintains 45 Gy compared to 42.7, 38.3, and 34.0 Gy for iso-shifts of 0.5, 1 and 1.5 cm). Altering the MLC portal shape is demonstrated as a new and effective solution to independent prostate movement during concurrent treatment.

Accurate Monte Carlo simulations for nozzle design, commissioning and quality assurance for a proton radiation therapy facility.

PubMed

Paganetti, H; Jiang, H; Lee, S Y; Kooy, H M

2004-07-01

Monte Carlo dosimetry calculations are essential methods in radiation therapy. To take full advantage of this tool, the beam delivery system has to be simulated in detail and the initial beam parameters have to be known accurately. The modeling of the beam delivery system itself opens various areas where Monte Carlo calculations prove extremely helpful, such as for design and commissioning of a therapy facility as well as for quality assurance verification. The gantry treatment nozzles at the Northeast Proton Therapy Center (NPTC) at Massachusetts General Hospital (MGH) were modeled in detail using the GEANT4.5.2 Monte Carlo code. For this purpose, various novel solutions for simulating irregular shaped objects in the beam path, like contoured scatterers, patient apertures or patient compensators, were found. The four-dimensional, in time and space, simulation of moving parts, such as the modulator wheel, was implemented. Further, the appropriate physics models and cross sections for proton therapy applications were defined. We present comparisons between measured data and simulations. These show that by modeling the treatment nozzle with millimeter accuracy, it is possible to reproduce measured dose distributions with an accuracy in range and modulation width, in the case of a spread-out Bragg peak (SOBP), of better than 1 mm. The excellent agreement demonstrates that the simulations can even be used to generate beam data for commissioning treatment planning systems. The Monte Carlo nozzle model was used to study mechanical optimization in terms of scattered radiation and secondary radiation in the design of the nozzles. We present simulations on the neutron background. Further, the Monte Carlo calculations supported commissioning efforts in understanding the sensitivity of beam characteristics and how these influence the dose delivered. We present the sensitivity of dose distributions in water with respect to various beam parameters and geometrical misalignments. This allows the definition of tolerances for quality assurance and the design of quality assurance procedures.

Evaluation of Accuracy of Six Blood Glucose Monitoring Systems and Modeling of Possibly Related Insulin Dosing Errors.

PubMed

Baumstark, Annette; Jendrike, Nina; Pleus, Stefan; Haug, Cornelia; Freckmann, Guido

2017-10-01

Self-monitoring of blood glucose (BG) is an essential part of diabetes therapy. Accurate and reliable results from BG monitoring systems (BGMS) are important especially when they are used to calculate insulin doses. This study aimed at assessing system accuracy of BGMS and possibly related insulin dosing errors. System accuracy of six different BGMS (Accu-Chek ® Aviva Nano, Accu-Chek Mobile, Accu-Chek Performa Nano, CONTOUR ® NEXT LINK 2.4, FreeStyle Lite, OneTouch ® Verio ® IQ) was assessed in comparison to a glucose oxidase and a hexokinase method. Study procedures and analysis were based on ISO 15197:2013/EN ISO 15197:2015, clause 6.3. In addition, insulin dosing error was modeled. In the comparison against the glucose oxidase method, five out of six BGMS fulfilled ISO 15197:2013 accuracy criteria. Up to 14.3%/4.3%/0.3% of modeled doses resulted in errors exceeding ±0.5/±1.0/±1.5 U and missing the modeled target by 20 mg/dL/40 mg/dL/60 mg/dL, respectively. Compared against the hexokinase method, five out of six BGMS fulfilled ISO 15197:2013 accuracy criteria. Up to 25.0%/10.5%/3.2% of modeled doses resulted in errors exceeding ±0.5/±1.0/±1.5 U, respectively. Differences in system accuracy were found, even among BGMS that fulfilled the minimum system accuracy criteria of ISO 15197:2013. In the error model, considerable insulin dosing errors resulted for some of the investigated systems. Diabetes patients on insulin therapy should be able to rely on their BGMS' readings; therefore, they require highly accurate BGMS, in particular, when making therapeutic decisions.

SU-G-JeP2-09: Minimal Skin Dose Increase in Longitudinal Rotating Biplanar Linac-MR Systems: Examination of Radiation Energy and Flattening Filter Design

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fallone, B; Keyvanloo, A; Burke, B

Purpose: To quantify increase in entrance skin-dose due to magnetic fields of the Alberta longitudinal linac-MR by examining the effect of radiation energy and flattening filter, using Monte Carlo calculations and accurate 3-D models of the magnetic field. Methods: The 3-D magnetic fields generated by the bi-planar Linac-MR are calculated with FEM using Opera-3D. BEAMnrc simulates the particle phase-space in the presence of the rapidly decaying fringe field of 0.5T MRI assembled with a Varian 600C linac with an isocentre distance of 130 cm for 6 MV and 10 MV beams. Skin doses are calculated at an average depth ofmore » 70 µm using DOSXYZnrc with varying SSDs and field sizes. Furthermore, flattening filters are reshaped to compensate for the significant drop in dose rate due to increased SAD of 130 cm and skin-doses are evaluated. Results: The confinement effect of the MRI fringe field on the contaminant electrons is minimal. For SSDs of 100 – 120 cm the increase in skin dose is ∼6% – 19% and ∼1% – 9% for the 6 and 10 MV beams, respectively. For 6MV, skin dose increases from ∼10.5% to 1.5%. for field-size increases of 5×5 cm2 to 20×20 cm2. For 10 MV, skin dose increases by ∼6% for a 5×5 cm2 field, and decreases by ∼1.5% for a 20×20 cm2 field. The reshaped flattening filter increases the dose rate from 355 MU/min to 529 MU/min (6 MV) or 604 MU/min (10 MV), while the skin-dose increases by only an additional ∼2.6% (all percent increases in skin dose are relative to Dmax). Conclusion: There is minimal increase in the entrance skin dose and minimal/no decrease in the dose rate of the Alberta longitudinal linac-MR system. There is even lower skin-dose increase at 10 MV. Funding: Alberta Innovates - Health Solutions (AIHS) Conflict of Interest: Fallone is a co-founder and CEO of MagnetTx Oncology Solutions (under discussions to license Alberta bi-planar linac MR for commercialization)« less

Absorbed dose measurements for kV-cone beam computed tomography in image-guided radiation therapy

NASA Astrophysics Data System (ADS)

Hioki, Kazunari; Araki, Fujio; Ohno, Takeshi; Nakaguchi, Yuji; Tomiyama, Yuuki

2014-12-01

In this study, we develope a novel method to directly evaluate an absorbed dose-to-water for kilovoltage-cone beam computed tomography (kV-CBCT) in image-guided radiation therapy (IGRT). Absorbed doses for the kV-CBCT systems of the Varian On-Board Imager (OBI) and the Elekta X-ray Volumetric Imager (XVI) were measured by a Farmer ionization chamber with a 60Co calibration factor. The chamber measurements were performed at the center and four peripheral points in body-type (30 cm diameter and 51 cm length) and head-type (16 cm diameter and 33 cm length) cylindrical water phantoms. The measured ionization was converted to the absorbed dose-to-water by using a 60Co calibration factor and a Monte Carlo (MC)-calculated beam quality conversion factor, kQ, for 60Co to kV-CBCT. The irradiation for OBI and XVI was performed with pelvis and head modes for the body- and the head-type phantoms, respectively. In addition, the dose distributions in the phantom for both kV-CBCT systems were calculated with MC method and were compared with measured values. The MC-calculated doses were calibrated at the center in the water phantom and compared with measured doses at four peripheral points. The measured absorbed doses at the center in the body-type phantom were 1.96 cGy for OBI and 0.83 cGy for XVI. The peripheral doses were 2.36-2.90 cGy for OBI and 0.83-1.06 cGy for XVI. The doses for XVI were lower up to approximately one-third of those for OBI. Similarly, the measured doses at the center in the head-type phantom were 0.48 cGy for OBI and 0.21 cGy for XVI. The peripheral doses were 0.26-0.66 cGy for OBI and 0.16-0.30 cGy for XVI. The calculated peripheral doses agreed within 3% in the pelvis mode and within 4% in the head mode with measured doses for both kV-CBCT systems. In addition, the absorbed dose determined in this study was approximately 4% lower than that in TG-61 but the absorbed dose by both methods was in agreement within their combined uncertainty. This method is more robust and accurate compared to the dosimetry based on a conventional air-kerma calibration factor. Therefore, it is possible to be used as a standard dosimetry protocol for kV-CBCT in IGRT.

Suitability of point kernel dose calculation techniques in brachytherapy treatment planning

PubMed Central

Lakshminarayanan, Thilagam; Subbaiah, K. V.; Thayalan, K.; Kannan, S. E.

2010-01-01

Brachytherapy treatment planning system (TPS) is necessary to estimate the dose to target volume and organ at risk (OAR). TPS is always recommended to account for the effect of tissue, applicator and shielding material heterogeneities exist in applicators. However, most brachytherapy TPS software packages estimate the absorbed dose at a point, taking care of only the contributions of individual sources and the source distribution, neglecting the dose perturbations arising from the applicator design and construction. There are some degrees of uncertainties in dose rate estimations under realistic clinical conditions. In this regard, an attempt is made to explore the suitability of point kernels for brachytherapy dose rate calculations and develop new interactive brachytherapy package, named as BrachyTPS, to suit the clinical conditions. BrachyTPS is an interactive point kernel code package developed to perform independent dose rate calculations by taking into account the effect of these heterogeneities, using two regions build up factors, proposed by Kalos. The primary aim of this study is to validate the developed point kernel code package integrated with treatment planning computational systems against the Monte Carlo (MC) results. In the present work, three brachytherapy applicators commonly used in the treatment of uterine cervical carcinoma, namely (i) Board of Radiation Isotope and Technology (BRIT) low dose rate (LDR) applicator and (ii) Fletcher Green type LDR applicator (iii) Fletcher Williamson high dose rate (HDR) applicator, are studied to test the accuracy of the software. Dose rates computed using the developed code are compared with the relevant results of the MC simulations. Further, attempts are also made to study the dose rate distribution around the commercially available shielded vaginal applicator set (Nucletron). The percentage deviations of BrachyTPS computed dose rate values from the MC results are observed to be within plus/minus 5.5% for BRIT LDR applicator, found to vary from 2.6 to 5.1% for Fletcher green type LDR applicator and are up to −4.7% for Fletcher-Williamson HDR applicator. The isodose distribution plots also show good agreements with the results of previous literatures. The isodose distributions around the shielded vaginal cylinder computed using BrachyTPS code show better agreement (less than two per cent deviation) with MC results in the unshielded region compared to shielded region, where the deviations are observed up to five per cent. The present study implies that the accurate and fast validation of complicated treatment planning calculations is possible with the point kernel code package. PMID:20589118

Impact of interpatient variability on organ dose estimates according to MIRD schema: Uncertainty and variance-based sensitivity analysis.

PubMed

Zvereva, Alexandra; Kamp, Florian; Schlattl, Helmut; Zankl, Maria; Parodi, Katia

2018-05-17

Variance-based sensitivity analysis (SA) is described and applied to the radiation dosimetry model proposed by the Committee on Medical Internal Radiation Dose (MIRD) for the organ-level absorbed dose calculations in nuclear medicine. The uncertainties in the dose coefficients thus calculated are also evaluated. A Monte Carlo approach was used to compute first-order and total-effect SA indices, which rank the input factors according to their influence on the uncertainty in the output organ doses. These methods were applied to the radiopharmaceutical (S)-4-(3- 18 F-fluoropropyl)-L-glutamic acid ( 18 F-FSPG) as an example. Since 18 F-FSPG has 11 notable source regions, a 22-dimensional model was considered here, where 11 input factors are the time-integrated activity coefficients (TIACs) in the source regions and 11 input factors correspond to the sets of the specific absorbed fractions (SAFs) employed in the dose calculation. The SA was restricted to the foregoing 22 input factors. The distributions of the input factors were built based on TIACs of five individuals to whom the radiopharmaceutical 18 F-FSPG was administered and six anatomical models, representing two reference, two overweight, and two slim individuals. The self-absorption SAFs were mass-scaled to correspond to the reference organ masses. The estimated relative uncertainties were in the range 10%-30%, with a minimum and a maximum for absorbed dose coefficients for urinary bladder wall and heart wall, respectively. The applied global variance-based SA enabled us to identify the input factors that have the highest influence on the uncertainty in the organ doses. With the applied mass-scaling of the self-absorption SAFs, these factors included the TIACs for absorbed dose coefficients in the source regions and the SAFs from blood as source region for absorbed dose coefficients in highly vascularized target regions. For some combinations of proximal target and source regions, the corresponding cross-fire SAFs were found to have an impact. Global variance-based SA has been for the first time applied to the MIRD schema for internal dose calculation. Our findings suggest that uncertainties in computed organ doses can be substantially reduced by performing an accurate determination of TIACs in the source regions, accompanied by the estimation of individual source region masses along with the usage of an appropriate blood distribution in a patient's body and, in a few cases, the cross-fire SAFs from proximal source regions. © 2018 American Association of Physicists in Medicine.

Specific absorbed fractions of electrons and photons for Rad-HUMAN phantom using Monte Carlo method

NASA Astrophysics Data System (ADS)

Wang, Wen; Cheng, Meng-Yun; Long, Peng-Cheng; Hu, Li-Qin

2015-07-01

The specific absorbed fractions (SAF) for self- and cross-irradiation are effective tools for the internal dose estimation of inhalation and ingestion intakes of radionuclides. A set of SAFs of photons and electrons were calculated using the Rad-HUMAN phantom, which is a computational voxel phantom of a Chinese adult female that was created using the color photographic image of the Chinese Visible Human (CVH) data set by the FDS Team. The model can represent most Chinese adult female anatomical characteristics and can be taken as an individual phantom to investigate the difference of internal dose with Caucasians. In this study, the emission of mono-energetic photons and electrons of 10 keV to 4 MeV energy were calculated using the Monte Carlo particle transport calculation code MCNP. Results were compared with the values from ICRP reference and ORNL models. The results showed that SAF from the Rad-HUMAN have similar trends but are larger than those from the other two models. The differences were due to the racial and anatomical differences in organ mass and inter-organ distance. The SAFs based on the Rad-HUMAN phantom provide an accurate and reliable data for internal radiation dose calculations for Chinese females. Supported by Strategic Priority Research Program of Chinese Academy of Sciences (XDA03040000), National Natural Science Foundation of China (910266004, 11305205, 11305203) and National Special Program for ITER (2014GB112001)

Imaging doses in radiation therapy from kilovoltage cone-beam computed tomography

NASA Astrophysics Data System (ADS)

Hyer, Daniel Ellis

Advances in radiation treatment delivery, such as intensity modulated radiation therapy (IMRT), have made it possible to deliver large doses of radiation with a high degree of conformity. While highly conformal treatments offers the advantage of sparing surrounding normal tissue, this benefit can only be realized if the patient is accurately positioned during each treatment fraction. The need to accurately position the patient has led to the development and use of gantry mounted kilovoltage cone-beam computed tomography (kV-CBCT) systems. These systems are used to acquire high resolution volumetric images of the patient which are then digitally registered with the planning CT dataset to confirm alignment of the patient on the treatment table. While kV-CBCT is a very useful tool for aligning the patient prior to treatment, daily use in a high fraction therapy regimen results in a substantial radiation dose. In order to quantify the radiation dose associated with CBCT imaging, an anthropomorphic phantom representing a 50th percentile adult male and a fiber-optic coupled (FOC) dosimetry system were both constructed as part of this dissertation. These tools were then used to directly measure organ doses incurred during clinical protocols for the head, chest, and pelvis. For completeness, the dose delivered from both the X-ray Volumetric Imager (XVI, Elekta Oncology Systems, Crawley, UK) and the On-Board Imager (OBI, Varian Medical Systems, Palo Alto, CA) were investigated. While this study provided a direct measure of organ doses for estimating risk to the patient, a practical method for estimating organ doses that could be performed with phantoms and dosimeters currently available at most clinics was also desired. To accomplish this goal, a 100 mm pencil ion chamber was used to measure the "cone beam dose index" (CBDI) inside standard CT dose index (CTDI) acrylic phantoms. A weighted CBDI (CBDIw), similar to the weighted CT dose index (CTDIw), was then calculated to represent the average dose in the acrylic phantom. By comparing this value to the measured organ doses, organ dose conversion coefficients were developed. These conversion coefficients allow specific organ doses to be estimated quickly and easily using readily available clinical equipment.

SU-F-T-258: Efficacy of Exit Fluence-Based Dose Calculation for Prostate Radiation Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siebers, J; Gardner, J; Neal, B

Purpose: To investigate the efficacy of exit-fluence-based dose computation for prostate radiotherapy by determining if it estimates true dose more accurately than the original planning dose. Methods: Virtual exit-fluencebased dose computation was performed for 19 patients, each with 9–12 repeat CT images. For each patient, a 78 Gy treatment plan was created utilizing 5 mm CTV-to-PTV and OAR-to-PRV margins. A Monte Carlo framework was used to compute dose and exit-fluence images for the planning image and for each repeat CT image based on boney-anatomyaligned and prostate-centroid-aligned CTs. Identical source particles were used for the MC dose-computations on the planning andmore » repeat CTs to maximize correlation. The exit-fluence-based dose and image were computed by multiplying source particle weights by FC(x,y)=FP(x,y)/FT(x,y), where (x,y) are the source particle coordinates projected to the exit-fluence plane and we denote the dose/fluence from the plan by (DP,FP), from the repeat-CT as (DT,FT), and the exit-fluence computation by (DFC,FFC). DFC mimics exit-fluence backprojection through the planning image as FT=FFC. Dose estimates were intercompared to judge the efficacy of exit-fluence-based dose computation. Results: Boney- and prostate-centroid aligned results are combined as there is no statistical difference between them, yielding 420 dose comparisons per dose-volume metric. DFC is more accurate than DP for 46%, 33%, and 44% of cases in estimating CTV D98, D50, and D2 respectively. DFC improved rectum D50 and D2 estimates 54% and 49% respectively and bladder D50 and D2 47 and 49% respectively. While averaged over all patients and images DFC and DP were within 3.1% of DT, they differed from DT by as much as 22% for GTV D98, 71% for the Bladder D50, 17% for Bladder D2, 19% for Rectum D2. Conclusion: Exit-fluence based dose computations infrequently improve CTV or OAR dose estimates and should be used with caution. Research supported in part by Varian Medical Systems.« less

Implementation and application of an interactive user-friendly validation software for RADIANCE

NASA Astrophysics Data System (ADS)

Sundaram, Anand; Boonn, William W.; Kim, Woojin; Cook, Tessa S.

2012-02-01

RADIANCE extracts CT dose parameters from dose sheets using optical character recognition and stores the data in a relational database. To facilitate validation of RADIANCE's performance, a simple user interface was initially implemented and about 300 records were evaluated. Here, we extend this interface to achieve a wider variety of functions and perform a larger-scale validation. The validator uses some data from the RADIANCE database to prepopulate quality-testing fields, such as correspondence between calculated and reported total dose-length product. The interface also displays relevant parameters from the DICOM headers. A total of 5,098 dose sheets were used to test the performance accuracy of RADIANCE in dose data extraction. Several search criteria were implemented. All records were searchable by accession number, study date, or dose parameters beyond chosen thresholds. Validated records were searchable according to additional criteria from validation inputs. An error rate of 0.303% was demonstrated in the validation. Dose monitoring is increasingly important and RADIANCE provides an open-source solution with a high level of accuracy. The RADIANCE validator has been updated to enable users to test the integrity of their installation and verify that their dose monitoring is accurate and effective.

An in vivo dose verification method for SBRT-VMAT delivery using the EPID.

PubMed

McCowan, P M; Van Uytven, E; Van Beek, T; Asuni, G; McCurdy, B M C

2015-12-01

Radiation treatments have become increasingly more complex with the development of volumetric modulated arc therapy (VMAT) and the use of stereotactic body radiation therapy (SBRT). SBRT involves the delivery of substantially larger doses over fewer fractions than conventional therapy. SBRT-VMAT treatments will strongly benefit from in vivo patient dose verification, as any errors in delivery can be more detrimental to the radiobiology of the patient as compared to conventional therapy. Electronic portal imaging devices (EPIDs) are available on most commercial linear accelerators (Linacs) and their documented use for dosimetry makes them valuable tools for patient dose verification. In this work, the authors customize and validate a physics-based model which utilizes on-treatment EPID images to reconstruct the 3D dose delivered to the patient during SBRT-VMAT delivery. The SBRT Linac head, including jaws, multileaf collimators, and flattening filter, were modeled using Monte Carlo methods and verified with measured data. The simulation provides energy spectrum data that are used by their "forward" model to then accurately predict fluence generated by a SBRT beam at a plane above the patient. This fluence is then transported through the patient and then the dose to the phosphor layer in the EPID is calculated. Their "inverse" model back-projects the EPID measured focal fluence to a plane upstream of the patient and recombines it with the extra-focal fluence predicted by the forward model. This estimate of total delivered fluence is then forward projected onto the patient's density matrix and a collapsed cone convolution algorithm calculates the dose delivered to the patient. The model was tested by reconstructing the dose for two prostate, three lung, and two spine SBRT-VMAT treatment fractions delivered to an anthropomorphic phantom. It was further validated against actual patient data for a lung and spine SBRT-VMAT plan. The results were verified with the treatment planning system (TPS) (ECLIPSE AAA) dose calculation. The SBRT-VMAT reconstruction model performed very well when compared to the TPS. A stringent 2%/2 mm χ-comparison calculation gave pass rates better than 91% for the prostate plans, 88% for the lung plans, and 86% for the spine plans for voxels containing 80% or more of the prescribed dose. Patient data were 86% for the lung and 95% for the spine. A 3%/3 mm χ-comparison was also performed and gave pass rates better than 93% for all plan types. The authors have customized and validated a robust, physics-based model that calculates the delivered dose to a patient for SBRT-VMAT delivery using on-treatment EPID images. The accuracy of the results indicates that this approach is suitable for clinical implementation. Future work will incorporate this model into both offline and real-time clinical adaptive radiotherapy.

Poster — Thur Eve — 46: Monte Carlo model of the Novalis Classic 6MV stereotactic linear accelerator using the GATE simulation platform

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wiebe, J; Department of Physics and Astronomy, University of Calgary, Calgary, AB; Ploquin, N

2014-08-15

Monte Carlo (MC) simulation is accepted as the most accurate method to predict dose deposition when compared to other methods in radiation treatment planning. Current dose calculation algorithms used for treatment planning can become inaccurate when small radiation fields and tissue inhomogeneities are present. At our centre the Novalis Classic linear accelerator (linac) is used for Stereotactic Radiosurgery (SRS). The first MC model to date of the Novalis Classic linac was developed at our centre using the Geant4 Application for Tomographic Emission (GATE) simulation platform. GATE is relatively new, open source MC software built from CERN's Geometry and Tracking 4more » (Geant4) toolkit. The linac geometry was modeled using manufacturer specifications, as well as in-house measurements of the micro MLC's. Among multiple model parameters, the initial electron beam was adjusted so that calculated depth dose curves agreed with measured values. Simulations were run on the European Grid Infrastructure through GateLab. Simulation time is approximately 8 hours on GateLab for a complete head model simulation to acquire a phase space file. Current results have a majority of points within 3% of the measured dose values for square field sizes ranging from 6×6 mm{sup 2} to 98×98 mm{sup 2} (maximum field size on the Novalis Classic linac) at 100 cm SSD. The x-ray spectrum was determined from the MC data as well. The model provides an investigation into GATE'S capabilities and has the potential to be used as a research tool and an independent dose calculation engine for clinical treatment plans.« less

Quantitative evaluation of patient-specific quality assurance using online dosimetry system

NASA Astrophysics Data System (ADS)

Jung, Jae-Yong; Shin, Young-Ju; Sohn, Seung-Chang; Min, Jung-Whan; Kim, Yon-Lae; Kim, Dong-Su; Choe, Bo-Young; Suh, Tae-Suk

2018-01-01

In this study, we investigated the clinical performance of an online dosimetry system (Mobius FX system, MFX) by 1) dosimetric plan verification using gamma passing rates and dose volume metrics and 2) error-detection capability evaluation by deliberately introduced machine error. Eighteen volumetric modulated arc therapy (VMAT) plans were studied. To evaluate the clinical performance of the MFX, we used gamma analysis and dose volume histogram (DVH) analysis. In addition, to evaluate the error-detection capability, we used gamma analysis and DVH analysis utilizing three types of deliberately introduced errors (Type 1: gantry angle-independent multi-leaf collimator (MLC) error, Type 2: gantry angle-dependent MLC error, and Type 3: gantry angle error). A dosimetric verification comparison of physical dosimetry system (Delt4PT) and online dosimetry system (MFX), gamma passing rates of the two dosimetry systems showed very good agreement with treatment planning system (TPS) calculation. For the average dose difference between the TPS calculation and the MFX measurement, most of the dose metrics showed good agreement within a tolerance of 3%. For the error-detection comparison of Delta4PT and MFX, the gamma passing rates of the two dosimetry systems did not meet the 90% acceptance criterion with the magnitude of error exceeding 2 mm and 1.5 ◦, respectively, for error plans of Types 1, 2, and 3. For delivery with all error types, the average dose difference of PTV due to error magnitude showed good agreement between calculated TPS and measured MFX within 1%. Overall, the results of the online dosimetry system showed very good agreement with those of the physical dosimetry system. Our results suggest that a log file-based online dosimetry system is a very suitable verification tool for accurate and efficient clinical routines for patient-specific quality assurance (QA).

SU-F-T-281: Monte Carlo Investigation of Sources of Dosimetric Discrepancies with 2D Arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Afifi, M; Deiab, N; El-Farrash, A

2016-06-15

Purpose: Intensity modulated radiation therapy (IMRT) poses a number of challenges for properly measuring commissioning data and quality assurance (QA). Understanding the limitations and use of dosimeters to measure these dose distributions is critical to safe IMRT implementation. In this work, we used Monte Carlo simulations to investigate the possible sources of discrepancy between our measurement with 2D array system and our dose calculation using our treatment planning system (TPS). Material and Methods: MCBEAM and MCSIM Monte Carlo codes were used for treatment head simulation and phantom dose calculation. Accurate modeling of a 6MV beam from Varian trilogy machine wasmore » verified by comparing simulated and measured percentage depth doses and profiles. Dose distribution inside the 2D array was calculated using Monte Carlo simulations and our TPS. Then Cross profiles for different field sizes were compared with actual measurements for zero and 90° gantry angle setup. Through the analysis and comparison, we tried to determine the differences and quantify a possible angular calibration factor. Results: Minimum discrepancies was seen in the comparison between the simulated and the measured profiles for the zero gantry angles at all studied field sizes (4×4cm{sup 2}, 10×10cm{sup 2}, 15×15cm{sup 2}, and 20×20cm{sup 2}). Discrepancies between our measurements and calculations increased dramatically for the cross beam profiles at the 90° gantry angle. This could ascribe mainly to the different attenuation caused by the layer of electronics at the base behind the ion chambers in the 2D array. The degree of attenuation will vary depending on the angle of beam incidence. Correction factors were implemented to correct the errors. Conclusion: Monte Carlo modeling of the 2D arrays and the derivation of angular dependence correction factors will allow for improved accuracy of the device for IMRT QA.« less

TH-AB-BRA-07: PENELOPE-Based GPU-Accelerated Dose Calculation System Applied to MRI-Guided Radiation Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Y; Mazur, T; Green, O

Purpose: The clinical commissioning of IMRT subject to a magnetic field is challenging. The purpose of this work is to develop a GPU-accelerated Monte Carlo dose calculation platform based on PENELOPE and then use the platform to validate a vendor-provided MRIdian head model toward quality assurance of clinical IMRT treatment plans subject to a 0.35 T magnetic field. Methods: We first translated PENELOPE from FORTRAN to C++ and validated that the translation produced equivalent results. Then we adapted the C++ code to CUDA in a workflow optimized for GPU architecture. We expanded upon the original code to include voxelized transportmore » boosted by Woodcock tracking, faster electron/positron propagation in a magnetic field, and several features that make gPENELOPE highly user-friendly. Moreover, we incorporated the vendor-provided MRIdian head model into the code. We performed a set of experimental measurements on MRIdian to examine the accuracy of both the head model and gPENELOPE, and then applied gPENELOPE toward independent validation of patient doses calculated by MRIdian’s KMC. Results: We achieve an average acceleration factor of 152 compared to the original single-thread FORTRAN implementation with the original accuracy preserved. For 16 treatment plans including stomach (4), lung (2), liver (3), adrenal gland (2), pancreas (2), spleen (1), mediastinum (1) and breast (1), the MRIdian dose calculation engine agrees with gPENELOPE with a mean gamma passing rate of 99.1% ± 0.6% (2%/2 mm). Conclusions: We developed a Monte Carlo simulation platform based on a GPU-accelerated version of PENELOPE. We validated that both the vendor provided head model and fast Monte Carlo engine used by the MRIdian system are accurate in modeling radiation transport in a patient using 2%/2 mm gamma criteria. Future applications of this platform will include dose validation and accumulation, IMRT optimization, and dosimetry system modeling for next generation MR-IGRT systems.« less

Final Aperture Superposition Technique applied to fast calculation of electron output factors and depth dose curves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faddegon, B.A.; Villarreal-Barajas, J.E.; Mt. Diablo Regional Cancer Center, 2450 East Street, Concord, California

2005-11-15

The Final Aperture Superposition Technique (FAST) is described and applied to accurate, near instantaneous calculation of the relative output factor (ROF) and central axis percentage depth dose curve (PDD) for clinical electron beams used in radiotherapy. FAST is based on precalculation of dose at select points for the two extreme situations of a fully open final aperture and a final aperture with no opening (fully shielded). This technique is different than conventional superposition of dose deposition kernels: The precalculated dose is differential in position of the electron or photon at the downstream surface of the insert. The calculation for amore » particular aperture (x-ray jaws or MLC, insert in electron applicator) is done with superposition of the precalculated dose data, using the open field data over the open part of the aperture and the fully shielded data over the remainder. The calculation takes explicit account of all interactions in the shielded region of the aperture except the collimator effect: Particles that pass from the open part into the shielded part, or visa versa. For the clinical demonstration, FAST was compared to full Monte Carlo simulation of 10x10,2.5x2.5, and 2x8 cm{sup 2} inserts. Dose was calculated to 0.5% precision in 0.4x0.4x0.2 cm{sup 3} voxels, spaced at 0.2 cm depth intervals along the central axis, using detailed Monte Carlo simulation of the treatment head of a commercial linear accelerator for six different electron beams with energies of 6-21 MeV. Each simulation took several hours on a personal computer with a 1.7 Mhz processor. The calculation for the individual inserts, done with superposition, was completed in under a second on the same PC. Since simulations for the pre calculation are only performed once, higher precision and resolution can be obtained without increasing the calculation time for individual inserts. Fully shielded contributions were largest for small fields and high beam energy, at the surface, reaching a maximum of 5.6% at 21 MeV. Contributions from the collimator effect were largest for the large field size, high beam energy, and shallow depths, reaching a maximum of 4.7% at 21 MeV. Both shielding contributions and the collimator effect need to be taken into account to achieve an accuracy of 2%. FAST takes explicit account of the shielding contributions. With the collimator effect set to that of the largest field in the FAST calculation, the difference in dose on the central axis (product of ROF and PDD) between FAST and full simulation was generally under 2%. The maximum difference of 2.5% exceeded the statistical precision of the calculation by four standard deviations. This occurred at 18 MeV for the 2.5x2.5 cm{sup 2} field. The differences are due to the method used to account for the collimator effect.« less

SU-E-T-16: A Comparison of Expected Dwell Times and Dose Variations for NAMD Patients Treated with An Episcleral Brachytherapy Device

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamilton, R; Patel, P; Balaggan, K

2015-06-15

Purpose: To evaluate the variations in dwell times and doses expected when using an episcleral brachytherapy device for treatment of neovascular agerelated macular degeneration (n-AMD) based on accurate imaging modalities Methods: Data from 40 eyes from 40 subjects with known n- AMD acquired through the Distance of Choroid Study (DOCS) conducted at Moorfields Eye Hospital was used to determine the target depth; the distance from the outer scleral surface of the eye, through the choroid, to the apex of the choroidal neovascularization (CNV). Each subject underwent, in triplicate, enhanced-depth Spectral Domain Optical Coherence Tomography (SD-OCT), Swept Source Optical Coherence Tomography,more » (SS-OCT) and Ocular Ultrasound (O-US). These data are the most comprehensive and accurate measurements of the dimensions of the CNV and adjacent layers of the eye for this cohort of patients. During treatment of n-AMD, patients receive a dose of 24Gy to the apex at the target depth. Using the percentage depth dose for a Sr-90 episcleral brachytherapy device, dwell times and doses to the apex were computed to determine the expected variations. Results: The mean target depth and the 95% confidence interval (CI) determined by combining O-US with SD-OCT were 1326 (956,1696)µm and with SS-OCT were 1332 (970,1693)µm. The calculated corresponding mean dwell times and 95% (CI) were 334 (223,445)s and 335 (226,445)s for SD-OCT and SS-OCT determined depths, respectively. The corresponding mean apex dose and 95% (CI) were 24 (35.9,18.0)Gy (SD-OCT) and 24 (35.6,18.1)Gy (SS-OCT). Conclusion: For episcleral brachytherapy treatment of n-AMD, using a patient population average target depth for treatment planning is inadequate, resulting in dose variations of a factor of approximately two over the 95% CI and larger variations for a nontrivial segment of the population. Each patient should have individualized imaging studies to determine the target depth for use in the dwell time calculation. Study was sponsored by Salutaris Medical Devices, Ltd., a subsidiary of Salutaris Medical Devices, Inc. Hamilton and Marsteller are founders of Salutaris Medical Devices, Inc. Drew, McGovern and Vitali are minor equity holders in Salutaris Medical Devices, Inc.« less

SU-E-J-110: Dosimetric Analysis of Respiratory Motion Based On Four-Dimensional Dose Accumulation in Liver Stereotactic Body Radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, S; Kim, D; Kim, T

2015-06-15

Purpose: Respiratory motion in thoracic and abdominal region could lead to significant underdosing of target and increased dose to healthy tissues. The aim of this study is to evaluate the dosimetric effect of respiratory motion in conventional 3D dose by comparing 4D deformable dose in liver stereotactic body radiotherapy (SBRT). Methods: Five patients who had previously treated liver SBRT were included in this study. Four-dimensional computed tomography (4DCT) images with 10 phases for all patients were acquired on multi-slice CT scanner (Siemens, Somatom definition). Conventional 3D planning was performed using the average intensity projection (AIP) images. 4D dose accumulation wasmore » calculated by summation of dose distribution for all phase images of 4DCT using deformable image registration (DIR) . The target volume and normal organs dose were evaluated with the 4D dose and compared with those from 3D dose. And also, Index of achievement (IOA) which assesses the consistency between planned dose and prescription dose was used to compare target dose distribution between 3D and 4D dose. Results: Although the 3D dose calculation considered the moving target coverage, significant differences of various dosimetric parameters between 4D and 3D dose were observed in normal organs and PTV. The conventional 3D dose overestimated dose to PTV, however, there was no significant difference for GTV. The average difference of IOA which become ‘1’ in an ideal case was 3.2% in PTV. The average difference of liver and duodenum was 5% and 16% respectively. Conclusion: 4D dose accumulation which can provide dosimetric effect of respiratory motion has a possibility to predict the more accurate delivered dose to target and normal organs and improve treatment accuracy. This work was supported by the Radiation Technology R&D program (No. 2013M2A2A7043498) and the Mid-career Researcher Program (2014R1A2A1A10050270) through the National Research Foundation of Korea funded by the Ministry of Science, ICT&Future Planning (MSIP) of Korea.« less

Out-of-field in vivo dosimetry using TLD in SABR for primary kidney cancer involving mixed photon fields.

PubMed

Lonski, P; Keehan, S; Siva, S; Pham, D; Franich, R D; Taylor, M L; Kron, T

2017-05-01

To assess out-of-field dose using three different variants of LiF thermoluminescence dosimeters (TLD) for ten patients who underwent stereotactic ablative body radiotherapy (SABR) for primary renal cell carcinoma (RCC) and compare with treatment planning system (TPS) dose calculations. Thermoluminescent dosimeter (TLD) measurements were conducted at 20, 30, 40 and 50cm from isocentre on ten patients undergoing SABR for primary RCC. Three types of high-sensitivity LiF:Mg,Cu,P TLD material with different 6 Li/ 7 Li isotope ratios were used. Patient plans were calculated using Eclipse Anisotropic Analytical Algorithm (AAA) for clinical evaluation and recalculated using Pencil Beam Convolution (PBC) algorithm for comparison. Both AAA and PBC showed diminished accuracy for photon doses at increasing distance out-of-field. At 50cm, measured photon dose was 0.3cGy normalised to a 10Gy prescription on average with only small variation across all patients. This is likely due to the leakage component of the out-of-field dose. The 6 Li-enriched TLD materials showed increased signal attributable to additional neutron contribution. LiF:Mg,Cu,P TLD containing 6 Li is sensitive enough to measure out-of-field dose 50cm from isocentre however will over-estimate the photon component of out-of-field dose in high energy treatments due to the presence of thermal neutrons. 7 Li enriched materials which are insensitive to neutrons are therefore required for accurate photon dosimetry. Neutron signal has been shown here to increase with MUs and is higher for patients treated using certain non coplanar beam arrangements. Further work is required to convert this additional neutron signal to dose. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Effect of intra-fraction motion on the accumulated dose for free-breathing MR-guided stereotactic body radiation therapy of renal-cell carcinoma

NASA Astrophysics Data System (ADS)

Stemkens, Bjorn; Glitzner, Markus; Kontaxis, Charis; de Senneville, Baudouin Denis; Prins, Fieke M.; Crijns, Sjoerd P. M.; Kerkmeijer, Linda G. W.; Lagendijk, Jan J. W.; van den Berg, Cornelis A. T.; Tijssen, Rob H. N.

2017-09-01

Stereotactic body radiation therapy (SBRT) has shown great promise in increasing local control rates for renal-cell carcinoma (RCC). Characterized by steep dose gradients and high fraction doses, these hypo-fractionated treatments are, however, prone to dosimetric errors as a result of variations in intra-fraction respiratory-induced motion, such as drifts and amplitude alterations. This may lead to significant variations in the deposited dose. This study aims to develop a method for calculating the accumulated dose for MRI-guided SBRT of RCC in the presence of intra-fraction respiratory variations and determine the effect of such variations on the deposited dose. For this, RCC SBRT treatments were simulated while the underlying anatomy was moving, based on motion information from three motion models with increasing complexity: (1) STATIC, in which static anatomy was assumed, (2) AVG-RESP, in which 4D-MRI phase-volumes were time-weighted, and (3) PCA, a method that generates 3D volumes with sufficient spatio-temporal resolution to capture respiration and intra-fraction variations. Five RCC patients and two volunteers were included and treatments delivery was simulated, using motion derived from subject-specific MR imaging. Motion was most accurately estimated using the PCA method with root-mean-squared errors of 2.7, 2.4, 1.0 mm for STATIC, AVG-RESP and PCA, respectively. The heterogeneous patient group demonstrated relatively large dosimetric differences between the STATIC and AVG-RESP, and the PCA reconstructed dose maps, with hotspots up to 40% of the D99 and an underdosed GTV in three out of the five patients. This shows the potential importance of including intra-fraction motion variations in dose calculations.

A Comparison of Model Calculation and Measurement of Absorbed Dose for Proton Irradiation. Chapter 5

NASA Technical Reports Server (NTRS)

Zapp, N.; Semones, E.; Saganti, P.; Cucinotta, F.

2003-01-01

With the increase in the amount of time spent EVA that is necessary to complete the construction and subsequent maintenance of ISS, it will become increasingly important for ground support personnel to accurately characterize the radiation exposures incurred by EVA crewmembers. Since exposure measurements cannot be taken within the organs of interest, it is necessary to estimate these exposures by calculation. To validate the methods and tools used to develop these estimates, it is necessary to model experiments performed in a controlled environment. This work is such an effort. A human phantom was outfitted with detector equipment and then placed in American EMU and Orlan-M EVA space suits. The suited phantom was irradiated at the LLUPTF with proton beams of known energies. Absorbed dose measurements were made by the spaceflight operational dosimetrist from JSC at multiple sites in the skin, eye, brain, stomach, and small intestine locations in the phantom. These exposures are then modeled using the BRYNTRN radiation transport code developed at the NASA Langley Research Center, and the CAM (computerized anatomical male) human geometry model of Billings and Yucker. Comparisons of absorbed dose calculations with measurements show excellent agreement. This suggests that there is reason to be confident in the ability of both the transport code and the human body model to estimate proton exposure in ground-based laboratory experiments.

"Measurements of the neutron spectrum in transit to Mars on the Mars Science Laboratory", Köhler et al.

NASA Astrophysics Data System (ADS)

Miller, Jack

2015-04-01

The Mars Science Laboratory (MSL) spacecraft carried the Curiosity rover to Mars. While the dramatic, successful landing of Curiosity and its subsequent exploration of the Martian surface have justifiably generated great excitement, from the standpoint of the health of crewmembers on missions to Mars, knowledge of the environment between Earth and Mars is critical. This paper reports data taken during the cruise phase of the MSL by the Radiation Assessment Detector (RAD). The results are of great interest for several reasons. They are a direct measurement of the radiation environment during what will be a significant fraction of the duration of a proposed human mission to Mars; they were made behind the de facto shielding provided by various spacecraft components; and, in particular, they are a measurement of the contribution to radiation dose by neutrons. The neutron environment inside spacecraft is produced primarily by galactic cosmic ray ions interacting in shielding materials, and given the high biological effectiveness of neutrons and the increased contribution of neutrons to dose with increased depth in shielding, accurate knowledge of the neutron energy spectrum behind shielding is vital. The results show a relatively modest contribution from neutrons and gammas compared to that from charged particles, but also a discrepancy in both dose and dose rate between the data and simulations. The failure of the calculations to accurately reproduce the data is significant, given that future manned spacecraft will be more heavily shielded (and thus produce more secondary neutrons) and that spacecraft design will rely on simulations and model calculations of radiation transport. The methodology of risk estimation continues to evolve, and incorporates our knowledge of both the physical and biological effects of radiation. The relatively large uncertainties in the biological data, and the difficulties in reducing those uncertainties, makes it all the more important to improve both the accuracy and the precision of the physics data.

Using radiance predicted by the P3 approximation in a spherical geometry to predict tissue optical properties

NASA Astrophysics Data System (ADS)

Dickey, Dwayne J.; Moore, Ronald B.; Tulip, John

2001-01-01

For photodynamic therapy of solid tumors, such as prostatic carcinoma, to be achieved, an accurate model to predict tissue parameters and light dose must be found. Presently, most analytical light dosimetry models are fluence based and are not clinically viable for tissue characterization. Other methods of predicting optical properties, such as Monet Carlo, are accurate but far too time consuming for clinical application. However, radiance predicted by the P3-Approximation, an anaylitical solution to the transport equation, may be a viable and accurate alternative. The P3-Approximation accurately predicts optical parameters in intralipid/methylene blue based phantoms in a spherical geometry. The optical parameters furnished by the radiance, when introduced into fluence predicted by both P3- Approximation and Grosjean Theory, correlate well with experimental data. The P3-Approximation also predicts the optical properties of prostate tissue, agreeing with documented optical parameters. The P3-Approximation could be the clinical tool necessary to facilitate PDT of solid tumors because of the limited number of invasive measurements required and the speed in which accurate calculations can be performed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, J; Gu, X; Lu, W

Purpose: A novel distance-dose weighting method for label fusion was developed to increase segmentation accuracy in dosimetrically important regions for prostate radiation therapy. Methods: Label fusion as implemented in the original SIMPLE (OS) for multi-atlas segmentation relies iteratively on the majority vote to generate an estimated ground truth and DICE similarity measure to screen candidates. The proposed distance-dose weighting puts more values on dosimetrically important regions when calculating similarity measure. Specifically, we introduced distance-to-dose error (DDE), which converts distance to dosimetric importance, in performance evaluation. The DDE calculates an estimated DE error derived from surface distance differences between the candidatemore » and estimated ground truth label by multiplying a regression coefficient. To determine the coefficient at each simulation point on the rectum, we fitted DE error with respect to simulated voxel shift. The DEs were calculated by the multi-OAR geometry-dosimetry training model previously developed in our research group. Results: For both the OS and the distance-dose weighted SIMPLE (WS) results, the evaluation metrics for twenty patients were calculated using the ground truth segmentation. The mean difference of DICE, Hausdorff distance, and mean absolute distance (MAD) between OS and WS have shown 0, 0.10, and 0.11, respectively. In partial MAD of WS which calculates MAD within a certain PTV expansion voxel distance, the lower MADs were observed at the closer distances from 1 to 8 than those of OS. The DE results showed that the segmentation from WS produced more accurate results than OS. The mean DE error of V75, V70, V65, and V60 were decreased by 1.16%, 1.17%, 1.14%, and 1.12%, respectively. Conclusion: We have demonstrated that the method can increase the segmentation accuracy in rectum regions adjacent to PTV. As a result, segmentation using WS have shown improved dosimetric accuracy than OS. The WS will provide dosimetrically important label selection strategy in multi-atlas segmentation. CPRIT grant RP150485.« less

Low-dose dynamic myocardial perfusion CT image reconstruction using pre-contrast normal-dose CT scan induced structure tensor total variation regularization

NASA Astrophysics Data System (ADS)

Gong, Changfei; Han, Ce; Gan, Guanghui; Deng, Zhenxiang; Zhou, Yongqiang; Yi, Jinling; Zheng, Xiaomin; Xie, Congying; Jin, Xiance

2017-04-01

Dynamic myocardial perfusion CT (DMP-CT) imaging provides quantitative functional information for diagnosis and risk stratification of coronary artery disease by calculating myocardial perfusion hemodynamic parameter (MPHP) maps. However, the level of radiation delivered by dynamic sequential scan protocol can be potentially high. The purpose of this work is to develop a pre-contrast normal-dose scan induced structure tensor total variation regularization based on the penalized weighted least-squares (PWLS) criteria to improve the image quality of DMP-CT with a low-mAs CT acquisition. For simplicity, the present approach was termed as ‘PWLS-ndiSTV’. Specifically, the ndiSTV regularization takes into account the spatial-temporal structure information of DMP-CT data and further exploits the higher order derivatives of the objective images to enhance denoising performance. Subsequently, an effective optimization algorithm based on the split-Bregman approach was adopted to minimize the associative objective function. Evaluations with modified dynamic XCAT phantom and preclinical porcine datasets have demonstrated that the proposed PWLS-ndiSTV approach can achieve promising gains over other existing approaches in terms of noise-induced artifacts mitigation, edge details preservation, and accurate MPHP maps calculation.

A Method to Improve Electron Density Measurement of Cone-Beam CT Using Dual Energy Technique

PubMed Central

Men, Kuo; Dai, Jian-Rong; Li, Ming-Hui; Chen, Xin-Yuan; Zhang, Ke; Tian, Yuan; Huang, Peng; Xu, Ying-Jie

2015-01-01

Purpose. To develop a dual energy imaging method to improve the accuracy of electron density measurement with a cone-beam CT (CBCT) device. Materials and Methods. The imaging system is the XVI CBCT system on Elekta Synergy linac. Projection data were acquired with the high and low energy X-ray, respectively, to set up a basis material decomposition model. Virtual phantom simulation and phantoms experiments were carried out for quantitative evaluation of the method. Phantoms were also scanned twice with the high and low energy X-ray, respectively. The data were decomposed into projections of the two basis material coefficients according to the model set up earlier. The two sets of decomposed projections were used to reconstruct CBCT images of the basis material coefficients. Then, the images of electron densities were calculated with these CBCT images. Results. The difference between the calculated and theoretical values was within 2% and the correlation coefficient of them was about 1.0. The dual energy imaging method obtained more accurate electron density values and reduced the beam hardening artifacts obviously. Conclusion. A novel dual energy CBCT imaging method to calculate the electron densities was developed. It can acquire more accurate values and provide a platform potentially for dose calculation. PMID:26346510

SU-C-213-04: Application of Depth Sensing and 3D-Printing Technique for Total Body Irradiation (TBI) Patient Measurement and Treatment Planning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, M; Suh, T; Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul

2015-06-15

Purpose: To develop and validate an innovative method of using depth sensing cameras and 3D printing techniques for Total Body Irradiation (TBI) treatment planning and compensator fabrication. Methods: A tablet with motion tracking cameras and integrated depth sensing was used to scan a RANDOTM phantom arranged in a TBI treatment booth to detect and store the 3D surface in a point cloud (PC) format. The accuracy of the detected surface was evaluated by comparison to extracted measurements from CT scan images. The thickness, source to surface distance and off-axis distance of the phantom at different body section was measured formore » TBI treatment planning. A 2D map containing a detailed compensator design was calculated to achieve uniform dose distribution throughout the phantom. The compensator was fabricated using a 3D printer, silicone molding and tungsten powder. In vivo dosimetry measurements were performed using optically stimulated luminescent detectors (OSLDs). Results: The whole scan of the anthropomorphic phantom took approximately 30 seconds. The mean error for thickness measurements at each section of phantom compare to CT was 0.44 ± 0.268 cm. These errors resulted in approximately 2% dose error calculation and 0.4 mm tungsten thickness deviation for the compensator design. The accuracy of 3D compensator printing was within 0.2 mm. In vivo measurements for an end-to-end test showed the overall dose difference was within 3%. Conclusion: Motion cameras and depth sensing techniques proved to be an accurate and efficient tool for TBI patient measurement and treatment planning. 3D printing technique improved the efficiency and accuracy of the compensator production and ensured a more accurate treatment delivery.« less

Model-based dose calculations for COMS eye plaque brachytherapy using an anatomically realistic eye phantom

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lesperance, Marielle; Inglis-Whalen, M.; Thomson, R. M., E-mail: rthomson@physics.carleton.ca

Purpose : To investigate the effects of the composition and geometry of ocular media and tissues surrounding the eye on dose distributions for COMS eye plaque brachytherapy with{sup 125}I, {sup 103}Pd, or {sup 131}Cs seeds, and to investigate doses to ocular structures. Methods : An anatomically and compositionally realistic voxelized eye model with a medial tumor is developed based on a literature review. Mass energy absorption and attenuation coefficients for ocular media are calculated. Radiation transport and dose deposition are simulated using the EGSnrc Monte Carlo user-code BrachyDose for a fully loaded COMS eye plaque within a water phantom andmore » our full eye model for the three radionuclides. A TG-43 simulation with the same seed configuration in a water phantom neglecting the plaque and interseed effects is also performed. The impact on dose distributions of varying tumor position, as well as tumor and surrounding tissue media is investigated. Each simulation and radionuclide is compared using isodose contours, dose volume histograms for the lens and tumor, maximum, minimum, and average doses to structures of interest, and doses to voxels of interest within the eye. Results : Mass energy absorption and attenuation coefficients of the ocular media differ from those of water by as much as 12% within the 20–30 keV photon energy range. For all radionuclides studied, average doses to the tumor and lens regions in the full eye model differ from those for the plaque in water by 8%–10% and 13%–14%, respectively; the average doses to the tumor and lens regions differ between the full eye model and the TG-43 simulation by 2%–17% and 29%–34%, respectively. Replacing the surrounding tissues in the eye model with water increases the maximum and average doses to the lens by 2% and 3%, respectively. Substituting the tumor medium in the eye model for water, soft tissue, or an alternate melanoma composition affects tumor dose compared to the default eye model simulation by up to 16%. In the full eye model simulations, the average dose to the lens is larger by 7%–9% than the dose to the center of the lens, and the maximum dose to the optic nerve is 17%–22% higher than the dose to the optic disk for all radionuclides. In general, when normalized to the same prescription dose at the tumor apex, doses delivered to all structures of interest in the full eye model are lowest for{sup 103}Pd and highest for {sup 131}Cs, except for the tumor where the average dose is highest for {sup 103}Pd and lowest for {sup 131}Cs. Conclusions : The eye is not radiologically water-equivalent, as doses from simulations of the plaque in the full eye model differ considerably from doses for the plaque in a water phantom and from simulated TG-43 calculated doses. This demonstrates the importance of model-based dose calculations for eye plaque brachytherapy, for which accurate elemental compositions of ocular media are necessary.« less

Electron Accelerator Shielding Design of KIPT Neutron Source Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhong, Zhaopeng; Gohar, Yousry

The Argonne National Laboratory of the United States and the Kharkov Institute of Physics and Technology of the Ukraine have been collaborating on the design, development and construction of a neutron source facility at Kharkov Institute of Physics and Technology utilizing an electron-accelerator-driven subcritical assembly. The electron beam power is 100 kW using 100-MeV electrons. The facility was designed to perform basic and applied nuclear research, produce medical isotopes, and train nuclear specialists. The biological shield of the accelerator building was designed to reduce the biological dose to less than 5.0e-03 mSv/h during operation. The main source of the biologicalmore » dose for the accelerator building is the photons and neutrons generated from different interactions of leaked electrons from the electron gun and the accelerator sections with the surrounding components and materials. The Monte Carlo N-particle extended code (MCNPX) was used for the shielding calculations because of its capability to perform electron-, photon-, and neutron-coupled transport simulations. The photon dose was tallied using the MCNPX calculation, starting with the leaked electrons. However, it is difficult to accurately tally the neutron dose directly from the leaked electrons. The neutron yield per electron from the interactions with the surrounding components is very small, similar to 0.01 neutron for 100-MeV electron and even smaller for lower-energy electrons. This causes difficulties for the Monte Carlo analyses and consumes tremendous computation resources for tallying the neutron dose outside the shield boundary with an acceptable accuracy. To avoid these difficulties, the SOURCE and TALLYX user subroutines of MCNPX were utilized for this study. The generated neutrons were banked, together with all related parameters, for a subsequent MCNPX calculation to obtain the neutron dose. The weight windows variance reduction technique was also utilized for both neutron and photon dose calculations. Two shielding materials, heavy concrete and ordinary concrete, were considered for the shield design. The main goal is to maintain the total dose outside the shield boundary less than 5.0e-03 mSv/h during operation. The shield configuration and parameters of the accelerator building were determined and are presented in this paper. Copyright (C) 2016, Published by Elsevier Korea LLC on behalf of Korean Nuclear Society.« less

Monte Carlo based, patient-specific RapidArc QA using Linac log files.

PubMed

Teke, Tony; Bergman, Alanah M; Kwa, William; Gill, Bradford; Duzenli, Cheryl; Popescu, I Antoniu

2010-01-01

A Monte Carlo (MC) based QA process to validate the dynamic beam delivery accuracy for Varian RapidArc (Varian Medical Systems, Palo Alto, CA) using Linac delivery log files (DynaLog) is presented. Using DynaLog file analysis and MC simulations, the goal of this article is to (a) confirm that adequate sampling is used in the RapidArc optimization algorithm (177 static gantry angles) and (b) to assess the physical machine performance [gantry angle and monitor unit (MU) delivery accuracy]. Ten clinically acceptable RapidArc treatment plans were generated for various tumor sites and delivered to a water-equivalent cylindrical phantom on the treatment unit. Three Monte Carlo simulations were performed to calculate dose to the CT phantom image set: (a) One using a series of static gantry angles defined by 177 control points with treatment planning system (TPS) MLC control files (planning files), (b) one using continuous gantry rotation with TPS generated MLC control files, and (c) one using continuous gantry rotation with actual Linac delivery log files. Monte Carlo simulated dose distributions are compared to both ionization chamber point measurements and with RapidArc TPS calculated doses. The 3D dose distributions were compared using a 3D gamma-factor analysis, employing a 3%/3 mm distance-to-agreement criterion. The dose difference between MC simulations, TPS, and ionization chamber point measurements was less than 2.1%. For all plans, the MC calculated 3D dose distributions agreed well with the TPS calculated doses (gamma-factor values were less than 1 for more than 95% of the points considered). Machine performance QA was supplemented with an extensive DynaLog file analysis. A DynaLog file analysis showed that leaf position errors were less than 1 mm for 94% of the time and there were no leaf errors greater than 2.5 mm. The mean standard deviation in MU and gantry angle were 0.052 MU and 0.355 degrees, respectively, for the ten cases analyzed. The accuracy and flexibility of the Monte Carlo based RapidArc QA system were demonstrated. Good machine performance and accurate dose distribution delivery of RapidArc plans were observed. The sampling used in the TPS optimization algorithm was found to be adequate.

An MCNP-based model of a medical linear accelerator x-ray photon beam.

PubMed

Ajaj, F A; Ghassal, N M

2003-09-01

The major components in the x-ray photon beam path of the treatment head of the VARIAN Clinac 2300 EX medical linear accelerator were modeled and simulated using the Monte Carlo N-Particle radiation transport computer code (MCNP). Simulated components include x-ray target, primary conical collimator, x-ray beam flattening filter and secondary collimators. X-ray photon energy spectra and angular distributions were calculated using the model. The x-ray beam emerging from the secondary collimators were scored by considering the total x-ray spectra from the target as the source of x-rays at the target position. The depth dose distribution and dose profiles at different depths and field sizes have been calculated at a nominal operating potential of 6 MV and found to be within acceptable limits. It is concluded that accurate specification of the component dimensions, composition and nominal accelerating potential gives a good assessment of the x-ray energy spectra.

Modeling of beam customization devices in the pencil-beam splitting algorithm for heavy charged particle radiotherapy.

PubMed

Kanematsu, Nobuyuki

2011-03-07

A broad-beam-delivery system for radiotherapy with protons or ions often employs multiple collimators and a range-compensating filter, which offer complex and potentially useful beam customization. It is however difficult for conventional pencil-beam algorithms to deal with fine structures of these devices due to beam-size growth during transport. This study aims to avoid the difficulty with a novel computational model. The pencil beams are initially defined at the range-compensating filter with angular-acceptance correction for upstream collimation followed by stopping and scattering. They are individually transported with possible splitting near the aperture edge of a downstream collimator to form a sharp field edge. The dose distribution for a carbon-ion beam was calculated and compared with existing experimental data. The penumbra sizes of various collimator edges agreed between them to a submillimeter level. This beam-customization model will be used in the greater framework of the pencil-beam splitting algorithm for accurate and efficient patient dose calculation.

The impact of smart metal artefact reduction algorithm for use in radiotherapy treatment planning.

PubMed

Guilfoile, Connor; Rampant, Peter; House, Michael

2017-06-01

The presence of metal artefacts in computed tomography (CT) create issues in radiation oncology. The loss of anatomical information and incorrect Hounsfield unit (HU) values produce inaccuracies in dose calculations, providing suboptimal patient treatment. Metal artefact reduction (MAR) algorithms were developed to combat these problems. This study provides a qualitative and quantitative analysis of the "Smart MAR" software (General Electric Healthcare, Chicago, IL, USA), determining its usefulness in a clinical setting. A detailed analysis was conducted using both patient and phantom data, noting any improvements in HU values and dosimetry with the GE-MAR enabled. This study indicates qualitative improvements in severity of the streak artefacts produced by metals, allowing for easier patient contouring. Furthermore, the GE-MAR managed to recover previously lost anatomical information. Additionally, phantom data showed an improvement in HU value with GE-MAR correction, producing more accurate point dose calculations in the treatment planning system. Overall, the GE-MAR is a useful tool and is suitable for clinical environments.

Pin-photodiode array for the measurement of fan-beam energy and air kerma distributions of X-ray CT scanners.

PubMed

Haba, Tomonobu; Koyama, Shuji; Aoyama, Takahiko; Kinomura, Yutaka; Ida, Yoshihiro; Kobayashi, Masanao; Kameyama, Hiroshi; Tsutsumi, Yoshinori

2016-07-01

Patient dose estimation in X-ray computed tomography (CT) is generally performed by Monte Carlo simulation of photon interactions within anthropomorphic or cylindrical phantoms. An accurate Monte Carlo simulation requires an understanding of the effects of the bow-tie filter equipped in a CT scanner, i.e. the change of X-ray energy and air kerma along the fan-beam arc of the CT scanner. To measure the effective energy and air kerma distributions, we devised a pin-photodiode array utilizing eight channels of X-ray sensors arranged at regular intervals along the fan-beam arc of the CT scanner. Each X-ray sensor consisted of two plate type of pin silicon photodiodes in tandem - front and rear photodiodes - and of a lead collimator, which only allowed X-rays to impinge vertically to the silicon surface of the photodiodes. The effective energy of the X-rays was calculated from the ratio of the output voltages of the photodiodes and the dose was calculated from the output voltage of the front photodiode using the energy and dose calibration curves respectively. The pin-photodiode array allowed the calculation of X-ray effective energies and relative doses, at eight points simultaneously along the fan-beam arc of a CT scanner during a single rotation of the scanner. The fan-beam energy and air kerma distributions of CT scanners can be effectively measured using this pin-photodiode array. Copyright © 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Accuracy of Monte Carlo simulations compared to in-vivo MDCT dosimetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bostani, Maryam, E-mail: mbostani@mednet.ucla.edu; McMillan, Kyle; Cagnon, Chris H.

Purpose: The purpose of this study was to assess the accuracy of a Monte Carlo simulation-based method for estimating radiation dose from multidetector computed tomography (MDCT) by comparing simulated doses in ten patients to in-vivo dose measurements. Methods: MD Anderson Cancer Center Institutional Review Board approved the acquisition of in-vivo rectal dose measurements in a pilot study of ten patients undergoing virtual colonoscopy. The dose measurements were obtained by affixing TLD capsules to the inner lumen of rectal catheters. Voxelized patient models were generated from the MDCT images of the ten patients, and the dose to the TLD for allmore » exposures was estimated using Monte Carlo based simulations. The Monte Carlo simulation results were compared to the in-vivo dose measurements to determine accuracy. Results: The calculated mean percent difference between TLD measurements and Monte Carlo simulations was −4.9% with standard deviation of 8.7% and a range of −22.7% to 5.7%. Conclusions: The results of this study demonstrate very good agreement between simulated and measured doses in-vivo. Taken together with previous validation efforts, this work demonstrates that the Monte Carlo simulation methods can provide accurate estimates of radiation dose in patients undergoing CT examinations.« less

Comparative analysis of dose rates in bricks determined by neutron activation analysis, alpha counting and X-ray fluorescence analysis for the thermoluminescence fine grain dating method

NASA Astrophysics Data System (ADS)

Bártová, H.; Kučera, J.; Musílek, L.; Trojek, T.

2014-11-01

In order to evaluate the age from the equivalent dose and to obtain an optimized and efficient procedure for thermoluminescence (TL) dating, it is necessary to obtain the values of both the internal and the external dose rates from dated samples and from their environment. The measurements described and compared in this paper refer to bricks from historic buildings and a fine-grain dating method. The external doses are therefore negligible, if the samples are taken from a sufficient depth in the wall. However, both the alpha dose rate and the beta and gamma dose rates must be taken into account in the internal dose. The internal dose rate to fine-grain samples is caused by the concentrations of natural radionuclides 238U, 235U, 232Th and members of their decay chains, and by 40K concentrations. Various methods can be used for determining trace concentrations of these natural radionuclides and their contributions to the dose rate. The dose rate fraction from 238U and 232Th can be calculated, e.g., from the alpha count rate, or from the concentrations of 238U and 232Th, measured by neutron activation analysis (NAA). The dose rate fraction from 40K can be calculated from the concentration of potassium measured, e.g., by X-ray fluorescence analysis (XRF) or by NAA. Alpha counting and XRF are relatively simple and are accessible for an ordinary laboratory. NAA can be considered as a more accurate method, but it is more demanding regarding time and costs, since it needs a nuclear reactor as a neutron source. A comparison of these methods allows us to decide whether the time- and cost-saving simpler techniques introduce uncertainty that is still acceptable.

SU-E-T-205: Improving Quality Assurance of HDR Brachytherapy: Verifying Agreement Between Planned and Delivered Dose Distributions Using DICOM RTDose and Advanced Film Dosimetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palmer, A L; University of Surrey, Guildford, Surrey; Bradley, D A

Purpose: HDR brachytherapy is undergoing significant development, and quality assurance (QA) checks must keep pace. Current recommendations do not adequately verify delivered against planned dose distributions: This is particularly relevant for new treatment planning system (TPS) calculation algorithms (non TG-43 based), and an era of significant patient-specific plan optimisation. Full system checks are desirable in modern QA recommendations, complementary to device-centric individual tests. We present a QA system incorporating TPS calculation, dose distribution export, HDR unit performance, and dose distribution measurement. Such an approach, more common in external beam radiotherapy, has not previously been reported in the literature for brachytherapy.more » Methods: Our QA method was tested at 24 UK brachytherapy centres. As a novel approach, we used the TPS DICOM RTDose file export to compare planned dose distribution with that measured using Gafchromic EBT3 films placed around clinical brachytherapy treatment applicators. Gamma analysis was used to compare the dose distributions. Dose difference and distance to agreement were determined at prescription Point A. Accurate film dosimetry was achieved using a glass compression plate at scanning to ensure physically-flat films, simultaneous scanning of known dose films with measurement films, and triple-channel dosimetric analysis. Results: The mean gamma pass rate of RTDose compared to film-measured dose distributions was 98.1% at 3%(local), 2 mm criteria. The mean dose difference, measured to planned, at Point A was -0.5% for plastic treatment applicators and -2.4% for metal applicators, due to shielding not accounted for in TPS. The mean distance to agreement was 0.6 mm. Conclusion: It is recommended to develop brachytherapy QA to include full-system verification of agreement between planned and delivered dose distributions. This is a novel approach for HDR brachytherapy QA. A methodology using advanced film dosimetry and gamma comparison to DICOM RTDose files has been demonstrated as suitable to fulfil this need.« less

Comparison of arterial input functions measured from ultra-fast dynamic contrast enhanced MRI and dynamic contrast enhanced computed tomography in prostate cancer patients

NASA Astrophysics Data System (ADS)

Wang, Shiyang; Lu, Zhengfeng; Fan, Xiaobing; Medved, Milica; Jiang, Xia; Sammet, Steffen; Yousuf, Ambereen; Pineda, Federico; Oto, Aytekin; Karczmar, Gregory S.

2018-02-01

The purpose of this study was to evaluate the accuracy of arterial input functions (AIFs) measured from dynamic contrast enhanced (DCE) MRI following a low dose of contrast media injection. The AIFs measured from DCE computed tomography (CT) were used as ‘gold standard’. A total of twenty patients received CT and MRI scans on the same day. Patients received 120 ml Iohexol in DCE-CT and a low dose of (0.015 mM kg-1) of gadobenate dimeglumine in DCE-MRI. The AIFs were measured in the iliac artery and normalized to the CT and MRI contrast agent doses. To correct for different temporal resolution and sampling periods of CT and MRI, an empirical mathematical model (EMM) was used to fit the AIFs first. Then numerical AIFs (AIFCT and AIFMRI) were calculated based on fitting parameters. The AIFMRI was convolved with a ‘contrast agent injection’ function (AIFMRICON ) to correct for the difference between MRI and CT contrast agent injection times (~1.5 s versus 30 s). The results show that the EMMs accurately fitted AIFs measured from CT and MRI. There was no significant difference (p  >  0.05) between the maximum peak amplitude of AIFs from CT (22.1  ±  4.1 mM/dose) and MRI after convolution (22.3  ±  5.2 mM/dose). The shapes of the AIFCT and AIFMRICON were very similar. Our results demonstrated that AIFs can be accurately measured by MRI following low dose contrast agent injection.

Performance of commercial platforms for rapid genotyping of polymorphisms affecting warfarin dose.

PubMed

King, Cristi R; Porche-Sorbet, Rhonda M; Gage, Brian F; Ridker, Paul M; Renaud, Yannick; Phillips, Michael S; Eby, Charles

2008-06-01

Initiation of warfarin therapy is associated with bleeding owing to its narrow therapeutic window and unpredictable therapeutic dose. Pharmacogenetic-based dosing algorithms can improve accuracy of initial warfarin dosing but require rapid genotyping for cytochrome P-450 2C9 (CYP2C9) *2 and *3 single nucleotide polymorphisms (SNPs) and a vitamin K epoxide reductase (VKORC1) SNP. We evaluated 4 commercial systems: INFINITI analyzer (AutoGenomics, Carlsbad, CA), Invader assay (Third Wave Technologies, Madison, WI), Tag-It Mutation Detection assay (Luminex Molecular Diagnostics, formerly Tm Bioscience, Toronto, Canada), and Pyrosequencing (Biotage, Uppsala, Sweden). We genotyped 112 DNA samples and resolved any discrepancies with bidirectional sequencing. The INFINITI analyzer was 100% accurate for all SNPs and required 8 hours. Invader and Tag-It were 100% accurate for CYP2C9 SNPs, 99% accurate for VKORC1 -1639/3673 SNP, and required 3 hours and 8 hours, respectively. Pyrosequencing was 99% accurate for CYP2C9 *2, 100% accurate for CYP2C9 *3, and 100% accurate for VKORC1 and required 4 hours. Current commercial platforms provide accurate and rapid genotypes for pharmacogenetic dosing during initiation of warfarin therapy.

Confirmation of skin doses resulting from bolus effect of intervening alpha-cradle and carbon fiber couch in radiotherapy.

PubMed

Chan, Maria F; Chiu-Tsao, Sou-Tung; Li, Jingdong; Schupak, Karen; Parhar, Preeti; Burman, Chandra

2012-12-01

In this study, we verified the treatment planning calculations of skin doses with the incorporation of the bolus effect due to the intervening alpha-cradle (AC) and carbon fiber couch (CFC) using radiochromic EBT2 films. A polystyrene phantom (25 × 25 × 15 cm(3)) with six EBT2 films separated by polystyrene slabs, at depths of 0, 0.1, 0.2, 0.5, 1, 1.4 cm, was positioned above an AC, which was ~1 cm thick. The phantom and AC assembly were CT scanned and the CT-images were transferred to the treatment planning system (TPS) for calculations in three scenarios: (A) ignoring AC and CFC, (B) accounting for AC only, (C) accounting for both AC and CFC. A single posterior 10 × 10 cm(2) field, a pair of posterior-oblique 10 × 10 cm(2) fields, and a posterior IMRT field (6 MV photons from a Varian Trilogy linac) were planned. For each radiation field configuration, the same MU were used in all three scenarios in the TPS. Each plan for scenario C was delivered to expose a stack of EBT2 films in the phantom through AC and CFC. In addition, in vivo EBT2 film measurement on a lung cancer patient immobilized with AC undergoing IMRT was also included in this study. Point doses and planar distributions generated from the TPS for the three scenarios were compared with the data from the EBT2 film measurements. For all the field arrangements, the EBT2 film data including the in vivo measurement agreed with the doses calculated for scenario (C), within the uncertainty of the EBT2 measurements (~4%). For the single posterior field (a pair of posterior-oblique fields), the TPS generated doses were lower than the EBT2 doses by 34%, 33%, 31%, 13% (34%, 31%, 31%, 11%) for scenario A and by 27%, 25%, 22%, 8% (25%, 21%, 21%, 6%) for scenario B at the depths of 0, 0.1, 0.2, 0.5 cm, respectively. For the IMRT field, the 2D dose distributions at each depth calculated in scenario C agree with those measured data. When comparing the central axis doses for the IMRT field, we found the TPS generated doses for scenario A (B) were lower than the EBT2 data by 35%, 34%, 31%, 16% (29%, 26%, 23%, 10%) at the depths of 0, 0.1, 0.2, 0.5 cm, respectively. There were no significant differences for the depths of 1.0 and 1.4 cm for all the radiation fields studied. TPS calculation of doses in the skin layers accounting for AC and CFC was verified by EBT2 film data. Ignoring the presence of AC and/or CFC in TPS calculation would significantly underestimate the doses in the skin layers. For the clinicians, as more hypofractionated regimens and stereotactic regimens are being used, this information will be useful to avoid potential serious skin toxicities, and also assist in clinical decisions and report these doses accurately to relevant clinical trials/cooperative groups, such as RTOG.

SU-E-J-43: Deformed Planning CT as An Electron Density Substitute for Cone-Beam CT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mishra, K; Godley, A

2014-06-01

Purpose: To confirm that deforming the planning CT to the daily Cone-Beam CTs (CBCT) can provide suitable electron density for adaptive planning. We quantify the dosimetric difference between plans calculated on deformed planning CTs (DPCT) and daily CT-on-rails images (CTOR). CTOR is used as a test of the method as CTOR already contains accurate electron density to compare against. Methods: Five prostate only IMRT patients, each with five CTOR images, were selected and re-planned on Panther (Prowess Inc.) with a uniform 5 mm PTV expansion, prescribed 78 Gy. The planning CT was deformed to match each CTOR using ABAS (Elektamore » Inc.). Contours were drawn on the CTOR, and copied to the DPCT. The original treatment plan was copied to both the CTOR and DPCT, keeping the center of the prostate as the isocenter. The plans were then calculated using the collapsed cone heterogeneous dose engine of Prowess and typical DVH planning parameters used to compare them. Results: Each DPCT was visually compared to its CTOR with no differences observed. The agreement of the copied CTOR contours with the DPCT anatomy further demonstrated the deformation accuracy. The plans calculated using CTOR and DPCT were compared. Over the 25 plan pairs, the average difference between them for prostate D100, D98 and D95 were 0.5%, 0.2%, and 0.2%; PTV D98, D95 and mean dose: 0.3%, 0.2% and 0.3%; bladder V70, V60 and mean dose: 1.1%, 0.7%, and 0.2%; and rectum mean dose: 0.3%. (D100 is the dose covering 100% of the target; V70 is the volume of the organ receiving 70 Gy). Conclusion: We observe negligible difference between the dose calculated on the DPCT and the CTOR, implying that deformed planning CTs are a suitable substitute for electron density. The method can now be applied to CBCTs. Research version of Panther provided by Prowess Inc. Research version of ABAS provided by Elekta Inc.« less

Organ-specific SPECT activity calibration using 3D printed phantoms for molecular radiotherapy dosimetry.

PubMed

Robinson, Andrew P; Tipping, Jill; Cullen, David M; Hamilton, David; Brown, Richard; Flynn, Alex; Oldfield, Christopher; Page, Emma; Price, Emlyn; Smith, Andrew; Snee, Richard

2016-12-01

Patient-specific absorbed dose calculations for molecular radiotherapy require accurate activity quantification. This is commonly derived from Single-Photon Emission Computed Tomography (SPECT) imaging using a calibration factor relating detected counts to known activity in a phantom insert. A series of phantom inserts, based on the mathematical models underlying many clinical dosimetry calculations, have been produced using 3D printing techniques. SPECT/CT data for the phantom inserts has been used to calculate new organ-specific calibration factors for (99m) Tc and (177)Lu. The measured calibration factors are compared to predicted values from calculations using a Gaussian kernel. Measured SPECT calibration factors for 3D printed organs display a clear dependence on organ shape for (99m) Tc and (177)Lu. The observed variation in calibration factor is reproduced using Gaussian kernel-based calculation over two orders of magnitude change in insert volume for (99m) Tc and (177)Lu. These new organ-specific calibration factors show a 24, 11 and 8 % reduction in absorbed dose for the liver, spleen and kidneys, respectively. Non-spherical calibration factors from 3D printed phantom inserts can significantly improve the accuracy of whole organ activity quantification for molecular radiotherapy, providing a crucial step towards individualised activity quantification and patient-specific dosimetry. 3D printed inserts are found to provide a cost effective and efficient way for clinical centres to access more realistic phantom data.

DEVELOPMENT OF A MULTIMODAL MONTE CARLO BASED TREATMENT PLANNING SYSTEM.

PubMed

Kumada, Hiroaki; Takada, Kenta; Sakurai, Yoshinori; Suzuki, Minoru; Takata, Takushi; Sakurai, Hideyuki; Matsumura, Akira; Sakae, Takeji

2017-10-26

To establish boron neutron capture therapy (BNCT), the University of Tsukuba is developing a treatment device and peripheral devices required in BNCT, such as a treatment planning system. We are developing a new multimodal Monte Carlo based treatment planning system (developing code: Tsukuba Plan). Tsukuba Plan allows for dose estimation in proton therapy, X-ray therapy and heavy ion therapy in addition to BNCT because the system employs PHITS as the Monte Carlo dose calculation engine. Regarding BNCT, several verifications of the system are being carried out for its practical usage. The verification results demonstrate that Tsukuba Plan allows for accurate estimation of thermal neutron flux and gamma-ray dose as fundamental radiations of dosimetry in BNCT. In addition to the practical use of Tsukuba Plan in BNCT, we are investigating its application to other radiation therapies. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Developability assessment of clinical drug products with maximum absorbable doses.

PubMed

Ding, Xuan; Rose, John P; Van Gelder, Jan

2012-05-10

Maximum absorbable dose refers to the maximum amount of an orally administered drug that can be absorbed in the gastrointestinal tract. Maximum absorbable dose, or D(abs), has proved to be an important parameter for quantifying the absorption potential of drug candidates. The purpose of this work is to validate the use of D(abs) in a developability assessment context, and to establish appropriate protocol and interpretation criteria for this application. Three methods for calculating D(abs) were compared by assessing how well the methods predicted the absorption limit for a set of real clinical candidates. D(abs) was calculated for these clinical candidates by means of a simple equation and two computer simulation programs, GastroPlus and an program developed at Eli Lilly and Company. Results from single dose escalation studies in Phase I clinical trials were analyzed to identify the maximum absorbable doses for these compounds. Compared to the clinical results, the equation and both simulation programs provide conservative estimates of D(abs), but in general D(abs) from the computer simulations are more accurate, which may find obvious advantage for the simulations in developability assessment. Computer simulations also revealed the complex behavior associated with absorption saturation and suggested in most cases that the D(abs) limit is not likely to be achieved in a typical clinical dose range. On the basis of the validation findings, an approach is proposed for assessing absorption potential, and best practices are discussed for the use of D(abs) estimates to inform clinical formulation development strategies. Copyright © 2012 Elsevier B.V. All rights reserved.

SU-E-J-135: Feasibility of Using Quantitative Cone Beam CT for Proton Adaptive Planning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jingqian, W; Wang, Q; Zhang, X

2015-06-15

Purpose: To investigate the feasibility of using scatter corrected cone beam CT (CBCT) for proton adaptive planning. Methods: Phantom study was used to evaluate the CT number difference between the planning CT (pCT), quantitative CBCT (qCBCT) with scatter correction and calibrated Hounsfield units using adaptive scatter kernel superposition (ASKS) technique, and raw CBCT (rCBCT). After confirming the CT number accuracy, prostate patients, each with a pCT and several sets of weekly CBCT, were investigated for this study. Spot scanning proton treatment plans were independently generated on pCT, qCBCT and rCBCT. The treatment plans were then recalculated on all images. Dose-volume-histogrammore » (DVH) parameters and gamma analysis were used to compare between dose distributions. Results: Phantom study suggested that Hounsfield unit accuracy for different materials are within 20 HU for qCBCT and over 250 HU for rCBCT. For prostate patients, proton dose could be calculated accurately on qCBCT but not on rCBCT. When the original plan was recalculated on qCBCT, tumor coverage was maintained when anatomy was consistent with pCT. However, large dose variance was observed when patient anatomy change. Adaptive plan using qCBCT was able to recover tumor coverage and reduce dose to normal tissue. Conclusion: It is feasible to use qu antitative CBCT (qCBCT) with scatter correction and calibrated Hounsfield units for proton dose calculation and adaptive planning in proton therapy. Partly supported by Varian Medical Systems.« less

The use of National Weather Service Data to Compute the Dose to the MEOI.

PubMed

Vickers, Linda

2018-05-01

The Turner method is the "benchmark method" for computing the stability class that is used to compute the X/Q (s m). The Turner method should be used to ascertain the validity of X/Q results determined by other methods. This paper used site-specific meteorological data obtained from the National Weather Service. The Turner method described herein is simple, quick, accurate, and transparent because all of the data, calculations, and results are visible for verification and validation with published literature.

The application of polymer gel dosimeters to dosimetry for targeted radionuclide therapy

NASA Astrophysics Data System (ADS)

Gear, J. I.; Flux, G. D.; Charles-Edwards, E.; Partridge, M.; Cook, G.; Ott, R. J.

2006-07-01

There is a lack of standardized methodology to perform dose calculations for targeted radionuclide therapy and at present no method exists to objectively evaluate the various approaches employed. The aim of the work described here was to investigate the practicality and accuracy of calibrating polymer gel dosimeters such that dose measurements resulting from complex activity distributions can be verified. Twelve vials of the polymer gel dosimeter, 'MAGIC', were uniformly mixed with varying concentrations of P-32 such that absorbed doses ranged from 0 to 30 Gy after a period of 360 h before being imaged on a magnetic resonance scanner. In addition, nine vials were prepared and irradiated using an external 6 MV x-ray beam. Magnetic resonance transverse relaxation time, T2, maps were obtained using a multi-echo spin echo sequence and converted to R2 maps (where T2 = 1/R2). Absorbed doses for P-32 irradiated gel were calculated according to the medical internal radiation dose schema using EGSnrc Monte Carlo simulations. Here the energy deposited in cylinders representing the irradiated vials was scored. A relationship between dose and R2 was determined. Effects from oxygen contamination were present in the internally irradiated vials. An increase in O2 sensitivity over those gels irradiated externally was thought to be a result of the longer irradiation period. However, below the region of contamination dose response appeared homogenous. Due do a drop-off of dose at the periphery of the internally irradiated vials, magnetic resonance ringing artefacts were observed. The ringing did not greatly affect the accuracy of calibration, which was comparable for both methods. The largest errors in calculated dose originated from the initial activity measurements, and were approximately 10%. Measured R2 values ranged from 5-35 s-1 with an average standard deviation of 1%. A clear relationship between R2 and dose was observed, with up to 40% increased sensitivity for internally irradiated gels. Curve fits to the calibration data followed a single exponential function. The correlation coefficients for internally and externally irradiated gels were 0.991 and 0.985, respectively. With the ability to accurately calibrate internally dosed polymer gels, this technology shows promise as a means to evaluate dosimetry methods, particularly in cases of non-uniform uptake of a radionuclide.

SU-F-T-410: Investigation of Treatment Planning Accuracy with the Presence of Magnetic Injection Port (breast Tissue Expander)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, W; Wagar, M; Lyatskaya, Y

2016-06-15

Purpose: Mastectomy patients with breast reconstruction usually have a magnetic injection port inside the breast during radiation treatments. The magnet has a very high CT number and produces severe streaking artifact across the entire breast in CT images. Our routine strategy is to replace the artifact volumes with uniform water, and it is necessary to validate that the planned dose, with such an artifact correction, is sufficiently accurate. Methods: A phantom was made with a gelatine-filled container sitting on a Matrixx detector, and the magnetic port was inserted into gelatine with specific depths and orientations. The phantom was scanned onmore » a CT simulator and imported into Eclipse for treatment planning. The dose distribution at the Matrixx detector plane was calculated for raw CT images and artifact-corrected images. The treatment beams were then delivered to the phantom and the dose distributions were acquired by the Matrixx detector. Gamma index was calculated to compare the planned dose and the measurement. Results: Three field sizes (10×10, 15×15 and 20×20) and two depths (50mm and 20mm) were investigated. With the 2%/2mm or 3%/3mm criteria, several points (6–10) failed in the plan for raw CT images, and the number of failure was reduced close to zero for the corrected CT images. An assignment of 10,000 HU to the magnet further reduced the dose error directly under the magnet. Conclusion: It is validated that our routine strategy of artifact correction can effectively reduce the number of failures in the detector plane. It is also recommended to set the magnet with a CT number of 10,000HU, which could potentially improve the dose calculation at the points right behind the magnet.« less

GATE Monte Carlo simulation of dose distribution using MapReduce in a cloud computing environment.

PubMed

Liu, Yangchuan; Tang, Yuguo; Gao, Xin

2017-12-01

The GATE Monte Carlo simulation platform has good application prospects of treatment planning and quality assurance. However, accurate dose calculation using GATE is time consuming. The purpose of this study is to implement a novel cloud computing method for accurate GATE Monte Carlo simulation of dose distribution using MapReduce. An Amazon Machine Image installed with Hadoop and GATE is created to set up Hadoop clusters on Amazon Elastic Compute Cloud (EC2). Macros, the input files for GATE, are split into a number of self-contained sub-macros. Through Hadoop Streaming, the sub-macros are executed by GATE in Map tasks and the sub-results are aggregated into final outputs in Reduce tasks. As an evaluation, GATE simulations were performed in a cubical water phantom for X-ray photons of 6 and 18 MeV. The parallel simulation on the cloud computing platform is as accurate as the single-threaded simulation on a local server and the simulation correctness is not affected by the failure of some worker nodes. The cloud-based simulation time is approximately inversely proportional to the number of worker nodes. For the simulation of 10 million photons on a cluster with 64 worker nodes, time decreases of 41× and 32× were achieved compared to the single worker node case and the single-threaded case, respectively. The test of Hadoop's fault tolerance showed that the simulation correctness was not affected by the failure of some worker nodes. The results verify that the proposed method provides a feasible cloud computing solution for GATE.

Evaluation of a head-repositioner and Z-plate system for improved accuracy of dose delivery.

PubMed

Charney, Sarah C; Lutz, Wendell R; Klein, Mary K; Jones, Pamela D

2009-01-01

Radiation therapy requires accurate dose delivery to targets often identifiable only on computed tomography (CT) images. Translation between the isocenter localized on CT and laser setup for radiation treatment, and interfractional head repositioning are frequent sources of positioning error. The objective was to design a simple, accurate apparatus to eliminate these sources of error. System accuracy was confirmed with phantom and in vivo measurements. A head repositioner that fixates the maxilla via dental mold with fiducial marker Z-plates attached was fabricated to facilitate the connection between the isocenter on CT and laser treatment setup. A phantom study targeting steel balls randomly located within the head repositioner was performed. The center of each ball was marked on a transverse CT slice on which six points of the Z-plate were also visible. Based on the relative position of the six Z-plate points and the ball center, the laser setup position on each Z-plate and a top plate was calculated. Based on these setup marks, orthogonal port films, directed toward each target, were evaluated for accuracy without regard to visual setup. A similar procedure was followed to confirm accuracy of in vivo treatment setups in four dogs using implanted gold seeds. Sequential port films of three dogs were made to confirm interfractional accuracy. Phantom and in vivo measurements confirmed accuracy of 2 mm between isocenter on CT and the center of the treatment dose distribution. Port films confirmed similar accuracy for interfractional treatments. The system reliably connects CT target localization to accurate initial and interfractional radiation treatment setup.

TH-E-BRE-09: TrueBeam Monte Carlo Absolute Dose Calculations Using Monitor Chamber Backscatter Simulations and Linac-Logged Target Current

DOE Office of Scientific and Technical Information (OSTI.GOV)

A, Popescu I; Lobo, J; Sawkey, D

2014-06-15

Purpose: To simulate and measure radiation backscattered into the monitor chamber of a TrueBeam linac; establish a rigorous framework for absolute dose calculations for TrueBeam Monte Carlo (MC) simulations through a novel approach, taking into account the backscattered radiation and the actual machine output during beam delivery; improve agreement between measured and simulated relative output factors. Methods: The ‘monitor backscatter factor’ is an essential ingredient of a well-established MC absolute dose formalism (the MC equivalent of the TG-51 protocol). This quantity was determined for the 6 MV, 6X FFF, and 10X FFF beams by two independent Methods: (1) MC simulationsmore » in the monitor chamber of the TrueBeam linac; (2) linac-generated beam record data for target current, logged for each beam delivery. Upper head MC simulations used a freelyavailable manufacturer-provided interface to a cloud-based platform, allowing use of the same head model as that used to generate the publicly-available TrueBeam phase spaces, without revealing the upper head design. The MC absolute dose formalism was expanded to allow direct use of target current data. Results: The relation between backscatter, number of electrons incident on the target for one monitor unit, and MC absolute dose was analyzed for open fields, as well as a jaw-tracking VMAT plan. The agreement between the two methods was better than 0.15%. It was demonstrated that the agreement between measured and simulated relative output factors improves across all field sizes when backscatter is taken into account. Conclusion: For the first time, simulated monitor chamber dose and measured target current for an actual TrueBeam linac were incorporated in the MC absolute dose formalism. In conjunction with the use of MC inputs generated from post-delivery trajectory-log files, the present method allows accurate MC dose calculations, without resorting to any of the simplifying assumptions previously made in the TrueBeam MC literature. This work has been partially funded by Varian Medical Systems.« less

Practical use of a plastic scintillator for quality assurance of electron beam therapy.

PubMed

Yogo, Katsunori; Tatsuno, Yuya; Tsuneda, Masato; Aono, Yuki; Mochizuki, Daiki; Fujisawa, Yoshiki; Matsushita, Akihiro; Ishigami, Minoru; Ishiyama, Hiromichi; Hayakawa, Kazushige

2017-06-07

Quality assurance (QA) of clinical electron beams is essential for performing accurate and safe radiation therapy. However, with advances in radiation therapy, QA has become increasingly labor-intensive and time-consuming. In this paper, we propose a tissue-equivalent plastic scintillator for quick and easy QA of clinical electron beams. The proposed tool comprises a plastic scintillator plate and a charge-coupled device camera that enable the scintillation light by electron beams to be recorded with high sensitivity and high spatial resolution. Further, the Cerenkov image is directly subtracted from the scintillation image to discriminate Cerenkov emissions and accurately measure the dose profiles of electron beams with high spatial resolution. Compared with conventional methods, discrepancies in the depth profile improved from 7% to 2% in the buildup region via subtractive corrections. Further, the output brightness showed good linearity with dose, good reproducibility (deviations below 1%), and dose rate independence (within 0.5%). The depth of 50% dose measured with the tool, an index of electron beam quality, was within  ±0.5 mm of that obtained with an ionization chamber. Lateral brightness profiles agreed with the lateral dose profiles to within 4% and no significant improvement was obtained using Cerenkov corrections. Field size agreed to within 0.5 mm with those obtained with ionization chamber. For clinical QA of electron boost treatment, a disk scintillator that mimics the shape of a patient's breast is applied. The brightness distribution and dose, calculated using a treatment planning system, was generally acceptable for clinical use, except in limited zones. Overall, the proposed plastic scintillator plate tool efficiently performs QA for electron beam therapy and enables simultaneous verification of output constancy, beam quality, depth, and lateral dose profiles during monthly QAs at lower doses of irradiation (small monitor units, MUs).

SU-E-J-92: On-Line Cone Beam CT Based Planning for Emergency and Palliative Radiation Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Held, M; Morin, O; Pouliot, J

2014-06-01

Purpose: To evaluate and develop the feasibility of on-line cone beam CT based planning for emergency and palliative radiotherapy treatments. Methods: Subsequent to phantom studies, a case library of 28 clinical megavoltage cone beam CT (MVCBCT) was built to assess dose-planning accuracies on MVCBCT for all anatomical sites. A simple emergency treatment plan was created on the MVCBCT and copied to its reference CT. The agreement between the dose distributions of each image pair was evaluated by the mean dose difference of the dose volume and the gamma index of the central 2D axial plane. An array of popular urgentmore » and palliative cases was also evaluated for imaging component clearance and field-of-view. Results: The treatment cases were categorized into four groups (head and neck, thorax/spine, pelvis and extremities). Dose distributions for head and neck treatments were predicted accurately in all cases with a gamma index of >95% for 2% and 2 mm criteria. Thoracic spine treatments had a gamma index as low as 60% indicating a need for better uniformity correction and tissue density calibration. Small anatomy changes between CT and MVCBCT could contribute to local errors. Pelvis and sacral spine treatment cases had a gamma index between 90% and 98% for 3%/3 mm criteria. The limited FOV became an issue for large pelvis patients. Imaging clearance was difficult for cases where the tumor was positioned far off midline. Conclusion: The MVCBCT based dose planning and delivery approach is feasible in many treatment cases. Dose distributions for head and neck patients are unrestrictedly predictable. Some FOV restrictions apply to other treatment sites. Lung tissue is most challenging for accurate dose calculations given the current imaging filters and corrections. Additional clinical cases for extremities need to be included in the study to assess the full range of site-specific planning accuracies. This work is supported by Siemens.« less

Investigation of Presage 3D Dosimetry as a Method of Clinically Intuitive Quality Assurance and Comparison to a Semi-3D Delta4 System

NASA Astrophysics Data System (ADS)

Crockett, Ethan Van

The need for clinically intuitive metrics for patient-specific quality assurance in radiation therapy has been well-documented (Zhen, Nelms et al. 2011). A novel transform method has shown to be effective at converting full-density 3D dose measurements made in a phantom to dose values in the patient geometry, enabling comparisons using clinically intuitive metrics such as dose-volume histograms (Oldham et al. 2011). This work investigates the transform method and compares its calculated dose-volume histograms (DVHs) to DVH values calculated by a Delta4 QA device (Scandidos), marking the first comparison of a true 3D system to a semi-3D device using clinical metrics. Measurements were made using Presage 3D dosimeters, which were readout by an in-house optical-CT scanner. Three patient cases were chosen for the study: one head-and-neck VMAT treatment and two spine IMRT treatments. The transform method showed good agreement with the planned dose values for all three cases. Furthermore, the transformed DVHs adhered to the planned dose with more accuracy than the Delta4 DVHs. The similarity between the Delta4 DVHs and the transformed DVHs, however, was greater for one of the spine cases than it was for the head-and-neck case, implying that the accuracy of the Delta4 Anatomy software may vary from one treatment site to another. Overall, the transform method, which incorporates data from full-density 3D dose measurements, provides clinically intuitive results that are more accurate and consistent than the corresponding results from a semi-3D Delta 4 system.

A feasibility study to calculate unshielded fetal doses to pregnant patients in 6-MV photon treatments using Monte Carlo methods and anatomically realistic phantoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bednarz, Bryan; Xu, X. George

2008-07-15

A Monte Carlo-based procedure to assess fetal doses from 6-MV external photon beam radiation treatments has been developed to improve upon existing techniques that are based on AAPM Task Group Report 36 published in 1995 [M. Stovall et al., Med. Phys. 22, 63-82 (1995)]. Anatomically realistic models of the pregnant patient representing 3-, 6-, and 9-month gestational stages were implemented into the MCNPX code together with a detailed accelerator model that is capable of simulating scattered and leakage radiation from the accelerator head. Absorbed doses to the fetus were calculated for six different treatment plans for sites above the fetusmore » and one treatment plan for fibrosarcoma in the knee. For treatment plans above the fetus, the fetal doses tended to increase with increasing stage of gestation. This was due to the decrease in distance between the fetal body and field edge with increasing stage of gestation. For the treatment field below the fetus, the absorbed doses tended to decrease with increasing gestational stage of the pregnant patient, due to the increasing size of the fetus and relative constant distance between the field edge and fetal body for each stage. The absorbed doses to the fetus for all treatment plans ranged from a maximum of 30.9 cGy to the 9-month fetus to 1.53 cGy to the 3-month fetus. The study demonstrates the feasibility to accurately determine the absorbed organ doses in the mother and fetus as part of the treatment planning and eventually in risk management.« less

Monte Carlo N Particle code - Dose distribution of clinical electron beams in inhomogeneous phantoms

PubMed Central

Nedaie, H. A.; Mosleh-Shirazi, M. A.; Allahverdi, M.

2013-01-01

Electron dose distributions calculated using the currently available analytical methods can be associated with large uncertainties. The Monte Carlo method is the most accurate method for dose calculation in electron beams. Most of the clinical electron beam simulation studies have been performed using non- MCNP [Monte Carlo N Particle] codes. Given the differences between Monte Carlo codes, this work aims to evaluate the accuracy of MCNP4C-simulated electron dose distributions in a homogenous phantom and around inhomogeneities. Different types of phantoms ranging in complexity were used; namely, a homogeneous water phantom and phantoms made of polymethyl methacrylate slabs containing different-sized, low- and high-density inserts of heterogeneous materials. Electron beams with 8 and 15 MeV nominal energy generated by an Elekta Synergy linear accelerator were investigated. Measurements were performed for a 10 cm × 10 cm applicator at a source-to-surface distance of 100 cm. Individual parts of the beam-defining system were introduced into the simulation one at a time in order to show their effect on depth doses. In contrast to the first scattering foil, the secondary scattering foil, X and Y jaws and applicator provide up to 5% of the dose. A 2%/2 mm agreement between MCNP and measurements was found in the homogenous phantom, and in the presence of heterogeneities in the range of 1-3%, being generally within 2% of the measurements for both energies in a "complex" phantom. A full-component simulation is necessary in order to obtain a realistic model of the beam. The MCNP4C results agree well with the measured electron dose distributions. PMID:23533162

SU-F-T-657: In-Room Neutron Dose From High Energy Photon Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Christ, D; Ding, G

Purpose: To estimate neutron dose inside the treatment room from photodisintegration events in high energy photon beams using Monte Carlo simulations and experimental measurements. Methods: The Monte Carlo code MCNP6 was used for the simulations. An Eberline ESP-1 Smart Portable Neutron Detector was used to measure neutron dose. A water phantom was centered at isocenter on the treatment couch, and the detector was placed near the phantom. A Varian 2100EX linear accelerator delivered an 18MV open field photon beam to the phantom at 400MU/min, and a camera captured the detector readings. The experimental setup was modeled in the Monte Carlomore » simulation. The source was modeled for two extreme cases: a) hemispherical photon source emitting from the target and b) cone source with an angle of the primary collimator cone. The model includes the target, primary collimator, flattening filter, secondary collimators, water phantom, detector and concrete walls. Energy deposition tallies were measured for neutrons in the detector and for photons at the center of the phantom. Results: For an 18MV beam with an open 10cm by 10cm field and the gantry at 180°, the Monte Carlo simulations predict the neutron dose in the detector to be 0.11% of the photon dose in the water phantom for case a) and 0.01% for case b). The measured neutron dose is 0.04% of the photon dose. Considering the range of neutron dose predicted by Monte Carlo simulations, the calculated results are in good agreement with measurements. Conclusion: We calculated in-room neutron dose by using Monte Carlo techniques, and the predicted neutron dose is confirmed by experimental measurements. If we remodel the source as an electron beam hitting the target for a more accurate representation of the bremsstrahlung fluence, it is feasible that the Monte Carlo simulations can be used to help in shielding designs.« less

Some computer graphical user interfaces in radiation therapy.

PubMed

Chow, James C L

2016-03-28

In this review, five graphical user interfaces (GUIs) used in radiation therapy practices and researches are introduced. They are: (1) the treatment time calculator, superficial X-ray treatment time calculator (SUPCALC) used in the superficial X-ray radiation therapy; (2) the monitor unit calculator, electron monitor unit calculator (EMUC) used in the electron radiation therapy; (3) the multileaf collimator machine file creator, sliding window intensity modulated radiotherapy (SWIMRT) used in generating fluence map for research and quality assurance in intensity modulated radiation therapy; (4) the treatment planning system, DOSCTP used in the calculation of 3D dose distribution using Monte Carlo simulation; and (5) the monitor unit calculator, photon beam monitor unit calculator (PMUC) used in photon beam radiation therapy. One common issue of these GUIs is that all user-friendly interfaces are linked to complex formulas and algorithms based on various theories, which do not have to be understood and noted by the user. In that case, user only needs to input the required information with help from graphical elements in order to produce desired results. SUPCALC is a superficial radiation treatment time calculator using the GUI technique to provide a convenient way for radiation therapist to calculate the treatment time, and keep a record for the skin cancer patient. EMUC is an electron monitor unit calculator for electron radiation therapy. Instead of doing hand calculation according to pre-determined dosimetric tables, clinical user needs only to input the required drawing of electron field in computer graphical file format, prescription dose, and beam parameters to EMUC to calculate the required monitor unit for the electron beam treatment. EMUC is based on a semi-experimental theory of sector-integration algorithm. SWIMRT is a multileaf collimator machine file creator to generate a fluence map produced by a medical linear accelerator. This machine file controls the multileaf collimator to deliver intensity modulated beams for a specific fluence map used in quality assurance or research. DOSCTP is a treatment planning system using the computed tomography images. Radiation beams (photon or electron) with different energies and field sizes produced by a linear accelerator can be placed in different positions to irradiate the tumour in the patient. DOSCTP is linked to a Monte Carlo simulation engine using the EGSnrc-based code, so that 3D dose distribution can be determined accurately for radiation therapy. Moreover, DOSCTP can be used for treatment planning of patient or small animal. PMUC is a GUI for calculation of the monitor unit based on the prescription dose of patient in photon beam radiation therapy. The calculation is based on dose corrections in changes of photon beam energy, treatment depth, field size, jaw position, beam axis, treatment distance and beam modifiers. All GUIs mentioned in this review were written either by the Microsoft Visual Basic.net or a MATLAB GUI development tool called GUIDE. In addition, all GUIs were verified and tested using measurements to ensure their accuracies were up to clinical acceptable levels for implementations.

Solar particle event organ doses and dose equivalents for interplanetary crews: variations due to body size

NASA Technical Reports Server (NTRS)

Zapp, E. N.; Townsend, L. W.; Cucinotta, F. A.

2002-01-01

Proper assessments of spacecraft shielding requirements and concomitant estimates of risk to critical body organs of spacecraft crews from energetic space radiation require accurate, quantitative methods of characterizing the compositional changes in these radiation fields as they pass through the spacecraft and overlying tissue. When estimating astronaut radiation organ doses and dose equivalents it is customary to use the Computerized Anatomical Man (CAM) model of human geometry to account for body self-shielding. Usually, the distribution for the 50th percentile man (175 cm height; 70 kg mass) is used. Most male members of the U.S. astronaut corps are taller and nearly all have heights that deviate from the 175 cm mean. In this work, estimates of critical organ doses and dose equivalents for interplanetary crews exposed to an event similar to the October 1989 solar particle event are presented for male body sizes that vary from the 5th to the 95th percentiles. Overall the results suggest that calculations of organ dose and dose equivalent may vary by as much as approximately 15% as body size is varied from the 5th to the 95th percentile in the population used to derive the CAM model data. c2002 Published by Elsevier Science Ltd on behalf of COSPAR.

An in vivo dose verification method for SBRT–VMAT delivery using the EPID

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCowan, P. M., E-mail: peter.mccowan@cancercare.mb.ca; Medical Physics Department, CancerCare Manitoba, 675 McDermot Avenue, Winnipeg, Manitoba R3E 0V9; Van Uytven, E.

2015-12-15

Purpose: Radiation treatments have become increasingly more complex with the development of volumetric modulated arc therapy (VMAT) and the use of stereotactic body radiation therapy (SBRT). SBRT involves the delivery of substantially larger doses over fewer fractions than conventional therapy. SBRT–VMAT treatments will strongly benefit from in vivo patient dose verification, as any errors in delivery can be more detrimental to the radiobiology of the patient as compared to conventional therapy. Electronic portal imaging devices (EPIDs) are available on most commercial linear accelerators (Linacs) and their documented use for dosimetry makes them valuable tools for patient dose verification. In thismore » work, the authors customize and validate a physics-based model which utilizes on-treatment EPID images to reconstruct the 3D dose delivered to the patient during SBRT–VMAT delivery. Methods: The SBRT Linac head, including jaws, multileaf collimators, and flattening filter, were modeled using Monte Carlo methods and verified with measured data. The simulation provides energy spectrum data that are used by their “forward” model to then accurately predict fluence generated by a SBRT beam at a plane above the patient. This fluence is then transported through the patient and then the dose to the phosphor layer in the EPID is calculated. Their “inverse” model back-projects the EPID measured focal fluence to a plane upstream of the patient and recombines it with the extra-focal fluence predicted by the forward model. This estimate of total delivered fluence is then forward projected onto the patient’s density matrix and a collapsed cone convolution algorithm calculates the dose delivered to the patient. The model was tested by reconstructing the dose for two prostate, three lung, and two spine SBRT–VMAT treatment fractions delivered to an anthropomorphic phantom. It was further validated against actual patient data for a lung and spine SBRT–VMAT plan. The results were verified with the treatment planning system (TPS) (ECLIPSE AAA) dose calculation. Results: The SBRT–VMAT reconstruction model performed very well when compared to the TPS. A stringent 2%/2 mm χ-comparison calculation gave pass rates better than 91% for the prostate plans, 88% for the lung plans, and 86% for the spine plans for voxels containing 80% or more of the prescribed dose. Patient data were 86% for the lung and 95% for the spine. A 3%/3 mm χ-comparison was also performed and gave pass rates better than 93% for all plan types. Conclusions: The authors have customized and validated a robust, physics-based model that calculates the delivered dose to a patient for SBRT–VMAT delivery using on-treatment EPID images. The accuracy of the results indicates that this approach is suitable for clinical implementation. Future work will incorporate this model into both offline and real-time clinical adaptive radiotherapy.« less

Commissioning dose computation models for spot scanning proton beams in water for a commercially available treatment planning system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, X. R.; Poenisch, F.; Lii, M.

2013-04-15

Purpose: To present our method and experience in commissioning dose models in water for spot scanning proton therapy in a commercial treatment planning system (TPS). Methods: The input data required by the TPS included in-air transverse profiles and integral depth doses (IDDs). All input data were obtained from Monte Carlo (MC) simulations that had been validated by measurements. MC-generated IDDs were converted to units of Gy mm{sup 2}/MU using the measured IDDs at a depth of 2 cm employing the largest commercially available parallel-plate ionization chamber. The sensitive area of the chamber was insufficient to fully encompass the entire lateralmore » dose deposited at depth by a pencil beam (spot). To correct for the detector size, correction factors as a function of proton energy were defined and determined using MC. The fluence of individual spots was initially modeled as a single Gaussian (SG) function and later as a double Gaussian (DG) function. The DG fluence model was introduced to account for the spot fluence due to contributions of large angle scattering from the devices within the scanning nozzle, especially from the spot profile monitor. To validate the DG fluence model, we compared calculations and measurements, including doses at the center of spread out Bragg peaks (SOBPs) as a function of nominal field size, range, and SOBP width, lateral dose profiles, and depth doses for different widths of SOBP. Dose models were validated extensively with patient treatment field-specific measurements. Results: We demonstrated that the DG fluence model is necessary for predicting the field size dependence of dose distributions. With this model, the calculated doses at the center of SOBPs as a function of nominal field size, range, and SOBP width, lateral dose profiles and depth doses for rectangular target volumes agreed well with respective measured values. With the DG fluence model for our scanning proton beam line, we successfully treated more than 500 patients from March 2010 through June 2012 with acceptable agreement between TPS calculated and measured dose distributions. However, the current dose model still has limitations in predicting field size dependence of doses at some intermediate depths of proton beams with high energies. Conclusions: We have commissioned a DG fluence model for clinical use. It is demonstrated that the DG fluence model is significantly more accurate than the SG fluence model. However, some deficiencies in modeling the low-dose envelope in the current dose algorithm still exist. Further improvements to the current dose algorithm are needed. The method presented here should be useful for commissioning pencil beam dose algorithms in new versions of TPS in the future.« less

Commissioning dose computation models for spot scanning proton beams in water for a commercially available treatment planning system

PubMed Central

Zhu, X. R.; Poenisch, F.; Lii, M.; Sawakuchi, G. O.; Titt, U.; Bues, M.; Song, X.; Zhang, X.; Li, Y.; Ciangaru, G.; Li, H.; Taylor, M. B.; Suzuki, K.; Mohan, R.; Gillin, M. T.; Sahoo, N.

2013-01-01

Purpose: To present our method and experience in commissioning dose models in water for spot scanning proton therapy in a commercial treatment planning system (TPS). Methods: The input data required by the TPS included in-air transverse profiles and integral depth doses (IDDs). All input data were obtained from Monte Carlo (MC) simulations that had been validated by measurements. MC-generated IDDs were converted to units of Gy mm2/MU using the measured IDDs at a depth of 2 cm employing the largest commercially available parallel-plate ionization chamber. The sensitive area of the chamber was insufficient to fully encompass the entire lateral dose deposited at depth by a pencil beam (spot). To correct for the detector size, correction factors as a function of proton energy were defined and determined using MC. The fluence of individual spots was initially modeled as a single Gaussian (SG) function and later as a double Gaussian (DG) function. The DG fluence model was introduced to account for the spot fluence due to contributions of large angle scattering from the devices within the scanning nozzle, especially from the spot profile monitor. To validate the DG fluence model, we compared calculations and measurements, including doses at the center of spread out Bragg peaks (SOBPs) as a function of nominal field size, range, and SOBP width, lateral dose profiles, and depth doses for different widths of SOBP. Dose models were validated extensively with patient treatment field-specific measurements. Results: We demonstrated that the DG fluence model is necessary for predicting the field size dependence of dose distributions. With this model, the calculated doses at the center of SOBPs as a function of nominal field size, range, and SOBP width, lateral dose profiles and depth doses for rectangular target volumes agreed well with respective measured values. With the DG fluence model for our scanning proton beam line, we successfully treated more than 500 patients from March 2010 through June 2012 with acceptable agreement between TPS calculated and measured dose distributions. However, the current dose model still has limitations in predicting field size dependence of doses at some intermediate depths of proton beams with high energies. Conclusions: We have commissioned a DG fluence model for clinical use. It is demonstrated that the DG fluence model is significantly more accurate than the SG fluence model. However, some deficiencies in modeling the low-dose envelope in the current dose algorithm still exist. Further improvements to the current dose algorithm are needed. The method presented here should be useful for commissioning pencil beam dose algorithms in new versions of TPS in the future. PMID:23556893

Commissioning dose computation models for spot scanning proton beams in water for a commercially available treatment planning system.

PubMed

Zhu, X R; Poenisch, F; Lii, M; Sawakuchi, G O; Titt, U; Bues, M; Song, X; Zhang, X; Li, Y; Ciangaru, G; Li, H; Taylor, M B; Suzuki, K; Mohan, R; Gillin, M T; Sahoo, N

2013-04-01

To present our method and experience in commissioning dose models in water for spot scanning proton therapy in a commercial treatment planning system (TPS). The input data required by the TPS included in-air transverse profiles and integral depth doses (IDDs). All input data were obtained from Monte Carlo (MC) simulations that had been validated by measurements. MC-generated IDDs were converted to units of Gy mm(2)/MU using the measured IDDs at a depth of 2 cm employing the largest commercially available parallel-plate ionization chamber. The sensitive area of the chamber was insufficient to fully encompass the entire lateral dose deposited at depth by a pencil beam (spot). To correct for the detector size, correction factors as a function of proton energy were defined and determined using MC. The fluence of individual spots was initially modeled as a single Gaussian (SG) function and later as a double Gaussian (DG) function. The DG fluence model was introduced to account for the spot fluence due to contributions of large angle scattering from the devices within the scanning nozzle, especially from the spot profile monitor. To validate the DG fluence model, we compared calculations and measurements, including doses at the center of spread out Bragg peaks (SOBPs) as a function of nominal field size, range, and SOBP width, lateral dose profiles, and depth doses for different widths of SOBP. Dose models were validated extensively with patient treatment field-specific measurements. We demonstrated that the DG fluence model is necessary for predicting the field size dependence of dose distributions. With this model, the calculated doses at the center of SOBPs as a function of nominal field size, range, and SOBP width, lateral dose profiles and depth doses for rectangular target volumes agreed well with respective measured values. With the DG fluence model for our scanning proton beam line, we successfully treated more than 500 patients from March 2010 through June 2012 with acceptable agreement between TPS calculated and measured dose distributions. However, the current dose model still has limitations in predicting field size dependence of doses at some intermediate depths of proton beams with high energies. We have commissioned a DG fluence model for clinical use. It is demonstrated that the DG fluence model is significantly more accurate than the SG fluence model. However, some deficiencies in modeling the low-dose envelope in the current dose algorithm still exist. Further improvements to the current dose algorithm are needed. The method presented here should be useful for commissioning pencil beam dose algorithms in new versions of TPS in the future.

SU-F-BRF-09: A Non-Rigid Point Matching Method for Accurate Bladder Dose Summation in Cervical Cancer HDR Brachytherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, H; Zhen, X; Zhou, L

2014-06-15

Purpose: To propose and validate a deformable point matching scheme for surface deformation to facilitate accurate bladder dose summation for fractionated HDR cervical cancer treatment. Method: A deformable point matching scheme based on the thin plate spline robust point matching (TPSRPM) algorithm is proposed for bladder surface registration. The surface of bladders segmented from fractional CT images is extracted and discretized with triangular surface mesh. Deformation between the two bladder surfaces are obtained by matching the two meshes' vertices via the TPS-RPM algorithm, and the deformation vector fields (DVFs) characteristic of this deformation is estimated by B-spline approximation. Numerically, themore » algorithm is quantitatively compared with the Demons algorithm using five clinical cervical cancer cases by several metrics: vertex-to-vertex distance (VVD), Hausdorff distance (HD), percent error (PE), and conformity index (CI). Experimentally, the algorithm is validated on a balloon phantom with 12 surface fiducial markers. The balloon is inflated with different amount of water, and the displacement of fiducial markers is benchmarked as ground truth to study TPS-RPM calculated DVFs' accuracy. Results: In numerical evaluation, the mean VVD is 3.7(±2.0) mm after Demons, and 1.3(±0.9) mm after TPS-RPM. The mean HD is 14.4 mm after Demons, and 5.3mm after TPS-RPM. The mean PE is 101.7% after Demons and decreases to 18.7% after TPS-RPM. The mean CI is 0.63 after Demons, and increases to 0.90 after TPS-RPM. In the phantom study, the mean Euclidean distance of the fiducials is 7.4±3.0mm and 4.2±1.8mm after Demons and TPS-RPM, respectively. Conclusions: The bladder wall deformation is more accurate using the feature-based TPS-RPM algorithm than the intensity-based Demons algorithm, indicating that TPS-RPM has the potential for accurate bladder dose deformation and dose summation for multi-fractional cervical HDR brachytherapy. This work is supported in part by the National Natural ScienceFoundation of China (no 30970866 and no 81301940)« less

WE-DE-201-07: Measurement of Real-Time Dose for Tandem and Ovoid Brachytherapy Procedures Using a High Precision Optical Fiber Radiation Detector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belley, MD; Current Address Rhode Island Hospital, Providence, RI; Faught, A

Purpose: Development of a novel on-line dosimetry tool is needed to move toward patient-specific quality assurance measurements for Ir-192 HDR brachytherapy to verify accurate dose delivery to the intended location. This work describes the development and use of a nano-crystalline yttrium oxide inorganic scintillator based optical-fiber detector capable of acquiring real-time high-precision dose measurements during tandem and ovoid (T&O) gynecological (GYN) applicator Ir-192 HDR brachytherapy procedures. Methods: An optical-fiber detector was calibrated by acquiring light output measurements in liquid water at 3, 5, 7, and 9cm radial source-detector-distances from an Ir-192 HDR source. A regression model was fit to themore » data to describe the relative light output per unit dose (TG-43 derived) as a function of source-detector-distance. Next, the optical-fiber detector was attached to a vaginal balloon fixed to a Varian Fletcher-Suit-Delclos-style applicator (to mimic clinical setup), and localized by acquiring high-resolution computed tomography (CT) images. To compare the physical point dose to the TPS calculated values (TG-43 and Acuros-BV), a phantom measurement was performed, by submerging the T&O applicator in a liquid water bath and delivering a treatment template representative of a clinical T&O procedure. The fiber detector collected scintillation signal as a function of time, and the calibration data was applied to calculate both real-time dose rate, and cumulative dose. Results: Fiber cumulative dose values were 100.0cGy, 94.3cGy, and 348.9cGy from the tandem, left ovoid, and right ovoid dwells, respectively (total of 443.2cGy). A plot of real time dose rate during the treatment was also acquired. The TPS values at the fiber location were 458.4cGy using TG-43, and 437.6cGy using Acuros-BV calculated as Dm,m (per TG-186). Conclusion: The fiber measured dose value agreement was 3% vs TG-43 and −1% vs Acuros-BV. This fiber detector opens up new possibilities for performing patient-specific quality assurance for Ir-192 HDR GYN procedures. Funding from Coulter Foundation, Duke Bio-medical Engineering. Company is being created around the detector technology. Duke holds patents on the technology.« less

Stereotactic radiotherapy of intrapulmonary lesions: comparison of different dose calculation algorithms for Oncentra MasterPlan®.

PubMed

Troeller, Almut; Garny, Sylvia; Pachmann, Sophia; Kantz, Steffi; Gerum, Sabine; Manapov, Farkhad; Ganswindt, Ute; Belka, Claus; Söhn, Matthias

2015-02-22

The use of high accuracy dose calculation algorithms, such as Monte Carlo (MC) and Collapsed Cone (CC) determine dose in inhomogeneous tissue more accurately than pencil beam (PB) algorithms. However, prescription protocols based on clinical experience with PB are often used for treatment plans calculated with CC. This may lead to treatment plans with changes in field size (FS) and changes in dose to organs at risk (OAR), especially for small tumor volumes in lung tissue treated with SABR. We re-evaluated 17 3D-conformal treatment plans for small intrapulmonary lesions with a prescription of 60 Gy in fractions of 7.5 Gy to the 80% isodose. All treatment plans were initially calculated in Oncentra MasterPlan® using a PB algorithm and recalculated with CC (CCre-calc). Furthermore, a CC-based plan with coverage similar to the PB plan (CCcov) and a CC plan with relaxed coverage criteria (CCclin), were created. The plans were analyzed in terms of Dmean, Dmin, Dmax and coverage for GTV, PTV and ITV. Changes in mean lung dose (MLD), V10Gy and V20Gy were evaluated for the lungs. The re-planned CC plans were compared to the original PB plans regarding changes in total monitor units (MU) and average FS. When PB plans were recalculated with CC, the average V60Gy of GTV, ITV and PTV decreased by 13.2%, 19.9% and 41.4%, respectively. Average Dmean decreased by 9% (GTV), 11.6% (ITV) and 14.2% (PTV). Dmin decreased by 18.5% (GTV), 21.3% (ITV) and 17.5% (PTV). Dmax declined by 7.5%. PTV coverage correlated with PTV volume (p < 0.001). MLD, V10Gy, and V20Gy were significantly reduced in the CC plans. Both, CCcov and CCclin had significantly increased MUs and FS compared to PB. Recalculation of PB plans for small lung lesions with CC showed a strong decline in dose and coverage in GTV, ITV and PTV, and declined dose in the lung. Thus, switching from a PB algorithm to CC, while aiming to obtain similar target coverage, can be associated with application of more MU and extension of radiotherapy fields, causing greater OAR exposition.

Recent developments and comprehensive evaluations of a GPU-based Monte Carlo package for proton therapy

PubMed Central

Qin, Nan; Botas, Pablo; Giantsoudi, Drosoula; Schuemann, Jan; Tian, Zhen; Jiang, Steve B.; Paganetti, Harald; Jia, Xun

2016-01-01

Monte Carlo (MC) simulation is commonly considered as the most accurate dose calculation method for proton therapy. Aiming at achieving fast MC dose calculations for clinical applications, we have previously developed a GPU-based MC tool, gPMC. In this paper, we report our recent updates on gPMC in terms of its accuracy, portability, and functionality, as well as comprehensive tests on this tool. The new version, gPMC v2.0, was developed under the OpenCL environment to enable portability across different computational platforms. Physics models of nuclear interactions were refined to improve calculation accuracy. Scoring functions of gPMC were expanded to enable tallying particle fluence, dose deposited by different particle types, and dose-averaged linear energy transfer (LETd). A multiple counter approach was employed to improve efficiency by reducing frequency of memory writing conflict at scoring. For dose calculation, accuracy improvements over gPMC v1.0 were observed in both water phantom cases and a patient case. For a prostate cancer case planned using high-energy proton beams, dose discrepancies in beam entrance and target region seen in gPMC v1.0 with respect to the gold standard tool for proton Monte Carlo simulations (TOPAS) results were substantially reduced and gamma test passing rate (1%/1mm) was improved from 82.7% to 93.1%. Average relative difference in LETd between gPMC and TOPAS was 1.7%. Average relative differences in dose deposited by primary, secondary, and other heavier particles were within 2.3%, 0.4%, and 0.2%. Depending on source proton energy and phantom complexity, it took 8 to 17 seconds on an AMD Radeon R9 290x GPU to simulate 107 source protons, achieving less than 1% average statistical uncertainty. As beam size was reduced from 10×10 cm2 to 1×1 cm2, time on scoring was only increased by 4.8% with eight counters, in contrast to a 40% increase using only one counter. With the OpenCL environment, the portability of gPMC v2.0 was enhanced. It was successfully executed on different CPUs and GPUs and its performance on different devices varied depending on processing power and hardware structure. PMID:27694712

Evaluation of effective dose with chest digital tomosynthesis system using Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Kim, Dohyeon; Jo, Byungdu; Lee, Youngjin; Park, Su-Jin; Lee, Dong-Hoon; Kim, Hee-Joung

2015-03-01

Chest digital tomosynthesis (CDT) system has recently been introduced and studied. This system offers the potential to be a substantial improvement over conventional chest radiography for the lung nodule detection and reduces the radiation dose with limited angles. PC-based Monte Carlo program (PCXMC) simulation toolkit (STUK, Helsinki, Finland) is widely used to evaluate radiation dose in CDT system. However, this toolkit has two significant limits. Although PCXMC is not possible to describe a model for every individual patient and does not describe the accurate X-ray beam spectrum, Geant4 Application for Tomographic Emission (GATE) simulation describes the various size of phantom for individual patient and proper X-ray spectrum. However, few studies have been conducted to evaluate effective dose in CDT system with the Monte Carlo simulation toolkit using GATE. The purpose of this study was to evaluate effective dose in virtual infant chest phantom of posterior-anterior (PA) view in CDT system using GATE simulation. We obtained the effective dose at different tube angles by applying dose actor function in GATE simulation which was commonly used to obtain the medical radiation dosimetry. The results indicated that GATE simulation was useful to estimate distribution of absorbed dose. Consequently, we obtained the acceptable distribution of effective dose at each projection. These results indicated that GATE simulation can be alternative method of calculating effective dose in CDT applications.

Patterns of patient specific dosimetry in total body irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akino, Yuichi; Department of Radiation Oncology, Osaka University Graduate School of Medicine, Suita, Osaka 565-0871; McMullen, Kevin P.

2013-04-15

Purpose: Total body irradiation (TBI) has been used for bone marrow transplant for hematologic and immune deficiency conditions. The goal of TBI is to deliver a homogeneous dose to the entire body, with a generally accepted range of dose uniformity being within {+-}10% of the prescribed dose. The moving table technique for TBI could make dose uniform in whole body by adjusting couch speed. However, it is difficult to accurately estimate the actual dose by calculation and hence in vivo dosimetry (IVD) is routinely performed. Here, the authors present patterns of patient-specific IVD in 161 TBI patients treated at ourmore » institution. Methods: Cobalt-60 teletherapy unit (Model C9 Cobalt-60 teletherapy unit, Picker X-ray Corporation) with customized moving bed (SITI Industrial Products, Inc., Fishers, IN) were used for TBI treatment. During treatment, OneDose{sup TM} (Sicel Technology, NC) Metal Oxide-silicon Semiconductor Field Effect Transistor detectors were placed at patient body surface; both entrance and exit side of the beam at patient head, neck, mediastinum, umbilicus, and knee to estimate midplane dose. When large differences (>10%) between the prescribed and measured dose were observed, dose delivery was corrected for subsequent fractions by the adjustment of couch speed and/or bolus placement. Under IRB exempt status, the authors retrospectively analyzed the treatment records of 161 patients who received TBI treatment between 2006 and 2011. Results: Across the entire cohort, the median {+-} SD (range) percent variance between calculated and measured dose for head, neck, mediastinum, umbilicus, and knee was -2.3 {+-} 10.2% (-66.2 to +35.3), 1.1 {+-} 11.5% (-62.2 to +40.3), -1.9 {+-} 9.5% (-66.4 to +46.6), -1.1 {+-} 7.2% (-35.2 to +42.9), and 3.4 {+-} 12.2% (-47.9 to +108.5), respectively. More than half of treatments were within {+-}10% of the prescribed dose for all anatomical regions. For 80% of treatments (10%-90%), dose at the umbilicus was within {+-}10%. However, some large differences greater than 35% were also found at several points. For one case, the knee received double the prescribed dose. When the dose differences for multiple fractions were averaged, compliance ({+-}10%) between the prescription and measured dose was improved compared to the dose difference of the first single fraction, for example, as at umbilicus, which improved from 83.9% to 98.5%. Conclusions: Actual dose measurement analysis of TBI patients revealed a potentially wide variance from the calculated dose. Based from their IVD method for TBI using Cobalt-60 irradiator and moving table, {+-}10% over entire body is hard to achieve. However, it can be significantly improved with immediate feedback after the first fraction prior to subsequent treatments.« less

Quantification of pulmonary vessel diameter in low-dose CT images

NASA Astrophysics Data System (ADS)

Rudyanto, Rina D.; Ortiz de Solórzano, Carlos; Muñoz-Barrutia, Arrate

2015-03-01

Accurate quantification of vessel diameter in low-dose Computer Tomography (CT) images is important to study pulmonary diseases, in particular for the diagnosis of vascular diseases and the characterization of morphological vascular remodeling in Chronic Obstructive Pulmonary Disease (COPD). In this study, we objectively compare several vessel diameter estimation methods using a physical phantom. Five solid tubes of differing diameters (from 0.898 to 3.980 mm) were embedded in foam, simulating vessels in the lungs. To measure the diameters, we first extracted the vessels using either of two approaches: vessel enhancement using multi-scale Hessian matrix computation, or explicitly segmenting them using intensity threshold. We implemented six methods to quantify the diameter: three estimating diameter as a function of scale used to calculate the Hessian matrix; two calculating equivalent diameter from the crosssection area obtained by thresholding the intensity and vesselness response, respectively; and finally, estimating the diameter of the object using the Full Width Half Maximum (FWHM). We find that the accuracy of frequently used methods estimating vessel diameter from the multi-scale vesselness filter depends on the range and the number of scales used. Moreover, these methods still yield a significant error margin on the challenging estimation of the smallest diameter (on the order or below the size of the CT point spread function). Obviously, the performance of the thresholding-based methods depends on the value of the threshold. Finally, we observe that a simple adaptive thresholding approach can achieve a robust and accurate estimation of the smallest vessels diameter.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kauweloa, K; Gutierrez, A; Bergamo, A

Purpose: There is growing interest about biological effective dose (BED) and its application in treatment plan evaluation due to its stronger correlation with treatment outcome. An approximate biological effective dose (BEDA) equation was introduced to simplify BED calculations by treatment planning systems in multi-phase treatments. The purpose of this work is to reveal its mathematical properties relative to the true, multi-phase BED (BEDT) equation. Methods: The BEDT equation was derived and used to reveal the mathematical properties of BEDA. MATLAB (MathWorks, Natick, MA) was used to simulate and analyze common and extreme clinical multi-phase cases. In those cases, percent errormore » (Perror) and Bland-Altman analysis were used to study the significance of the inaccuracies of BEDA for different combinations of total doses, numbers of fractions, doses per fractions and α over β values. All the calculations were performed on a voxel-basis in order to study how dose distributions would affect the accuracy of BEDA. Results: When the voxel dose-per-fractions (DPF) delivered by both phases are equal, BEDA and BEDT are equal. In heterogeneous dose distributions, which significantly vary between the phases, there are fewer occurrences of equal DPFs and hence the imprecision of BEDA is greater. It was shown that as the α over β ratio increased the accuracy of BEDA would improve. Examining twenty-four cases, it was shown that the range of DPF ratios for a 3 Perror varied from 0.32 to 7.50Gy, whereas for Perror of 1 the range varied from 0.50 to 2.96Gy. Conclusion: The DPF between the different phases should be equal in order to render BEDA accurate. OARs typically receive heterogeneous dose distributions hence the probability of equal DPFs is low. Consequently, the BEDA equation should only be used for targets or OARs that receive uniform or very similar dose distributions by the different treatment phases.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yi, B; Chung, H; Mutaf, Y

Purpose: To test a novel total body irradiation (TBI) system using conformal partial arc with patient lying on the stationary couch which is biologically equivalent to a moving couch TBI. This improves the scanning field TBI, which is previously presented. Methods: The Uniform MU Modulated arc Segments TBI or UMMS-TBI scans the treatment plane with a constant machine dose rate and a constant gantry rotation speed. A dynamic MLC pattern which moves while gantry rotates has been designed so that the treatment field moves same distance at the treatment plane per each gantry angle, while maintaining same treatment field sizemore » (34cm) at the plane. Dose across the plane varies due to the geometric differences including the distance from the source to a point of interest and the different attenuation from the slanted depth which changes the effective depth. Beam intensity is modulated to correct the dose variation across the plane by assigning the number of gantry angles inversely proportional to the uncorrected dose. Results: Measured dose and calculated dose matched within 1 % for central axis and 3% for off axis for various patient scenarios. Dose from different distance does not follow the inverse square relation as it is predicted from calculation. Dose uniformity better than 5% across 180 cm at 10cm depth is achieved by moving the gantry from −55 to +55 deg. Total treatment time for 2 Gy AP/PA fields is 40–50 minutes excluding patient set up time, at the machine dose rate of 200 MU/min. Conclusion: This novel technique, yet accurate but easy to implement enables TBI treatment in a small treatment room with less program development preparation than other techniques. The VMAT function of treatment delivery is not required to modulate beams. One delivery pattern can be used for different patients by changing the monitor units.« less

Do we need 3D tube current modulation information for accurate organ dosimetry in chest CT? Protocols dose comparisons.

PubMed

Lopez-Rendon, Xochitl; Zhang, Guozhi; Coudyzer, Walter; Develter, Wim; Bosmans, Hilde; Zanca, Federica

2017-11-01

To compare the lung and breast dose associated with three chest protocols: standard, organ-based tube current modulation (OBTCM) and fast-speed scanning; and to estimate the error associated with organ dose when modelling the longitudinal (z-) TCM versus the 3D-TCM in Monte Carlo simulations (MC) for these three protocols. Five adult and three paediatric cadavers with different BMI were scanned. The CTDI vol of the OBTCM and the fast-speed protocols were matched to the patient-specific CTDI vol of the standard protocol. Lung and breast doses were estimated using MC with both z- and 3D-TCM simulated and compared between protocols. The fast-speed scanning protocol delivered the highest doses. A slight reduction for breast dose (up to 5.1%) was observed for two of the three female cadavers with the OBTCM in comparison to the standard. For both adult and paediatric, the implementation of the z-TCM data only for organ dose estimation resulted in 10.0% accuracy for the standard and fast-speed protocols, while relative dose differences were up to 15.3% for the OBTCM protocol. At identical CTDI vol values, the standard protocol delivered the lowest overall doses. Only for the OBTCM protocol is the 3D-TCM needed if an accurate (<10.0%) organ dosimetry is desired. • The z-TCM information is sufficient for accurate dosimetry for standard protocols. • The z-TCM information is sufficient for accurate dosimetry for fast-speed scanning protocols. • For organ-based TCM schemes, the 3D-TCM information is necessary for accurate dosimetry. • At identical CTDI vol , the fast-speed scanning protocol delivered the highest doses. • Lung dose was higher in XCare than standard protocol at identical CTDI vol .

Application of the piecewise rational quadratic interpolant to the AUC calculation in the bioavailability study.

PubMed

Akhter, Khalid P; Ahmad, Mahmood; Khan, Shujaat Ali; Ramzan, Munazza; Shafi, Ishrat; Muryam, Burhana; Javed, Zafar; Murtaza, Ghulam

2012-01-01

This study presents an application of the piecewise rational quadratic interpolant to the AUC calculation in the bioavailability study. The objective of this work is to find an area under the plasma concentration-time curve (AUC) for multiple doses of salbutamol sulfate sustained release tablets (Ventolin oral tablets SR 8 mg, GSK, Pakistan) in the group of 24 healthy adults by using computational mathematics techniques. Following the administration of 4 doses of Ventolin tablets 12 hourly to 24 healthy human subjects and bioanalysis of obtained plasma samples, plasma drug concentration-time profile was constructed. The approximated AUC was computed by using computational mathematics techniques such as extended rectangular, extended trapezium and extended Simpson's rule and compared with exact value of AUC calculated by using software - Kinetica to find best computational mathematics method that gives AUC values closest to exact. The exact values of AUC for four consecutive doses of Ventolin oral tablets were 150.58, 157.81, 164.41 and 162.78 ngxh/mL while the closest approximated AUC values were 149.24, 157.33, 164.25 and 162.28 ngxh/mL, respectively, as found by extended rectangular rule. The errors in the approximated values of AUC were negligible. It is concluded that all computational tools approximated values of AUC accurately but the extended rectangular rule gives slightly better approximated values of AUC as compared to extended trapezium and extended Simpson's rules.

A comparison between anisotropic analytical and multigrid superposition dose calculation algorithms in radiotherapy treatment planning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Vincent W.C., E-mail: htvinwu@polyu.edu.hk; Tse, Teddy K.H.; Ho, Cola L.M.

2013-07-01

Monte Carlo (MC) simulation is currently the most accurate dose calculation algorithm in radiotherapy planning but requires relatively long processing time. Faster model-based algorithms such as the anisotropic analytical algorithm (AAA) by the Eclipse treatment planning system and multigrid superposition (MGS) by the XiO treatment planning system are 2 commonly used algorithms. This study compared AAA and MGS against MC, as the gold standard, on brain, nasopharynx, lung, and prostate cancer patients. Computed tomography of 6 patients of each cancer type was used. The same hypothetical treatment plan using the same machine and treatment prescription was computed for each casemore » by each planning system using their respective dose calculation algorithm. The doses at reference points including (1) soft tissues only, (2) bones only, (3) air cavities only, (4) soft tissue-bone boundary (Soft/Bone), (5) soft tissue-air boundary (Soft/Air), and (6) bone-air boundary (Bone/Air), were measured and compared using the mean absolute percentage error (MAPE), which was a function of the percentage dose deviations from MC. Besides, the computation time of each treatment plan was recorded and compared. The MAPEs of MGS were significantly lower than AAA in all types of cancers (p<0.001). With regards to body density combinations, the MAPE of AAA ranged from 1.8% (soft tissue) to 4.9% (Bone/Air), whereas that of MGS from 1.6% (air cavities) to 2.9% (Soft/Bone). The MAPEs of MGS (2.6%±2.1) were significantly lower than that of AAA (3.7%±2.5) in all tissue density combinations (p<0.001). The mean computation time of AAA for all treatment plans was significantly lower than that of the MGS (p<0.001). Both AAA and MGS algorithms demonstrated dose deviations of less than 4.0% in most clinical cases and their performance was better in homogeneous tissues than at tissue boundaries. In general, MGS demonstrated relatively smaller dose deviations than AAA but required longer computation time.« less

SU-F-J-146: Experimental Validation of 6 MV Photon PDD in Parallel Magnetic Field Calculated by EGSnrc

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghila, A; Steciw, S; Fallone, B

Purpose: Integrated linac-MR systems are uniquely suited for real time tumor tracking during radiation treatment. Understanding the magnetic field dose effects and incorporating them in treatment planning is paramount for linac-MR clinical implementation. We experimentally validated the EGSnrc dose calculations in the presence of a magnetic field parallel to the radiation beam travel. Methods: Two cylindrical bore electromagnets produced a 0.21 T magnetic field parallel to the central axis of a 6 MV photon beam. A parallel plate ion chamber was used to measure the PDD in a polystyrene phantom, placed inside the bore in two setups: phantom top surfacemore » coinciding with the magnet bore center (183 cm SSD), and with the magnet bore’s top surface (170 cm SSD). We measured the field of the magnet at several points and included the exact dimensions of the coils to generate a 3D magnetic field map in a finite element model. BEAMnrc and DOSXYZnrc simulated the PDD experiments in parallel magnetic field (i.e. 3D magnetic field included) and with no magnetic field. Results: With the phantom surface at the top of the electromagnet, the surface dose increased by 10% (compared to no-magnetic field), due to electrons being focused by the smaller fringe fields of the electromagnet. With the phantom surface at the bore center, the surface dose increased by 30% since extra 13 cm of air column was in relatively higher magnetic field (>0.13T) in the magnet bore. EGSnrc Monte Carlo code correctly calculated the radiation dose with and without the magnetic field, and all points passed the 2%, 2 mm Gamma criterion when the ion chamber’s entrance window and air cavity were included in the simulated phantom. Conclusion: A parallel magnetic field increases the surface and buildup dose during irradiation. The EGSnrc package can model these magnetic field dose effects accurately. Dr. Fallone is a co-founder and CEO of MagnetTx Oncology Solutions (under discussions to license Alberta bi-planar linac MR for commercialization).« less

Defined daily doses (DDD) do not accurately reflect opioid doses used in contemporary chronic pain treatment.

PubMed

Nielsen, Suzanne; Gisev, Natasa; Bruno, Raimondo; Hall, Wayne; Cohen, Milton; Larance, Briony; Campbell, Gabrielle; Shanahan, Marian; Blyth, Fiona; Lintzeris, Nicholas; Pearson, Sallie; Mattick, Richard; Degenhardt, Louisa

2017-05-01

To assess how well the defined daily dose (DDD) metric reflects opioid utilisation among chronic non-cancer pain patients. Descriptive, cross-sectional study, utilising a 7-day medication diary. Community-based treatment settings, Australia. A sample of 1101 people prescribed opioids for chronic non-cancer pain. Opioid dose data was collected via a self-completed 7-day medication diary capturing names, strengths and doses of each medication taken in the past week. Median daily dose was calculated for each opioid. Comparisons were made to the World Health Organization's (WHO) DDD metric. WHO DDDs ranged from 0.6 to 7.1 times the median opioid doses used by the sample. For transdermal fentanyl and oral hydromorphone, the median dose was comparable with the DDD. The DDD for methadone was 0.6 times lower than the median doses used by this sample of chronic pain patients. In contrast, the DDD for oxycodone and transdermal buprenorphine, the most commonly used strong opioids for chronic pain in Australia, was two to seven times higher than actual doses used. For many opioids, there are key differences between the actual doses used in clinical practice and the WHO's DDDs. The interpretation of opioid utilisation studies using population-level DDDs may be limited, and a recalibration of the DDD for many opioids or the reporting of opioid utilisation in oral morphine equivalent doses is recommended. Copyright © 2017 John Wiley & Sons, Ltd. Copyright © 2017 John Wiley & Sons, Ltd.