A method to estimate the effect of deformable image registration uncertainties on daily dose mapping

PubMed Central

Murphy, Martin J.; Salguero, Francisco J.; Siebers, Jeffrey V.; Staub, David; Vaman, Constantin

2012-01-01

Purpose: To develop a statistical sampling procedure for spatially-correlated uncertainties in deformable image registration and then use it to demonstrate their effect on daily dose mapping. Methods: Sequential daily CT studies are acquired to map anatomical variations prior to fractionated external beam radiotherapy. The CTs are deformably registered to the planning CT to obtain displacement vector fields (DVFs). The DVFs are used to accumulate the dose delivered each day onto the planning CT. Each DVF has spatially-correlated uncertainties associated with it. Principal components analysis (PCA) is applied to measured DVF error maps to produce decorrelated principal component modes of the errors. The modes are sampled independently and reconstructed to produce synthetic registration error maps. The synthetic error maps are convolved with dose mapped via deformable registration to model the resulting uncertainty in the dose mapping. The results are compared to the dose mapping uncertainty that would result from uncorrelated DVF errors that vary randomly from voxel to voxel. Results: The error sampling method is shown to produce synthetic DVF error maps that are statistically indistinguishable from the observed error maps. Spatially-correlated DVF uncertainties modeled by our procedure produce patterns of dose mapping error that are different from that due to randomly distributed uncertainties. Conclusions: Deformable image registration uncertainties have complex spatial distributions. The authors have developed and tested a method to decorrelate the spatial uncertainties and make statistical samples of highly correlated error maps. The sample error maps can be used to investigate the effect of DVF uncertainties on daily dose mapping via deformable image registration. An initial demonstration of this methodology shows that dose mapping uncertainties can be sensitive to spatial patterns in the DVF uncertainties. PMID:22320766

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

Optimization of equivalent uniform dose using the L-curve criterion.

PubMed

Chvetsov, Alexei V; Dempsey, James F; Palta, Jatinder R

2007-10-07

Optimization of equivalent uniform dose (EUD) in inverse planning for intensity-modulated radiation therapy (IMRT) prevents variation in radiobiological effect between different radiotherapy treatment plans, which is due to variation in the pattern of dose nonuniformity. For instance, the survival fraction of clonogens would be consistent with the prescription when the optimized EUD is equal to the prescribed EUD. One of the problems in the practical implementation of this approach is that the spatial dose distribution in EUD-based inverse planning would be underdetermined because an unlimited number of nonuniform dose distributions can be computed for a prescribed value of EUD. Together with ill-posedness of the underlying integral equation, this may significantly increase the dose nonuniformity. To optimize EUD and keep dose nonuniformity within reasonable limits, we implemented into an EUD-based objective function an additional criterion which ensures the smoothness of beam intensity functions. This approach is similar to the variational regularization technique which was previously studied for the dose-based least-squares optimization. We show that the variational regularization together with the L-curve criterion for the regularization parameter can significantly reduce dose nonuniformity in EUD-based inverse planning.

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

Comparison of individual and composite field analysis using array detector for Intensity Modulated Radiotherapy dose verification.

PubMed

Saminathan, Sathiyan; Chandraraj, Varatharaj; Sridhar, C H; Manickam, Ravikumar

2012-01-01

To compare the measured and calculated individual and composite field planar dose distribution of Intensity Modulated Radiotherapy plans. The measurements were performed in Clinac DHX linear accelerator with 6 MV photons using Matrixx device and a solid water phantom. The 20 brain tumor patients were selected for this study. The IMRT plan was carried out for all the patients using Eclipse treatment planning system. The verification plan was produced for every original plan using CT scan of Matrixx embedded in the phantom. Every verification field was measured by the Matrixx. The TPS calculated and measured dose distributions were compared for individual and composite fields. The percentage of gamma pixel match for the dose distribution patterns were evaluated using gamma histogram. The gamma pixel match was 95-98% for 41 fields (39%) and 98% for 59 fields (61%) with individual fields. The percentage of gamma pixel match was 95-98% for 5 patients and 98% for other 12 patients with composite fields. Three patients showed a gamma pixel match of less than 95%. The comparison of percentage gamma pixel match for individual and composite fields showed more than 2.5% variation for 6 patients, more than 1% variation for 4 patients, while the remaining 10 patients showed less than 1% variation. The individual and composite field measurements showed good agreement with TPS calculated dose distribution for the studied patients. The measurement and data analysis for individual fields is a time consuming process, the composite field analysis may be sufficient enough for smaller field dose distribution analysis with array detectors.

Monte Carlo Assessments of Absorbed Doses to the Hands of Radiopharmaceutical Workers Due to Photon Emitters

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

Ilas, Dan; Eckerman, Keith F; Karagiannis, Harriet

This paper describes the characterization of radiation doses to the hands of nuclear medicine technicians resulting from the handling of radiopharmaceuticals. Radiation monitoring using ring dosimeters indicates that finger dosimeters that are used to show compliance with applicable regulations may overestimate or underestimate radiation doses to the skin depending on the nature of the particular procedure and the radionuclide being handled. To better understand the parameters governing the absorbed dose distributions, a detailed model of the hands was created and used in Monte Carlo simulations of selected nuclear medicine procedures. Simulations of realistic configurations typical for workers handling radiopharmaceuticals weremore » performedfor a range of energies of the source photons. The lack of charged-particle equilibrium necessitated full photon-electron coupled transport calculations. The results show that the dose to different regions of the fingers can differ substantially from dosimeter readings when dosimeters are located at the base of the finger. We tried to identify consistent patterns that relate the actual dose to the dosimeter readings. These patterns depend on the specific work conditions and can be used to better assess the absorbed dose to different regions of the exposed skin.« less

Dose Assessments to the Hands of Radiopharmaceutical Workers

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

Ilas, Dan; Eckerman, Keith F; Sherbini, Sami

This paper describes the characterization of radiation doses to the hands of nuclear medicine technicians resulting from the handling of radiopharmaceuticals. Radiation monitoring using ring dosimeters indicates that finger dosimeters may overestimate or underestimate the radiation doses to the skin that are used to show compliance with applicable regulations depending on the nature of the particular procedure and the radioisotope being handled. To better understand the parameters governing the absorbed dose distributions, a detailed model of the hands was created and used in Monte Carlo simulations of selected nuclear medicine procedures. Simulations on realistic configurations typical for workers handling radiopharmaceuticalsmore » were performed for a range of energies of the source photons. The lack of charged-particle equilibrium necessitated full photon-electron coupled transport calculations. The results show that the dose to different regions of the fingers can differ substantially from the dosimeters' readings when the dosimeters are located at the base of the finger. We tried to identify consistent patterns that relate the actual dose to the dosimeter readings. These patterns depend on the specific work conditions and can be used to better assess the absorbed dose to different regions of the exposed skin.« less

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

Wulff, J; Huggins, A

Purpose: The shape of a single beam in proton PBS influences the resulting dose distribution. Spot profiles are modelled as two-dimensional Gaussian (single/ double) distributions in treatment planning systems (TPS). Impact of slight deviations from an ideal Gaussian on resulting dose distributions is typically assumed to be small due to alleviation by multiple Coulomb scattering (MCS) in tissue and superposition of many spots. Quantitative limits are however not clear per se. Methods: A set of 1250 deliberately deformed profiles with sigma=4 mm for a Gaussian fit were constructed. Profiles and fit were normalized to the same area, resembling output calibrationmore » in the TPS. Depth-dependent MCS was considered. The deviation between deformed and ideal profiles was characterized by root-mean-squared deviation (RMSD), skewness/ kurtosis (SK) and full-width at different percentage of maximum (FWxM). The profiles were convolved with different fluence patterns (regular/ random) resulting in hypothetical dose distributions. The resulting deviations were analyzed by applying a gamma-test. Results were compared to measured spot profiles. Results: A clear correlation between pass-rate and profile metrics could be determined. The largest impact occurred for a regular fluence-pattern with increasing distance between single spots, followed by a random distribution of spot weights. The results are strongly dependent on gamma-analysis dose and distance levels. Pass-rates of >95% at 2%/2 mm and 40 mm depth (=70 MeV) could only be achieved for RMSD<10%, deviation in FWxM at 20% and root of quadratic sum of SK <0.8. As expected the results improve for larger depths. The trends were well resembled for measured spot profiles. Conclusion: All measured profiles from ProBeam sites passed the criteria. Given the fact, that beam-line tuning can result shape distortions, the derived criteria represent a useful QA tool for commissioning and design of future beam-line optics.« less

Experimental validation of a deforming grid 4D dose calculation for PBS proton therapy.

PubMed

Krieger, Miriam; Klimpki, Grischa; Fattori, Giovanni; Hrbacek, Jan; Oxley, David; Safai, Sairos; Weber, Damien C; Lomax, Antony J; Zhang, Ye

2018-03-01

The aim of this study was to verify the temporal accuracy of the estimated dose distribution by a 4D dose calculation (4DDC) in comparison to measurements. A single-field plan (0.6 Gy), optimised for a liver patient case (CTV volume: 403cc), was delivered to a homogeneous PMMA phantom and measured by a high resolution scintillating-CCD system at two water equivalent depths. Various motion scenarios (no motion and motions with amplitude of 10 mm and two periods: 3.7 s and 4.4 s) were simulated using a 4D Quasar phantom and logged by an optical tracking system in real-time. Three motion mitigation approaches (single delivery, 6[Formula: see text] layered and volumetric rescanning) were applied, resulting in 10 individual measurements. 4D dose distributions were retrospectively calculated in water by taking into account the delivery log files (retrospective) containing information on the actually delivered spot positions, fluences, and time stamps. Moreover, in order to evaluate the sensitivity of the 4DDC inputs, the corresponding prospective 4DDCs were performed as a comparison, using the estimated time stamps of the spot delivery and repeated periodical motion patterns. 2D gamma analyses and dose-difference-histograms were used to quantify the agreement between measurements and calculations for all pixels with [Formula: see text]5% of the maximum calculated dose. The results show that a mean gamma score of 99.2% with standard deviation 1.0% can be achieved for 3%/3 mm criteria and all scenarios can reach a score of more than 95%. The average area with more than 5% dose difference was 6.2%. Deviations due to input uncertainties were obvious for single scan deliveries but could be smeared out once rescanning was applied. Thus, the deforming grid 4DDC has been demonstrated to be able to predict the complex patterns of 4D dose distributions for PBS proton therapy with high dosimetric and geometric accuracy, and it can be used as a valid clinical tool for 4D treatment planning, motion mitigation selection, and eventually 4D optimisation applications if the correct temporal information is available.

Experimental validation of a deforming grid 4D dose calculation for PBS proton therapy

NASA Astrophysics Data System (ADS)

Krieger, Miriam; Klimpki, Grischa; Fattori, Giovanni; Hrbacek, Jan; Oxley, David; Safai, Sairos; Weber, Damien C.; Lomax, Antony J.; Zhang, Ye

2018-03-01

The aim of this study was to verify the temporal accuracy of the estimated dose distribution by a 4D dose calculation (4DDC) in comparison to measurements. A single-field plan (0.6 Gy), optimised for a liver patient case (CTV volume: 403cc), was delivered to a homogeneous PMMA phantom and measured by a high resolution scintillating-CCD system at two water equivalent depths. Various motion scenarios (no motion and motions with amplitude of 10 mm and two periods: 3.7 s and 4.4 s) were simulated using a 4D Quasar phantom and logged by an optical tracking system in real-time. Three motion mitigation approaches (single delivery, 6× layered and volumetric rescanning) were applied, resulting in 10 individual measurements. 4D dose distributions were retrospectively calculated in water by taking into account the delivery log files (retrospective) containing information on the actually delivered spot positions, fluences, and time stamps. Moreover, in order to evaluate the sensitivity of the 4DDC inputs, the corresponding prospective 4DDCs were performed as a comparison, using the estimated time stamps of the spot delivery and repeated periodical motion patterns. 2D gamma analyses and dose-difference-histograms were used to quantify the agreement between measurements and calculations for all pixels with > 5% of the maximum calculated dose. The results show that a mean gamma score of 99.2% with standard deviation 1.0% can be achieved for 3%/3 mm criteria and all scenarios can reach a score of more than 95%. The average area with more than 5% dose difference was 6.2%. Deviations due to input uncertainties were obvious for single scan deliveries but could be smeared out once rescanning was applied. Thus, the deforming grid 4DDC has been demonstrated to be able to predict the complex patterns of 4D dose distributions for PBS proton therapy with high dosimetric and geometric accuracy, and it can be used as a valid clinical tool for 4D treatment planning, motion mitigation selection, and eventually 4D optimisation applications if the correct temporal information is available.

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

Stewart, J; Lindsay, P; University of Toronto, Toronto

Purpose: Recent progress in small animal radiotherapy systems has provided the foundation for delivering the heterogeneous, millimeter scale dose distributions demanded by preclinical radiobiology investigations. Despite advances in preclinical dose planning, delivery of highly heterogeneous dose distributions is constrained by the fixed collimation systems and large x-ray focal spot common in small animal radiotherapy systems. This work proposes a dual focal spot dose optimization and delivery method with a large x-ray focal spot used to deliver homogeneous dose regions and a small focal spot to paint spatially heterogeneous dose regions. Methods: Two-dimensional dose kernels were measured for a 1 mmmore » circular collimator with radiochromic film at 10 mm depth in a solid water phantom for the small and large x-ray focal spots on a recently developed small animal microirradiator. These kernels were used in an optimization framework which segmented a desired dose distribution into low- and high-spatial frequency regions for delivery by the large and small focal spot, respectively. For each region, the method determined an optimal set of stage positions and beam-on times. The method was demonstrated by optimizing a bullseye pattern consisting of 0.75 mm radius circular target and 0.5 and 1.0 mm wide rings alternating between 0 and 2 Gy. Results: Compared to a large focal spot technique, the dual focal spot technique improved the optimized dose distribution: 69.2% of the optimized dose was within 0.5 Gy of the intended dose for the large focal spot, compared to 80.6% for the dual focal spot method. The dual focal spot design required 14.0 minutes of optimization, and will require 178.3 minutes for automated delivery. Conclusion: The dual focal spot optimization and delivery framework is a novel option for delivering conformal and heterogeneous dose distributions at the preclinical level and provides a new experimental option for unique radiobiological investigations. Funding Support: this work is supported by funding the National Sciences and Engineering Research Council of Canada, and a Mitacs-accelerate fellowship. Conflict of Interest: Dr. Lindsay and Dr. Jaffray are listed as inventors of the small animal microirradiator described herein. This system has been licensed for commercial development.« less

Updating source term and atmospheric dispersion simulations for the dose reconstruction in Fukushima Daiichi Nuclear Power Station Accident

NASA Astrophysics Data System (ADS)

Nagai, Haruyasu; Terada, Hiroaki; Tsuduki, Katsunori; Katata, Genki; Ota, Masakazu; Furuno, Akiko; Akari, Shusaku

2017-09-01

In order to assess the radiological dose to the public resulting from the Fukushima Daiichi Nuclear Power Station (FDNPS) accident in Japan, especially for the early phase of the accident when no measured data are available for that purpose, the spatial and temporal distribution of radioactive materials in the environment are reconstructed by computer simulations. In this study, by refining the source term of radioactive materials discharged into the atmosphere and modifying the atmospheric transport, dispersion and deposition model (ATDM), the atmospheric dispersion simulation of radioactive materials is improved. Then, a database of spatiotemporal distribution of radioactive materials in the air and on the ground surface is developed from the output of the simulation. This database is used in other studies for the dose assessment by coupling with the behavioral pattern of evacuees from the FDNPS accident. By the improvement of the ATDM simulation to use a new meteorological model and sophisticated deposition scheme, the ATDM simulations reproduced well the 137Cs and 131I deposition patterns. For the better reproducibility of dispersion processes, further refinement of the source term was carried out by optimizing it to the improved ATDM simulation by using new monitoring data.

SU-F-T-513: Dosimetric Validation of Spatially Fractionated Radiotherapy Using Gel Dosimetry

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

Papanikolaou, P; Watts, L; Kirby, N

2016-06-15

Purpose: Spatially fractionated radiation therapy, also known as GRID therapy, is used to treat large solid tumors by irradiating the target to a single dose of 10–20Gy through spatially distributed beamlets. We have investigated the use of a 3D gel for dosimetric characterization of GRID therapy. Methods: GRID therapy is an external beam analog of volumetric brachytherapy, whereby we produce a distribution of hot and cold dose columns inside the tumor volume. Such distribution can be produced with a block or by using a checker-like pattern with MLC. We have studied both types of GRID delivery. A cube shaped acrylicmore » phantom was filled with polymer gel and served as a 3D dosimeter. The phantom was scanned and the CT images were used to produce two plans in Pinnacle, one with the grid block and one with the MLC defined grid. A 6MV beam was used for the plan with a prescription of 1500cGy at dmax. The irradiated phantom was scanned in a 3T MRI scanner. Results: 3D dose maps were derived from the MR scans of the gel dosimeter and were found to be in good agreement with the predicted dose distribution from the RTP system. Gamma analysis showed a passing rate of 93% for 5% dose and 2mm DTA scoring criteria. Both relative and absolute dose profiles are in good agreement, except in the peripheral beamlets where the gel measured slightly higher dose, possibly because of the changing head scatter conditions that the RTP is not fully accounting for. Our results have also been benchmarked against ionization chamber measurements. Conclusion: We have investigated the use of a polymer gel for the 3D dosimetric characterization and evaluation of GRID therapy. Our results demonstrated that the planning system can predict fairly accurately the dose distribution for GRID type therapy.« less

Algorithm of pulmonary emphysema extraction using low dose thoracic 3D CT images

NASA Astrophysics Data System (ADS)

Saita, S.; Kubo, M.; Kawata, Y.; Niki, N.; Nakano, Y.; Omatsu, H.; Tominaga, K.; Eguchi, K.; Moriyama, N.

2006-03-01

Recently, due to aging and smoking, emphysema patients are increasing. The restoration of alveolus which was destroyed by emphysema is not possible, thus early detection of emphysema is desired. We describe a quantitative algorithm for extracting emphysematous lesions and quantitatively evaluate their distribution patterns using low dose thoracic 3-D CT images. The algorithm identified lung anatomies, and extracted low attenuation area (LAA) as emphysematous lesion candidates. Applying the algorithm to 100 thoracic 3-D CT images and then by follow-up 3-D CT images, we demonstrate its potential effectiveness to assist radiologists and physicians to quantitatively evaluate the emphysematous lesions distribution and their evolution in time interval changes.

Two-dimensional dosimetry of radiotherapeutical proton beams using thermoluminescence foils.

PubMed

Czopyk, L; Klosowski, M; Olko, P; Swakon, J; Waligorski, M P R; Kajdrowicz, T; Cuttone, G; Cirrone, G A P; Di Rosa, F

2007-01-01

In modern radiation therapy such as intensity modulated radiation therapy or proton therapy, one is able to cover the target volume with improved dose conformation and to spare surrounding tissue with help of modern measurement techniques. Novel thermoluminescence dosimetry (TLD) foils, developed from the hot-pressed mixture of LiF:Mg,Cu,P (MCP TL) powder and ethylene-tetrafluoroethylene (ETFE) copolymer, have been applied for 2-D dosimetry of radiotherapeutical proton beams at INFN Catania and IFJ Krakow. A TLD reader with 70 mm heating plate and CCD camera was used to read the 2-D emission pattern of irradiated foils. The absorbed dose profiles were evaluated, taking into account correction factors specific for TLD such as dose and energy response. TLD foils were applied for measuring of dose distributions within an eye phantom and compared with predictions obtained from the MCNPX code and Eclipse Ocular Proton Planning (Varian Medical Systems) clinical radiotherapy planning system. We demonstrate the possibility of measuring 2-D dose distributions with point resolution of about 0.5 x 0.5 mm(2).

Proposed linear energy transfer areal detector for protons using radiochromic film.

PubMed

Mayer, Rulon; Lin, Liyong; Fager, Marcus; Douglas, Dan; McDonough, James; Carabe, Alejandro

2015-04-01

Radiation therapy depends on predictably and reliably delivering dose to tumors and sparing normal tissues. Protons with kinetic energy of a few hundred MeV can selectively deposit dose to deep seated tumors without an exit dose, unlike x-rays. The better dose distribution is attributed to a phenomenon known as the Bragg peak. The Bragg peak is due to relatively high energy deposition within a given distance or high Linear Energy Transfer (LET). In addition, biological response to radiation depends on the dose, dose rate, and localized energy deposition patterns or LET. At present, the LET can only be measured at a given fixed point and the LET spatial distribution can only be inferred from calculations. The goal of this study is to develop and test a method to measure LET over extended areas. Traditionally, radiochromic films are used to measure dose distribution but not for LET distribution. We report the first use of these films for measuring the spatial distribution of the LET deposited by protons. The radiochromic film sensitivity diminishes for large LET. A mathematical model correlating the film sensitivity and LET is presented to justify relating LET and radiochromic film relative sensitivity. Protons were directed parallel to radiochromic film sandwiched between solid water slabs. This study proposes the scaled-normalized difference (SND) between the Treatment Planning system (TPS) and measured dose as the metric describing the LET. The SND is correlated with a Monte Carlo (MC) calculation of the LET spatial distribution for a large range of SNDs. A polynomial fit between the SND and MC LET is generated for protons having a single range of 20 cm with narrow Bragg peak. Coefficients from these fitted polynomial fits were applied to measured proton dose distributions with a variety of ranges. An identical procedure was applied to the protons deposited from Spread Out Bragg Peak and modulated by 5 cm. Gamma analysis is a method for comparing the calculated LET with the LET measured using radiochromic film at the pixel level over extended areas. Failure rates using gamma analysis are calculated for areas in the dose distribution using parameters of 25% of MC LET and 3 mm. The processed dose distributions find 5%-10% failure rates for the narrow 12.5 and 15 cm proton ranges and 10%-15% for proton ranges of 15, 17.5, and 20 cm and modulated by 5 cm. It is found through gamma analysis that the measured proton energy deposition in radiochromic film and TPS can be used to determine LET. This modified film dosimetry provides an experimental areal LET measurement that can verify MC calculations, support LET point measurements, possibly enhance biologically based proton treatment planning, and determine the polymerization process within the radiochromic film.

Intra-tumor distribution of PEGylated liposome upon repeated injection: No possession by prior dose.

PubMed

Nakamura, Hiroyuki; Abu Lila, Amr S; Nishio, Miho; Tanaka, Masao; Ando, Hidenori; Kiwada, Hiroshi; Ishida, Tatsuhiro

2015-12-28

Liposomes have proven to be a viable means for the delivery of chemotherapeutic agents to solid tumors. However, significant variability has been detected in their intra-tumor accumulation and distribution, resulting in compromised therapeutic outcomes. We recently examined the intra-tumor accumulation and distribution of weekly sequentially administered oxaliplatin (l-OHP)-containing PEGylated liposomes. In that study, the first and second doses of l-OHP-containing PEGylated liposomes were distributed diversely and broadly within tumor tissues, resulting in a potent anti-tumor efficacy. However, little is known about the mechanism underlying such a diverse and broad liposome distribution. Therefore, in the present study, we investigated the influence of dosage interval on the intra-tumor accumulation and distribution of "empty" PEGylated liposomes. Intra-tumor distribution of sequentially administered "empty" PEGylated liposomes was altered in a dosing interval-dependent manner. In addition, the intra-tumor distribution pattern was closely related to the chronological alteration of tumor blood flow as well as vascular permeability in the growing tumor tissue. These results suggest that the sequential administrations of PEGylated liposomes in well-spaced intervals might allow the distribution to different areas and enhance the total bulk accumulation within tumor tissue, resulting in better therapeutic efficacy of the encapsulated payload. This study may provide useful information for a better design of therapeutic regimens involving multiple administrations of nanocarrier drug delivery systems. Copyright © 2015 Elsevier B.V. All rights reserved.

Image processing techniques revealing the relationship between the field-measured ambient gamma dose equivalent rate and geological conditions at a granitic area, Velence Mountains, Hungary

NASA Astrophysics Data System (ADS)

Beltran Torres, Silvana; Petrik, Attila; Zsuzsanna Szabó, Katalin; Jordan, Gyozo; Szabó, Csaba

2017-04-01

In order to estimate the annual dose that the public receive from natural radioactivity, the identification of the potential risk areas is required which, in turn, necessitates understanding the relationship between the spatial distribution of natural radioactivity and the geogenic risk factors (e.g., rock types, dykes, faults, soil conditions, etc.). A detailed spatial analysis of ambient gamma dose equivalent rate was performed in the western side of Velence Mountains, the largest outcropped granitic area in Hungary. In order to assess the role of local geology in the spatial distribution of ambient gamma dose rates, field measurements were carried out at ground level at 300 sites along a 250 m x 250 m regular grid in a total surface of 14.7 km2. Digital image processing methods were applied to identify anomalies, heterogeneities and spatial patterns in the measured gamma dose rates, including local maxima and minima determination, digital cross sections, gradient magnitude and gradient direction, second derivative profile curvature, local variability, lineament density, 2D autocorrelation and directional variogram analyses. Statistical inference showed that different gamma dose rate levels are associated with the rock types (i.e., Carboniferous granite, Pleistocene colluvial, proluvial, deluvial sediments and talus, and Pannonian sand and pebble), with the highest level on the Carboniferous granite including outlying values. Moreover, digital image processing revealed that linear gamma dose rate spatial features are parallel to the SW-NE dyke system and possibly to the NW-SE main fractures. The results of this study underline the importance of understanding the role of geogenic risk factors influencing the ambient gamma dose rate received by public. The study also demonstrates the power of the image processing techniques for the identification of spatial pattern in field-measured geogenic radiation.

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

Trofimov, A; Carpenter, K; Shih, HA

Purpose: To quantify daily set-up variations in fractionated proton therapy of ocular melanomas, and to assess the effect on the fidelity of delivered distribution to the plan. Methods: In a typical five-fraction course, daily set-up is achieved by matching the position of fiducial markers in orthogonal radiographs to the images generated by treatment planning program. A patient maintains the required gaze direction voluntarily, without the aid of fixation devices. Confirmation radiographs are acquired to assess intrafractional changes. For this study, daily radiographs were analyzed to determine the daily iso-center position and apparent gaze direction, which were then transferred to themore » planning system to calculate the dose delivered in individual fractions, and accumulated dose for the entire course. Dose-volume metrics were compared between the planned and accumulated distributions for the tumor and organs at risk, for representative cases that varied by location within the ocular globe. Results: The analysis of the first set of cases (3 posterior, 3 transequatorial and 4 anterior tumors) revealed varying dose deviation patterns, depending on the tumor location. For anterior and posterior tumors, the largest dose increases were observed in the lens and ciliary body, while for the equatorial tumors, macula, optic nerve and disk, were most often affected. The iso-center position error was below 1.3 mm (95%-confidence interval), and the standard deviation of daily polar and azimuthal gaze set-up were 1.5 and 3 degrees, respectively. Conclusion: We quantified interfractional and intrafractional set-up variation, and estimated their effect on the delivered dose for representative cases. Current safety margins are sufficient to maintain the target coverage, however, the dose delivered to critical structures often deviates from the plan. The ongoing analysis will further explore the patterns of dose deviation, and may help to identify particular treatment scenarios which are at a higher risk for such deviations.« less

Background of Civil Defense and Current Damage Limiting Studies.

ERIC Educational Resources Information Center

Romm, Joseph

A brief history of civil defense administration precedes analysis of nuclear attack conditions and the influence of protective measures. Damage limitation procedure is explained in terms of--(1) blast effects, (2) radiation doses, (3) geographical fallout distribution patterns, and (4) national shelter needs. Major concept emphasis relates to--(1)…

A scintillating gas detector for 2D dose measurements in clinical carbon beams.

PubMed

Seravalli, E; de Boer, M; Geurink, F; Huizenga, J; Kreuger, R; Schippers, J M; van Eijk, C W E; Voss, B

2008-09-07

A two-dimensional position sensitive dosimetry system based on a scintillating gas detector has been developed for pre-treatment verification of dose distributions in hadron therapy. The dosimetry system consists of a chamber filled with an Ar/CF4 scintillating gas mixture, inside which two cascaded gas electron multipliers (GEMs) are mounted. A GEM is a thin kapton foil with copper cladding structured with a regular pattern of sub-mm holes. The primary electrons, created in the detector's sensitive volume by the incoming beam, drift in an electric field towards the GEMs and undergo gas multiplication in the GEM holes. During this process, photons are emitted by the excited Ar/CF4 gas molecules and detected by a mirror-lens-CCD camera system. Since the amount of emitted light is proportional to the dose deposited in the sensitive volume of the detector by the incoming beam, the intensity distribution of the measured light spot is proportional to the 2D hadron dose distribution. For a measurement of a 3D dose distribution, the scintillating gas detector is mounted at the beam exit side of a water-bellows phantom, whose thickness can be varied in steps. In this work, the energy dependence of the output signal of the scintillating gas detector has been verified in a 250 MeV/u clinical 12C ion beam by means of a depth-dose curve measurement. The underestimation of the measured signal at the Bragg peak depth is only 9% with respect to an air-filled ionization chamber. This is much smaller than the underestimation found for a scintillating Gd2O2S:Tb ('Lanex') screen under the same measurement conditions (43%). Consequently, the scintillating gas detector is a promising device for verifying dose distributions in high LET beams, for example to check hadron therapy treatment plans which comprise beams with different energies.

A scintillating gas detector for 2D dose measurements in clinical carbon beams

NASA Astrophysics Data System (ADS)

Seravalli, E.; de Boer, M.; Geurink, F.; Huizenga, J.; Kreuger, R.; Schippers, J. M.; van Eijk, C. W. E.; Voss, B.

2008-09-01

A two-dimensional position sensitive dosimetry system based on a scintillating gas detector has been developed for pre-treatment verification of dose distributions in hadron therapy. The dosimetry system consists of a chamber filled with an Ar/CF4 scintillating gas mixture, inside which two cascaded gas electron multipliers (GEMs) are mounted. A GEM is a thin kapton foil with copper cladding structured with a regular pattern of sub-mm holes. The primary electrons, created in the detector's sensitive volume by the incoming beam, drift in an electric field towards the GEMs and undergo gas multiplication in the GEM holes. During this process, photons are emitted by the excited Ar/CF4 gas molecules and detected by a mirror-lens-CCD camera system. Since the amount of emitted light is proportional to the dose deposited in the sensitive volume of the detector by the incoming beam, the intensity distribution of the measured light spot is proportional to the 2D hadron dose distribution. For a measurement of a 3D dose distribution, the scintillating gas detector is mounted at the beam exit side of a water-bellows phantom, whose thickness can be varied in steps. In this work, the energy dependence of the output signal of the scintillating gas detector has been verified in a 250 MeV/u clinical 12C ion beam by means of a depth-dose curve measurement. The underestimation of the measured signal at the Bragg peak depth is only 9% with respect to an air-filled ionization chamber. This is much smaller than the underestimation found for a scintillating Gd2O2S:Tb ('Lanex') screen under the same measurement conditions (43%). Consequently, the scintillating gas detector is a promising device for verifying dose distributions in high LET beams, for example to check hadron therapy treatment plans which comprise beams with different energies.

Semi-3D dosimetry of high dose rate brachytherapy using a novel Gafchromic EBT3 film-array water phantom

NASA Astrophysics Data System (ADS)

Palmer, A. L.; Nisbet, A.; Bradley, D. A.

2013-06-01

There is a need to modernise clinical brachytherapy dosimetry measurement beyond traditional point dose verification to enable appropriate quality control within 3D treatment environments. This is to keep pace with the 3D clinical and planning approaches which often include significant patient-specific optimisation away from 'standard loading patterns'. A multi-dimension measurement system is required to provide assurance of the complex 3D dose distributions, to verify equipment performance, and to enable quality audits. However, true 3D dose measurements around brachytherapy applicators are often impractical due to their complex shapes and the requirement for close measurement distances. A solution utilising an array of radiochromic film (Gafchromic EBT3) positioned within a water filled phantom is presented. A calibration function for the film has been determined over 0 to 90Gy dose range using three colour channel analysis (FilmQAPro software). Film measurements of the radial dose from a single HDR source agree with TPS and Monte Carlo calculations within 5 % up to 50 mm from the source. Film array measurements of the dose distribution around a cervix applicator agree with TPS calculations generally within 4 mm distance to agreement. The feasibility of film array measurements for semi-3D dosimetry in clinical HDR applications is demonstrated.

Quantitative evaluation of local pulmonary distribution of TiO2 in rats following single or multiple intratracheal administrations of TiO2 nanoparticles using X-ray fluorescence microscopy.

PubMed

Zhang, Guihua; Shinohara, Naohide; Kano, Hirokazu; Senoh, Hideki; Suzuki, Masaaki; Sasaki, Takeshi; Fukushima, Shoji; Gamo, Masashi

2016-10-01

Uneven pulmonary nanoparticle (NP) distribution has been described when using single-dose intratracheal administration tests. Multiple-dose intratracheal administrations with small quantities of NPs are expected to improve the unevenness of each dose. The differences in local pulmonary NP distribution (called microdistribution) between single- and multiple-dose administrations may cause differential pulmonary responses; however, this has not been evaluated. Here, we quantitatively evaluated the pulmonary microdistribution (per mesh: 100 μm × 100 μm) of TiO2 in lung sections from rats following one, two, three, or four doses of TiO2 NPs at a same total dosage of 10 mg kg(-1) using X-ray fluorescence microscopy. The results indicate that: (i) multiple-dose administrations show lower variations in TiO2 content (ng mesh(-1) ) for sections of each lobe; (ii) TiO2 appears to be deposited more in the right caudal and accessory lobes located downstream of the administration direction of NP suspensions, and less so in the right middle lobes, irrespective of the number of doses; (iii) there are not prominent differences in the pattern of pulmonary TiO2 microdistribution between rats following single and multiple doses of TiO2 NPs. Additionally, the estimation of pulmonary TiO2 deposition for multiple-dose administrations imply that every dose of TiO2 would be randomly deposited only in part of the fixed 30-50% of lung areas. The evidence suggests that multiple-dose administrations do not offer remarkable advantages over single-dose administration on the pulmonary NP microdistribution, although multiple-dose administrations may reduce variations in the TiO2 content for each lung lobe. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Three-dimensional cluster formation and structure in heterogeneous dose distribution of intensity modulated radiation therapy.

PubMed

Chao, Ming; Wei, Jie; Narayanasamy, Ganesh; Yuan, Yading; Lo, Yeh-Chi; Peñagarícano, José A

2018-05-01

To investigate three-dimensional cluster structure and its correlation to clinical endpoint in heterogeneous dose distributions from intensity modulated radiation therapy. Twenty-five clinical plans from twenty-one head and neck (HN) patients were used for a phenomenological study of the cluster structure formed from the dose distributions of organs at risks (OARs) close to the planning target volumes (PTVs). Initially, OAR clusters were searched to examine the pattern consistence among ten HN patients and five clinically similar plans from another HN patient. Second, clusters of the esophagus from another ten HN patients were scrutinized to correlate their sizes to radiobiological parameters. Finally, an extensive Monte Carlo (MC) procedure was implemented to gain deeper insights into the behavioral properties of the cluster formation. Clinical studies showed that OAR clusters had drastic differences despite similar PTV coverage among different patients, and the radiobiological parameters failed to positively correlate with the cluster sizes. MC study demonstrated the inverse relationship between the cluster size and the cluster connectivity, and the nonlinear changes in cluster size with dose thresholds. In addition, the clusters were insensitive to the shape of OARs. The results demonstrated that the cluster size could serve as an insightful index of normal tissue damage. The clinical outcome of the same dose-volume might be potentially different. Copyright © 2018 Elsevier B.V. All rights reserved.

Proposed linear energy transfer areal detector for protons using radiochromic film

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

Mayer, Rulon; Lin, Liyong; Fager, Marcus

2015-04-15

Radiation therapy depends on predictably and reliably delivering dose to tumors and sparing normal tissues. Protons with kinetic energy of a few hundred MeV can selectively deposit dose to deep seated tumors without an exit dose, unlike x-rays. The better dose distribution is attributed to a phenomenon known as the Bragg peak. The Bragg peak is due to relatively high energy deposition within a given distance or high Linear Energy Transfer (LET). In addition, biological response to radiation depends on the dose, dose rate, and localized energy deposition patterns or LET. At present, the LET can only be measured atmore » a given fixed point and the LET spatial distribution can only be inferred from calculations. The goal of this study is to develop and test a method to measure LET over extended areas. Traditionally, radiochromic films are used to measure dose distribution but not for LET distribution. We report the first use of these films for measuring the spatial distribution of the LET deposited by protons. The radiochromic film sensitivity diminishes for large LET. A mathematical model correlating the film sensitivity and LET is presented to justify relating LET and radiochromic film relative sensitivity. Protons were directed parallel to radiochromic film sandwiched between solid water slabs. This study proposes the scaled-normalized difference (SND) between the Treatment Planning system (TPS) and measured dose as the metric describing the LET. The SND is correlated with a Monte Carlo (MC) calculation of the LET spatial distribution for a large range of SNDs. A polynomial fit between the SND and MC LET is generated for protons having a single range of 20 cm with narrow Bragg peak. Coefficients from these fitted polynomial fits were applied to measured proton dose distributions with a variety of ranges. An identical procedure was applied to the protons deposited from Spread Out Bragg Peak and modulated by 5 cm. Gamma analysis is a method for comparing the calculated LET with the LET measured using radiochromic film at the pixel level over extended areas. Failure rates using gamma analysis are calculated for areas in the dose distribution using parameters of 25% of MC LET and 3 mm. The processed dose distributions find 5%–10% failure rates for the narrow 12.5 and 15 cm proton ranges and 10%–15% for proton ranges of 15, 17.5, and 20 cm and modulated by 5 cm. It is found through gamma analysis that the measured proton energy deposition in radiochromic film and TPS can be used to determine LET. This modified film dosimetry provides an experimental areal LET measurement that can verify MC calculations, support LET point measurements, possibly enhance biologically based proton treatment planning, and determine the polymerization process within the radiochromic film.« less

Short communication: Experimental toxocarosis in Chinese Kun Ming mice: Dose-dependent larval distribution and modulation of immune responses.

PubMed

Ma, Guangxu; Tan, Yancai; Hu, Ling; Luo, Yongfang; Zhu, Honghong; Zhou, Rongqiong

2015-12-01

Toxocarosis is an important parasitic zoonosis which is mainly caused by the infective larvae of Toxocara canis. To identify whether there are correlations among the infectious dose, the larval migrans and immune modulation in inbred Chinese Kun Ming (KM) mice, experimental infections were carried out with a range of dosages of 100, 500, 1000, 2000, and 3000 embryonated eggs (EE). Pathogenic reactions were observed in terms of physical and central nervous symptoms. Distributions of T. canis larvae in liver, lung, kidney, heart and brain organs were respectively detected by scanning tissue sections. Moreover, quantitative real-time PCR was employed to identify the variations of Th2 immune response. The results showed that high inocula resulted in advanced larval emergences and arrested migrations in liver, lung, kidney and brain. However, no larvae were found in any of the histological sections of heart tissues. Higher levels of interleukin (IL)-4, IL-5, and IL-10 were detected along with the increasing inoculation doses, but the heaviest inoculum (3000 EE in this study) resulted in the sharp reduction of these ILs. Although no neurological symptoms or mortalities were noticed, these results indicated dose-dependent distribution patterns and immune regulations of T. canis larvae infection in KM mice. Copyright © 2015 Elsevier Ltd. All rights reserved.

Quantifying the interplay effect in prostate IMRT delivery using a convolution-based method.

PubMed

Li, Haisen S; Chetty, Indrin J; Solberg, Timothy D

2008-05-01

The authors present a segment-based convolution method to account for the interplay effect between intrafraction organ motion and the multileaf collimator position for each particular segment in intensity modulated radiation therapy (IMRT) delivered in a step-and-shoot manner. In this method, the static dose distribution attributed to each segment is convolved with the probability density function (PDF) of motion during delivery of the segment, whereas in the conventional convolution method ("average-based convolution"), the static dose distribution is convolved with the PDF averaged over an entire fraction, an entire treatment course, or even an entire patient population. In the case of IMRT delivered in a step-and-shoot manner, the average-based convolution method assumes that in each segment the target volume experiences the same motion pattern (PDF) as that of population. In the segment-based convolution method, the dose during each segment is calculated by convolving the static dose with the motion PDF specific to that segment, allowing both intrafraction motion and the interplay effect to be accounted for in the dose calculation. Intrafraction prostate motion data from a population of 35 patients tracked using the Calypso system (Calypso Medical Technologies, Inc., Seattle, WA) was used to generate motion PDFs. These were then convolved with dose distributions from clinical prostate IMRT plans. For a single segment with a small number of monitor units, the interplay effect introduced errors of up to 25.9% in the mean CTV dose compared against the planned dose evaluated by using the PDF of the entire fraction. In contrast, the interplay effect reduced the minimum CTV dose by 4.4%, and the CTV generalized equivalent uniform dose by 1.3%, in single fraction plans. For entire treatment courses delivered in either a hypofractionated (five fractions) or conventional (> 30 fractions) regimen, the discrepancy in total dose due to interplay effect was negligible.

A study of surface dosimetry for breast cancer radiotherapy treatments using Gafchromic EBT2 film

PubMed Central

Hill, Robin F.; Whitaker, May; Kim, Jung‐Ha; Kuncic, Zdenka

2012-01-01

The present study quantified surface doses on several rectangular phantom setups and on curved surface phantoms for a 6 MV photon field using the Attix parallel‐plate chamber and Gafchromic EBT2 film. For the rectangular phantom setups, the surface doses on a homogenous water equivalent phantom and a water equivalent phantom with 60 mm thick lung equivalent material were measured. The measurement on the homogenous phantom setup showed consistency in surface and near‐surface doses between an open field and enhanced dynamic wedge (EDW) fields, whereas physical wedged fields showed small differences. Surface dose measurements made using the EBT2 film showed good agreement with results of the Attix chamber and results obtained in previous studies which used other dosimeters within the measurement uncertainty of 3.3%. The surface dose measurements on the phantom setup with lung equivalent material showed a small increase without bolus and up to 6.9% increase with bolus simulating the increase of chest wall thickness. Surface doses on the cylindrical CT phantom and customized Perspex chest phantom were measured using the EBT2 film with and without bolus. The results indicate the important role of the presence of bolus if the clinical target volume (CTV) is quite close to the surface. Measurements on the cylindrical phantom suggest that surface doses at the oblique positions of 60° and 90° are mainly caused by the lateral scatter from the material inside the phantom. In the case of a single tangential irradiation onto Perspex chest phantom, the distribution of the surface dose with and without bolus materials showed opposing inclination patterns, whereas the dose distribution for two opposed tangential fields gave symmetric dose distribution. This study also demonstrates the suitability of Gafchromic EBT2 film for surface dose measurements in megavoltage photon beams. PACS number: 87.53.Bn PMID:22584169

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

Mao, R; Tian, L; Ge, H

Purpose: To evaluate the dosimetry of microscopic disease (MD) region of lung cancer in stereotactic body radiation therapy (SBRT). Methods: For simplicity, we assume organ moves along one dimension. The probability distribution function of tumor position was calculated according to the breathing cycle. The dose to the MD region was obtained through accumulating the treatment planning system calculated doses at different positions in a breathing cycle. A phantom experiment was then conducted to validate the calculated results using a motion phantom (The CIRS ‘Dynamic’ Thorax Phantom). The simulated breathing pattern used a cos4(x) curve with an amplitude of 10mm. Amore » 3-D conformal 7-field plan with 6X energy was created and the dose was calculated in the average intensity projection (AIP) simulation CT images. Both films (EBT2) and optically stimulated luminescence (OSL) detectors were inserted in the target of the phantom to measure the dose during radiation delivery (Varian Truebeam) and results were compared to planning dose parameters. Results: The Gamma analysis (3%/3mm) between measured dose using EBT2 film and calculated dose using AIP was 80.5%, indicating substantial dosimetric differences. While the Gamma analysis (3%/3mm) between measured dose using EBT2 and accumulated dose using 4D-CT was 98.9%, indicating the necessity of dose accumulation using 4D-CT. The measured doses using OSL and theoretically calculated doses using probability distribution function at the corresponding position were comparable. Conclusion: Use of static dose calculation in the treatment planning system could substantially underestimate the actually delivered dose in the MD region for a moving target. Funding Supported by NSFC, No.81372436.« less

Inherent smoothness of intensity patterns for intensity modulated radiation therapy generated by simultaneous projection algorithms

NASA Astrophysics Data System (ADS)

Xiao, Ying; Michalski, Darek; Censor, Yair; Galvin, James M.

2004-07-01

The efficient delivery of intensity modulated radiation therapy (IMRT) depends on finding optimized beam intensity patterns that produce dose distributions, which meet given constraints for the tumour as well as any critical organs to be spared. Many optimization algorithms that are used for beamlet-based inverse planning are susceptible to large variations of neighbouring intensities. Accurately delivering an intensity pattern with a large number of extrema can prove impossible given the mechanical limitations of standard multileaf collimator (MLC) delivery systems. In this study, we apply Cimmino's simultaneous projection algorithm to the beamlet-based inverse planning problem, modelled mathematically as a system of linear inequalities. We show that using this method allows us to arrive at a smoother intensity pattern. Including nonlinear terms in the simultaneous projection algorithm to deal with dose-volume histogram (DVH) constraints does not compromise this property from our experimental observation. The smoothness properties are compared with those from other optimization algorithms which include simulated annealing and the gradient descent method. The simultaneous property of these algorithms is ideally suited to parallel computing technologies.

The calculation of radial dose from heavy ions: predictions of biological action cross sections

NASA Technical Reports Server (NTRS)

Katz, R.; Cucinotta, F. A.; Zhang, C. X.; Wilson, J. W. (Principal Investigator)

1996-01-01

The track structure model of heavy ion cross sections was developed by Katz and co-workers in the 1960s. In this model the action cross section is evaluated by mapping the dose-response of a detector to gamma rays (modeled from biological target theory) onto the radial dose distribution from delta rays about the path of the ion. This is taken to yield the radial distribution of probability for a "hit" (an interaction leading to an observable end-point). Radial integration of the probability yields the cross section. When different response from ions of different Z having the same stopping power is observed this model may be indicated. Since the 1960s there have been several developments in the computation of the radial dose distribution, in the measurement of these distributions, and in new radiobiological data against which to test the model. The earliest model, by Butts and Katz made use of simplified delta ray distribution functions, of simplified electron range-energy relations, and neglected angular distributions. Nevertheless it made possible the calculation of cross sections for the inactivation of enzymes and viruses, and allowed extension to tracks in nuclear emulsions and other detectors and to biological cells. It set the pattern for models of observable effects in the matter through which the ion passed. Here we outline subsequent calculations of radial dose which make use of improved knowledge of the electron emission spectrum, the electron range-energy relation, the angular distribution, and some considerations of molecular excitation, of particular interest both close to the path of the ion and the outer limits of electron penetration. These are applied to the modeling of action cross sections for the inactivation of several strains of E-coli and B. subtilis spores where extensive measurements in the "thin-down" region have been made with heavy ion beams. Such calculations serve to test the radial dose calculations at the outer limit of electron penetration. We lack data from which to test these calculations in regions close to the path of the ion aside from our earliest work on latent tracks in plastics, though it appears that the criterion then suggested for the threshold of track formation, of a minimal dose at a minimal distance (of about 20 angstroms, in plastics), remains valid.

Proton radiography and proton computed tomography based on time-resolved dose measurements

NASA Astrophysics Data System (ADS)

Testa, Mauro; Verburg, Joost M.; Rose, Mark; Min, Chul Hee; Tang, Shikui; Hassane Bentefour, El; Paganetti, Harald; Lu, Hsiao-Ming

2013-11-01

We present a proof of principle study of proton radiography and proton computed tomography (pCT) based on time-resolved dose measurements. We used a prototype, two-dimensional, diode-array detector capable of fast dose rate measurements, to acquire proton radiographic images expressed directly in water equivalent path length (WEPL). The technique is based on the time dependence of the dose distribution delivered by a proton beam traversing a range modulator wheel in passive scattering proton therapy systems. The dose rate produced in the medium by such a system is periodic and has a unique pattern in time at each point along the beam path and thus encodes the WEPL. By measuring the time dose pattern at the point of interest, the WEPL to this point can be decoded. If one measures the time-dose patterns at points on a plane behind the patient for a beam with sufficient energy to penetrate the patient, the obtained 2D distribution of the WEPL forms an image. The technique requires only a 2D dosimeter array and it uses only the clinical beam for a fraction of second with negligible dose to patient. We first evaluated the accuracy of the technique in determining the WEPL for static phantoms aiming at beam range verification of the brain fields of medulloblastoma patients. Accurate beam ranges for these fields can significantly reduce the dose to the cranial skin of the patient and thus the risk of permanent alopecia. Second, we investigated the potential features of the technique for real-time imaging of a moving phantom. Real-time tumor tracking by proton radiography could provide more accurate validations of tumor motion models due to the more sensitive dependence of proton beam on tissue density compared to x-rays. Our radiographic technique is rapid (˜100 ms) and simultaneous over the whole field, it can image mobile tumors without the problem of interplay effect inherently challenging for methods based on pencil beams. Third, we present the reconstructed pCT images of a cylindrical phantom containing inserts of different materials. As for all conventional pCT systems, the method illustrated in this work produces tomographic images that are potentially more accurate than x-ray CT in providing maps of proton relative stopping power (RSP) in the patient without the need for converting x-ray Hounsfield units to proton RSP. All phantom tests produced reasonable results, given the currently limited spatial and time resolution of the prototype detector. The dose required to produce one radiographic image, with the current settings, is ˜0.7 cGy. Finally, we discuss a series of techniques to improve the resolution and accuracy of radiographic and tomographic images for the future development of a full-scale detector.

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

Menegotti, L.; Delana, A.; Martignano, A.

Film dosimetry is an attractive tool for dose distribution verification in intensity modulated radiotherapy (IMRT). A critical aspect of radiochromic film dosimetry is the scanner used for the readout of the film: the output needs to be calibrated in dose response and corrected for pixel value and spatial dependent nonuniformity caused by light scattering; these procedures can take a long time. A method for a fast and accurate calibration and uniformity correction for radiochromic film dosimetry is presented: a single film exposure is used to do both calibration and correction. Gafchromic EBT films were read with two flatbed charge coupledmore » device scanners (Epson V750 and 1680Pro). The accuracy of the method is investigated with specific dose patterns and an IMRT beam. The comparisons with a two-dimensional array of ionization chambers using a 18x18 cm{sup 2} open field and an inverse pyramid dose pattern show an increment in the percentage of points which pass the gamma analysis (tolerance parameters of 3% and 3 mm), passing from 55% and 64% for the 1680Pro and V750 scanners, respectively, to 94% for both scanners for the 18x18 open field, and from 76% and 75% to 91% for the inverse pyramid pattern. Application to an IMRT beam also shows better gamma index results, passing from 88% and 86% for the two scanners, respectively, to 94% for both. The number of points and dose range considered for correction and calibration appears to be appropriate for use in IMRT verification. The method showed to be fast and to correct properly the nonuniformity and has been adopted for routine clinical IMRT dose verification.« less

A Proton Beam Therapy System Dedicated to Spot-Scanning Increases Accuracy with Moving Tumors by Real-Time Imaging and Gating and Reduces Equipment Size

PubMed Central

Shimizu, Shinichi; Miyamoto, Naoki; Matsuura, Taeko; Fujii, Yusuke; Umezawa, Masumi; Umegaki, Kikuo; Hiramoto, Kazuo; Shirato, Hiroki

2014-01-01

Purpose A proton beam therapy (PBT) system has been designed which dedicates to spot-scanning and has a gating function employing the fluoroscopy-based real-time-imaging of internal fiducial markers near tumors. The dose distribution and treatment time of the newly designed real-time-image gated, spot-scanning proton beam therapy (RGPT) were compared with free-breathing spot-scanning proton beam therapy (FBPT) in a simulation. Materials and Methods In-house simulation tools and treatment planning system VQA (Hitachi, Ltd., Japan) were used for estimating the dose distribution and treatment time. Simulations were performed for 48 motion parameters (including 8 respiratory patterns and 6 initial breathing timings) on CT data from two patients, A and B, with hepatocellular carcinoma and with clinical target volumes 14.6 cc and 63.1 cc. The respiratory patterns were derived from the actual trajectory of internal fiducial markers taken in X-ray real-time tumor-tracking radiotherapy (RTRT). Results With FBPT, 9/48 motion parameters achieved the criteria of successful delivery for patient A and 0/48 for B. With RGPT 48/48 and 42/48 achieved the criteria. Compared with FBPT, the mean liver dose was smaller with RGPT with statistical significance (p<0.001); it decreased from 27% to 13% and 28% to 23% of the prescribed doses for patients A and B, respectively. The relative lengthening of treatment time to administer 3 Gy (RBE) was estimated to be 1.22 (RGPT/FBPT: 138 s/113 s) and 1.72 (207 s/120 s) for patients A and B, respectively. Conclusions This simulation study demonstrated that the RGPT was able to improve the dose distribution markedly for moving tumors without very large treatment time extension. The proton beam therapy system dedicated to spot-scanning with a gating function for real-time imaging increases accuracy with moving tumors and reduces the physical size, and subsequently the cost of the equipment as well as of the building housing the equipment. PMID:24747601

On the interplay effects with proton scanning beams in stage III lung cancer.

PubMed

Li, Yupeng; Kardar, Laleh; Li, Xiaoqiang; Li, Heng; Cao, Wenhua; Chang, Joe Y; Liao, Li; Zhu, Ronald X; Sahoo, Narayan; Gillin, Michael; Liao, Zhongxing; Komaki, Ritsuko; Cox, James D; Lim, Gino; Zhang, Xiaodong

2014-02-01

To assess the dosimetric impact of interplay between spot-scanning proton beam and respiratory motion in intensity-modulated proton therapy (IMPT) for stage III lung cancer. Eleven patients were sampled from 112 patients with stage III nonsmall cell lung cancer to well represent the distribution of 112 patients in terms of target size and motion. Clinical target volumes (CTVs) and planning target volumes (PTVs) were defined according to the authors' clinical protocol. Uniform and realistic breathing patterns were considered along with regular- and hypofractionation scenarios. The dose contributed by a spot was fully calculated on the computed tomography (CT) images corresponding to the respiratory phase that the spot is delivered, and then accumulated to the reference phase of the 4DCT to generate the dynamic dose that provides an estimation of what might be delivered under the influence of interplay effect. The dynamic dose distributions at different numbers of fractions were compared with the corresponding 4D composite dose which is the equally weighted average of the doses, respectively, computed on respiratory phases of a 4DCT image set. Under regular fractionation, the average and maximum differences in CTV coverage between the 4D composite and dynamic doses after delivery of all 35 fractions were no more than 0.2% and 0.9%, respectively. The maximum differences between the two dose distributions for the maximum dose to the spinal cord, heart V40, esophagus V55, and lung V20 were 1.2 Gy, 0.1%, 0.8%, and 0.4%, respectively. Although relatively large differences in single fraction, correlated with small CTVs relative to motions, were observed, the authors' biological response calculations suggested that this interfractional dose variation may have limited biological impact. Assuming a hypofractionation scenario, the differences between the 4D composite and dynamic doses were well confined even for single fraction. Despite the presence of interplay effect, the delivered dose may be reliably estimated using the 4D composite dose. In general the interplay effect may not be a primary concern with IMPT for lung cancers for the authors' institution. The described interplay analysis tool may be used to provide additional confidence in treatment delivery.

Estimation of annual occupational effective doses from external ionizing radiation at medical institutions in Kenya

NASA Astrophysics Data System (ADS)

Korir, Geoffrey; Wambani, Jeska; Korir, Ian

2011-04-01

This study details the distribution and trends of doses due to occupational radiation exposure among radiation workers from participating medical institutions in Kenya, where monthly dose measurements were collected for a period of one year ranging from January to December in 2007. A total of 367 medical radiation workers were monitored using thermoluminescent dosemeters. They included radiologists (27%), oncologists (2%), dentists (4%), Physicists (5%), technologists (45%), nurses (4%), film processor technicians (3%), auxiliary staff (4%), and radiology office staff (5%). The average annual effective dose of all categories of staff was found to range from 1.19 to 2.52 mSv. This study formed the initiation stage of wider, comprehensive and more frequent monitoring of occupational radiation exposures and long-term investigations into its accumulation patterns in our country.

Low doses of six toxicants change plant size distribution in dense populations of Lactuca sativa.

PubMed

Belz, Regina G; Patama, Marjo; Sinkkonen, Aki

2018-08-01

Toxicants are known to have negligible or stimulatory, i.e. hormetic, effects at low doses below those that decrease the mean response of a plant population. Our earlier observations indicated that at such low toxicant doses the growth of very fast- and slow-growing seedlings is selectively altered, even if the population mean remains constant. Currently, it is not known how common these selective low-dose effects are, whether they are similar among fast- and slow-growing seedlings, and whether they occur concurrently with hormetic effects. We tested the response of Lactuca sativa in complete dose-response experiments to six different toxicants at doses that did not decrease population mean and beyond. The tested toxicants were IAA, parthenin, HHCB, 4-tert-octylphenol, glyphosate, and pelargonic acid. Each experiment consisted of 14,400-16,800 seedlings, 12-14 concentrations, 24 replicates per concentration and 50 germinated seeds per replicate. We analyzed the commonness of selective low-dose effects and explored if toxic effects and hormetic stimulation among fast- and slow-growing individuals occurred at the same concentrations as they occur at the population level. Irrespective of the observed response pattern and toxicant, selective low-dose effects were found. Toxin effects among fast-growing individuals usually started at higher doses compared to the population mean, while the opposite was found among slow-growing individuals. Very low toxin exposures tended to homogenize plant populations due to selective effects, while higher, but still hormetic doses tended to heterogenize plant populations. Although the extent of observed size segregation varied with the specific toxin tested, we conclude that a dose-dependent alteration in size distribution of a plant population may generally apply for many toxin exposures. Copyright © 2018 Elsevier B.V. All rights reserved.

4D dose calculation and delivery with interplay effects between respiratory motion and uniform scanning proton beam

NASA Astrophysics Data System (ADS)

Zhao, Qingya

2011-12-01

Proton radiotherapy has advantages to deliver accurate high conformal radiation dose to the tumor while sparing the surrounding healthy tissue and critical structures. However, the treatment effectiveness is degraded greatly due to patient free breathing during treatment delivery. Motion compensation for proton radiotherapy is especially challenging as proton beam is more sensitive to the density change along the beam path. Tumor respiratory motion during treatment delivery will affect the proton dose distribution and the selection of optimized parameters for treatment planning, which has not been fully addressed yet in the existing approaches for proton dose calculation. The purpose of this dissertation is to develop an approach for more accurate dose delivery to a moving tumor in proton radiotherapy, i.e., 4D proton dose calculation and delivery, for the uniform scanning proton beam. A three-step approach has been carried out to achieve this goal. First, a solution for the proton output factor calculation which will convert the prescribed dose to machine deliverable monitor unit for proton dose delivery has been proposed and implemented. The novel sector integration method is accurate and time saving, which considers the various beam scanning patterns and treatment field parameters, such as aperture shape, aperture size, measuring position, beam range, and beam modulation. Second, tumor respiratory motion behavior has been statistically characterized and the results have been applied to advanced image guided radiation treatment. Different statistical analysis and correlation discovery approaches have been investigated. The internal / external motion correlation patterns have been simulated, analyzed, and applied in a new hybrid gated treatment to improve the target coverage. Third, a dose calculation method has been developed for 4D proton treatment planning which integrates the interplay effects of tumor respiratory motion patterns and proton beam delivery mechanism. These three steps provide an innovative integrated framework for accurate 4D proton dose calculation and treatment planning for a moving tumor, which extends the functionalities of existing 3D planning systems. In short, this dissertation work addresses a few important problems for effective proton radiotherapy to a moving target. The outcomes of the dissertation are very useful for motion compensation with advanced image guided proton treatment.

Breaking the power law: Multiscale simulations of self-ion irradiated tungsten

NASA Astrophysics Data System (ADS)

Jin, Miaomiao; Permann, Cody; Short, Michael P.

2018-06-01

The initial stage of radiation defect creation has often been shown to follow a power law distribution at short time scales, recently so with tungsten, following many self-organizing patterns found in nature. The evolution of this damage, however, is dominated by interactions between defect clusters, as the coalescence of smaller defects into clusters depends on the balance between transport, absorption, and emission to/from existing clusters. The long-time evolution of radiation-induced defects in tungsten is studied with cluster dynamics parameterized with lower length scale simulations, and is shown to deviate from a power law size distribution. The effects of parameters such as dose rate and total dose, as parameters affecting the strength of the driving force for defect evolution, are also analyzed. Excellent agreement is achieved with regards to an experimentally measured defect size distribution at 30 K. This study provides another satisfactory explanation for experimental observations in addition to that of primary radiation damage, which should be reconciled with additional validation data.

Correction of respiratory motion for IMRT using aperture adaptive technique and visual guidance: A feasibility study

NASA Astrophysics Data System (ADS)

Chen, Ho-Hsing; Wu, Jay; Chuang, Keh-Shih; Kuo, Hsiang-Chi

2007-07-01

Intensity-modulated radiation therapy (IMRT) utilizes nonuniform beam profile to deliver precise radiation doses to a tumor while minimizing radiation exposure to surrounding normal tissues. However, the problem of intrafraction organ motion distorts the dose distribution and leads to significant dosimetric errors. In this research, we applied an aperture adaptive technique with a visual guiding system to toggle the problem of respiratory motion. A homemade computer program showing a cyclic moving pattern was projected onto the ceiling to visually help patients adjust their respiratory patterns. Once the respiratory motion becomes regular, the leaf sequence can be synchronized with the target motion. An oscillator was employed to simulate the patient's breathing pattern. Two simple fields and one IMRT field were measured to verify the accuracy. Preliminary results showed that after appropriate training, the amplitude and duration of volunteer's breathing can be well controlled by the visual guiding system. The sharp dose gradient at the edge of the radiation fields was successfully restored. The maximum dosimetric error in the IMRT field was significantly decreased from 63% to 3%. We conclude that the aperture adaptive technique with the visual guiding system can be an inexpensive and feasible alternative without compromising delivery efficiency in clinical practice.

SU-F-T-436: A Method to Evaluate Dosimetric Properties of SFGRT in Eclipse TPS

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

Xu, M; Tobias, R; Pankuch, M

Purpose: The objective was to develop a method for dose distribution calculation of spatially-fractionated-GRID-radiotherapy (SFGRT) in Eclipse treatment-planning-system (TPS). Methods: Patient treatment-plans with SFGRT for bulky tumors were generated in Varian Eclipse version11. A virtual structure based on the GRID pattern was created and registered to a patient CT image dataset. The virtual GRID structure was positioned on the iso-center level together with matching beam geometries to simulate a commercially available GRID block made of brass. This method overcame the difficulty in treatment-planning and dose-calculation due to the lack o-the option to insert a GRID block add-on in Eclipse TPS.more » The patient treatment-planning displayed GRID effects on the target, critical structures, and dose distribution. The dose calculations were compared to the measurement results in phantom. Results: The GRID block structure was created to follow the beam divergence to the patient CT images. The inserted virtual GRID block made it possible to calculate the dose distributions and profiles at various depths in Eclipse. The virtual GRID block was added as an option to TPS. The 3D representation of the isodose distribution of the spatially-fractionated beam was generated in axial, coronal, and sagittal planes. Physics of GRID can be different from that for fields shaped by regular blocks because the charge-particle-equilibrium cannot be guaranteed for small field openings. Output factor (OF) measurement was required to calculate the MU to deliver the prescribed dose. The calculated OF based on the virtual GRID agreed well with the measured OF in phantom. Conclusion: The method to create the virtual GRID block has been proposed for the first time in Eclipse TPS. The dosedistributions, in-plane and cross-plane profiles in PTV can be displayed in 3D-space. The calculated OF’s based on the virtual GRID model compare well to the measured OF’s for SFGRT clinical use.« less

SU-G-BRB-07: Developing a QA Procedure for Gated VMAT SABR Treatments Using 10 MV Beam in Flattening-Filter Free Mode

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

Chitsazzadeh, S; Wells, D; Mestrovic, A

2016-06-15

Purpose: To develop a QA procedure for gated VMAT stereotactic ablative radiotherapy (SABR) treatments. Methods: An interface was constructed to attach the translational stage of a Quasar respiratory motion phantom to a pinpoint ion chamber insert and move the ion chamber inside an ArcCheck diode array. The Quasar phantom controller used a patient specific breathing pattern to translate the ion chamber in a superior-inferior direction inside the ArcCheck. An amplitude-based RPM tracking system was specified to turn the beam on during the exhale phase of the breathing pattern. SABR plans were developed using Eclipse for liver PTVs ranging in sizemore » from 3-12 cm in diameter using a 2-arc VMAT technique. Dose was measured in the middle of the penumbra region, where the high dose gradient allowed for sensitive detection of any inaccuracies in gated dose delivery. The overall fidelity of the dose distribution was confirmed using ArcCheck. The sensitivity of the gating QA procedure was investigated with respect to the following four parameters: PTV size, duration of exhale, baseline drift, and gating window size. Results: The difference between the measured dose to a point in the penumbra and the Eclipse calculated dose was under 2% for small residual motions. The QA procedure was independent of PTV size and duration of exhale. Baseline drift and gating window size, however, significantly affected the penumbral dose measurement, with differences of up to 30% compared to Eclipse. Conclusion: This study described a highly sensitive QA procedure for gated VMAT SABR treatments. The QA outcome was dependent on the gating window size and baseline drift. Analysis of additional patient breathing patterns will be required to determine a clinically relevant gating window size and an appropriate tolerance level for this procedure.« less

Carbon-11-cocaine binding compared at subpharmacological and pharmacological doses: A PET study

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

Volkow, N.D.; Fowler, J.S.; Logan, J.

The authors have characterized cocaine binding in the brain to a high-affinity site on the dopamine transporter using PET and tracer doses of [{sup 11}C]cocaine in the baboon in vivo. The binding pattern, however, of cocaine at tracer (subpharmacological) doses may differ from that observed when the drug is taken in behaviorally active doses, particularly since in vitro studies have shown that cocaine also binds to low affinity binding sites. PET was used to compare and characterize [{sup 11}C]cocaine binding in the baboon brain at low subpharmacological (18 {mu}g average dose) and at pharmacological (8000 {mu}g) doses. Serial studies onmore » the same day in the same baboon were used to assess the reproducibility of repeated measures and to assess the effects of drugs which inhibit the dopamine, norepinephrine and serotonin transporters. Time-activity curves from brain and the arterial plasma input function were used to calculate the steady-state distribution volume (DV). At subpharmacological doses, [{sup 11}C]cocaine had a more homogeneous distribution. Bmax/Kd for sub-pharmacological [{sup 11}C]cocaine corresponded to 0.5-0.6 and for pharmacological [{sup 11}C]cocaine it corresponded to 0.1-0.2. Two-point Scatchard analysis gave Bmax = 2300 pmole/g and Kd = 3600 nM. Bmax/Kd for sub-pharmacological doses of [{sup 11}C]cocaine was decreased by cocaine and drugs that inhibit the dopamine transporter, to 0.1-0.2, but not by drugs that inhibit the serotonin or the norepinephrine transporter. None of these drugs changed Bmax/Kd for a pharmacological dose of [{sup 11}C]cocaine. At subpharmacological doses, [{sup 11}C]cocaine binds predominantly to a high-affinity site on the dopamine transporter. 36 refs., 4 figs., 5 tabs.« less

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

Lin, Liyong, E-mail: linl@uphs.upenn.edu; Huang, Sheng; Kang, Minglei

Purpose: The purpose of this paper is to demonstrate the utility of a comprehensive test pattern in validating calculation models that include the halo component (low-dose tails) of proton pencil beam scanning (PBS) spots. Such a pattern has been used previously for quality assurance purposes to assess spot shape, position, and dose. Methods: In this study, a scintillation detector was used to measure the test pattern in air at isocenter for two proton beam energies (115 and 225 MeV) of two IBA universal nozzles (UN #1 and UN #2). Planar measurements were compared with calculated dose distributions based on themore » weighted superposition of location-independent (UN #1) or location-dependent (UN #2) spot profiles, previously measured using a pair-magnification method and between two nozzles. Results: Including the halo component below 1% of the central dose is shown to improve the gamma-map comparison between calculation and measurement from 94.9% to 98.4% using 2 mm/2% criteria for the 115 MeV proton beam of UN #1. In contrast, including the halo component below 1% of the central dose does not improve the gamma agreement for the 115 MeV proton beam of UN #2, due to the cutoff of the halo component at off-axis locations. When location-dependent spot profiles are used for calculation instead of spot profiles at central axis, the gamma agreement is improved from 98.0% to 99.5% using 2 mm/2% criteria. The two nozzles clearly have different characteristics, as a direct comparison of measured data shows a passing rate of 89.7% for the 115 MeV proton beam. At 225 MeV, the corresponding gamma comparisons agree better between measurement and calculation, and between measurements in the two nozzles. Conclusions: In addition to confirming the primary component of individual PBS spot profiles, a comprehensive test pattern is useful for the validation of the halo component at off-axis locations, especially for low energy protons.« less

Spatial features of dose-surface maps from deformably-registered plans correlate with late gastrointestinal complications

NASA Astrophysics Data System (ADS)

Moulton, Calyn R.; House, Michael J.; Lye, Victoria; Tang, Colin I.; Krawiec, Michele; Joseph, David J.; Denham, James W.; Ebert, Martin A.

2017-05-01

This study investigates the associations between spatial distribution of dose to the rectal surface and observed gastrointestinal toxicities after deformably registering each phase of a combined external beam radiotherapy (EBRT)/high-dose-rate brachytherapy (HDRBT) prostate cancer treatment. The study contains data for 118 patients where the HDRBT CT was deformably-registered to the EBRT CT. The EBRT and registered HDRBT TG43 dose distributions in a reference 2 Gy/fraction were 3D-summed. Rectum dose-surface maps (DSMs) were obtained by virtually unfolding the rectum surface slice-by-slice. Associations with late peak gastrointestinal toxicities were investigated using voxel-wise DSM analysis as well as parameterised spatial patterns. The latter were obtained by thresholding DSMs from 1-80 Gy (increment  =  1) and extracting inferior-superior extent, left-right extent, area, perimeter, compactness, circularity and ellipse fit parameters. Logistic regressions and Mann-Whitney U-tests were used to correlate features with toxicities. Rectal bleeding, stool frequency, diarrhoea and urgency/tenesmus were associated with greater lateral and/or longitudinal spread of the high doses near the anterior rectal surface. Rectal bleeding and stool frequency were also influenced by greater low-intermediate doses to the most inferior 20% of the rectum and greater low-intermediate-high doses to 40-80% of the rectum length respectively. Greater low-intermediate doses to the superior 20% and inferior 20% of the rectum length were associated with anorectal pain and urgency/tenesmus respectively. Diarrhoea, completeness of evacuation and proctitis were also related to greater low doses to the posterior side of the rectum. Spatial features for the intermediate-high dose regions such as area, perimeter, compactness, circularity, ellipse eccentricity and confinement to ellipse fits were strongly associated with toxicities other than anorectal pain. Consequently, toxicity is related to the shape of isodoses as well as dose coverage. The findings indicate spatial constraints on doses to certain sections of the rectum may be important for reducing toxicities and optimising dose.

Palliative radiation therapy practice for advanced esophageal carcinoma in Africa.

PubMed

Sharma, V; Gaye, P M; Wahab, S A; Ndlovu, N; Ngoma, T; Vanderpuye, V; Sowuhami, A; Dawotola, D A; Kigula-Mugambe, J; Jeremic, B

2010-04-01

While numerous surveys of pattern of practices of palliative radiotherapy (RT) in advanced esophageal cancers have been published in developed countries, there is no such survey in African countries. During and after a regional training course by the International Atomic Energy Agency (IAEA) in palliative cancer care, a questionnaire was distributed to African RT centers to gather information about infrastructure and human resources available, and the pattern of practice of palliative RT for esophageal cancers. Twenty-four of the 35 centers (60%) completed the questionnaire. Twenty out of 23 (87%) centers treat patients with esophageal cancer presenting with dysphagia using external beam RT (16 centers external beam RT alone and 4 centers also use brachytherapy as a boost). Twelve (60%) centers prescribe RT doses of 30 Gy in 10 fractions and 2 centers 20 Gy in 5 fractions. Eighteen centers (78%) have low dose rate (LDR) brachytherapy, and 9 (39%) centers have high dose rate (HDR) brachytherapy. One center only used HDR brachytherapy alone to a dose of 16 Gy in 2 fractions over 8 days. RT remains a major component of treatment of patients with esophageal cancers in African countries. Still, there is a great variety among centers in both indications for RT and its characteristics for a treatment indication.

The simulation of decontamination works in premises of the research reactor in NRC 'Kurchatov institute'

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

Danilovich, Alexey; Ivanov, Oleg; Potapov, Victor

2013-07-01

Application of remote sensing methods using a spectrometric collimated system allows obtaining information about features of a formation of radiation fields in contaminated premises. This information helps in a preparation of a phased plan for dismantling of contaminated equipment. When the survey of technological premises of the research reactor at the Russian Research Centre 'Kurchatov institute' was conducted the remote controlled collimated spectrometric system was used. With its help the scanning of surveyed premises were carried out. As a result of this work, the distribution pattern of radionuclides activity was restored. The simulation of decontamination works was carried out andmore » maps of the distribution of activity and dose rate for surveyed premises were plotted and superimposed on its photo for situations before and after decontamination. The use of obtained results will allow significantly reduce radiation dose for staff at work on dismantling. (authors)« less

Magnetic nanoparticle hyperthermia enhances radiation therapy: A study in mouse models of human prostate cancer

PubMed Central

Attaluri, Anilchandra; Kandala, Sri Kamal; Wabler, Michele; Zhou, Haoming; Cornejo, Christine; Armour, Michael; Hedayati, Mohammad; Zhang, Yonggang; DeWeese, Theodore L.; Herman, Cila; Ivkov, Robert

2015-01-01

Purpose We aimed to characterise magnetic nanoparticle hyperthermia (mNPH) with radiation therapy (RT) for prostate cancer. Methods Human prostate cancer subcutaneous tumours, PC3 and LAPC-4, were grown in nude male mice. When tumours measured 150 mm3 magnetic iron oxide nanoparticles (MIONPs) were injected into tumours to a target dose of 5.5 mg Fe/cm3 tumour, and treated 24 h later by exposure to alternating magnetic field (AMF). Mice were randomly assigned to one of four cohorts to characterise (1) intratumour MIONP distribution, (2) effects of variable thermal dose mNPH (fixed AMF peak amplitude 24 kA/m at 160±5 kHz) with/without RT (5 Gy), (3) effects of RT (RT5: 5 Gy; RT8: 8 Gy), and (4) fixed thermal dose mNPH (43 °C for 20min) with/without RT (5 Gy). MIONP concentration and distribution were assessed following sacrifice and tissue harvest using inductively coupled plasma mass spectrometry (ICP-MS) and Prussian blue staining, respectively. Tumour growth was monitored and compared among treated groups. Results LAPC-4 tumours retained higher MIONP concentration and more uniform distribution than did PC3 tumours. AMF power modulation provided similar thermal dose for mNPH and combination therapy groups (CEM43: LAPC-4: 33.6 ± 3.4 versus 25.9 ± 0.8, and PC3: 27.19 ± 0.7 versus 27.50 ± 0.6), thereby overcoming limitations of MIONP distribution and yielding statistically significant tumour growth delay. Conclusion PC3 and LAPC-4 tumours represent two biological models that demonstrate different patterns of nanoparticle retention and distribution, offering a model to make comparisons of these effects for mNPH. Modulating power for mNPH offers potential to overcome limitations of MIONP distribution to enhance mNPH. PMID:25811736

Magnetic nanoparticle hyperthermia enhances radiation therapy: A study in mouse models of human prostate cancer.

PubMed

Attaluri, Anilchandra; Kandala, Sri Kamal; Wabler, Michele; Zhou, Haoming; Cornejo, Christine; Armour, Michael; Hedayati, Mohammad; Zhang, Yonggang; DeWeese, Theodore L; Herman, Cila; Ivkov, Robert

2015-06-01

We aimed to characterise magnetic nanoparticle hyperthermia (mNPH) with radiation therapy (RT) for prostate cancer. Human prostate cancer subcutaneous tumours, PC3 and LAPC-4, were grown in nude male mice. When tumours measured 150 mm3 magnetic iron oxide nanoparticles (MIONPs) were injected into tumours to a target dose of 5.5 mg Fe/cm3 tumour, and treated 24 h later by exposure to alternating magnetic field (AMF). Mice were randomly assigned to one of four cohorts to characterise (1) intratumour MIONP distribution, (2) effects of variable thermal dose mNPH (fixed AMF peak amplitude 24 kA/m at 160 ± 5 kHz) with/without RT (5 Gy), (3) effects of RT (RT5: 5 Gy; RT8: 8 Gy), and (4) fixed thermal dose mNPH (43 °C for 20 min) with/without RT (5 Gy). MIONP concentration and distribution were assessed following sacrifice and tissue harvest using inductively coupled plasma mass spectrometry (ICP-MS) and Prussian blue staining, respectively. Tumour growth was monitored and compared among treated groups. LAPC-4 tumours retained higher MIONP concentration and more uniform distribution than did PC3 tumours. AMF power modulation provided similar thermal dose for mNPH and combination therapy groups (CEM43: LAPC-4: 33.6 ± 3.4 versus 25.9 ± 0.8, and PC3: 27.19 ± 0.7 versus 27.50 ± 0.6), thereby overcoming limitations of MIONP distribution and yielding statistically significant tumour growth delay. PC3 and LAPC-4 tumours represent two biological models that demonstrate different patterns of nanoparticle retention and distribution, offering a model to make comparisons of these effects for mNPH. Modulating power for mNPH offers potential to overcome limitations of MIONP distribution to enhance mNPH.

Polymer gel dosimetry for measuring the dose near thin high-Z materials irradiated with high energy photon beams.

PubMed

Warmington, Leighton L; Gopishankar, N; Broadhurst, John H; Watanabe, Yoichi

2016-12-01

To investigate the feasibility of three-dimensional (3D) dose measurements near thin high-Z materials placed in a water-like medium by using a polymer gel dosimeter (PGD) when the medium was irradiated with high energy photon beams. PGD is potentially a useful tool for this application because it can record the dose around a small object made of a high-Z material in a continuous 3D medium. In this study, the authors manufactured a methacrylic acid-based normoxic PGD, nMAG. Two 0.5 mm thick lead foils (1 × 1 cm) were placed in foil supports with 0.7 cm separation in a 1000 ml polystyrene container filled with nMAG. The authors used two foil configurations, i.e., orthogonal and parallel. In the orthogonal configuration, two foils were placed in the direction orthogonal to the beam axis. The parallel configuration had two foils arranged in parallel to the beam axis. The phantom was irradiated with an 18 MV photon beam of 5 × 5 cm field size. It was imaged with a three-Tesla (3 T) magnetic resonance imaging (MRI) scanned using the Car-Purcell-Meiboom-Gill pulse sequence. The spin-spin relaxation time (R2) to-dose calibration data were obtained by using small vials filled with nMAG and exposing to known doses. The DOSXYZnrc Monte Carlo (MC) code was used to get the expected dose distributions. More than 35 × 10 6 of histories were simulated so that the average error was less than 1%. An in-house matlab-based software was used to obtain the dose distributions from the measured R2 data as well as to compare the measurements and the MC predictions. The dose change due to the presence of the foils was studied by comparing the dose distributions with and without foils (or the reference). For the orthogonal configuration, the measured dose along the beam axis showed an increase in the upstream side of the first foil, between the foils, and on the downstream side of the second foil. The range of increased dose area was 1.1 cm in the upstream of the first foil. However, in the downstream of the second foil, it was 0.2 cm, beyond which the dose fell below the reference dose by 10%. The dose profile between the foils showed a well-like shape with the minimum dose still larger than the reference dose by 1.8%. The minimum dose point was closer to the first foil than to the second foil. For the parallel configuration, the dose between foils was the largest at the center. The increased dose area opposite to the gap between foils extended outward to 1 cm. The spatial dose distributions of PGD and MC showed the same geometrical patterns except for the points inside the foils for both orthogonal and parallel foil arrangements. The authors demonstrated that the nMAG PGD with MRI could be used to measure the 3D dosimetric structures at the mm-scale in the vicinity of the foil. The current study provided more accurate 3D spatial dose distribution than the previous studies. Furthermore, the measurements were validated by the MC simulation.

Conformal and intensity modulated irradiation of head and neck cancer: the potential for improved target irradiation, salivary gland function, and quality of life.

PubMed

Eisbruch, A; Dawson, L A; Kim, H M; Bradford, C R; Terrell, J E; Chepeha, D B; Teknos, T N; Anzai, Y; Marsh, L H; Martel, M K; Ten Haken, R K; Wolf, G T; Ship, J A

1999-01-01

To develop techniques which facilitate sparing of the major salivary glands while adequately treating the targets in patients requiring comprehensive bilateral neck irradiation (RT). Conformal and static, multisegmental intensity modulated (IMRT) techniques have been developed. The salivary flow rates before and periodically after RT have been measured selectively from each major salivary gland and the residual flows correlated with glands' dose volume histograms. Subjective xerostomia questionnaires have been developed and validated. The pattern of local-regional recurrences has been examined using CT scans at the time of recurrence, transferring the recurrence volumes to the planning CT scans and regenerating the dose distributions at the recurrence sites. Target coverage and dose homogeneity in IMRT treatment plans were found to be significantly better than standard RT plans. Significant parotid gland sparing was achieved. The relationships among dose, irradiated volume and saliva flow rates from the parotid glands were characterized by dose and volume thresholds. A mean dose of 26 Gy was found to be the threshold for stimulated saliva. Subjective xerostomia was significantly reduced in patients irradiated with parotid sparing techniques, compared to patients with similar tumors treated with standard RT. The large majority of recurrences occurred inside high-risk targets. Tangible gains in salivary gland sparing and target coverage are being achieved and an improvement in some measures of quality of life is suggested by our findings. A mean parotid gland dose of < or = 26 Gy should be a planning objective if significant parotid function preservation is desired. The pattern of recurrence suggests that careful escalation of the dose to targets judged to be at highest risk may improve tumor control.

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

Xu, Jia; Zhang, Ziang; Weng, Zhankun

This paper presents a new method for the generation of cross-scale laser interference patterns and the fabrication of moth-eye structures on silicon. In the method, moth-eye structures were produced on a surface of silicon wafer using direct six-beam laser interference lithography to improve the antireflection performance of the material surface. The periodic dot arrays of the moth-eye structures were formed due to the ablation of the irradiance distribution of interference patterns on the wafer surface. The shape, size, and distribution of the moth-eye structures can be adjusted by controlling the wavelength, incidence angles, and exposure doses in a direct six-beammore » laser interference lithography setup. The theoretical and experimental results have shown that direct six-beam laser interference lithography can provide a way to fabricate cross-scale moth-eye structures for antireflection applications.« less

Thermal Characteristics of ThermoBrachytherapy Surface Applicators (TBSA) for Treating Chestwall Recurrence

PubMed Central

Arunachalam, K.; Maccarini, P. F.; Craciunescu, O. I.; Schlorff, J. L.; Stauffer, P. R.

2010-01-01

Purpose To study temperature and thermal dose distributions of ThermoBrachytherapy Surface Applicators (TBSA) developed for concurrent or sequential high dose rate (HDR) brachytherapy and microwave hyperthermia treatment of chest wall recurrence and other superficial disease. Methods A steady state thermodynamics model coupled with the fluid dynamics of water bolus and electromagnetic radiation of hyperthermia applicator is used to characterize the temperature distributions achievable with TBSA applicators in an elliptical phantom model of the human torso. Power deposited by 915 MHz conformal microwave array (CMA) applicators is used to assess the specific absorption rate (SAR) distributions of rectangular (500 cm2) and L-shaped (875 cm2) TBSA. The SAR distribution in tissue and fluid flow distribution inside the Dual-Input Dual-Output (DIDO) water bolus are coupled to solve the steady state temperature and thermal dose distributions of rectangular TBSA (R-TBSA) for superficial tumor targets extending 10–15 mm beneath the skin surface. Thermal simulations are carried out for a range of bolus inlet temperature (Tb=38–43°C), water flow rate (Qb=2–4 L/min) and tumor blood perfusion (ωb=2–5 kg/m3/s) to characterize their influence on thermal dosimetry. Results Steady state SAR patterns of R- and L-TBSA demonstrate the ability to produce conformal and localized power deposition inside tumor target sparing surrounding normal tissues and nearby critical organs. Acceptably low variation in tissue surface cooling and surface temperature homogeneity was observed for the new DIDO bolus at 2 L/min water flow rate. Temperature depth profiles and thermal dose volume histograms indicate bolus inlet temperature (Tb) to be the most influential factor on thermal dosimetry. A 42 °C water bolus was observed to be the optimal choice for superficial tumors extending 10–15 mm from the surface even under significant blood perfusion. Lower bolus temperature may be chosen to reduce thermal enhancement ratio (TER) in the most sensitive skin where maximum radiation dose is delivered and to extend thermal enhancement of radiation dose deeper. Conclusion This computational study indicates that well-localized elevation of tumor target temperature to 40–44 °C can be accomplished by large surface-conforming TBSA applicators using appropriate selection of coupling bolus temperature. PMID:20224154

RadNuc: A graphical user interface to deliver dose rate patterns encountered in nuclear medicine with a 137Cs irradiator

PubMed Central

Pasternack, Jordan B.; Howell, Roger W.

2012-01-01

The temporal variations in absorbed dose rates to organs and tissues in the body are very large in diagnostic and therapeutic nuclear medicine. The response of biological endpoints of relevance to radiation safety and therapeutic efficacy are generally modulated by dose rate. Therefore, it is important to understand how the complex dose rate patterns encountered in nuclear medicine impact relevant biological responses. Accordingly, a graphical user interface (GUI) was created to control a cesium-137 irradiator to deliver such dose rate patterns. Methods Visual Basic 6.0 was used to create a user-friendly GUI to control the dose rate by varying the thickness of a mercury attenuator. The GUI facilitates the delivery of a number of dose rate patterns including constant, exponential increase or decrease, and multi-component exponential. Extensive visual feedback is provided by the GUI during both the planning and delivery stages. Results The GUI controlled irradiator can achieve a maximum dose rate of 40 cGy/hr and a minimum dose rate of 0.01 cGy/hr. Addition of machined lead blocks can be used to further reduce the minimum dose rate to 0.0001 cGy/hr. Measured dose rate patterns differed from programmed dose rate patterns in total dose by 3.2% to 8.4%. Conclusion The GUI controlled irradiator is able to accurately create dose rate patterns encountered in nuclear medicine and other related fields. This makes it an invaluable tool for studying the effects of chronic constant and variable low dose rates on biological tissues in the contexts of both radiation protection and clinical administration of internal radionuclides. PMID:23265668

RadNuc: a graphical user interface to deliver dose rate patterns encountered in nuclear medicine with a 137Cs irradiator.

PubMed

Pasternack, Jordan B; Howell, Roger W

2013-02-01

The temporal variations in absorbed dose rates to organs and tissues in the body are very large in diagnostic and therapeutic nuclear medicine. The response of biological endpoints of relevance to radiation safety and therapeutic efficacy is generally modulated by dose rate. Therefore, it is important to understand how the complex dose rate patterns encountered in nuclear medicine impact relevant biological responses. Accordingly, a graphical user interface (GUI) was created to control a cesium-137 irradiator to deliver such dose rate patterns. Visual Basic 6.0 was used to create a user-friendly GUI to control the dose rate by varying the thickness of a mercury attenuator. The GUI facilitates the delivery of a number of dose rate patterns including constant, exponential increase or decrease, and multi-component exponential. Extensive visual feedback is provided by the GUI during both the planning and delivery stages. The GUI controlled irradiator can achieve a maximum dose rate of 40 cGy/h and a minimum dose rate of 0.01 cGy/h. Addition of machined lead blocks can be used to further reduce the minimum dose rate to 0.0001 cGy/h. Measured dose rate patterns differed from programmed dose rate patterns in total dose by 3.2% to 8.4%. The GUI controlled irradiator is able to accurately create dose rate patterns encountered in nuclear medicine and other related fields. This makes it an invaluable tool for studying the effects of chronic constant and variable low dose rates on biological tissues in the contexts of both radiation protection and clinical administration of internal radionuclides. Copyright © 2013 Elsevier Inc. All rights reserved.

In vivo drug metabolite identification in preclinical ADME studies by means of UPLC/TWIMS/high resolution-QTOF MS(E) and control comparison: cost and benefit of vehicle-dosed control samples.

PubMed

Fiebig, Lukas; Laux, Ralf; Binder, Rudolf; Ebner, Thomas

2016-10-01

1. Liquid chromatography (LC)-high resolution mass spectrometry (HRMS) techniques proved to be well suited for the identification of predicted and unexpected drug metabolites in complex biological matrices. 2. To efficiently discriminate between drug-related and endogenous matrix compounds, however, sophisticated postacquisition data mining tools, such as control comparison techniques are needed. For preclinical absorption, distribution, metabolism and excretion (ADME) studies that usually lack a placebo-dosed control group, the question arises how high-quality control data can be yielded using only a minimum number of control animals. 3. In the present study, the combination of LC-traveling wave ion mobility separation (TWIMS)-HRMS(E) and multivariate data analysis was used to study the polymer patterns of the frequently used formulation constituents polyethylene glycol 400 and polysorbate 80 in rat plasma and urine after oral and intravenous administration, respectively. 4. Complex peak patterns of both constituents were identified underlining the general importance of a vehicle-dosed control group in ADME studies for control comparison. Furthermore, the detailed analysis of administration route, blood sampling time and gender influences on both vehicle peak pattern as well as endogenous matrix background revealed that high-quality control data is obtained when (i) control animals receive an intravenous dose of the vehicle, (ii) the blood sampling time point is the same for analyte and control sample and (iii) analyte and control samples of the same gender are compared.

On the interplay effects with proton scanning beams in stage III lung cancer

PubMed Central

Li, Yupeng; Kardar, Laleh; Li, Xiaoqiang; Li, Heng; Cao, Wenhua; Chang, Joe Y.; Liao, Li; Zhu, Ronald X.; Sahoo, Narayan; Gillin, Michael; Liao, Zhongxing; Komaki, Ritsuko; Cox, James D.; Lim, Gino; Zhang, Xiaodong

2014-01-01

Purpose: To assess the dosimetric impact of interplay between spot-scanning proton beam and respiratory motion in intensity-modulated proton therapy (IMPT) for stage III lung cancer. Methods: Eleven patients were sampled from 112 patients with stage III nonsmall cell lung cancer to well represent the distribution of 112 patients in terms of target size and motion. Clinical target volumes (CTVs) and planning target volumes (PTVs) were defined according to the authors' clinical protocol. Uniform and realistic breathing patterns were considered along with regular- and hypofractionation scenarios. The dose contributed by a spot was fully calculated on the computed tomography (CT) images corresponding to the respiratory phase that the spot is delivered, and then accumulated to the reference phase of the 4DCT to generate the dynamic dose that provides an estimation of what might be delivered under the influence of interplay effect. The dynamic dose distributions at different numbers of fractions were compared with the corresponding 4D composite dose which is the equally weighted average of the doses, respectively, computed on respiratory phases of a 4DCT image set. Results: Under regular fractionation, the average and maximum differences in CTV coverage between the 4D composite and dynamic doses after delivery of all 35 fractions were no more than 0.2% and 0.9%, respectively. The maximum differences between the two dose distributions for the maximum dose to the spinal cord, heart V40, esophagus V55, and lung V20 were 1.2 Gy, 0.1%, 0.8%, and 0.4%, respectively. Although relatively large differences in single fraction, correlated with small CTVs relative to motions, were observed, the authors' biological response calculations suggested that this interfractional dose variation may have limited biological impact. Assuming a hypofractionation scenario, the differences between the 4D composite and dynamic doses were well confined even for single fraction. Conclusions: Despite the presence of interplay effect, the delivered dose may be reliably estimated using the 4D composite dose. In general the interplay effect may not be a primary concern with IMPT for lung cancers for the authors' institution. The described interplay analysis tool may be used to provide additional confidence in treatment delivery. PMID:24506612

Pharmacokinetics of vephylline--a new N-substituted theophylline derivative.

PubMed

Staneva, D; Mihailova, D; Astroug, H; Prodanova, K; Micheva, M

1988-01-01

Vephylline (7,2-bis-2-hydroxyethylamino-1, 3-dimethylxanthine tartarate) is a xanthine derivative with high bronchodilating activity, low toxicity, and weak effects on the central nervous system. The aim of this study is to determine the pharmacokinetic parameters of vephylline after intravenous and oral (in solution and in tablets) administration to rabbits. Vephylline (dose 50 mg/kg b.w. intravenousely and orally in solution and dose 53.5 mg/kg b.w. in the form of tablets) is administered to the rabbits in an autocontrol crossover design at 7-days intervals. After the intravenous administration the distribution is relatively fast (t1/2 alpha = 3.28h). High values of the apparent volume of distribution--12.15 1/kg suggest tissue accumulation. Elimination is considerably slower (t1/2 beta = 19,00 h) than distribution. After oral administration of the drug in solution the absorption half-life is short and the bioavailability is relatively high. Peak plasma levels are attained at the first hour. The differences in the distribution and elimination patterns for vephylline and theophyline could determine a longer effect for the new bronchodilating drug. The results are discussed in regard to the future clinical application of vephylline.

WE-EF-BRA-07: High Performance Preclinical Irradiation Through Optimized Dual Focal Spot Dose Painting and Online Virtual Isocenter Radiation Field Targeting

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

Stewart, J; Princess Margaret Cancer Centre, University Health Network, Toronto, CA; Lindsay, P

Purpose: Advances in radiotherapy practice facilitated by collimation systems to shape radiation fields and image guidance to target these conformal beams have motivated proposals for more complex dose patterns to improve the therapeutic ratio. Recent progress in small animal radiotherapy platforms has provided the foundation to validate the efficacy of such interventions, but robustly delivering heterogeneous dose distributions at the scale and accuracy demanded by preclinical studies remains challenging. This work proposes a dual focal spot optimization method to paint spatially heterogeneous dose regions and an online virtual isocenter targeting method to accurately target the dose distributions. Methods: Two-dimensional dosemore » kernels were empirically measured for the 1 mm diameter circular collimator with radiochromic film in a solid water phantom for the small and large x-ray focal spots on the X-RAD 225Cx microirradiator. These kernels were used in an optimization framework which determined a set of animal stage positions, beam-on times, and focal spot settings to optimally deliver a given desired dose distribution. An online method was developed which defined a virtual treatment isocenter based on a single image projection of the collimated radiation field. The method was demonstrated by optimization of a 6 mm circular 2 Gy target adjoining a 4 mm semicircular avoidance region. Results: The dual focal spot technique improved the optimized dose distribution with the proportion of avoidance region receiving more than 0.5 Gy reduced by 40% compared to the large focal spot technique. Targeting tests performed by irradiating ball bearing targets on radiochromic film pieced revealed the online targeting method improved the three-dimensional accuracy from 0.48 mm to 0.15 mm. Conclusion: The dual focal spot optimization and online virtual isocenter targeting framework is a robust option for delivering dose at the preclinical level and provides a new experimental option for unique radiobiological investigations This work is supported, in part, by the Natural Sciences and Engineering Research Council of Canada and a Mitacs-Accelerate fellowship. P.E. Lindsay, and D.A. Jaffray are listed as inventors of the system described herein. This system has been licensed to Precision X-Ray Inc. for commercial development.« less

SU-F-T-549: Validation of a Method for in Vivo 3D Dose Reconstruction for SBRT Using a New Transmission Detector

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

Nakaguchi, Y; Shimohigashi, Y; Onizuka, R

Purpose: Recently, there has been increased clinical use of stereotactic body radiation therapy (SBRT). SBRT 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. In vivo dose measurements, a commercially available quality assurance platform which is able to correlate the delivered dose to the patient’s anatomy and take into account tissue inhomogeneity, is the COMPASS system (IBA Dosimetry, Germany) using a new transmission detector (Dolphin, IBA Dosimetry). In this work, we evaluate a method for in vivo 3D dosemore » reconstruction for SBRT using a new transmission detector, which was developed for in vivo dose verification for intensity-modulated radiation therapy (IMRT). Methods: We evaluated the accuracy of measurement for SBRT using simple small fields (2×2−10×10 cm2), a multileaf collimator (MLC) test pattern, and clinical cases. The dose distributions from the COMPASS were compared with those of EDR2 films (Kodak, USA) and the Monte Carlo simulations (MC). For clinical cases, we compared MC using dose-volume-histograms (DVHs) and dose profiles. Results: The dose profiles from the COMPASS for small fields and the complicated MLC test pattern agreed with those of EDR2 films, and MC within 3%. This showed the COMPASS with Dolphin system showed good spatial resolution and can measure small fields which are required for SBRT. Those results also suggest that COMPASS with Dolphin is able to detect MLC leaf position errors for SBRT. In clinical cases, the COMPASS with Dolphin agreed well with MC. The Dolphin detector, which consists of ionization chambers, provided stable measurement. Conclusion: COMPASS with Dolphin detector showed a useful in vivo 3D dose reconstruction for SBRT. The accuracy of the results indicates that this approach is suitable for clinical implementation.« less

Inferring ultraviolet anatomical exposure patterns while distinguishing the relative contribution of radiation components

NASA Astrophysics Data System (ADS)

Vuilleumier, Laurent; Milon, Antoine; Bulliard, Jean-Luc; Moccozet, Laurent; Vernez, David

2013-05-01

Exposure to solar ultraviolet (UV) radiation is the main causative factor for skin cancer. UV exposure depends on environmental and individual factors, but individual exposure data remain scarce. While ground UV irradiance is monitored via different techniques, it is difficult to translate such observations into human UV exposure or dose because of confounding factors. A multi-disciplinary collaboration developed a model predicting the dose and distribution of UV exposure on the basis of ground irradiation and morphological data. Standard 3D computer graphics techniques were adapted to develop a simulation tool that estimates solar exposure of a virtual manikin depicted as a triangle mesh surface. The amount of solar energy received by various body locations is computed for direct, diffuse and reflected radiation separately. Dosimetric measurements obtained in field conditions were used to assess the model performance. The model predicted exposure to solar UV adequately with a symmetric mean absolute percentage error of 13% and half of the predictions within 17% range of the measurements. Using this tool, solar UV exposure patterns were investigated with respect to the relative contribution of the direct, diffuse and reflected radiation. Exposure doses for various body parts and exposure scenarios of a standing individual were assessed using erythemally-weighted UV ground irradiance data measured in 2009 at Payerne, Switzerland as input. For most anatomical sites, mean daily doses were high (typically 6.2-14.6 Standard Erythemal Dose, SED) and exceeded recommended exposure values. Direct exposure was important during specific periods (e.g. midday during summer), but contributed moderately to the annual dose, ranging from 15 to 24% for vertical and horizontal body parts, respectively. Diffuse irradiation explained about 80% of the cumulative annual exposure dose.

SU-E-T-551: PTV Is the Worst-Case of CTV in Photon Therapy

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

Harrington, D; Liu, W; Park, P

2014-06-01

Purpose: To examine the supposition of the static dose cloud and adequacy of the planning target volume (PTV) dose distribution as the worst-case representation of clinical target volume (CTV) dose distribution for photon therapy in head and neck (H and N) plans. Methods: Five diverse H and N plans clinically delivered at our institution were selected. Isocenter for each plan was shifted positively and negatively in the three cardinal directions by a displacement equal to the PTV expansion on the CTV (3 mm) for a total of six shifted plans per original plan. The perturbed plan dose was recalculated inmore » Eclipse (AAA v11.0.30) using the same, fixed fluence map as the original plan. The dose distributions for all plans were exported from the treatment planning system to determine the worst-case CTV dose distributions for each nominal plan. Two worst-case distributions, cold and hot, were defined by selecting the minimum or maximum dose per voxel from all the perturbed plans. The resulting dose volume histograms (DVH) were examined to evaluate the worst-case CTV and nominal PTV dose distributions. Results: Inspection demonstrates that the CTV DVH in the nominal dose distribution is indeed bounded by the CTV DVHs in the worst-case dose distributions. Furthermore, comparison of the D95% for the worst-case (cold) CTV and nominal PTV distributions by Pearson's chi-square test shows excellent agreement for all plans. Conclusion: The assumption that the nominal dose distribution for PTV represents the worst-case dose distribution for CTV appears valid for the five plans under examination. Although the worst-case dose distributions are unphysical since the dose per voxel is chosen independently, the cold worst-case distribution serves as a lower bound for the worst-case possible CTV coverage. Minor discrepancies between the nominal PTV dose distribution and worst-case CTV dose distribution are expected since the dose cloud is not strictly static. This research was supported by the NCI through grant K25CA168984, by The Lawrence W. and Marilyn W. Matteson Fund for Cancer Research, and by the Fraternal Order of Eagles Cancer Research Fund, the Career Development Award Program at Mayo Clinic.« less

Single dose pharmacokinetics of fenspiride hydrochloride: phase I clinical trial.

PubMed

Montes, B; Catalan, M; Roces, A; Jeanniot, J P; Honorato, J M

1993-01-01

The absolute bioavailability of fenspiride has been studied in twelve healthy volunteers. It was administered IV and orally in single doses of 80 mg fenspiride hydrochloride according to a randomised crossover pattern. Following IV administration, the plasma clearance of fenspiride was about 184 ml.min-1, and its apparent volume of distribution was moderately large (215 l). When given orally as a tablet, fenspiride exhibited fairly slow ab- sorption; the maximum plasma concentration (206 ng.ml-1) was achieved 6 h after administration. The absolute bioavailability was almost complete (90%). The tablet had slow release characteristics. The elimination half-life obtained from the plasma data was 14 to 16 h independent of the route of administration.

Salivary gland sparing and improved target irradiation by conformal and intensity modulated irradiation of head and neck cancer.

PubMed

Eisbruch, Avraham; Ship, Jonathan A; Dawson, Laura A; Kim, Hyungjin M; Bradford, Carol R; Terrell, Jeffrey E; Chepeha, Douglas B; Teknos, Theodore N; Hogikyan, Norman D; Anzai, Yoshimi; Marsh, Lon H; Ten Haken, Randall K; Wolf, Gregory T

2003-07-01

The goals of this study were to facilitate sparing of the major salivary glands while adequately treating tumor targets in patients requiring comprehensive bilateral neck irradiation (RT), and to assess the potential for improved xerostomia. Since 1994 techniques of target irradiation and locoregional tumor control with conformal and intensity modulated radiation therapy (IMRT) have been developed. In patients treated with these modalities, the salivary flow rates before and periodically after RT have been measured selectively from each major salivary gland and the residual flows correlated with glands' dose volume histograms (DVHs). In addition, subjective xerostomia questionnaires have been developed and validated. The pattern of locoregional recurrence has been examined from computed tomography (CT) scans at the time of recurrence, transferring the recurrence volumes to the planning CT scans, and regenerating the dose distributions at the recurrence sites. Treatment plans for target coverage and dose homogeneity using static, multisegmental IMRT were found to be significantly better than standard RT plans. In addition, significant parotid gland sparing was achieved in the conformal plans. The relationships among dose, irradiated volume, and the residual saliva flow rates from the parotid glands were characterized by dose and volume thresholds. A mean radiation dose of 26 Gy was found to be the threshold for preserved stimulated saliva flow. Xerostomia questionnaire scores suggested that xerostomia was significantly reduced in patients irradiated with bilateral neck, parotid-sparing RT, compared to patients with similar tumors treated with standard RT. Examination of locoregional tumor recurrence patterns revealed that the large majority of recurrences occurred inside targets, in areas that had been judged to be at high risk and that had received RT doses according to the perceived risk. Tangible gains in salivary gland sparing and target coverage are being achieved, and an improvement in some measures of quality of life is suggested by our findings. Additional reduction of xerostomia may be achieved by further sparing of the salivary glands and the non-involved oral cavity. A mean parotid gland dose of < or = 26 Gy should be a planning objective if significant parotid function preservation is desired. The pattern of recurrence suggests that careful escalation of the dose to areas judged to be at highest risk may improve tumor control.

Field-size dependence of doses of therapeutic carbon beams.

PubMed

Kusano, Yohsuke; Kanai, Tatsuaki; Yonai, Shunsuke; Komori, Masataka; Ikeda, Noritoshi; Tachikawa, Yuji; Ito, Atsushi; Uchida, Hirohisa

2007-10-01

To estimate the physical dose at the center of spread-out Bragg peaks (SOBP) for various conditions of the irradiation system, a semiempirical approach was applied. The dose at the center of the SOBP depends on the field size because of large-angle scattering particles in the water phantom. For a small field of 5 x 5 cm2, the dose was reduced to 99.2%, 97.5%, and 96.5% of the dose used for the open field in the case of 290, 350, and 400 MeV/n carbon beams, respectively. Based on the three-Gaussian form of the lateral dose distributions of the carbon pencil beam, which has previously been shown to be effective for describing scattered carbon beams, we reconstructed the dose distributions of the SOBP beam. The reconstructed lateral dose distribution reproduced the measured lateral dose distributions very well. The field-size dependencies calculated using the reconstructed lateral dose distribution of the therapeutic carbon beam agreed with the measured dose dependency very well. The reconstructed beam was also used for irregularly shaped fields. The resultant dose distribution agreed with the measured dose distribution. The reconstructed beams were found to be applicable to the treatment-planning system.

The DosiMap, a new 2D scintillating dosimeter for IMRT quality assurance: characterization of two Cerenkov discrimination methods.

PubMed

Frelin, A M; Fontbonne, J M; Ban, G; Colin, J; Labalme, M; Batalla, A; Vela, A; Boher, P; Braud, M; Leroux, T

2008-05-01

New radiation therapy techniques such as IMRT present significant efficiency due to their highly conformal dose distributions. A consequence of the complexity of their dose distributions (high gradients, small irradiation fields, low dose distribution, ...) is the requirement for better precision quality assurance than in classical radiotherapy in order to compare the conformation of the delivered dose with the planned dose distribution and to guarantee the quality of the treatment. Currently this control is mostly performed by matrices of ionization chambers, diode detectors, dosimetric films, portal imaging, or dosimetric gels. Another approach is scintillation dosimetry, which has been developed in the last 15 years mainly through scintillating fiber devices. Despite having many advantages over other methods it is still at an experimental level for routine dosimetry because the Cerenkov radiation produced under irradiation represents an important stem effect. A new 2D water equivalent scintillating dosimeter, the DosiMap, and two different Cerenkov discrimination methods were developed with the collaboration of the Laboratoire de Physique Corpusculaire of Caen, the Comprehensive Cancer Center François Baclesse, and the ELDIM Co., in the frame of the MAESTRO European project. The DosiMap consists of a plastic scintillating sheet placed inside a transparent polystyrene phantom. The light distribution produced under irradiation is recorded by a CCD camera. Our first Cerenkov discrimination technique is subtractive. It uses a chessboard pattern placed in front of the scintillator, which provides a background signal containing only Cerenkov light. Our second discrimination technique is colorimetric. It performs a spectral analysis of the light signal, which allows the unfolding of the Cerenkov radiation and the scintillation. Tests were carried out with our DosiMap prototype and the performances of the two discrimination methods were assessed. The comparison of the dose measurements performed with the DosiMap and with dosimetric films for three different irradiation configurations showed discrepancies smaller than 3.5% for a 2 mm spatial resolution. Two innovative discrimination solutions were demonstrated to separate the scintillation from the Cerenkov radiation. It was also shown that the DosiMap, which is water equivalent, fast, and user friendly, is a very promising tool for radiotherapy quality assurance.

Organ distribution of technetium-99m-labeled Corynebacterium parvum in normal and tumor-bearing mice

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

Barth, R.F.; Singla, O.

1978-01-01

The distribution patterns were studied for /sup 99m/Tc-labeled Corynebacterium parvum in normal and tumor-bearing mice. C57BL/6 mice were given i.v., i.p., or s.c. injections of 250 ..mu..g of /sup 99m/Tc-labeled C. parvum and killed at 10 min, 1, 4, and 24 hr. After iv. administration, labeled organisms were distributed primarily to the liver, the lungs, and the blood (46% of injected dose), followed by the gastrointestinal tract, the spleen, and the kidneys (11%). Total recoverable radioactivity, which was defined as the percentage of injected dose that was recovered, ranged from 59% at 10 min to 15% at 24 hr. Inmore » contrast to this, /sup 99m/TcS colloid, an inert particulate material, was localized almost entirely in the liver, and the amount recoverable remained constant over 24 hr. One hr after i.p. administration of /sup 99m/Tc-labeled C. parvum, the gastrointestinal tract accounted for 27% of the injected radioactivity, followed by liver, blood, and spleen (12%). This was rapidly excreted between 4 and 24 hr, at which time only 12% of the injected dose was recovered. The skin accounted for 54.6% of the injected radioactivity 1 hr after s.c. injection, 6% 4 hr after s.c. injection, and 0.8% at 24 hr after s.c. injection.« less

Dynamic scan control in STEM: Spiral scans

DOE PAGES

Lupini, Andrew R.; Borisevich, Albina Y.; Kalinin, Sergei V.; ...

2016-06-13

Here, scanning transmission electron microscopy (STEM) has emerged as one of the foremost techniques to analyze materials at atomic resolution. However, two practical difficulties inherent to STEM imaging are: radiation damage imparted by the electron beam, which can potentially damage or otherwise modify the specimen and slow-scan image acquisition, which limits the ability to capture dynamic changes at high temporal resolution. Furthermore, due in part to scan flyback corrections, typical raster scan methods result in an uneven distribution of dose across the scanned area. A method to allow extremely fast scanning with a uniform residence time would enable imaging atmore » low electron doses, ameliorating radiation damage and at the same time permitting image acquisition at higher frame-rates while maintaining atomic resolution. The practical complication is that rastering the STEM probe at higher speeds causes significant image distortions. Non-square scan patterns provide a solution to this dilemma and can be tailored for low dose imaging conditions. Here, we develop a method for imaging with alternative scan patterns and investigate their performance at very high scan speeds. A general analysis for spiral scanning is presented here for the following spiral scan functions: Archimedean, Fermat, and constant linear velocity spirals, which were tested for STEM imaging. The quality of spiral scan STEM images is generally comparable with STEM images from conventional raster scans, and the dose uniformity can be improved.« less

Dynamic scan control in STEM: Spiral scans

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

Lupini, Andrew R.; Borisevich, Albina Y.; Kalinin, Sergei V.

Here, scanning transmission electron microscopy (STEM) has emerged as one of the foremost techniques to analyze materials at atomic resolution. However, two practical difficulties inherent to STEM imaging are: radiation damage imparted by the electron beam, which can potentially damage or otherwise modify the specimen and slow-scan image acquisition, which limits the ability to capture dynamic changes at high temporal resolution. Furthermore, due in part to scan flyback corrections, typical raster scan methods result in an uneven distribution of dose across the scanned area. A method to allow extremely fast scanning with a uniform residence time would enable imaging atmore » low electron doses, ameliorating radiation damage and at the same time permitting image acquisition at higher frame-rates while maintaining atomic resolution. The practical complication is that rastering the STEM probe at higher speeds causes significant image distortions. Non-square scan patterns provide a solution to this dilemma and can be tailored for low dose imaging conditions. Here, we develop a method for imaging with alternative scan patterns and investigate their performance at very high scan speeds. A general analysis for spiral scanning is presented here for the following spiral scan functions: Archimedean, Fermat, and constant linear velocity spirals, which were tested for STEM imaging. The quality of spiral scan STEM images is generally comparable with STEM images from conventional raster scans, and the dose uniformity can be improved.« less

Amplitude gating for a coached breathing approach in respiratory gated 10 MV flattening filter‐free VMAT delivery

PubMed Central

Lee, Richard; Gete, Ermias; Duzenli, Cheryl

2015-01-01

The purpose of this study was to investigate amplitude gating combined with a coached breathing strategy for 10 MV flattening filter‐free (FFF) volumetric‐modulated arc therapy (VMAT) on the Varian TrueBeam linac. Ten patient plans for VMAT SABR liver were created using the Eclipse treatment planning system (TPS). The verification plans were then transferred to a CT‐scanned Quasar phantom and delivered on a TrueBeam linac using a 10 MV FFF beam and Varian's real‐time position management (RPM) system for respiratory gating based on breathing amplitude. Breathing traces were acquired from ten patients using two kinds of breathing patterns: free breathing and an interrupted (~5 s pause) end of exhale coached breathing pattern. Ion chamber and Gafchromic film measurements were acquired for a gated delivery while the phantom moved under the described breathing patterns, as well as for a nongated stationary phantom delivery. The gate window was set to obtain a range of residual target motion from 2–5 mm. All gated deliveries on a moving phantom have been shown to be dosimetrically equivalent to the nongated deliveries on a static phantom, with differences in point dose measurements under 1% and average gamma 2%/2 mm agreement above 98.7%. Comparison with the treatment planning system also resulted in good agreement, with differences in point‐dose measurements under 2.5% and average gamma 3%/3 mm agreement of 97%. The use of a coached breathing pattern significantly increases the duty cycle, compared with free breathing, and allows for shorter treatment times. Patients' free‐breathing patterns contain considerable variability and, although dosimetric results for gated delivery may be acceptable, it is difficult to achieve efficient treatment delivery. A coached breathing pattern combined with a 5 mm amplitude gate, resulted in both high‐quality dose distributions and overall shortest gated beam delivery times. PACS number: 87.55.Qr PMID:26219000

Commissioning dosimetry and in situ dose mapping of a semi-industrial Cobalt-60 gamma-irradiation facility using Fricke and Ceric-cerous dosimetry system and comparison with Monte Carlo simulation data

NASA Astrophysics Data System (ADS)

Mortuza, Md Firoz; Lepore, Luigi; Khedkar, Kalpana; Thangam, Saravanan; Nahar, Arifatun; Jamil, Hossen Mohammad; Bandi, Laxminarayan; Alam, Md Khorshed

2018-03-01

Characterization of a 90 kCi (3330 TBq), semi-industrial, cobalt-60 gamma irradiator was performed by commissioning dosimetry and in-situ dose mapping experiments with Ceric-cerous and Fricke dosimetry systems. Commissioning dosimetry was carried out to determine dose distribution pattern of absorbed dose in the irradiation cell and products. To determine maximum and minimum absorbed dose, overdose ratio and dwell time of the tote boxes, homogeneous dummy product (rice husk) with a bulk density of 0.13 g/cm3 were used in the box positions of irradiation chamber. The regions of minimum absorbed dose of the tote boxes were observed in the lower zones of middle plane and maximum absorbed doses were found in the middle position of front plane. Moreover, as a part of dose mapping, dose rates in the wall positions and some selective strategic positions were also measured to carry out multiple irradiation program simultaneously, especially for low dose research irradiation program. In most of the cases, Monte Carlo simulation data, using Monte Carlo N-Particle eXtended code version MCNPX 2.7., were found to be in congruence with experimental values obtained from Ceric-cerous and Fricke dosimetry; however, in close proximity positions from the source, the dose rate variation between chemical dosimetry and MCNP was higher than distant positions.

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

3D dosimetric validation of motion compensation concepts in radiotherapy using an anthropomorphic dynamic lung phantom

NASA Astrophysics Data System (ADS)

Mann, P.; Witte, M.; Moser, T.; Lang, C.; Runz, A.; Johnen, W.; Berger, M.; Biederer, J.; Karger, C. P.

2017-01-01

In this study, we developed a new setup for the validation of clinical workflows in adaptive radiation therapy, which combines a dynamic ex vivo porcine lung phantom and three-dimensional (3D) polymer gel dosimetry. The phantom consists of an artificial PMMA-thorax and contains a post mortem explanted porcine lung to which arbitrary breathing patterns can be applied. A lung tumor was simulated using the PAGAT (polyacrylamide gelatin gel fabricated at atmospheric conditions) dosimetry gel, which was evaluated in three dimensions by magnetic resonance imaging (MRI). To avoid bias by reaction with oxygen and other materials, the gel was collocated inside a BAREX™ container. For calibration purposes, the same containers with eight gel samples were irradiated with doses from 0 to 7 Gy. To test the technical feasibility of the system, a small spherical dose distribution located completely within the gel volume was planned. Dose delivery was performed under static and dynamic conditions of the phantom with and without motion compensation by beam gating. To verify clinical target definition and motion compensation concepts, the entire gel volume was homogeneously irradiated applying adequate margins in case of the static phantom and an additional internal target volume in case of dynamically operated phantom without and with gated beam delivery. MR-evaluation of the gel samples and comparison of the resulting 3D dose distribution with the planned dose distribution revealed a good agreement for the static phantom. In case of the dynamically operated phantom without motion compensation, agreement was very poor while additional application of motion compensation techniques restored the good agreement between measured and planned dose. From these experiments it was concluded that the set up with the dynamic and anthropomorphic lung phantom together with 3D-gel dosimetry provides a valuable and versatile tool for geometrical and dosimetrical validation of motion compensated treatment concepts in adaptive radiotherapy.

Keeping an eye on the ring: COMS plaque loading optimization for improved dose conformity and homogeneity.

PubMed

Gagne, Nolan L; Cutright, Daniel R; Rivard, Mark J

2012-09-01

To improve tumor dose conformity and homogeneity for COMS plaque brachytherapy by investigating the dosimetric effects of varying component source ring radionuclides and source strengths. The MCNP5 Monte Carlo (MC) radiation transport code was used to simulate plaque heterogeneity-corrected dose distributions for individually-activated source rings of 14, 16 and 18 mm diameter COMS plaques, populated with (103)Pd, (125)I and (131)Cs sources. Ellipsoidal tumors were contoured for each plaque size and MATLAB programming was developed to generate tumor dose distributions for all possible ring weighting and radionuclide permutations for a given plaque size and source strength resolution, assuming a 75 Gy apical prescription dose. These dose distributions were analyzed for conformity and homogeneity and compared to reference dose distributions from uniformly-loaded (125)I plaques. The most conformal and homogeneous dose distributions were reproduced within a reference eye environment to assess organ-at-risk (OAR) doses in the Pinnacle(3) treatment planning system (TPS). The gamma-index analysis method was used to quantitatively compare MC and TPS-generated dose distributions. Concentrating > 97% of the total source strength in a single or pair of central (103)Pd seeds produced the most conformal dose distributions, with tumor basal doses a factor of 2-3 higher and OAR doses a factor of 2-3 lower than those of corresponding uniformly-loaded (125)I plaques. Concentrating 82-86% of the total source strength in peripherally-loaded (131)Cs seeds produced the most homogeneous dose distributions, with tumor basal doses 17-25% lower and OAR doses typically 20% higher than those of corresponding uniformly-loaded (125)I plaques. Gamma-index analysis found > 99% agreement between MC and TPS dose distributions. A method was developed to select intra-plaque ring radionuclide compositions and source strengths to deliver more conformal and homogeneous tumor dose distributions than uniformly-loaded (125)I plaques. This method may support coordinated investigations of an appropriate clinical target for eye plaque brachytherapy.

Using the ovarian sensitivity index to define poor, normal, and high response after controlled ovarian hyperstimulation in the long gonadotropin-releasing hormone-agonist protocol: suggestions for a new principle to solve an old problem.

PubMed

Huber, Malin; Hadziosmanovic, Nermin; Berglund, Lars; Holte, Jan

2013-11-01

To explore the utility of using the ratio between oocyte yield and total dose of FSH, i.e., the ovarian sensitivity index (OSI), to define ovarian response patterns. Retrospective cross-sectional study. University-affiliated private center. The entire unselected cohort of 7,520 IVF/intracytoplasmic sperm injection treatments (oocyte pick-ups [OPUs]) during an 8-year period (long GnRH agonist-recombinant FSH protocol). None. The distribution of the OSI (oocytes recovered × 1,000/total dose of FSH), the cutoff levels for poor and high response, set at ±1 SD, and the relationship between OSI and treatment outcome. OSI showed a log-normal distribution with cutoff levels for poor and high response at 1.697/IU and 10.07/IU, respectively. A nomogram is presented. Live-birth rates per OPU were 10.5 ± 0.1%, 26.9 ± 0.6%, and 36.0 ± 1.4% for poor, normal, and high response treatments, respectively. The predictive power (C-statistic) for OSI to predict live birth was superior to that of oocyte yield. The OSI improves the definition of ovarian response patterns because it takes into account the degree of stimulation. The nomogram presents evidence-based cutoff levels for poor, normal, and high response and could be used for unifying study designs involving ovarian response patterns. Copyright © 2013 American Society for Reproductive Medicine. Published by Elsevier Inc. All rights reserved.

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

Lin, L; Huang, S; Kang, M

Purpose: The purpose of this manuscript is to demonstrate the utility of a comprehensive test pattern in validating calculation models of the low-dose tails of proton pencil beam scanning (PBS) spots. Such a pattern has been used previously for quality assurance purposes to assess spot shape and location, and for determining monitor units. Methods: In this study, a scintillation detector was used to measure the test pattern in air at isocenter for two proton beam energies (115 and 225 MeV) of two IBA universal nozzles (UN). Planar measurements were compared with calculated dose distribution based on the weighted superposition ofmore » spot profiles previously measured using a pair-magnification method. Results: Including the halo component below 1% of the central dose is shown to improve the gamma-map comparison between calculation and measurement from 94.9% to 98.4% using 2 mm/2% criteria for the 115 MeV proton beam of UN #1. In contrast, including the halo component below 1% of the central dose does not improve the gamma agreement for the 115 MeV proton beam of UN #2, due to the cutoff of the halo component at off-axis locations. When location-dependent spot profiles are used for calculation instead of spot profiles at central axis, the gamma agreement is improved from 98.0% to 99.5% using 2 mm/2% criteria. The cutoff of the halo component is smaller at higher energies, and is not observable for the 225 MeV proton beam for UN #2. Conclusion: In conclusion, the use of a comprehensive test pattern can facilitate the validation of the halo component of proton PBS spots at off axis locations. The cutoff of the halo component should be taken into consideration for large fields or PBS systems that intend to trim spot profiles using apertures. This work was supported by the US Army Medical Research and Materiel Command under Contract Agreement No. DAMD17-W81XWH-07-2-0121 and W81XWH-09-2-0174.« 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.

Advanced treatment planning using direct 4D optimisation for pencil-beam scanned particle therapy

NASA Astrophysics Data System (ADS)

Bernatowicz, Kinga; Zhang, Ye; Perrin, Rosalind; Weber, Damien C.; Lomax, Antony J.

2017-08-01

We report on development of a new four-dimensional (4D) optimisation approach for scanned proton beams, which incorporates both irregular motion patterns and the delivery dynamics of the treatment machine into the plan optimiser. Furthermore, we assess the effectiveness of this technique to reduce dose to critical structures in proximity to moving targets, while maintaining effective target dose homogeneity and coverage. The proposed approach has been tested using both a simulated phantom and a clinical liver cancer case, and allows for realistic 4D calculations and optimisation using irregular breathing patterns extracted from e.g. 4DCT-MRI (4D computed tomography-magnetic resonance imaging). 4D dose distributions resulting from our 4D optimisation can achieve almost the same quality as static plans, independent of the studied geometry/anatomy or selected motion (regular and irregular). Additionally, current implementation of the 4D optimisation approach requires less than 3 min to find the solution for a single field planned on 4DCT of a liver cancer patient. Although 4D optimisation allows for realistic calculations using irregular breathing patterns, it is very sensitive to variations from the planned motion. Based on a sensitivity analysis, target dose homogeneity comparable to static plans (D5-D95  <5%) has been found only for differences in amplitude of up to 1 mm, for changes in respiratory phase  <200 ms and for changes in the breathing period of  <20 ms in comparison to the motions used during optimisation. As such, methods to robustly deliver 4D optimised plans employing 4D intensity-modulated delivery are discussed.

Fabrication of topical metered dose film forming sprays for pain management.

PubMed

Ranade, Sneha; Bajaj, Amrita; Londhe, Vaishali; Babul, Najib; Kao, Danny

2017-03-30

Topical film-forming metered dose spray formulations were designed for management of pain. Ropivacaine, a local anesthetic is explored for its topical efficacy in alleviating pain. Metered dose spray containers, organic solvents, film forming polymers and permeation enhancers were utilized to fabricate the Metered Dose topical spray. Factors like viscosity, spray pattern, spray angle, volume of actuation, droplet size distribution of the metered dose spray formulation and drying time, flexibility and wash-ability of the film formed after spraying were assessed. Permeation of the drug into the porcine skin was observed based on ex-vivo diffusion studies and confocal microscopy. The results indicated a high level of drug concentration in the skin layers. Anti-nociceptive efficacy of the formulations was assessed on Wistar rats by hot plate and tail flick tests, based on the response to pain perception. The results were comparable to the conventional lidocaine gel. Topical film forming sprays have the ability to provide an accurate, long lasting and patient compliant delivery of drugs on the skin as compared to conventional gels. Copyright © 2017 Elsevier B.V. All rights reserved.

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.

Low dose aerosol fitness at the innate phase of murine infection better predicts virulence amongst clinical strains of Mycobacterium tuberculosis.

PubMed

Caceres, Neus; Llopis, Isaac; Marzo, Elena; Prats, Clara; Vilaplana, Cristina; de Viedma, Dario Garcia; Samper, Sofía; Lopez, Daniel; Cardona, Pere-Joan

2012-01-01

Evaluation of a quick and easy model to determine the intrinsic ability of clinical strains to generate active TB has been set by assuming that this is linked to the fitness of Mycobacterium tuberculosis strain at the innate phase of the infection. Thus, the higher the bacillary load, the greater the possibility of inducting liquefaction, and thus active TB, once the adaptive response is set. The virulence of seven clinical Mycobacterium tuberculosis strains isolated in Spain was tested by determining the bacillary concentration in the spleen and lung of mice at weeks 0, 1 and 2 after intravenous (IV) inoculation of 10⁴ CFU, and by determining the growth in vitro until the stationary phase had been reached. Cord distribution automated analysis showed two clear patterns related to the high and low fitness in the lung after IV infection. This pattern was not seen in the in vitro fitness tests, which clearly favored the reference strain (H37Rv). Subsequent determination using a more physiological low-dose aerosol (AER) inoculation with 10² CFU showed a third pattern in which the three best values coincided with the highest dissemination capacity according to epidemiological data. The fitness obtained after low dose aerosol administration in the presence of the innate immune response is the most predictive factor for determining the virulence of clinical strains. This gives support to a mechanism of the induction of active TB derived from the dynamic hypothesis of latent tuberculosis infection.

Dose to the Developing Dentition During Therapeutic Irradiation: Organ at Risk Determination and Clinical Implications

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

Thompson, Reid F., E-mail: Reid.Thompson@uphs.upenn.edu; Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania; Schneider, Ralf A., E-mail: ralf.schneider@psi.ch

Purpose: Irradiation of pediatric facial structures can cause severe impairment of permanent teeth later in life. We therefore focused on primary and permanent teeth as organs at risk, investigating the ability to identify individual teeth in children and infants and to correlate dose distributions with subsequent dental toxicity. Methods and Materials: We retrospectively reviewed 14 pediatric patients who received a maximum dose >20 Gy(relative biological effectiveness, RBE) to 1 or more primary or permanent teeth between 2003 and 2009. The patients (aged 1-16 years) received spot-scanning proton therapy with 46 to 66 Gy(RBE) in 23 to 33 daily fractions formore » a variety of tumors, including rhabdomyosarcoma (n=10), sarcoma (n=2), teratoma (n=1), and carcinoma (n=1). Individual teeth were contoured on axial slices from planning computed tomography (CT) scans. Dose-volume histogram data were retrospectively obtained from total calculated delivered treatments. Dental follow-up information was obtained from external care providers. Results: All primary teeth and permanent incisors, canines, premolars, and first and second molars were identifiable on CT scans in all patients as early as 1 year of age. Dose-volume histogram analysis showed wide dose variability, with a median 37 Gy(RBE) per tooth dose range across all individuals, and a median 50 Gy(RBE) intraindividual dose range across all teeth. Dental follow-up revealed absence of significant toxicity in 7 of 10 patients but severe localized toxicity in teeth receiving >20 Gy(RBE) among 3 patients who were all treated at <4 years of age. Conclusions: CT-based assessment of dose distribution to individual teeth is feasible, although delayed calcification may complicate tooth identification in the youngest patients. Patterns of dental dose exposure vary markedly within and among patients, corresponding to rapid dose falloff with protons. Severe localized dental toxicity was observed in a few patients receiving the largest doses of radiation at the youngest ages; however, multiple factors including concurrent chemotherapy confounded the dose-effect relationship. Further studies with larger cohorts and appropriate controls will be required.« less

Choline distribution and metabolism in pregnant rats and fetuses are influenced by the choline content of the maternal diet.

PubMed

Garner, S C; Mar, M H; Zeisel, S H

1995-11-01

Choline supplementation of pregnant rats between d 12 and 17 of pregnancy permanently enhances the spatial memory of offspring; however, the mechanism is unknown. We examined the effect of choline supplementation on metabolism of orally ingested choline by nonmated rats and pregnant rats and their fetuses. We studied the metabolism of an acute oral dose of 14C-choline chloride in pregnant and nonmated rats with and without choline supplementation (25 mmol/L choline chloride in water) on d 12-17 of pregnancy. During the first 2 h after oral dosing, plasma radiolabeled choline was detectable, whereas plasma choline metabolites contributed little to total radioactivity at any time. The pattern of accumulation of label in placentas was similar in all groups. Fetal tissues (i.e., brain, liver and carcass remnant) contained primarily 14C-phosphatidylcholine and 14C-phosphorylcholine. Also, we examined the fetal tissue distribution of isotopically labeled (deuterated) choline derived from the diet and from the dietary choline supplement. The distribution patterns for radiolabeled choline metabolites in fetuses of supplemented dams accumulated significantly (P < 0.01) more of their total choline and its metabolites than fetuses of control dams during d 12-17 of gestation (50 vs. 20%). In fetuses from supplemented dams, betaine concentrations were greater than in fetuses from control dams in all organs assayed (by 36-57%). Phosphorylcholine concentrations in brain of fetuses from supplemented dams were also greater. These experiments identify potential metabolites of choline that might mediate the observed effects on brain development in the rats.

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

Uchida, Y; Tachibana, H

Purpose: For head and neck VMAT (HN-VMAT), variations of position and deformation of patient’s shoulders is a concern to affect inaccuracy of dose distribution. It has been reported that the setup error of the shoulders was variable from 5 mm – 1 cm. The beams of the HN-VMAT pass through the shoulders. We assessed the impact of shoulder deformation to dose distribution for HN-VMAT. Methods: One HN-VMAT plan was generated using a patient’s CT. The patient’s CT was deformed using ImSimQA (Oncology Systems Limited, Shrewsbury, Shropshire, UK) to generate several patterns of the shoulders’ deformations when the right and leftmore » humeral heads were shifted with 3, 6, and 15 mm in the superior and inferior directions (SI), 3, 5, and 15 mm in the anterior and posterior directions (AP), and 5 and 15 mm in the right or left direction (LR). DVH comparison was performed in the different deformation patterns. The dosimetric parameters of D95% for CTV70Gy, CTV60Gy and CTV54Gy and dmax for Spinal cord were also measured. Gamma index evaluation (Criteria: 3%/2mm) was performed to exhibit clinically tolerable area in the comparison. Results: DVH comparison shows similar for all structures. As the comparison for the dosimetric parameters, the variations of D95% in the LR and AP were within 1%. There were larger variations in the SI than those in the other directions, however were within 1.5%. In gamma index evaluation, the small spots with higher gamma index values were appeared when the shift was 6 mm, however the pass ratio was 99.13%. Conclusion: HN-VMAT should be robust for shoulder deformation and geometric accuracy within 6 mm from patient’s setup and image-guided radiotherapy may be clinically acceptable for target dose coverage or normal tissue dose sparing.« less

Pinolenic Acid in Structured Triacylglycerols Exhibits Superior Intestinal Lymphatic Absorption As Compared to Pinolenic Acid in Natural Pine Nut Oil.

PubMed

Chung, Min-Yu; Woo, Hyunjoon; Kim, Juyeon; Kong, Daecheol; Choi, Hee-Don; Choi, In-Wook; Kim, In-Hwan; Noh, Sang K; Kim, Byung Hee

2017-03-01

The positional distribution pattern of fatty acids (FAs) in the triacylglycerols (TAGs) affects intestinal absorption of these FAs. The aim of this study was to compare lymphatic absorption of pinolenic acid (PLA) present in structured pinolenic TAG (SPT) where PLA was evenly distributed on the glycerol backbone, with absorption of pine nut oil (PNO) where PLA was predominantly positioned at the sn-3 position. SPT was prepared via the nonspecific lipase-catalyzed esterification of glycerol with free FA obtained from PNO. Lymphatic absorption of PLA from PNO and from SPT was compared in a rat model of lymphatic cannulation. Significantly (P < 0.05) greater amounts of PLA were detected in lymph collected for 8 h from an emulsion containing SPT (28.5 ± 0.7% dose) than from an emulsion containing PNO (26.2 ± 0.6% dose), thereby indicating that PLA present in SPT has a greater capacity for lymphatic absorption than PLA from PNO.

Dosimetric and Clinical Analysis of Spatial Distribution of the Radiation Dose in Gamma Knife Radiosurgery for Vestibular Schwannoma

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

Massager, Nicolas, E-mail: nmassage@ulb.ac.be; Neurosurgery-Department, Hospital Erasme, Brussels; Lonneville, Sarah

2011-11-15

Objectives: We investigated variations in the distribution of radiation dose inside (dose inhomogeneity) and outside (dose falloff) the target volume during Gamma Knife (GK) irradiation of vestibular schwannoma (VS). We analyzed the relationship between some parameters of dose distribution and the clinical and radiological outcome of patients. Methods and Materials: Data from dose plans of 203 patients treated for a vestibular schwannoma by GK C using same prescription dose (12 Gy at the 50% isodose) were collected. Four different dosimetric indexes were defined and calculated retrospectively in all plannings on the basis of dose-volume histograms: Paddick conformity index (PI), gradientmore » index (GI), homogeneity index (HI), and unit isocenter (UI). The different measures related to distribution of the radiation dose were compared with hearing and tumor outcome of 203 patients with clinical and radiological follow-up of minimum 2 years. Results: Mean, median, SD, and ranges of the four indexes of dose distribution analyzed were calculated; large variations were found between dose plans. We found a high correlation between the target volume and PI, GI, and UI. No significant association was found between the indexes of dose distribution calculated in this study and tumor control, tumor volume shrinkage, hearing worsening, loss of functional hearing, or complete hearing loss at last follow-up. Conclusions: Parameters of distribution of the radiation dose during GK radiosurgery for VS can be highly variable between dose plans. The tumor and hearing outcome of patients treated is not significantly related to these global indexes of dose distribution inside and around target volume. In GK radiosurgery for VS, the outcome seems more to be influenced by local radiation dose delivered to specific structures or volumes than by global dose gradients.« less

SU-E-T-295: Simultaneous Beam Sampling and Aperture Shape Optimization for Station Parameter Optimized Radiation Therapy (SPORT)

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

Zarepisheh, M; Li, R; Xing, L

Purpose: Station Parameter Optimized Radiation Therapy (SPORT) was recently proposed to fully utilize the technical capability of emerging digital LINACs, in which the station parameters of a delivery system, (such as aperture shape and weight, couch position/angle, gantry/collimator angle) are optimized altogether. SPORT promises to deliver unprecedented radiation dose distributions efficiently, yet there does not exist any optimization algorithm to implement it. The purpose of this work is to propose an optimization algorithm to simultaneously optimize the beam sampling and aperture shapes. Methods: We build a mathematical model whose variables are beam angles (including non-coplanar and/or even nonisocentric beams) andmore » aperture shapes. To solve the resulting large scale optimization problem, we devise an exact, convergent and fast optimization algorithm by integrating three advanced optimization techniques named column generation, gradient method, and pattern search. Column generation is used to find a good set of aperture shapes as an initial solution by adding apertures sequentially. Then we apply the gradient method to iteratively improve the current solution by reshaping the aperture shapes and updating the beam angles toward the gradient. Algorithm continues by pattern search method to explore the part of the search space that cannot be reached by the gradient method. Results: The proposed technique is applied to a series of patient cases and significantly improves the plan quality. In a head-and-neck case, for example, the left parotid gland mean-dose, brainstem max-dose, spinal cord max-dose, and mandible mean-dose are reduced by 10%, 7%, 24% and 12% respectively, compared to the conventional VMAT plan while maintaining the same PTV coverage. Conclusion: Combined use of column generation, gradient search and pattern search algorithms provide an effective way to optimize simultaneously the large collection of station parameters and significantly improves quality of resultant treatment plans as compared with conventional VMAT or IMRT treatments.« less

Dose and Duration of Opioid Use in Patients with Cancer and Noncancer Pain at an Outpatient Hospital Setting in Malaysia.

PubMed

Zin, Che S; Rahman, Norny A; Ismail, Che R; Choy, Leong W

2017-07-01

There are currently limited data available on the patterns of opioid prescribing in Malaysia. This study investigated the patterns of opioid prescribing and characterized the dosing and duration of opioid use in patients with noncancer and cancer pain. This retrospective, cross-sectional study was conducted at an outpatient hospital setting in Malaysia. All prescriptions for opioids (dihydrocodeine, fentanyl, morphine, and oxycodone) issued between January 2013 and December 2014 were examined. The number of prescriptions and patients, the distribution of mean daily dose, annual total days covered with opioids, and annual total opioid dose at the individual level were calculated and stratified by noncancer and cancer groups. A total of 1015 opioid prescriptions were prescribed for 347 patients from 2013 to 2014. Approximately 41.5% of patients (N = 144/347) and 58.5% (N = 203/347) were associated with noncancer and cancer diagnosis, respectively. Oxycodone (38.0%) was the highest prescribed primarily for the noncancer group. The majority of patients in both noncancer (74.3%) and cancer (60.4%) groups were receiving mean daily doses of < 50 mg morphine equivalents. The chronic use of opioids (> 90 days per year) was associated with 21.8% of patients in the noncancer group and 17.5% in the cancer group. The finding from this study showed that 41.5% of opioid users at an outpatient hospital setting in Malaysia received opioids for noncancer pain and 21.8% of these users were using opioids for longer than 90 days. The average daily dose in the majority of patients in both groups of noncancer and cancer was modest. © 2016 World Institute of Pain.

Comparative absorption, distribution, and excretion of titanium dioxide and zinc oxide nanoparticles after repeated oral administration.

PubMed

Cho, Wan-Seob; Kang, Byeong-Cheol; Lee, Jong Kwon; Jeong, Jayoung; Che, Jeong-Hwan; Seok, Seung Hyeok

2013-03-26

The in vivo kinetics of nanoparticles is an essential to understand the hazard of nanoparticles. Here, the absorption, distribution, and excretion patterns of titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles following oral administration were evaluated. Nanoparticles were orally administered to rats for 13 weeks (7 days/week). Samples of blood, tissues (liver, kidneys, spleen, and brain), urine, and feces were obtained at necropsy. The level of Ti or Zn in each sample was measured using inductively coupled plasma-mass spectrometry. TiO₂ nanoparticles had extremely low absorption, while ZnO nanoparticles had higher absorption and a clear dose-response curve. Tissue distribution data showed that TiO₂ nanoparticles were not significantly increased in sampled organs, even in the group receiving the highest dose (1041.5 mg/kg body weight). In contrast, Zn concentrations in the liver and kidney were significantly increased compared with the vehicle control. ZnO nanoparticles in the spleen and brain were minimally increased. Ti concentrations were not significantly increased in the urine, while Zn levels were significantly increased in the urine, again with a clear dose-response curve. Very high concentrations of Ti were detected in the feces, while much less Zn was detected in the feces. Compared with TiO₂ nanoparticles, ZnO nanoparticles demonstrated higher absorption and more extensive organ distribution when administered orally. The higher absorption of ZnO than TiO₂ nanoparticles might be due to the higher dissolution rate in acidic gastric fluid, although more thorough studies are needed.

Exposure to atmospheric radon.

PubMed Central

Steck, D J; Field, R W; Lynch, C F

1999-01-01

We measured radon (222Rn) concentrations in Iowa and Minnesota and found that unusually high annual average radon concentrations occur outdoors in portions of central North America. In some areas, outdoor concentrations exceed the national average indoor radon concentration. The general spatial patterns of outdoor radon and indoor radon are similar to the spatial distribution of radon progeny in the soil. Outdoor radon exposure in this region can be a substantial fraction of an individual's total radon exposure and is highly variable across the population. Estimated lifetime effective dose equivalents for the women participants in a radon-related lung cancer study varied by a factor of two at the median dose, 8 mSv, and ranged up to 60 mSv (6 rem). Failure to include these doses can reduce the statistical power of epidemiologic studies that examine the lung cancer risk associated with residential radon exposure. Images Figure 1 Figure 2 Figure 3 Figure 4 PMID:9924007

A motion phantom study on helical tomotherapy: the dosimetric impacts of delivery technique and motion

NASA Astrophysics Data System (ADS)

Kanagaki, Brian; Read, Paul W.; Molloy, Janelle A.; Larner, James M.; Sheng, Ke

2007-01-01

Helical tomotherapy (HT) can potentially be used for lung cancer treatment including stereotactic radiosurgery because of its advanced image guidance and its ability to deliver highly conformal dose distributions. However, previous theoretical and simulation studies reported that the effect of respiratory motion on statically planned tomotherapy treatments may cause substantial differences between the calculated and actual delivered radiation isodose distribution, particularly when the treatment is hypofractionated. In order to determine the dosimetric effects of motion upon actual HT treatment delivery, phantom film dosimetry measurements were performed under static and moving conditions using a clinical HT treatment unit. The motion phantom system was constructed using a programmable motor, a base, a moving platform and a life size lung heterogeneity phantom with wood inserts representing lung tissue with a 3.0 cm diameter spherical tumour density equivalent insert. In order to determine the effects of different motion and tomotherapy delivery parameters, treatment plans were created using jaw sizes of 1.04 cm and 2.47 cm, with incremental gantry rotation periods between the minimum allowed (10 s) and the maximum allowed (60 s). The couch speed varied from 0.009 cm s-1 to 0.049 cm s-1, and delivered to a phantom under static and dynamic conditions with peak-to-peak motion amplitudes of 1.2 cm and 2 cm and periods of 3 and 5 s to simulate human respiratory motion of lung tumours. A cylindrical clinical target volume (CTV) was contoured to tightly enclose the tumour insert. 2.0 Gy was prescribed to 95% of the CTV. Two-dimensional dose was measured by a Kodak EDR2 film. Dynamic phantom doses were then quantitatively compared to static phantom doses in terms of axial dose profiles, cumulative dose volume histograms (DVH), percentage of CTV receiving the prescription dose and the minimum dose received by 95% of the CTV. The larger motion amplitude resulted in more under-dosing at the ends of the CTV in the axis of motion, and this effect was greater for the smaller jaw size plans. Due to the size of the penumbra, the 2.47 cm jaw plans provide adequate coverage for smaller amplitudes of motion, ±0.6 cm in our experiment, without adding any additional margin in the axis of motion to the treatment volume. The periodic heterogeneous patterns described by previous studies were not observed from the single fraction of the phantom measurement. Besides the jaw sizes, CTV dose coverage is not significantly dependent on machine and phantom motion periods. The lack of adverse synchronization patterns from both results validate that HT is a safe technique for treating moving target and hypofractionation.

Lhermitte Sign After Chemo-IMRT of Head-and-Neck Cancer: Incidence, Doses, and Potential Mechanisms

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

Pak, Daniel; Vineberg, Karen; Feng, Felix

2012-08-01

Purpose: We have observed a higher rate of Lhermitte sign (LS) after chemo-intensity-modulated radiotherapy (IMRT) of head-and-neck cancer than the published rates after conventional radiotherapy. We hypothesized that the inhomogeneous spinal cord dose distributions produced by IMRT caused a 'bath-and-shower' effect, characterized by low doses in the vicinity of high doses, reducing spinal cord tolerance. Methods and Materials: Seventy-three patients with squamous cell carcinoma of the oropharynx participated in a prospective study of IMRT concurrent with weekly carboplatin and paclitaxel. Of these, 15 (21%) reported LS during at least 2 consecutive follow-up visits. Mean dose, maximum dose, and partial volumemore » and absolute volume (in milliliters) of spinal cord receiving specified doses ({>=}10 Gy, {>=}20 Gy, {>=}30 Gy, and {>=}40 Gy), as well as the pattern of dose distributions at the 'anatomic' spinal cord (from the base of the skull to the aortic arch) and 'plan-related' spinal cord (from the top through the bottom of the planning target volumes), were compared between LS patients and 34 non-LS patients. Results: LS patients had significantly higher spinal cord mean doses, V{sub 30}, V{sub 40}, and absolute volumes receiving 30 Gy or more and 40 Gy or more compared with the non-LS patients (p < 0.05). The strongest predictors of LS were higher V{sub 40} and higher cord volumes receiving 40 Gy or more (p {<=} 0.007). There was no evidence of larger spinal cord volumes receiving low doses in the vicinity of higher doses (bath-and-shower effect) in LS compared with non-LS patients. Conclusions: Greater mean dose, V{sub 30}, V{sub 40}, and cord volumes receiving 30 Gy or more and 40 Gy or more characterized LS compared with non-LS patients. Bath-and-shower effects could not be validated in this study as a potential contributor to LS. The higher-than-expected rates of LS may be because of the specific concurrent chemotherapy agents or more accurate identification of LS in the setting of a prospective study.« less

QMRA for Drinking Water: 2. The Effect of Pathogen Clustering in Single-Hit Dose-Response Models.

PubMed

Nilsen, Vegard; Wyller, John

2016-01-01

Spatial and/or temporal clustering of pathogens will invalidate the commonly used assumption of Poisson-distributed pathogen counts (doses) in quantitative microbial risk assessment. In this work, the theoretically predicted effect of spatial clustering in conventional "single-hit" dose-response models is investigated by employing the stuttering Poisson distribution, a very general family of count distributions that naturally models pathogen clustering and contains the Poisson and negative binomial distributions as special cases. The analysis is facilitated by formulating the dose-response models in terms of probability generating functions. It is shown formally that the theoretical single-hit risk obtained with a stuttering Poisson distribution is lower than that obtained with a Poisson distribution, assuming identical mean doses. A similar result holds for mixed Poisson distributions. Numerical examples indicate that the theoretical single-hit risk is fairly insensitive to moderate clustering, though the effect tends to be more pronounced for low mean doses. Furthermore, using Jensen's inequality, an upper bound on risk is derived that tends to better approximate the exact theoretical single-hit risk for highly overdispersed dose distributions. The bound holds with any dose distribution (characterized by its mean and zero inflation index) and any conditional dose-response model that is concave in the dose variable. Its application is exemplified with published data from Norovirus feeding trials, for which some of the administered doses were prepared from an inoculum of aggregated viruses. The potential implications of clustering for dose-response assessment as well as practical risk characterization are discussed. © 2016 Society for Risk Analysis.

Efficient clearance of Aβ protofibrils in AβPP-transgenic mice treated with a brain-penetrating bifunctional antibody.

PubMed

Syvänen, Stina; Hultqvist, Greta; Gustavsson, Tobias; Gumucio, Astrid; Laudon, Hanna; Söderberg, Linda; Ingelsson, Martin; Lannfelt, Lars; Sehlin, Dag

2018-05-24

Amyloid-β (Aβ) immunotherapy is one of the most promising disease-modifying strategies for Alzheimer's disease (AD). Despite recent progress targeting aggregated forms of Aβ, low antibody brain penetrance remains a challenge. In the present study, we used transferrin receptor (TfR)-mediated transcytosis to facilitate brain uptake of our previously developed Aβ protofibril-selective mAb158, with the aim of increasing the efficacy of immunotherapy directed toward soluble Aβ protofibrils. Aβ protein precursor (AβPP)-transgenic mice (tg-ArcSwe) were given a single dose of mAb158, modified for TfR-mediated transcytosis (RmAb158-scFv8D3), in comparison with an equimolar dose or a tenfold higher dose of unmodified recombinant mAb158 (RmAb158). Soluble Aβ protofibrils and total Aβ in the brain were measured by enzyme-linked immunosorbent assay (ELISA). Brain distribution of radiolabeled antibodies was visualized by positron emission tomography (PET) and ex vivo autoradiography. ELISA analysis of Tris-buffered saline brain extracts demonstrated a 40% reduction of soluble Aβ protofibrils in both RmAb158-scFv8D3- and high-dose RmAb158-treated mice, whereas there was no Aβ protofibril reduction in mice treated with a low dose of RmAb158. Further, ex vivo autoradiography and PET imaging revealed different brain distribution patterns of RmAb158-scFv8D3 and RmAb158, suggesting that these antibodies may affect Aβ levels by different mechanisms. With a combination of biochemical and imaging analyses, this study demonstrates that antibodies engineered to be transported across the blood-brain barrier can be used to increase the efficacy of Aβ immunotherapy. This strategy may allow for decreased antibody doses and thereby reduced side effects and treatment costs.

Improved Hyperthermia Treatment of Tumors Under Consideration of Magnetic Nanoparticle Distribution Using Micro-CT Imaging.

PubMed

Dähring, H; Grandke, J; Teichgräber, U; Hilger, I

2015-12-01

Heterogeneous magnetic nanoparticle (MNP) distributions within tumors can cause regions of temperature under dosage and reduce the therapeutic efficiency. Here, micro-computed tomography (CT) imaging was used as a tool to determine the MNP distribution in vivo. The therapeutic success was evaluated based on tumor volume and temperature distribution. Tumor-bearing mice were intratumorally injected with iron oxide particles. MNP distribution was assessed by micro-CT with a low radiation dose protocol. MNPs were clearly visible, and the exact distribution to nontumor structures was detected by micro-CT. Knowledge of the intratumoral MNP distribution allowed the generation of higher temperatures within the tumor and led to higher temperature values after exposure to an alternating magnetic field (AMF). Consequently, the tumor size after 28 days was reduced to 14 and 73 % of the initial tumor volume for the MNP/AMF/CT and MNP/AMF groups, respectively. The MNP distribution pattern mainly governed the generated temperature spots in the tumor. Knowing the MNP distribution enabled individualized hyperthermia treatment and improved the overall therapeutic efficiency.

SU-E-T-09: A Clinical Implementation and Optimized Dosimetry Study of Freiberg Flap Skin Surface Treatment in High Dose Rate Brachytherapy

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

Syh, J; Syh, J; Patel, B

Purpose: This case study was designated to confirm the optimized plan was used to treat skin surface of left leg in three stages. 1. To evaluate dose distribution and plan quality by alternating of the source loading catheters pattern in flexible Freiberg Flap skin surface (FFSS) applicator. 2. To investigate any impact on Dose Volume Histogram (DVH) of large superficial surface target volume coverage. 3. To compare the dose distribution if it was treated with electron beam. Methods: The Freiburg Flap is a flexible mesh style surface mold for skin radiation or intraoperative surface treatments. The Freiburg Flap consists ofmore » multiple spheres that are attached to each other, holding and guiding up to 18 treatment catheters. The Freiburg Flap also ensures a constant distance of 5mm from the treatment catheter to the surface. Three treatment trials with individual planning optimization were employed: 18 channels, 9 channels of FF and 6 MeV electron beam. The comparisons were highlighted in target coverage, dose conformity and dose sparing of surrounding tissues. Results: The first 18 channels brachytherapy plan was generated with 18 catheters inside the skin-wrapped up flap (Figure 1A). A second 9 catheters plan was generated associated with the same calculation points which were assigned to match prescription for target coverage as 18 catheters plan (Figure 1B). The optimized inverse plan was employed to reduce the dose to adjacent structures such as tibia or fibula. The comparison of DVH’s was depicted on Figure 2. External beam of electron RT plan was depicted in Figure 3. Overcall comparisons among these three were illustrated in Conclusion: The 9-channel Freiburg flap flexible skin applicator offers a reasonably acceptable plan without compromising the coverage. Electron beam was discouraged to use to treat curved skin surface because of low target coverage and high dose in adjacent tissues.« less

Dry powder dosing in liquid vehicles: ocular tolerance and scintigraphic evaluation of a perfluorocarbon suspension.

PubMed

Zhu, Y; Wilson, C G; Meadows, D; Olejnik, O; Frier, M; Washington, N; Musson, R

1999-11-30

The ocular tolerance and precorneal disposition of 99mTc-labelled sterile carbon-perfluorodecalin (PFD) and carbon-aqueous suspensions were examined in a cohort of healthy volunteers. Formulations were prepared in PFD or saline using charcoal particles, radiolabelled with [99mTc]diethylenetriaminepentaacetic acid (DTPA) under GMP conditions. Colloidal silicon dioxide was used as a suspending agent. Ocular tolerance was examined following the instillation of each formulation to the eyes of 12 volunteers. The precorneal distribution of both formulations in man was monitored using gamma scintigraphy. Dynamic and static data acquisitions were taken over a period of 150 min after dosing. Carbon particulates suspended in PFD did not show any irritation to the eye. Administration of PFD formulation in man produced a significant increase in ocular retention over a saline formulation (mean residence time (MRT)=157+/-42 and 0.29+/-0.08 min, respectively, P=0.0001). Distribution of the carbon in man followed the same pattern as in a previous reported study in animals. The carbon deposited uniformly along the lid margin in the case of the PFD vehicle, whereas it agglomerated following dosing in the saline vehicle and was ejected from the eye. The novel non-aqueous vehicle system is able to significantly improve the ocular retention of charcoal particles in man and provides a unique distribution of the particles in the eye, which suggests a potential for the PFD system for the treatment of periocular diseases.

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

3D modeling of effects of increased oxygenation and activity concentration in tumors treated with radionuclides and antiangiogenic drugs

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

Lagerloef, Jakob H.; Kindblom, Jon; Bernhardt, Peter

Purpose: Formation of new blood vessels (angiogenesis) in response to hypoxia is a fundamental event in the process of tumor growth and metastatic dissemination. However, abnormalities in tumor neovasculature often induce increased interstitial pressure (IP) and further reduce oxygenation (pO{sub 2}) of tumor cells. In radiotherapy, well-oxygenated tumors favor treatment. Antiangiogenic drugs may lower IP in the tumor, improving perfusion, pO{sub 2} and drug uptake, by reducing the number of malfunctioning vessels in the tissue. This study aims to create a model for quantifying the effects of altered pO{sub 2}-distribution due to antiangiogenic treatment in combination with radionuclide therapy. Methods:more » Based on experimental data, describing the effects of antiangiogenic agents on oxygenation of GlioblastomaMultiforme (GBM), a single cell based 3D model, including 10{sup 10} tumor cells, was developed, showing how radionuclide therapy response improves as tumor oxygenation approaches normal tissue levels. The nuclides studied were {sup 90}Y, {sup 131}I, {sup 177}Lu, and {sup 211}At. The absorbed dose levels required for a tumor control probability (TCP) of 0.990 are compared for three different log-normal pO{sub 2}-distributions: {mu}{sub 1} = 2.483, {sigma}{sub 1} = 0.711; {mu}{sub 2} = 2.946, {sigma}{sub 2} = 0.689; {mu}{sub 3} = 3.689, and {sigma}{sub 3} = 0.330. The normal tissue absorbed doses will, in turn, depend on this. These distributions were chosen to represent the expected oxygen levels in an untreated hypoxic tumor, a hypoxic tumor treated with an anti-VEGF agent, and in normal, fully-oxygenated tissue, respectively. The former two are fitted to experimental data. The geometric oxygen distributions are simulated using two different patterns: one Monte Carlo based and one radially increasing, while keeping the log-normal volumetric distributions intact. Oxygen and activity are distributed, according to the same pattern. Results: As tumor pO{sub 2} approaches normal tissue levels, the therapeutic effect is improved so that the normal tissue absorbed doses can be decreased by more than 95%, while retaining TCP, in the most favorable scenario and by up to about 80% with oxygen levels previously achieved in vivo, when the least favourable oxygenation case is used as starting point. The major difference occurs in poorly oxygenated cells. This is also where the pO{sub 2}-dependence of the oxygen enhancement ratio is maximal. Conclusions: Improved tumor oxygenation together with increased radionuclide uptake show great potential for optimising treatment strategies, leaving room for successive treatments, or lowering absorbed dose to normal tissues, due to increased tumor response. Further studies of the concomitant use of antiangiogenic drugs and radionuclide therapy therefore appear merited.« less

Generation of uniformly distributed dose points for anatomy-based three-dimensional dose optimization methods in brachytherapy.

PubMed

Lahanas, M; Baltas, D; Giannouli, S; Milickovic, N; Zamboglou, N

2000-05-01

We have studied the accuracy of statistical parameters of dose distributions in brachytherapy using actual clinical implants. These include the mean, minimum and maximum dose values and the variance of the dose distribution inside the PTV (planning target volume), and on the surface of the PTV. These properties have been studied as a function of the number of uniformly distributed sampling points. These parameters, or the variants of these parameters, are used directly or indirectly in optimization procedures or for a description of the dose distribution. The accurate determination of these parameters depends on the sampling point distribution from which they have been obtained. Some optimization methods ignore catheters and critical structures surrounded by the PTV or alternatively consider as surface dose points only those on the contour lines of the PTV. D(min) and D(max) are extreme dose values which are either on the PTV surface or within the PTV. They must be avoided for specification and optimization purposes in brachytherapy. Using D(mean) and the variance of D which we have shown to be stable parameters, achieves a more reliable description of the dose distribution on the PTV surface and within the PTV volume than does D(min) and D(max). Generation of dose points on the real surface of the PTV is obligatory and the consideration of catheter volumes results in a realistic description of anatomical dose distributions.

3-D DNA methylation phenotypes correlate with cytotoxicity levels in prostate and liver cancer cell models

PubMed Central

2013-01-01

Background The spatial organization of the genome is being evaluated as a novel indicator of toxicity in conjunction with drug-induced global DNA hypomethylation and concurrent chromatin reorganization. 3D quantitative DNA methylation imaging (3D-qDMI) was applied as a cell-by-cell high-throughput approach to investigate this matter by assessing genome topology through represented immunofluorescent nuclear distribution patterns of 5-methylcytosine (MeC) and global DNA (4,6-diamidino-2-phenylindole = DAPI) in labeled nuclei. Methods Differential progression of global DNA hypomethylation was studied by comparatively dosing zebularine (ZEB) and 5-azacytidine (AZA). Treated and untreated (control) human prostate and liver cancer cells were subjected to confocal scanning microscopy and dedicated 3D image analysis for the following features: differential nuclear MeC/DAPI load and codistribution patterns, cell similarity based on these patterns, and corresponding differences in the topology of low-intensity MeC (LIM) and low in intensity DAPI (LID) sites. Results Both agents generated a high fraction of similar MeC phenotypes across applied concentrations. ZEB exerted similar effects at 10–100-fold higher drug concentrations than its AZA analogue: concentration-dependent progression of global cytosine demethylation, validated by measuring differential MeC levels in repeat sequences using MethyLight, and the concurrent increase in nuclear LIM densities correlated with cellular growth reduction and cytotoxicity. Conclusions 3D-qDMI demonstrated the capability of quantitating dose-dependent drug-induced spatial progression of DNA demethylation in cell nuclei, independent from interphase cell-cycle stages and in conjunction with cytotoxicity. The results support the notion of DNA methylation topology being considered as a potential indicator of causal impacts on chromatin distribution with a conceivable application in epigenetic drug toxicology. PMID:23394161

Distribution patterns of lentic-breeding amphibians in relation to ultraviolet radiation exposure in western North America

USGS Publications Warehouse

Adams, Michael J.; Hossack, B.R.; Knapp, R.A.; Corn, P.S.; Diamond, S.A.; Trenham, P.C.; Fagre, D.B.

2005-01-01

An increase in ultraviolet-B (UV-B) radiation has been posited to be a potential factor in the decline of some amphibian population. This hypothesis has received support from laboratory and field experiments showing that current levels of UV-B can cause embryo mortality in some species, but little research has addressed whether UV-B is influencing the distribution of amphibian populations. We compared patterns of amphibian presence to site-specific estimates of UV-B dose at 683 ponds and lakes in Glacier, Olympic, and Sequoia–Kings Canyon National Parks. All three parks are located in western North America, a region with a concentration of documented amphibian declines. Site-specific daily UV-B dose was estimated using modeled and field-collected data to incorporate the effects of elevation, landscape, and water-column dissolved organic carbon. Of the eight species we examined (Ambystoma gracile, Ambystoma macrodactylum, Bufo boreas, Pseudacris regilla, Rana cascadae, Rana leuteiventris, Rana muscosa, Taricha granulosa), two species (T. granulosa and A. macrodactylum) had quadratic relationships with UV-B that could have resulted from negative UV-B effects. Both species were most likely to occur at moderate UV-B levels. Ambystoma macrodactylum showed this pattern only in Glacier National Park. Occurrence of A. macrodactylum increased as UV-B increased in Olympic National Park despite UV-B levels similar to those recorded in Glacier. We also found marginal support for a negative association with UV-B for P. regilla in one of the two parks where it occurred. We did not find evidence of a negative UV-B effect for any other species. Much more work is still needed to determine whether UV-B, either alone or in concert with other factors, is causing widespread population losses in amphibians.

Algorithm of pulmonary emphysema extraction using thoracic 3D CT images

NASA Astrophysics Data System (ADS)

Saita, Shinsuke; Kubo, Mitsuru; Kawata, Yoshiki; Niki, Noboru; Nakano, Yasutaka; Ohmatsu, Hironobu; Tominaga, Keigo; Eguchi, Kenji; Moriyama, Noriyuki

2007-03-01

Recently, due to aging and smoking, emphysema patients are increasing. The restoration of alveolus which was destroyed by emphysema is not possible, thus early detection of emphysema is desired. We describe a quantitative algorithm for extracting emphysematous lesions and quantitatively evaluate their distribution patterns using low dose thoracic 3-D CT images. The algorithm identified lung anatomies, and extracted low attenuation area (LAA) as emphysematous lesion candidates. Applying the algorithm to thoracic 3-D CT images and then by follow-up 3-D CT images, we demonstrate its potential effectiveness to assist radiologists and physicians to quantitatively evaluate the emphysematous lesions distribution and their evolution in time interval changes.

Gallium uptake in tryptophan-related pulmonary disease

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

Kim, S.M.; Park, C.H.; Intenzo, C.M.

1991-02-01

We describe a patient who developed fever, fatigue, muscle weakness, dyspnea, skin rash, and eosinophilia after taking high doses of tryptophan for insomnia for two years. A gallium-67 scan revealed diffuse increased uptake in the lung and no abnormal uptake in the muscular distribution. Bronchoscopy and biopsy confirmed inflammatory reactions with infiltration by eosinophils, mast cells, and lymphocytes. CT scan showed an interstitial alveolar pattern without fibrosis. EMG demonstrated diffuse myopathy. Muscle biopsy from the right thigh showed an inflammatory myositis with eosinophilic and lymphocytic infiltrations.

Three-Dimensional Radiobiologic Dosimetry: Application of Radiobiologic Modeling to Patient-Specific 3-Dimensional Imaging–Based Internal Dosimetry

PubMed Central

Prideaux, Andrew R.; Song, Hong; Hobbs, Robert F.; He, Bin; Frey, Eric C.; Ladenson, Paul W.; Wahl, Richard L.; Sgouros, George

2010-01-01

Phantom-based and patient-specific imaging-based dosimetry methodologies have traditionally yielded mean organ-absorbed doses or spatial dose distributions over tumors and normal organs. In this work, radiobiologic modeling is introduced to convert the spatial distribution of absorbed dose into biologically effective dose and equivalent uniform dose parameters. The methodology is illustrated using data from a thyroid cancer patient treated with radioiodine. Methods Three registered SPECT/CT scans were used to generate 3-dimensional images of radionuclide kinetics (clearance rate) and cumulated activity. The cumulated activity image and corresponding CT scan were provided as input into an EGSnrc-based Monte Carlo calculation: The cumulated activity image was used to define the distribution of decays, and an attenuation image derived from CT was used to define the corresponding spatial tissue density and composition distribution. The rate images were used to convert the spatial absorbed dose distribution to a biologically effective dose distribution, which was then used to estimate a single equivalent uniform dose for segmented volumes of interest. Equivalent uniform dose was also calculated from the absorbed dose distribution directly. Results We validate the method using simple models; compare the dose-volume histogram with a previously analyzed clinical case; and give the mean absorbed dose, mean biologically effective dose, and equivalent uniform dose for an illustrative case of a pediatric thyroid cancer patient with diffuse lung metastases. The mean absorbed dose, mean biologically effective dose, and equivalent uniform dose for the tumor were 57.7, 58.5, and 25.0 Gy, respectively. Corresponding values for normal lung tissue were 9.5, 9.8, and 8.3 Gy, respectively. Conclusion The analysis demonstrates the impact of radiobiologic modeling on response prediction. The 57% reduction in the equivalent dose value for the tumor reflects a high level of dose nonuniformity in the tumor and a corresponding reduced likelihood of achieving a tumor response. Such analyses are expected to be useful in treatment planning for radionuclide therapy. PMID:17504874

Low Dose Aerosol Fitness at the Innate Phase of Murine Infection Better Predicts Virulence amongst Clinical Strains of Mycobacterium tuberculosis

PubMed Central

Caceres, Neus; Llopis, Isaac; Marzo, Elena; Prats, Clara; Vilaplana, Cristina; de Viedma, Dario Garcia; Samper, Sofía; Lopez, Daniel; Cardona, Pere-Joan

2012-01-01

Background Evaluation of a quick and easy model to determine the intrinsic ability of clinical strains to generate active TB has been set by assuming that this is linked to the fitness of Mycobacterium tuberculosis strain at the innate phase of the infection. Thus, the higher the bacillary load, the greater the possibility of inducting liquefaction, and thus active TB, once the adaptive response is set. Methodology/Principal Findings The virulence of seven clinical Mycobacterium tuberculosis strains isolated in Spain was tested by determining the bacillary concentration in the spleen and lung of mice at weeks 0, 1 and 2 after intravenous (IV) inoculation of 104 CFU, and by determining the growth in vitro until the stationary phase had been reached. Cord distribution automated analysis showed two clear patterns related to the high and low fitness in the lung after IV infection. This pattern was not seen in the in vitro fitness tests, which clearly favored the reference strain (H37Rv). Subsequent determination using a more physiological low-dose aerosol (AER) inoculation with 102 CFU showed a third pattern in which the three best values coincided with the highest dissemination capacity according to epidemiological data. Conclusions/Significance The fitness obtained after low dose aerosol administration in the presence of the innate immune response is the most predictive factor for determining the virulence of clinical strains. This gives support to a mechanism of the induction of active TB derived from the dynamic hypothesis of latent tuberculosis infection. PMID:22235258

Theoretical study of the influence of a heterogeneous activity distribution on intratumoral absorbed dose distribution.

PubMed

Bao, Ande; Zhao, Xia; Phillips, William T; Woolley, F Ross; Otto, Randal A; Goins, Beth; Hevezi, James M

2005-01-01

Radioimmunotherapy of hematopoeitic cancers and micrometastases has been shown to have significant therapeutic benefit. The treatment of solid tumors with radionuclide therapy has been less successful. Previous investigations of intratumoral activity distribution and studies on intratumoral drug delivery suggest that a probable reason for the disappointing results in solid tumor treatment is nonuniform intratumoral distribution coupled with restricted intratumoral drug penetrance, thus inhibiting antineoplastic agents from reaching the tumor's center. This paper describes a nonuniform intratumoral activity distribution identified by limited radiolabeled tracer diffusion from tumor surface to tumor center. This activity was simulated using techniques that allowed the absorbed dose distributions to be estimated using different intratumoral diffusion capabilities and calculated for tumors of varying diameters. The influences of these absorbed dose distributions on solid tumor radionuclide therapy are also discussed. The absorbed dose distribution was calculated using the dose point kernel method that provided for the application of a three-dimensional (3D) convolution between a dose rate kernel function and an activity distribution function. These functions were incorporated into 3D matrices with voxels measuring 0.10 x 0.10 x 0.10 mm3. At this point fast Fourier transform (FFT) and multiplication in frequency domain followed by inverse FFT (iFFT) were used to effect this phase of the dose calculation process. The absorbed dose distribution for tumors of 1, 3, 5, 10, and 15 mm in diameter were studied. Using the therapeutic radionuclides of 131I, 186Re, 188Re, and 90Y, the total average dose, center dose, and surface dose for each of the different tumor diameters were reported. The absorbed dose in the nearby normal tissue was also evaluated. When the tumor diameters exceed 15 mm, a much lower tumor center dose is delivered compared with tumors between 3 and 5 mm in diameter. Based on these findings, the use of higher beta-energy radionuclides, such as 188Re and 90Y is more effective in delivering a higher absorbed dose to the tumor center at tumor diameters around 10 mm.

Monte Carlo simulation of radiation transport and dose deposition from locally released gold nanoparticles labeled with 111In, 177Lu or 90Y incorporated into tissue implantable depots

NASA Astrophysics Data System (ADS)

Lai, Priscilla; Cai, Zhongli; Pignol, Jean-Philippe; Lechtman, Eli; Mashouf, Shahram; Lu, Yijie; Winnik, Mitchell A.; Jaffray, David A.; Reilly, Raymond M.

2017-11-01

Permanent seed implantation (PSI) brachytherapy is a highly conformal form of radiation therapy but is challenged with dose inhomogeneity due to its utilization of low energy radiation sources. Gold nanoparticles (AuNP) conjugated with electron emitting radionuclides have recently been developed as a novel form of brachytherapy and can aid in homogenizing dose through physical distribution of radiolabeled AuNP when injected intratumorally (IT) in suspension. However, the distribution is unpredictable and precise placement of many injections would be difficult. Previously, we reported the design of a nanoparticle depot (NPD) that can be implanted using PSI techniques and which facilitates controlled release of AuNP. We report here the 3D dose distribution resulting from a NPD incorporating AuNP labeled with electron emitters (90Y, 177Lu, 111In) of different energies using Monte Carlo based voxel level dosimetry. The MCNP5 Monte Carlo radiation transport code was used to assess differences in dose distribution from simulated NPD and conventional brachytherapy sources, positioned in breast tissue simulating material. We further compare these dose distributions in mice bearing subcutaneous human breast cancer xenografts implanted with 177Lu-AuNP NPD, or injected IT with 177Lu-AuNP in suspension. The radioactivity distributions were derived from registered SPECT/CT images and time-dependent dose was estimated. Results demonstrated that the dose distribution from NPD reduced the maximum dose 3-fold when compared to conventional seeds. For simulated NPD, as well as NPD implanted in vivo, 90Y delivered the most homogeneous dose distribution. The tumor radioactivity in mice IT injected with 177Lu-AuNP redistributed while radioactivity in the NPD remained confined to the implant site. The dose distribution from radiolabeled AuNP NPD were predictable and concentric in contrast to IT injected radiolabeled AuNP, which provided irregular and temporally variant dose distributions. The use of NPD may serve as an intermediate between PSI and radiation delivered by radiolabeled AuNP by providing a controlled method to improve delivery of prescribed doses as well as homogenize dose from low penetrating electron sources.

Three-dimensional radiotherapy of head and neck and esophageal carcinomas: a monoisocentric treatment technique to achieve improved dose distributions.

PubMed

Ahmad, M; Nath, R

2001-02-20

The specific aim of three-dimensional conformal radiotherapy is to deliver adequate therapeutic radiation dose to the target volume while concomitantly keeping the dose to surrounding and intervening normal tissues to a minimum. The objective of this study is to examine dose distributions produced by various radiotherapy techniques used in managing head and neck tumors when the upper part of the esophagus is also involved. Treatment planning was performed with a three-dimensional (3-D) treatment planning system. Computerized tomographic (CT) scans used by this system to generate isodose distributions and dose-volume histograms were obtained directly from the CT scanner, which is connected via ethernet cabling to the 3-D planning system. These are useful clinical tools for evaluating the dose distribution to the treatment volume, clinical target volume, gross tumor volume, and certain critical organs. Using 6 and 18 MV photon beams, different configurations of standard treatment techniques for head and neck and esophageal carcinoma were studied and the resulting dose distributions were analyzed. Film validation dosimetry in solid-water phantom was performed to assess the magnitude of dose inhomogeneity at the field junction. Real-time dose measurements on patients using diode dosimetry were made and compared with computed dose values. With regard to minimizing radiation dose to surrounding structures (i.e., lung, spinal cord, etc.), the monoisocentric technique gave the best isodose distributions in terms of dose uniformity. The mini-mantle anterior-posterior/posterior-anterior (AP/PA) technique produced grossly non-uniform dose distribution with excessive hot spots. The dose measured on the patient during the treatment agrees to within +/- 5 % with the computed dose. The protocols presented in this work for simulation, immobilization and treatment planning of patients with head and neck and esophageal tumors provide the optimum dose distributions in the target volume with reduced irradiation of surrounding non-target tissues, and can be routinely implemented in a radiation oncology department. The presence of a real-time dose-measuring system plays an important role in verifying the actual delivery of radiation dose.

Spatial distributions of dose enhancement around a gold nanoparticle at several depths of proton Bragg peak

NASA Astrophysics Data System (ADS)

Kwon, Jihun; Sutherland, Kenneth; Hashimoto, Takayuki; Shirato, Hiroki; Date, Hiroyuki

2016-10-01

Gold nanoparticles (GNPs) have been recognized as a promising candidate for a radiation sensitizer. A proton beam incident on a GNP can produce secondary electrons, resulting in an enhancement of the dose around the GNP. However, little is known about the spatial distribution of dose enhancement around the GNP, especially in the direction along the incident proton. The purpose of this study is to determine the spatial distribution of dose enhancement by taking the incident direction into account. Two steps of calculation were conducted using the Geant4 Monte Carlo simulation toolkit. First, the energy spectra of 100 and 195 MeV protons colliding with a GNP were calculated at the Bragg peak and three other depths around the peak in liquid water. Second, the GNP was bombarded by protons with the obtained energy spectra. Radial dose distributions were computed along the incident beam direction. The spatial distributions of the dose enhancement factor (DEF) and subtracted dose (Dsub) were then evaluated. The spatial DEF distributions showed hot spots in the distal radial region from the proton beam axis. The spatial Dsub distribution isotropically spread out around the GNP. Low energy protons caused higher and wider dose enhancement. The macroscopic dose enhancement in clinical applications was also evaluated. The results suggest that the consideration of the spatial distribution of GNPs in treatment planning will maximize the potential of GNPs.

Modeling Freedom From Progression for Standard-Risk Medulloblastoma: A Mathematical Tumor Control Model With Multiple Modes of Failure

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

Brodin, N. Patrik, E-mail: nils.patrik.brodin@rh.dk; Niels Bohr Institute, University of Copenhagen, Copenhagen; Vogelius, Ivan R.

2013-10-01

Purpose: As pediatric medulloblastoma (MB) is a relatively rare disease, it is important to extract the maximum information from trials and cohort studies. Here, a framework was developed for modeling tumor control with multiple modes of failure and time-to-progression for standard-risk MB, using published pattern of failure data. Methods and Materials: Outcome data for standard-risk MB published after 1990 with pattern of relapse information were used to fit a tumor control dose-response model addressing failures in both the high-dose boost volume and the elective craniospinal volume. Estimates of 5-year event-free survival from 2 large randomized MB trials were used tomore » model the time-to-progression distribution. Uncertainty in freedom from progression (FFP) was estimated by Monte Carlo sampling over the statistical uncertainty in input data. Results: The estimated 5-year FFP (95% confidence intervals [CI]) for craniospinal doses of 15, 18, 24, and 36 Gy while maintaining 54 Gy to the posterior fossa was 77% (95% CI, 70%-81%), 78% (95% CI, 73%-81%), 79% (95% CI, 76%-82%), and 80% (95% CI, 77%-84%) respectively. The uncertainty in FFP was considerably larger for craniospinal doses below 18 Gy, reflecting the lack of data in the lower dose range. Conclusions: Estimates of tumor control and time-to-progression for standard-risk MB provides a data-driven setting for hypothesis generation or power calculations for prospective trials, taking the uncertainties into account. The presented methods can also be applied to incorporate further risk-stratification for example based on molecular biomarkers, when the necessary data become available.« less

Rapid phase-correlated rescanning irradiation improves treatment time in carbon-ion scanning beam treatment under irregular breathing

NASA Astrophysics Data System (ADS)

Mori, Shinichiro; Furukawa, Takuji

2016-05-01

To shorten treatment time in pencil beam scanning irradiation, we developed rapid phase-controlled rescanning (rPCR), which irradiates two or more isoenergy layers in a single gating window. Here, we evaluated carbon-ion beam dose distribution with rapid and conventional PCR (cPCR). 4 dimensional computed tomography (4DCT) imaging was performed on 12 subjects with lung or liver tumors. To compensate for intrafractional range variation, the field-specific target volume (FTV) was calculated using 4DCT within the gating window (T20-T80). We applied an amplitude-based gating strategy, in which the beam is on when the tumor is within the gating window defined by treatment planning. Dose distributions were calculated for layered phase-controlled rescanning under an irregular respiratory pattern, although a single 4DCT data set was used. The number of rescannings was eight times. The prescribed doses were 48 Gy(RBE)/1 fr (where RBE is relative biological effectiveness) delivered via four beam ports to the FTV for the lung cases and 45 Gy(RBE)/2 fr delivered via two beam ports to the FTV for the liver cases. In the liver cases, the accumulated dose distributions showed an increased magnitude of hot/cold spots with rPCR compared with cPCR. The results of the dose assessment metrics for the cPCR and rPCR were very similar. The D 95, D max, and D min values (cPCR/rPCR) averaged over all the patients were 96.3  ±  0.9%/96.0  ±  1.2%, 107.3  ±  3.6%/107.1  ±  2.9%, and 88.8  ±  3.2%/88.1  ±  3.1%, respectively. The treatment times in cPCR and rPCR were 110.7 s and 53.5 s, respectively. rPCR preserved dose conformation under irregular respiratory motion and reduced the total treatment time compared with cPCR.

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

Devpura, S; Li, H; Liu, C

Purpose: To correlate dose distributions computed using six algorithms for recurrent early stage non-small cell lung cancer (NSCLC) patients treated with stereotactic body radiotherapy (SBRT), with outcome (local failure). Methods: Of 270 NSCLC patients treated with 12Gyx4, 20 were found to have local recurrence prior to the 2-year time point. These patients were originally planned with 1-D pencil beam (1-D PB) algorithm. 4D imaging was performed to manage tumor motion. Regions of local failures were determined from follow-up PET-CT scans. Follow-up CT images were rigidly fused to the planning CT (pCT), and recurrent tumor volumes (Vrecur) were mapped to themore » pCT. Dose was recomputed, retrospectively, using five algorithms: 3-D PB, collapsed cone convolution (CCC), anisotropic analytical algorithm (AAA), AcurosXB, and Monte Carlo (MC). Tumor control probability (TCP) was computed using the Marsden model (1,2). Patterns of failure were classified as central, in-field, marginal, and distant for Vrecur ≥95% of prescribed dose, 95–80%, 80–20%, and ≤20%, respectively (3). Results: Average PTV D95 (dose covering 95% of the PTV) for 3-D PB, CCC, AAA, AcurosXB, and MC relative to 1-D PB were 95.3±2.1%, 84.1±7.5%, 84.9±5.7%, 86.3±6.0%, and 85.1±7.0%, respectively. TCP values for 1-D PB, 3-D PB, CCC, AAA, AcurosXB, and MC were 98.5±1.2%, 95.7±3.0, 79.6±16.1%, 79.7±16.5%, 81.1±17.5%, and 78.1±20%, respectively. Patterns of local failures were similar for 1-D and 3D PB plans, which predicted that the majority of failures occur in centraldistal regions, with only ∼15% occurring distantly. However, with convolution/superposition and MC type algorithms, the majority of failures (65%) were predicted to be distant, consistent with the literature. Conclusion: Based on MC and convolution/superposition type algorithms, average PTV D95 and TCP were ∼15% lower than the planned 1-D PB dose calculation. Patterns of failure results suggest that MC and convolution/superposition type algorithms predict different outcomes for patterns of failure relative to PB algorithms. Work supported in part by Varian Medical Systems, Palo Alto, CA.« less

Assessing correlations between the spatial distribution of the dose to the rectal wall and late rectal toxicity after prostate radiotherapy: an analysis of data from the MRC RT01 trial (ISRCTN 47772397)

NASA Astrophysics Data System (ADS)

Buettner, Florian; Gulliford, Sarah L.; Webb, Steve; Sydes, Matthew R.; Dearnaley, David P.; Partridge, Mike

2009-11-01

Many studies have been performed to assess correlations between measures derived from dose-volume histograms and late rectal toxicities for radiotherapy of prostate cancer. The purpose of this study was to quantify correlations between measures describing the shape and location of the dose distribution and different outcomes. The dose to the rectal wall was projected on a two-dimensional map. In order to characterize the dose distribution, its centre of mass, longitudinal and lateral extent, and eccentricity were calculated at different dose levels. Furthermore, the dose-surface histogram (DSH) was determined. Correlations between these measures and seven clinically relevant rectal-toxicity endpoints were quantified by maximally selected standardized Wilcoxon rank statistics. The analysis was performed using data from the RT01 prostate radiotherapy trial. For some endpoints, the shape of the dose distribution is more strongly correlated with the outcome than simple DSHs. Rectal bleeding was most strongly correlated with the lateral extent of the dose distribution. For loose stools, the strongest correlations were found for longitudinal extent; proctitis was most strongly correlated with DSH. For the other endpoints no statistically significant correlations could be found. The strengths of the correlations between the shape of the dose distribution and outcome differed considerably between the different endpoints. Due to these significant correlations, it is desirable to use shape-based tools in order to assess the quality of a dose distribution.

A Bayesian Dose-finding Design for Oncology Clinical Trials of Combinational Biological Agents

PubMed Central

Cai, Chunyan; Yuan, Ying; Ji, Yuan

2013-01-01

Treating patients with novel biological agents is becoming a leading trend in oncology. Unlike cytotoxic agents, for which efficacy and toxicity monotonically increase with dose, biological agents may exhibit non-monotonic patterns in their dose-response relationships. Using a trial with two biological agents as an example, we propose a dose-finding design to identify the biologically optimal dose combination (BODC), which is defined as the dose combination of the two agents with the highest efficacy and tolerable toxicity. A change-point model is used to reflect the fact that the dose-toxicity surface of the combinational agents may plateau at higher dose levels, and a flexible logistic model is proposed to accommodate the possible non-monotonic pattern for the dose-efficacy relationship. During the trial, we continuously update the posterior estimates of toxicity and efficacy and assign patients to the most appropriate dose combination. We propose a novel dose-finding algorithm to encourage sufficient exploration of untried dose combinations in the two-dimensional space. Extensive simulation studies show that the proposed design has desirable operating characteristics in identifying the BODC under various patterns of dose-toxicity and dose-efficacy relationships. PMID:24511160

Anderson localization of graphene by helium ion irradiation

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

Naitou, Y., E-mail: yu-naitou@aist.go.jp; Ogawa, S.

Irradiation of a single-layer graphene (SLG) with accelerated helium ions (He{sup +}) controllably generates defect distributions, which create a charge carrier scattering source within the SLG. We report direct experimental observation of metal-insulator transition in SLG on SiO{sub 2}/Si substrates induced by Anderson localization. This transition was investigated using scanning capacitance microscopy by monitoring the He{sup +} dose conditions on the SLG. The experimental data show that a defect density of more than ∼1.2% induced Anderson localization. We also investigated the localization length by determining patterned placement of the defects and estimated the length to be several dozen nanometers. Thesemore » findings provide valuable insight for patterning and designing graphene-based nanostructures using helium ion microscopy.« less

Differential pencil beam dose computation model for photons.

PubMed

Mohan, R; Chui, C; Lidofsky, L

1986-01-01

Differential pencil beam (DPB) is defined as the dose distribution relative to the position of the first collision, per unit collision density, for a monoenergetic pencil beam of photons in an infinite homogeneous medium of unit density. We have generated DPB dose distribution tables for a number of photon energies in water using the Monte Carlo method. The three-dimensional (3D) nature of the transport of photons and electrons is automatically incorporated in DPB dose distributions. Dose is computed by evaluating 3D integrals of DPB dose. The DPB dose computation model has been applied to calculate dose distributions for 60Co and accelerator beams. Calculations for the latter are performed using energy spectra generated with the Monte Carlo program. To predict dose distributions near the beam boundaries defined by the collimation system as well as blocks, we utilize the angular distribution of incident photons. Inhomogeneities are taken into account by attenuating the primary photon fluence exponentially utilizing the average total linear attenuation coefficient of intervening tissue, by multiplying photon fluence by the linear attenuation coefficient to yield the number of collisions in the scattering volume, and by scaling the path between the scattering volume element and the computation point by an effective density.

Testing the enemy release hypothesis: abundance and distribution patterns of helminth communities in grey mullets (Teleostei: Mugilidae) reveal the success of invasive species.

PubMed

Sarabeev, Volodimir; Balbuena, Juan Antonio; Morand, Serge

2017-09-01

The abundance and aggregation patterns of helminth communities of two grey mullet hosts, Liza haematocheilus and Mugil cephalus, were studied across 14 localities in Atlantic and Pacific marine areas. The analysis matched parasite communities of (i) L. haematocheilus across its native and introduced populations (Sea of Japan and Sea of Azov, respectively) and (ii) the introduced population of L. haematocheilus with native populations of M. cephalus (Mediterranean, Azov-Black and Japan Seas). The total mean abundance (TMA), as a feature of the infection level in helminth communities, and slope b of the Taylor's power law, as a measure of parasite aggregation at the infra and component-community levels, were estimated and compared between host species and localities using ANOVA. The TMA of the whole helminth community in the introduced population of L. haematocheilus was over 15 times lower than that of the native population, but the difference was less pronounced for carried (monogeneans) than for acquired (adult and larval digeneans) parasite communities. Similar to the abundance pattern, the species distribution in communities from the invasive population of L. haematocheilus was less aggregated than from its native population for endoparasitic helminths, including adult and larval digeneans, while monogeneans showed a similar pattern of distribution in the compared populations of L. haematocheilus. The aggregation level of the whole helminth community, endoparasitic helminths, adult and larval digeneans was lower in the invasive host species in comparison with native ones as shown by differences in the slope b. An important theoretical implication from this study is that the pattern of parasite aggregation may explain the success of invasive species in ecosystems. Because the effects of parasites on host mortality are likely dose-dependent, the proportion of susceptible host individuals in invasive species is expected to be lower, as the helminth distribution in the invasive host was featured by a higher number of uninfected hosts and a shorter distribution tail when compared with native species. Copyright © 2017 Australian Society for Parasitology. Published by Elsevier Ltd. All rights reserved.

Three-dimensional electron diffraction of plant light-harvesting complex

PubMed Central

Wang, Da Neng; Kühlbrandt, Werner

1992-01-01

Electron diffraction patterns of two-dimensional crystals of light-harvesting chlorophyll a/b-protein complex (LHC-II) from photosynthetic membranes of pea chloroplasts, tilted at different angles up to 60°, were collected to 3.2 Å resolution at -125°C. The reflection intensities were merged into a three-dimensional data set. The Friedel R-factor and the merging R-factor were 21.8 and 27.6%, respectively. Specimen flatness and crystal size were critical for recording electron diffraction patterns from crystals at high tilts. The principal sources of experimental error were attributed to limitations of the number of unit cells contributing to an electron diffraction pattern, and to the critical electron dose. The distribution of strong diffraction spots indicated that the three-dimensional structure of LHC-II is less regular than that of other known membrane proteins and is not dominated by a particular feature of secondary structure. ImagesFIGURE 1FIGURE 2 PMID:19431817

Development of a patient-specific 3D dose evaluation program for QA in radiation therapy

NASA Astrophysics Data System (ADS)

Lee, Suk; Chang, Kyung Hwan; Cao, Yuan Jie; Shim, Jang Bo; Yang, Dae Sik; Park, Young Je; Yoon, Won Sup; Kim, Chul Yong

2015-03-01

We present preliminary results for a 3-dimensional dose evaluation software system ( P DRESS, patient-specific 3-dimensional dose real evaluation system). Scanned computed tomography (CT) images obtained by using dosimetry were transferred to the radiation treatment planning system (ECLIPSE, VARIAN, Palo Alto, CA) where the intensity modulated radiation therapy (IMRT) nasopharynx plan was designed. We used a 10 MV photon beam (CLiX, VARIAN, Palo Alto, CA) to deliver the nasopharynx treatment plan. After irradiation, the TENOMAG dosimeter was scanned using a VISTA ™ scanner. The scanned data were reconstructed using VistaRecon software to obtain a 3D dose distribution of the optical density. An optical-CT scanner was used to readout the dose distribution in the gel dosimeter. Moreover, we developed the P DRESS by using Flatform, which were developed by our group, to display the 3D dose distribution by loading the DICOM RT data which are exported from the radiotherapy treatment plan (RTP) and the optical-CT reconstructed VFF file, into the independent P DRESS with an ioniz ation chamber and EBT film was used to compare the dose distribution calculated from the RTP with that measured by using a gel dosimeter. The agreement between the normalized EBT, the gel dosimeter and RTP data was evaluated using both qualitative and quantitative methods, such as the isodose distribution, dose difference, point value, and profile. The profiles showed good agreement between the RTP data and the gel dosimeter data, and the precision of the dose distribution was within ±3%. The results from this study showed significantly discrepancies between the dose distribution calculated from the treatment plan and the dose distribution measured by a TENOMAG gel and by scanning with an optical CT scanner. The 3D dose evaluation software system ( P DRESS, patient specific dose real evaluation system), which were developed in this study evaluates the accuracies of the three-dimensional dose distributions. Further applications of the system utility are expected to result from future studies.

SU-E-I-15: Quantitative Evaluation of Dose Distributions From Axial, Helical and Cone-Beam CT Imaging by Measurement Using a Two-Dimensional Diode-Array Detector

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

Chacko, M; Aldoohan, S; Sonnad, J

2015-06-15

Purpose: To evaluate quantitatively dose distributions from helical, axial and cone-beam CT clinical imaging techniques by measurement using a two-dimensional (2D) diode-array detector. Methods: 2D-dose distributions from selected clinical protocols used for axial, helical and cone-beam CT imaging were measured using a diode-array detector (MapCheck2). The MapCheck2 is composed from solid state diode detectors that are arranged in horizontal and vertical lines with a spacing of 10 mm. A GE-Light-Speed CT-simulator was used to acquire axial and helical CT images and a kV on-board-imager integrated with a Varian TrueBeam-STx machine was used to acquire cone-beam CT (CBCT) images. Results: Themore » dose distributions from axial, helical and cone-beam CT were non-uniform over the region-of-interest with strong spatial and angular dependence. In axial CT, a large dose gradient was measured that decreased from lateral sides to the middle of the phantom due to large superficial dose at the side of the phantom in comparison with larger beam attenuation at the center. The dose decreased at the superior and inferior regions in comparison to the center of the phantom in axial CT. An asymmetry was found between the right-left or superior-inferior sides of the phantom which possibly to angular dependence in the dose distributions. The dose level and distribution varied from one imaging technique into another. For the pelvis technique, axial CT deposited a mean dose of 3.67 cGy, helical CT deposited a mean dose of 1.59 cGy, and CBCT deposited a mean dose of 1.62 cGy. Conclusions: MapCheck2 provides a robust tool to measure directly 2D-dose distributions for CT imaging with high spatial resolution detectors in comparison with ionization chamber that provides a single point measurement or an average dose to the phantom. The dose distributions measured with MapCheck2 consider medium heterogeneity and can represent specific patient dose.« less

The effects of small field dosimetry on the biological models used in evaluating IMRT dose distributions

NASA Astrophysics Data System (ADS)

Cardarelli, Gene A.

The primary goal in radiation oncology is to deliver lethal radiation doses to tumors, while minimizing dose to normal tissue. IMRT has the capability to increase the dose to the targets and decrease the dose to normal tissue, increasing local control, decrease toxicity and allow for effective dose escalation. This advanced technology does present complex dose distributions that are not easily verified. Furthermore, the dose inhomogeneity caused by non-uniform dose distributions seen in IMRT treatments has caused the development of biological models attempting to characterize the dose-volume effect in the response of organized tissues to radiation. Dosimetry of small fields can be quite challenging when measuring dose distributions for high-energy X-ray beams used in IMRT. The proper modeling of these small field distributions is essential in reproducing accurate dose for IMRT. This evaluation was conducted to quantify the effects of small field dosimetry on IMRT plan dose distributions and the effects on four biological model parameters. The four biological models evaluated were: (1) the generalized Equivalent Uniform Dose (gEUD), (2) the Tumor Control Probability (TCP), (3) the Normal Tissue Complication Probability (NTCP) and (4) the Probability of uncomplicated Tumor Control (P+). These models are used to estimate local control, survival, complications and uncomplicated tumor control. This investigation compares three distinct small field dose algorithms. Dose algorithms were created using film, small ion chamber, and a combination of ion chamber measurements and small field fitting parameters. Due to the nature of uncertainties in small field dosimetry and the dependence of biological models on dose volume information, this examination quantifies the effects of small field dosimetry techniques on radiobiological models and recommends pathways to reduce the errors in using these models to evaluate IMRT dose distributions. This study demonstrates the importance of valid physical dose modeling prior to the use of biological modeling. The success of using biological function data, such as hypoxia, in clinical IMRT planning will greatly benefit from the results of this study.

[Clinical evaluation of heavy-particle radiotherapy using dose volume histogram (DVH)].

PubMed

Terahara, A; Nakano, T; Tsujii, H

1998-01-01

Radiotherapy with heavy particles such as proton and heavy-charged particles is a promising modality for treatment of localized malignant tumors because of the good dose distribution. A dose calculation and radiotherapy planning system which is essential for this kind of treatment has been developed in recent years. It has the capability to compute the dose volume histogram (DVH) which contains dose-volume information for the target volume and other interesting volumes. Recently, DVH is commonly used to evaluate and compare dose distributions in radiotherapy with both photon and heavy particles, and it shows that a superior dose distribution is obtained in heavy particle radiotherapy. DVH is also utilized for the evaluation of dose distribution related to clinical outcomes. Besides models such as normal tissue complication probability (NTCP) and tumor control probability (TCP), which can be calculated from DVH are proposed by several authors, they are applied to evaluate dose distributions themselves and to evaluate them in relation to clinical results. DVH is now a useful and important tool, but further studies are needed to use DVH and these models practically for clinical evaluation of heavy-particle radiotherapy.

Optimization of the temporal pattern of applied dose for a single fraction of radiation: Implications for radiation therapy

NASA Astrophysics Data System (ADS)

Altman, Michael B.

The increasing prevalence of intensity modulated radiation therapy (IMRT) as a treatment modality has led to a renewed interest in the potential for interaction between prolonged treatment time, as frequently associated with IMRT, and the underlying radiobiology of the irradiated tissue. A particularly relevant aspect of radiobiology is cell repair capacity, which influences cell survival, and thus directly relates to the ability to control tumors and spare normal tissues. For a single fraction of radiation, the linear quadratic (LQ) model is commonly used to relate the radiation dose to the fraction of cells surviving. The LQ model implies a dependence on two time-related factors which correlate to radiobiological effects: the duration of radiation application, and the functional form of how the dose is applied over that time (the "temporal pattern of applied dose"). Although the former has been well studied, the latter has not. Thus, the goal of this research is to investigate the impact of the temporal pattern of applied dose on the survival of human cells and to explore how the manipulation of this temporal dose pattern may be incorporated into an IMRT-based radiation therapy treatment planning scheme. The hypothesis is that the temporal pattern of applied dose in a single fraction of radiation can be optimized to maximize or minimize cell kill. Furthermore, techniques which utilize this effect could have clinical ramifications. In situations where increased cell kill is desirable, such as tumor control, or limiting the degree of cell kill is important, such as the sparing of normal tissue, temporal sequences of dose which maximize or minimize cell kill (temporally "optimized" sequences) may provide greater benefit than current clinically used radiation patterns. In the first part of this work, an LQ-based modeling analysis of effects of the temporal pattern of dose on cell kill is performed. Through this, patterns are identified for maximizing cell kill for a given radiation pattern by concentrating the highest doses in the middle of a fraction (a "Triangle" pattern), or minimizing cell kill by placing the highest doses near the beginning and end (a "V-shaped" pattern). The conditions under which temporal optimization effects are most acute are also identified: irradiation of low alpha/beta tissues, long fraction durations, and high doses/fx. An in vitro study is then performed which verifies that the temporal effects and trends predicted by the modeling study are clearly manifested in human cells. Following this a phantom which could allow similar in vitro radiobiological experiments in a 3-dimensional clinically-based environment is designed, created, and dosimetrically assessed using TLDs, film, and biological assay-based techniques. The phantom is found to be a useful and versatile tool for such experiments. A scheme for utilizing the phantom in a clinical treatment environment is then developed. This includes a demonstration of prototype methods for optimizing the temporal pattern of applied dose in clinical IMRT plans to manipulate tissue-dependent effects. Looking toward future experimental validation of such plans using the phantom, an analysis of the suitability of biological assays for use in phantom-based in vitro experiments is performed. Finally, a discussion is provided about the steps necessary to integrate temporal optimization into in vivo experiments and ultimately into a clinical radiation therapy environment. If temporal optimization is ultimately shown to have impact in vivo, the successful implementation of the methods developed in this study could enhance the efficacy and care of thousands of patients receiving radiotherapy.

SU-F-BRD-16: Under Dose Regions Recalculated by Monte Carlo Cannot Predict the Local Failure for NSCLC Patients Treated with SBRT

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

Liu, H; Cherian, S; Stephans, K

2014-06-15

Purpose: To investigate whether Monte Carlo (MC) recalculated dose distributions can predict the geometric location of the recurrence for nonsmall cell lung cancer (NSCLC) patients treated with stereotactic body radiotherapy (SBRT). Methods: Thirty NSCLC patients with local recurrence were retrospectively selected for this study. The recurred gross target volumes (rGTV) were delineated on the follow-up CT/PET images and then rigidly transferred via imaging fusion to the original planning CTs. Failure pattern was defined according to the overlap between the rGTV and planning GTV (pGTV) as: (a) in-field failure (≥80%), (b) marginal failure (20%–80%), and (c) out-of-field failure (≤20%). All clinicalmore » plans were calculated initially with pencil beam (PB) with or without heterogeneity correction dependent of protocols. These plans were recalculated with MC with heterogeneity correction. Because of non-uniform dose distributions in the rGTVs, the rGTVs were further divided into four regions: inside the pGTV (GTVin), inside the PTV (PTVin), outside the pGTV (GTVout), and outside the PTV (PTVout). The mean doses to these regions were reported and analyzed separately. Results: Among 30 patients, 10 patients had infield recurrences, 15 marginal and 5 out-of-field failures. With MC calculations, D95 and D99 of the PTV were reduced by (10.6 ± 7.4)% and (11.7 ± 7.9)%. The average MC calculated mean doses of GTVin, GTVout, PTVin and PTVout were 48.2 ± 5.3 Gy, 48.2 ± 5.5 Gy, 46.3 ± 6.2 Gy and 46.6 ± 5.6 Gy, respectively. No significant dose differences between GTVin and GTVout (p=0.65), PTVin and PTVout (p=0.19) were observed, using the paired students t-test. Conclusion: Although the PB calculations underestimated the tumor target doses, the geometric location of the recurrence did not correlate with the mean doses of subsections of the recurrent GTV. Under dose regions recalculated by MC cannot predict the local failure for NSCLC patients treated with SBRT.« less

Impact of temporal probability in 4D dose calculation for lung tumors.

PubMed

Rouabhi, Ouided; Ma, Mingyu; Bayouth, John; Xia, Junyi

2015-11-08

The purpose of this study was to evaluate the dosimetric uncertainty in 4D dose calculation using three temporal probability distributions: uniform distribution, sinusoidal distribution, and patient-specific distribution derived from the patient respiratory trace. Temporal probability, defined as the fraction of time a patient spends in each respiratory amplitude, was evaluated in nine lung cancer patients. Four-dimensional computed tomography (4D CT), along with deformable image registration, was used to compute 4D dose incorporating the patient's respiratory motion. First, the dose of each of 10 phase CTs was computed using the same planning parameters as those used in 3D treatment planning based on the breath-hold CT. Next, deformable image registration was used to deform the dose of each phase CT to the breath-hold CT using the deformation map between the phase CT and the breath-hold CT. Finally, the 4D dose was computed by summing the deformed phase doses using their corresponding temporal probabilities. In this study, 4D dose calculated from the patient-specific temporal probability distribution was used as the ground truth. The dosimetric evaluation matrix included: 1) 3D gamma analysis, 2) mean tumor dose (MTD), 3) mean lung dose (MLD), and 4) lung V20. For seven out of nine patients, both uniform and sinusoidal temporal probability dose distributions were found to have an average gamma passing rate > 95% for both the lung and PTV regions. Compared with 4D dose calculated using the patient respiratory trace, doses using uniform and sinusoidal distribution showed a percentage difference on average of -0.1% ± 0.6% and -0.2% ± 0.4% in MTD, -0.2% ± 1.9% and -0.2% ± 1.3% in MLD, 0.09% ± 2.8% and -0.07% ± 1.8% in lung V20, -0.1% ± 2.0% and 0.08% ± 1.34% in lung V10, 0.47% ± 1.8% and 0.19% ± 1.3% in lung V5, respectively. We concluded that four-dimensional dose computed using either a uniform or sinusoidal temporal probability distribution can approximate four-dimensional dose computed using the patient-specific respiratory trace.

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

Mwidu, U; Devic, S; Shehadeh, M

Purpose: A retrospective comparison of dose distributions achievable by High dose rate brachytherapy (HDRBT), Helical TomoTherapy (TOMO), CyberKnife (CK) and RapidArc (RA) in locally advanced inoperable cervical cancer patients is presented. Methods: Five patients with advanced stage cervical carcinoma were selected for this study after a full course of external beam radiotherapy (EBRT), chemotherapy and HDR Brachytherapy. To highlight any significant similarities/differences in dose distributions, high-risk clinical target volume (HRCTV) coverage, organs at risk (OAR) sparing, and machine specific delivery limitations, we used D90 (dose received by 90% of the volume) as the parameter for HRCTV coverage as recommended bymore » the GEC-ESTRO Working Group. We also compared both integral and differential dose volume histograms (DVH) between different dose distributions treatment modalities for HRCTV and OAR. Results: TOMO and RA provided the most conformal dose distributions to HRCTV. Median doses (in Gy) to organs at risk were; for rectal wall: 1.7±0.6, 2.5±0.6,1.2±0.3, and 1.5±0.6, and for bladder wall: 1.6±0.1, 2.4±0.4, 0.8±0.6, and 1.5±0.5, for HDRBT, TOMO, CK, and RA, respectively. Conclusion: Contemporary EBRT modalities might be able to replace brachytherapy treatments for cervix cancer. While brachytherapy dose distributions feature high dose gradients, EBRT modalities provide highly conformal dose distributions to the target. However, it is still not clear whether a highly conformal dose or high gradient dose is more clinically relevant for the HRCTV in cervix cancer patients.« less

MO-FG-BRA-05: Dosimetric and Radiobiological Validation of Respiratory Gating in Conventional and Hypofractionated Radiotherapy of the Lung: Effect of Dose, Dose Rate, Gating Window and Breathing Pattern

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

Cervino, L; Soultan, D; Pettersson, N

2016-06-15

Purpose: to evaluate the dosimetric and radiobiological consequences from having different gating windows, dose rates, and breathing patterns in gated VMAT lung radiotherapy. Methods: A novel 3D-printed moving phantom with central high and peripheral low tracer uptake regions was 4D FDG-PET/CT-scanned using ideal, patient-specific regular, and irregular breathing patterns. A scan of the stationary phantom was obtained as a reference. Target volumes corresponding to different uptake regions were delineated. Simultaneous integrated boost (SIB) 6 MV VMAT plans were produced for conventional and hypofractionated radiotherapy, using 30–70 and 100% cycle gating scenarios. Prescribed doses were 200 cGy with SIB to 240more » cGy to high uptake volume for conventional, and 800 with SIB to 900 cGy for hypofractionated plans. Dose rates of 600 MU/min (conventional and hypofractionated) and flattening filter free 1400 MU/min (hypofractionated) were used. Ion chamber measurements were performed to verify delivered doses. Vials with A549 cells placed in locations matching ion chamber measurements were irradiated using the same plans to measure clonogenic survival. Differences in survival for the different doses, dose rates, gating windows, and breathing patterns were analyzed. Results: Ion chamber measurements agreed within 3% of the planned dose, for all locations, breathing patterns and gating windows. Cell survival depended on dose alone, and not on gating window, breathing pattern, MU rate, or delivery time. The surviving fraction varied from approximately 40% at 2Gy to 1% for 9 Gy and was within statistical uncertainty relative to that observed for the stationary phantom. Conclusions: Use of gated VMAT in PET-driven SIB radiotherapy was validated using ion chamber measurements and cell survival assays for conventional and hypofractionated radiotherapy.« less

Oscillation patterns are enhanced and firing threshold is lowered in medullary respiratory neuron discharges by threshold doses of a μ-opioid receptor agonist

PubMed Central

Mifflin, Steve W.

2017-01-01

μ-Opioid receptors are distributed widely in the brain stem respiratory network, and opioids with selectivity for μ-type receptors slow in vivo respiratory rhythm in lowest effective doses. Several studies have reported μ-opioid receptor effects on the three-phase rhythm of respiratory neurons, but there are until now no reports of opioid effects on oscillatory activity within respiratory discharges. In this study, effects of the μ-opioid receptor agonist fentanyl on spike train discharge properties of several different types of rhythm-modulating medullary respiratory neuron discharges were analyzed. Doses of fentanyl that were just sufficient for prolongation of discharges and slowing of the three-phase respiratory rhythm also produced pronounced enhancement of spike train properties. Oscillation and burst patterns detected by autocorrelation measurements were greatly enhanced, and interspike intervals were prolonged. Spike train properties under control conditions and after fentanyl were uniform within each experiment, but varied considerably between experiments, which might be related to variability in acid-base balance in the brain stem extracellular fluid. Discharge threshold was shifted to more negative levels of membrane potential. The effects on threshold are postulated to result from opioid-mediated disinhibition and postsynaptic enhancement of N-methyl-d- aspartate receptor current. Lowering of firing threshold, enhancement of spike train oscillations and bursts and prolongation of discharges by lowest effective doses of fentanyl could represent compensatory adjustments in the brain stem respiratory network to override opioid blunting of CO2/pH chemosensitivity. PMID:28202437

Oscillation patterns are enhanced and firing threshold is lowered in medullary respiratory neuron discharges by threshold doses of a μ-opioid receptor agonist.

PubMed

Lalley, Peter M; Mifflin, Steve W

2017-05-01

μ-Opioid receptors are distributed widely in the brain stem respiratory network, and opioids with selectivity for μ-type receptors slow in vivo respiratory rhythm in lowest effective doses. Several studies have reported μ-opioid receptor effects on the three-phase rhythm of respiratory neurons, but there are until now no reports of opioid effects on oscillatory activity within respiratory discharges. In this study, effects of the μ-opioid receptor agonist fentanyl on spike train discharge properties of several different types of rhythm-modulating medullary respiratory neuron discharges were analyzed. Doses of fentanyl that were just sufficient for prolongation of discharges and slowing of the three-phase respiratory rhythm also produced pronounced enhancement of spike train properties. Oscillation and burst patterns detected by autocorrelation measurements were greatly enhanced, and interspike intervals were prolonged. Spike train properties under control conditions and after fentanyl were uniform within each experiment, but varied considerably between experiments, which might be related to variability in acid-base balance in the brain stem extracellular fluid. Discharge threshold was shifted to more negative levels of membrane potential. The effects on threshold are postulated to result from opioid-mediated disinhibition and postsynaptic enhancement of N -methyl-d- aspartate receptor current. Lowering of firing threshold, enhancement of spike train oscillations and bursts and prolongation of discharges by lowest effective doses of fentanyl could represent compensatory adjustments in the brain stem respiratory network to override opioid blunting of CO 2 /pH chemosensitivity. Copyright © 2017 the American Physiological Society.

SU-F-T-380: Comparing the Effect of Respiration On Dose Distribution Between Conventional Tangent Pair and IMRT Techniques for Adjuvant Radiotherapy in Early Stage Breast Cancer

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

Wu, M; Ramaseshan, R

2016-06-15

Purpose: In this project, we compared the conventional tangent pair technique to IMRT technique by analyzing the dose distribution. We also investigated the effect of respiration on planning target volume (PTV) dose coverage in both techniques. Methods: In order to implement IMRT technique a template based planning protocol, dose constrains and treatment process was developed. Two open fields with optimized field weights were combined with two beamlet optimization fields in IMRT plans. We compared the dose distribution between standard tangential pair and IMRT. The improvement in dose distribution was measured by parameters such as conformity index, homogeneity index and coveragemore » index. Another end point was the IMRT technique will reduce the planning time for staff. The effect of patient’s respiration on dose distribution was also estimated. The four dimensional computed tomography (4DCT) for different phase of breathing cycle was used to evaluate the effect of respiration on IMRT planned dose distribution. Results: We have accumulated 10 patients that acquired 4DCT and planned by both techniques. Based on the preliminary analysis, the dose distribution in IMRT technique was better than conventional tangent pair technique. Furthermore, the effect of respiration in IMRT plan was not significant as evident from the 95% isodose line coverage of PTV drawn on all phases of 4DCT. Conclusion: Based on the 4DCT images, the breathing effect on dose distribution was smaller than what we expected. We suspect that there are two reasons. First, the PTV movement due to respiration was not significant. It might be because we used a tilted breast board to setup patients. Second, the open fields with optimized field weights in IMRT technique might reduce the breathing effect on dose distribution. A further investigation is necessary.« less

Marqibo® (vincristine sulfate liposome injection) improves the pharmacokinetics and pharmacodynamics of vincristine.

PubMed

Silverman, Jeffrey A; Deitcher, Steven R

2013-03-01

Vincristine (VCR) is a mainstay of treatment of hematologic malignancies and solid tumors due to its well-defined mechanism of action, demonstrated anticancer activity and its ability to be combined with other agents. VCR is an M-phase cell cycle-specific anticancer drug with activity that is concentration and exposure duration dependent. The pharmacokinetic profile of standard VCR is described by a bi-exponential elimination pattern with a very fast initial distribution half-life followed by a longer elimination half-life. VCR also has a large volume of distribution, suggesting diffuse distribution and tissue binding. These properties may limit optimal drug exposure and delivery to target tissues as well as clinical utility as a single agent or as an effective component of multi-agent regimens. Vincristine sulfate liposome injection (VSLI), Marqibo(®), is a sphingomyelin and cholesterol-based nanoparticle formulation of VCR that was designed to overcome the dosing and pharmacokinetic limitations of standard VCR. VSLI was developed to increase the circulation time, optimize delivery to target tissues and facilitate dose intensification without increasing toxicity. In xenograft studies in mice, VSLI had a higher maximum tolerated dose, superior antitumor activity and delivered higher amounts of active drug to target tissues compared to standard VCR. VSLI recently received accelerated FDA approval for use in adults with advanced, relapsed and refractory Philadelphia chromosome-negative ALL and is in development for untreated adult ALL, pediatric ALL and untreated aggressive NHL. Here, we summarize the nonclinical data for VSLI that support its continued clinical development and recent approval for use in adult ALL.

Failure-probability driven dose painting

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

Vogelius, Ivan R.; Håkansson, Katrin; Due, Anne K.

Purpose: To demonstrate a data-driven dose-painting strategy based on the spatial distribution of recurrences in previously treated patients. The result is a quantitative way to define a dose prescription function, optimizing the predicted local control at constant treatment intensity. A dose planning study using the optimized dose prescription in 20 patients is performed.Methods: Patients treated at our center have five tumor subvolumes from the center of the tumor (PET positive volume) and out delineated. The spatial distribution of 48 failures in patients with complete clinical response after (chemo)radiation is used to derive a model for tumor control probability (TCP). Themore » total TCP is fixed to the clinically observed 70% actuarial TCP at five years. Additionally, the authors match the distribution of failures between the five subvolumes to the observed distribution. The steepness of the dose–response is extracted from the literature and the authors assume 30% and 20% risk of subclinical involvement in the elective volumes. The result is a five-compartment dose response model matching the observed distribution of failures. The model is used to optimize the distribution of dose in individual patients, while keeping the treatment intensity constant and the maximum prescribed dose below 85 Gy.Results: The vast majority of failures occur centrally despite the small volumes of the central regions. Thus, optimizing the dose prescription yields higher doses to the central target volumes and lower doses to the elective volumes. The dose planning study shows that the modified prescription is clinically feasible. The optimized TCP is 89% (range: 82%–91%) as compared to the observed TCP of 70%.Conclusions: The observed distribution of locoregional failures was used to derive an objective, data-driven dose prescription function. The optimized dose is predicted to result in a substantial increase in local control without increasing the predicted risk of toxicity.« less

Measurement of relative depth-dose distribution in radiochromic film dosimeters irradiated with 43-70 keV electron beam for industrial application

NASA Astrophysics Data System (ADS)

Matsui, Shinjiro; Hattori, Takeaki; Nonaka, Takashi; Watanabe, Yuki; Morita, Ippei; Kondo, Junichi; Ishikawa, Masayoshi; Mori, Yoshitaka

2018-05-01

The relative dose in a layer, which is thinner than the thickness of the dosimeter is evaluated using simulated depth-dose distributions, and the measured responses of dosimeters with acceleration voltages from 43 to 70 kV, via ultra-low-energy electron beam (ULEB) irradiation. By stacking thin film dosimeters, we confirmed that the simulated depth-dose distributions coincided with the measured depth-dose curve within the measurement uncertainty (k = 2). Using the measurement dose of the 47 μm dosimeter and the simulated depth-dose distribution, the dose of 11 μm dosimeters in the surface was evaluated within the measurement uncertainty (k = 2). We also verified the effectiveness of this method for a thinner layer by changing the acceleration voltage of the irradiation source. We evaluated the relative dose for an adjusted depth of energy deposition from 4.4 μm to 22.8 μm. As a result, this method was found to be effective for a thickness, which is less than the thickness of the dosimeter. When irradiation conditions are well known with accuracy, using the confirmed relative depth-dose distributions across any dosimeter thickness range, a dose evaluation, in several μm steps will possibly improve the design of industrial ULEB processes.

Novel Radiobiological Gamma Index for Evaluation of 3-Dimensional Predicted Dose Distribution

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

Sumida, Iori, E-mail: sumida@radonc.med.osaka-u.ac.jp; Yamaguchi, Hajime; Kizaki, Hisao

2015-07-15

Purpose: To propose a gamma index-based dose evaluation index that integrates the radiobiological parameters of tumor control (TCP) and normal tissue complication probabilities (NTCP). Methods and Materials: Fifteen prostate and head and neck (H&N) cancer patients received intensity modulated radiation therapy. Before treatment, patient-specific quality assurance was conducted via beam-by-beam analysis, and beam-specific dose error distributions were generated. The predicted 3-dimensional (3D) dose distribution was calculated by back-projection of relative dose error distribution per beam. A 3D gamma analysis of different organs (prostate: clinical [CTV] and planned target volumes [PTV], rectum, bladder, femoral heads; H&N: gross tumor volume [GTV], CTV,more » spinal cord, brain stem, both parotids) was performed using predicted and planned dose distributions under 2%/2 mm tolerance and physical gamma passing rate was calculated. TCP and NTCP values were calculated for voxels with physical gamma indices (PGI) >1. We propose a new radiobiological gamma index (RGI) to quantify the radiobiological effects of TCP and NTCP and calculate radiobiological gamma passing rates. Results: The mean RGI gamma passing rates for prostate cases were significantly different compared with those of PGI (P<.03–.001). The mean RGI gamma passing rates for H&N cases (except for GTV) were significantly different compared with those of PGI (P<.001). Differences in gamma passing rates between PGI and RGI were due to dose differences between the planned and predicted dose distributions. Radiobiological gamma distribution was visualized to identify areas where the dose was radiobiologically important. Conclusions: RGI was proposed to integrate radiobiological effects into PGI. This index would assist physicians and medical physicists not only in physical evaluations of treatment delivery accuracy, but also in clinical evaluations of predicted dose distribution.« less

DMLC tracking and gating can improve dose coverage for prostate VMAT

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

Colvill, E.; Northern Sydney Cancer Centre, Royal North Shore Hospital, Sydney, NSW 2065; School of Physics, University of Sydney, NSW 2006

2014-09-15

Purpose: To assess and compare the dosimetric impact of dynamic multileaf collimator (DMLC) tracking and gating as motion correction strategies to account for intrafraction motion during conventionally fractionated prostate radiotherapy. Methods: A dose reconstruction method was used to retrospectively assess the dose distributions delivered without motion correction during volumetric modulated arc therapy fractions for 20 fractions of five prostate cancer patients who received conventionally fractionated radiotherapy. These delivered dose distributions were compared with the dose distributions which would have been delivered had DMLC tracking or gating motion correction strategies been implemented. The delivered dose distributions were constructed by incorporating themore » observed prostate motion with the patient's original treatment plan to simulate the treatment delivery. The DMLC tracking dose distributions were constructed using the same dose reconstruction method with the addition of MLC positions from Linac log files obtained during DMLC tracking simulations with the observed prostate motions input to the DMLC tracking software. The gating dose distributions were constructed by altering the prostate motion to simulate the application of a gating threshold of 3 mm for 5 s. Results: The delivered dose distributions showed that dosimetric effects of intrafraction prostate motion could be substantial for some fractions, with an estimated dose decrease of more than 19% and 34% from the planned CTVD{sub 99%} and PTV D{sub 95%} values, respectively, for one fraction. Evaluation of dose distributions for DMLC tracking and gating deliveries showed that both interventions were effective in improving the CTV D{sub 99%} for all of the selected fractions to within 4% of planned value for all fractions. For the delivered dose distributions the difference in rectum V{sub 65%} for the individual fractions from planned ranged from −44% to 101% and for the bladder V{sub 65%} the range was −61% to 26% from planned. The application of tracking decreased the maximum rectum and bladder V{sub 65%} difference to 6% and 4%, respectively. Conclusions: For the first time, the dosimetric impact of DMLC tracking and gating to account for intrafraction motion during prostate radiotherapy has been assessed and compared with no motion correction. Without motion correction intrafraction prostate motion can result in a significant decrease in target dose coverage for a small number of individual fractions. This is unlikely to effect the overall treatment for most patients undergoing conventionally fractionated treatments. Both DMLC tracking and gating demonstrate dose distributions for all assessed fractions that are robust to intrafraction motion.« less

Skin dose mapping for non-uniform x-ray fields using a backscatter point spread function

NASA Astrophysics Data System (ADS)

Vijayan, Sarath; Xiong, Zhenyu; Shankar, Alok; Rudin, Stephen; Bednarek, Daniel R.

2017-03-01

Beam shaping devices like ROI attenuators and compensation filters modulate the intensity distribution of the xray beam incident on the patient. This results in a spatial variation of skin dose due to the variation of primary radiation and also a variation in backscattered radiation from the patient. To determine the backscatter component, backscatter point spread functions (PSF) are generated using EGS Monte-Carlo software. For this study, PSF's were determined by simulating a 1 mm beam incident on the lateral surface of an anthropomorphic head phantom and a 20 cm thick PMMA block phantom. The backscatter PSF's for the head phantom and PMMA phantom are curve fit with a Lorentzian function after being normalized to the primary dose intensity (PSFn). PSFn is convolved with the primary dose distribution to generate the scatter dose distribution, which is added to the primary to obtain the total dose distribution. The backscatter convolution technique is incorporated in the dose tracking system (DTS), which tracks skin dose during fluoroscopic procedures and provides a color map of the dose distribution on a 3D patient graphic model. A convolution technique is developed for the backscatter dose determination for the nonuniformly spaced graphic-model surface vertices. A Gafchromic film validation was performed for shaped x-ray beams generated with an ROI attenuator and with two compensation filters inserted into the field. The total dose distribution calculated by the backscatter convolution technique closely agreed with that measured with the film.

SU-G-TeP3-03: Dose Enhancement of Gold Nanoparticle in Proton Therapy: A Monte Carlo Study Based On the Transmission Electron Microscopy Imaging

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

Ma, Y; Beaulieu, L; Laprise-Pelletier, M

2016-06-15

Purpose: Gold nanoparticle (GNP) is a promising radiosensitizer that selectively boosts tumor dose in radiotherapy. Transmission electron microscopy (TEM) imaging observations recently revealed for the first time that GNP exists in vivo in the form of highly localized vesicles, instead of hypothetical uniform distribution. This work investigates the corresponding difference of energy deposition in proton therapy. Methods: First, single vesicles of various radii were constructed by packing GNPs (as Φ50 nm gold spheres) in spheres and were simulated, as well as a single GNP. The radial energy depositions (REDs) were scored using 100 concentric spherical shells from 0.1µm to 10µm,more » 0.1µm thickness each, for both vesicles and GNP, and compared. TEM images, 8 days after injection in a PC3 prostate cancer murine model, were used to extract position/dimension of vesicles, as well as contours of cytoplasmic and nucleus membranes. Vesicles were then constructed based on the TEM images. A 100 MeV proton beam was studied by using the Geant4-DNA code, which simulates all energy deposition events. Results: The vesicle REDs, normalized to the same proton energy loss as in a single GNP, are larger (smaller) than that of a single GNP when radius >2µm (<2µm). The peak increase (at about 3µm radius) is about 10% and 18% for Φ1µm and Φ1.6µm vesicles respectively, relative to a single GNP. The TEM-based simulation resulted in a larger energy deposition (by about one order of magnitude) that follows completely different pattern from that of hypothetical GNP distributions (regular dotted pattern in extracellular and/or extranucleus regions). Conclusion: The in vivo energy deposition, both in pattern and magnitude, of proton therapy is greatly affected by the true distribution of the GNP, as illustrated by the presence of GNP vesicles compared to hypothetical scenarios. Work supported by NSERC Discovery Grant #435510, Canada.« less

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

Optimized Dose Distribution of Gammamed Plus Vaginal Cylinders

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

Supe, Sanjay S.; Bijina, T.K.; Varatharaj, C.

2009-04-01

Endometrial carcinoma is the most common malignancy arising in the female genital tract. Intracavitary vaginal cuff irradiation may be given alone or with external beam irradiation in patients determined to be at risk for locoregional recurrence. Vaginal cylinders are often used to deliver a brachytherapy dose to the vaginal apex and upper vagina or the entire vaginal surface in the management of postoperative endometrial cancer or cervical cancer. The dose distributions of HDR vaginal cylinders must be evaluated carefully, so that clinical experiences with LDR techniques can be used in guiding optimal use of HDR techniques. The aim of thismore » study was to optimize dose distribution for Gammamed plus vaginal cylinders. Placement of dose optimization points was evaluated for its effect on optimized dose distributions. Two different dose optimization point models were used in this study, namely non-apex (dose optimization points only on periphery of cylinder) and apex (dose optimization points on periphery and along the curvature including the apex points). Thirteen dwell positions were used for the HDR dosimetry to obtain a 6-cm active length. Thus 13 optimization points were available at the periphery of the cylinder. The coordinates of the points along the curvature depended on the cylinder diameters and were chosen for each cylinder so that four points were distributed evenly in the curvature portion of the cylinder. Diameter of vaginal cylinders varied from 2.0 to 4.0 cm. Iterative optimization routine was utilized for all optimizations. The effects of various optimization routines (iterative, geometric, equal times) was studied for the 3.0-cm diameter vaginal cylinder. The effect of source travel step size on the optimized dose distributions for vaginal cylinders was also evaluated. All optimizations in this study were carried for dose of 6 Gy at dose optimization points. For both non-apex and apex models of vaginal cylinders, doses for apex point and three dome points were higher for the apex model compared with the non-apex model. Mean doses to the optimization points for both the cylinder models and all the cylinder diameters were 6 Gy, matching with the prescription dose of 6 Gy. Iterative optimization routine resulted in the highest dose to apex point and dome points. The mean dose for optimization point was 6.01 Gy for iterative optimization and was much higher than 5.74 Gy for geometric and equal times routines. Step size of 1 cm gave the highest dose to the apex point. This step size was superior in terms of mean dose to optimization points. Selection of dose optimization points for the derivation of optimized dose distributions for vaginal cylinders affects the dose distributions.« less

Surface Modification of Silicone Rubber for Adhesion Patterning of Mesenchymal Stem Cells by Water Cluster Ion Beam

NASA Astrophysics Data System (ADS)

Sommani, Piyanuch; Ichihashi, Gaku; Ryuto, Hiromichi; Tsuji, Hiroshi; Gotoh, Yasuhito; Takaoka, Gikan H.

2011-01-01

Biocompatibility of silicone rubber sheet (SR) was improved by the water cluster ion irradiation for adhesion patterning of mesenchymal stem cells (MSCs). The water cluster ions were irradiated at acceleration voltage of 6 kV and doses of 1014-1016 ions/cm2. The effect of ion dose on changes in wettability and surface atomic bonding state was observed. Compared to the unirradiated SR, about four-time smoother surface on the irradiated one was observed. Water contact angle decreased with an increase in the ion dose up to 1×1015 ions/cm2. With an increase in ion dose, XPS showed decrease of atomic carbon due to lateral sputtering effect and increase of atomic oxygen due to surface oxidation. After 7 days in vitro culture, the complete adhesion pattern of the rat MSCs was obtained on the irradiated SR at dose of 1×1015 ions/cm2, corresponding to the low contact angle of 87°. At low dose, the partial pattern on the irradiated region was observed instead.

Solar UV dose patterns in Italy.

PubMed

Meloni, D; Casale, G R; Siani, A M; Palmieri, S; Cappellani, F

2000-06-01

Since 1992 solar ultraviolet (UV) spectral irradiance (290-325 nm) has been measured at two Italian stations of Rome (urban site) and Ispra (semirural site) using Brewer spectrophotometry. The data collected under all sky conditions, are compared with the output of a sophisticated radiative transfer model (System for Transfer of Atmospheric Radiation--STAR model). The STAR multiple scattering scheme is able to cope with all physical processes relevant to the UV transfer through the atmosphere. The experience so far acquired indicates that, in spite of the unavoidable uncertainties in the input parameters (ozone, aerosol, surface albedo, pressure, temperature, relative humidity, cloud cover), measured and computed clear sky iradiances are in reasonable agreement. The STAR model is applied to build up the solar UV geographic patterns in Italy: the daily dose in the range 290-325 nm is computed at about 70 sites where a thorough and homogeneous climatology is available. For each month the concept of an idealized "standard day" is introduced and the surface distribution of solar UV field determined. The map of solar UV patterns for Italy, available for the first time, meets the study requirements in the field of skin and eye epidemiology, as well as in other investigations dealing with the impact of UV on the biosphere. The results are interpreted in terms of atmospheric and meteorological parameters modulating UV radiation reaching the ground.

Experimental verification of a 4D MLEM reconstruction algorithm used for in-beam PET measurements in particle therapy

NASA Astrophysics Data System (ADS)

Stützer, K.; Bert, C.; Enghardt, W.; Helmbrecht, S.; Parodi, K.; Priegnitz, M.; Saito, N.; Fiedler, F.

2013-08-01

In-beam positron emission tomography (PET) has been proven to be a reliable technique in ion beam radiotherapy for the in situ and non-invasive evaluation of the correct dose deposition in static tumour entities. In the presence of intra-fractional target motion an appropriate time-resolved (four-dimensional, 4D) reconstruction algorithm has to be used to avoid reconstructed activity distributions suffering from motion-related blurring artefacts and to allow for a dedicated dose monitoring. Four-dimensional reconstruction algorithms from diagnostic PET imaging that can properly handle the typically low counting statistics of in-beam PET data have been adapted and optimized for the characteristics of the double-head PET scanner BASTEI installed at GSI Helmholtzzentrum Darmstadt, Germany (GSI). Systematic investigations with moving radioactive sources demonstrate the more effective reduction of motion artefacts by applying a 4D maximum likelihood expectation maximization (MLEM) algorithm instead of the retrospective co-registration of phasewise reconstructed quasi-static activity distributions. Further 4D MLEM results are presented from in-beam PET measurements of irradiated moving phantoms which verify the accessibility of relevant parameters for the dose monitoring of intra-fractionally moving targets. From in-beam PET listmode data sets acquired together with a motion surrogate signal, valuable images can be generated by the 4D MLEM reconstruction for different motion patterns and motion-compensated beam delivery techniques.

Magnetic imaging of cyanide-bridged co-ordination nanoparticles grafted on FIB-patterned Si substrates.

PubMed

Ghirri, Alberto; Candini, Andrea; Evangelisti, Marco; Gazzadi, Gian Carlo; Volatron, Florence; Fleury, Benoit; Catala, Laure; David, Christophe; Mallah, Talal; Affronte, Marco

2008-12-01

Prussian blue CsNiCr nanoparticles are used to decorate selected portions of a Si substrate. For successful grafting to take place, the Si surface needs first to be chemically functionalized. Low-dose focused ion beam patterning on uniformly functionalized surfaces selects those portions that will not participate in the grafting process. Step-by-step control is assured by atomic force and high-resolution scanning electron microscopy, revealing a submonolayer distribution of the grafted nanoparticles. By novel scanning Hall-probe microscopy, an in-depth investigation of the magnetic response of the nanoparticles to varying temperature and applied magnetic field is provided. The magnetic images acquired suggest that low-temperature canted ferromagnetism is found in the grafted nanoparticles, similar to what is observed in the equivalent bulk material.

SU-E-CAMPUS-T-03: Four-Dimensional Dose Distribution Measurement Using Plastic Scintillator

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

Hashimoto, M; Kozuka, T; Oguchi, M

2014-06-15

Purpose: To develop the detector for the four-dimensional dose distribution measurement. Methods: We made the prototype detector for four-dimensional dose distribution measurement using a cylindrical plastic scintillator (5 cm diameter) and a conical reflection grass. The plastic scintillator is used as a phantom. When the plastic scintillator is irradiated, the scintillation light was emitted according to absorbed dose distribution. The conical reflection grass was arranged to surround the plastic scintillator, which project to downstream the projection images of the scintillation light. Then, the projection image was reflected to 45 degree direction by flat reflection grass, and was recorded by camcorder.more » By reconstructing the three-dimensional dose distribution from the projection image recorded in each frame, we could obtain the four-dimensional dose distribution. First, we tested the characteristic according to the amount of emitted light. Then we compared of the light profile and the dose profile calculated with the radiotherapy treatment planning system. Results: The dose dependency of the amount of light showed linearity. The pixel detecting smaller amount of light had high sensitivity than the pixel detecting larger amount of light. However the difference of the sensitivity could be corrected from the amount of light detected in each pixel. Both of the depth light profile through the conical reflection grass and the depth dose profile showed the same attenuation in the region deeper than peak depth. In lateral direction, the difference of the both profiles was shown at outside field and penumbra region. We consider that the difference is occurred due to the scatter of the scintillation light in the plastic scintillator block. Conclusion: It was possible to obtain the amount of light corresponding to the absorbed dose distribution from the prototype detector. Four-dimensional dose distributions can be reconstructed with high accuracy by the correction of the scattered light.« less

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

Schedule for CT image guidance in treating prostate cancer with helical tomotherapy

PubMed Central

Beldjoudi, G; Yartsev, S; Bauman, G; Battista, J; Van Dyk, J

2010-01-01

The aim of this study was to determine the effect of reducing the number of image guidance sessions and patient-specific target margins on the dose distribution in the treatment of prostate cancer with helical tomotherapy. 20 patients with prostate cancer who were treated with helical tomotherapy using daily megavoltage CT (MVCT) imaging before treatment served as the study population. The average geometric shifts applied for set-up corrections, as a result of co-registration of MVCT and planning kilovoltage CT studies over an increasing number of image guidance sessions, were determined. Simulation of the consequences of various imaging scenarios on the dose distribution was performed for two patients with different patterns of interfraction changes in anatomy. Our analysis of the daily set-up correction shifts for 20 prostate cancer patients suggests that the use of four fractions would result in a population average shift that was within 1 mm of the average obtained from the data accumulated over all daily MVCT sessions. Simulation of a scenario in which imaging sessions are performed at a reduced frequency and the planning target volume margin is adapted provided significantly better sparing of organs at risk, with acceptable reproducibility of dose delivery to the clinical target volume. Our results indicate that four MVCT sessions on helical tomotherapy are sufficient to provide information for the creation of personalised target margins and the establishment of the new reference position that accounts for the systematic error. This simplified approach reduces overall treatment session time and decreases the imaging dose to the patient. PMID:19505966

Optimization of the temporal pattern of radiation: An IMRT based study

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

Altman, Michael B.; Chmura, Steven J.; Deasy, Joseph O.

Purpose: To investigate how the temporal pattern of dose applied during a single-intensity modulated radiation therapy (IMRT) fraction can be arranged to maximize or minimize cell kill. Methods and Materials: Using the linear-quadratic repair-time model and a simplified IMRT delivery pattern model, the surviving fraction of cells for a single fraction was calculated for all permutations of the dose delivery pattern for an array of clinically based IMRT cases. Maximization of cell kill was achieved by concentrating the highest doses in the middle of a fraction, while minimization was achieved by spreading the highest doses between the beginning and end.more » The percent difference between maximum and minimum cell kill (%Diff{sub min/max}) and the difference between maximum and minimum total doses normalized to 2 Gy/fx ({delta}NTD{sub 2Gy}) was calculated for varying fraction durations (T), {alpha}/{beta} ratios, and doses/fx. Results: %Diff{sub min/max} and {delta}NTD{sub 2Gy} both increased with increasing T and with decreasing {alpha}/{beta}. The largest increases occurred with dose/fx. With {alpha}/{beta} = 3 Gy and 30 min/fx, %Diff{sub min/max} ranged from 2.7-5.3% for 2 Gy/fx to 48.6-74.1% for 10 Gy/fx, whereas {delta}NTD{sub 2Gy} ranged from 1.2 Gy-2.4 Gy for 30 fractions of 2 Gy/fx to 2.3-4.8 Gy for 2 fractions of 10.84 Gy/fx. Using {alpha}/{beta} = 1.5 Gy, an analysis of prostate hypofractionation schemes yielded differences in clinical outcome based on the pattern of applied dose ranging from 3.2%-6.1% of the treated population. Conclusions: Rearrangement of the temporal pattern of dose for a single IMRT fraction could be used to optimize cell kill and to directly, though modestly, affect treatment outcome.« less

Evaluation of nonrigid registration models for interfraction dose accumulation in radiotherapy

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

Janssens, Guillaume; Orban de Xivry, Jonathan; Fekkes, Stein

2009-09-15

Purpose: Interfraction dose accumulation is necessary to evaluate the dose distribution of an entire course of treatment by adding up multiple dose distributions of different treatment fractions. This accumulation of dose distributions is not straightforward as changes in the patient anatomy may occur during treatment. For this purpose, the accuracy of nonrigid registration methods is assessed for dose accumulation based on the calculated deformations fields. Methods: A phantom study using a deformable cubic silicon phantom with implanted markers and a cylindrical silicon phantom with MOSFET detectors has been performed. The phantoms were deformed and images were acquired using a cone-beammore » CT imager. Dose calculations were performed on these CT scans using the treatment planning system. Nonrigid CT-based registration was performed using two different methods, the Morphons and Demons. The resulting deformation field was applied on the dose distribution. For both phantoms, accuracy of the registered dose distribution was assessed. For the cylindrical phantom, also measured dose values in the deformed conditions were compared with the dose values of the registered dose distributions. Finally, interfraction dose accumulation for two treatment fractions of a patient with primary rectal cancer has been performed and evaluated using isodose lines and the dose volume histograms of the target volume and normal tissue. Results: A significant decrease in the difference in marker or MOSFET position was observed after nonrigid registration methods (p<0.001) for both phantoms and with both methods, as well as a significant decrease in the dose estimation error (p<0.01 for the cubic phantom and p<0.001 for the cylindrical) with both methods. Considering the whole data set at once, the difference between estimated and measured doses was also significantly decreased using registration (p<0.001 for both methods). The patient case showed a slightly underdosed planning target volume and an overdosed bladder volume due to anatomical deformations. Conclusions: Dose accumulation using nonrigid registration methods is possible using repeated CT imaging. This opens possibilities for interfraction dose accumulation and adaptive radiotherapy to incorporate possible differences in dose delivered to the target volume and organs at risk due to anatomical deformations.« less

The nonuniformity of antibody distribution in the kidney and its influence on dosimetry.

PubMed

Flynn, Aiden A; Pedley, R Barbara; Green, Alan J; Dearling, Jason L; El-Emir, Ethaar; Boxer, Geoffrey M; Boden, Robert; Begent, Richard H J

2003-02-01

The therapeutic efficacy of radiolabeled antibody fragments can be limited by nephrotoxicity, particularly when the kidney is the major route of extraction from the circulation. Conventional dose estimates in kidney assume uniform dose deposition, but we have shown increased antibody localization in the cortex after glomerular filtration. The purpose of this study was to measure the radioactivity in cortex relative to medulla for a range of antibodies and to assess the validity of the assumption of uniformity of dose deposition in the whole kidney and in the cortex for these antibodies with a range of radionuclides. Storage phosphor plate technology (radioluminography) was used to acquire images of the distributions of a range of antibodies of various sizes, labeled with 125I, in kidney sections. This allowed the calculation of the antibody concentration in the cortex relative to the medulla. Beta-particle point dose kernels were then used to generate the dose-rate distributions from 14C, 131I, 186Re, 32P and 90Y. The correlation between the actual dose-rate distribution and the corresponding distribution calculated assuming uniform antibody distribution throughout the kidney was used to test the validity of estimating dose by assuming uniformity in the kidney and in the cortex. There was a strong inverse relationship between the ratio of the radioactivity in the cortex relative to that in the medulla and the antibody size. The nonuniformity of dose deposition was greatest with the smallest antibody fragments but became more uniform as the range of the emissions from the radionuclide increased. Furthermore, there was a strong correlation between the actual dose-rate distribution and the distribution when assuming a uniform source in the kidney for intact antibodies along with medium- to long-range radionuclides, but there was no correlation for small antibody fragments with any radioisotope or for short-range radionuclides with any antibody. However, when the cortex was separated from the whole kidney, the correlation between the actual dose-rate distribution and the assumed dose-rate distribution, if the source was uniform, increased significantly. During radioimmunotherapy, the extent of nonuniformity of dose deposition in the kidney depends on the properties of the antibody and radionuclide. For dosimetry estimates, the cortex should be taken as a separate source region when the radiopharmaceutical is small enough to be filtered by the glomerulus.

Design and characterization of a new high-dose-rate brachytherapy Valencia applicator for larger skin lesions

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

Candela-Juan, C., E-mail: ccanjuan@gmail.com; Niatsetski, Y.; Laarse, R. van der

Purpose: The aims of this study were (i) to design a new high-dose-rate (HDR) brachytherapy applicator for treating surface lesions with planning target volumes larger than 3 cm in diameter and up to 5 cm in size, using the microSelectron-HDR or Flexitron afterloader (Elekta Brachytherapy) with a {sup 192}Ir source; (ii) to calculate by means of the Monte Carlo (MC) method the dose distribution for the new applicator when it is placed against a water phantom; and (iii) to validate experimentally the dose distributions in water. Methods: The PENELOPE2008 MC code was used to optimize dwell positions and dwell times.more » Next, the dose distribution in a water phantom and the leakage dose distribution around the applicator were calculated. Finally, MC data were validated experimentally for a {sup 192}Ir mHDR-v2 source by measuring (i) dose distributions with radiochromic EBT3 films (ISP); (ii) percentage depth–dose (PDD) curve with the parallel-plate ionization chamber Advanced Markus (PTW); and (iii) absolute dose rate with EBT3 films and the PinPoint T31016 (PTW) ionization chamber. Results: The new applicator is made of tungsten alloy (Densimet) and consists of a set of interchangeable collimators. Three catheters are used to allocate the source at prefixed dwell positions with preset weights to produce a homogenous dose distribution at the typical prescription depth of 3 mm in water. The same plan is used for all available collimators. PDD, absolute dose rate per unit of air kerma strength, and off-axis profiles in a cylindrical water phantom are reported. These data can be used for treatment planning. Leakage around the applicator was also scored. The dose distributions, PDD, and absolute dose rate calculated agree within experimental uncertainties with the doses measured: differences of MC data with chamber measurements are up to 0.8% and with radiochromic films are up to 3.5%. Conclusions: The new applicator and the dosimetric data provided here will be a valuable tool in clinical practice, making treatment of large skin lesions simpler, faster, and safer. Also the dose to surrounding healthy tissues is minimal.« less

Seasonal influenza vaccine dose distribution in 157 countries (2004-2011).

PubMed

Palache, Abraham; Oriol-Mathieu, Valerie; Abelin, Atika; Music, Tamara

2014-11-12

Globally there are an estimated 3-5 million cases of severe influenza illness every year, resulting in 250,000-500,000 deaths. At the World Health Assembly in 2003, World Health Organization (WHO) resolved to increase influenza vaccine coverage rates (VCR) for high-risk groups, particularly focusing on at least 75% of the elderly by 2010. But systematic worldwide data have not been available to assist public health authorities to monitor vaccine uptake and review progress toward vaccination coverage targets. In 2008, the International Federation of Pharmaceutical Manufacturers and Associations Influenza Vaccine Supply task force (IFPMA IVS) developed a survey methodology to assess global influenza vaccine dose distribution. The current survey results represent 2011 data and demonstrate the evolution of the absolute number distributed between 2004 and 2011 inclusive, and the evolution in the per capita doses distributed in 2008-2011. Global distribution of IFPMA IVS member doses increased approximately 86.9% between 2004 and 2011, but only approximately 12.1% between 2008 and 2011. The WHO's regions in Eastern Mediterranean (EMRO), Southeast Asian (SEARO) and Africa (AFRO) together account for about 47% of the global population, but only 3.7% of all IFPMA IVS doses distributed. While distributed doses have globally increased, they have decreased in EURO and EMRO since 2009. Dose distribution can provide a reasonable proxy of vaccine utilization. Based on the dose distribution, we conclude that seasonal influenza VCR in many countries remains well below the WHA's VCR targets and below the recommendations of the Council of the European Union in EURO. Inter- and intra-regional disparities in dose distribution trends call into question the impact of current vaccine recommendations at achieving coverage targets. Additional policy measures, particularly those that influence patients adherence to vaccination programs, such as reimbursement, healthcare provider knowledge, attitudes, practices, and communications, are required for VCR targets to be met and benefit public health. Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved.

WE-G-16A-01: Evolution of Radiation Treatment Planning

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

Rothenberg, L; Mohan, R; Van Dyk, J

Welcome and Introduction - Lawrence N. Rothenberg This symposium is one a continuing series of presentations at AAPM Annual Meetings on the historical aspects of medical physics, radiology, and radiation oncology that have been organized by the AAPM History Committee. Information on previous presentations including “Early Developments in Teletherapy” (Indianapolis 2013), “Historical Aspects of Cross-Sectional Imaging” (Charlotte 2012), “Historical Aspects of Brachytherapy” (Vancouver 2011), “50 Years of Women in Medical Physics” (Houston 2008), and “Roentgen's Early Investigations” (Minneapolis 2007) can be found in the Education Section of the AAPM Website. The Austin 2014 History Symposium will be on “Evolution ofmore » Radiation Treatment Planning.” Overview - Radhe Mohan Treatment planning is one of the most critical components in the chain of radiation therapy of cancers. Treatment plans of today contain a wide variety of sophisticated information conveying the potential clinical effectiveness of the designed treatment to practitioners. Examples of such information include dose distributions superimposed on three- or even four-dimensional anatomic images; dose volume histograms, dose, dose-volume and dose-response indices for anatomic structures of interest; etc. These data are used for evaluating treatment plans and for making treatment decisions. The current state-of-the-art has evolved from the 1940s era when the dose to the tumor and normal tissues was estimated approximately by manual means. However, the symposium will cover the history of the field from the late-1950's, when computers were first introduced for treatment planning, to the present state involving the use of high performance computing and advanced multi-dimensional anatomic, functional and biological imaging, focusing only on external beam treatment planning. The symposium will start with a general overview of the treatment planning process including imaging, structure delineation, assignment of dose requirements, consideration of uncertainties, selection of beam configurations and shaping of beams, and calculations, optimization and evaluation of dose distributions. This will be followed by three presentations covering the evolution of treatment planning, which parallels the evolution of computers, availability of advanced volumetric imaging and the development of novel technologies such as dynamic multi-leaf collimators and online image guidance. This evolution will be divided over three distinct periods - prior to 1970's, the 2D era; from 1980 to the mid-1990's, the 3D era; and from the mid 1990's to today, the IMRT era. When the World was Flat: The Two-Dimensional Radiation Therapy Era” - Jacob Van Dyk In the 2D era, anatomy was defined with the aid of solder wires, special contouring devices and projection x-rays. Dose distributions were calculated manually from single field, flat surface isodoses on transparencies. Precalculated atlases of generic dose distributions were produced by the International Atomic Energy Agency. Massive time-shared main frames and mini-computers were used to compute doses at individual points or dose distributions in a single plane. Beam shapes were generally rectangular, with wedges, missing tissue compensators and occasional blocks to shield critical structures. Dose calculations were measurement-based or they used primary and scatter calculations based on scatter-air ratio methodologies. Dose distributions were displayed on line printers as alpha-numeric character maps or isodose patterns made with pen plotters. More than Pretty Pictures: 3D Treatment Planning and Conformal Therapy - Benedick A. Fraass The introduction of computed tomography allowed the delineation of anatomy three-dimensionally and, supported partly by contracts from the National Cancer Institute, made possible the introduction and clinical use of 3D treatment planning, leading to development and use of 3D conformal therapy in the 1980's. 3D computer graphics and 3D anatomical structure definitions made possible Beam's Eye View (BEV) displays, making conformal beam shaping and much more sophisticated beam arrangements possible. These conformal plans significantly improved target dose coverage as well as normal tissue sparing. The use of dose volume histograms, gross/clinical/planning target volumes, MRI and PET imaging, multileaf collimators, and computer-controlled treatment delivery made sophisticated planning approaches practical. The significant improvements in dose distributions and analysis achievable with 3D conformal therapy made possible formal dose escalation and normal tissue tolerance clinical studies that set new and improved expectations for improved local control and decreasing complications in many clinical sites. From the Art to the State of the Art: Inverse Planning and IMRT - Thomas R. Bortfeld While the potential of intensity modulation was recognized in the mid- 1980's, intensity-modulated radiotherapy (IMRT) did not become a reality until the mid-1990's. Broad beams of photons could be sub-divided into narrow beamlets whose intensities could be determined using sophisticated optimization algorithms to appropriately balance tumor dose with normal tissue sparing. The development of dynamic multi-leaf collimators (on conventional linear accelerators as well as in helical delivery devices) enabled the efficient delivery of IMRT. The evolution of IMRT planning is continuing in the form of Volumetric Modulated Arc Therapy (VMAT) and through advanced optimization tools, such as multi-criteria optimization, automated IMRT planning, and robust optimization to protect dose distributions against uncertainties. IMRT also facilitates “dose painting” in which different sub-volumes of the target are prescribed different doses. Clearly, these advancements are being made possible by the increasing power and lower cost of computers and developments in other fields such as imaging and operations research. Summary - Radhe Mohan The history does not end here. The advancement of treatment planning is expected to continue, leading to further automation and improvements in conformality and robustness of dose distributions, particularly in the area of particle therapy. Radiobiological modeling will gain emphasis as part of the planning process. Learning Objectives: The scope of changes in technology and the capabilities of radiation treatment planning The impact of these changes in the quality of treatment plans and optimality of dose distributions The impact of development in other fields (imaging, computers, operations research, etc.) on the evolution of radiation treatment planning.« less

Four-year post-exposure assay of vegetation surrounding project pinstripe: demonstration of the utility of delayed damage appraisals. [Larrea divaricata, Ephedra funerea, Atriplex confertifolia

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

Ragsdale, H.L.; Rhoads, W.A.

1974-01-01

This report illustrates the feasibility of using temporally-delayed vegetation assays to determine radiation damage, by documenting the radiation damage resulting from the accidental venting of radioactive materials during Project Pinstripe, Frenchman's Flat, Nevada Test Site, in April, 1966. Evidence of desert shrub radiation damage was first observed and photographed, in April, 1968. Systematic study of the vegetation was initiated in October, 1970, and evidence of radiation damage documented over 72.9 hectares adjacent to the vent. Beta doses were estimated at 15--21 krads based on gamma exposure dose measurements. The minimum beta dose estimate was substantially greater than the theoretical lethalmore » dose for the shrub, Larrea divaricata. Radiation damage to the shrubs, Larrea divaricata, Ephedra funerea, and Atriplex confertifolia was expressed as differential bud mortality, partial death of shrub crowns with and without crown regrowth, and total shrub crown death without crown regrowth. Each of the shrub populations was statistically different from its control population with respect to the distribution of individuals among damage classes. Generally, damage patterns were similar to those observed at two previously-studied Plowshare events.« less

Design of a tracking device for on-line dose monitoring in hadrontherapy

NASA Astrophysics Data System (ADS)

Battistoni, G.; Collamati, F.; De Lucia, E.; Faccini, R.; Marafini, M.; Mattei, I.; Muraro, S.; Paramatti, R.; Patera, V.; Pinci, D.; Rucinski, A.; Russomando, A.; Sarti, A.; Sciubba, A.; Solfaroli Camillocci, E.; Toppi, M.; Traini, G.; Voena, C.

2017-02-01

Hadrontherapy is a technique for cancer treatment that exploits ion beams (mostly protons and carbons). A critical issue is the accuracy that is achievable when monitoring the dose released by the beam to the tumor and to the surrounding tissues. We present the design of a tracking device, developed in the framework of the INSIDE project [1], capable of monitoring in real time the longitudinal profile of the dose delivered in the patient. This is possible by detecting the secondary particles produced by the interaction of the beam in the tissues. The position of the Bragg peak can be correlated to the charged particles emission point distribution measurement. The tracking device will be able to provide a fast response on the dose pattern by tracking the secondary charged fragments. The tracks are detected using 6 planes of scintillating fibers, providing the 3D coordinates of the track intersection with each plane. The fibers planes are followed by a plastic scintillator and by a small calorimeter built with a pixelated Lutetium Fine Silicate (LFS) crystal. A complete detector simulation, followed by the event reconstruction, has been performed to determine the achievable monitoring spatial resolution.

Examples for the importance of radiophysical measurements in clinical phototherapy.

PubMed

Schneider, Lars Alexander; Wlaschek, Meinhard; Dissemond, Joachim; Scharffetter-Kochanek, Karin

2007-05-01

Optimal UV therapy requires regular surveillance of the variables that influence therapeutic success. In daily practice, phototherapy equipment is often operated with an attitude of "autocontrol." This implies that thorough control measurements of the emission spectra and calibration of UV fluences are not routinely performed. For both quality control and patient safety, it is essential to regularly check whether a UV source is providing the right target spectrum with the correct dose to the skin. We have exemplarily taken three UV sources currently used in clinical practice and performed radiophysical measurements, i. e. determined emission spectra, radiation output and correctness of dose calculation. All three sources revealed either a largely inhomogeneous distribution pattern of radiation intensity, variation of radiation intensity over time or insufficient filtering of the UV lamp emission spectrum. Furthermore the dose calculation procedures had to be revised because of significant differences between the estimated and the administered UV doses. Radiophysical measurement of all UV-equipment in clinical use is a simple and effective way to improve the safety and reliability of phototherapy. Such measurements help to uncover technical flaws in radiation sources and prevent unnecessary side effects and UV exposure risks for the patient.

Comparison of gamma radiation effects on natural corn and potato starches and modified cassava starch

NASA Astrophysics Data System (ADS)

Teixeira, Bruna S.; Garcia, Rafael H. L.; Takinami, Patricia Y. I.; del Mastro, Nelida L.

2018-01-01

The objective of this work was to evaluate the effect of irradiation treatment on physicochemical properties of three natural polymers, i.e. native potato and corn starches and a typical Brazilian product, cassava starch modified through fermentation -sour cassava- and also to prepare composite hydrocolloid films based on them. Starches were irradiated in a 60Co irradiation chamber in doses up to 15 kGy, dose rate about 1 kGy/h. Differences were found in granule size distribution upon irradiation, mainly for corn and cassava starch but radiation did not cause significant changes in granule morphology. The viscosity of the potato, corn and cassava starches hydrogels decreased as a function of absorbed dose. Comparing non-irradiated and irradiated starches, changes in the Fourier transform infrared (FTIR) spectra in the 2000-1500 cm-1 region for potato and corn starches were observed but not for the cassava starch. Maximum rupture force of the starch-based films was affected differently for each starch type; color analysis showed that doses of 15 kGy promoted a slight rise in the parameter b* (yellow color) while the parameter L* (lightness) was not significantly affected; X-ray diffraction patterns remained almost unchanged by irradiation.

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.

SU-E-T-188: Film Dosimetry Verification of Monte Carlo Generated Electron Treatment Plans

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

Enright, S; Asprinio, A; Lu, L

2014-06-01

Purpose: The purpose of this study was to compare dose distributions from film measurements to Monte Carlo generated electron treatment plans. Irradiation with electrons offers the advantages of dose uniformity in the target volume and of minimizing the dose to deeper healthy tissue. Using the Monte Carlo algorithm will improve dose accuracy in regions with heterogeneities and irregular surfaces. Methods: Dose distributions from GafChromic{sup ™} EBT3 films were compared to dose distributions from the Electron Monte Carlo algorithm in the Eclipse{sup ™} radiotherapy treatment planning system. These measurements were obtained for 6MeV, 9MeV and 12MeV electrons at two depths. Allmore » phantoms studied were imported into Eclipse by CT scan. A 1 cm thick solid water template with holes for bonelike and lung-like plugs was used. Different configurations were used with the different plugs inserted into the holes. Configurations with solid-water plugs stacked on top of one another were also used to create an irregular surface. Results: The dose distributions measured from the film agreed with those from the Electron Monte Carlo treatment plan. Accuracy of Electron Monte Carlo algorithm was also compared to that of Pencil Beam. Dose distributions from Monte Carlo had much higher pass rates than distributions from Pencil Beam when compared to the film. The pass rate for Monte Carlo was in the 80%–99% range, where the pass rate for Pencil Beam was as low as 10.76%. Conclusion: The dose distribution from Monte Carlo agreed with the measured dose from the film. When compared to the Pencil Beam algorithm, pass rates for Monte Carlo were much higher. Monte Carlo should be used over Pencil Beam for regions with heterogeneities and irregular surfaces.« less

Methods for Probabilistic Radiological Dose Assessment at a High-Level Radioactive Waste Repository.

NASA Astrophysics Data System (ADS)

Maheras, Steven James

Methods were developed to assess and evaluate the uncertainty in offsite and onsite radiological dose at a high-level radioactive waste repository to show reasonable assurance that compliance with applicable regulatory requirements will be achieved. Uncertainty in offsite dose was assessed by employing a stochastic precode in conjunction with Monte Carlo simulation using an offsite radiological dose assessment code. Uncertainty in onsite dose was assessed by employing a discrete-event simulation model of repository operations in conjunction with an occupational radiological dose assessment model. Complementary cumulative distribution functions of offsite and onsite dose were used to illustrate reasonable assurance. Offsite dose analyses were performed for iodine -129, cesium-137, strontium-90, and plutonium-239. Complementary cumulative distribution functions of offsite dose were constructed; offsite dose was lognormally distributed with a two order of magnitude range. However, plutonium-239 results were not lognormally distributed and exhibited less than one order of magnitude range. Onsite dose analyses were performed for the preliminary inspection, receiving and handling, and the underground areas of the repository. Complementary cumulative distribution functions of onsite dose were constructed and exhibited less than one order of magnitude range. A preliminary sensitivity analysis of the receiving and handling areas was conducted using a regression metamodel. Sensitivity coefficients and partial correlation coefficients were used as measures of sensitivity. Model output was most sensitive to parameters related to cask handling operations. Model output showed little sensitivity to parameters related to cask inspections.

Dose distribution for dental cone beam CT and its implication for defining a dose index

PubMed Central

Pauwels, R; Theodorakou, C; Walker, A; Bosmans, H; Jacobs, R; Horner, K; Bogaerts, R

2012-01-01

Objectives To characterize the dose distribution for a range of cone beam CT (CBCT) units, investigating different field of view sizes, central and off-axis geometries, full or partial rotations of the X-ray tube and different clinically applied beam qualities. The implications of the dose distributions on the definition and practicality of a CBCT dose index were assessed. Methods Dose measurements on CBCT devices were performed by scanning cylindrical head-size water and polymethyl methacrylate phantoms, using thermoluminescent dosemeters, a small-volume ion chamber and radiochromic films. Results It was found that the dose distribution can be asymmetrical for dental CBCT exposures throughout a homogeneous phantom, owing to an asymmetrical positioning of the isocentre and/or partial rotation of the X-ray source. Furthermore, the scatter tail along the z-axis was found to have a distinct shape, generally resulting in a strong drop (90%) in absorbed dose outside the primary beam. Conclusions There is no optimal dose index available owing to the complicated exposure geometry of CBCT and the practical aspects of quality control measurements. Practical validation of different possible dose indices is needed, as well as the definition of conversion factors to patient dose. PMID:22752320

SU-G-TeP3-01: A New Approach for Calculating Variable Relative Biological Effectiveness in IMPT Optimization

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

Cao, W; Randeniya, K; Grosshans, D

2016-06-15

Purpose: To investigate the impact of a new approach for calculating relative biological effectiveness (RBE) in intensity-modulated proton therapy (IMPT) optimization on RBE-weighted dose distributions. This approach includes the nonlinear RBE for the high linear energy transfer (LET) region, which was revealed by recent experiments at our institution. In addition, this approach utilizes RBE data as a function of LET without using dose-averaged LET in calculating RBE values. Methods: We used a two-piece function for calculating RBE from LET. Within the Bragg peak, RBE is linearly correlated to LET. Beyond the Bragg peak, we use a nonlinear (quadratic) RBE functionmore » of LET based on our experimental. The IMPT optimization was devised to incorporate variable RBE by maximizing biological effect (based on the Linear Quadratic model) in tumor and minimizing biological effect in normal tissues. Three glioblastoma patients were retrospectively selected from our institution in this study. For each patient, three optimized IMPT plans were created based on three RBE resolutions, i.e., fixed RBE of 1.1 (RBE-1.1), variable RBE based on linear RBE and LET relationship (RBE-L), and variable RBE based on linear and quadratic relationship (RBE-LQ). The RBE weighted dose distributions of each optimized plan were evaluated in terms of different RBE values, i.e., RBE-1.1, RBE-L and RBE-LQ. Results: The RBE weighted doses recalculated from RBE-1.1 based optimized plans demonstrated an increasing pattern from using RBE-1.1, RBE-L to RBE-LQ consistently for all three patients. The variable RBE (RBE-L and RBE-LQ) weighted dose distributions recalculated from RBE-L and RBE-LQ based optimization were more homogenous within the targets and better spared in the critical structures than the ones recalculated from RBE-1.1 based optimization. Conclusion: We implemented a new approach for RBE calculation and optimization and demonstrated potential benefits of improving tumor coverage and normal sparing in IMPT planning.« less

SU-D-BRC-03: Development and Validation of an Online 2D Dose Verification System for Daily Patient Plan Delivery Accuracy Check

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

Zhao, J; Hu, W; Xing, Y

Purpose: All plan verification systems for particle therapy are designed to do plan verification before treatment. However, the actual dose distributions during patient treatment are not known. This study develops an online 2D dose verification tool to check the daily dose delivery accuracy. Methods: A Siemens particle treatment system with a modulated scanning spot beam is used in our center. In order to do online dose verification, we made a program to reconstruct the delivered 2D dose distributions based on the daily treatment log files and depth dose distributions. In the log files we can get the focus size, positionmore » and particle number for each spot. A gamma analysis is used to compare the reconstructed dose distributions with the dose distributions from the TPS to assess the daily dose delivery accuracy. To verify the dose reconstruction algorithm, we compared the reconstructed dose distributions to dose distributions measured using PTW 729XDR ion chamber matrix for 13 real patient plans. Then we analyzed 100 treatment beams (58 carbon and 42 proton) for prostate, lung, ACC, NPC and chordoma patients. Results: For algorithm verification, the gamma passing rate was 97.95% for the 3%/3mm and 92.36% for the 2%/2mm criteria. For patient treatment analysis,the results were 97.7%±1.1% and 91.7%±2.5% for carbon and 89.9%±4.8% and 79.7%±7.7% for proton using 3%/3mm and 2%/2mm criteria, respectively. The reason for the lower passing rate for the proton beam is that the focus size deviations were larger than for the carbon beam. The average focus size deviations were −14.27% and −6.73% for proton and −5.26% and −0.93% for carbon in the x and y direction respectively. Conclusion: The verification software meets our requirements to check for daily dose delivery discrepancies. Such tools can enhance the current treatment plan and delivery verification processes and improve safety of clinical treatments.« less

Development of a high precision dosimetry system for the measurement of surface dose rate distribution for eye applicators.

PubMed

Eichmann, Marion; Flühs, Dirk; Spaan, Bernhard

2009-10-01

The therapeutic outcome of the therapy with ophthalmic applicators is highly dependent on the application of a sufficient dose to the tumor, whereas the dose applied to the surrounding tissue needs to be minimized. The goal for the newly developed apparatus described in this work is the determination of the individual applicator surface dose rate distribution with a high spatial resolution and a high precision in dose rate with respect to time and budget constraints especially important for clinical procedures. Inhomogeneities of the dose rate distribution can be detected and taken into consideration for the treatment planning. In order to achieve this, a dose rate profile as well as a surface profile of the applicator are measured and correlated with each other. An instrumental setup has been developed consisting of a plastic scintillator detector system and a newly designed apparatus for guiding the detector across the applicator surface at a constant small distance. It performs an angular movement of detector and applicator with high precision. The measurements of surface dose rate distributions discussed in this work demonstrate the successful operation of the measuring setup. Measuring the surface dose rate distribution with a small distance between applicator and detector and with a high density of measuring points results in a complete and gapless coverage of the applicator surface, being capable of distinguishing small sized spots with high activities. The dosimetrical accuracy of the measurements and its analysis is sufficient (uncertainty in the dose rate in terms of absorbed dose to water is <7%), especially when taking the surgical techniques in positioning of the applicator on the eyeball into account. The method developed so far allows a fully automated quality assurance of eye applicators even under clinical conditions. These measurements provide the basis for future calculation of a full 3D dose rate distribution, which then can be used as input for a refined clinical treatment planning system. The improved dose rate measurements will facilitate a clinical study, which could correlate the therapeutic outcome of a brachytherapy treatment with an applicator and its individual dose rate distribution.

Development of a high precision dosimetry system for the measurement of surface dose rate distribution for eye applicators

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

Eichmann, Marion; Fluehs, Dirk; Spaan, Bernhard

2009-10-15

Purpose: The therapeutic outcome of the therapy with ophthalmic applicators is highly dependent on the application of a sufficient dose to the tumor, whereas the dose applied to the surrounding tissue needs to be minimized. The goal for the newly developed apparatus described in this work is the determination of the individual applicator surface dose rate distribution with a high spatial resolution and a high precision in dose rate with respect to time and budget constraints especially important for clinical procedures. Inhomogeneities of the dose rate distribution can be detected and taken into consideration for the treatment planning. Methods: Inmore » order to achieve this, a dose rate profile as well as a surface profile of the applicator are measured and correlated with each other. An instrumental setup has been developed consisting of a plastic scintillator detector system and a newly designed apparatus for guiding the detector across the applicator surface at a constant small distance. It performs an angular movement of detector and applicator with high precision. Results: The measurements of surface dose rate distributions discussed in this work demonstrate the successful operation of the measuring setup. Measuring the surface dose rate distribution with a small distance between applicator and detector and with a high density of measuring points results in a complete and gapless coverage of the applicator surface, being capable of distinguishing small sized spots with high activities. The dosimetrical accuracy of the measurements and its analysis is sufficient (uncertainty in the dose rate in terms of absorbed dose to water is <7%), especially when taking the surgical techniques in positioning of the applicator on the eyeball into account. Conclusions: The method developed so far allows a fully automated quality assurance of eye applicators even under clinical conditions. These measurements provide the basis for future calculation of a full 3D dose rate distribution, which then can be used as input for a refined clinical treatment planning system. The improved dose rate measurements will facilitate a clinical study, which could correlate the therapeutic outcome of a brachytherapy treatment with an applicator and its individual dose rate distribution.« less

Voxel-based population analysis for correlating local dose and rectal toxicity in prostate cancer radiotherapy

NASA Astrophysics Data System (ADS)

Acosta, Oscar; Drean, Gael; Ospina, Juan D.; Simon, Antoine; Haigron, Pascal; Lafond, Caroline; de Crevoisier, Renaud

2013-04-01

The majority of current models utilized for predicting toxicity in prostate cancer radiotherapy are based on dose-volume histograms. One of their main drawbacks is the lack of spatial accuracy, since they consider the organs as a whole volume and thus ignore the heterogeneous intra-organ radio-sensitivity. In this paper, we propose a dose-image-based framework to reveal the relationships between local dose and toxicity. In this approach, the three-dimensional (3D) planned dose distributions across a population are non-rigidly registered into a common coordinate system and compared at a voxel level, therefore enabling the identification of 3D anatomical patterns, which may be responsible for toxicity, at least to some extent. Additionally, different metrics were employed in order to assess the quality of the dose mapping. The value of this approach was demonstrated by prospectively analyzing rectal bleeding (⩾Grade 1 at 2 years) according to the CTCAE v3.0 classification in a series of 105 patients receiving 80 Gy to the prostate by intensity modulated radiation therapy (IMRT). Within the patients presenting bleeding, a significant dose excess (6 Gy on average, p < 0.01) was found in a region of the anterior rectal wall. This region, close to the prostate (1 cm), represented less than 10% of the rectum. This promising voxel-wise approach allowed subregions to be defined within the organ that may be involved in toxicity and, as such, must be considered during the inverse IMRT planning step.

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

Petasecca, M., E-mail: marcop@uow.edu.au; Newall, M. K.; Aldosari, A. H.

Purpose: Spatial and temporal resolutions are two of the most important features for quality assurance instrumentation of motion adaptive radiotherapy modalities. The goal of this work is to characterize the performance of the 2D high spatial resolution monolithic silicon diode array named “MagicPlate-512” for quality assurance of stereotactic body radiation therapy (SBRT) and stereotactic radiosurgery (SRS) combined with a dynamic multileaf collimator (MLC) tracking technique for motion compensation. Methods: MagicPlate-512 is used in combination with the movable platform HexaMotion and a research version of radiofrequency tracking system Calypso driving MLC tracking software. The authors reconstruct 2D dose distributions of smallmore » field square beams in three modalities: in static conditions, mimicking the temporal movement pattern of a lung tumor and tracking the moving target while the MLC compensates almost instantaneously for the tumor displacement. Use of Calypso in combination with MagicPlate-512 requires a proper radiofrequency interference shielding. Impact of the shielding on dosimetry has been simulated by GEANT4 and verified experimentally. Temporal and spatial resolutions of the dosimetry system allow also for accurate verification of segments of complex stereotactic radiotherapy plans with identification of the instant and location where a certain dose is delivered. This feature allows for retrospective temporal reconstruction of the delivery process and easy identification of error in the tracking or the multileaf collimator driving systems. A sliding MLC wedge combined with the lung motion pattern has been measured. The ability of the MagicPlate-512 (MP512) in 2D dose mapping in all three modes of operation was benchmarked by EBT3 film. Results: Full width at half maximum and penumbra of the moving and stationary dose profiles measured by EBT3 film and MagicPlate-512 confirm that motion has a significant impact on the dose distribution. Motion, no motion, and motion with MLC tracking profiles agreed within 1 and 0.4 mm, respectively, for all field sizes tested. Use of electromagnetic tracking system generates a fluctuation of the detector baseline up to 10% of the full scale signal requiring a proper shielding strategy. MagicPlate-512 is also able to reconstruct the dose variation pulse-by-pulse in each pixel of the detector. An analysis of the dose transients with motion and motion with tracking shows that the tracking feedback algorithm used for this experiment can compensate effectively only the effect of the slower transient components. The fast changing components of the organ motion can contribute only to discrepancy of the order of 15% in penumbral region while the slower components can change the dose profile up to 75% of the expected dose. Conclusions: MagicPlate-512 is shown to be, potentially, a valid alternative to film or 2D ionizing chambers for quality assurance dosimetry in SRS or SBRT. Its high spatial and temporal resolutions allow for accurate reconstruction of the profile in any conditions with motion and with tracking of the motion. It shows excellent performance to reconstruct the dose deposition in real time or retrospectively as a function of time for detailed analysis of the effect of motion in a specific pixel or area of interest.« less

Spatially patterned matrix elasticity directs stem cell fate

NASA Astrophysics Data System (ADS)

Yang, Chun; DelRio, Frank W.; Ma, Hao; Killaars, Anouk R.; Basta, Lena P.; Kyburz, Kyle A.; Anseth, Kristi S.

2016-08-01

There is a growing appreciation for the functional role of matrix mechanics in regulating stem cell self-renewal and differentiation processes. However, it is largely unknown how subcellular, spatial mechanical variations in the local extracellular environment mediate intracellular signal transduction and direct cell fate. Here, the effect of spatial distribution, magnitude, and organization of subcellular matrix mechanical properties on human mesenchymal stem cell (hMSCs) function was investigated. Exploiting a photodegradation reaction, a hydrogel cell culture substrate was fabricated with regions of spatially varied and distinct mechanical properties, which were subsequently mapped and quantified by atomic force microscopy (AFM). The variations in the underlying matrix mechanics were found to regulate cellular adhesion and transcriptional events. Highly spread, elongated morphologies and higher Yes-associated protein (YAP) activation were observed in hMSCs seeded on hydrogels with higher concentrations of stiff regions in a dose-dependent manner. However, when the spatial organization of the mechanically stiff regions was altered from a regular to randomized pattern, lower levels of YAP activation with smaller and more rounded cell morphologies were induced in hMSCs. We infer from these results that irregular, disorganized variations in matrix mechanics, compared with regular patterns, appear to disrupt actin organization, and lead to different cell fates; this was verified by observations of lower alkaline phosphatase (ALP) activity and higher expression of CD105, a stem cell marker, in hMSCs in random versus regular patterns of mechanical properties. Collectively, this material platform has allowed innovative experiments to elucidate a novel spatial mechanical dosing mechanism that correlates to both the magnitude and organization of spatial stiffness.

Is Dose Deformation–Invariance Hypothesis Verified in Prostate IGRT?

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

Simon, Antoine, E-mail: antoine.simon@univ-rennes1.fr; Laboratoire Traitement du Signal et de l'Image, Université de Rennes 1, 35000 Rennes; Le Maitre, Amandine

Purpose: To assess dose uncertainties resulting from the dose deformation–invariance hypothesis in prostate cone beam computed tomography (CT)–based image guided radiation therapy (IGRT), namely to evaluate whether rigidly propagated planned dose distribution enables good estimation of fraction dose distributions. Methods and Materials: Twenty patients underwent a CT scan for planning intensity modulated radiation therapy–IGRT delivering 80 Gy to the prostate, followed by weekly CT scans. Two methods were used to obtain the dose distributions on the weekly CT scans: (1) recalculating the dose using the original treatment plan; and (2) rigidly propagating the planned dose distribution. The cumulative doses were then estimatedmore » in the organs at risk for each dose distribution by deformable image registration. The differences between recalculated and propagated doses were finally calculated for the fraction and the cumulative dose distributions, by use of per-voxel and dose-volume histogram (DVH) metrics. Results: For the fraction dose, the mean per-voxel absolute dose difference was <1 Gy for 98% and 95% of the fractions for the rectum and bladder, respectively. The maximum dose difference within 1 voxel reached, however, 7.4 Gy in the bladder and 8.0 Gy in the rectum. The mean dose differences were correlated with gas volume for the rectum and patient external contour variations for the bladder. The mean absolute differences for the considered volume receiving greater than or equal to dose x (V{sub x}) of the DVH were between 0.37% and 0.70% for the rectum and between 0.53% and 1.22% for the bladder. For the cumulative dose, the mean differences in the DVH were between 0.23% and 1.11% for the rectum and between 0.55% and 1.66% for the bladder. The largest dose difference was 6.86%, for bladder V{sub 80Gy}. The mean dose differences were <1.1 Gy for the rectum and <1 Gy for the bladder. Conclusions: The deformation–invariance hypothesis was corroborated for the organs at risk in prostate IGRT except in cases of a large disappearance or appearance of rectal gas for the rectum and large external contour variations for the bladder.« 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

Biophysical modeling of fragment length distributions of DNA plasmids after X and heavy-ion irradiation analyzed by atomic force microscopy.

PubMed

Elsässer, Thilo; Brons, Stephan; Psonka, Katarzyna; Scholz, Michael; Gudowska-Nowak, Ewa; Taucher-Scholz, Gisela

2008-06-01

The investigation of fragment length distributions of plasmid DNA gives insight into the influence of localized energy distribution on the induction of DNA damage, particularly the clustering of double-strand breaks. We present an approach that determines the fragment length distributions of plasmid DNA after heavy-ion irradiation by using the Local Effect Model. We find a good agreement of our simulations with experimental fragment distributions derived from atomic force microscopy (AFM) studies by including experimental constraints typical for AFM. Our calculations reveal that by comparing the fragmentation in terms of fluence, we can uniquely distinguish the effect of different radiation qualities. For very high-LET irradiation using nickel or uranium ions, no difference between their fragment distributions can be expected for the same dose level. However, for carbon ions with an intermediate LET, the fragmentation pattern differs from the distribution for very high-LET particles. The results of the model calculations can be used to determine the optimal experimental parameters for a demonstration of the influence of track structure on primary radiation damage. Additionally, we compare the results of our model for two different plasmid geometries.

Converging stereotactic radiotherapy using kilovoltage X-rays: experimental irradiation of normal rabbit lung and dose-volume analysis with Monte Carlo simulation.

PubMed

Kawase, Takatsugu; Kunieda, Etsuo; Deloar, Hossain M; Tsunoo, Takanori; Seki, Satoshi; Oku, Yohei; Saitoh, Hidetoshi; Saito, Kimiaki; Ogawa, Eileen N; Ishizaka, Akitoshi; Kameyama, Kaori; Kubo, Atsushi

2009-10-01

To validate the feasibility of developing a radiotherapy unit with kilovoltage X-rays through actual irradiation of live rabbit lungs, and to explore the practical issues anticipated in future clinical application to humans through Monte Carlo dose simulation. A converging stereotactic irradiation unit was developed, consisting of a modified diagnostic computed tomography (CT) scanner. A tiny cylindrical volume in 13 normal rabbit lungs was individually irradiated with single fractional absorbed doses of 15, 30, 45, and 60 Gy. Observational CT scanning of the whole lung was performed every 2 weeks for 30 weeks after irradiation. After 30 weeks, histopathologic specimens of the lungs were examined. Dose distribution was simulated using the Monte Carlo method, and dose-volume histograms were calculated according to the data. A trial estimation of the effect of respiratory movement on dose distribution was made. A localized hypodense change and subsequent reticular opacity around the planning target volume (PTV) were observed in CT images of rabbit lungs. Dose-volume histograms of the PTVs and organs at risk showed a focused dose distribution to the target and sufficient dose lowering in the organs at risk. Our estimate of the dose distribution, taking respiratory movement into account, revealed dose reduction in the PTV. A converging stereotactic irradiation unit using kilovoltage X-rays was able to generate a focused radiobiologic reaction in rabbit lungs. Dose-volume histogram analysis and estimated sagittal dose distribution, considering respiratory movement, clarified the characteristics of the irradiation received from this type of unit.

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

Derivation of mean dose tolerances for new fractionation schemes and treatment modalities

NASA Astrophysics Data System (ADS)

Perkó, Zoltán; Bortfeld, Thomas; Hong, Theodore; Wolfgang, John; Unkelbach, Jan

2018-02-01

Avoiding toxicities in radiotherapy requires the knowledge of tolerable organ doses. For new, experimental fractionation schemes (e.g. hypofractionation) these are typically derived from traditional schedules using the biologically effective dose (BED) model. In this report we investigate the difficulties of establishing mean dose tolerances that arise since the mean BED depends on the entire spatial dose distribution, rather than on the dose level alone. A formula has been derived to establish mean physical dose constraints such that they are mean BED equivalent to a reference treatment scheme. This formula constitutes a modified BED equation where the influence of the spatial dose distribution is summarized in a single parameter, the dose shape factor. To quantify effects we analyzed 24 liver cancer patients for whom both proton and photon IMRT treatment plans were available. The results show that the standard BED equation—neglecting the spatial dose distribution—can overestimate mean dose tolerances for hypofractionated treatments by up to 20%. The shape difference between photon and proton dose distributions can cause 30-40% differences in mean physical dose for plans having identical mean BEDs. Converting hypofractionated, 5/15-fraction proton doses to mean BED equivalent photon doses in traditional 35-fraction regimens resulted in up to 10 Gy higher doses than applying the standard BED formula. The dose shape effect should be accounted for to avoid overestimation of mean dose tolerances, particularly when estimating constraints for hypofractionated regimens. Additionally, tolerances established for one treatment modality cannot necessarily be applied to other modalities with drastically different dose distributions, such as proton therapy. Last, protons may only allow marginal (5-10%) dose escalation if a fraction-size adjusted organ mean dose is constraining instead of a physical dose.

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

Perko, Z; Bortfeld, T; Hong, T

Purpose: The safe use of radiotherapy requires the knowledge of tolerable organ doses. For experimental fractionation schemes (e.g. hypofractionation) these are typically extrapolated from traditional fractionation schedules using the Biologically Effective Dose (BED) model. This work demonstrates that using the mean dose in the standard BED equation may overestimate tolerances, potentially leading to unsafe treatments. Instead, extrapolation of mean dose tolerances should take the spatial dose distribution into account. Methods: A formula has been derived to extrapolate mean physical dose constraints such that they are mean BED equivalent. This formula constitutes a modified BED equation where the influence of themore » spatial dose distribution is summarized in a single parameter, the dose shape factor. To quantify effects we analyzed 14 liver cancer patients previously treated with proton therapy in 5 or 15 fractions, for whom also photon IMRT plans were available. Results: Our work has two main implications. First, in typical clinical plans the dose distribution can have significant effects. When mean dose tolerances are extrapolated from standard fractionation towards hypofractionation they can be overestimated by 10–15%. Second, the shape difference between photon and proton dose distributions can cause 30–40% differences in mean physical dose for plans having the same mean BED. The combined effect when extrapolating proton doses to mean BED equivalent photon doses in traditional 35 fraction regimens resulted in up to 7–8 Gy higher doses than when applying the standard BED formula. This can potentially lead to unsafe treatments (in 1 of the 14 analyzed plans the liver mean dose was above its 32 Gy tolerance). Conclusion: The shape effect should be accounted for to avoid unsafe overestimation of mean dose tolerances, particularly when estimating constraints for hypofractionated regimens. In addition, tolerances established for a given treatment modality cannot necessarily be applied to other modalities with drastically different dose distributions.« less

SU-E-T-113: Dose Distribution Using Respiratory Signals and Machine Parameters During Treatment

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

Imae, T; Haga, A; Saotome, N

Purpose: Volumetric modulated arc therapy (VMAT) is a rotational intensity-modulated radiotherapy (IMRT) technique capable of acquiring projection images during treatment. Treatment plans for lung tumors using stereotactic body radiotherapy (SBRT) are calculated with planning computed tomography (CT) images only exhale phase. Purpose of this study is to evaluate dose distribution by reconstructing from only the data such as respiratory signals and machine parameters acquired during treatment. Methods: Phantom and three patients with lung tumor underwent CT scans for treatment planning. They were treated by VMAT while acquiring projection images to derive their respiratory signals and machine parameters including positions ofmore » multi leaf collimators, dose rates and integrated monitor units. The respiratory signals were divided into 4 and 10 phases and machine parameters were correlated with the divided respiratory signals based on the gantry angle. Dose distributions of each respiratory phase were calculated from plans which were reconstructed from the respiratory signals and the machine parameters during treatment. The doses at isocenter, maximum point and the centroid of target were evaluated. Results and Discussion: Dose distributions during treatment were calculated using the machine parameters and the respiratory signals detected from projection images. Maximum dose difference between plan and in treatment distribution was −1.8±0.4% at centroid of target and dose differences of evaluated points between 4 and 10 phases were no significant. Conclusion: The present method successfully evaluated dose distribution using respiratory signals and machine parameters during treatment. This method is feasible to verify the actual dose for moving target.« less

Estimation of the influence of radical effect in the proton beams using a combined approach with physical data and gel data

NASA Astrophysics Data System (ADS)

Haneda, K.

2016-04-01

The purpose of this study was to estimate an impact on radical effect in the proton beams using a combined approach with physical data and gel data. The study used two dosimeters: ionization chambers and polymer gel dosimeters. Polymer gel dosimeters have specific advantages when compared to other dosimeters. They can measure chemical reaction and they are at the same time a phantom that can map in three dimensions continuously and easily. First, a depth-dose curve for a 210 MeV proton beam measured using an ionization chamber and a gel dosimeter. Second, the spatial distribution of the physical dose was calculated by Monte Carlo code system PHITS: To verify of the accuracy of Monte Carlo calculation, and the calculation results were compared with experimental data of the ionization chamber. Last, to evaluate of the rate of the radical effect against the physical dose. The simulation results were compared with the measured depth-dose distribution and showed good agreement. The spatial distribution of a gel dose with threshold LET value of proton beam was calculated by the same simulation code. Then, the relative distribution of the radical effect was calculated from the physical dose and gel dose. The relative distribution of the radical effect was calculated at each depth as the quotient of relative dose obtained using physical and gel dose. The agreement between the relative distributions of the gel dosimeter and Radical effect was good at the proton beams.

Sci-Fri PM: Radiation Therapy, Planning, Imaging, and Special Techniques - 06: Patient-specific QA Procedure for Gated VMAT SABR Treatments using 10x Beam in Flattening-Filter Free Mode

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

Mestrovic, Ante; Chitsazzadeh, Shadi; Wells, Derek

2016-08-15

Purpose: To develop a highly sensitive patient specific QA procedure for gated VMAT stereotactic ablative radiotherapy (SABR) treatments. Methods: A platform was constructed to attach the translational stage of a Quasar respiratory motion phantom to a pinpoint ion chamber insert and move the ion chamber inside the ArcCheck. The Quasar phantom controller uses a patient-specific breathing pattern to translate the ion chamber in a superior-inferior direction inside the ArcCheck. With this system the ion chamber is used to QA the correct phase of the gated delivery and the ArcCheck diodes are used to QA the overall dose distribution. This novelmore » approach requires a single plan delivery for a complete QA of a gated plan. The sensitivity of the gating QA procedure was investigated with respect to the following parameters: PTV size, exhale duration, baseline drift, gating window size. Results: The difference between the measured dose to a point in the penumbra and the Eclipse calculated dose was under 2% for small residual motions. The QA procedure was independent of PTV size and duration of exhale. Baseline drift and gating window size, however, significantly affected the penumbral dose measurement, with differences of up to 30% compared to Eclipse. Conclusion: This study described a highly sensitive QA procedure for gated VMAT SABR treatments. The QA outcome was dependent on the gating window size and baseline drift. Analysis of additional patient breathing patterns is currently undergoing to determine a clinically relevant gating window size and an appropriate tolerance level for this procedure.« less

Dosage and Distribution in Morphosyntax Intervention: Current Evidence and Future Needs

ERIC Educational Resources Information Center

Proctor-Williams, Kerry

2009-01-01

This article reviews the effectiveness of dose forms and the efficacy of dosage and distribution in morphosyntax intervention for children. Dose forms include the commonly used techniques, procedures, and intervention contexts that constitute teaching episodes; dosage includes the quantitative measures of dose, dose frequency, total intervention…

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

Ono, Tomohiro; Miyabe, Yuki, E-mail: miyabe@kuhp.kyoto-u.ac.jp; Yamada, Masahiro

Purpose: The Vero4DRT system has the capability for dynamic tumor-tracking (DTT) stereotactic irradiation using a unique gimbaled x-ray head. The purposes of this study were to develop DTT conformal arc irradiation and to estimate its geometric and dosimetric accuracy. Methods: The gimbaled x-ray head, supported on an O-ring gantry, was moved in the pan and tilt directions during O-ring gantry rotation. To evaluate the mechanical accuracy, the gimbaled x-ray head was moved during the gantry rotating according to input command signals without a target tracking, and a machine log analysis was performed. The difference between a command and a measuredmore » position was calculated as mechanical error. To evaluate beam-positioning accuracy, a moving phantom, which had a steel ball fixed at the center, was driven based on a sinusoidal wave (amplitude [A]: 20 mm, time period [T]: 4 s), a patient breathing motion with a regular pattern (A: 16 mm, average T: 4.5 s), and an irregular pattern (A: 7.2–23.0 mm, T: 2.3–10.0 s), and irradiated with DTT during gantry rotation. The beam-positioning error was evaluated as the difference between the centroid position of the irradiated field and the steel ball on images from an electronic portal imaging device. For dosimetric accuracy, dose distributions in static and moving targets were evaluated with DTT conformal arc irradiation. Results: The root mean squares (RMSs) of the mechanical error were up to 0.11 mm for pan motion and up to 0.14 mm for tilt motion. The RMSs of the beam-positioning error were within 0.23 mm for each pattern. The dose distribution in a moving phantom with tracking arc irradiation was in good agreement with that in static conditions. Conclusions: The gimbal positional accuracy was not degraded by gantry motion. As in the case of a fixed port, the Vero4DRT system showed adequate accuracy of DTT conformal arc irradiation.« less

Coupled in silico platform: Computational fluid dynamics (CFD) and physiologically-based pharmacokinetic (PBPK) modelling.

PubMed

Vulović, Aleksandra; Šušteršič, Tijana; Cvijić, Sandra; Ibrić, Svetlana; Filipović, Nenad

2018-02-15

One of the critical components of the respiratory drug delivery is the manner in which the inhaled aerosol is deposited in respiratory tract compartments. Depending on formulation properties, device characteristics and breathing pattern, only a certain fraction of the dose will reach the target site in the lungs, while the rest of the drug will deposit in the inhalation device or in the mouth-throat region. The aim of this study was to link the Computational fluid dynamics (CFD) with physiologically-based pharmacokinetic (PBPK) modelling in order to predict aerolisolization of different dry powder formulations, and estimate concomitant in vivo deposition and absorption of amiloride hydrochloride. Drug physicochemical properties were experimentally determined and used as inputs for the CFD simulations of particle flow in the generated 3D geometric model of Aerolizer® dry powder inhaler (DPI). CFD simulations were used to simulate air flow through Aerolizer® inhaler and Discrete Phase Method (DPM) was used to simulate aerosol particles deposition within the fluid domain. The simulated values for the percent emitted dose were comparable to the values obtained using Andersen cascade impactor (ACI). However, CFD predictions indicated that aerosolized DPI have smaller particle size and narrower size distribution than assumed based on ACI measurements. Comparison with the literature in vivo data revealed that the constructed drug-specific PBPK model was able to capture amiloride absorption pattern following oral and inhalation administration. The PBPK simulation results, based on the CFD generated particle distribution data as input, illustrated the influence of formulation properties on the expected drug plasma concentration profiles. The model also predicted the influence of potential changes in physiological parameters on the extent of inhaled amiloride absorption. Overall, this study demonstrated the potential of the combined CFD-PBPK approach to model inhaled drug bioperformance, and suggested that CFD generated results might serve as input for the prediction of drug deposition pattern in vivo. Copyright © 2017 Elsevier B.V. All rights reserved.

Tissue distribution of zinc and subtle oxidative stress effects after dietary administration of ZnO nanoparticles to rainbow trout.

PubMed

Connolly, Mona; Fernández, Marta; Conde, Estefanía; Torrent, Fernando; Navas, José M; Fernández-Cruz, María L

2016-05-01

The increasing use of ZnO nanoparticles (ZnO NPs) in different fields has raised concerns about the possible environmental risks associated with these NPs entering aquatic systems. In this study, using a dietary exposure route, we have analysed the tissue distribution and depuration pattern of Zn as well as any associated redox balance disturbances in rainbow trout (Oncorhynchus mykiss) following exposure to ZnO NPs (20-30nm). Fish were fed a diet spiked with ZnO NPs prepared from a dispersion in sunflower oil at doses of 300 or 1000mg ZnO NPs/kg feed for 10days. This uptake phase was followed by a 28days depuration phase in which fish from all groups received untreated feed. While no overt signs of toxicity were observed and no important effects in fish growth (weight and length) or in the hepatosomatic index among groups were recorded, we observed high levels of Zn bioaccumulation in the gills and intestine of exposed fish following exposure to both dose levels. Zn levels were not eliminated during the depuration phase and we have evidenced oxidative stress responses in gills associated with such long term ZnO NPs bioaccumulation and lack of elimination. Furthermore, exposures to higher doses of ZnO NPs (1000mg/kg feed) resulted in Zn distribution to the liver of fish following 10days of exposure. Fish from this exposure group experienced biochemical disturbances associated with oxidative stress in the liver and ethoxy-resorufin-O-deethylase (EROD) activity which may point to the ability of ZnO NPs or its ions to interfere with cytochrome P450 metabolic processes. Copyright © 2016 Elsevier B.V. All rights reserved.

SU-F-19A-10: Recalculation and Reporting Clinical HDR 192-Ir Head and Neck Dose Distributions Using Model Based Dose Calculation

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

Carlsson Tedgren, A; Persson, M; Nilsson, J

Purpose: To retrospectively re-calculate dose distributions for selected head and neck cancer patients, earlier treated with HDR 192Ir brachytherapy, using Monte Carlo (MC) simulations and compare results to distributions from the planning system derived using TG43 formalism. To study differences between dose to medium (as obtained with the MC code) and dose to water in medium as obtained through (1) ratios of stopping powers and (2) ratios of mass energy absorption coefficients between water and medium. Methods: The MC code Algebra was used to calculate dose distributions according to earlier actual treatment plans using anonymized plan data and CT imagesmore » in DICOM format. Ratios of stopping power and mass energy absorption coefficients for water with various media obtained from 192-Ir spectra were used in toggling between dose to water and dose to media. Results: Differences between initial planned TG43 dose distributions and the doses to media calculated by MC are insignificant in the target volume. Differences are moderate (within 4–5 % at distances of 3–4 cm) but increase with distance and are most notable in bone and at the patient surface. Differences between dose to water and dose to medium are within 1-2% when using mass energy absorption coefficients to toggle between the two quantities but increase to above 10% for bone using stopping power ratios. Conclusion: MC predicts target doses for head and neck cancer patients in close agreement with TG43. MC yields improved dose estimations outside the target where a larger fraction of dose is from scattered photons. It is important with awareness and a clear reporting of absorbed dose values in using model based algorithms. Differences in bone media can exceed 10% depending on how dose to water in medium is defined.« less

Isobio software: biological dose distribution and biological dose volume histogram from physical dose conversion using linear-quadratic-linear model.

PubMed

Jaikuna, Tanwiwat; Khadsiri, Phatchareewan; Chawapun, Nisa; Saekho, Suwit; Tharavichitkul, Ekkasit

2017-02-01

To develop an in-house software program that is able to calculate and generate the biological dose distribution and biological dose volume histogram by physical dose conversion using the linear-quadratic-linear (LQL) model. The Isobio software was developed using MATLAB version 2014b to calculate and generate the biological dose distribution and biological dose volume histograms. The physical dose from each voxel in treatment planning was extracted through Computational Environment for Radiotherapy Research (CERR), and the accuracy was verified by the differentiation between the dose volume histogram from CERR and the treatment planning system. An equivalent dose in 2 Gy fraction (EQD 2 ) was calculated using biological effective dose (BED) based on the LQL model. The software calculation and the manual calculation were compared for EQD 2 verification with pair t -test statistical analysis using IBM SPSS Statistics version 22 (64-bit). Two and three-dimensional biological dose distribution and biological dose volume histogram were displayed correctly by the Isobio software. Different physical doses were found between CERR and treatment planning system (TPS) in Oncentra, with 3.33% in high-risk clinical target volume (HR-CTV) determined by D 90% , 0.56% in the bladder, 1.74% in the rectum when determined by D 2cc , and less than 1% in Pinnacle. The difference in the EQD 2 between the software calculation and the manual calculation was not significantly different with 0.00% at p -values 0.820, 0.095, and 0.593 for external beam radiation therapy (EBRT) and 0.240, 0.320, and 0.849 for brachytherapy (BT) in HR-CTV, bladder, and rectum, respectively. The Isobio software is a feasible tool to generate the biological dose distribution and biological dose volume histogram for treatment plan evaluation in both EBRT and BT.

Direct nano-patterning of graphene with helium ion beams

NASA Astrophysics Data System (ADS)

Naitou, Y.; Iijima, T.; Ogawa, S.

2015-01-01

Helium ion microscopy (HIM) was used for direct nano-patterning of single-layer graphene (SLG) on SiO2/Si substrates. This technique involves irradiation of the sample with accelerated helium ions (He+). Doses of 2.0 × 1016 He+ cm-2 from a 30 kV beam induced a metal-insulator transition in the SLG. The resolution of HIM patterning on SLG was investigated by fabricating nanoribbons and nanostructures. Analysis of scanning capacitance microscopy measurements revealed that the spatial resolution of HIM patterning depended on the dosage of He+ in a non-monotonic fashion. Increasing the dose from 2.0 × 1016 to 5.0 × 1016 He+ cm-2 improved the spatial resolution to several tens of nanometers. However, doses greater than 1.0 × 1017 He+ cm-2 degraded the patterning characteristics. Direct patterning using HIM is a versatile approach to graphene fabrication and can be applied to graphene-based devices.

Evaluation of polymer gels and MRI as a 3-D dosimeter for intensity-modulated radiation therapy.

PubMed

Low, D A; Dempsey, J F; Venkatesan, R; Mutic, S; Markman, J; Mark Haacke, E; Purdy, J A

1999-08-01

BANG gel (MGS Research, Inc., Guilford, CT) has been evaluated for measuring intensity-modulated radiation therapy (IMRT) dose distributions. Treatment plans with target doses of 1500 cGy were generated by the Peacock IMRT system (NOMOS Corp., Sewickley, PA) using test target volumes. The gels were enclosed in 13 cm outer diameter cylindrical glass vessels. Dose calibration was conducted using seven smaller (4 cm diameter) cylindrical glass vessels irradiated to 0-1800 cGy in 300 cGy increments. Three-dimensional maps of the proton relaxation rate R2 were obtained using a 1.5 T magnetic resonance imaging (MRI) system (Siemens Medical Systems, Erlangen, Germany) and correlated with dose. A Hahn spin echo sequence was used with TR = 3 s, TE = 20 and 100 ms, NEX = 1, using 1 x 1 x 3 mm3 voxels. The MRI measurements were repeated weekly to identify the gel-aging characteristics. Ionization chamber, thermoluminescent dosimetry (TLD), and film dosimetry measurements of the IMRT dose distributions were obtained to compare against the gel results. The other dosimeters were used in a phantom with the same external cross-section as the gel phantom. The irradiated R2 values of the large vessels did not precisely track the smaller vessels, so the ionization chamber measurements were used to normalize the gel dose distributions. The point-to-point standard deviation of the gel dose measurements was 7.0 cGy. When compared with the ionization chamber measurements averaged over the chamber volume, 1% agreement was obtained. Comparisons against radiographic film dose distribution measurements and the treatment planning dose distribution calculation were used to determine the spatial localization accuracy of the gel and MRI. Spatial localization was better than 2 mm, and the dose was accurately determined by the gel both within and outside the target. The TLD chips were placed throughout the phantom to determine gel measurement precision in high- and low-dose regions. A multidimensional dose comparison tool that simultaneously examines the dose-difference and distance-to-agreement was used to evaluate the gel in both low-and high-dose gradient regions. When 3% and 3 mm criteria were used for the comparisons, more than 90% of the TLD measurements agreed with the gel, with the worst of 309 TLD chip measurements disagreeing by 40% of the criteria. All four MRI measurement session gel-measured dose distributions were compared to evaluate the time behavior of the gel. The low-dose regions were evaluated by comparison with TLD measurements at selected points, while high-dose regions were evaluated by directly comparing measured dose distributions. Tests using the multidimensional comparison tool showed detectable degradation beyond one week postirradiation, but all low-dose measurements passed relative to the test criteria and the dose distributions showed few regions that failed.

Analysis of mixing conditions and multistage irradiation impact on NOx removal efficiency in the electron beam flue gas treatment process.

PubMed

Pawelec, Andrzej; Dobrowolski, Andrzej

2017-01-01

In the process of electron beam flue gas treatment (EBFGT), most energy is spent on NO x removal. The dose distribution in the reactor is not uniform and the flue gas flow pattern plays an important role in the process efficiency. It was found that proper construction of the reactor may increase the energy efficiency of the process. The impact of the number of irradiation stages and mixing conditions on NO x removal efficiency was investigated for an ideal case and a practical solution was presented and compared with previously known EBFGT reactor constructions. The research was performed by means of computational fluid dynamics methods in combination with empirical Wittig formula. Two versions of dose distribution were taken for calculations. The results of the research show that for an ideal case, application of multistage irradiation and interstage mixing may reduce the energy consumption in the process by up to 39%. On the other side, simulation of reactor construction modification for two-stage irradiation results in 25% energy consumption reduction. The results of presented case study may be applied for improving the existing reactors and proper design of future installations.

Radionuclides in the soil around the largest coal-fired power plant in Serbia: radiological hazard, relationship with soil characteristics and spatial distribution.

PubMed

Ćujić, Mirjana; Dragović, Snežana; Đorđević, Milan; Dragović, Ranko; Gajić, Boško; Miljanić, Šćepan

2015-07-01

Primordial radionuclides, (238)U, (232)Th and (40)K were determined in soil samples collected at two depths (0-10 and 10-20 cm) in the vicinity of the largest coal-fired power plant in Serbia, and their spatial distribution was analysed using ordinary kriging. Mean values of activity concentrations for these depths were 50.7 Bq kg(-1) for (238)U, 48.7 Bq kg(-1) for (232)Th and 560 Bq kg(-1) for (40)K. Based on the measured activity concentrations, the radiological hazard due to naturally occurring radionuclides in soil was assessed. The value of the mean total absorbed dose rate was 76.3 nGy h(-1), which is higher than the world average. The annual effective dose due to these radionuclides ranged from 51.4 to 114.2 μSv. Applying cluster analysis, correlations between radionuclides and soil properties were determined. The distribution pattern of natural radionuclides in the environment surrounding the coal-fired power plant and their enrichment in soil at some sampling sites were in accordance with dispersion models of fly ash emissions. From the results obtained, it can be concluded that operation of the coal-fired power plant has no significant negative impact on the surrounding environment with regard to the content of natural radionuclides.

SU-E-T-374: Evaluation and Verification of Dose Calculation Accuracy with Different Dose Grid Sizes for Intracranial Stereotactic Radiosurgery

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

Han, C; Schultheiss, T

Purpose: In this study, we aim to evaluate the effect of dose grid size on the accuracy of calculated dose for small lesions in intracranial stereotactic radiosurgery (SRS), and to verify dose calculation accuracy with radiochromic film dosimetry. Methods: 15 intracranial lesions from previous SRS patients were retrospectively selected for this study. The planning target volume (PTV) ranged from 0.17 to 2.3 cm{sup 3}. A commercial treatment planning system was used to generate SRS plans using the volumetric modulated arc therapy (VMAT) technique using two arc fields. Two convolution-superposition-based dose calculation algorithms (Anisotropic Analytical Algorithm and Acuros XB algorithm) weremore » used to calculate volume dose distribution with dose grid size ranging from 1 mm to 3 mm with 0.5 mm step size. First, while the plan monitor units (MU) were kept constant, PTV dose variations were analyzed. Second, with 95% of the PTV covered by the prescription dose, variations of the plan MUs as a function of dose grid size were analyzed. Radiochomic films were used to compare the delivered dose and profile with the calculated dose distribution with different dose grid sizes. Results: The dose to the PTV, in terms of the mean dose, maximum, and minimum dose, showed steady decrease with increasing dose grid size using both algorithms. With 95% of the PTV covered by the prescription dose, the total MU increased with increasing dose grid size in most of the plans. Radiochromic film measurements showed better agreement with dose distributions calculated with 1-mm dose grid size. Conclusion: Dose grid size has significant impact on calculated dose distribution in intracranial SRS treatment planning with small target volumes. Using the default dose grid size could lead to under-estimation of delivered dose. A small dose grid size should be used to ensure calculation accuracy and agreement with QA measurements.« less

Probability Distribution of Dose and Dose-Rate Effectiveness Factor for use in Estimating Risks of Solid Cancers From Exposure to Low-Let Radiation.

PubMed

Kocher, David C; Apostoaei, A Iulian; Hoffman, F Owen; Trabalka, John R

2018-06-01

This paper presents an analysis to develop a subjective state-of-knowledge probability distribution of a dose and dose-rate effectiveness factor for use in estimating risks of solid cancers from exposure to low linear energy transfer radiation (photons or electrons) whenever linear dose responses from acute and chronic exposure are assumed. A dose and dose-rate effectiveness factor represents an assumption that the risk of a solid cancer per Gy at low acute doses or low dose rates of low linear energy transfer radiation, RL, differs from the risk per Gy at higher acute doses, RH; RL is estimated as RH divided by a dose and dose-rate effectiveness factor, where RH is estimated from analyses of dose responses in Japanese atomic-bomb survivors. A probability distribution to represent uncertainty in a dose and dose-rate effectiveness factor for solid cancers was developed from analyses of epidemiologic data on risks of incidence or mortality from all solid cancers as a group or all cancers excluding leukemias, including (1) analyses of possible nonlinearities in dose responses in atomic-bomb survivors, which give estimates of a low-dose effectiveness factor, and (2) comparisons of risks in radiation workers or members of the public from chronic exposure to low linear energy transfer radiation at low dose rates with risks in atomic-bomb survivors, which give estimates of a dose-rate effectiveness factor. Probability distributions of uncertain low-dose effectiveness factors and dose-rate effectiveness factors for solid cancer incidence and mortality were combined using assumptions about the relative weight that should be assigned to each estimate to represent its relevance to estimation of a dose and dose-rate effectiveness factor. The probability distribution of a dose and dose-rate effectiveness factor for solid cancers developed in this study has a median (50th percentile) and 90% subjective confidence interval of 1.3 (0.47, 3.6). The harmonic mean is 1.1, which implies that the arithmetic mean of an uncertain estimate of the risk of a solid cancer per Gy at low acute doses or low dose rates of low linear energy transfer radiation is only about 10% less than the mean risk per Gy at higher acute doses. Data were also evaluated to define a low acute dose or low dose rate of low linear energy transfer radiation, i.e., a dose or dose rate below which a dose and dose-rate effectiveness factor should be applied in estimating risks of solid cancers.

Rational evaluation of the therapeutic effect and dosimetry of auger electrons for radionuclide therapy in a cell culture model.

PubMed

Shinohara, Ayaka; Hanaoka, Hirofumi; Sakashita, Tetsuya; Sato, Tatsuhiko; Yamaguchi, Aiko; Ishioka, Noriko S; Tsushima, Yoshito

2018-02-01

Radionuclide therapy with low-energy auger electron emitters may provide high antitumor efficacy while keeping the toxicity to normal organs low. Here we evaluated the usefulness of an auger electron emitter and compared it with that of a beta emitter for tumor treatment in in vitro models and conducted a dosimetry simulation using radioiodine-labeled metaiodobenzylguanidine (MIBG) as a model compound. We evaluated the cellular uptake of 125 I-MIBG and the therapeutic effects of 125 I- and 131 I-MIBG in 2D and 3D PC-12 cell culture models. We used a Monte Carlo simulation code (PHITS) to calculate the absorbed radiation dose of 125 I or 131 I in computer simulation models for 2D and 3D cell cultures. In the dosimetry calculation for the 3D model, several distribution patterns of radionuclide were applied. A higher cumulative dose was observed in the 3D model due to the prolonged retention of MIBG compared to the 2D model. However, 125 I-MIBG showed a greater therapeutic effect in the 2D model compared to the 3D model (respective EC 50 values in the 2D and 3D models: 86.9 and 303.9 MBq/cell), whereas 131 I-MIBG showed the opposite result (respective EC 50 values in the 2D and 3D models: 49.4 and 30.2 MBq/cell). The therapeutic effect of 125 I-MIBG was lower than that of 131 I-MIBG in both models, but the radionuclide-derived difference was smaller in the 2D model. The dosimetry simulation with PHITS revealed the influence of the radiation quality, the crossfire effect, radionuclide distribution, and tumor shape on the absorbed dose. Application of the heterogeneous distribution series dramatically changed the radiation dose distribution of 125 I-MIBG, and mitigated the difference between the estimated and measured therapeutic effects of 125 I-MIBG. The therapeutic effect of 125 I-MIBG was comparable to that of 131 I-MIBG in the 2D model, but the efficacy was inferior to that of 131 I-MIBG in the 3D model, since the crossfire effect is negligible and the homogeneous distribution of radionuclides was insufficient. Thus, auger electrons would be suitable for treating small-sized tumors. The design of radiopharmaceuticals with auger electron emitters requires particularly careful consideration of achieving a homogeneous distribution of the compound in the tumor.

Survey of distribution of seasonal influenza vaccine doses in 201 countries (2004-2015): The 2003 World Health Assembly resolution on seasonal influenza vaccination coverage and the 2009 influenza pandemic have had very little impact on improving influenza control and pandemic preparedness.

PubMed

Palache, A; Abelin, A; Hollingsworth, R; Cracknell, W; Jacobs, C; Tsai, T; Barbosa, P

2017-08-24

There is no global monitoring system for influenza vaccination coverage, making it difficult to assess progress towards the 2003 World Health Assembly (WHA) vaccination coverage target. In 2008, the IFPMA Influenza Vaccine Supply International Task Force (IVS) developed a survey method to assess the global distribution of influenza vaccine doses as a proxy for vaccination coverage rates. The latest dose distribution data for 2014 and 2015 was used to update previous analyses. Data were confidentially collected and aggregated by the IFPMA Secretariat, and combined with previous IFPMA IVS survey data (2004-2013). Data were available from 201 countries over the 2004-2015 period. A "hurdle" rate was defined as the number of doses required to reach 15.9% of the population in 2008. Overall, the number of distributed doses progressively increased between 2004 and 2011, driven by a 150% increase in AMRO, then plateaued. One percent fewer doses were distributed in 2015 than in 2011. Twenty-three countries were above the hurdle rate in 2015, compared to 15 in 2004, but distribution was highly uneven in and across all WHO regions. Three WHO regions (AMRO, EURO and WPRO) accounted for about 95% of doses distributed. But in EURO and WPRO, distribution rates in 2015 were only marginally higher than in 2004, and in EURO there was an overall downward trend in dose distribution. The vast majority of countries cannot meet the 2003WHA coverage targets and are inadequately prepared for a global influenza pandemic. With only 5% of influenza vaccine doses being distributed to 50% of the world's population, there is urgency to redress the gross inequities in disease prevention and in pandemic preparedness. The 2003WHA resolution must be reviewed and revised and a call issued for the renewed commitment of Member States to influenza vaccination coverage targets. Copyright © 2017. Published by Elsevier Ltd.

Proton depth dose distribution: 3-D calculation of dose distributions from solar flare irradiation

NASA Astrophysics Data System (ADS)

Leavitt, Dennis D.

1990-11-01

Relative depth dose distribution to the head from 3 typical solar flare proton events were calculated for 3 different exposure geometries: (1) single directional radiation incident upon a fixed head; (2) single directional radiation incident upon head rotating axially (2-D rotation); and (3) omnidirectional radiation incident upon head (3-D rotation). Isodose distributions in the transverse plane intersecting isocenter are presented for each of the 3 solar flare events in all 3 exposure geometries. In all 3 calculation configurations the maximum predicted dose occurred on the surface of the head. The dose at the isocenter of the head relative to the surface dose for the 2-D and 3-D rotation geometries ranged from 2 to 19 percent, increasing with increasing energy of the event. The calculations suggest the superficially located organs (lens of the eye and skin) are at greatest risk for the proton events studied here.

The effect of dose heterogeneity on radiation risk in medical imaging.

PubMed

Samei, Ehsan; Li, Xiang; Chen, Baiyu; Reiman, Robert

2013-06-01

The current estimations of risk associated with medical imaging procedures rely on assessing the organ dose via direct measurements or simulation. The dose to each organ is assumed to be homogeneous. To take into account the differences in radiation sensitivities, the mean organ doses are weighted by a corresponding tissue-weighting coefficients provided by ICRP to calculate the effective dose, which has been used as a surrogate of radiation risk. However, those coefficients were derived under the assumption of a homogeneous dose distribution within each organ. That assumption is significantly violated in most medical-imaging procedures. In helical chest CT, for example, superficial organs (e.g. breasts) demonstrate a heterogeneous dose distribution, whereas organs on the peripheries of the irradiation field (e.g. liver) might possess a discontinuous dose profile. Projection radiography and mammography involve an even higher level of organ dose heterogeneity spanning up to two orders of magnitude. As such, mean dose or point measured dose values do not reflect the maximum energy deposited per unit volume of the organ. In this paper, the magnitude of the dose heterogeneity in both CT and projection X-ray imaging was reported, using Monte Carlo methods. The lung dose demonstrated factors of 1.7 and 2.2 difference between the mean and maximum dose for chest CT and radiography, respectively. The corresponding values for the liver were 1.9 and 3.5. For mammography and breast tomosynthesis, the difference between mean glandular dose and maximum glandular dose was 3.1. Risk models based on the mean dose were found to provide a reasonable reflection of cancer risk. However, for leukaemia, they were found to significantly under-represent the risk when the organ dose distribution is heterogeneous. A systematic study is needed to develop a risk model for heterogeneous dose distributions.

Development of probabilistic internal dosimetry computer code

NASA Astrophysics Data System (ADS)

Noh, Siwan; Kwon, Tae-Eun; Lee, Jai-Ki

2017-02-01

Internal radiation dose assessment involves biokinetic models, the corresponding parameters, measured data, and many assumptions. Every component considered in the internal dose assessment has its own uncertainty, which is propagated in the intake activity and internal dose estimates. For research or scientific purposes, and for retrospective dose reconstruction for accident scenarios occurring in workplaces having a large quantity of unsealed radionuclides, such as nuclear power plants, nuclear fuel cycle facilities, and facilities in which nuclear medicine is practiced, a quantitative uncertainty assessment of the internal dose is often required. However, no calculation tools or computer codes that incorporate all the relevant processes and their corresponding uncertainties, i.e., from the measured data to the committed dose, are available. Thus, the objective of the present study is to develop an integrated probabilistic internal-dose-assessment computer code. First, the uncertainty components in internal dosimetry are identified, and quantitative uncertainty data are collected. Then, an uncertainty database is established for each component. In order to propagate these uncertainties in an internal dose assessment, a probabilistic internal-dose-assessment system that employs the Bayesian and Monte Carlo methods. Based on the developed system, we developed a probabilistic internal-dose-assessment code by using MATLAB so as to estimate the dose distributions from the measured data with uncertainty. Using the developed code, we calculated the internal dose distribution and statistical values ( e.g. the 2.5th, 5th, median, 95th, and 97.5th percentiles) for three sample scenarios. On the basis of the distributions, we performed a sensitivity analysis to determine the influence of each component on the resulting dose in order to identify the major component of the uncertainty in a bioassay. The results of this study can be applied to various situations. In cases of severe internal exposure, the causation probability of a deterministic health effect can be derived from the dose distribution, and a high statistical value ( e.g., the 95th percentile of the distribution) can be used to determine the appropriate intervention. The distribution-based sensitivity analysis can also be used to quantify the contribution of each factor to the dose uncertainty, which is essential information for reducing and optimizing the uncertainty in the internal dose assessment. Therefore, the present study can contribute to retrospective dose assessment for accidental internal exposure scenarios, as well as to internal dose monitoring optimization and uncertainty reduction.

Real-time dose calculation and visualization for the proton therapy of ocular tumours

NASA Astrophysics Data System (ADS)

Pfeiffer, Karsten; Bendl, Rolf

2001-03-01

A new real-time dose calculation and visualization was developed as part of the new 3D treatment planning tool OCTOPUS for proton therapy of ocular tumours within a national research project together with the Hahn-Meitner Institut Berlin. The implementation resolves the common separation between parameter definition, dose calculation and evaluation and allows a direct examination of the expected dose distribution while adjusting the treatment parameters. The new tool allows the therapist to move the desired dose distribution under visual control in 3D to the appropriate place. The visualization of the resulting dose distribution as a 3D surface model, on any 2D slice or on the surface of specified ocular structures is done automatically when adapting parameters during the planning process. In addition, approximate dose volume histograms may be calculated with little extra time. The dose distribution is calculated and visualized in 200 ms with an accuracy of 6% for the 3D isodose surfaces and 8% for other objects. This paper discusses the advantages and limitations of this new approach.

An automated optimization tool for high-dose-rate (HDR) prostate brachytherapy with divergent needle pattern

NASA Astrophysics Data System (ADS)

Borot de Battisti, M.; Maenhout, M.; de Senneville, B. Denis; Hautvast, G.; Binnekamp, D.; Lagendijk, J. J. W.; van Vulpen, M.; Moerland, M. A.

2015-10-01

Focal high-dose-rate (HDR) for prostate cancer has gained increasing interest as an alternative to whole gland therapy as it may contribute to the reduction of treatment related toxicity. For focal treatment, optimal needle guidance and placement is warranted. This can be achieved under MR guidance. However, MR-guided needle placement is currently not possible due to space restrictions in the closed MR bore. To overcome this problem, a MR-compatible, single-divergent needle-implant robotic device is under development at the University Medical Centre, Utrecht: placed between the legs of the patient inside the MR bore, this robot will tap the needle in a divergent pattern from a single rotation point into the tissue. This rotation point is just beneath the perineal skin to have access to the focal prostate tumor lesion. Currently, there is no treatment planning system commercially available which allows optimization of the dose distribution with such needle arrangement. The aim of this work is to develop an automatic inverse dose planning optimization tool for focal HDR prostate brachytherapy with needle insertions in a divergent configuration. A complete optimizer workflow is proposed which includes the determination of (1) the position of the center of rotation, (2) the needle angulations and (3) the dwell times. Unlike most currently used optimizers, no prior selection or adjustment of input parameters such as minimum or maximum dose or weight coefficients for treatment region and organs at risk is required. To test this optimizer, a planning study was performed on ten patients (treatment volumes ranged from 8.5 cm3to 23.3 cm3) by using 2-14 needle insertions. The total computation time of the optimizer workflow was below 20 min and a clinically acceptable plan was reached on average using only four needle insertions.

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

Ma, Y; Lacroix, F; Lavallee, M

Purpose: To evaluate the commercially released Collapsed Cone convolution-based(CCC) dose calculation module of the Elekta OncentraBrachy(OcB) treatment planning system(TPS). Methods: An allwater phantom was used to perform TG43 benchmarks with single source and seventeen sources, separately. Furthermore, four real-patient heterogeneous geometries (chestwall, lung, breast and prostate) were used. They were selected based on their clinical representativity of a class of clinical anatomies that pose clear challenges. The plans were used as is(no modification). For each case, TG43 and CCC calculations were performed in the OcB TPS, with TG186-recommended materials properly assigned to ROIs. For comparison, Monte Carlo simulation was runmore » for each case with the same material scheme and grid mesh as TPS calculations. Both modes of CCC (standard and high quality) were tested. Results: For the benchmark case, the CCC dose, when divided by that of TG43, yields hot-n-cold spots in a radial pattern. The pattern of the high mode is denser than that of the standard mode and is representative of angular dicretization. The total deviation ((hot-cold)/TG43) is 18% for standard mode and 11% for high mode. Seventeen dwell positions help to reduce “ray-effect”, with the total deviation to 6% (standard) and 5% (high), respectively. For the four patient cases, CCC produces, as expected, more realistic dose distributions than TG43. A close agreement was observed between CCC and MC for all isodose lines, from 20% and up; the 10% isodose line of CCC appears shifted compared to that of MC. The DVH plots show dose deviations of CCC from MC in small volume, high dose regions (>100% isodose). For patient cases, the difference between standard and high modes is almost undiscernable. Conclusion: OncentraBrachy CCC algorithm marks a significant dosimetry improvement relative to TG43 in real-patient cases. Further researches are recommended regarding the clinical implications of the above observations. Support provided by a CIHR grant and CCC system provided by Elekta-Nucletron.« less

Mesoscopic in vivo 3-D tracking of sparse cell populations using angular multiplexed optical projection tomography

PubMed Central

Chen, Lingling; Alexandrov, Yuriy; Kumar, Sunil; Andrews, Natalie; Dallman, Margaret J.; French, Paul M. W.; McGinty, James

2015-01-01

We describe an angular multiplexed imaging technique for 3-D in vivo cell tracking of sparse cell distributions and optical projection tomography (OPT) with superior time-lapse resolution and a significantly reduced light dose compared to volumetric time-lapse techniques. We demonstrate that using dual axis OPT, where two images are acquired simultaneously at different projection angles, can enable localization and tracking of features in 3-D with a time resolution equal to the camera frame rate. This is achieved with a 200x reduction in light dose compared to an equivalent volumetric time-lapse single camera OPT acquisition with 200 projection angles. We demonstrate the application of this technique to mapping the 3-D neutrophil migration pattern observed over ~25.5 minutes in a live 2 day post-fertilisation transgenic LysC:GFP zebrafish embryo following a tail wound. PMID:25909009

Low-dose patterning of platinum nanoclusters on carbon nanotubes by focused-electron-beam-induced deposition as studied by TEM

PubMed Central

Bittencourt, Carla; Bals, Sara; Van Tendeloo, Gustaaf

2013-01-01

Summary Focused-electron-beam-induced deposition (FEBID) is used as a direct-write approach to decorate ultrasmall Pt nanoclusters on carbon nanotubes at selected sites in a straightforward maskless manner. The as-deposited nanostructures are studied by transmission electron microscopy (TEM) in 2D and 3D, demonstrating that the Pt nanoclusters are well-dispersed, covering the selected areas of the CNT surface completely. The ability of FEBID to graft nanoclusters on multiple sides, through an electron-transparent target within one step, is unique as a physical deposition method. Using high-resolution TEM we have shown that the CNT structure can be well preserved thanks to the low dose used in FEBID. By tuning the electron-beam parameters, the density and distribution of the nanoclusters can be controlled. The purity of as-deposited nanoclusters can be improved by low-energy electron irradiation at room temperature. PMID:23399584

Mesoscopic in vivo 3-D tracking of sparse cell populations using angular multiplexed optical projection tomography.

PubMed

Chen, Lingling; Alexandrov, Yuriy; Kumar, Sunil; Andrews, Natalie; Dallman, Margaret J; French, Paul M W; McGinty, James

2015-04-01

We describe an angular multiplexed imaging technique for 3-D in vivo cell tracking of sparse cell distributions and optical projection tomography (OPT) with superior time-lapse resolution and a significantly reduced light dose compared to volumetric time-lapse techniques. We demonstrate that using dual axis OPT, where two images are acquired simultaneously at different projection angles, can enable localization and tracking of features in 3-D with a time resolution equal to the camera frame rate. This is achieved with a 200x reduction in light dose compared to an equivalent volumetric time-lapse single camera OPT acquisition with 200 projection angles. We demonstrate the application of this technique to mapping the 3-D neutrophil migration pattern observed over ~25.5 minutes in a live 2 day post-fertilisation transgenic LysC:GFP zebrafish embryo following a tail wound.

Patterns of Failure After Proton Therapy in Medulloblastoma; Linear Energy Transfer Distributions and Relative Biological Effectiveness Associations for Relapses

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

Sethi, Roshan V.; Giantsoudi, Drosoula; Raiford, Michael

2014-03-01

Purpose: The pattern of failure in medulloblastoma patients treated with proton radiation therapy is unknown. For this increasingly used modality, it is important to ensure that outcomes are comparable to those in modern photon series. It has been suggested this pattern may differ from photons because of variations in linear energy transfer (LET) and relative biological effectiveness (RBE). In addition, the use of matching fields for delivery of craniospinal irradiation (CSI) may influence patterns of relapse. Here we report the patterns of failure after the use of protons, compare it to that in the available photon literature, and determine themore » LET and RBE values in areas of recurrence. Methods and Materials: Retrospective review of patients with medulloblastoma treated with proton radiation therapy at Massachusetts General Hospital (MGH) between 2002 and 2011. We documented the locations of first relapse. Discrete failures were contoured on the original planning computed tomography scan. Monte Carlo calculation methods were used to estimate the proton LET distribution. Models were used to estimate RBE values based on the LET distributions. Results: A total of 109 patients were followed for a median of 38.8 months (range, 1.4-119.2 months). Of the patients, 16 experienced relapse. Relapse involved the supratentorial compartment (n=8), spinal compartment (n=11), and posterior fossa (n=5). Eleven failures were isolated to a single compartment; 6 failures in the spine, 4 failures in the supratentorium, and 1 failure in the posterior fossa. The remaining patients had multiple sites of disease. One isolated spinal failure occurred at the spinal junction of 2 fields. None of the 70 patients treated with an involved-field-only boost failed in the posterior fossa outside of the tumor bed. We found no correlation between Monte Carlo-calculated LET distribution and regions of recurrence. Conclusions: The most common site of failure in patients treated with protons for medulloblastoma was outside of the posterior fossa. The most common site for isolated local failure was the spine. We recommend consideration of spinal imaging in follow-up and careful attention to dose distribution in the spinal junction regions. Development of techniques that do not require field matching may be of benefit. We did not identify a direct correlation between lower LET values and recurrence in medulloblastoma patients treated with proton therapy. Patterns of failure do not appear to differ from those in patients treated with photon therapy.« less

PROPOSALS FOR THE ESTABLISHMENT OF NATIONAL DIAGNOSTIC REFERENCE LEVELS FOR RADIOGRAPHY FOR ADULT PATIENTS BASED ON REGIONAL DOSE SURVEYS IN RUSSIAN FEDERATION.

PubMed

Vodovatov, A V; Balonov, M I; Golikov, V Yu; Shatsky, I G; Chipiga, L A; Bernhardsson, C

2017-04-01

In 2009-2014, dose surveys aimed to collect adult patient data and parameters of most common radiographic examinations were performed in six Russian regions. Typical patient doses were estimated for the selected examinations both in entrance surface dose and in effective dose. 75%-percentiles of typical patient effective dose distributions were proposed as preliminary regional diagnostic reference levels (DRLs) for radiography. Differences between the 75%-percentiles of regional typical patient dose distributions did not exceed 30-50% for the examinations with standardized clinical protocols (skull, chest and thoracic spine) and a factor of 1.5 for other examinations. Two different approaches for establishing national DRLs were evaluated: as a 75%-percentile of a pooled regional sample of patient typical doses (pooled method) and as a median of 75%-percentiles of regional typical patient dose distributions (median method). Differences between pooled and median methods for effective dose did not exceed 20%. It was proposed to establish Russian national DRLs in effective dose using a pooled method. In addition, the local authorities were granted an opportunity to establish regional DRLs if the local radiological practice and typical patient dose distributions are significantly different. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

The influence of age at time of exposure to sup 226 Ra or sup 239 Pu on distribution, retention, postinjection survival, and tumor induction in beagle dogs

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

Bruenger, F.W.; Lloyd, R.D.; Miller, S.C.

The influence of age at injection of 226Ra or 239Pu on skeletal deposition and local distribution, the pattern of bone tumor formation, and postinjection survival was assessed in parallel short-term studies of mechanisms and lifetime toxicity. Beagles received a single intravenous injection of 226Ra or 239Pu at 3 months (juveniles), 17-19 months (young adults) or 60 months (mature). Data from short-term studies of mechanisms and dosimetry and from one dosage level of each of the toxicity experiments were compared. Skeletal growth and turnover produced differential initial deposition and distribution patterns typical for each age group. At 1 week after injection,more » skeletal retention of 226Ra or 239Pu was 68 and 68%, respectively, in the juveniles, 32 and 46% in the young adults, and 31 and 43% in the mature dogs. Comparing individual bones in the juveniles, gradients in the concentration of 239Pu were small since all bones were actively growing, but substantial gradients, corresponding to centers of ossification, were present within individual bones. In other age groups, local concentration gradients were less pronounced, but much larger differences were present among the various bones. In the toxicity study all animals injected with either 41 kBq 226Ra/kg or 11 kBq 239Pu/kg have died. The cumulative average skeletal doses to the presumed time of start of tumor growth (1 year before death) were 25 and 4 Gy, respectively, for the juveniles, 22 and 5 Gy for the young adults, and 15 and 4 Gy for the mature dogs. The highest bone tumor incidence was seen in the young adult groups. Differences were observed in location of bone tumors between dogs in the same age group given radium or plutonium and among age groups injected with either radionuclide, some of which could be explained by differences in local dose distributions.« less

Quantifying the Combined Effect of Radiation Therapy and Hyperthermia in Terms of Equivalent Dose Distributions

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

Kok, H. Petra, E-mail: H.P.Kok@amc.uva.nl; Crezee, Johannes; Franken, Nicolaas A.P.

2014-03-01

Purpose: To develop a method to quantify the therapeutic effect of radiosensitization by hyperthermia; to this end, a numerical method was proposed to convert radiation therapy dose distributions with hyperthermia to equivalent dose distributions without hyperthermia. Methods and Materials: Clinical intensity modulated radiation therapy plans were created for 15 prostate cancer cases. To simulate a clinically relevant heterogeneous temperature distribution, hyperthermia treatment planning was performed for heating with the AMC-8 system. The temperature-dependent parameters α (Gy{sup −1}) and β (Gy{sup −2}) of the linear–quadratic model for prostate cancer were estimated from the literature. No thermal enhancement was assumed for normalmore » tissue. The intensity modulated radiation therapy plans and temperature distributions were exported to our in-house-developed radiation therapy treatment planning system, APlan, and equivalent dose distributions without hyperthermia were calculated voxel by voxel using the linear–quadratic model. Results: The planned average tumor temperatures T90, T50, and T10 in the planning target volume were 40.5°C, 41.6°C, and 42.4°C, respectively. The planned minimum, mean, and maximum radiation therapy doses were 62.9 Gy, 76.0 Gy, and 81.0 Gy, respectively. Adding hyperthermia yielded an equivalent dose distribution with an extended 95% isodose level. The equivalent minimum, mean, and maximum doses reflecting the radiosensitization by hyperthermia were 70.3 Gy, 86.3 Gy, and 93.6 Gy, respectively, for a linear increase of α with temperature. This can be considered similar to a dose escalation with a substantial increase in tumor control probability for high-risk prostate carcinoma. Conclusion: A model to quantify the effect of combined radiation therapy and hyperthermia in terms of equivalent dose distributions was presented. This model is particularly instructive to estimate the potential effects of interaction from different treatment modalities.« less

Relationship between Individual External Doses, Ambient Dose Rates and Individuals' Activity-Patterns in Affected Areas in Fukushima following the Fukushima Daiichi Nuclear Power Plant Accident.

PubMed

Naito, Wataru; Uesaka, Motoki; Yamada, Chie; Kurosawa, Tadahiro; Yasutaka, Tetsuo; Ishii, Hideki

2016-01-01

The accident at Fukushima Daiichi Nuclear Power Plant on March 11, 2011, released radioactive material into the atmosphere and contaminated the land in Fukushima and several neighboring prefectures. Five years after the nuclear disaster, the radiation levels have greatly decreased due to physical decay, weathering, and decontamination operations in Fukushima. The populations of 12 communities were forced to evacuate after the accident; as of March 2016, the evacuation order has been lifted in only a limited area, and permanent habitation is still prohibited in most of the areas. In order for the government to lift the evacuation order and for individuals to return to their original residential areas, it is important to assess current and future realistic individual external doses. Here, we used personal dosimeters along with the Global Positioning System and Geographic Information System to understand realistic individual external doses and to relate individual external doses, ambient doses, and activity-patterns of individuals in the affected areas in Fukushima. The results showed that the additional individual external doses were well correlated to the additional ambient doses based on the airborne monitoring survey. The results of linear regression analysis suggested that the additional individual external doses were on average about one-fifth that of the additional ambient doses. The reduction factors, which are defined as the ratios of the additional individual external doses to the additional ambient doses, were calculated to be on average 0.14 and 0.32 for time spent at home and outdoors, respectively. Analysis of the contribution of various activity patterns to the total individual external dose demonstrated good agreement with the average fraction of time spent daily in each activity, but the contribution due to being outdoors varied widely. These results are a valuable contribution to understanding realistic individual external doses and the corresponding airborne monitoring-based ambient doses and time-activity patterns of individuals. Moreover, the results provide important information for predicting future cumulative doses after the return of residents to evacuation order areas in Fukushima.

Relationship between Individual External Doses, Ambient Dose Rates and Individuals’ Activity-Patterns in Affected Areas in Fukushima following the Fukushima Daiichi Nuclear Power Plant Accident

PubMed Central

Kurosawa, Tadahiro; Yasutaka, Tetsuo; Ishii, Hideki

2016-01-01

The accident at Fukushima Daiichi Nuclear Power Plant on March 11, 2011, released radioactive material into the atmosphere and contaminated the land in Fukushima and several neighboring prefectures. Five years after the nuclear disaster, the radiation levels have greatly decreased due to physical decay, weathering, and decontamination operations in Fukushima. The populations of 12 communities were forced to evacuate after the accident; as of March 2016, the evacuation order has been lifted in only a limited area, and permanent habitation is still prohibited in most of the areas. In order for the government to lift the evacuation order and for individuals to return to their original residential areas, it is important to assess current and future realistic individual external doses. Here, we used personal dosimeters along with the Global Positioning System and Geographic Information System to understand realistic individual external doses and to relate individual external doses, ambient doses, and activity-patterns of individuals in the affected areas in Fukushima. The results showed that the additional individual external doses were well correlated to the additional ambient doses based on the airborne monitoring survey. The results of linear regression analysis suggested that the additional individual external doses were on average about one-fifth that of the additional ambient doses. The reduction factors, which are defined as the ratios of the additional individual external doses to the additional ambient doses, were calculated to be on average 0.14 and 0.32 for time spent at home and outdoors, respectively. Analysis of the contribution of various activity patterns to the total individual external dose demonstrated good agreement with the average fraction of time spent daily in each activity, but the contribution due to being outdoors varied widely. These results are a valuable contribution to understanding realistic individual external doses and the corresponding airborne monitoring-based ambient doses and time-activity patterns of individuals. Moreover, the results provide important information for predicting future cumulative doses after the return of residents to evacuation order areas in Fukushima. PMID:27494021

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.

Radiation exposure assessment for portsmouth naval shipyard health studies.

PubMed

Daniels, R D; Taulbee, T D; Chen, P

2004-01-01

Occupational radiation exposures of 13,475 civilian nuclear shipyard workers were investigated as part of a retrospective mortality study. Estimates of annual, cumulative and collective doses were tabulated for future dose-response analysis. Record sets were assembled and amended through range checks, examination of distributions and inspection. Methods were developed to adjust for administrative overestimates and dose from previous employment. Uncertainties from doses below the recording threshold were estimated. Low-dose protracted radiation exposures from submarine overhaul and repair predominated. Cumulative doses are best approximated by a hybrid log-normal distribution with arithmetic mean and median values of 20.59 and 3.24 mSv, respectively. The distribution is highly skewed with more than half the workers having cumulative doses <10 mSv and >95% having doses <100 mSv. The maximum cumulative dose is estimated at 649.39 mSv from 15 person-years of exposure. The collective dose was 277.42 person-Sv with 96.8% attributed to employment at Portsmouth Naval Shipyard.

Update on the Use of Botulinum Toxin Therapy for Focal and Task-Specific Dystonias.

PubMed

Lungu, Codrin; Ahmad, Omar F

2016-02-01

Focal dystonia is defined by anatomical distribution and represents a distinct entity from generalized dystonia. Task-specific dystonia occurs in the context of specific patterns of movement. Botulinum neurotoxin (BoNT) injections are the treatment of choice in most cases. Several formulations are available; the approved indications, dosing, and some administration details, differ between them. The major forms of focal and task-specific dystonia are reviewed, along with the evidence for BoNT therapy, the expected benefit and side effects, and practical points guiding the injections. Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.

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

Gorissen, BL; Giantsoudi, D; Unkelbach, J

Purpose: Cell survival experiments suggest that the relative biological effectiveness (RBE) of proton beams depends on linear energy transfer (LET), leading to higher RBE near the end of range. With intensity-modulated proton therapy (IMPT), multiple treatment plans that differ in the dose contribution per field may yield a similar physical dose distribution, but the RBE-weighted dose distribution may be disparate. RBE models currently do not have the required predictive power to be included in an optimization model due to the variations in experimental data. We propose an LET-based planning method that guides IMPT optimization models towards plans with reduced RBE-weightedmore » dose in surrounding organs at risk (OARs) compared to inverse planning based on physical dose alone. Methods: Optimization models for physical dose are extended with a term for dose times LET (doseLET). Monte Carlo code is used to generate the physical dose and doseLET distribution of each individual pencil beam. The method is demonstrated for an atypical meningioma patient where the target volume abuts the brainstem and partially overlaps with the optic nerve. Results: A reference plan optimized based on physical dose alone yields high doseLET values in parts of the brainstem and optic nerve. Minimizing doseLET in these critical structures as an additional planning goal reduces the risk of high RBE-weighted dose. The resulting treatment plan avoids the distal fall-off of the Bragg peaks for shaping the dose distribution in front of critical stuctures. The maximum dose in the OARs evaluated with RBE models from literature is reduced by 8–14\\% with our method compared to conventional planning. Conclusion: LET-based inverse planning for IMPT offers the ability to reduce the RBE-weighted dose in OARs without sacrificing target dose. This project was in part supported by NCI - U19 CA 21239.« less

Mechanistic simulation of normal-tissue damage in radiotherapy—implications for dose-volume analyses

NASA Astrophysics Data System (ADS)

Rutkowska, Eva; Baker, Colin; Nahum, Alan

2010-04-01

A radiobiologically based 3D model of normal tissue has been developed in which complications are generated when 'irradiated'. The aim is to provide insight into the connection between dose-distribution characteristics, different organ architectures and complication rates beyond that obtainable with simple DVH-based analytical NTCP models. In this model the organ consists of a large number of functional subunits (FSUs), populated by stem cells which are killed according to the LQ model. A complication is triggered if the density of FSUs in any 'critical functioning volume' (CFV) falls below some threshold. The (fractional) CFV determines the organ architecture and can be varied continuously from small (series-like behaviour) to large (parallel-like). A key feature of the model is its ability to account for the spatial dependence of dose distributions. Simulations were carried out to investigate correlations between dose-volume parameters and the incidence of 'complications' using different pseudo-clinical dose distributions. Correlations between dose-volume parameters and outcome depended on characteristics of the dose distributions and on organ architecture. As anticipated, the mean dose and V20 correlated most strongly with outcome for a parallel organ, and the maximum dose for a serial organ. Interestingly better correlation was obtained between the 3D computer model and the LKB model with dose distributions typical for serial organs than with those typical for parallel organs. This work links the results of dose-volume analyses to dataset characteristics typical for serial and parallel organs and it may help investigators interpret the results from clinical studies.

Biological effective dose for comparison and combination of external beam and low-dose rate interstitial brachytherapy prostate cancer treatment plans

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

Jani, Ashesh B.; Hand, Christopher M.; Lujan, Anthony E.

2004-03-31

We report a methodology for comparing and combining dose information from external beam radiotherapy (EBRT) and interstitial brachytherapy (IB) components of prostate cancer treatment using the biological effective dose (BED). On a prototype early-stage prostate cancer patient treated with EBRT and low-dose rate I-125 brachytherapy, a 3-dimensional dose distribution was calculated for each of the EBRT and IB portions of treatment. For each component of treatment, the BED was calculated on a point-by-point basis to produce a BED distribution. These individual BED distributions could then be summed for combined therapies. BED dose-volume histograms (DVHs) of the prostate, urethra, rectum, andmore » bladder were produced and compared for various combinations of EBRT and IB. Transformation to BED enabled computation of the relative contribution of each modality to the prostate dose, as the relative weighting of EBRT and IB was varied. The BED-DVHs of the prostate and urethra demonstrated dramatically increased inhomogeneity with the introduction of even a small component of IB. However, increasing the IB portion relative to the EBRT component resulted in lower dose to the surrounding normal structures, as evidenced by the BED-DVHs of the bladder and rectum. Conformal EBRT and low-dose rate IB conventional dose distributions were successfully transformed to the common 'language' of BED distributions for comparison and for merging prostate cancer radiation treatment plans. The results of this analysis can assist physicians in quantitatively determining the best combination and weighting of radiation treatment modalities for individual patients.« less

TU-H-CAMPUS-IeP1-05: A Framework for the Analytic Calculation of Patient-Specific Dose Distribution Due to CBCT Scan for IGRT

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

Youn, H; Jeon, H; Nam, J

Purpose: To investigate the feasibility of an analytic framework to estimate patients’ absorbed dose distribution owing to daily cone-beam CT scan for image-guided radiation treatment. Methods: To compute total absorbed dose distribution, we separated the framework into primary and scattered dose calculations. Using the source parameters such as voltage, current, and bowtie filtration, for the primary dose calculation, we simulated the forward projection from the source to each voxel of an imaging object including some inhomogeneous inserts. Then we calculated the primary absorbed dose at each voxel based on the absorption probability deduced from the HU values and Beer’s law.more » In sequence, all voxels constructing the phantom were regarded as secondary sources to radiate scattered photons for scattered dose calculation. Details of forward projection were identical to that of the previous step. The secondary source intensities were given by using scatter-to- primary ratios provided by NIST. In addition, we compared the analytically calculated dose distribution with their Monte Carlo simulation results. Results: The suggested framework for absorbed dose estimation successfully provided the primary and secondary dose distributions of the phantom. Moreover, our analytic dose calculations and Monte Carlo calculations were well agreed each other even near the inhomogeneous inserts. Conclusion: This work indicated that our framework can be an effective monitor to estimate a patient’s exposure owing to cone-beam CT scan for image-guided radiation treatment. Therefore, we expected that the patient’s over-exposure during IGRT might be prevented by our framework.« less

SU-G-BRA-14: Dose in a Rigidly Moving Phantom with Jaw and MLC Compensation

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

Chao, E; Lucas, D

Purpose: To validate dose calculation for a rigidly moving object with jaw motion and MLC shifts to compensate for the motion in a TomoTherapy™ treatment delivery. Methods: An off-line version of the TomoTherapy dose calculator was extended to perform dose calculations for rigidly moving objects. A variety of motion traces were added to treatment delivery plans, along with corresponding jaw compensation and MLC shift compensation profiles. Jaw compensation profiles were calculated by shifting the jaws such that the center of the treatment beam moved by an amount equal to the motion in the longitudinal direction. Similarly, MLC compensation profiles weremore » calculated by shifting the MLC leaves by an amount that most closely matched the motion in the transverse direction. The same jaw and MLC compensation profiles were used during simulated treatment deliveries on a TomoTherapy system, and film measurements were obtained in a rigidly moving phantom. Results: The off-line TomoTherapy dose calculator accurately predicted dose profiles for a rigidly moving phantom along with jaw motion and MLC shifts to compensate for the motion. Calculations matched film measurements to within 2%/1 mm. Jaw and MLC compensation substantially reduced the discrepancy between the delivered dose distribution and the calculated dose with no motion. For axial motion, the compensated dose matched the no-motion dose within 2%/1mm. For transverse motion, the dose matched within 2%/3mm (approximately half the width of an MLC leaf). Conclusion: The off-line TomoTherapy dose calculator accurately computes dose delivered to a rigidly moving object, and accurately models the impact of moving the jaws and shifting the MLC leaf patterns to compensate for the motion. Jaw tracking and MLC leaf shifting can effectively compensate for the dosimetric impact of motion during a TomoTherapy treatment delivery.« less

Verification of Dose Distribution in Carbon Ion Radiation Therapy for Stage I Lung Cancer

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

Irie, Daisuke; Saitoh, Jun-ichi, E-mail: junsaito@gunma-u.ac.jp; Shirai, Katsuyuki

Purpose: To evaluate robustness of dose distribution of carbon-ion radiation therapy (C-ion RT) in non-small cell lung cancer (NSCLC) and to identify factors affecting the dose distribution by simulated dose distribution. Methods and Materials: Eighty irradiation fields for delivery of C-ion RT were analyzed in 20 patients with stage I NSCLC. Computed tomography images were obtained twice before treatment initiation. Simulated dose distribution was reconstructed on computed tomography for confirmation under the same settings as actual treatment with respiratory gating and bony structure matching. Dose-volume histogram parameters, such as %D95 (percentage of D95 relative to the prescribed dose), were calculated.more » Patients with any field for which the %D95 of gross tumor volume (GTV) was below 90% were classified as unacceptable for treatment, and the optimal target margin for such cases was examined. Results: Five patients with a total of 8 fields (10% of total number of fields analyzed) were classified as unacceptable according to %D95 of GTV, although most patients showed no remarkable change in the dose-volume histogram parameters. Receiver operating characteristic curve analysis showed that tumor displacement and change in water-equivalent pathlength were significant predictive factors of unacceptable cases (P<.001 and P=.002, respectively). The main cause of degradation of the dose distribution was tumor displacement in 7 of the 8 unacceptable fields. A 6-mm planning target volume margin ensured a GTV %D95 of >90%, except in 1 extremely unacceptable field. Conclusions: According to this simulation analysis of C-ion RT for stage I NSCLC, a few fields were reported as unacceptable and required resetting of body position and reconfirmation. In addition, tumor displacement and change in water-equivalent pathlength (bone shift and/or chest wall thickness) were identified as factors influencing the robustness of dose distribution. Such uncertainties should be regarded in planning.« less

Realistic dosimetry for studies on biological responses to X-rays and γ-rays

PubMed Central

Shahmohammadi Beni, Mehrdad; Krstic, Dragana; Nikezic, Dragoslav

2017-01-01

ABSTRACT A calibration coefficient R (= DA/DE) for photons was employed to characterize the photon dose in radiobiological experiments, where DA was the actual dose delivered to cells and DE was the dose recorded by an ionization chamber. R was determined using the Monte Carlo N-Particle version 5 (MCNP-5) code. Photons with (i) discrete energies, and (ii) continuous-energy distributions under different beam conditioning were considered. The four studied monoenergetic photons had energies E = 0.01, 0.1, 1 and 2 MeV. Photons with E = 0.01 MeV gave R values significantly different from unity, while those with E > 0.1 MeV gave R ≈ 1. Moreover, R decreased monotonically with increasing thickness of water medium above the cells for E = 0.01, 1 or 2 MeV due to energy loss of photons in the medium. For E = 0.1 MeV, the monotonic pattern no longer existed due to the dose delivered to the cells by electrons created through the photoelectric effect close to the medium–cell boundary. The continuous-energy distributions from the X-Rad 320 Biological Irradiator (voltage = 150 kV) were also studied under three different beam conditions: (a) F0: no filter used, (b) F1: using a 2 mm-thick Al filter, and (c) F2: using a filter made of (1.5 mm Al + 0.25 mm Cu + 0.75 mm Sn), giving mean output photon energies of 47.4, 57.3 and 102 keV, respectively. R varied from ~1.04 to ~1.28 for F0, from ~1.13 to ~1.21 for F1, and was very close to unity for F2. PMID:28444359

Four-dimensional layer-stacking carbon-ion beam dose distribution by use of a lung numeric phantom.

PubMed

Mori, Shinichiro; Kumagai, Motoki; Miki, Kentaro

2015-07-01

To extend layer-stacking irradiation to accommodate intrafractional organ motion, we evaluated the carbon-ion layer-stacking dose distribution using a numeric lung phantom. We designed several types of range compensators. The planning target volume was calculated from the respective respiratory phases for consideration of intrafractional beam range variation. The accumulated dose distribution was calculated by registering of the dose distributions at respective phases to that at the reference phase. We evaluated the dose distribution based on the following six parameters: motion displacement, direction, gating window, respiratory cycle, range-shifter change time, and prescribed dose. All parameters affected the dose conformation to the moving target. By shortening of the gating window, dose metrics for superior-inferior (SI) and anterior-posterior (AP) motions were decreased from a D95 of 94 %, Dmax of 108 %, and homogeneity index (HI) of 23 % at T00-T90, to a D95 of 93 %, Dmax of 102 %, and HI of 20 % at T40-T60. In contrast, all dose metrics except the HI were independent of respiratory cycle. All dose metrics in SI motion were almost the same in respective motion displacement, with a D95 of 94 %, Dmax of 108 %, Dmin of 89 %, and HI of 23 % for the ungated phase, and D95 of 93 %, Dmax of 102 %, Dmin of 85 %, and HI of 20 % for the gated phase. The dose conformation to a moving target was improved by the gating strategy and by an increase in the prescribed dose. A combination of these approaches is a practical means of adding them to existing treatment protocols without modifications.

Development of a Spect-Based Three-Dimensional Treatment Planner for Radionuclide Therapy with Iodine -131.

NASA Astrophysics Data System (ADS)

Giap, Huan Bosco

Accurate calculation of absorbed dose to target tumors and normal tissues in the body is an important requirement for establishing fundamental dose-response relationships for radioimmunotherapy. Two major obstacles have been the difficulty in obtaining an accurate patient-specific 3-D activity map in-vivo and calculating the resulting absorbed dose. This study investigated a methodology for 3-D internal dosimetry, which integrates the 3-D biodistribution of the radionuclide acquired from SPECT with a dose-point kernel convolution technique to provide the 3-D distribution of absorbed dose. Accurate SPECT images were reconstructed with appropriate methods for noise filtering, attenuation correction, and Compton scatter correction. The SPECT images were converted into activity maps using a calibration phantom. The activity map was convolved with an ^{131}I dose-point kernel using a 3-D fast Fourier transform to yield a 3-D distribution of absorbed dose. The 3-D absorbed dose map was then processed to provide the absorbed dose distribution in regions of interest. This methodology can provide heterogeneous distributions of absorbed dose in volumes of any size and shape with nonuniform distributions of activity. Comparison of the activities quantitated by our SPECT methodology to true activities in an Alderson abdominal phantom (with spleen, liver, and spherical tumor) yielded errors of -16.3% to 4.4%. Volume quantitation errors ranged from -4.0 to 5.9% for volumes greater than 88 ml. The percentage differences of the average absorbed dose rates calculated by this methodology and the MIRD S-values were 9.1% for liver, 13.7% for spleen, and 0.9% for the tumor. Good agreement (percent differences were less than 8%) was found between the absorbed dose due to penetrating radiation calculated from this methodology and TLD measurement. More accurate estimates of the 3 -D distribution of absorbed dose can be used as a guide in specifying the minimum activity to be administered to patients to deliver a prescribed absorbed dose to tumor without exceeding the toxicity limits of normal tissues.

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.

Dreaming, fenfluramine, and vitamin C.

PubMed

Mullen, A; Wilson, C W; Wilson, B P

1977-01-08

The effect of increasing doses of fenfluramine on dream patterns was studied in 20 patients receiving a reducing diet with or without a controlled dietary intake of vitamin C daily. The dream pattern was unchanged in six patients and dreams disappeared in another who normally dreamed often. In 13 patients dreams increased in frequency and intensity, and in five the dreams assumed frightening proportions. There was a significant straight-line relation between response and the size of the dose. When placebo tablets were given to four patients their dreams disappeared or assumed their pretreatment normal pattern. Absence of vitamin C from the diet did not significantly affect the dream pattern. That fenfluramine has dose-related cerebral effects should be remembered in patients with a history of mental illness.

Dreaming, fenfluramine, and vitamin C.

PubMed Central

Mullen, A; Wilson, C W; Wilson, B P

1977-01-01

The effect of increasing doses of fenfluramine on dream patterns was studied in 20 patients receiving a reducing diet with or without a controlled dietary intake of vitamin C daily. The dream pattern was unchanged in six patients and dreams disappeared in another who normally dreamed often. In 13 patients dreams increased in frequency and intensity, and in five the dreams assumed frightening proportions. There was a significant straight-line relation between response and the size of the dose. When placebo tablets were given to four patients their dreams disappeared or assumed their pretreatment normal pattern. Absence of vitamin C from the diet did not significantly affect the dream pattern. That fenfluramine has dose-related cerebral effects should be remembered in patients with a history of mental illness. PMID:318898

Comparative toxicity and tissue distribution of lead acetate in weanling and adult rats.

PubMed Central

Rader, J I; Peeler, J T; Mahaffey, K R

1981-01-01

The relative toxicity of low doses of lead acetate provided steadily in drinking water or by mouth once per week was studied in weanling and adult rats. Free erythrocyte protoporphyrin and urinary delta-aminolevulinic acid levels were measured, as well as lead levels in blood and kidney. The accumulation of lead in brain tissue and in bone (femur) was measured to determine the effect of age and schedule of administration on tissue distribution and retention of lead. Total intakes of lead during the 60-week experimental period were: weanling and adult rats exposed to drinking water supplemented with 200 microgram of lead acetate/ml: 127 +/- 10 mg and 160 +/- 16 mg, respectively; weanling and adult rats dosed with lead acetate orally once per week: 132 mg and 161 mg, respectively. Increased toxic effects of lead in the weanling animals were apparent in most of the parameters measured (urinary delta-aminolevulinic acid and blood, brain, femur and kidney lead levels). This pattern was observed in weanling rats exposed to lead steadily through drinking water or dosed orally with an equivalent quantity of lead once per week. Lead levels in blood were highly correlated with the accumulation of lead in brain, femur, and kidney tissue in both groups of weanling rats. In adult rats, significant correlations between blood lead and kidney lead and between blood lead and femur lead were found only in the rats receiving lead steadily in drinking water. PMID:7333253

Late ophthalmological complications after total body irradiation in non-human primates

NASA Technical Reports Server (NTRS)

Niemer-Tucker, M. M.; Sterk, C. C.; de Wolff-Rouendaal, D.; Lee, A. C.; Lett, J. T.; Cox, A.; Emmanouilidis-van der Spek, K.; Davelaar, J.; Lambooy, A. C.; Mooy, C. M.;

Statistical methods for clinical verification of dose response parameters related to esophageal stricture and AVM obliteration from radiotherapy

NASA Astrophysics Data System (ADS)

Mavroidis, Panayiotis; Lind, Bengt K.; Theodorou, Kyriaki; Laurell, Göran; Fernberg, Jan-Olof; Lefkopoulos, Dimitrios; Kappas, Constantin; Brahme, Anders

2004-08-01

The purpose of this work is to provide some statistical methods for evaluating the predictive strength of radiobiological models and the validity of dose-response parameters for tumour control and normal tissue complications. This is accomplished by associating the expected complication rates, which are calculated using different models, with the clinical follow-up records. These methods are applied to 77 patients who received radiation treatment for head and neck cancer and 85 patients who were treated for arteriovenous malformation (AVM). The three-dimensional dose distribution delivered to esophagus and AVM nidus and the clinical follow-up results were available for each patient. Dose-response parameters derived by a maximum likelihood fitting were used as a reference to evaluate their compatibility with the examined treatment methodologies. The impact of the parameter uncertainties on the dose-response curves is demonstrated. The clinical utilization of the radiobiological parameters is illustrated. The radiobiological models (relative seriality and linear Poisson) and the reference parameters are validated to prove their suitability in reproducing the treatment outcome pattern of the patient material studied (through the probability of finding a worse fit, area under the ROC curve and khgr2 test). The analysis was carried out for the upper 5 cm of the esophagus (proximal esophagus) where all the strictures are formed, and the total volume of AVM. The estimated confidence intervals of the dose-response curves appear to have a significant supporting role on their clinical implementation and use.

Dose-current discharge correlation analysis in a Mather type Plasma Focus device for medical applications

NASA Astrophysics Data System (ADS)

Sumini, M.; Mostacci, D.; Tartari, A.; Mazza, A.; Cucchi, G.; Isolan, L.; Buontempo, F.; Zironi, I.; Castellani, G.

2017-11-01

In a Plasma Focus device the plasma collapses into the pinch where it reaches thermonuclear conditions for a few tens of nanoseconds, becoming a multi-radiation source. The nature of the radiation generated depends on the gas filling the chamber and the device working parameters. The self-collimated electron beam generated in the backward direction with respect to the plasma motion is one of the main radiation sources of interest also for medical applications. The electron beam may be guided against a high Z material target to produce an X-ray beam. This technique offers an ultra-high dose rate source of X-rays, able to deliver during the pinch a massive dose (up to 1 Gy per discharge for the PFMA-3 test device), as measured with EBT3 GafchromicⒸfilm tissue equivalent dosimeters. Given the stochastic behavior of the discharge process, a reliable on-line estimate of the dose-delivered is a very challenging task, in some way preventing a systematic application as a potentially interesting therapy device. This work presents an approach to linking the dose registered by the EBT3 GafchromicⒸfilms with the information contained in the signal recorded during the current discharge process. Processing the signal with the Wigner-Ville distribution, a spectrogram was obtained, displaying the information on intensity at various frequency scales, identifying the band of frequencies representative of the pinch events and define some patterns correlated with the dose.

SU-E-T-558: Assessing the Effect of Inter-Fractional Motion in Esophageal Sparing Plans.

PubMed

Williamson, R; Bluett, J; Niedzielski, J; Liao, Z; Gomez, D; Court, L

2012-06-01

To compare esophageal dose distributions in esophageal sparing IMRT plans with predicted dose distributions which include the effect of inter-fraction motion. Seven lung cancer patients were used, each with a standard and an esophageal sparing plan (74Gy, 2Gy fractions). The average max dose to esophagus was 8351cGy and 7758cGy for the standard and sparing plans, respectively. The average length of esophagus for which the total circumference was treated above 60Gy (LETT60) was 9.4cm in the standard plans and 5.8cm in the sparing plans. In order to simulate inter-fractional motion, a three-dimensional rigid shift was applied to the calculated dose field. A simulated course of treatment consisted of a single systematic shift applied throughout the treatment as well a random shift for each of the 37 fractions. Both systematic and random shifts were generated from Gaussian distributions of 3mm and 5mm standard deviation. Each treatment course was simulated 1000 times to obtain an expected distribution of the delivered dose. Simulated treatment dose received by the esophagus was less than dose seen in the treatment plan. The average reduction in maximum esophageal dose for the standard plans was 234cGy and 386cGY for the 3mm and 5mm Gaussian distributions, respectively. The average reduction in LETT60 was 0.6cm and 1.7cm, for the 3mm and 5mm distributions respectively. For the esophageal sparing plans, the average reduction in maximum esophageal dose was 94cGy and 202cGy for 3mm and 5mm Gaussian distributions, respectively. The average change in LETT60 for the esophageal sparing plans was smaller, at 0.1cm (increase) and 0.6cm (reduction), for the 3mm and 5mm distributions, respectively. Interfraction motion consistently reduced the maximum doses to the esophagus for both standard and esophageal sparing plans. © 2012 American Association of Physicists in Medicine.

[Comparison of SIB-IMRT treatment plans for upper esophageal carcinoma].

PubMed

Fu, Wei-hua; Wang, Lv-hua; Zhou, Zong-mei; Dai, Jian-rong; Hu, Yi-min

2003-06-01

To implement simultaneous integrated boost intensity-modulated radiotherapy(SIB-IMRT) plans for upper esophageal carcinoma and investigate the dose profiles of tumor and electively treated region and the dose to organs at risk (OARs). SIB-IMRT plans were designed for two patients with upper esophageal carcinoma. Two target volumes were predefined: PTV1, the target volume of the primary lesion, which was given to 67.2 Gy, and PTV2, the target volume of electively treated region, which was given to 50.4 Gy. With the same dose-volume constraints, but different beams arrangements (3, 5, 7, or 9 equispaced coplanar beams), four plans were generated. Indices, including dose distribution, dose volume histogram (DVH) and conformity index, were used for comparison of these plans. The plan with three intensity-modulated beams could produce good dose distribution for the two target volumes. The dose conformity to targets and the dose to OARs were improved as the beam number increased. The dose distributions in targets changed little when the beam number increased from 7 to 9. Five to seven intensity-modulated beams can produce desirable dose distributions for simultaneous integrated boost (SIB) treatment for upper esophageal carcinoma. The primary tumor can get higher equivalent dose by SIB treatments. It is easier and more efficient to design plans with equispaced coplanar beams. The efficacy of SIB-IMRT remains to be determined by the clinical outcome.

Dose Distribution in Cone-Beam Breast Computed Tomography: An Experimental Phantom Study

NASA Astrophysics Data System (ADS)

Russo, Paolo; Lauria, Adele; Mettivier, Giovanni; Montesi, Maria Cristina; Villani, Natalia

2010-02-01

We measured the spatial distribution of absorbed dose in a 14 cm diameter PMMA half-ellipsoid phantom simulating the uncompressed breast, using an X-ray cone-beam breast computed tomography apparatus, assembled for laboratory tests. Thermoluminescent dosimeters (TLD-100) were placed inside the phantom in six positions, both axially and at the phantom periphery. To study the dose distribution inside the PMMA phantom two experimental setups were adopted with effective energies in the range 28.7-44.4 keV. Different values of effective energies were obtained by combining different configurations of added Cu filtration (0.05 mm or 0.2 mm) and tube voltages (from 50 kVp to 80 kVp). Dose values obtained by TLDs in different positions inside the PMMA are reported. To evaluate the dose distribution in the breast shaped volume, the values measured were normalized to the one obtained in the inner position inside the phantom. Measurements with a low energy setup show a gradual increment of dose going from the "chest wall" to the "nipple" (63% more at the "nipple" compared to the central position). Likewise, a gradual increment is observed going from the breast axis toward the periphery (82% more at the "skin" compared to the central position). A more uniform distribution of dose inside the PMMA was obtained with a high energy setup (the maximum variation was 33% at 35.5 keV effective energy in the radial direction). The most uniform distribution is obtained at 44.4 keV. The results of this study show how the dose is distributed: it varies as a function of effective energy of the incident X-ray beam and as a function of the position inside the volume (axial or peripheral position).

Practice patterns of radiotherapy in cervical cancer among member groups of the Gynecologic Cancer Intergroup (GCIG).

PubMed

Gaffney, David K; Du Bois, Andreas; Narayan, Kailash; Reed, Nick; Toita, Takafumi; Pignata, Sandro; Blake, Peter; Portelance, Lorraine; Sadoyze, Azmat; Pötter, Richard; Colombo, Alessandro; Randall, Marcus; Mirza, Mansoor R; Trimble, Edward L

2007-06-01

The aim of this study was to describe radiotherapeutic practice of the treatment of cervical cancer in member groups of the Gynecologic Cancer Intergroup (GCIG). A survey was developed and distributed to the members of the GCIG focusing on details of radiotherapy practice. Different scenarios were queried including advanced cervical cancer, postoperative patients, and para-aortic-positive lymph node cases. Items focused on indications for radiation therapy, radiation fields, dose, use of chemotherapy, brachytherapy and others. The cooperative groups from North America were compared with the other groups to evaluate potential differences in radiotherapy doses. A total of 39 surveys were returned from 13 different cooperative groups. For the treatment of advanced cervical cancer, external beam pelvic doses and total doses to point A were 47 + 3.5 Gy (mean + SD) and 79.1 + 7.9 Gy, respectively. Point A doses were not different between the North American cooperative groups compared with the others (p = 0.103). All groups used concomitant chemotherapy, with 30 of 36 respondents using weekly cisplatin. Of 33 respondents, 31 intervened for a low hemoglobin level. For a para-aortic field, the upper border was most commonly (15 of 24) at the T12-L1 interspace. Maintenance chemotherapy (after radiotherapy) was not performed by 68% of respondents. For vaginal brachytherapy after hysterectomy, 23 groups performed HDR brachytherapy and four groups used LDR brachytherapy. In the use of brachytherapy, there was no uniformity in dose prescription. Radiotherapy practices among member groups of the GCIG are similar in terms of both doses and use of chemotherapy.

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

Saleh, H; Ferjani, S; Masssey, V

Purpose: Perform dosimetric comparison between planned and delivered dose in the junction area, measure daily dose variation in the arc junction area for pediatric patients treated for medulloblastoma using Craniospinal axis irradiation(CSI) Material and methods Dose comparison in the junction area, daily dose variation in the arc junction area for a Rando Phantom and 5 pediatric patients treated using CSI technique were analyzed. Plans were created using the Eclipse treatment planning system. Two arcs for cranium and 1 arc for spine region were used. Planar dose matrix was created by projecting phantom and patient plan into the ArcCheck phantom. EBT3more » film was placed in the middle of ArcCheck plug to measure dose distribution in the junction areaDuring patient treatment, strip of EBT3 film was placed daily at each junction area for verification. EBT3 films were scanned using a flatbed scanner, Epson Expression 10000 XL. Film QA pro software was used to analyze film. Scanning and analysis was performed according to vendor recommendations and AAPM TG-55 report. Films were scanned and analyzed daily after each treatment and at the end of treatment course. Planar dose distributions from films were compared with planar dose distribution from treatment planning system. Results: Comparison of planned vs. measured dose distributions for patients have passing rates of 90%–100% with 3% and 3 mm gamma analysis. In some of the treatment fractions, daily setup film showed variation in dose distribution in the junction area. Conclusion: It is critical to measure dose distribution in the arc junction area and use additional quality assurance measures to verify daily setup for CSI patient where one or more junctions are present. EBT3 film prove to be a good tool to achieve this task considering flexibility associated with the film such as symmetry, self-developing and ease of use.« less

Total body irradiation, toward optimal individual delivery: dose evaluation with metal oxide field effect transistors, thermoluminescence detectors, and a treatment planning system.

PubMed

Bloemen-van Gurp, Esther J; Mijnheer, Ben J; Verschueren, Tom A M; Lambin, Philippe

2007-11-15

To predict the three-dimensional dose distribution of our total body irradiation technique, using a commercial treatment planning system (TPS). In vivo dosimetry, using metal oxide field effect transistors (MOSFETs) and thermoluminescence detectors (TLDs), was used to verify the calculated dose distributions. A total body computed tomography scan was performed and loaded into our TPS, and a three-dimensional-dose distribution was generated. In vivo dosimetry was performed at five locations on the patient. Entrance and exit dose values were converted to midline doses using conversion factors, previously determined with phantom measurements. The TPS-predicted dose values were compared with the MOSFET and TLD in vivo dose values. The MOSFET and TLD dose values agreed within 3.0% and the MOSFET and TPS data within 0.5%. The convolution algorithm of the TPS, which is routinely applied in the clinic, overestimated the dose in the lung region. Using a superposition algorithm reduced the calculated lung dose by approximately 3%. The dose inhomogeneity, as predicted by the TPS, can be reduced using a simple intensity-modulated radiotherapy technique. The use of a TPS to calculate the dose distributions in individual patients during total body irradiation is strongly recommended. Using a TPS gives good insight of the over- and underdosage in a patient and the influence of patient positioning on dose homogeneity. MOSFETs are suitable for in vivo dosimetry purposes during total body irradiation, when using appropriate conversion factors. The MOSFET, TLD, and TPS results agreed within acceptable margins.

A comparison of intensity modulated x-ray therapy to intensity modulated proton therapy for the delivery of non-uniform dose distributions

NASA Astrophysics Data System (ADS)

Flynn, Ryan

2007-12-01

The distribution of biological characteristics such as clonogen density, proliferation, and hypoxia throughout tumors is generally non-uniform, therefore it follows that the optimal dose prescriptions should also be non-uniform and tumor-specific. Advances in intensity modulated x-ray therapy (IMXT) technology have made the delivery of custom-made non-uniform dose distributions possible in practice. Intensity modulated proton therapy (IMPT) has the potential to deliver non-uniform dose distributions as well, while significantly reducing normal tissue and organ at risk dose relative to IMXT. In this work, a specialized treatment planning system was developed for the purpose of optimizing and comparing biologically based IMXT and IMPT plans. The IMXT systems of step-and-shoot (IMXT-SAS) and helical tomotherapy (IMXT-HT) and the IMPT systems of intensity modulated spot scanning (IMPT-SS) and distal gradient tracking (IMPT-DGT), were simulated. A thorough phantom study was conducted in which several subvolumes, which were contained within a base tumor region, were boosted or avoided with IMXT and IMPT. Different boosting situations were simulated by varying the size, proximity, and the doses prescribed to the subvolumes, and the size of the phantom. IMXT and IMPT were also compared for a whole brain radiation therapy (WBRT) case, in which a brain metastasis was simultaneously boosted and the hippocampus was avoided. Finally, IMXT and IMPT dose distributions were compared for the case of non-uniform dose prescription in a head and neck cancer patient that was based on PET imaging with the Cu(II)-diacetyl-bis(N4-methylthiosemicarbazone (Cu-ATSM) hypoxia marker. The non-uniform dose distributions within the tumor region were comparable for IMXT and IMPT. IMPT, however, was capable of delivering the same non-uniform dose distributions within a tumor using a 180° arc as for a full 360° rotation, which resulted in the reduction of normal tissue integral dose by a factor of up to three relative to IMXT, and the complete sparing of organs at risk distal to the tumor region.

SU-F-T-159: Monte Carlo Simulation Studies of Three-Dimensional Dose Distribution for Polymer Gel Dosimeter and Radiochromic Gel Dosimeter in a Proton Beam

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

Park, M; Kim, G; Jung, H

Purpose: The purpose of this simulation study is to evaluate the proton detectability of gel dosimeters, and estimate the three-dimensional dose distribution of protons in the radiochromic gel and polymer gel dosimeter compared with the dose distribution in water. Methods: The commercial composition ratios of normoxic polymer gel and LCV micelle radiochromic gel were included in this simulation study. The densities of polymer and radiochromic gel were 1.024 and 1.005 g/cm3, respectively. The 50, 80 and 140 MeV proton beam energies were selected. The dose distributions of protons in the polymer and radiochromic gel were simulated using Monte Carlo radiationmore » transport code (MCNPX 2.7.0, Los Alamos Laboratory). The water equivalent depth profiles and the dose distributions of two gel dosimeters were compared for the water. Results: In case of irradiating 50, 80 and 140 MeV proton beam to water phantom, the reference Bragg-peak depths are represented at 2.22, 5.18 and 13.98 cm, respectively. The difference in the water equivalent depth is represented to about 0.17 and 0.37 cm in the radiochromic gel and polymer gel dosimeter, respectively. The proton absorbed doses in the radiochromic gel dosimeter are calculated to 2.41, 3.92 and 6.90 Gy with increment of incident proton energies. In the polymer gel dosimeter, the absorbed doses are calculated to 2.37, 3.85 and 6.78 Gy with increment of incident proton energies. The relative absorbed dose in radiochromic gel (about 0.47 %) is similar to that of water than the relative absorbed dose of polymer gel (about 2.26 %). In evaluating the proton dose distribution, we found that the dose distribution of both gel dosimeters matched that of water in most cases. Conclusion: As the dosimetry device, the radiochromic gel dosimeter has the potential particle detectability and is feasible to use for quality assurance of proton beam therapy beam.« less

SU-E-T-753: Three-Dimensional Dose Distributions of Incident Proton Particle in the Polymer Gel Dosimeter and the Radiochromic Gel Dosimeter: A Simulation Study with MCNP Code

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

Park, M; Kim, G; Ji, Y

Purpose: The purpose of this study is to estimate the three-dimensional dose distributions in the polymer and the radiochromic gel dosimeter, and to identify the detectability of both gel dosimeters by comparing with the water phantom in case of irradiating the proton particles. Methods: The normoxic polymer gel and the LCV micelle radiochromic gel were used in this study. The densities of polymer and the radiochromic gel dosimeter were 1.024 and 1.005 g/cm{sup 3}, respectively. The dose distributions of protons in the polymer and radiochromic gel were simulated using Monte Carlo radiation transport code (MCNPX, Los Alamos National Laboratory). Themore » shape of phantom irradiated by proton particles was a hexahedron with the dimension of 12.4 × 12.4 × 15.0 cm{sup 3}. The energies of proton beam were 50, 80, and 140 MeV energies were directed to top of the surface of phantom. The cross-sectional view of proton dose distribution in both gel dosimeters was estimated with the water phantom and evaluated by the gamma evaluation method. In addition, the absorbed dose(Gy) was also calculated for evaluating the proton detectability. Results: The evaluation results show that dose distributions in both gel dosimeters at intermediated section and Bragg-peak region are similar with that of the water phantom. At entrance section, however, inconsistencies of dose distribution are represented, compared with water. The relative absorbed doses in radiochromic and polymer gel dosimeter were represented to be 0.47 % and 2.26 % difference, respectively. These results show that the radiochromic gel dosimeter was better matched than the water phantom in the absorbed dose evaluation. Conclusion: The polymer and the radiochromic gel dosimeter show similar characteristics in dose distributions for the proton beams at intermediate section and Bragg-peak region. Moreover the calculated absorbed dose in both gel dosimeters represents similar tendency by comparing with that in water phantom.« less

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

Medina, L; Adrada, A; Filipuzzi, M

Purpose: The purpose of this paper is to characterize EBT3 using two types of scanner, analyzing the factors of influence of each dosimetry system. Methods: The film used in this study was GAFCHROMIC EBT3, the films were exposed at a dose range between 0Gy a 9Gy in a solid water phantom, SSD=100cm, 5cm depth and perpendicularly to the 6MV photon beam generated by a Novalis TX linear accelerator equipped with an HDMLC. A Farmer type ion chamber TN30013 (PTW) was used to determine the dose delivered to the film. The films were digitized with a scanner EPSON expression 10000XL andmore » the VIDAR DosimetryPro Adventage RED. Software RIT113v6.1 was used for construction of the calibration curve and analysis. The film characteristics investigated were: response at different dose levels, sensitivity to orientation and side and resolution through the results of the spatial response function by analyzing a step pattern. Additionally, 20 IMRT treatment fields were measured with both scanner and compared with calculated dose using gamma index analysis (3%-3mm). Results: The OD obtained for dose level 2Gy in the orientation portrait of the film on the scanner EPSON is (0,222±0,19) and for Vidar RED (0,252±0,10) and landscape is for EPSON (0,211±0,25) and for Vidar RED (0,250±0,11) . The orientation dependence with respect to film side is about 0,09% for EPSON and about 0.03% for VIDAR. The spatial response function increase in response to the Gaussian function FWHM EPSON scanner (0.18mm) compared with VIDAR scanner function (less than 0.06mm) was observed. We analyzed 20 total plan dose distributions the number of pixels with gamma>1 (3%-3mm) was 0.7%±1.2 [0.1%; 2.82%] for EBT3-VIDAR y 2%±2.9 [0.2%; 3.5%] for EBT3-EPSON. Conclusion: VIDAR scanner shows better sensitivity. EBT3 film shows a different response between portrait and landscape orientation. Step pattern is better reproduce by VIDAR scanner.« less

Monte Carlo Estimation of Absorbed Dose Distributions Obtained from Heterogeneous 106Ru Eye Plaques.

PubMed

Zaragoza, Francisco J; Eichmann, Marion; Flühs, Dirk; Sauerwein, Wolfgang; Brualla, Lorenzo

2017-09-01

The distribution of the emitter substance in 106 Ru eye plaques is usually assumed to be homogeneous for treatment planning purposes. However, this distribution is never homogeneous, and it widely differs from plaque to plaque due to manufacturing factors. By Monte Carlo simulation of radiation transport, we study the absorbed dose distribution obtained from the specific CCA1364 and CCB1256 106 Ru plaques, whose actual emitter distributions were measured. The idealized, homogeneous CCA and CCB plaques are also simulated. The largest discrepancy in depth dose distribution observed between the heterogeneous and the homogeneous plaques was 7.9 and 23.7% for the CCA and CCB plaques, respectively. In terms of isodose lines, the line referring to 100% of the reference dose penetrates 0.2 and 1.8 mm deeper in the case of heterogeneous CCA and CCB plaques, respectively, with respect to the homogeneous counterpart. The observed differences in absorbed dose distributions obtained from heterogeneous and homogeneous plaques are clinically irrelevant if the plaques are used with a lateral safety margin of at least 2 mm. However, these differences may be relevant if the plaques are used in eccentric positioning.

Detailed Distribution Map of Absorbed Dose Rate in Air in Tokatsu Area of Chiba Prefecture, Japan, Constructed by Car-Borne Survey 4 Years after the Fukushima Daiichi Nuclear Power Plant Accident.

PubMed

Inoue, Kazumasa; Arai, Moeko; Fujisawa, Makoto; Saito, Kyouko; Fukushi, Masahiro

2017-01-01

A car-borne survey was carried out in the northwestern, or Tokatsu, area of Chiba Prefecture, Japan, to make a detailed distribution map of absorbed dose rate in air four years after the Fukushima Daiichi Nuclear Power Plant accident. This area was chosen because it was the most heavily radionuclide contaminated part of Chiba Prefecture and it neighbors metropolitan Tokyo. Measurements were performed using a 3-in × 3-in NaI(Tl) scintillation spectrometer in June 2015. The survey route covered the whole Tokatsu area which includes six cities. A heterogeneous distribution of absorbed dose rate in air was observed on the dose distribution map. Especially, higher absorbed dose rates in air exceeding 80 nGy h-1 were observed along national roads constructed using high porosity asphalt, whereas lower absorbed dose rates in air were observed along local roads constructed using low porosity asphalt. The difference between these asphalt types resulted in a heterogeneous dose distribution in the Tokatsu area. The mean of the contribution ratio of artificial radionuclides to absorbed dose rate in air measured 4 years after the accident was 29% (9-50%) in the Tokatsu area. The maximum absorbed dose rate in air, 201 nGy h-1 was observed at Kashiwa City. Radiocesium was deposited in the upper 1 cm surface layer of the high porosity asphalt which was collected in Kashiwa City and the environmental half-life of the absorbed dose rate in air was estimated to be 1.7 years.

WE-A-17A-12: The Influence of Eye Plaque Design On Dose Distributions and Dose- Volume Histograms

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

Aryal, P; Molloy, JA; Rivard, MJ

Purpose: To investigate the effect of slot design of the model EP917 plaque on dose distributions and dose-volume histograms (DVHs). Methods: The dimensions and orientation of the slots in EP917 plaques were measured. In the MCNP5 radiation simulation geometry, dose distributions on orthogonal planes and DVHs for a tumor and sclera were generated for comparisons. 27 slot designs and 13 plaques were evaluated and compared with the published literature and the Plaque Simulator clinical treatment planning system. Results: The dosimetric effect of the gold backing composition and mass density was < 3%. Slot depth, width, and length changed the centralmore » axis (CAX) dose distributions by < 1% per 0.1 mm in design variation. Seed shifts in the slot towards the eye and shifts of the {sup 125} I-coated Ag rod within the capsule had the greatest impact on CAX dose distribution, increasing by 14%, 9%, 4%, and 2.5% at 1, 2, 5, and 10 mm, respectively, from the inner sclera. Along the CAX, dose from the full plaque geometry using the measured slot design was 3.4% ± 2.3% higher than the manufacturer-provided geometry. D{sub 10} for the simulated tumor, inner sclera, and outer sclera for the measured plaque was also higher, but 9%, 10%, and 20%, respectively. In comparison to the measured plaque design, a theoretical plaque having narrow and deep slots delivered 30%, 37%, and 62% lower D{sub 10} doses to the tumor, inner sclera, and outer sclera, respectively. CAX doses at −1, 0, 1, and 2 mm were also lower by a factor of 2.6, 1.4, 1.23, and 1.13, respectively. Conclusion: The study identified substantial sensitivity of the EP917 plaque dose distributions to slot design. However, it did not identify substantial dosimetric variations based on radionuclide choice ({sup 125}I, {sup 103}Pd, or {sup 131}Cs). COMS plaques provided lower scleral doses with similar tumor dose coverage.« less

SU-E-T-109: An Investigation of Including Variable Relative Biological Effectiveness in Intensity Modulated Proton Therapy Planning Optimization for Head and Neck Cancer Patients

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

Cao, W; Zaghian, M; Lim, G

2015-06-15

Purpose: The current practice of considering the relative biological effectiveness (RBE) of protons in intensity modulated proton therapy (IMPT) planning is to use a generic RBE value of 1.1. However, RBE is indeed a variable depending on the dose per fraction, the linear energy transfer, tissue parameters, etc. In this study, we investigate the impact of using variable RBE based optimization (vRBE-OPT) on IMPT dose distributions compared by conventional fixed RBE based optimization (fRBE-OPT). Methods: Proton plans of three head and neck cancer patients were included for our study. In order to calculate variable RBE, tissue specific parameters were obtainedmore » from the literature and dose averaged LET values were calculated by Monte Carlo simulations. Biological effects were calculated using the linear quadratic model and they were utilized in the variable RBE based optimization. We used a Polak-Ribiere conjugate gradient algorithm to solve the model. In fixed RBE based optimization, we used conventional physical dose optimization to optimize doses weighted by 1.1. IMPT plans for each patient were optimized by both methods (vRBE-OPT and fRBE-OPT). Both variable and fixed RBE weighted dose distributions were calculated for both methods and compared by dosimetric measures. Results: The variable RBE weighted dose distributions were more homogenous within the targets, compared with the fixed RBE weighted dose distributions for the plans created by vRBE-OPT. We observed that there were noticeable deviations between variable and fixed RBE weighted dose distributions if the plan were optimized by fRBE-OPT. For organs at risk sparing, dose distributions from both methods were comparable. Conclusion: Biological dose based optimization rather than conventional physical dose based optimization in IMPT planning may bring benefit in improved tumor control when evaluating biologically equivalent dose, without sacrificing OAR sparing, for head and neck cancer patients. The research is supported in part by National Institutes of Health Grant No. 2U19CA021239-35.« less

An assessment of a 3D EPID-based dosimetry system using conventional two- and three-dimensional detectors for VMAT.

PubMed

Stevens, S; Dvorak, P; Spevacek, V; Pilarova, K; Bray-Parry, M; Gesner, J; Richmond, A

2018-01-01

To provide a 3D dosimetric evaluation of a commercial portal dosimetry system using 2D/3D detectors under ideal conditions using VMAT. A 2D ion chamber array, radiochromic film and gel dosimeter were utilised to provide a dosimetric evaluation of transit phantom and pre-treatment 'fluence' EPID back-projected dose distributions for a standard VMAT plan. In-house 2D and 3D gamma methods compared pass statistics relative to each dosimeter and TPS dose distributions. Fluence mode and transit EPID dose distributions back-projected onto phantom geometry produced 2D gamma pass rates in excess of 97% relative to other tested detectors and exported TPS dose planes when a 3%, 3 mm global gamma criterion was applied. Use of a gel dosimeter within a glass vial allowed comparison of measured 3D dose distributions versus EPID 3D dose and TPS calculated distributions. 3D gamma comparisons between modalities at 3%, 3 mm gave pass rates in excess of 92%. Use of fluence mode was indicative of transit results under ideal conditions with slightly reduced dose definition. 3D EPID back projected dose distributions were validated against detectors in both 2D and 3D. Cross validation of transit dose delivered to a patient is limited due to reasons of practicality and the tests presented are recommended as a guideline for 3D EPID dosimetry commissioning; allowing direct comparison between detector, TPS, fluence and transit modes. The results indicate achievable gamma scores for a complex VMAT plan in a homogenous phantom geometry and contributes to growing experience of 3D EPID dosimetry. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Inclusion of dosimetric data as covariates in toxicity-related radiogenomic studies : A systematic review.

PubMed

Yahya, Noorazrul; Chua, Xin-Jane; Manan, Hanani A; Ismail, Fuad

2018-05-17

This systematic review evaluates the completeness of dosimetric features and their inclusion as covariates in genetic-toxicity association studies. Original research studies associating genetic features and normal tissue complications following radiotherapy were identified from PubMed. The use of dosimetric data was determined by mining the statement of prescription dose, dose fractionation, target volume selection or arrangement and dose distribution. The consideration of the dosimetric data as covariates was based on the statement mentioned in the statistical analysis section. The significance of these covariates was extracted from the results section. Descriptive analyses were performed to determine their completeness and inclusion as covariates. A total of 174 studies were found to satisfy the inclusion criteria. Studies published ≥2010 showed increased use of dose distribution information (p = 0.07). 33% of studies did not include any dose features in the analysis of gene-toxicity associations. Only 29% included dose distribution features as covariates and reported the results. 59% of studies which included dose distribution features found significant associations to toxicity. A large proportion of studies on the correlation of genetic markers with radiotherapy-related side effects considered no dosimetric parameters. Significance of dose distribution features was found in more than half of the studies including these features, emphasizing their importance. Completeness of radiation-specific clinical data may have increased in recent years which may improve gene-toxicity association studies.

Patient radiation doses in interventional cardiology in the U.S.: Advisory data sets and possible initial values for U.S. reference levels

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

Miller, Donald L.; Hilohi, C. Michael; Spelic, David C.

2012-10-15

Purpose: To determine patient radiation doses from interventional cardiology procedures in the U.S and to suggest possible initial values for U.S. benchmarks for patient radiation dose from selected interventional cardiology procedures [fluoroscopically guided diagnostic cardiac catheterization and percutaneous coronary intervention (PCI)]. Methods: Patient radiation dose metrics were derived from analysis of data from the 2008 to 2009 Nationwide Evaluation of X-ray Trends (NEXT) survey of cardiac catheterization. This analysis used deidentified data and did not require review by an IRB. Data from 171 facilities in 30 states were analyzed. The distributions (percentiles) of radiation dose metrics were determined for diagnosticmore » cardiac catheterizations, PCI, and combined diagnostic and PCI procedures. Confidence intervals for these dose distributions were determined using bootstrap resampling. Results: Percentile distributions (advisory data sets) and possible preliminary U.S. reference levels (based on the 75th percentile of the dose distributions) are provided for cumulative air kerma at the reference point (K{sub a,r}), cumulative air kerma-area product (P{sub KA}), fluoroscopy time, and number of cine runs. Dose distributions are sufficiently detailed to permit dose audits as described in National Council on Radiation Protection and Measurements Report No. 168. Fluoroscopy times are consistent with those observed in European studies, but P{sub KA} is higher in the U.S. Conclusions: Sufficient data exist to suggest possible initial benchmarks for patient radiation dose for certain interventional cardiology procedures in the U.S. Our data suggest that patient radiation dose in these procedures is not optimized in U.S. practice.« less

SU-E-T-397: Evaluation of Planned Dose Distributions by Monte Carlo (0.5%) and Ray Tracing Algorithm for the Spinal Tumors with CyberKnife

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

Cho, H; Brindle, J; Hepel, J

2015-06-15

Purpose: To analyze and evaluate dose distribution between Ray Tracing (RT) and Monte Carlo (MC) algorithms of 0.5% uncertainty on a critical structure of spinal cord and gross target volume and planning target volume. Methods: Twenty four spinal tumor patients were treated with stereotactic body radiotherapy (SBRT) by CyberKnife in 2013 and 2014. The MC algorithm with 0.5% of uncertainty is used to recalculate the dose distribution for the treatment plan of the patients using the same beams, beam directions, and monitor units (MUs). Results: The prescription doses are uniformly larger for MC plans than RT except one case. Upmore » to a factor of 1.19 for 0.25cc threshold volume and 1.14 for 1.2cc threshold volume of dose differences are observed for the spinal cord. Conclusion: The MC recalculated dose distributions are larger than the original MC calculations for the spinal tumor cases. Based on the accuracy of the MC calculations, more radiation dose might be delivered to the tumor targets and spinal cords with the increase prescription dose.« less

Direct measurement of the 3-dimensional DNA lesion distribution induced by energetic charged particles in a mouse model tissue

PubMed Central

Mirsch, Johanna; Tommasino, Francesco; Frohns, Antonia; Conrad, Sandro; Durante, Marco; Scholz, Michael; Friedrich, Thomas; Löbrich, Markus

2015-01-01

Charged particles are increasingly used in cancer radiotherapy and contribute significantly to the natural radiation risk. The difference in the biological effects of high-energy charged particles compared with X-rays or γ-rays is determined largely by the spatial distribution of their energy deposition events. Part of the energy is deposited in a densely ionizing manner in the inner part of the track, with the remainder spread out more sparsely over the outer track region. Our knowledge about the dose distribution is derived solely from modeling approaches and physical measurements in inorganic material. Here we exploited the exceptional sensitivity of γH2AX foci technology and quantified the spatial distribution of DNA lesions induced by charged particles in a mouse model tissue. We observed that charged particles damage tissue nonhomogenously, with single cells receiving high doses and many other cells exposed to isolated damage resulting from high-energy secondary electrons. Using calibration experiments, we transformed the 3D lesion distribution into a dose distribution and compared it with predictions from modeling approaches. We obtained a radial dose distribution with sub-micrometer resolution that decreased with increasing distance to the particle path following a 1/r2 dependency. The analysis further revealed the existence of a background dose at larger distances from the particle path arising from overlapping dose deposition events from independent particles. Our study provides, to our knowledge, the first quantification of the spatial dose distribution of charged particles in biologically relevant material, and will serve as a benchmark for biophysical models that predict the biological effects of these particles. PMID:26392532

Measurement and simulation of lineal energy distribution at the CERN high energy facility with a tissue equivalent proportional counter.

PubMed

Rollet, S; Autischer, M; Beck, P; Latocha, M

2007-01-01

The response of a tissue equivalent proportional counter (TEPC) in a mixed radiation field with a neutron energy distribution similar to the radiation field at commercial flight altitudes has been studied. The measurements have been done at the CERN-EU High-Energy Reference Field (CERF) facility where a well-characterised radiation field is available for intercomparison. The TEPC instrument used by the ARC Seibersdorf Research is filled with pure propane gas at low pressure and can be used to determine the lineal energy distribution of the energy deposition in a mass of gas equivalent to a 2 microm diameter volume of unit density tissue, of similar size to the nuclei of biological cells. The linearity of the detector response was checked both in term of dose and dose rate. The effect of dead-time has been corrected. The influence of the detector exposure location and orientation in the radiation field on the dose distribution was also studied as a function of the total dose. The microdosimetric distribution of the absorbed dose as a function of the lineal energy has been obtained and compared with the same distribution simulated with the FLUKA Monte Carlo transport code. The dose equivalent was calculated by folding this distribution with the quality factor as a function of linear energy transfer. The comparison between the measured and simulated distributions show that they are in good agreement. As a result of this study the detector is well characterised, thanks also to the numerical simulations the instrument response is well understood, and it's currently being used onboard the aircrafts to evaluate the dose to aircraft crew caused by cosmic radiation.

MagicPlate-512: A 2D silicon detector array for quality assurance of stereotactic motion adaptive radiotherapy.

PubMed

Petasecca, M; Newall, M K; Booth, J T; Duncan, M; Aldosari, A H; Fuduli, I; Espinoza, A A; Porumb, C S; Guatelli, S; Metcalfe, P; Colvill, E; Cammarano, D; Carolan, M; Oborn, B; Lerch, M L F; Perevertaylo, V; Keall, P J; Rosenfeld, A B

2015-06-01

Spatial and temporal resolutions are two of the most important features for quality assurance instrumentation of motion adaptive radiotherapy modalities. The goal of this work is to characterize the performance of the 2D high spatial resolution monolithic silicon diode array named "MagicPlate-512" for quality assurance of stereotactic body radiation therapy (SBRT) and stereotactic radiosurgery (SRS) combined with a dynamic multileaf collimator (MLC) tracking technique for motion compensation. MagicPlate-512 is used in combination with the movable platform HexaMotion and a research version of radiofrequency tracking system Calypso driving MLC tracking software. The authors reconstruct 2D dose distributions of small field square beams in three modalities: in static conditions, mimicking the temporal movement pattern of a lung tumor and tracking the moving target while the MLC compensates almost instantaneously for the tumor displacement. Use of Calypso in combination with MagicPlate-512 requires a proper radiofrequency interference shielding. Impact of the shielding on dosimetry has been simulated by (GEANT)4 and verified experimentally. Temporal and spatial resolutions of the dosimetry system allow also for accurate verification of segments of complex stereotactic radiotherapy plans with identification of the instant and location where a certain dose is delivered. This feature allows for retrospective temporal reconstruction of the delivery process and easy identification of error in the tracking or the multileaf collimator driving systems. A sliding MLC wedge combined with the lung motion pattern has been measured. The ability of the MagicPlate-512 (MP512) in 2D dose mapping in all three modes of operation was benchmarked by EBT3 film. Full width at half maximum and penumbra of the moving and stationary dose profiles measured by EBT3 film and MagicPlate-512 confirm that motion has a significant impact on the dose distribution. Motion, no motion, and motion with MLC tracking profiles agreed within 1 and 0.4 mm, respectively, for all field sizes tested. Use of electromagnetic tracking system generates a fluctuation of the detector baseline up to 10% of the full scale signal requiring a proper shielding strategy. MagicPlate-512 is also able to reconstruct the dose variation pulse-by-pulse in each pixel of the detector. An analysis of the dose transients with motion and motion with tracking shows that the tracking feedback algorithm used for this experiment can compensate effectively only the effect of the slower transient components. The fast changing components of the organ motion can contribute only to discrepancy of the order of 15% in penumbral region while the slower components can change the dose profile up to 75% of the expected dose. MagicPlate-512 is shown to be, potentially, a valid alternative to film or 2D ionizing chambers for quality assurance dosimetry in SRS or SBRT. Its high spatial and temporal resolutions allow for accurate reconstruction of the profile in any conditions with motion and with tracking of the motion. It shows excellent performance to reconstruct the dose deposition in real time or retrospectively as a function of time for detailed analysis of the effect of motion in a specific pixel or area of interest.

Real-World Dosing Patterns of Atomoxetine in Adults with Attention-Deficit/Hyperactivity Disorder.

PubMed

Kabul, Samaneh; Alatorre, Carlos; Montejano, Leslie B; Farr, Amanda M; Clemow, David B

2015-12-01

The aim was to investigate the dosing patterns of atomoxetine monotherapy in adult patients with attention-deficit/hyperactivity disorder (ADHD) in a retrospective analysis. Adult (≥ 18 years) patients with ADHD newly initiated on atomoxetine with ≥ 1 outpatient pharmacy claim for atomoxetine between January 2006 and December 2011 were selected from the Truven Health MarketScan(®) Commercial database. After a 30-day titration period, dosing patterns of atomoxetine monotherapy were analyzed in the 12 months following initiation. In addition, patient demographic and clinical characteristics were compared to identify characteristics associated with suboptimal versus recommended dosing. Of the 12,412 adult patients with ADHD newly initiated on atomoxetine, 4548 (36.6%) were suboptimally dosed, whereas 3323 (26.7%) were treated at recommended dose. Overall, study patients were treated at a mean (standard deviation [SD]) dose of 68.5 (44.9) mg/day. The suboptimal dosing cohort included significantly more females (54% vs. 44%, P < 0.001) and had fewer patients with pre-index use of other ADHD medications (17% vs. 20%, P < 0.001) compared with the recommended dosing cohort. Adult patients with ADHD receiving atomoxetine therapy in a real-world setting are often dosed suboptimally. Increasing the awareness on optimal dosing strategy among clinicians and patients is warranted to maximize the therapeutic benefits of atomoxetine among adult patients with ADHD. © 2015 Eli Lilly and Company. CNS Neuroscience and Therapeutics published by John Wiley & Sons Ltd.

Gamma Radiation Dose Rate in Air due to Terrestrial Radionuclides in Southern Brazil: Synthesis by Geological Units and Lithotypes Covered by the Serra do Mar Sul Aero-Geophysical Project

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

Bastos, Rodrigo O.; Appoloni, Carlos R.; Pinese, Jose P. P.

2008-08-07

The absorbed dose rates in air due to terrestrial radionuclides were estimated from aerial gamma spectrometric data for an area of 48,600 km{sup 2} in Southern Brazil. The source data was the Serra do Mar Sul Aero-Geophysical Project back-calibrated in a cooperative work among the Geological Survey of Brazil, the Geological Survey of Canada, and Paterson, Grant and Watson Ltd. The concentrations of eU (ppm), eTh (ppm) and K (%) were converted to dose rates in air (nGy{center_dot}h{sup -1}) by accounting for the contribution of each element's concentration. Regional variation was interpreted according to lithotypes and a synthesis was performedmore » according to the basic geological units present in the area. Higher values of total dose were estimated for felsic igneous and metamorphic rocks, with average values varying up to 119{+-}24 nGy{center_dot}h{sup -1}, obtained by Anitapolis syenite body. Sedimentary, metasedimentary and metamafic rocks presented the lower dose levels, and some beach deposits reached the lowest average total dose, 18.5{+-}8.2 nGy{center_dot}h{sup -1}. Thorium gives the main average contribution in all geological units, the highest value being reached by the nebulitic gneisses of Atuba Complex, 71{+-}23 nGy{center_dot}h{sup -1}. Potassium presents the lowest average contribution to dose rate in 53 of the 72 units analyzed, the highest contribution being obtained by intrusive alkaline bodies (28{+-}12 nGy{center_dot}h{sup -1}). The general pattern of geographic dose distribution respects well the hypotheses on geo-physicochemical behavior of radioactive elements.« less

A gradient of radioactive contamination in Dolon village near the SNTS and comparison of computed dose values with instrumental estimates for the 29 August, 1949 nuclear test.

PubMed

Stepanenko, Valeriy F; Hoshi, Masaharu; Dubasov, Yuriy V; Sakaguchi, Aya; Yamamoto, Masayoshi; Orlov, Mark Y; Bailiff, Ian K; Ivannikov, Alexander I; Skvortsov, Valeriy G; Iaskova, Elena K; Kryukova, Irina G; Zhumadilov, Kassym S; Endo, Satoru; Tanaka, Kenichi; Apsalikov, Kazbek N; Gusev, Boris I

2006-02-01

Spatial distributions of soil contamination by 137Cs (89 sampling points) and 239+240Pu (76 points) near and within Dolon village were analyzed. An essential exponential decrease of contamination was found in Dolon village: the distance of a half reduction in contamination is about 0.87-1.25 km (in a northwest-southeast direction from the supposed centerline of the radioactive trace). This fact is in agreement with the available exposure rate measurements near Dolon (September 1949 archive data): on the basis of a few measurements the pattern of the trace was estimated to comprise a narrow 2 km corridor of maximum exposure rate. To compare computed external doses in air with local dose estimates by retrospective luminescence dosimetry (RLD) the gradient of radioactive soil contamination within the village was accounted for. The computed dose associated with the central axis of the trace was found to be equal to 2260 mGy (calculations based on archive exposure rate data). Local doses near the RLD sampling points (southeast of the village) were calculated to be in the range 466-780 mGy (averaged value: 645+/-70 mGy), which is comparable with RLD data (averaged value 460+/-92 mGy with range 380-618 mGy). A comparison of the computed mean dose in the settlement with dose estimates by ESR tooth enamel dosimetry makes it possible to estimate the "upper level" of the "shielding and behavior" factor in dose reduction for inhabitants of Dolon village which was found to be 0.28+/-0.068.

A new transmission methodology for quality assurance in radiotherapy based on radiochromic film measurements

PubMed Central

do Amaral, Leonardo L.; Pavoni, Juliana F.; Sampaio, Francisco; Netto, Thomaz Ghilardi

2015-01-01

Despite individual quality assurance (QA) being recommended for complex techniques in radiotherapy (RT) treatment, the possibility of errors in dose delivery during therapeutic application has been verified. Therefore, it is fundamentally important to conduct in vivo QA during treatment. This work presents an in vivo transmission quality control methodology, using radiochromic film (RCF) coupled to the linear accelerator (linac) accessory holder. This QA methodology compares the dose distribution measured by the film in the linac accessory holder with the dose distribution expected by the treatment planning software. The calculated dose distribution is obtained in the coronal and central plane of a phantom with the same dimensions of the acrylic support used for positioning the film but in a source‐to‐detector distance (SDD) of 100 cm, as a result of transferring the IMRT plan in question with all the fields positioned with the gantry vertically, that is, perpendicular to the phantom. To validate this procedure, first of all a Monte Carlo simulation using PENELOPE code was done to evaluate the differences between the dose distributions measured by the film in a SDD of 56.8 cm and 100 cm. After that, several simple dose distribution tests were evaluated using the proposed methodology, and finally a study using IMRT treatments was done. In the Monte Carlo simulation, the mean percentage of points approved in the gamma function comparing the dose distribution acquired in the two SDDs were 99.92%±0.14%. In the simple dose distribution tests, the mean percentage of points approved in the gamma function were 99.85%±0.26% and the mean percentage differences in the normalization point doses were −1.41%. The transmission methodology was approved in 24 of 25 IMRT test irradiations. Based on these results, it can be concluded that the proposed methodology using RCFs can be applied for in vivo QA in RT treatments. PACS number: 87.55.Qr, 87.55.km, 87.55.N‐ PMID:26699306

Verification of the grid size and angular increment effects in lung stereotactic body radiation therapy using the dynamic conformal arc technique

NASA Astrophysics Data System (ADS)

Park, Hae-Jin; Suh, Tae-Suk; Park, Ji-Yeon; Lee, Jeong-Woo; Kim, Mi-Hwa; Oh, Young-Taek; Chun, Mison; Noh, O. Kyu; Suh, Susie

2013-06-01

The dosimetric effects of variable grid size and angular increment were systematically evaluated in the measured dose distributions of dynamic conformal arc therapy (DCAT) for lung stereotactic body radiation therapy (SBRT). Dose variations with different grid sizes (2, 3, and 4 mm) and angular increments (2, 4, 6, and 10°) for spherical planning target volumes (PTVs) were verified in a thorax phantom by using EBT2 films. Although the doses for identical PTVs were predicted for the different grid sizes, the dose discrepancy was evaluated using one measured dose distribution with the gamma tool because the beam was delivered in the same set-up for DCAT. The dosimetric effect of the angular increment was verified by comparing the measured dose area histograms of organs at risk (OARs) at each angular increment. When the difference in the OAR doses is higher than the uncertainty of the film dosimetry, the error is regarded as the angular increment effect in discretely calculated doses. In the results, even when a 2-mm grid size was used with an elaborate dose calculation, 4-mm grid size led to a higher gamma pass ratio due to underdosage, a steep-dose descent gradient, and lower estimated PTV doses caused by the smoothing effect in the calculated dose distribution. An undulating dose distribution and a difference in the maximum contralateral lung dose of up to 14% were observed in dose calculation using a 10° angular increment. The DCAT can be effectively applied for an approximately spherical PTV in a relatively uniform geometry, which is less affected by inhomogeneous materials and differences in the beam path length.

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.).

Development, survival and fitness performance of Helicoverpa zea (Lepidoptera: Noctuidae) in MON810 Bt field corn.

PubMed

Horner, T A; Dively, G P; Herbert, D A

2003-06-01

Helicoverpa zea (Boddie) development, survival, and feeding injury in MON810 transgenic ears of field corn (Zea mays L.) expressing Bacillus thuringiensis variety kurstaki (Bt) Cry1Ab endotoxins were compared with non-Bt ears at four geographic locations over two growing seasons. Expression of Cry1Ab endotoxin resulted in overall reductions in the percentage of damaged ears by 33% and in the amount of kernels consumed by 60%. Bt-induced effects varied significantly among locations, partly because of the overall level and timing of H. zea infestations, condition of silk tissue at the time of egg hatch, and the possible effects of plant stress. Larvae feeding on Bt ears produced scattered, discontinuous patches of partially consumed kernels, which were arranged more linearly than the compact feeding patterns in non-Bt ears. The feeding patterns suggest that larvae in Bt ears are moving about sampling kernels more frequently than larvae in non-Bt ears. Because not all kernels express the same level of endotoxin, the spatial heterogeneity of toxin distribution within Bt ears may provide an opportunity for development of behavioral responses in H. zea to avoid toxin. MON810 corn suppressed the establishment and development of H. zea to late instars by at least 75%. This level of control is considered a moderate dose, which may increase the risk of resistance development in areas where MON810 corn is widely adopted and H. zea overwinters successfully. Sublethal effects of MON810 corn resulted in prolonged larval and prepupal development, smaller pupae, and reduced fecundity of H. zea. The moderate dose effects and the spatial heterogeneity of toxin distribution among kernels could increase the additive genetic variance for both physiological and behavioral resistance in H. zea populations. Implications of localized population suppression are discussed.

Post-licensure safety monitoring of quadrivalent human papillomavirus vaccine in the Vaccine Adverse Event Reporting System (VAERS), 2009-2015.

PubMed

Arana, Jorge E; Harrington, Theresa; Cano, Maria; Lewis, Paige; Mba-Jonas, Adamma; Rongxia, Li; Stewart, Brock; Markowitz, Lauri E; Shimabukuro, Tom T

2018-03-20

The Food and Drug Administration (FDA) approved quadrivalent human papillomavirus vaccine (4vHPV) for use in females and males aged 9-26 years, since 2006 and 2009 respectively. We characterized reports to the Vaccine Adverse Event Reporting System (VAERS), a US spontaneous reporting system, in females and males who received 4vHPV vaccination. We searched VAERS for US reports of adverse events (AEs) following 4vHPV from January 2009 through December 2015. Signs and symptoms were coded using Medical Dictionary for Regulatory Activities (MedDRA). We calculated reporting rates and conducted empirical Bayesian data mining to identify disproportional reports. Clinicians reviewed available information, including medical records, and reports of selected pre-specified conditions. VAERS received 19,760 reports following 4vHPV; 60.2% in females, 17.2% in males, and in 22.6% sex was missing. Overall, 94.2% of reports were non-serious; dizziness, syncope and injection site reactions were commonly reported in both males and females. Headache, fatigue and nausea were commonly reported serious AEs. More than 60 million 4vHPV doses were distributed during the study period. Crude AE reporting rates were 327 reports per million 4vHPV doses distributed for all reports, and 19 per million for serious reports. Among 29 verified reports of death, there was no pattern of clustering of deaths by diagnosis, co-morbidities, age, or interval from vaccination to death. No new or unexpected safety concerns or reporting patterns of 4vHPV with clinically important AEs were detected. Safety profile of 4vHPV is consistent with data from pre-licensure trials and postmarketing safety data. Published by Elsevier Ltd.

Variation in intravenous iron use internationally and over time: the Dialysis Outcomes and Practice Patterns Study (DOPPS).

PubMed

Bailie, George R; Larkina, Maria; Goodkin, David A; Li, Yun; Pisoni, Ronald L; Bieber, Brian; Mason, Nancy; Tong, Lin; Locatelli, Francesco; Marshall, Mark R; Inaba, Masaki; Robinson, Bruce M

2013-10-01

To examine patterns of intravenous (IV) iron use across 12 countries from 1999 to 2011. Trends in iron use are described among 32 192 hemodialysis (HD) patients in the Dialysis Outcomes and Practice Patterns Study. Adjusted associations of IV iron dose with serum ferritin and transferrin saturation (TSAT) values were also studied. IV iron was administered to 50% of patients over 4 months in 1999, increasing to 71% during 2009-11, with increasing use in most countries. Among patients receiving IV iron, the mean monthly dose increased from 232 ± 167 to 281 ± 211 mg. Most countries used 3 to 4 doses/month, but Canada used about 2 doses/month, Italy increased from 3 to almost 6 doses/month and Germany used 5 to 6 doses/month. The USA and most European countries predominantly used iron sucrose and sodium ferric gluconate. A significant use of iron dextran was limited to Canada and France; iron polymaltose was used in Australia and New Zealand; and Japan used ferric oxide saccharate, chondroitin polysulfate iron complex and cideferron. Ferritin values rose in most countries: 22% of patients had ≥ 800 ng/mL in the recent years of study. TSAT levels increased to a lesser degree over time. Japan had much lower IV iron dosing and ferritin levels, but similar TSAT levels. In adjusted analyses, serum ferritin and TSAT levels increased signifcantly by 14 ng/mL and 0.16%, respectively, for every 100 mg/month higher mean monthly iron dose. IV iron prescription patterns varied between countries and changed over time from 1999 to 2011. IV iron use and dose increased in most countries, with notable increases in ferritin but not TSAT levels. With rising cumulative IV iron doses, studies of the effects of changing IV iron dosing and other anemia management practices on clinical outcomes should be a high priority.

NIRS external dose estimation system for Fukushima residents after the Fukushima Dai-ichi NPP accident

NASA Astrophysics Data System (ADS)

Akahane, Keiichi; Yonai, Shunsuke; Fukuda, Shigekazu; Miyahara, Nobuyuki; Yasuda, Hiroshi; Iwaoka, Kazuki; Matsumoto, Masaki; Fukumura, Akifumi; Akashi, Makoto

2013-04-01

The great east Japan earthquake and subsequent tsunamis caused Fukushima Dai-ichi Nuclear Power Plant (NPP) accident. National Institute of Radiological Sciences (NIRS) developed the external dose estimation system for Fukushima residents. The system is being used in the Fukushima health management survey. The doses can be obtained by superimposing the behavior data of the residents on the dose rate maps. For grasping the doses, 18 evacuation patterns of the residents were assumed by considering the actual evacuation information before using the survey data. The doses of the residents from the deliberate evacuation area were relatively higher than those from the area within 20 km radius. The estimated doses varied from around 1 to 6 mSv for the residents evacuated from the representative places in the deliberate evacuation area. The maximum dose in 18 evacuation patterns was estimated to be 19 mSv.

NIRS external dose estimation system for Fukushima residents after the Fukushima Dai-ichi NPP accident.

PubMed

Akahane, Keiichi; Yonai, Shunsuke; Fukuda, Shigekazu; Miyahara, Nobuyuki; Yasuda, Hiroshi; Iwaoka, Kazuki; Matsumoto, Masaki; Fukumura, Akifumi; Akashi, Makoto

2013-01-01

The great east Japan earthquake and subsequent tsunamis caused Fukushima Dai-ichi Nuclear Power Plant (NPP) accident. National Institute of Radiological Sciences (NIRS) developed the external dose estimation system for Fukushima residents. The system is being used in the Fukushima health management survey. The doses can be obtained by superimposing the behavior data of the residents on the dose rate maps. For grasping the doses, 18 evacuation patterns of the residents were assumed by considering the actual evacuation information before using the survey data. The doses of the residents from the deliberate evacuation area were relatively higher than those from the area within 20 km radius. The estimated doses varied from around 1 to 6 mSv for the residents evacuated from the representative places in the deliberate evacuation area. The maximum dose in 18 evacuation patterns was estimated to be 19 mSv.

Spatial frequency performance limitations of radiation dose optimization and beam positioning

NASA Astrophysics Data System (ADS)

Stewart, James M. P.; Stapleton, Shawn; Chaudary, Naz; Lindsay, Patricia E.; Jaffray, David A.

2018-06-01

The flexibility and sophistication of modern radiotherapy treatment planning and delivery methods have advanced techniques to improve the therapeutic ratio. Contemporary dose optimization and calculation algorithms facilitate radiotherapy plans which closely conform the three-dimensional dose distribution to the target, with beam shaping devices and image guided field targeting ensuring the fidelity and accuracy of treatment delivery. Ultimately, dose distribution conformity is limited by the maximum deliverable dose gradient; shallow dose gradients challenge techniques to deliver a tumoricidal radiation dose while minimizing dose to surrounding tissue. In this work, this ‘dose delivery resolution’ observation is rigorously formalized for a general dose delivery model based on the superposition of dose kernel primitives. It is proven that the spatial resolution of a delivered dose is bounded by the spatial frequency content of the underlying dose kernel, which in turn defines a lower bound in the minimization of a dose optimization objective function. In addition, it is shown that this optimization is penalized by a dose deposition strategy which enforces a constant relative phase (or constant spacing) between individual radiation beams. These results are further refined to provide a direct, analytic method to estimate the dose distribution arising from the minimization of such an optimization function. The efficacy of the overall framework is demonstrated on an image guided small animal microirradiator for a set of two-dimensional hypoxia guided dose prescriptions.

A graphical user interface (GUI) toolkit for the calculation of three-dimensional (3D) multi-phase biological effective dose (BED) distributions including statistical analyses.

PubMed

Kauweloa, Kevin I; Gutierrez, Alonso N; Stathakis, Sotirios; Papanikolaou, Niko; Mavroidis, Panayiotis

2016-07-01

A toolkit has been developed for calculating the 3-dimensional biological effective dose (BED) distributions in multi-phase, external beam radiotherapy treatments such as those applied in liver stereotactic body radiation therapy (SBRT) and in multi-prescription treatments. This toolkit also provides a wide range of statistical results related to dose and BED distributions. MATLAB 2010a, version 7.10 was used to create this GUI toolkit. The input data consist of the dose distribution matrices, organ contour coordinates, and treatment planning parameters from the treatment planning system (TPS). The toolkit has the capability of calculating the multi-phase BED distributions using different formulas (denoted as true and approximate). Following the calculations of the BED distributions, the dose and BED distributions can be viewed in different projections (e.g. coronal, sagittal and transverse). The different elements of this toolkit are presented and the important steps for the execution of its calculations are illustrated. The toolkit is applied on brain, head & neck and prostate cancer patients, who received primary and boost phases in order to demonstrate its capability in calculating BED distributions, as well as measuring the inaccuracy and imprecision of the approximate BED distributions. Finally, the clinical situations in which the use of the present toolkit would have a significant clinical impact are indicated. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Paraoxon and Pyridostigmine Interfere with Neural Stem Cell Differentiation

PubMed Central

Berríos, Verónica O.; Boukli, Nawal M.; Rodriguez, Jose W.; Negraes, Priscilla D.; Schwindt, Telma T.; Trujillo, Cleber A.; Oliveira, Sophia L. B.; Cubano, Luis A.; Ferchmin, P. A.; Eterovic, Vesna A.; Ulrich, Henning; Martins, Antonio H.

2015-01-01

Acetylcholinesterase (AChE) inhibition has been described as the main mechanism of organophosphate (OP)-evoked toxicity. OPs represent a human health threat, because chronic exposure to low doses can damage the developing brain, and acute exposure can produce long-lasting damage to adult brains, despite post-exposure medical countermeasures. Although the main mechanism of OP toxicity is AChE inhibition, several lines of evidence suggest that OPs also act by other mechanisms. We hypothesized that rat neural progenitor cells extracted on embryonic day 14.5 would be affected by constant inhibition of AChE from chronic exposure to OP or pyri-dostigmine (a reversible AChE blocker) during differentiation. In this work, the OP paraoxon decreased cell viability in concentrations >50 μM, as measured with the MTT assay; however, this effect was not dose-dependent. Reduced viability could not be attributed to blockade of AChE activity, since treatment with 200 μM pyri-dostigmine did not affect cell viability, even after 6 days. Although changes in protein expression patterns were noted in both treatments, the distribution of differentiated phenotypes, such as the percentages of neurons and glial cells, was not altered, as determined by flow cytometry. Since paraoxon and pyridostigmine each decreased neurite outgrowth (but did not prevent differentiation), we infer that developmental patterns may have been affected. PMID:25758980

Paraoxon and Pyridostigmine Interfere with Neural Stem Cell Differentiation.

PubMed

Berríos, Verónica O; Boukli, Nawal M; Rodriguez, Jose W; Negraes, Priscilla D; Schwindt, Telma T; Trujillo, Cleber A; Oliveira, Sophia L B; Cubano, Luis A; Ferchmin, P A; Eterović, Vesna A; Ulrich, Henning; Martins, Antonio H

2015-10-01

Acetylcholinesterase (AChE) inhibition has been described as the main mechanism of organophosphate (OP)-evoked toxicity. OPs represent a human health threat, because chronic exposure to low doses can damage the developing brain, and acute exposure can produce long-lasting damage to adult brains, despite post-exposure medical countermeasures. Although the main mechanism of OP toxicity is AChE inhibition, several lines of evidence suggest that OPs also act by other mechanisms. We hypothesized that rat neural progenitor cells extracted on embryonic day 14.5 would be affected by constant inhibition of AChE from chronic exposure to OP or pyridostigmine (a reversible AChE blocker) during differentiation. In this work, the OP paraoxon decreased cell viability in concentrations >50 μM, as measured with the MTT assay; however, this effect was not dose-dependent. Reduced viability could not be attributed to blockade of AChE activity, since treatment with 200 µM pyridostigmine did not affect cell viability, even after 6 days. Although changes in protein expression patterns were noted in both treatments, the distribution of differentiated phenotypes, such as the percentages of neurons and glial cells, was not altered, as determined by flow cytometry. Since paraoxon and pyridostigmine each decreased neurite outgrowth (but did not prevent differentiation), we infer that developmental patterns may have been affected.

Dual-energy computed tomography of the head: a phantom study assessing axial dose distribution, eye lens dose, and image noise level

NASA Astrophysics Data System (ADS)

Matsubara, Kosuke; Kawashima, Hiroki; Hamaguchi, Takashi; Takata, Tadanori; Kobayashi, Masanao; Ichikawa, Katsuhiro; Koshida, Kichiro

2016-03-01

The aim of this study was to propose a calibration method for small dosimeters to measure absorbed doses during dual- source dual-energy computed tomography (DECT) and to compare the axial dose distribution, eye lens dose, and image noise level between DE and standard, single-energy (SE) head CT angiography. Three DE (100/Sn140 kVp 80/Sn140 kVp, and 140/80 kVp) and one SE (120 kVp) acquisitions were performed using a second-generation dual-source CT device and a female head phantom, with an equivalent volumetric CT dose index. The axial absorbed dose distribution at the orbital level and the absorbed doses for the eye lens were measured using radiophotoluminescent glass dosimeters. CT attenuation numbers were obtained in the DE composite images and the SE images of the phantom at the orbital level. The doses absorbed at the orbital level and in the eye lens were lower and standard deviations for the CT attenuation numbers were slightly higher in the DE acquisitions than those in the SE acquisition. The anterior surface dose was especially higher in the SE acquisition than that in the DE acquisitions. Thus, DE head CT angiography can be performed with a radiation dose lower than that required for a standard SE head CT angiography, with a slight increase in the image noise level. The 100/Sn140 kVp acquisition revealed the most balanced axial dose distribution. In addition, our proposed method was effective for calibrating small dosimeters to measure absorbed doses in DECT.

Investigation of fabrication process for sub 20-nm dense pattern of non-chemically amplified electron beam resist based on acrylic polymers

NASA Astrophysics Data System (ADS)

Ochiai, Shunsuke; Takayama, Tomohiro; Kishimura, Yukiko; Asada, Hironori; Sonoda, Manae; Iwakuma, Minako; Hoshino, Ryoichi

2016-10-01

In this study, we examine exposure characteristics of a positive tone electron beam resist consisting of methyl α- chloroacrylate and α-methylstyrene by changing the development process conditions. 25/25 nm and 30/30 nm line-andspace (L/S) patterns (design value) are developed in amyl and heptyl acetates. The resist patterns developed at 0ºC for 120 s show the better shapes having the vertical sidewalls than those developed at 22 °C for 60 s. The dose margins of pattern formation for 0°C development become wider, although the sensitivities are lower. The effect of post exposure baking (PEB) on exposure characteristics is also investigated. Adding PEB process performed at 120°C for 2 min, the dose margin also becomes wider although the sensitivity is lower. 20/20 nm L/S patterns are fabricated by using PEB and/or 0°C development. Though the required exposure dose is larger, the resist pattern is improved by PEB and/or 0°C development. The formation of 35 nm pitch pattern is also presented.

Determination of spatial dose distribution in UCC treatments with LDR brachytherapy using Monte Carlo methods.

PubMed

Benites-Rengifo, Jorge Luis; Vega-Carrillo, Hector Rene

2018-05-19

Using Monte Carlos methods, with the MCNP5 code, a gynecological phantom and a vaginal cylinder were modeled. The spatial distribution of absorbed dose rates in Uterine Cervical Cancer treatment through low dose rate brachytherapy was determined. A liquid water gynecology computational phantom, including a vaginal cylinder applicator made of Lucite, was designed. The applicator has a linear array of four radioactive sources of Cesium 137. Around the vaginal cylinder, 13 water spherical cells of 0.5 cm-diameter were modeled to calculate absorbed dose emulating the procedure made by the treatment planning system. The gamma-ray fluence distribution was estimated, as well as the absorbed doses resulting approximately symmetrical for cells located at upper and lower of vaginal cylinder. Obtained results allow the use of the radioactive decay law to determine dose rate for Uterine Cervical Cancer using low dose rate brachytherapy. Copyright © 2018 Elsevier Ltd. All rights reserved.

Permeabilization of the plasma membrane of L1210 mouse leukemia cells using lithotripter shock waves.

PubMed

Gambihler, S; Delius, M; Ellwart, J W

1994-09-01

Permeabilization of L1210 cells by lithotripter shock waves in vitro was monitored by evaluating the accumulation of fluorescein-labeled dextrans with a relative molecular mass ranging from 3,900-2,000,000. Incubation with labeled dextran alone caused a dose- and time-dependent increase in cellular fluorescence as determined by flow cytometry, with a vesicular distribution pattern in the cells consistent with endocytotic uptake. Shock wave exposure prior to incubation with labeled dextran revealed similar fluorescence intensities compared to incubation with labeled dextran alone. When cells were exposed to shock waves in the presence of labeled dextran, mean cellular fluorescence was further increased, indicating additional internalization of the probe. Confocal laser scanning microscopy confirmed intracellular fluorescence of labeled dextran with a diffuse distribution pattern. Fluorescence-activated cell sorting with subsequent determination of proliferation revealed that permeabilized cells were viable and able to proliferate. Permeabilization of the membrane of L1210 cells by shock waves in vitro allowed loading of dextrans with a relative molecular mass up to 2,000,000. Permeabilization of tumor cells by shock waves provides a useful tool for introducing molecules into cells which might be of interest for drug targeting in tumor therapy in vivo.

Application of Natural Language Processing and Network Analysis Techniques to Post-market Reports for the Evaluation of Dose-related Anti-Thymocyte Globulin Safety Patterns.

PubMed

Botsis, Taxiarchis; Foster, Matthew; Arya, Nina; Kreimeyer, Kory; Pandey, Abhishek; Arya, Deepa

2017-04-26

To evaluate the feasibility of automated dose and adverse event information retrieval in supporting the identification of safety patterns. We extracted all rabbit Anti-Thymocyte Globulin (rATG) reports submitted to the United States Food and Drug Administration Adverse Event Reporting System (FAERS) from the product's initial licensure in April 16, 1984 through February 8, 2016. We processed the narratives using the Medication Extraction (MedEx) and the Event-based Text-mining of Health Electronic Records (ETHER) systems and retrieved the appropriate medication, clinical, and temporal information. When necessary, the extracted information was manually curated. This process resulted in a high quality dataset that was analyzed with the Pattern-based and Advanced Network Analyzer for Clinical Evaluation and Assessment (PANACEA) to explore the association of rATG dosing with post-transplant lymphoproliferative disorder (PTLD). Although manual curation was necessary to improve the data quality, MedEx and ETHER supported the extraction of the appropriate information. We created a final dataset of 1,380 cases with complete information for rATG dosing and date of administration. Analysis in PANACEA found that PTLD was associated with cumulative doses of rATG >8 mg/kg, even in periods where most of the submissions to FAERS reported low doses of rATG. We demonstrated the feasibility of investigating a dose-related safety pattern for a particular product in FAERS using a set of automated tools.

42 CFR 81.4 - Definition of terms used in this part.

Code of Federal Regulations, 2011 CFR

2011-10-01

...]. (e) Equivalent dose means the absorbed dose in a tissue or organ multiplied by a radiation weighting... dose means the portion of the equivalent dose that is received from radiation sources outside of the... pattern and level of radiation exposure. (h) Internal dose means the portion of the equivalent dose that...

Radiotherapy Dose Perturbation of Esophageal Stents Examined in an Experimental Model

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

Atwood, Todd F.; Hsu, Annie; Ogara, Maydeen M.

2012-04-01

Purpose: To investigate the radiotherapy dose perturbations caused by esophageal stents in patients undergoing external beam treatments for esophageal cancer. Methods and Materials: Four esophageal stents were examined (three metallic stents: WallFlex, Ultraflex, and Alveolus; one nonmetallic stent with limited radiopaque markers for visualization: Polyflex). All experiments were performed in a liquid water phantom with a custom acrylic stent holder. Radiochromic film was used to measure the dose distributions adjacent to the stents at locations proximal and distal to the radiation source. The stents were placed in an air-filled cavity to simulate the esophagus. Treatment plans were created and deliveredmore » for photon energies of 6 and 15 MV, and data analysis was performed on uniform regions of interest, according to the size and geometric placement of the films, to quantify the dose perturbations. Results: The three metallic stents produced the largest dose perturbations with distinct patterns of 'hot' spots (increased dose) measured proximal to the radiation source (up to 15.4%) and both 'cold' (decreased dose) and hot spots measured distal to the radiation source (range, -6.1%-5.8%). The polymeric Polyflex stent produced similar dose perturbations when the radiopaque markers were examined (range, -7.6%-15.4%). However, when the radiopaque markers were excluded from the analysis, the Polyflex stent produced significantly smaller dose perturbations, with maximum hot spots of 7.3% and cold spots of -3.2%. Conclusions: The dose perturbations caused by esophageal stents during the treatment of esophageal cancer using external beam radiotherapy should be understood. These perturbations will result in hot and cold spots in the esophageal mucosa, with varying magnitudes depending on the stent. The nonmetallic Polyflex stent appears to be the most suitable for patients undergoing radiotherapy, but further studies are necessary to determine the clinical significance of the dose perturbations.« less

Radiotherapy dose perturbation of esophageal stents examined in an experimental model.

PubMed

Atwood, Todd F; Hsu, Annie; Ogara, Maydeen M; Luba, Daniel G; Tamler, Bradley J; Disario, James A; Maxim, Peter G

2012-04-01

To investigate the radiotherapy dose perturbations caused by esophageal stents in patients undergoing external beam treatments for esophageal cancer. Four esophageal stents were examined (three metallic stents: WallFlex, Ultraflex, and Alveolus; one nonmetallic stent with limited radiopaque markers for visualization: Polyflex). All experiments were performed in a liquid water phantom with a custom acrylic stent holder. Radiochromic film was used to measure the dose distributions adjacent to the stents at locations proximal and distal to the radiation source. The stents were placed in an air-filled cavity to simulate the esophagus. Treatment plans were created and delivered for photon energies of 6 and 15 MV, and data analysis was performed on uniform regions of interest, according to the size and geometric placement of the films, to quantify the dose perturbations. The three metallic stents produced the largest dose perturbations with distinct patterns of "hot" spots (increased dose) measured proximal to the radiation source (up to 15.4%) and both "cold" (decreased dose) and hot spots measured distal to the radiation source (range, -6.1%-5.8%). The polymeric Polyflex stent produced similar dose perturbations when the radiopaque markers were examined (range, -7.6%-15.4%). However, when the radiopaque markers were excluded from the analysis, the Polyflex stent produced significantly smaller dose perturbations, with maximum hot spots of 7.3% and cold spots of -3.2%. The dose perturbations caused by esophageal stents during the treatment of esophageal cancer using external beam radiotherapy should be understood. These perturbations will result in hot and cold spots in the esophageal mucosa, with varying magnitudes depending on the stent. The nonmetallic Polyflex stent appears to be the most suitable for patients undergoing radiotherapy, but further studies are necessary to determine the clinical significance of the dose perturbations. Copyright © 2012 Elsevier Inc. All rights reserved.

NSR&D Program Fiscal Year 2015 Funded Research Stochastic Modeling of Radioactive Material Releases Final Report

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

Andrus, Jason P.; Pope, Chad; Toston, Mary

2016-12-01

Nonreactor nuclear facilities operating under the approval authority of the U.S. Department of Energy use unmitigated hazard evaluations to determine if potential radiological doses associated with design basis events challenge or exceed dose evaluation guidelines. Unmitigated design basis events that sufficiently challenge dose evaluation guidelines or exceed the guidelines for members of the public or workers, merit selection of safety structures, systems, or components or other controls to prevent or mitigate the hazard. Idaho State University, in collaboration with Idaho National Laboratory, has developed a portable and simple to use software application called SODA (Stochastic Objective Decision-Aide) that stochastically calculatesmore » the radiation dose distribution associated with hypothetical radiological material release scenarios. Rather than producing a point estimate of the dose, SODA produces a dose distribution result to allow a deeper understanding of the dose potential. SODA allows users to select the distribution type and parameter values for all of the input variables used to perform the dose calculation. Users can also specify custom distributions through a user defined distribution option. SODA then randomly samples each distribution input variable and calculates the overall resulting dose distribution. In cases where an input variable distribution is unknown, a traditional single point value can be used. SODA, developed using the MATLAB coding framework, has a graphical user interface and can be installed on both Windows and Mac computers. SODA is a standalone software application and does not require MATLAB to function. SODA provides improved risk understanding leading to better informed decision making associated with establishing nuclear facility material-at-risk limits and safety structure, system, or component selection. It is important to note that SODA does not replace or compete with codes such as MACCS or RSAC; rather it is viewed as an easy to use supplemental tool to help improve risk understanding and support better informed decisions. The SODA development project was funded through a grant from the DOE Nuclear Safety Research and Development Program.« less

NSR&D Program Fiscal Year 2015 Funded Research Stochastic Modeling of Radioactive Material Releases Final Report

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

Andrus, Jason P.; Pope, Chad; Toston, Mary

Nonreactor nuclear facilities operating under the approval authority of the U.S. Department of Energy use unmitigated hazard evaluations to determine if potential radiological doses associated with design basis events challenge or exceed dose evaluation guidelines. Unmitigated design basis events that sufficiently challenge dose evaluation guidelines or exceed the guidelines for members of the public or workers, merit selection of safety structures, systems, or components or other controls to prevent or mitigate the hazard. Idaho State University, in collaboration with Idaho National Laboratory, has developed a portable and simple to use software application called SODA (Stochastic Objective Decision-Aide) that stochastically calculatesmore » the radiation dose distribution associated with hypothetical radiological material release scenarios. Rather than producing a point estimate of the dose, SODA produces a dose distribution result to allow a deeper understanding of the dose potential. SODA allows users to select the distribution type and parameter values for all of the input variables used to perform the dose calculation. Users can also specify custom distributions through a user defined distribution option. SODA then randomly samples each distribution input variable and calculates the overall resulting dose distribution. In cases where an input variable distribution is unknown, a traditional single point value can be used. SODA, developed using the MATLAB coding framework, has a graphical user interface and can be installed on both Windows and Mac computers. SODA is a standalone software application and does not require MATLAB to function. SODA provides improved risk understanding leading to better informed decision making associated with establishing nuclear facility material-at-risk limits and safety structure, system, or component selection. It is important to note that SODA does not replace or compete with codes such as MACCS or RSAC; rather it is viewed as an easy to use supplemental tool to help improve risk understanding and support better informed decisions. The SODA development project was funded through a grant from the DOE Nuclear Safety Research and Development Program.« less

Multiple comparisons permutation test for image based data mining in radiotherapy.

PubMed

Chen, Chun; Witte, Marnix; Heemsbergen, Wilma; van Herk, Marcel

2013-12-23

: Comparing incidental dose distributions (i.e. images) of patients with different outcomes is a straightforward way to explore dose-response hypotheses in radiotherapy. In this paper, we introduced a permutation test that compares images, such as dose distributions from radiotherapy, while tackling the multiple comparisons problem. A test statistic Tmax was proposed that summarizes the differences between the images into a single value and a permutation procedure was employed to compute the adjusted p-value. We demonstrated the method in two retrospective studies: a prostate study that relates 3D dose distributions to failure, and an esophagus study that relates 2D surface dose distributions of the esophagus to acute esophagus toxicity. As a result, we were able to identify suspicious regions that are significantly associated with failure (prostate study) or toxicity (esophagus study). Permutation testing allows direct comparison of images from different patient categories and is a useful tool for data mining in radiotherapy.

Subtypes of breast cancer show different spatial distributions of brain metastases.

PubMed

Kyeong, Sunghyon; Cha, Yoon Jin; Ahn, Sung Gwe; Suh, Sang Hyun; Son, Eun Ju; Ahn, Sung Jun

2017-01-01

The aim of our study was to test the hypothesis that the spatial distribution of breast cancer brain metastases (BM) differ according to their biological subtypes. MR images of 100 patients with BM from primary breast cancer were retrospectively reviewed. Patients were divided according to the biological subtype of the primary tumor, (triple-negative: 24, HER2 positive: 48, luminal: 28). All images marked with BMs were standardized to the human brain MRI atlas provided by the Montreal Neurological Institute 152 database. Distribution pattern of BM was evaluated with intra-group and intergroup analysis. In intra-group analysis, hot spots of metastases from triple-negative are evenly distributed in the brain, meanwhile BMs from HER2 positive and luminal type occur dominantly in occipital lobe and cerebellum. In intergroup analysis, BMs from triple-negative type occurred more often in frontal lobe, limbic region, and parietal lobe, compared with other types (P < .05). Breast cancer subtypes tend to demonstrate different spatial distributions of their BMs. These findings may have direct implications for dose modulation in prophylactic irradiation as well as for differential diagnoses. Thus, this result should be validated in future study with a larger population.

SU-F-T-62: Three-Dimensional Dosimetric Gamma Analysis for Impacts of Tissue Inhomogeneity Using Monte Carlo Simulation in Intracavitary Brachytheray for Cervix Carcinoma

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

Nguyen, Tran Thi Thao; Nakamoto, Takahiro; Shibayama, Yusuke

Purpose: The aim of this study was to investigate the impacts of tissue inhomogeneity on dose distributions using a three-dimensional (3D) gamma analysis in cervical intracavitary brachytherapy using Monte Carlo (MC) simulations. Methods: MC simulations for comparison of dose calculations were performed in a water phantom and a series of CT images of a cervical cancer patient (stage: Ib; age: 27) by employing a MC code, Particle and Heavy Ion Transport Code System (PHIT) version 2.73. The {sup 192}Ir source was set at fifteen dwell positions, according to clinical practice, in an applicator consisting of a tandem and two ovoids.more » Dosimetric comparisons were performed for the dose distributions in the water phantom and CT images by using gamma index image and gamma pass rate (%). The gamma index is the minimum Euclidean distance between two 3D spatial dose distributions of the water phantom and CT images in a same space. The gamma pass rates (%) indicate the percentage of agreement points, which mean that two dose distributions are similar, within an acceptance criteria (3 mm/3%). The volumes of physical and clinical interests for the gamma analysis were a whole calculated volume and a region larger than t% of a dose (close to a target), respectively. Results: The gamma pass rates were 77.1% for a whole calculated volume and 92.1% for a region within 1% dose region. The differences of 7.7% to 22.9 % between two dose distributions in the water phantom and CT images were found around the applicator region and near the target. Conclusion: This work revealed the large difference on the dose distributions near the target in the presence of the tissue inhomogeneity. Therefore, the tissue inhomogeneity should be corrected in the dose calculation for clinical treatment.« less

TU-C-BRE-11: 3D EPID-Based in Vivo Dosimetry: A Major Step Forward Towards Optimal Quality and Safety in Radiation Oncology Practice

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

Mijnheer, B; Mans, A; Olaciregui-Ruiz, I

Purpose: To develop a 3D in vivo dosimetry method that is able to substitute pre-treatment verification in an efficient way, and to terminate treatment delivery if the online measured 3D dose distribution deviates too much from the predicted dose distribution. Methods: A back-projection algorithm has been further developed and implemented to enable automatic 3D in vivo dose verification of IMRT/VMAT treatments using a-Si EPIDs. New software tools were clinically introduced to allow automated image acquisition, to periodically inspect the record-and-verify database, and to automatically run the EPID dosimetry software. The comparison of the EPID-reconstructed and planned dose distribution is donemore » offline to raise automatically alerts and to schedule actions when deviations are detected. Furthermore, a software package for online dose reconstruction was also developed. The RMS of the difference between the cumulative planned and reconstructed 3D dose distributions was used for triggering a halt of a linac. Results: The implementation of fully automated 3D EPID-based in vivo dosimetry was able to replace pre-treatment verification for more than 90% of the patient treatments. The process has been fully automated and integrated in our clinical workflow where over 3,500 IMRT/VMAT treatments are verified each year. By optimizing the dose reconstruction algorithm and the I/O performance, the delivered 3D dose distribution is verified in less than 200 ms per portal image, which includes the comparison between the reconstructed and planned dose distribution. In this way it was possible to generate a trigger that can stop the irradiation at less than 20 cGy after introducing large delivery errors. Conclusion: The automatic offline solution facilitated the large scale clinical implementation of 3D EPID-based in vivo dose verification of IMRT/VMAT treatments; the online approach has been successfully tested for various severe delivery errors.« less

Comparative dosimetry of diode and diamond detectors in electron beams for intraoperative radiation therapy.

PubMed

Björk, P; Knöös, T; Nilsson, P

2000-11-01

The aim of the present study is to examine the validity of using silicon semiconductor detectors in degraded electron beams with a broad energy spectrum and a wide angular distribution. A comparison is made with diamond detector measurements, which is the dosimeter considered to give the best results provided that dose rate effects are corrected for. Two-dimensional relative absorbed dose distributions in electron beams (6-20 MeV) for intraoperative radiation therapy (IORT) are measured in a water phantom. To quantify deviations between the detectors, a dose comparison tool that simultaneously examines the dose difference and distance to agreement (DTA) is used to evaluate the results in low- and high-dose gradient regions, respectively. Uncertainties of the experimental measurement setup (+/- 1% and +/- 0.5 mm) are taken into account by calculating a composite distribution that fails this dose-difference and DTA acceptance limit. Thus, the resulting area of disagreement should be related to differences in detector performance. The dose distributions obtained with the diode are generally in very good agreement with diamond detector measurements. The buildup region and the dose falloff region show good agreement with increasing electron energy, while the region outside the radiation field close to the water surface shows an increased difference with energy. The small discrepancies in the composite distributions are due to several factors: (a) variation of the silicon-to-water collision stopping-power ratio with electron energy, (b) a more pronounced directional dependence for diodes than for diamonds, and (c) variation of the electron fluence perturbation correction factor with depth. For all investigated treatment cones and energies, the deviation is within dose-difference and DTA acceptance criteria of +/- 3% and +/- 1 mm, respectively. Therefore, p-type silicon diodes are well suited, in the sense that they give results in close agreement with diamond detectors, for practical measurements of relative absorbed dose distributions in degraded electron beams used for IORT.

Estimation of ambient dose equivalent distribution in the 18F-FDG administration room using Monte Carlo simulation.

PubMed

Nagamine, Shuji; Fujibuchi, Toshioh; Umezu, Yoshiyuki; Himuro, Kazuhiko; Awamoto, Shinichi; Tsutsui, Yuji; Nakamura, Yasuhiko

2017-03-01

In this study, we estimated the ambient dose equivalent rate (hereafter "dose rate") in the fluoro-2-deoxy-D-glucose (FDG) administration room in our hospital using Monte Carlo simulations, and examined the appropriate medical-personnel locations and a shielding method to reduce the dose rate during FDG injection using a lead glass shield. The line source was assumed to be the FDG feed tube and the patient a cube source. The dose rate distribution was calculated with a composite source that combines the line and cube sources. The dose rate distribution was also calculated when a lead glass shield was placed in the rear section of the lead-acrylic shield. The dose rate behind the automatic administration device decreased by 87 % with respect to that behind the lead-acrylic shield. Upon positioning a 2.8-cm-thick lead glass shield, the dose rate behind the lead-acrylic shield decreased by 67 %.

Assessment of radiation doses from residential smoke detectors that contain americium-241

NASA Astrophysics Data System (ADS)

Odonnell, F. R.; Etnier, E. L.; Holton, G. A.; Travis, C. C.

1981-10-01

External dose equivalents and internal dose commitments were estimated for individuals and populations from annual distribution, use, and disposal of 10 million ionization chamber smoke detectors that contain 110 kBq americium-241 each. Under exposure scenarios developed for normal distribution, use, and disposal using the best available information, annual external dose equivalents to average individuals were estimated to range from 4 fSv to 20 nSv for total body and from 7 fSv to 40 nSv for bone. Internal dose commitments to individuals under post disposal scenarios were estimated to range from 0.006 to 80 micro-Sv (0.0006 to 8 mrem) to total body and from 0.06 to 800 micro-Sv to bone. The total collective dose (the sum of external dose equivalents and 50-year internal dose commitments) for all individuals involved with distribution, use, or disposal of 10 million smoke detectors was estimated to be about 0.38 person-Sv (38 person-rem) to total body and 00 ft squared.

Monte Carlo simulation of depth-dose distributions in TLD-100 under 90Sr-90Y irradiation.

PubMed

Rodríguez-Villafuerte, M; Gamboa-deBuen, I; Brandan, M E

1997-04-01

In this work the depth-dose distribution in TLD-100 dosimeters under beta irradiation from a 90Sr-90Y source was investigated using the Monte Carlo method. Comparisons between the simulated data and experimental results showed that the depth-dose distribution is strongly affected by the different components of both the source and dosimeter holders due to the large number of electron scattering events.

Treatment of solid tumors by interstitial release of recoiling short-lived alpha emitters

NASA Astrophysics Data System (ADS)

Arazi, L.; Cooks, T.; Schmidt, M.; Keisari, Y.; Kelson, I.

2007-08-01

A new method utilizing alpha particles to treat solid tumors is presented. Tumors are treated with interstitial radioactive sources which continually release short-lived alpha emitting atoms from their surface. The atoms disperse inside the tumor, delivering a high dose through their alpha decays. We implement this scheme using thin wire sources impregnated with 224Ra, which release by recoil 220Rn, 216Po and 212Pb atoms. This work aims to demonstrate the feasibility of our method by measuring the activity patterns of the released radionuclides in experimental tumors. Sources carrying 224Ra activities in the range 10-130 kBq were used in experiments on murine squamous cell carcinoma tumors. These included gamma spectroscopy of the dissected tumors and major organs, Fuji-plate autoradiography of histological tumor sections and tissue damage detection by Hematoxylin-Eosin staining. The measurements focused on 212Pb and 212Bi. The 220Rn/216Po distribution was treated theoretically using a simple diffusion model. A simplified scheme was used to convert measured 212Pb activities to absorbed dose estimates. Both physical and histological measurements confirmed the formation of a 5-7 mm diameter necrotic region receiving a therapeutic alpha-particle dose around the source. The necrotic regions shape closely corresponded to the measured activity patterns. 212Pb was found to leave the tumor through the blood at a rate which decreased with tumor mass. Our results suggest that the proposed method, termed DART (diffusing alpha-emitters radiation therapy), may potentially be useful for the treatment of human patients.

Detection of DNA Damage by Space Radiation in Human Fibroblast Cells Flown on the International Space Station

NASA Technical Reports Server (NTRS)

Wu, Honglu; Lu, Tao; Wong, Michael; Beno, Jonathan; Countryman, Stefanie; Stodieck, Louis; Karouia, Fathi; Zhang, Ye

2015-01-01

Although charged particles in space have been detected with radiation detectors on board spacecraft since the early discovery of the Van Allen Belt, reports on effects of direct exposure to space radiation in biological systems have been limited. Measurement of biological effects of space radiation has been difficult due to the low dose and low dose rate nature of the radiation environment, and the difficulty in separating the radiation effects from microgravity and other space environmental factors. In astronauts, only a small number of changes, such as increased chromosome aberrations in lymphocytes and early onset of cataracts, attributed primarily to the exposure to space radiation. In a recent experiment, human fibroblast cells were flown on the International Space Station (ISS). Cells fixed on Days 3 and 14 after reaching orbit were analyzed for phosphorylation of a histone protein H2AX by immunofluorescent staining of cells, which is a widely used marker for DNA double strand breaks. The 3-dimensional gamma-H2AX foci were captured with a laser confocal microscope. Quantitative analysis revealed a small fraction of foci that were larger and displayed a track pattern in the flight samples in comparison to the ground control. Human fibroblast cells were also exposed to low dose rate gamma rays, as well as to protons and Fe ions. Comparison of the pattern and distribution of the foci after gamma ray and charged particle exposure to our flight results confirmed that the foci found in the flown cells were indeed induced by space radiation.

Dose Distribution in Bladder and Surrounding Normal Tissues in Relation to Bladder Volume in Conformal Radiotherapy for Bladder Cancer

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

Majewski, Wojciech, E-mail: wmajewski1@poczta.onet.p; Wesolowska, Iwona; Urbanczyk, Hubert

2009-12-01

Purpose: To estimate bladder movements and changes in dose distribution in the bladder and surrounding tissues associated with changes in bladder filling and to estimate the internal treatment margins. Methods and Materials: A total of 16 patients with bladder cancer underwent planning computed tomography scans with 80- and 150-mL bladder volumes. The bladder displacements associated with the change in volume were measured. Each patient had treatment plans constructed for a 'partially empty' (80 mL) and a 'partially full' (150 mL) bladder. An additional plan was constructed for tumor irradiation alone. A subsequent 9 patients underwent sequential weekly computed tomography scanningmore » during radiotherapy to verify the bladder movements and estimate the internal margins. Results: Bladder movements were mainly observed cranially, and the estimated internal margins were nonuniform and largest (>2 cm) anteriorly and cranially. The dose distribution in the bladder worsened if the bladder increased in volume: 70% of patients (11 of 16) would have had bladder underdosed to <95% of the prescribed dose. The dose distribution in the rectum and intestines was better with a 'partially empty' bladder (volume that received >70%, 80%, and 90% of the prescribed dose was 23%, 20%, and 15% for the rectum and 162, 144, 123 cm{sup 3} for the intestines, respectively) than with a 'partially full' bladder (volume that received >70%, 80%, and 90% of the prescribed dose was 28%, 24%, and 18% for the rectum and 180, 158, 136 cm{sup 3} for the intestines, respectively). The change in bladder filling during RT was significant for the dose distribution in the intestines. Tumor irradiation alone was significantly better than whole bladder irradiation in terms of organ sparing. Conclusion: The displacements of the bladder due to volume changes were mainly related to the upper wall. The internal margins should be nonuniform, with the largest margins cranially and anteriorly. The changes in bladder filling during RT could influence the dose distribution in the bladder and intestines. The dose distribution in the rectum and bowel was slightly better with a 'partially empty' than with a 'full' bladder.« less

A 3D isodose manipulation tool for interactive dose shaping

NASA Astrophysics Data System (ADS)

Kamerling, C. P.; Ziegenhein, P.; Heinrich, H.; Oelfke, U.

2014-03-01

The interactive dose shaping (IDS) planning paradigm aims to perform interactive local dose adaptations of an IMRT plan without compromising already established valuable dose features in real-time. In this work we introduce an interactive 3D isodose manipulation tool which enables local modifications of a dose distribution intuitively by direct manipulation of an isodose surface. We developed an in-house IMRT TPS framework employing an IDS engine as well as a 3D GUI for dose manipulation and visualization. In our software an initial dose distribution can be interactively modified through an isodose surface manipulation tool by intuitively clicking on an isodose surface. To guide the user interaction, the position of the modification is indicated by a sphere while the mouse cursor hovers the isodose surface. The sphere's radius controls the locality of the modification. The tool induces a dose modification as a direct change of dose in one or more voxels, which is incrementally obtained by fluence adjustments. A subsequent recovery step identifies voxels with violated dose features and aims to recover their original dose. We showed a proof of concept study for the proposed tool by adapting the dose distribution of a prostate case (9 beams, coplanar). Single dose modifications take less than 2 seconds on an actual desktop PC.

Detailed Distribution Map of Absorbed Dose Rate in Air in Tokatsu Area of Chiba Prefecture, Japan, Constructed by Car-Borne Survey 4 Years after the Fukushima Daiichi Nuclear Power Plant Accident

PubMed Central

Inoue, Kazumasa; Arai, Moeko; Fujisawa, Makoto; Saito, Kyouko; Fukushi, Masahiro

2017-01-01

A car-borne survey was carried out in the northwestern, or Tokatsu, area of Chiba Prefecture, Japan, to make a detailed distribution map of absorbed dose rate in air four years after the Fukushima Daiichi Nuclear Power Plant accident. This area was chosen because it was the most heavily radionuclide contaminated part of Chiba Prefecture and it neighbors metropolitan Tokyo. Measurements were performed using a 3-in × 3-in NaI(Tl) scintillation spectrometer in June 2015. The survey route covered the whole Tokatsu area which includes six cities. A heterogeneous distribution of absorbed dose rate in air was observed on the dose distribution map. Especially, higher absorbed dose rates in air exceeding 80 nGy h-1 were observed along national roads constructed using high porosity asphalt, whereas lower absorbed dose rates in air were observed along local roads constructed using low porosity asphalt. The difference between these asphalt types resulted in a heterogeneous dose distribution in the Tokatsu area. The mean of the contribution ratio of artificial radionuclides to absorbed dose rate in air measured 4 years after the accident was 29% (9–50%) in the Tokatsu area. The maximum absorbed dose rate in air, 201 nGy h-1 was observed at Kashiwa City. Radiocesium was deposited in the upper 1 cm surface layer of the high porosity asphalt which was collected in Kashiwa City and the environmental half-life of the absorbed dose rate in air was estimated to be 1.7 years. PMID:28129382

SEMICONDUCTOR TECHNOLOGY: An efficient dose-compensation method for proximity effect correction

NASA Astrophysics Data System (ADS)

Ying, Wang; Weihua, Han; Xiang, Yang; Renping, Zhang; Yang, Zhang; Fuhua, Yang

2010-08-01

A novel simple dose-compensation method is developed for proximity effect correction in electron-beam lithography. The sizes of exposed patterns depend on dose factors while other exposure parameters (including accelerate voltage, resist thickness, exposing step size, substrate material, and so on) remain constant. This method is based on two reasonable assumptions in the evaluation of the compensated dose factor: one is that the relation between dose factors and circle-diameters is linear in the range under consideration; the other is that the compensated dose factor is only affected by the nearest neighbors for simplicity. Four-layer-hexagon photonic crystal structures were fabricated as test patterns to demonstrate this method. Compared to the uncorrected structures, the homogeneity of the corrected hole-size in photonic crystal structures was clearly improved.

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

Unkelbach, J; Perko, Z; Wolfgang, J

Purpose: Stereotactic body radiotherapy (SBRT) has become an established treatment option for liver cancer. For patients with large tumors, the prescription dose is often limited by constraints on the mean liver dose, leading to tumor recurrence. In this work, we demonstrate that spatiotemporal fractionation schemes, ie delivering distinct dose distributions in different fractions, may allow for a 10% increase in biologically effective dose (BED) in the tumor compared to current practice where each fraction delivers the same dose distribution. Methods: We consider rotation therapy delivered with x-ray beams. Treatment plan optimization is performed using objective functions evaluated for the cumulativemore » BED delivered at the end of treatment. This allows for simultaneously optimizing multiple distinct treatment plans for different fractions. Results: The treatment that optimally exploits fractionation effects is designed such that each fraction delivers a similar dose bath to the uninvolved liver while delivering high single fraction doses to complementary parts of the target volume. Thereby, partial hypofractionation in the tumor is achieved along with near uniform fractionation in the surrounding liver - leading to an improvement in the therapeutic ratio. The benefit of such spatiotemporal fractionation schemes depends on tumor geometry and location as well as the number of fractions. For 5-fraction treatments (allowing for 5 distinct dose distributions) an improvement in the order of 10% is observed. Conclusion: Delivering distinct dose distributions in different fractions, purely motivated by fractionation effects rather than geometric changes, may improve the therapeutic ratio. For treatment sites where the prescriptions dose is limited by mean dose constraints in the surrounding organ, such as liver cancer, this approach may facilitate biological dose escalation and improved cure rates.« less

SU-F-J-194: Development of Dose-Based Image Guided Proton Therapy Workflow

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

Pham, R; Sun, B; Zhao, T

Purpose: To implement image-guided proton therapy (IGPT) based on daily proton dose distribution. Methods: Unlike x-ray therapy, simple alignment based on anatomy cannot ensure proper dose coverage in proton therapy. Anatomy changes along the beam path may lead to underdosing the target, or overdosing the organ-at-risk (OAR). With an in-room mobile computed tomography (CT) system, we are developing a dose-based IGPT software tool that allows patient positioning and treatment adaption based on daily dose distributions. During an IGPT treatment, daily CT images are acquired in treatment position. After initial positioning based on rigid image registration, proton dose distribution is calculatedmore » on daily CT images. The target and OARs are automatically delineated via deformable image registration. Dose distributions are evaluated to decide if repositioning or plan adaptation is necessary in order to achieve proper coverage of the target and sparing of OARs. Besides online dose-based image guidance, the software tool can also map daily treatment doses to the treatment planning CT images for offline adaptive treatment. Results: An in-room helical CT system is commissioned for IGPT purposes. It produces accurate CT numbers that allow proton dose calculation. GPU-based deformable image registration algorithms are developed and evaluated for automatic ROI-delineation and dose mapping. The online and offline IGPT functionalities are evaluated with daily CT images of the proton patients. Conclusion: The online and offline IGPT software tool may improve the safety and quality of proton treatment by allowing dose-based IGPT and adaptive proton treatments. Research is partially supported by Mevion Medical Systems.« less

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

Purwaningsih, Anik

Dosimetric data for a brachytherapy source should be known before it used for clinical treatment. Iridium-192 source type H01 was manufactured by PRR-BATAN aimed to brachytherapy is not yet known its dosimetric data. Radial dose function and anisotropic dose distribution are some primary keys in brachytherapy source. Dose distribution for Iridium-192 source type H01 was obtained from the dose calculation formalism recommended in the AAPM TG-43U1 report using MCNPX 2.6.0 Monte Carlo simulation code. To know the effect of cavity on Iridium-192 type H01 caused by manufacturing process, also calculated on Iridium-192 type H01 if without cavity. The result ofmore » calculation of radial dose function and anisotropic dose distribution for Iridium-192 source type H01 were compared with another model of Iridium-192 source.« less

Dosimetry for a uterine cervix cancer treatment

NASA Astrophysics Data System (ADS)

Rodríguez-Ponce, Miguel; Rodríguez-Villafuerte, Mercedes; Sánchez-Castro, Ricardo

2003-09-01

The dose distribution around the 3M 137Cs brachytherapy source as well as the same source inside the Amersham ASN 8231 applicator was measured using thermoluminescent dosimeters and radiochromic films. Some of the results were compared with those obtained from a Monte Carlo simulation and a good agreement was observed. The teletherapy dose distribution was measured using a pin-point ionization chamber. In addition, the experimental measurements and the Monte Carlo results were used to estimate the dose received in the rectum and bladder of an hypothetical patient treated with brachytherapy and compared with the dose distribution obtained from the Hospital's brachytherapy planning system. A 20 % dose reduction to the rectum and bladder was observed in both Monte Carlo and experimental measurements, compared with the results of the planning system, which results in a better dose control to these structures.

Voxel-based dose prediction with multi-patient atlas selection for automated radiotherapy treatment planning

NASA Astrophysics Data System (ADS)

McIntosh, Chris; Purdie, Thomas G.

2017-01-01

Automating the radiotherapy treatment planning process is a technically challenging problem. The majority of automated approaches have focused on customizing and inferring dose volume objectives to be used in plan optimization. In this work we outline a multi-patient atlas-based dose prediction approach that learns to predict the dose-per-voxel for a novel patient directly from the computed tomography planning scan without the requirement of specifying any objectives. Our method learns to automatically select the most effective atlases for a novel patient, and then map the dose from those atlases onto the novel patient. We extend our previous work to include a conditional random field for the optimization of a joint distribution prior that matches the complementary goals of an accurately spatially distributed dose distribution while still adhering to the desired dose volume histograms. The resulting distribution can then be used for inverse-planning with a new spatial dose objective, or to create typical dose volume objectives for the canonical optimization pipeline. We investigated six treatment sites (633 patients for training and 113 patients for testing) and evaluated the mean absolute difference in all DVHs for the clinical and predicted dose distribution. The results on average are favorable in comparison to our previous approach (1.91 versus 2.57). Comparing our method with and without atlas-selection further validates that atlas-selection improved dose prediction on average in whole breast (0.64 versus 1.59), prostate (2.13 versus 4.07), and rectum (1.46 versus 3.29) while it is less important in breast cavity (0.79 versus 0.92) and lung (1.33 versus 1.27) for which there is high conformity and minimal dose shaping. In CNS brain, atlas-selection has the potential to be impactful (3.65 versus 5.09), but selecting the ideal atlas is the most challenging.

Dose mapping inside a gamma irradiator measured with doped silica fibre dosimetry and Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Moradi, F.; Khandaker, M. U.; Mahdiraji, G. A.; Ung, N. M.; Bradley, D. A.

2017-11-01

In recent years doped silica fibre thermoluminescent dosimeters (TLD) have been demonstrated to have considerable potential for irradiation applications, benefitting from the available sensitivity, spatial resolution and dynamic dose range, with primary focus being on the needs of medical dosimetry. Present study concerns the dose distribution inside a cylindrically shaped gamma-ray irradiator cavity, with irradiator facilities such as the familiar 60Co versions being popularly used in industrial applications. Quality assurance of the radiation dose distribution inside the irradiation cell of such a device is of central importance in respect of the delivered dose to the irradiated material. Silica fibre TLD dose-rates obtained within a Gammacell-220 irradiator cavity show the existence of non-negligible dose distribution heterogeneity, by up to 20% and 26% in the radial and axial directions respectively, Monte Carlo simulations and available literature providing some support for present findings. In practice, it is evident that there is need to consider making corrections to nominal dose-rates in order to avoid the potential for under-dosing.

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-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

Dosimetry of a Small-Animal Irradiation Model using a 6 MV Linear Accelerator

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

Fitch, F. Moran; Martinez-Davalos, A.; Garcia-Garduno, O. A.

2010-12-07

A custom made rat-like phantom was used to measure dose distributions using a 6 MV linear accelerator. The phantom has air cavities that simulate the lungs and cylindrical inserts that simulate the backbone. The calculated dose distributions were obtained with the BrainScan v.5.31 TPS software. For the irradiation two cases were considered: (a) near the region where the phantom has two air cavities that simulate the lungs, and (b) with an entirely uniform phantom. The treatment plan consisted of two circular cone arcs that imparted a 500 cGy dose to a simulated lesion in the backbone. We measured dose distributionsmore » using EBT2 GafChromic film and an Epson Perfection V750 scanner working in transmission mode. Vertical and horizontal profiles, isodose curves from 50 to 450 cGy, dose and distance to agreement (DTA) histograms and Gamma index were obtained to compare the dose distributions using DoseLab v4.11. As a result, these calculations show very good agreement between calculated and measured dose distribution in both cases. With a 2% 2 mm criteria 100% of the points pass the Gamma test for the uniform case, while 98.9% of the points do it for the lungs case.« less

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.

[The use of polymer gel dosimetry to measure dose distribution around metallic implants].

PubMed

Nagahata, Tomomasa; Yamaguchi, Hajime; Monzen, Hajime; Nishimura, Yasumasa

2014-10-01

A semi-solid polymer dosimetry system using agar was developed to measure the dose distribution close to metallic implants. Dosimetry of heterogeneous fields where electron density markedly varies is often problematic. This prompted us to develop a polymer gel dosimetry technique using agar to measure the dose distribution near substance boundaries. Varying the concentration of an oxygen scavenger (tetra-hydroxymethyl phosphonium chloride) showed the absorbed dose and transverse relaxation rate of the magnetic resonance signal to be linear between 3 and 12 Gy. Although a change in the dosimeter due to oxidization was observed in room air after 24 hours, no such effects were observed in the first 4 hours. The dose distribution around the metal implants was measured using agar dosimetry. The metals tested were a lead rod, a titanium hip joint, and a metallic stent. A maximum 30% dose increase was observed near the lead rod, but only a 3% increase in the absorbed dose was noted near the surface of the titanium hip joint and metallic stent. Semi-solid polymer dosimetry using agar thus appears to be a useful method for dosimetry around metallic substances.

Dose and scatter characteristics of a novel cone beam CT system for musculoskeletal extremities

NASA Astrophysics Data System (ADS)

Zbijewski, W.; Sisniega, A.; Vaquero, J. J.; Muhit, A.; Packard, N.; Senn, R.; Yang, D.; Yorkston, J.; Carrino, J. A.; Siewerdsen, J. H.

2012-03-01

A novel cone-beam CT (CBCT) system has been developed with promising capabilities for musculoskeletal imaging (e.g., weight-bearing extremities and combined radiographic / volumetric imaging). The prototype system demonstrates diagnostic-quality imaging performance, while the compact geometry and short scan orbit raise new considerations for scatter management and dose characterization that challenge conventional methods. The compact geometry leads to elevated, heterogeneous x-ray scatter distributions - even for small anatomical sites (e.g., knee or wrist), and the short scan orbit results in a non-uniform dose distribution. These complex dose and scatter distributions were investigated via experimental measurements and GPU-accelerated Monte Carlo (MC) simulation. The combination provided a powerful basis for characterizing dose distributions in patient-specific anatomy, investigating the benefits of an antiscatter grid, and examining distinct contributions of coherent and incoherent scatter in artifact correction. Measurements with a 16 cm CTDI phantom show that the dose from the short-scan orbit (0.09 mGy/mAs at isocenter) varies from 0.16 to 0.05 mGy/mAs at various locations on the periphery (all obtained at 80 kVp). MC estimation agreed with dose measurements within 10-15%. Dose distribution in patient-specific anatomy was computed with MC, confirming such heterogeneity and highlighting the elevated energy deposition in bone (factor of ~5-10) compared to soft-tissue. Scatter-to-primary ratio (SPR) up to ~1.5-2 was evident in some regions of the knee. A 10:1 antiscatter grid was found earlier to result in significant improvement in soft-tissue imaging performance without increase in dose. The results of MC simulations elucidated the mechanism behind scatter reduction in the presence of a grid. A ~3-fold reduction in average SPR was found in the MC simulations; however, a linear grid was found to impart additional heterogeneity in the scatter distribution, mainly due to the increase in the contribution of coherent scatter with increased spatial variation. Scatter correction using MC-generated scatter distributions demonstrated significant improvement in cupping and streaks. Physical experimentation combined with GPU-accelerated MC simulation provided a sophisticated, yet practical approach in identifying low-dose acquisition techniques, optimizing scatter correction methods, and evaluating patientspecific dose.

THE DISTRIBUTION OF 51CR-LABELED LYMPHOCYTES INTO ANTIGEN-STIMULATED MICE

PubMed Central

Zatz, Marion M.; Lance, Eugene M.

1971-01-01

The localization of syngeneic 51Cr-labeled lymph node cells was investigated in CBA/J mice previously challenged with sheep erythrocytes, Salmonella H antigen, keyhole limpet hemocyanin, C57BL/6J skin, or rat skin. The effect of time, dose, and route of antigen administration on lymphocyte migration was studied in both primary and secondary responses. When the distribution pattern of lymphocytes was examined after 20–24 hr, it was found that increased localization of labeled cells occurred in spleen after intravenous or intraperitoneal antigen injection, and in draining lymph nodes after subcutaneous antigen injection or skin grafting. Increased localization (trapping) of lymphocytes was antigen dose dependent and could be demonstrated when 1–6 hr had elapsed between intravenous antigen administration, or when 24 hr had elapsed between subcutaneous antigen administration and intravenous cell infusion. Trapping was transient, lasting approximately 24 hr. Maximal trapping of lymphocytes in the draining nodes occurred 9 days after skin grafting in the first-set allograft response, and 3 days after grafting in the second-set allograft and first-set xenograft responses. The cell type trapped, the specificity and mechanism of action of the trap, and the role of lymphocyte trapping in the initiation of immune responses are discussed. PMID:4934148

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.

Mechanisms of Low Dose Radiation-induced T helper Cell Function

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

Gridley, Daila S.

Exposure to radiation above levels normally encountered on Earth can occur during wartime, accidents such as those at Three Mile Island and Chernobyl, and detonation of “dirty bombs” by terrorists. Relatively high levels of radiation exposure can also occur in certain occupations (low-level waste sites, nuclear power plants, nuclear medicine facilities, airline industry, and space agencies). Depression or dysfunction of the highly radiosensitive cells of the immune system can lead to serious consequences, including increased risk for infections, cancer, hypersensitivity reactions, poor wound healing, and other pathologies. The focus of this research was on the T helper (Th) subset ofmore » lymphocytes that secrete cytokines (proteins), and thus control many actions and interactions of other cell types that make up what is collectively known as the immune system. The Department of Energy (DOE) Low Dose Radiation Program is concerned with mechanisms altered by exposure to high energy photons (x- and gamma-rays), protons and electrons. This study compared, for the first time, the low-dose effects of two of these radiation forms, photons and protons, on the response of Th cells, as well as other cell types with which they communicate. The research provided insights regarding gene expression patterns and capacity to secrete potent immunostimulatory and immunosuppressive cytokines, some of which are implicated in pathophysiological processes. Furthermore, the photon versus proton comparison was important not only to healthy individuals who may be exposed, but also to patients undergoing radiotherapy, since many medical centers in the United States, as well as worldwide, are now building proton accelerators. The overall hypothesis of this study was that whole-body exposure to low-dose photons (gamma-rays) will alter CD4+ Th cell function. We further proposed that exposure to low-dose proton radiation will induce a different pattern of gene and functional changes compared to photons. Over the course of this research, tissues other than spleens were archived and with funding obtained from other sources, including the Department of Radiation Medicine at the Loma Linda University Medical Center, some additional assays were performed. Furthermore, groups of additional mice were included that were pre-exposed to low-dose photons before irradiating with acute photons, protons, and simulated solar particle event (SPE) protons. Hence, the original support together with the additional funding for our research led to generation of much valuable information that was originally not anticipated. Some of the data has already resulted in published articles, manuscripts in review, and a number of presentations at scientific conferences and workshops. Difficulties in reliable and reproducible quantification of secreted cytokines using multi-plex technology delayed completion of this study for a period of time. However, final analyses of the remaining data are currently being performed and should result in additional publications and presentations in the near future. Some of the most notable conclusions, thus far, are briefly summarized below: - Distribution of leukocytes were dependent upon cell type, radiation quality, body compartment analyzed, and time after exposure. Low-dose protons tended to have less effect on numbers of major leukocyte populations and T cell subsets compared to low-dose photons. - The patterns of gene and cytokine expression in CD4+ T cells after protracted low-dose irradiation were significantly modified and highly dependent upon the total dose and time after exposure. - Patterns of gene and cytokine expression differed substantially among groups exposed to low-dose photons versus low-dose protons; differences were also noted among groups exposed to much higher doses of photons, protons, and simulated SPE protons. - Some measurements indicated that exposure to low-dose photon radiation, especially 0.01 Gy, significantly “normalized” at least some adverse effects of simulated SPE protons, thereby suggesting that this low level of radiation may induce protective mechanisms against a relatively large radiation event. - Analysis of signal transduction pathways in CD4+ T cells showed that whole-body priming with 0.01 Gy photons before exposure to simulated SPE protons significantly increased expression of p38MAPK and NF-kappaB, while JNK expression was decreased. Overall, it appears that the p38MAPK signaling pathway may be most important in inducing a radioprotective response.« 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-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

TU-D-209-02: A Backscatter Point Spread Function for Entrance Skin Dose Determination

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

Vijayan, S; Xiong, Z; Shankar, A

Purpose: To determine the distribution of backscattered radiation to the skin resulting from a non-uniform distribution of primary radiation through convolution with a backscatter point spread function (PSF). Methods: A backscatter PSF is determined using Monte Carlo simulation of a 1 mm primary beam incident on a 30 × 30 cm × 20 cm thick PMMA phantom using EGSnrc software. A primary profile is similarly obtained without the phantom and the difference from the total provides the backscatter profile. This scatter PSF characterizes the backscatter spread for a “point” primary interaction and can be convolved with the entrance primary dosemore » distribution to obtain the total entrance skin dose. The backscatter PSF was integrated into the skin dose tracking system (DTS), a graphical utility for displaying the color-coded skin dose distribution on a 3D graphic of the patient during interventional fluoroscopic procedures. The backscatter convolution method was validated for the non-uniform beam resulting from the use of an ROI attenuator. The ROI attenuator is a copper sheet with about 20% primary transmission (0.7 mm thick) containing a circular aperture; this attenuator is placed in the beam to reduce dose in the periphery while maintaining full dose in the region of interest. The DTS calculated primary plus backscatter distribution is compared to that measured with GafChromic film and that calculated using EGSnrc Monte-Carlo software. Results: The PSF convolution method used in the DTS software was able to account for the spread of backscatter from the ROI region to the region under the attenuator. The skin dose distribution determined using DTS with the ROI attenuator was in good agreement with the distributions measured with Gafchromic film and determined by Monte Carlo simulation Conclusion: The PSF convolution technique provides an accurate alternative for entrance skin dose determination with non-uniform primary x-ray beams. Partial support from NIH Grant R01-EB002873 and Toshiba Medical Systems Corp.« less

SU-E-T-243: MonteCarlo Simulation Study of Polymer and Radiochromic Gel for Three-Dimensional Proton Dose Distribution

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

Park, M; Jung, H; Kim, G

2014-06-01

Purpose: To estimate the three dimensional dose distributions in a polymer gel and a radiochromic gel by comparing with the virtual water phantom exposed to proton beams by applying Monte Carlo simulation. Methods: The polymer gel dosimeter is the compositeness material of gelatin, methacrylic acid, hydroquinone, tetrakis, and distilled water. The radiochromic gel is PRESAGE product. The densities of polymer and radiochromic gel were 1.040 and 1.0005 g/cm3, respectively. The shape of water phantom was a hexahedron with the size of 13 × 13 × 15 cm3. The proton beam energies of 72 and 116 MeV were used in themore » simulation. Proton beam was directed to the top of the phantom with Z-axis and the shape of beam was quadrangle with 10 × 10 cm2 dimension. The Percent depth dose and the dose distribution were evaluated for estimating the dose distribution of proton particle in two gel dosimeters, and compared with the virtual water phantom. Results: The Bragg-peak for proton particles in two gel dosimeters was similar to the virtual water phantom. Bragg-peak regions of polymer gel, radiochromic gel, and virtual water phantom were represented in the identical region (4.3 cm) for 72 MeV proton beam. For 116 MeV proton beam, the Bragg-peak regions of polymer gel, radiochromic gel, and virtual water phantom were represented in 9.9, 9.9 and 9.7 cm, respectively. The dose distribution of proton particles in polymer gel, radiochromic gel, and virtual water phantom was approximately identical in the case of 72 and 116 MeV energies. The errors for the simulation were under 10%. Conclusion: This work indicates the evaluation of three dimensional dose distributions by exposing proton particles to polymer and radiochromic gel dosimeter by comparing with the water phantom. The polymer gel and the radiochromic gel dosimeter show similar dose distributions for the proton beams.« less

Reconstructing the deposition environment and long-term fate of Chernobyl 137Cs at the floodplain scale through mobile gamma spectrometry.

PubMed

Varley, Adam; Tyler, Andrew; Bondar, Yuri; Hosseini, Ali; Zabrotski, Viachaslau; Dowdall, Mark

2018-09-01

Cs-137 is considered to be the most significant anthropogenic contributor to human dose and presents a particularly difficult remediation challenge after a dispersal following nuclear incident. The Chernobyl Nuclear Power Plant meltdown in April 1986 represents the largest nuclear accident in history and released over 80 PBq of 137 Cs into the environment. As a result, much of the land in close proximity to Chernobyl, which includes the Polessie State Radioecology Reserve in Belarus, remains highly contaminated with 137 Cs to such an extent they remain uninhabitable. Whilst there is a broad scale understanding of the depositional patterns within and beyond the exclusion zone, detailed mapping of the distribution is often limited. New developments in mobile gamma spectrometry provide the opportunity to map the fallout of 137 Cs and begin to reconstruct the depositional environment and the long-term behaviour of 137 Cs in the environment. Here, full gamma spectrum analysis using algorithms based on the peak-valley ratio derived from Monte Carlo simulations are used to estimate the total 137 Cs deposition and its depth distribution in the soil. The results revealed a pattern of 137 Cs distribution consistent with the deposition occurring at a time of flooding, which is validated by review of satellite imagery acquired at similar times of the year. The results were also consistent with systematic burial of the fallout 137 Cs by annual flooding events. These results were validated by sediment cores collected along a transect across the flood plain. The true merit of the approach was confirmed by exposing new insights into the spatial distribution and long term fate of 137 Cs across the floodplain. Such systematic patterns of behaviour are likely to be fundamental to the understanding of the radioecological behaviour of 137 Cs whilst also providing a tracer for quantifying the ecological controls on sediment movement and deposition at a landscape scale. Copyright © 2018 Elsevier Ltd. All rights reserved.

Reformulation of a clinical-dose system for carbon-ion radiotherapy treatment planning at the National Institute of Radiological Sciences, Japan

NASA Astrophysics Data System (ADS)

Inaniwa, Taku; Kanematsu, Nobuyuki; Matsufuji, Naruhiro; Kanai, Tatsuaki; Shirai, Toshiyuki; Noda, Koji; Tsuji, Hiroshi; Kamada, Tadashi; Tsujii, Hirohiko

2015-04-01

At the National Institute of Radiological Sciences (NIRS), more than 8,000 patients have been treated for various tumors with carbon-ion (C-ion) radiotherapy in the past 20 years based on a radiobiologically defined clinical-dose system. Through clinical experience, including extensive dose escalation studies, optimum dose-fractionation protocols have been established for respective tumors, which may be considered as the standards in C-ion radiotherapy. Although the therapeutic appropriateness of the clinical-dose system has been widely demonstrated by clinical results, the system incorporates several oversimplifications such as dose-independent relative biological effectiveness (RBE), empirical nuclear fragmentation model, and use of dose-averaged linear energy transfer to represent the spectrum of particles. We took the opportunity to update the clinical-dose system at the time we started clinical treatment with pencil beam scanning, a new beam delivery method, in 2011. The requirements for the updated system were to correct the oversimplifications made in the original system, while harmonizing with the original system to maintain the established dose-fractionation protocols. In the updated system, the radiation quality of the therapeutic C-ion beam was derived with Monte Carlo simulations, and its biological effectiveness was predicted with a theoretical model. We selected the most used C-ion beam with αr = 0.764 Gy-1 and β = 0.0615 Gy-2 as reference radiation for RBE. The C-equivalent biological dose distribution is designed to allow the prescribed survival of tumor cells of the human salivary gland (HSG) in entire spread-out Bragg peak (SOBP) region, with consideration to the dose dependence of the RBE. This C-equivalent biological dose distribution is scaled to a clinical dose distribution to harmonize with our clinical experiences with C-ion radiotherapy. Treatment plans were made with the original and the updated clinical-dose systems, and both physical and clinical dose distributions were compared with regard to the prescribed dose level, beam energy, and SOBP width. Both systems provided uniform clinical dose distributions within the targets consistent with the prescriptions. The mean physical doses delivered to targets by the updated system agreed with the doses by the original system within ±1.5% for all tested conditions. The updated system reflects the physical and biological characteristics of the therapeutic C-ion beam more accurately than the original system, while at the same time allowing the continued use of the dose-fractionation protocols established with the original system at NIRS.

Transient enhancement of pericardium, peritoneum, soft tissues and perhaps lymphatics after large doses of contrast administration: an overlooked phenomenon?

PubMed

Behr, Gerald G; Berdon, Walter E; Griscom, N Thorne

2012-06-01

An infant with complex cyanotic congenital heart disease was recently encountered whose radiographs seemed to show enhancement of pericardium, peritoneal mesothelium and body wall fascial planes without enhancement of the liver or spleen after very large doses of intravenous contrast. Although patterns of postcontrast enhancement have been described previously, this pattern seems to be unique. We report the unusual postcontrast opacification pattern and speculate about its underlying mechanism.

Chronic effects of environmentally-relevant concentrations of lead in Pelophylax nigromaculata tadpoles: Threshold dose and adverse effects.

PubMed

Huang, Min-Yi; Duan, Ren-Yan; Ji, Xiang

2014-06-01

Lead (Pb) is a common heavy metal in the natural environment, but its concentration has been increasing alongside widespread industrial and agricultural development in China. The dark-spotted frog Pelophylax (formerly Rana) nigromaculata (Anura: Ranidae) is distributed across East Asia and inhabits anthropogenic habitats such as farmland. Here, P. nigromaculata tadpoles (Gosner stage 19-46) were exposed to Pb at different concentrations (0, 40, 80, 160, 320, 640 and 1280µg/L) and Pb-induced survival, metamorphosis time, development, malformations, mobility and gonad structure were monitored. The results showed that above the threshold concentration of Pb, adverse effects were obvious. As the concentration of Pb increased, the adverse effects on different traits followed different patterns: the effects on hindlimb length, survival rate, metamorphosis rate, total malformation rate, swimming speed and jumping speed largely exhibited a linear pattern; the effects on snout-vent length, body mass and forelimb length largely exhibited a bimodal pattern. Sex ratio and gonadal histology were not affected by Pb, suggesting that Pb is not strongly estrogenic in P. nigromaculata. Copyright © 2014 Elsevier Inc. All rights reserved.

SU-F-I-34: How Does Longitudinal Dose Profile Change with Tube Current Distribution in CT?

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

Li, X; Yang, K; Liu, B

Purpose: To investigate how longitudinal dose profile D{sub L}(z) in 30 cm-diameter water cylinder change with tube current (mA) distribution and scan length. Methods: A constant and four variable mA distributions from two previous papers [Dixon et al., Med. Phys. 40, 111920 (14pp.) (2013); Zhang et al., Med. Phys. 41, 091911 (9pp.) (2014)] were adopted in three scan lengths of 10, 28.6, and 50 cm, and all mA distributions had the same average mA over scan ranges. Using the symmetry based dose calculation algorithms and the previously published CT dose equilibration data [Li et al., Med. Phys. 40, 031903 (10pp.)more » (2013); 41, 111910 (5pp.) (2014)], the authors calculated DL(z) on the phantom central and peripheral axes. Kolmogorov-Smirnov (K-S) test was used to compare the lineshapes of two arbitrary distributions. Results: In constant mA scans, D{sub L}(z) was “bell-shaped”. In variable mA scans, D{sub L}(z) approximately followed the mA lineshape, and the K-S distance generally changed with mA distribution. The distance decreased with scan length, and was larger on the central axis than on the peripheral axis. However, the opposite trends were found in the K-S distance between the D{sub L}(z) distributions of constant and variable mA distributions. Conclusion: Radiation dose from TCM scan is best evaluated using the specific tube current distribution. A constant mA based evaluation may lead to inconsistent longitudinal dose profile with that of TCM scan. Their difference in lineshape is larger on the phantom peripheral axis than on the central axis and increases with scan length. This work confirms that radiation dose in CT depends on not only local mA but also the overall mA distribution and scan length. On the other hand, the concept of regional tube current may be useful when scan length is large, tube current peaks near scan range edge, or the target site is superficial.« less

Pharmacokinetics, metabolism and urinary detection time of flunixin after intravenous administration in camels.

PubMed

Wasfi, I A; Boni, N S; Abdel Hadi, A; Elghazali, M; Zorob, O; Alkatheeri, N A; Barezaiq, I M

1998-06-01

The pharmacokinetics of flunixin were determined after an intravenous dose of 1.1 mg/kg body weight in six camels and 2.2 mg/kg body weight in four camels. The data obtained (mean +/- SEM) for the low and high dose, respectively, were as follows: The elimination half-lives (t1/2 beta) were 3.76 +/- 0.24 and 4.08 +/- 0.49 h, the steady state volumes of distribution (Vdss) were 320.61 +/- 38.53 and 348.84 +/- 35.36 mL/kg body weight, total body clearances (ClT) were 88.96 +/- 6.63 and 84.86 +/- 4.95 mL/h/kg body weight and renal clearances (Clr) were 0.52 +/- 0.09 and 0.62 +/- 0.18 mL/h/kg body weight. A hydroxylated metabolite of flunixin was identified by gas chromatography/mass spectrometry (GC/MS) under electron and chemical ionization and its major fragmentation pattern was verified by tandem mass spectrometry (GC/MS/MS) using neutral loss, daughter and parent scan modes. The detection times for flunixin and its hydroxylated metabolite in urine after an intravenous (i.v.) dose of 2.2 mg/kg body weight were 96 and 48 h, respectively.

Evolutionary dynamics of incubation periods

PubMed Central

Ottino-Loffler, Bertrand; Scott, Jacob G

2017-01-01

The incubation period for typhoid, polio, measles, leukemia and many other diseases follows a right-skewed, approximately lognormal distribution. Although this pattern was discovered more than sixty years ago, it remains an open question to explain its ubiquity. Here, we propose an explanation based on evolutionary dynamics on graphs. For simple models of a mutant or pathogen invading a network-structured population of healthy cells, we show that skewed distributions of incubation periods emerge for a wide range of assumptions about invader fitness, competition dynamics, and network structure. The skewness stems from stochastic mechanisms associated with two classic problems in probability theory: the coupon collector and the random walk. Unlike previous explanations that rely crucially on heterogeneity, our results hold even for homogeneous populations. Thus, we predict that two equally healthy individuals subjected to equal doses of equally pathogenic agents may, by chance alone, show remarkably different time courses of disease. PMID:29266000

Evolutionary dynamics of incubation periods.

PubMed

Ottino-Loffler, Bertrand; Scott, Jacob G; Strogatz, Steven H

2017-12-21

The incubation period for typhoid, polio, measles, leukemia and many other diseases follows a right-skewed, approximately lognormal distribution. Although this pattern was discovered more than sixty years ago, it remains an open question to explain its ubiquity. Here, we propose an explanation based on evolutionary dynamics on graphs. For simple models of a mutant or pathogen invading a network-structured population of healthy cells, we show that skewed distributions of incubation periods emerge for a wide range of assumptions about invader fitness, competition dynamics, and network structure. The skewness stems from stochastic mechanisms associated with two classic problems in probability theory: the coupon collector and the random walk. Unlike previous explanations that rely crucially on heterogeneity, our results hold even for homogeneous populations. Thus, we predict that two equally healthy individuals subjected to equal doses of equally pathogenic agents may, by chance alone, show remarkably different time courses of disease.

Frequency and distribution of incidental findings deemed appropriate for S modifier designation on low-dose CT in a lung cancer screening program.

PubMed

Reiter, Michael J; Nemesure, Allison; Madu, Ezemonye; Reagan, Lisa; Plank, April

2018-06-01

To describe the frequency, distribution and reporting patterns of incidental findings receiving the Lung-RADS S modifier on low-dose chest computed tomography (CT) among lung cancer screening participants. This retrospective investigation included 581 individuals who received baseline low-dose chest CT for lung cancer screening between October 2013 and June 2017 at a single center. Incidental findings resulting in assignment of Lung-RADS S modifier were recorded as were incidental abnormalities detailed within the body of the radiology report only. A subset of 60 randomly selected CTs was reviewed by a second (blinded) radiologist to evaluate inter-rater variability of Lung-RADS reporting. A total of 261 (45%) participants received the Lung-RADS S modifier on baseline CT with 369 incidental findings indicated as potentially clinically significant. Coronary artery calcification was most commonly reported, accounting for 182 of the 369 (49%) findings. An additional 141 incidentalomas of the same types as these 369 findings were described in reports but were not labelled with the S modifier. Therefore, as high as 69% (402 of 581) of participants could have received the S modifier if reporting was uniform. Inter-radiologist concordance of S modifier reporting in a subset of 60 participants was poor (42% agreement, kappa = 0.2). Incidental findings are commonly identified on chest CT for lung cancer screening, yet reporting of the S modifier within Lung-RADS is inconsistent. Specific guidelines are necessary to better define potentially clinically significant abnormalities and to improve reporting uniformity. Copyright © 2018 Elsevier B.V. All rights reserved.

Evaluation of the Percutaneous Absorption of Ketamine HCl, Gabapentin, Clonidine HCl, and Baclofen, in Compounded Transdermal Pain Formulations, Using the Franz Finite Dose Model.

PubMed

Bassani, August S; Banov, Daniel

2016-02-01

This study evaluates the ability of four commonly used analgesics (ketamine HCl, gabapentin, clonidine HCl, and baclofen), when incorporated into two transdermal compounding bases, Lipoderm and Lipoderm ActiveMax, to penetrate human cadaver trunk skin in vitro, using the Franz finite dose model. In vitro experimental study. Methods. Ketamine HCl 5% w/w, gabapentin 10% w/w, clonidine HCl 0.2% w/w, and baclofen 2% w/w were compounded into two transdermal bases, Lipoderm and Lipoderm ActiveMax. Each compounded drug formulation was tested on skin from three different donors and three replicate skin sections per donor. The Franz finite dose model was used in this study to evaluate the percutaneous absorption and distribution of drugs within each formulation. Rapid penetration to peak flux was detected for gabapentin and baclofen at approximately 1 hour after application. Clonidine HCl also had a rapid penetration to peak flux occurring approximately 1 hour after application and had a secondary peak at approximately 40 hours. Ketamine HCl exhibited higher overall absorption rates than the other drugs, and peaked at 6–10 hours. Similar patterns of drug distribution within the skin were also observed using both transdermal bases. This study suggests that the combination of these 4 analgesic drugs can be successfully delivered transdermally, using either Lipoderm or Lipoderm ActiveMax. Compounded transdermal drug preparations may then provide physicians with an alternative to traditional oral pain management regimens that can be personalized to the specific patient with the potential for enhanced pain control.

Assessment of dosimetric impact of system specific geometric distortion in an MRI only based radiotherapy workflow for prostate

NASA Astrophysics Data System (ADS)

Gustafsson, C.; Nordström, F.; Persson, E.; Brynolfsson, J.; Olsson, L. E.

2017-04-01

Dosimetric errors in a magnetic resonance imaging (MRI) only radiotherapy workflow may be caused by system specific geometric distortion from MRI. The aim of this study was to evaluate the impact on planned dose distribution and delineated structures for prostate patients, originating from this distortion. A method was developed, in which computer tomography (CT) images were distorted using the MRI distortion field. The displacement map for an optimized MRI treatment planning sequence was measured using a dedicated phantom in a 3 T MRI system. To simulate the distortion aspects of a synthetic CT (electron density derived from MR images), the displacement map was applied to CT images, referred to as distorted CT images. A volumetric modulated arc prostate treatment plan was applied to the original CT and the distorted CT, creating a reference and a distorted CT dose distribution. By applying the inverse of the displacement map to the distorted CT dose distribution, a dose distribution in the same geometry as the original CT images was created. For 10 prostate cancer patients, the dose difference between the reference dose distribution and inverse distorted CT dose distribution was analyzed in isodose level bins. The mean magnitude of the geometric distortion was 1.97 mm for the radial distance of 200-250 mm from isocenter. The mean percentage dose differences for all isodose level bins, were  ⩽0.02% and the radiotherapy structure mean volume deviations were  <0.2%. The method developed can quantify the dosimetric effects of MRI system specific distortion in a prostate MRI only radiotherapy workflow, separated from dosimetric effects originating from synthetic CT generation. No clinically relevant dose difference or structure deformation was found when 3D distortion correction and high acquisition bandwidth was used. The method could be used for any MRI sequence together with any anatomy of interest.

Assessment of dosimetric impact of system specific geometric distortion in an MRI only based radiotherapy workflow for prostate.

PubMed

Gustafsson, C; Nordström, F; Persson, E; Brynolfsson, J; Olsson, L E

2017-04-21

Dosimetric errors in a magnetic resonance imaging (MRI) only radiotherapy workflow may be caused by system specific geometric distortion from MRI. The aim of this study was to evaluate the impact on planned dose distribution and delineated structures for prostate patients, originating from this distortion. A method was developed, in which computer tomography (CT) images were distorted using the MRI distortion field. The displacement map for an optimized MRI treatment planning sequence was measured using a dedicated phantom in a 3 T MRI system. To simulate the distortion aspects of a synthetic CT (electron density derived from MR images), the displacement map was applied to CT images, referred to as distorted CT images. A volumetric modulated arc prostate treatment plan was applied to the original CT and the distorted CT, creating a reference and a distorted CT dose distribution. By applying the inverse of the displacement map to the distorted CT dose distribution, a dose distribution in the same geometry as the original CT images was created. For 10 prostate cancer patients, the dose difference between the reference dose distribution and inverse distorted CT dose distribution was analyzed in isodose level bins. The mean magnitude of the geometric distortion was 1.97 mm for the radial distance of 200-250 mm from isocenter. The mean percentage dose differences for all isodose level bins, were  ⩽0.02% and the radiotherapy structure mean volume deviations were  <0.2%. The method developed can quantify the dosimetric effects of MRI system specific distortion in a prostate MRI only radiotherapy workflow, separated from dosimetric effects originating from synthetic CT generation. No clinically relevant dose difference or structure deformation was found when 3D distortion correction and high acquisition bandwidth was used. The method could be used for any MRI sequence together with any anatomy of interest.

SU-E-T-609: Perturbation Effects of Pedicle Screws On Radiotherapy Dose Distributions

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

Bar-Deroma, R; Borzov, E; Nevelsky, A

2015-06-15

Purpose: Radiation therapy in conjunction with surgical implant fixation is a common combined treatment in case of bone metastases. However, metal implants generally used in orthopedic implants perturb radiation dose distributions. Carbon-Fiber Reinforced (CFR) PEEK material has been recently introduced for production of intramedullary screws and plates. Gold powder can be added to the CFR-PEEK material in order to enhance visibility of the screws during intraoperative imaging procedures. In this work, we investigated the perturbation effects of the pedicle screws made of CFR-PEEK, CFR-PEEK with added gold powder (CFR-PEEK-AU) and Titanium (Ti) on radiotherapy dose distributions. Methods: Monte Carlo (MC)more » simulations were performed using the EGSnrc code package for 6MV beams with 10×10 fields at SSD=100cm. By means of MC simulations, dose distributions around titanium, CFR- PEEK and CFR-PEEK-AU screws (manufactured by Carbo-Fix Orthopedics LTD, Israel) placed in a water phantom were calculated. The screw axis was either parallel or perpendicular to the beam axis. Dose perturbation (relative to dose in homogeneous water phantom) was assessed. Results: Maximum overdose due to backscatter was 10% for the Ti screws, 5% for the CFR-PEEK-AU screws and effectively zero for the CFR-PEEK screws. Maximum underdose due to attenuation was 25% for the Ti screws, 15% for the CFR-PEEK-AU screws and 5% for the CFR-PEEK screws. Conclusion: Titanium screws introduce the largest distortion on the radiation dose distribution. The gold powder added to the CFR-PEEK material improves visibility at the cost of increased dose perturbation. CFR-PEEK screws caused minimal alteration on the dose distribution. This can decrease possible over and underdose of adjacent tissue and thus favorably influence treatment efficiency. The use of such implants has potential clinical advantage in the treatment of neoplastic bone disease.« less

Helical Tomotherapy for Whole-Brain Irradiation With Integrated Boost to Multiple Brain Metastases: Evaluation of Dose Distribution Characteristics and Comparison With Alternative Techniques

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

Levegrün, Sabine, E-mail: sabine.levegruen@uni-due.de; Pöttgen, Christoph; Wittig, Andrea

2013-07-15

Purpose: To quantitatively evaluate dose distribution characteristics achieved with helical tomotherapy (HT) for whole-brain irradiation (WBRT) with integrated boost (IB) to multiple brain metastases in comparison with alternative techniques. Methods and Materials: Dose distributions for 23 patients with 81 metastases treated with WBRT (30 Gy/10 fractions) and IB (50 Gy) were analyzed. The median number of metastases per patient (N{sub mets}) was 3 (range, 2-8). Mean values of the composite planning target volume of all metastases per patient (PTV{sub mets}) and of the individual metastasis planning target volume (PTV{sub ind} {sub met}) were 8.7 ± 8.9 cm{sup 3} (range, 1.3-35.5more » cm{sup 3}) and 2.5 ± 4.5 cm{sup 3} (range, 0.19-24.7 cm{sup 3}), respectively. Dose distributions in PTV{sub mets} and PTV{sub ind} {sub met} were evaluated with respect to dose conformity (conformation number [CN], RTOG conformity index [PITV]), target coverage (TC), and homogeneity (homogeneity index [HI], ratio of maximum dose to prescription dose [MDPD]). The dependence of dose conformity on target size and N{sub mets} was investigated. The dose distribution characteristics were benchmarked against alternative irradiation techniques identified in a systematic literature review. Results: Mean ± standard deviation of dose distribution characteristics derived for PTV{sub mets} amounted to CN = 0.790 ± 0.101, PITV = 1.161 ± 0.154, TC = 0.95 ± 0.01, HI = 0.142 ± 0.022, and MDPD = 1.147 ± 0.029, respectively, demonstrating high dose conformity with acceptable homogeneity. Corresponding numbers for PTV{sub ind} {sub met} were CN = 0.708 ± 0.128, PITV = 1.174 ± 0.237, TC = 0.90 ± 0.10, HI = 0.140 ± 0.027, and MDPD = 1.129 ± 0.030, respectively. The target size had a statistically significant influence on dose conformity to PTV{sub mets} (CN = 0.737 for PTV{sub mets} ≤4.32 cm{sup 3} vs CN = 0.848 for PTV{sub mets} >4.32 cm{sup 3}, P=.006), in contrast to N{sub mets}. The achieved dose conformity to PTV{sub mets}, assessed by both CN and PITV, was in all investigated volume strata well within the best quartile of the values reported for alternative irradiation techniques. Conclusions: HT is a well-suited technique to deliver WBRT with IB to multiple brain metastases, yielding high-quality dose distributions. A multi-institutional prospective randomized phase 2 clinical trial to exploit efficacy and safety of the treatment concept is currently under way.« less

Adipose tissue content and distribution in children and adolescents with bronchial asthma.

PubMed

Umławska, Wioleta

2015-02-01

The excess of adipose tissue and the pattern of adipose tissue distribution in the body seem to play an important role in the complicated dependencies between obesity and risk of developing asthma. The aim of the present study was to determine nutritional status in children and adolescents with bronchial asthma with special emphasis on adipose tissue distribution evaluated on the basis of skin-fold thicknesses, and to determine the relationships between patterns of adipose tissue distribution and the course of the disease. Anthropometric data on height, weight, circumferences and skin-fold thicknesses were extracted from the medical histories of 261 children diagnosed with asthma bronchitis. Values for children with asthma were compared to Polish national growth reference charts. Distribution of subcutaneous adipose tissue was evaluated using principal components analysis (PCA). Multivariate linear regression analyses tested the effect of three factors on subcutaneous adipose tissue distribution: type of asthma, the severity of the disease and the duration of the disease. Mean body height in the children examined in this study was lower than in their healthy peers. Mean BMI and skin-fold thicknesses were significantly higher and lean body mass was lower in the study group. Excess body fat was noted, especially in girls. Adipose tissue was preferentially deposited in the trunk in girls with severe asthma, as well as in those who had been suffering from asthma for a longer time. The type of asthma, atopic or non-atopic, had no observable effect on subcutaneous adipose tissue distribution in children examined. The data suggest that long-treated subjects and those with severe bronchial asthma accumulate more adipose tissue on the trunk. It is important to regularly monitor nutritional status in children with asthma, especially in those receiving high doses of systemic or inhaled glucocorticosteroids, and long-term treatment as well. Copyright © 2014 Elsevier Ltd. All rights reserved.

SU-F-T-178: Optimized Design of a Diamond Detector Specifically Dedicated to the Dose Distribution Measurements in Clinical Proton Pencil Beams

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

Moignier, C; Pomorski, M; Agelou, M

2016-06-15

Purpose: In proton-therapy, pencil beam scanning (PBS) dosimetry presents a real challenge due to the small size of the beam (about 3 to 8 mm in FWHM), the pulsed high dose rate (up to 100 Gy/s) and the proton energy variation (about 30 MeV to 250 MeV). In the framework of French INSERM DEDIPRO project, a specifically dedicated single crystal diamond dosimeter (SCDDo) was developed with the objective of obtaining accurate measurements of the dose distribution in PBS modality. Methods: Monte Carlo simulations with MCNPX were performed. A small proton beam of 5 mm in FWHM was simulated as wellmore » as diamond devices with various size, thickness and holder composition. The calculated doses-to-diamond were compared with the doses-to-water in order to reduce the perturbation effects. Monte-Carlo simulations lead to an optimized SCDDo design for small proton beams dosimetry. Following the optimized design, SCDDos were mounted in water-equivalent holders with electrical connection adapted to standard electrometer. First, SCDDos performances (stability, repeatability, signal-to-background ratio…) were evaluated with conventional photon beams. Then, characterizations (dose linearity, dose rate dependence…) with wide proton beams were performed at proton-therapy center (IC-CPO) from Curie Institute (France) with the passive proton delivery technique, in order to confirm dosimetric requirements. Finally, depth-dose distributions were measured in a water tank, for native and modulated Bragg Peaks with the collimator of 12 cm, and compared to a commercial PPC05 parallel-plate ionization chamber reference detector. Lateral-dose profiles were also measured with the collimator of 5 mm, and compared to a commercial SFD diode. Results: The results show that SCDDo design does not disturb the dose distributions. Conclusion: The experimental dose distributions with the SCDDo are in good agreement with the commercial detectors and no energy dependence was observed with this device configuration.« less

Measurement of dose distribution in the spherical phantom onboard the ISS-KIBO module -MATROSHKA-R in KIBO-

NASA Astrophysics Data System (ADS)

Kodaira, Satoshi; Kawashima, Hajime; Kurano, Mieko; Uchihori, Yukio; Nikolaev, Igor; Ambrozova, Iva; Kitamura, Hisashi; Kartsev, Ivan; Tolochek, Raisa; Shurshakov, Vyacheslav

The measurement of dose equivalent and effective dose during manned space missions on the International Space Station (ISS) is important for evaluating the risk to astronaut health and safety when exposed to space radiation. The dosimetric quantities are constantly changing and strongly depend on the level of solar activity and the various spacecraft- and orbit-dependent parameters such as the shielding distribution in the ISS module, location of the spacecraft within its orbit relative to the Earth, the attitude (orientation) and altitude. Consequently, the continuous monitoring of dosimetric quantities is required to record and evaluate the personal radiation dose for crew members during spaceflight. The dose distributions in the phantom body and on its surface give crucial information to estimate the dose equivalent in the human body and effective dose in manned space mission. We have measured the absorbed dose and dose equivalent rates using passive dosimeters installed in the spherical phantom in Japanese Experiment Module (“KIBO”) of the ISS in the framework of Matroshka-R space experiment. The exposure duration was 114 days from May 21 to September 12, 2012. The phantom consists of tissue-equivalent material covered with a poncho jacket with 32 pockets on its surface and 20 container rods inside of the phantom. The phantom diameter is 35 cm and the mass is 32 kg. The passive dosimeters consisted of a combination of luminescent detectors of Al _{2}O _{3};C OSL and CaSO _{4}:Dy TLD and CR-39 plastic nuclear track detectors. As one of preliminary results, the dose distribution on the phantom surface measured with OSL detectors installed in the jacket pockets is found to be ranging from 340 muGy/day to 260 muGy/day. In this talk, we will present the detail dose distributions, and variations of LET spectra and quality factor obtained outside and inside of the spherical phantom installed in the ISS-KIBO.

High brachytherapy doses can counteract hypoxia in cervical cancer—a modelling study

NASA Astrophysics Data System (ADS)

Lindblom, Emely; Dasu, Alexandru; Beskow, Catharina; Toma-Dasu, Iuliana

2017-01-01

Tumour hypoxia is a well-known adverse factor for the outcome of radiotherapy. For cervical tumours in particular, several studies indicate large variability in tumour oxygenation. However, clinical evidence shows that the management of cervical cancer including brachytherapy leads to high rate of success. It was the purpose of this study to investigate whether the success of brachytherapy for cervical cancer, seemingly regardless of oxygenation status, could be explained by the characteristics of the brachytherapy dose distributions. To this end, a previously used in silico model of tumour oxygenation and radiation response was further developed to simulate the treatment of cervical cancer employing a combination of external beam radiotherapy and intracavitary brachytherapy. Using a clinically-derived brachytherapy dose distribution and assuming a homogeneous dose delivered by external radiotherapy, cell survival was assessed on voxel level by taking into account the variation of sensitivity with oxygenation as well as the effects of repair, repopulation and reoxygenation during treatment. Various scenarios were considered for the conformity of the brachytherapy dose distribution to the hypoxic region in the target. By using the clinically-prescribed brachytherapy dose distribution and varying the total dose delivered with external beam radiotherapy in 25 fractions, the resulting values of the dose for 50% tumour control, D 50, were in agreement with clinically-observed values for high cure rates if fast reoxygenation was assumed. The D 50 was furthermore similar for the different degrees of conformity of the brachytherapy dose distribution to the tumour, regardless of whether the hypoxic fraction was 10%, 25%, or 40%. To achieve 50% control with external RT only, a total dose of more than 70 Gy in 25 fractions would be required for all cases considered. It can thus be concluded that the high doses delivered in brachytherapy can counteract the increased radioresistance caused by hypoxia if fast reoxygenation is assumed.

SU-E-T-02: 90Y Microspheres Dosimetry Calculation with Voxel-S-Value Method: A Simple Use in the Clinic

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

Maneru, F; Gracia, M; Gallardo, N

2015-06-15

Purpose: To present a simple and feasible method of voxel-S-value (VSV) dosimetry calculation for daily clinical use in radioembolization (RE) with {sup 90}Y microspheres. Dose distributions are obtained and visualized over CT images. Methods: Spatial dose distributions and dose in liver and tumor are calculated for RE patients treated with Sirtex Medical miscrospheres at our center. Data obtained from the previous simulation of treatment were the basis for calculations: Tc-99m maggregated albumin SPECT-CT study in a gammacamera (Infinia, General Electric Healthcare.). Attenuation correction and ordered-subsets expectation maximization (OSEM) algorithm were applied.For VSV calculations, both SPECT and CT were exported frommore » the gammacamera workstation and registered with the radiotherapy treatment planning system (Eclipse, Varian Medical systems). Convolution of activity matrix and local dose deposition kernel (S values) was implemented with an in-house developed software based on Python code. The kernel was downloaded from www.medphys.it. Final dose distribution was evaluated with the free software Dicompyler. Results: Liver mean dose is consistent with Partition method calculations (accepted as a good standard). Tumor dose has not been evaluated due to the high dependence on its contouring. Small lesion size, hot spots in health tissue and blurred limits can affect a lot the dose distribution in tumors. Extra work includes: export and import of images and other dicom files, create and calculate a dummy plan of external radiotherapy, convolution calculation and evaluation of the dose distribution with dicompyler. Total time spent is less than 2 hours. Conclusion: VSV calculations do not require any extra appointment or any uncomfortable process for patient. The total process is short enough to carry it out the same day of simulation and to contribute to prescription decisions prior to treatment. Three-dimensional dose knowledge provides much more information than other methods of dose calculation usually applied in the clinic.« less

The estimation of absorbed dose rates for non-human biota : an extended inter-comparison.

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

Batlle, J. V. I.; Beaugelin-Seiller, K.; Beresford, N. A.

An exercise to compare 10 approaches for the calculation of unweighted whole-body absorbed dose rates was conducted for 74 radionuclides and five of the ICRP's Reference Animals and Plants, or RAPs (duck, frog, flatfish egg, rat and elongated earthworm), selected for this exercise to cover a range of body sizes, dimensions and exposure scenarios. Results were analysed using a non-parametric method requiring no specific hypotheses about the statistical distribution of data. The obtained unweighted absorbed dose rates for internal exposure compare well between the different approaches, with 70% of the results falling within a range of variation of {+-}20%. Themore » variation is greater for external exposure, although 90% of the estimates are within an order of magnitude of one another. There are some discernible patterns where specific models over- or under-predicted. These are explained based on the methodological differences including number of daughter products included in the calculation of dose rate for a parent nuclide; source-target geometry; databases for discrete energy and yield of radionuclides; rounding errors in integration algorithms; and intrinsic differences in calculation methods. For certain radionuclides, these factors combine to generate systematic variations between approaches. Overall, the technique chosen to interpret the data enabled methodological differences in dosimetry calculations to be quantified and compared, allowing the identification of common issues between different approaches and providing greater assurance on the fundamental dose conversion coefficient approaches used in available models for assessing radiological effects to biota.« less

Systematic evaluation of four-dimensional hybrid depth scanning for carbon-ion lung therapy.

PubMed

Mori, Shinichiro; Furukawa, Takuji; Inaniwa, Taku; Zenklusen, Silvan; Nakao, Minoru; Shirai, Toshiyuki; Noda, Koji

2013-03-01

Irradiation of a moving target with a scanning beam requires a comprehensive understanding of organ motion as well as a robust dose error mitigation technique. The authors studied the effects of intrafractional respiratory motion for carbon-ion pencil beam scanning with phase-controlled rescanning on dose distributions for lung tumors. To address density variations, they used 4DCT data. Dose distributions for various rescanning methods, such as simple layer rescanning (LR), volumetric rescanning, and phase-controlled rescanning (PCR), were calculated for a lung phantom and a lung patient studies. To ensure realism, they set the scanning parameters such as scanning velocity and energy variation time to be similar to those used at our institution. Evaluation metrics were determined with regard to clinical relevance, and consisted of (i) phase-controlled rescanning, (ii) sweep direction, (iii) target motion (direction and amplitude), (iv) respiratory cycle, and (v) prescribed dose. Spot weight maps were calculated by using a beam field-specific target volume, which takes account of range variations for respective respiratory phases. To emphasize the impact of intrafractional motion on the dose distribution, respiratory gating was not used. The accumulated dose was calculated by applying a B-spline-based deformable image registration, and the results for phase-controlled layered rescanning (PCRL) and phase-controlled volumetric rescanning (PCRV) were compared. For the phantom study, simple LR was unable to improve the dose distributions for an increased number of rescannings. The phase-controlled technique without rescanning (1×PCRL and 1×PCRV) degraded dose conformity significantly due to a reduced scan velocity. In contrast, 4×PCRL or more significantly and consistently improved dose distribution. PCRV showed interference effects, but in general also improved dose homogeneity with higher numbers of rescannings. Dose distributions with single PCRL∕PCRV with a sweep direction perpendicular to motion direction showed large hot∕cold spots; however, this effect vanished with higher numbers of rescannings for both methods. Similar observations were obtained for the other dose metrics, such as target motion (SI∕AP), amplitude (6-22 mm peak-to-peak) and respiratory period (3.0-5.0 s). For four or more rescannings, both methods showed significantly better results, albeit that volumetric PCR was more affected by interference effects, which lead to severe degradation of a few dose distributions. The clinical example showed the same tendencies as the phantom study. Dose assessment metrics (D95, Dmax∕Dmin, homogeneity index) were improved with an increasing number of PCRL∕PCRV, but with PCRL being more robust. PCRL requires a longer treatment time than PCRV for high numbers of rescannings in the NIRS scanning system but is more robust. Although four or more rescans provided good dose homogeneity and conformity, the authors prefer to use more rescannings for clinical cases to further minimize dose degradation effects due to organ motion.

Validation of the physical and RBE-weighted dose estimator based on PHITS coupled with a microdosimetric kinetic model for proton therapy.

PubMed

Takada, Kenta; Sato, Tatsuhiko; Kumada, Hiroaki; Koketsu, Junichi; Takei, Hideyuki; Sakurai, Hideyuki; Sakae, Takeji

2018-01-01

The microdosimetric kinetic model (MKM) is widely used for estimating relative biological effectiveness (RBE)-weighted doses for various radiotherapies because it can determine the surviving fraction of irradiated cells based on only the lineal energy distribution, and it is independent of the radiation type and ion species. However, the applicability of the method to proton therapy has not yet been investigated thoroughly. In this study, we validated the RBE-weighted dose calculated by the MKM in tandem with the Monte Carlo code PHITS for proton therapy by considering the complete simulation geometry of the clinical proton beam line. The physical dose, lineal energy distribution, and RBE-weighted dose for a 155 MeV mono-energetic and spread-out Bragg peak (SOBP) beam of 60 mm width were evaluated. In estimating the physical dose, the calculated depth dose distribution by irradiating the mono-energetic beam using PHITS was consistent with the data measured by a diode detector. A maximum difference of 3.1% in the depth distribution was observed for the SOBP beam. In the RBE-weighted dose validation, the calculated lineal energy distributions generally agreed well with the published measurement data. The calculated and measured RBE-weighted doses were in excellent agreement, except at the Bragg peak region of the mono-energetic beam, where the calculation overestimated the measured data by ~15%. This research has provided a computational microdosimetric approach based on a combination of PHITS and MKM for typical clinical proton beams. The developed RBE-estimator function has potential application in the treatment planning system for various radiotherapies. © The Author 2017. Published by Oxford University Press on behalf of The Japan Radiation Research Society and Japanese Society for Radiation Oncology.

Validation of the physical and RBE-weighted dose estimator based on PHITS coupled with a microdosimetric kinetic model for proton therapy

PubMed Central

Sato, Tatsuhiko; Kumada, Hiroaki; Koketsu, Junichi; Takei, Hideyuki; Sakurai, Hideyuki; Sakae, Takeji

2018-01-01

Abstract The microdosimetric kinetic model (MKM) is widely used for estimating relative biological effectiveness (RBE)-weighted doses for various radiotherapies because it can determine the surviving fraction of irradiated cells based on only the lineal energy distribution, and it is independent of the radiation type and ion species. However, the applicability of the method to proton therapy has not yet been investigated thoroughly. In this study, we validated the RBE-weighted dose calculated by the MKM in tandem with the Monte Carlo code PHITS for proton therapy by considering the complete simulation geometry of the clinical proton beam line. The physical dose, lineal energy distribution, and RBE-weighted dose for a 155 MeV mono-energetic and spread-out Bragg peak (SOBP) beam of 60 mm width were evaluated. In estimating the physical dose, the calculated depth dose distribution by irradiating the mono-energetic beam using PHITS was consistent with the data measured by a diode detector. A maximum difference of 3.1% in the depth distribution was observed for the SOBP beam. In the RBE-weighted dose validation, the calculated lineal energy distributions generally agreed well with the published measurement data. The calculated and measured RBE-weighted doses were in excellent agreement, except at the Bragg peak region of the mono-energetic beam, where the calculation overestimated the measured data by ~15%. This research has provided a computational microdosimetric approach based on a combination of PHITS and MKM for typical clinical proton beams. The developed RBE-estimator function has potential application in the treatment planning system for various radiotherapies. PMID:29087492

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.

Seasonal influenza vaccine dose distribution in 195 countries (2004-2013): Little progress in estimated global vaccination coverage.

PubMed

Palache, Abraham; Oriol-Mathieu, Valerie; Fino, Mireli; Xydia-Charmanta, Margarita

2015-10-13

Seasonal influenza is an important disease which results in 250,000-500,000 annual deaths worldwide. Global targets for vaccination coverage rates (VCRs) in high-risk groups are at least 75% in adults ≥65 years and increased coverage in other risk groups. The International Federation of Pharmaceutical Manufacturers and Associations Influenza Vaccine Supply (IFPMA IVS) International Task Force developed a survey methodology in 2008, to assess the global distribution of influenza vaccine doses as a proxy for VCRs. This paper updates the previous survey results on absolute numbers of influenza vaccine doses distributed between 2004 and 2013 inclusive, and dose distribution rates per 1000 population, and provides a qualitative assessment of the principal enablers and barriers to seasonal influenza vaccination. The two main findings from the quantitative portion of the survey are the continued negative trend for dose distribution in the EURO region and the perpetuation of appreciable differences in scale of dose distribution between WHO regions, with no observed convergence in the rates of doses distributed per 1000 population over time. The main findings from the qualitative portion of the survey were that actively managing the vaccination program in real-time and ensuring political commitment to vaccination are important enablers of vaccination, whereas insufficient access to vaccination and lack of political commitment to seasonal influenza vaccination programs are likely contributing to vaccination target failures. In all regions of the world, seasonal influenza vaccination is underutilized as a public health tool. The survey provides evidence of lost opportunity to protect populations against potentially serious influenza-associated disease. We call on the national and international public health communities to re-evaluate their political commitment to the prevention of the annual influenza disease burden and to develop a systematic approach to improve vaccine distribution equitably. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

Dose-volume histogram prediction using density estimation.

PubMed

Skarpman Munter, Johanna; Sjölund, Jens

2015-09-07

Knowledge of what dose-volume histograms can be expected for a previously unseen patient could increase consistency and quality in radiotherapy treatment planning. We propose a machine learning method that uses previous treatment plans to predict such dose-volume histograms. The key to the approach is the framing of dose-volume histograms in a probabilistic setting.The training consists of estimating, from the patients in the training set, the joint probability distribution of some predictive features and the dose. The joint distribution immediately provides an estimate of the conditional probability of the dose given the values of the predictive features. The prediction consists of estimating, from the new patient, the distribution of the predictive features and marginalizing the conditional probability from the training over this. Integrating the resulting probability distribution for the dose yields an estimate of the dose-volume histogram.To illustrate how the proposed method relates to previously proposed methods, we use the signed distance to the target boundary as a single predictive feature. As a proof-of-concept, we predicted dose-volume histograms for the brainstems of 22 acoustic schwannoma patients treated with stereotactic radiosurgery, and for the lungs of 9 lung cancer patients treated with stereotactic body radiation therapy. Comparing with two previous attempts at dose-volume histogram prediction we find that, given the same input data, the predictions are similar.In summary, we propose a method for dose-volume histogram prediction that exploits the intrinsic probabilistic properties of dose-volume histograms. We argue that the proposed method makes up for some deficiencies in previously proposed methods, thereby potentially increasing ease of use, flexibility and ability to perform well with small amounts of training data.

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

Stelljes, T. S., E-mail: tenzin.s.stelljes@uni-oldenburg.de; Looe, H. K.; Chofor, N.

Purpose: The dosimetric properties of the OCTAVIUS Detector 1500 (OD1500) ionization chamber array (PTW-Freiburg, Freiburg, Germany) have been investigated. A comparative study was carried out with the OCTAVIUS Detector 729 and OCTAVIUS Detector 1000 SRS arrays. Methods: The OD1500 array is an air vented ionization chamber array with 1405 detectors in a 27 × 27 cm{sup 2} measurement area arranged in a checkerboard pattern with a chamber-to-chamber distance of 10 mm in each row. A sampling step width of 5 mm can be achieved by merging two measurements shifted by 5 mm, thus fulfilling the Nyquist theorem for intensity modulatedmore » dose distributions. The stability, linearity, and dose per pulse dependence were investigated using a Semiflex 31013 chamber (PTW-Freiburg, Freiburg, Germany) as a reference detector. The effective depth of measurement was determined by measuring TPR curves with the array and a Roos chamber type 31004 (PTW-Freiburg, Freiburg, Germany). Comparative output factor measurements were performed with the array, the Semiflex 31010 ionization chamber and the Diode 60012 (both PTW-Freiburg, Freiburg, Germany). The energy dependence of the OD1500 was measured by comparing the array’s readings to those of a Semiflex 31010 ionization chamber for varying mean photon energies at the depth of measurement, applying to the Semiflex chamber readings the correction factor k{sub NR} for nonreference conditions. The Gaussian lateral dose response function of a single array detector was determined by searching the convolution kernel suitable to convert the slit beam profiles measured with a Diode 60012 into those measured with the array’s central chamber. An intensity modulated dose distribution measured with the array was verified by comparing a OD1500 measurement to TPS calculations and film measurements. Results: The stability and interchamber sensitivity variation of the OD1500 array were within ±0.2% and ±0.58%, respectively. Dose linearity was within 1% over the range from 5 to 1000 MU. The effective point of measurement of the OD1500 for dose measurements in RW3 phantoms was determined to be (8.7 ± 0.2) mm below its front surface. Output factors showed deviations below 1% for field sizes exceeding 4 × 4 cm{sup 2}. The dose per pulse dependence was smaller than 0.4% for doses per pulse from 0.2 to 1 mGy. The energy dependence of the array did not exceed ±0.9%. The parameter σ of the Gaussian lateral dose response function was determined as σ{sub 6MV} = (2.07 ± 0.02) mm for 6 MV and σ{sub 15MV} = (2.09 ± 0.02) mm for 15 MV. An IMRT verification showed passing rates well above 90% for a local 3 mm/3% criterion. Conclusions: The OD1500 array’s dosimetric properties showed the applicability of the array for clinical dosimetry with the possibility to increase the spatial sampling frequency and the coverage of a dose distribution with the sensitive areas of ionization chambers by merging two measurements.« less

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

Calculation of radiation therapy dose using all particle Monte Carlo transport

DOEpatents

Chandler, William P.; Hartmann-Siantar, Christine L.; Rathkopf, James A.

1999-01-01

The actual radiation dose absorbed in the body is calculated using three-dimensional Monte Carlo transport. Neutrons, protons, deuterons, tritons, helium-3, alpha particles, photons, electrons, and positrons are transported in a completely coupled manner, using this Monte Carlo All-Particle Method (MCAPM). The major elements of the invention include: computer hardware, user description of the patient, description of the radiation source, physical databases, Monte Carlo transport, and output of dose distributions. This facilitated the estimation of dose distributions on a Cartesian grid for neutrons, photons, electrons, positrons, and heavy charged-particles incident on any biological target, with resolutions ranging from microns to centimeters. Calculations can be extended to estimate dose distributions on general-geometry (non-Cartesian) grids for biological and/or non-biological media.

Calculation of radiation therapy dose using all particle Monte Carlo transport

DOEpatents

Chandler, W.P.; Hartmann-Siantar, C.L.; Rathkopf, J.A.

1999-02-09

The actual radiation dose absorbed in the body is calculated using three-dimensional Monte Carlo transport. Neutrons, protons, deuterons, tritons, helium-3, alpha particles, photons, electrons, and positrons are transported in a completely coupled manner, using this Monte Carlo All-Particle Method (MCAPM). The major elements of the invention include: computer hardware, user description of the patient, description of the radiation source, physical databases, Monte Carlo transport, and output of dose distributions. This facilitated the estimation of dose distributions on a Cartesian grid for neutrons, photons, electrons, positrons, and heavy charged-particles incident on any biological target, with resolutions ranging from microns to centimeters. Calculations can be extended to estimate dose distributions on general-geometry (non-Cartesian) grids for biological and/or non-biological media. 57 figs.

Differential Effects of Silver Nanoparticles and Silver Ions on Tissue Accumulation, Distribution, and Toxicity in the Sprague Dawley Rat Following Daily Oral Gavage Administration for 13 Weeks

PubMed Central

Boudreau, Mary D.; Imam, Mohammed S.; Paredes, Angel M.; Bryant, Matthew S.; Cunningham, Candice K.; Felton, Robert P.; Jones, Margie Y.; Davis, Kelly J.; Olson, Greg R.

2016-01-01

There are concerns within the regulatory and research communities regarding the health impact associated with consumer exposure to silver nanoparticles (AgNPs). This study evaluated particulate and ionic forms of silver and particle size for differences in silver accumulation, distribution, morphology, and toxicity when administered daily by oral gavage to Sprague Dawley rats for 13 weeks. Test materials and dose formulations were characterized by transmission electron microscopy (TEM), dynamic light scattering, and inductively coupled mass spectrometry (ICP-MS). Seven-week-old rats (10 rats per sex per group) were randomly assigned to treatments: AgNP (10, 75, and 110 nm) at 9, 18, and 36 mg/kg body weight (bw); silver acetate (AgOAc) at 100, 200, and 400 mg/kg bw; and controls (2 mM sodium citrate (CIT) or water). At termination, complete necropsies were conducted, histopathology, hematology, serum chemistry, micronuclei, and reproductive system analyses were performed, and silver accumulations and distributions were determined. Rats exposed to AgNP did not show significant changes in body weights or intakes of feed and water relative to controls, and blood, reproductive system, and genetic tests were similar to controls. Differences in the distributional pattern and morphology of silver deposits were observed by TEM: AgNP appeared predominantly within cells, while AgOAc had an affinity for extracellular membranes. Significant dose-dependent and AgNP size-dependent accumulations were detected in tissues by ICP-MS. In addition, sex differences in silver accumulations were noted for a number of tissues and organs, with accumulations being significantly higher in female rats, especially in the kidney, liver, jejunum, and colon. PMID:26732888

Experimental benchmarking of a Monte Carlo dose simulation code for pediatric CT

NASA Astrophysics Data System (ADS)

Li, Xiang; Samei, Ehsan; Yoshizumi, Terry; Colsher, James G.; Jones, Robert P.; Frush, Donald P.

2007-03-01

In recent years, there has been a desire to reduce CT radiation dose to children because of their susceptibility and prolonged risk for cancer induction. Concerns arise, however, as to the impact of dose reduction on image quality and thus potentially on diagnostic accuracy. To study the dose and image quality relationship, we are developing a simulation code to calculate organ dose in pediatric CT patients. To benchmark this code, a cylindrical phantom was built to represent a pediatric torso, which allows measurements of dose distributions from its center to its periphery. Dose distributions for axial CT scans were measured on a 64-slice multidetector CT (MDCT) scanner (GE Healthcare, Chalfont St. Giles, UK). The same measurements were simulated using a Monte Carlo code (PENELOPE, Universitat de Barcelona) with the applicable CT geometry including bowtie filter. The deviations between simulated and measured dose values were generally within 5%. To our knowledge, this work is one of the first attempts to compare measured radial dose distributions on a cylindrical phantom with Monte Carlo simulated results. It provides a simple and effective method for benchmarking organ dose simulation codes and demonstrates the potential of Monte Carlo simulation for investigating the relationship between dose and image quality for pediatric CT patients.

Noise spatial nonuniformity and the impact of statistical image reconstruction in CT myocardial perfusion imaging.

PubMed

Lauzier, Pascal Theriault; Tang, Jie; Speidel, Michael A; Chen, Guang-Hong

2012-07-01

To achieve high temporal resolution in CT myocardial perfusion imaging (MPI), images are often reconstructed using filtered backprojection (FBP) algorithms from data acquired within a short-scan angular range. However, the variation in the central angle from one time frame to the next in gated short scans has been shown to create detrimental partial scan artifacts when performing quantitative MPI measurements. This study has two main purposes. (1) To demonstrate the existence of a distinct detrimental effect in short-scan FBP, i.e., the introduction of a nonuniform spatial image noise distribution; this nonuniformity can lead to unexpectedly high image noise and streaking artifacts, which may affect CT MPI quantification. (2) To demonstrate that statistical image reconstruction (SIR) algorithms can be a potential solution to address the nonuniform spatial noise distribution problem and can also lead to radiation dose reduction in the context of CT MPI. Projection datasets from a numerically simulated perfusion phantom and an in vivo animal myocardial perfusion CT scan were used in this study. In the numerical phantom, multiple realizations of Poisson noise were added to projection data at each time frame to investigate the spatial distribution of noise. Images from all datasets were reconstructed using both FBP and SIR reconstruction algorithms. To quantify the spatial distribution of noise, the mean and standard deviation were measured in several regions of interest (ROIs) and analyzed across time frames. In the in vivo study, two low-dose scans at tube currents of 25 and 50 mA were reconstructed using FBP and SIR. Quantitative perfusion metrics, namely, the normalized upslope (NUS), myocardial blood volume (MBV), and first moment transit time (FMT), were measured for two ROIs and compared to reference values obtained from a high-dose scan performed at 500 mA. Images reconstructed using FBP showed a highly nonuniform spatial distribution of noise. This spatial nonuniformity led to large fluctuations in the temporal direction. In the numerical phantom study, the level of noise was shown to vary by as much as 87% within a given image, and as much as 110% between different time frames for a ROI far from isocenter. The spatially nonuniform noise pattern was shown to correlate with the source trajectory and the object structure. In contrast, images reconstructed using SIR showed a highly uniform spatial distribution of noise, leading to smaller unexpected noise fluctuations in the temporal direction when a short scan angular range was used. In the numerical phantom study, the noise varied by less than 37% within a given image, and by less than 20% between different time frames. Also, the noise standard deviation in SIR images was on average half of that of FBP images. In the in vivo studies, the deviation observed between quantitative perfusion metrics measured from low-dose scans and high-dose scans was mitigated when SIR was used instead of FBP to reconstruct images. (1) Images reconstructed using FBP suffered from nonuniform spatial noise levels. This nonuniformity is another manifestation of the detrimental effects caused by short-scan reconstruction in CT MPI. (2) Images reconstructed using SIR had a much lower and more uniform noise level and thus can be used as a potential solution to address the FBP nonuniformity. (3) Given the improvement in the accuracy of the perfusion metrics when using SIR, it may be desirable to use a statistical reconstruction framework to perform low-dose dynamic CT MPI.

Noise spatial nonuniformity and the impact of statistical image reconstruction in CT myocardial perfusion imaging

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

Lauzier, Pascal Theriault; Tang Jie; Speidel, Michael A.

Purpose: To achieve high temporal resolution in CT myocardial perfusion imaging (MPI), images are often reconstructed using filtered backprojection (FBP) algorithms from data acquired within a short-scan angular range. However, the variation in the central angle from one time frame to the next in gated short scans has been shown to create detrimental partial scan artifacts when performing quantitative MPI measurements. This study has two main purposes. (1) To demonstrate the existence of a distinct detrimental effect in short-scan FBP, i.e., the introduction of a nonuniform spatial image noise distribution; this nonuniformity can lead to unexpectedly high image noise andmore » streaking artifacts, which may affect CT MPI quantification. (2) To demonstrate that statistical image reconstruction (SIR) algorithms can be a potential solution to address the nonuniform spatial noise distribution problem and can also lead to radiation dose reduction in the context of CT MPI. Methods: Projection datasets from a numerically simulated perfusion phantom and an in vivo animal myocardial perfusion CT scan were used in this study. In the numerical phantom, multiple realizations of Poisson noise were added to projection data at each time frame to investigate the spatial distribution of noise. Images from all datasets were reconstructed using both FBP and SIR reconstruction algorithms. To quantify the spatial distribution of noise, the mean and standard deviation were measured in several regions of interest (ROIs) and analyzed across time frames. In the in vivo study, two low-dose scans at tube currents of 25 and 50 mA were reconstructed using FBP and SIR. Quantitative perfusion metrics, namely, the normalized upslope (NUS), myocardial blood volume (MBV), and first moment transit time (FMT), were measured for two ROIs and compared to reference values obtained from a high-dose scan performed at 500 mA. Results: Images reconstructed using FBP showed a highly nonuniform spatial distribution of noise. This spatial nonuniformity led to large fluctuations in the temporal direction. In the numerical phantom study, the level of noise was shown to vary by as much as 87% within a given image, and as much as 110% between different time frames for a ROI far from isocenter. The spatially nonuniform noise pattern was shown to correlate with the source trajectory and the object structure. In contrast, images reconstructed using SIR showed a highly uniform spatial distribution of noise, leading to smaller unexpected noise fluctuations in the temporal direction when a short scan angular range was used. In the numerical phantom study, the noise varied by less than 37% within a given image, and by less than 20% between different time frames. Also, the noise standard deviation in SIR images was on average half of that of FBP images. In the in vivo studies, the deviation observed between quantitative perfusion metrics measured from low-dose scans and high-dose scans was mitigated when SIR was used instead of FBP to reconstruct images. Conclusions: (1) Images reconstructed using FBP suffered from nonuniform spatial noise levels. This nonuniformity is another manifestation of the detrimental effects caused by short-scan reconstruction in CT MPI. (2) Images reconstructed using SIR had a much lower and more uniform noise level and thus can be used as a potential solution to address the FBP nonuniformity. (3) Given the improvement in the accuracy of the perfusion metrics when using SIR, it may be desirable to use a statistical reconstruction framework to perform low-dose dynamic CT MPI.« less

Noise spatial nonuniformity and the impact of statistical image reconstruction in CT myocardial perfusion imaging

PubMed Central

Lauzier, Pascal Thériault; Tang, Jie; Speidel, Michael A.; Chen, Guang-Hong

2012-01-01

Purpose: To achieve high temporal resolution in CT myocardial perfusion imaging (MPI), images are often reconstructed using filtered backprojection (FBP) algorithms from data acquired within a short-scan angular range. However, the variation in the central angle from one time frame to the next in gated short scans has been shown to create detrimental partial scan artifacts when performing quantitative MPI measurements. This study has two main purposes. (1) To demonstrate the existence of a distinct detrimental effect in short-scan FBP, i.e., the introduction of a nonuniform spatial image noise distribution; this nonuniformity can lead to unexpectedly high image noise and streaking artifacts, which may affect CT MPI quantification. (2) To demonstrate that statistical image reconstruction (SIR) algorithms can be a potential solution to address the nonuniform spatial noise distribution problem and can also lead to radiation dose reduction in the context of CT MPI. Methods: Projection datasets from a numerically simulated perfusion phantom and an in vivo animal myocardial perfusion CT scan were used in this study. In the numerical phantom, multiple realizations of Poisson noise were added to projection data at each time frame to investigate the spatial distribution of noise. Images from all datasets were reconstructed using both FBP and SIR reconstruction algorithms. To quantify the spatial distribution of noise, the mean and standard deviation were measured in several regions of interest (ROIs) and analyzed across time frames. In the in vivo study, two low-dose scans at tube currents of 25 and 50 mA were reconstructed using FBP and SIR. Quantitative perfusion metrics, namely, the normalized upslope (NUS), myocardial blood volume (MBV), and first moment transit time (FMT), were measured for two ROIs and compared to reference values obtained from a high-dose scan performed at 500 mA. Results: Images reconstructed using FBP showed a highly nonuniform spatial distribution of noise. This spatial nonuniformity led to large fluctuations in the temporal direction. In the numerical phantom study, the level of noise was shown to vary by as much as 87% within a given image, and as much as 110% between different time frames for a ROI far from isocenter. The spatially nonuniform noise pattern was shown to correlate with the source trajectory and the object structure. In contrast, images reconstructed using SIR showed a highly uniform spatial distribution of noise, leading to smaller unexpected noise fluctuations in the temporal direction when a short scan angular range was used. In the numerical phantom study, the noise varied by less than 37% within a given image, and by less than 20% between different time frames. Also, the noise standard deviation in SIR images was on average half of that of FBP images. In the in vivo studies, the deviation observed between quantitative perfusion metrics measured from low-dose scans and high-dose scans was mitigated when SIR was used instead of FBP to reconstruct images. Conclusions: (1) Images reconstructed using FBP suffered from nonuniform spatial noise levels. This nonuniformity is another manifestation of the detrimental effects caused by short-scan reconstruction in CT MPI. (2) Images reconstructed using SIR had a much lower and more uniform noise level and thus can be used as a potential solution to address the FBP nonuniformity. (3) Given the improvement in the accuracy of the perfusion metrics when using SIR, it may be desirable to use a statistical reconstruction framework to perform low-dose dynamic CT MPI. PMID:22830741

UV Disinfection System for Cabin Air

NASA Astrophysics Data System (ADS)

Lim, Soojung

Ultraviolet (UV) radiation is commonly used for disinfection of water. As a result of advancements made in the last 10-15 years, the analysis and design of UV disinfection systems for water is well developed. UV disinfection is also used for disinfection of air; however, despite the fact the UV-air systems have a longer record of application than UV-water systems, the methods used to analyze and design UV-air disinfection systems remain quite empirical. It is well-established that the effectiveness of UV-air systems is strongly affected by the type of microorganisms, the irradiation level/type (lamp power and wavelength), duration of irradiation (exposure time), air movement pattern (mixing degree), and relative humidity. This paper will describe ongoing efforts to evaluate, design and test a UV-air system based on first principles. Specific issues to be addressed in this work will include laboratory measurements of relevant kinetics (i.e., UV dose-response behavior) and numerical simulations designed to represent fluid mechanics and the radiation intensity field. UV dose-response behavior of test microorganism was measured using a laboratory (bench-scale) system. Target microorganisms (e.g., bacterial spores) were first applied to membrane filters at sub-monolayer coverage. The filters were then transferred to an environmental chamber at fixed relative humidity (RH) and allowed to equilibrate with their surroundings. Microorganisms were then subjected to UV exposure under a collimated beam. The experiment was repeated at RH values ranging from 20% to 100%. UV dose-response behavior was observed to vary with RH. For example, at 100% RH, a UV dose of 20 mJ/cm2 accomplished 90% (1 log10 units) of the B. subtilis spore inactivation, whereas 99 % (2 log10 units) inactivation was accomplished at this same UV dose under 20% RH conditions. However, at higher doses, the result was opposite of that in low dose. Reactor behavior is simulated using an integrated application of computational fluid dynamics (CFD) and radiation intensity field models. These simulations followed a Lagrangian approach, wherein the UV radiation intensity field was mapped onto simulated particle trajectories for prediction of the UV dose delivered to each particle. By repeating these calculations for a large number of simulated particle trajectories, an estimate of the UV dose distribution delivered by the reactor can be made. In turn, these dose distribution estimates are integrated with the UV dose-response behavior described above to yield an estimate of microbial inactivation accomplished by the reactor. This modeling approach has the advantage of allowing simulation of many reactor configurations in a relatively short period of time. Moreover, by following this approach of "numerical prototyping," it is possible to "build" and analyze several virtual reactors before the construction of a physical prototype. As such, this procedure allows effective development of efficient reactors.

Assessment of radiation doses from residential smoke detectors that contain americium-241

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

O'Donnell, F.R.; Etnier, E.L.; Holton, G.A.

1981-10-01

External dose equivalents and internal dose commitments were estimated for individuals and populations from annual distribution, use, and disposal of 10 million ionization chamber smoke detectors that contain 110 kBq (3 ..mu..Ci) americium-241 each. Under exposure scenarios developed for normal distribution, use, and disposal using the best available information, annual external dose equivalents to average individuals were estimated to range from 4 fSv (0.4 prem) to 20 nSv (2 ..mu..rem) for total body and from 7 fSv to 40 nSv for bone. Internal dose commitments to individuals under post disposal scenarios were estimated to range from 0.006 to 80 ..mu..Svmore » (0.0006 to 8 mrem) to total body and from 0.06 to 800 ..mu..Sv to bone. The total collective dose (the sum of external dose equivalents and 50-year internal dose commitments) for all individuals involved with distribution, use, or disposal of 10 million smoke detectors was estimated to be about 0.38 person-Sv (38 person-rem) to total body and 00 ft/sup 2/).« less

Multiple comparisons permutation test for image based data mining in radiotherapy

PubMed Central

2013-01-01

Comparing incidental dose distributions (i.e. images) of patients with different outcomes is a straightforward way to explore dose-response hypotheses in radiotherapy. In this paper, we introduced a permutation test that compares images, such as dose distributions from radiotherapy, while tackling the multiple comparisons problem. A test statistic Tmax was proposed that summarizes the differences between the images into a single value and a permutation procedure was employed to compute the adjusted p-value. We demonstrated the method in two retrospective studies: a prostate study that relates 3D dose distributions to failure, and an esophagus study that relates 2D surface dose distributions of the esophagus to acute esophagus toxicity. As a result, we were able to identify suspicious regions that are significantly associated with failure (prostate study) or toxicity (esophagus study). Permutation testing allows direct comparison of images from different patient categories and is a useful tool for data mining in radiotherapy. PMID:24365155

A mathematical deconvolution formulation for superficial dose distribution measurement by Cerenkov light dosimetry.

PubMed

Brost, Eric Edward; Watanabe, Yoichi

2018-06-01

Cerenkov photons are created by high-energy radiation beams used for radiation therapy. In this study, we developed a Cerenkov light dosimetry technique to obtain a two-dimensional dose distribution in a superficial region of medium from the images of Cerenkov photons by using a deconvolution method. An integral equation was derived to represent the Cerenkov photon image acquired by a camera for a given incident high-energy photon beam by using convolution kernels. Subsequently, an equation relating the planar dose at a depth to a Cerenkov photon image using the well-known relationship between the incident beam fluence and the dose distribution in a medium was obtained. The final equation contained a convolution kernel called the Cerenkov dose scatter function (CDSF). The CDSF function was obtained by deconvolving the Cerenkov scatter function (CSF) with the dose scatter function (DSF). The GAMOS (Geant4-based Architecture for Medicine-Oriented Simulations) Monte Carlo particle simulation software was used to obtain the CSF and DSF. The dose distribution was calculated from the Cerenkov photon intensity data using an iterative deconvolution method with the CDSF. The theoretical formulation was experimentally evaluated by using an optical phantom irradiated by high-energy photon beams. The intensity of the deconvolved Cerenkov photon image showed linear dependence on the dose rate and the photon beam energy. The relative intensity showed a field size dependence similar to the beam output factor. Deconvolved Cerenkov images showed improvement in dose profiles compared with the raw image data. In particular, the deconvolution significantly improved the agreement in the high dose gradient region, such as in the penumbra. Deconvolution with a single iteration was found to provide the most accurate solution of the dose. Two-dimensional dose distributions of the deconvolved Cerenkov images agreed well with the reference distributions for both square fields and a multileaf collimator (MLC) defined, irregularly shaped field. The proposed technique improved the accuracy of the Cerenkov photon dosimetry in the penumbra region. The results of this study showed initial validation of the deconvolution method for beam profile measurements in a homogeneous media. The new formulation accounted for the physical processes of Cerenkov photon transport in the medium more accurately than previously published methods. © 2018 American Association of Physicists in Medicine.

Osteosarcoma development following single inhalation exposure to americium-241 in beagle dogs.

PubMed

Gillett, N A; Hahn, F F; Mewhinney, J A; Muggenberg, B A

1985-10-01

Young, mature Beagle dogs underwent single inhalation exposure to respirable aerosols of 241AmO2 to determine the radiation dose distribution to tissues. The dogs were serially sacrificed to assess the clearance of 241Am from the lung, the rate of translocation to internal organs, the pattern of retention in the organs, and the rates and modes of excretion. Americium dioxide was relatively soluble in the lung, leading to the translocation of significant quantities of 241Am to bone and liver, thus delivering radiation doses to these tissues nearly equal to that received by the lung. Osteoblastic osteosarcomas developed in four dogs surviving more than 1000 days after exposure. Histologically, all of the osteosarcomas were associated with areas of radiation osteodystrophy characterized by bone infarction, peritrabecular new bone formation, marrow fibrosis, and microresorptive cavities. The retention and translocation of inhaled 241Am in dogs is similar to that of man, indicating that 241Am inhaled by humans may potentially result in significant risk of bone tumor development.

Tomotherapy as a tool in image-guided radiation therapy (IGRT): theoretical and technological aspects

PubMed Central

Yartsev, S; Kron, T; Van Dyk, J

2007-01-01

Helical tomotherapy (HT) is a novel treatment approach that combines Intensity-Modulate Radiation Therapy (IMRT) delivery with in-built image guidance using megavoltage (MV) CT scanning. The technique utilises a 6 MV linear accelerator mounted on a CT type ring gantry. The beam is collimated to a fan beam, which is intensity modulated using a binary multileaf collimator (MLC). As the patient advances slowly through the ring gantry, the linac rotates around the patient with a leaf-opening pattern optimised to deliver a highly conformal dose distribution to the target in the helical beam trajectory. The unit also allows the acquisition of MVCT images using the same radiation source detuned to reduce its effective energy to 3.5 MV, making the dose required for imaging less than 3 cGy. This paper discusses the major features of HT and describes the advantages and disadvantages of this approach in the context of the commercial Hi-ART system. PMID:21614257

Cost comparison of unit dose and traditional drug distribution in a long-term-care facility.

PubMed

Lepinski, P W; Thielke, T S; Collins, D M; Hanson, A

1986-11-01

Unit dose and traditional drug distribution systems were compared in a 352-bed long-term-care facility by analyzing nursing time, medication-error rate, medication costs, and waste. Time spent by nurses in preparing, administering, charting, and other tasks associated with medications was measured with a stop-watch on four different nursing units during six-week periods before and after the nursing home began using unit dose drug distribution. Medication-error rate before and after implementation of the unit dose system was determined by patient profile audits and medication inventories. Medication costs consisted of patient billing costs (acquisition cost plus fee) and cost of medications destroyed. The unit dose system required a projected 1507.2 hours less nursing time per year. Mean medication-error rates were 8.53% and 0.97% for the traditional and unit dose systems, respectively. Potential annual savings because of decreased medication waste with the unit dose system were $2238.72. The net increase in cost for the unit dose system was estimated at $615.05 per year, or approximately $1.75 per patient. The unit dose system appears safer and more time-efficient than the traditional system, although its costs are higher.

The incidence of blood contamination of lead unit dose containers with and without single-use protective inserts used with commercially prepared radiopharmaceutical unit doses.

PubMed

Pickett, M W; Kosegi, J E; Thomas, K S; Waterstram-Rich, K M

1998-09-01

This investigation evaluated the effectiveness of disposable plastic inserts in radiopharmaceutical unit dose lead containers (pigs) in preventing the distribution of doses in blood-contaminated containers. Technologists commonly dispose of the syringes by placing them into the lead pigs, leaving the needles uncapped. This process raises the question of unsuspected blood contamination of these pigs. Consequently, the distribution of commercially prepared radiopharmaceutical doses in reusable lead pigs may result in radiopharmaceutical doses being distributed in containers that are contaminated with blood. Using a simple chemical wipe test designed to determine the presence or absence of blood contamination, 618 pigs from commercial radiopharmacies throughout the U.S. were tested for contamination. The inside of the pigs and inserts, if present, were wiped before and after dose administration. Of the pigs tested, 292 came from radiopharmacies that used a protective, disposable plastic insert inside the pig, and 326 came from radiopharmacies that did not use an insert. Of those pigs without the protective disposable inserts, 39.3% arrived in the nuclear medicine department in pigs contaminated with blood. Of those pigs with inserts, 1% arrived with blood-contaminated inserts. After dose administration, 46.3% of the pigs without inserts were contaminated with blood and 3% of the protective inserts were contaminated. The proper use of disposable plastic inserts reduces the possibility of distributing radiopharmaceutical unit doses in containers contaminated with blood.

A Monte Carlo study of the impact of the choice of rectum volume definition on estimates of equivalent uniform doses and the volume parameter

NASA Astrophysics Data System (ADS)

Kvinnsland, Yngve; Muren, Ludvig Paul; Dahl, Olav

2004-08-01

Calculations of normal tissue complication probability (NTCP) values for the rectum are difficult because it is a hollow, non-rigid, organ. Finding the true cumulative dose distribution for a number of treatment fractions requires a CT scan before each treatment fraction. This is labour intensive, and several surrogate distributions have therefore been suggested, such as dose wall histograms, dose surface histograms and histograms for the solid rectum, with and without margins. In this study, a Monte Carlo method is used to investigate the relationships between the cumulative dose distributions based on all treatment fractions and the above-mentioned histograms that are based on one CT scan only, in terms of equivalent uniform dose. Furthermore, the effect of a specific choice of histogram on estimates of the volume parameter of the probit NTCP model was investigated. It was found that the solid rectum and the rectum wall histograms (without margins) gave equivalent uniform doses with an expected value close to the values calculated from the cumulative dose distributions in the rectum wall. With the number of patients available in this study the standard deviations of the estimates of the volume parameter were large, and it was not possible to decide which volume gave the best estimates of the volume parameter, but there were distinct differences in the mean values of the values obtained.

A missing dimension in measures of vaccination impacts

USGS Publications Warehouse

Gomes, M. Gabriela M.; Lipsitch, Marc; Wargo, Andrew R.; Kurath, Gael; Rebelo, Carlota; Medley, Graham F.; Coutinho, Antonio

2013-01-01

Immunological protection, acquired from either natural infection or vaccination, varies among hosts, reflecting underlying biological variation and affecting population-level protection. Owing to the nature of resistance mechanisms, distributions of susceptibility and protection entangle with pathogen dose in a way that can be decoupled by adequately representing the dose dimension. Any infectious processes must depend in some fashion on dose, and empirical evidence exists for an effect of exposure dose on the probability of transmission to mumps-vaccinated hosts [1], the case-fatality ratio of measles [2], and the probability of infection and, given infection, of symptoms in cholera [3]. Extreme distributions of vaccine protection have been termed leaky (partially protects all hosts) and all-or-nothing (totally protects a proportion of hosts) [4]. These distributions can be distinguished in vaccine field trials from the time dependence of infections [5]. Frailty mixing models have also been proposed to estimate the distribution of protection from time to event data [6], [7], although the results are not comparable across regions unless there is explicit control for baseline transmission [8]. Distributions of host susceptibility and acquired protection can be estimated from dose-response data generated under controlled experimental conditions [9]–[11] and natural settings [12], [13]. These distributions can guide research on mechanisms of protection, as well as enable model validity across the entire range of transmission intensities. We argue for a shift to a dose-dimension paradigm in infectious disease science and community health.

Linear energy transfer incorporated intensity modulated proton therapy optimization

NASA Astrophysics Data System (ADS)

Cao, Wenhua; Khabazian, Azin; Yepes, Pablo P.; Lim, Gino; Poenisch, Falk; Grosshans, David R.; Mohan, Radhe

2018-01-01

The purpose of this study was to investigate the feasibility of incorporating linear energy transfer (LET) into the optimization of intensity modulated proton therapy (IMPT) plans. Because increased LET correlates with increased biological effectiveness of protons, high LETs in target volumes and low LETs in critical structures and normal tissues are preferred in an IMPT plan. However, if not explicitly incorporated into the optimization criteria, different IMPT plans may yield similar physical dose distributions but greatly different LET, specifically dose-averaged LET, distributions. Conventionally, the IMPT optimization criteria (or cost function) only includes dose-based objectives in which the relative biological effectiveness (RBE) is assumed to have a constant value of 1.1. In this study, we added LET-based objectives for maximizing LET in target volumes and minimizing LET in critical structures and normal tissues. Due to the fractional programming nature of the resulting model, we used a variable reformulation approach so that the optimization process is computationally equivalent to conventional IMPT optimization. In this study, five brain tumor patients who had been treated with proton therapy at our institution were selected. Two plans were created for each patient based on the proposed LET-incorporated optimization (LETOpt) and the conventional dose-based optimization (DoseOpt). The optimized plans were compared in terms of both dose (assuming a constant RBE of 1.1 as adopted in clinical practice) and LET. Both optimization approaches were able to generate comparable dose distributions. The LET-incorporated optimization achieved not only pronounced reduction of LET values in critical organs, such as brainstem and optic chiasm, but also increased LET in target volumes, compared to the conventional dose-based optimization. However, on occasion, there was a need to tradeoff the acceptability of dose and LET distributions. Our conclusion is that the inclusion of LET-dependent criteria in the IMPT optimization could lead to similar dose distributions as the conventional optimization but superior LET distributions in target volumes and normal tissues. This may have substantial advantages in improving tumor control and reducing normal tissue toxicities.

Evaluation of ambient dose equivalent rates influenced by vertical and horizontal distribution of radioactive cesium in soil in Fukushima Prefecture.

PubMed

Malins, Alex; Kurikami, Hiroshi; Nakama, Shigeo; Saito, Tatsuo; Okumura, Masahiko; Machida, Masahiko; Kitamura, Akihiro

2016-01-01

The air dose rate in an environment contaminated with (134)Cs and (137)Cs depends on the amount, depth profile and horizontal distribution of these contaminants within the ground. This paper introduces and verifies a tool that models these variables and calculates ambient dose equivalent rates at 1 m above the ground. Good correlation is found between predicted dose rates and dose rates measured with survey meters in Fukushima Prefecture in areas contaminated with radiocesium from the Fukushima Dai-ichi Nuclear Power Plant accident. This finding is insensitive to the choice for modeling the activity depth distribution in the ground using activity measurements of collected soil layers, or by using exponential and hyperbolic secant fits to the measurement data. Better predictions are obtained by modeling the horizontal distribution of radioactive cesium across an area if multiple soil samples are available, as opposed to assuming a spatially homogeneous contamination distribution. Reductions seen in air dose rates above flat, undisturbed fields in Fukushima Prefecture are consistent with decrement by radioactive decay and downward migration of cesium into soil. Analysis of remediation strategies for farmland soils confirmed that topsoil removal and interchanging a topsoil layer with a subsoil layer result in similar reductions in the air dose rate. These two strategies are more effective than reverse tillage to invert and mix the topsoil. Copyright © 2015 Elsevier Ltd. All rights reserved.

Role of particle radiotherapy in the management of head and neck cancer.

PubMed

Laramore, George E

2009-05-01

Modern imaging techniques and powerful computers allow a radiation oncologist to design treatments delivering higher doses of radiation than previously possible. Dose distributions imposed by the physics of 'standard' photon and electron beams limit further dose escalation. Hadron radiotherapy offers advantages in either dose distribution and/or improved radiobiology that may significantly improve the treatment of certain head and neck malignancies. Clinical studies support the effectiveness of fast-neutron radiotherapy in the treatment of major and minor salivary gland tumors. Data show highly favorable outcomes with proton radiotherapy for skull-base malignancies and tumors near highly critical normal tissues compared with that expected with standard radiotherapy. Heavy-ion radiotherapy clinical studies are mainly being conducted with fully stripped carbon ions, and limited data seem to indicate a possible improvement over proton radiotherapy for the same subset of radioresistant tumors where neutrons show a benefit over photons. Fast-neutron radiotherapy has different radiobiological properties compared with standard radiotherapy but similar depth dose distributions. Its role in the treatment of head and neck cancer is currently limited to salivary gland malignancies and certain radioresistant tumors such as sarcomas. Protons have the same radiobiological properties as standard radiotherapy beams but more optimal depth dose distributions, making it particularly advantageous when treating tumors adjacent to highly critical structures. Heavy ions combine the radiobiological properties of fast neutrons with the physical dose distributions of protons, and preliminary data indicate their utility for radioresistant tumors adjacent to highly critical structures.

Feasibility of TCP-based dose painting by numbers applied to a prostate case with (18)F-choline PET imaging.

PubMed

Dirscherl, Thomas; Rickhey, Mark; Bogner, Ludwig

2012-02-01

A biologically adaptive radiation treatment method to maximize the TCP is shown. Functional imaging is used to acquire a heterogeneous dose prescription in terms of Dose Painting by Numbers and to create a patient-specific IMRT plan. Adapted from a method for selective dose escalation under the guidance of spatial biology distribution, a model, which translates heterogeneously distributed radiobiological parameters into voxelwise dose prescriptions, was developed. At the example of a prostate case with (18)F-choline PET imaging, different sets of reported values for the parameters were examined concerning their resulting range of dose values. Furthermore, the influence of each parameter of the linear-quadratic model was investigated. A correlation between PET signal and proliferation as well as cell density was assumed. Using our in-house treatment planning software Direct Monte Carlo Optimization (DMCO), a treatment plan based on the obtained dose prescription was generated. Gafchromic EBT films were irradiated for evaluation. When a TCP of 95% was aimed at, the maximal dose in a voxel of the prescription exceeded 100Gy for most considered parameter sets. One of the parameter sets resulted in a dose range of 87.1Gy to 99.3Gy, yielding a TCP of 94.7%, and was investigated more closely. The TCP of the plan decreased to 73.5% after optimization based on that prescription. The dose difference histogram of optimized and prescribed dose revealed a mean of -1.64Gy and a standard deviation of 4.02Gy. Film verification showed a reasonable agreement of planned and delivered dose. If the distribution of radiobiological parameters within a tumor is known, this model can be used to create a dose-painting by numbers plan which maximizes the TCP. It could be shown, that such a heterogeneous dose distribution is technically feasible. Copyright © 2012. Published by Elsevier GmbH.

Design of a modulated orthovoltage stereotactic radiosurgery system.

PubMed

Fagerstrom, Jessica M; Bender, Edward T; Lawless, Michael J; Culberson, Wesley S

2017-07-01

To achieve stereotactic radiosurgery (SRS) dose distributions with sharp gradients using orthovoltage energy fluence modulation with inverse planning optimization techniques. A pencil beam model was used to calculate dose distributions from an orthovoltage unit at 250 kVp. Kernels for the model were derived using Monte Carlo methods. A Genetic Algorithm search heuristic was used to optimize the spatial distribution of added tungsten filtration to achieve dose distributions with sharp dose gradients. Optimizations were performed for depths of 2.5, 5.0, and 7.5 cm, with cone sizes of 5, 6, 8, and 10 mm. In addition to the beam profiles, 4π isocentric irradiation geometries were modeled to examine dose at 0.07 mm depth, a representative skin depth, for the low energy beams. Profiles from 4π irradiations of a constant target volume, assuming maximally conformal coverage, were compared. Finally, dose deposition in bone compared to tissue in this energy range was examined. Based on the results of the optimization, circularly symmetric tungsten filters were designed to modulate the orthovoltage beam across the apertures of SRS cone collimators. For each depth and cone size combination examined, the beam flatness and 80-20% and 90-10% penumbrae were calculated for both standard, open cone-collimated beams as well as for optimized, filtered beams. For all configurations tested, the modulated beam profiles had decreased penumbra widths and flatness statistics at depth. Profiles for the optimized, filtered orthovoltage beams also offered decreases in these metrics compared to measured linear accelerator cone-based SRS profiles. The dose at 0.07 mm depth in the 4π isocentric irradiation geometries was higher for the modulated beams compared to unmodulated beams; however, the modulated dose at 0.07 mm depth remained <0.025% of the central, maximum dose. The 4π profiles irradiating a constant target volume showed improved statistics for the modulated, filtered distribution compared to the standard, open cone-collimated distribution. Simulations of tissue and bone confirmed previously published results that a higher energy beam (≥ 200 keV) would be preferable, but the 250 kVp beam was chosen for this work because it is available for future measurements. A methodology has been described that may be used to optimize the spatial distribution of added filtration material in an orthovoltage SRS beam to result in dose distributions with decreased flatness and penumbra statistics compared to standard open cones. This work provides the mathematical foundation for a novel, orthovoltage energy fluence-modulated SRS system. © 2017 American Association of Physicists in Medicine.

Frameless fractionated stereotactic radiation therapy of intracranial lesions: impact of cone beam CT based setup correction on dose distribution

PubMed Central

2013-01-01

Background The purpose of this study was to evaluate the impact of Cone Beam CT (CBCT) based setup correction on total dose distributions in fractionated frameless stereotactic radiation therapy of intracranial lesions. Methods Ten patients with intracranial lesions treated with 30 Gy in 6 fractions were included in this study. Treatment planning was performed with Oncentra® for a SynergyS® (Elekta Ltd, Crawley, UK) linear accelerator with XVI® Cone Beam CT, and HexaPOD™ couch top. Patients were immobilized by thermoplastic masks (BrainLab, Reuther). After initial patient setup with respect to lasers, a CBCT study was acquired and registered to the planning CT (PL-CT) study. Patient positioning was corrected according to the correction values (translational, rotational) calculated by the XVI® system. Afterwards a second CBCT study was acquired and registered to the PL-CT to confirm the accuracy of the corrections. An in-house developed software was used for rigid transformation of the PL-CT to the CBCT geometry, and dose calculations for each fraction were performed on the transformed CT. The total dose distribution was achieved by back-transformation and summation of the dose distributions of each fraction. Dose distributions based on PL-CT, CBCT (laser set-up), and final CBCT were compared to assess the influence of setup inaccuracies. Results The mean displacement vector, calculated over all treatments, was reduced from (4.3 ± 1.3) mm for laser based setup to (0.5 ± 0.2) mm if CBCT corrections were applied. The mean rotational errors around the medial-lateral, superior-inferior, anterior-posterior axis were reduced from (−0.1 ± 1.4)°, (0.1 ± 1.2)° and (−0.2 ± 1.0)°, to (0.04 ± 0.4)°, (0.01 ± 0.4)° and (0.02 ± 0.3)°. As a consequence the mean deviation between planned and delivered dose in the planning target volume (PTV) could be reduced from 12.3% to 0.4% for D95 and from 5.9% to 0.1% for Dav. Maximum deviation was reduced from 31.8% to 0.8% for D95, and from 20.4% to 0.1% for Dav. Conclusion Real dose distributions differ substantially from planned dose distributions, if setup is performed according to lasers only. Thermoplasic masks combined with a daily CBCT enabled a sufficient accuracy in dose distribution. PMID:23800172

Neutron emission and dose distribution from natural carbon irradiated with a 12 MeV amu-1 12C5+ ion beam.

PubMed

Nandy, Maitreyee; Sarkar, P K; Sanami, T; Takada, M; Shibata, T

2016-09-01

Measured neutron energy distribution emitted from a thick stopping target of natural carbon at 0°, 30°, 60° and 90° from nuclear reactions caused by 12 MeV amu -1 incident 12 C 5+ ions were converted to energy differential and total neutron absorbed dose as well as ambient dose equivalent H * (10) using the fluence-to-dose conversion coefficients provided by the ICRP. Theoretical estimates were obtained using the Monte Carlo nuclear reaction model code PACE and a few existing empirical formulations for comparison. Results from the PACE code showed an underestimation of the high-energy part of energy differential dose distributions at forward angles whereas the empirical formulation by Clapier and Zaidins (1983 Nucl. Instrum. Methods 217 489-94) approximated the energy integrated angular distribution of H * (10) satisfactorily. Using the measured data, the neutron doses received by some vital human organs were estimated for anterior-posterior exposure. The estimated energy-averaged quality factors were found to vary for different organs from about 7 to about 13. Emitted neutrons having energies above 20 MeV were found to contribute about 20% of the total dose at 0° while at 90° the contribution was reduced to about 2%.

Validation of Monte Carlo simulation of mammography with TLD measurement and depth dose calculation with a detailed breast model

NASA Astrophysics Data System (ADS)

Wang, Wenjing; Qiu, Rui; Ren, Li; Liu, Huan; Wu, Zhen; Li, Chunyan; Li, Junli

2017-09-01

Mean glandular dose (MGD) is not only determined by the compressed breast thickness (CBT) and the glandular content, but also by the distribution of glandular tissues in breast. Depth dose inside the breast in mammography has been widely concerned as glandular dose decreases rapidly with increasing depth. In this study, an experiment using thermo luminescent dosimeters (TLDs) was carried out to validate Monte Carlo simulations of mammography. Percent depth doses (PDDs) at different depth values were measured inside simple breast phantoms of different thicknesses. The experimental values were well consistent with the values calculated by Geant4. Then a detailed breast model with a CBT of 4 cm and a glandular content of 50%, which has been constructed in previous work, was used to study the effects of the distribution of glandular tissues in breast with Geant4. The breast model was reversed in direction of compression to get a reverse model with a different distribution of glandular tissues. Depth dose distributions and glandular tissue dose conversion coefficients were calculated. It revealed that the conversion coefficients were about 10% larger when the breast model was reversed, for glandular tissues in the reverse model are concentrated in the upper part of the model.

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.

Metabolic fate and disposition of [14C]hydroquinone given orally to Sprague-Dawley rats.

PubMed

Divincenzo, G D; Hamilton, M L; Reynolds, R C; Ziegler, D A

1984-10-01

Hydroquinone (HQ) is used widely in industry and in commerce and is considered to have a low degree of toxicity. Although the metabolism of HQ has been studied elsewhere, a complete materials balance has not been reported. We investigated the metabolism of HQ in naive and HQ pretreated male Sprague-Dawley rats. [14C]HQ was administered by gavage in single doses of 5, 30, or 200 mg/kg to naive rats. HQ was given repeatedly by gavage to male rats at 200 mg/kg for 4 consecutive days followed by a single dose with 200 mg/kg of [14C]HQ. In separate studies rats were fed 5.6% unlabeled HQ in the diet for 2 days or were dosed by gavage with 311 mg/kg [14C]HQ. The excretion patterns of [14C]HQ and its metabolites were similar for rats dosed singly or repeatedly. Rats given a single dose of 200 mg/kg of [14C]HQ excreted 91.9% of the dose in the urine within 2-4 days; 3.8% was excreted in the feces, about 0.4% was excreted in expired air, and 1.2% remained in the carcass. Radioactivity was widely distributed throughout the tissues with higher concentrations in the liver and kidneys. A decrease in 14C tissue concentrations occurred from 48 to 96 h. The only radiolabeled compounds in the urine were HQ (1.1-8.6% of the dose), hydroquinone monosulfate (25-42%), and hydroquinone monoglucuronide (56-66%). Similar findings were observed for rats given HQ in the feed. There were no significant increases from controls for absolute or relative liver weights, liver microsomal protein concentrations, cytochrome b-5, cytochrome P-450 or cytochrome c reductase activity in rats dosed repeatedly with 200 mg/kg HQ. Cytochrome P-450 values were slightly but significantly decreased in rats dosed repeatedly with HQ compared with controls.

Current practice of antibiotic prophylaxis for surgical fixation of closed long bone fractures: a survey of 297 members of the Orthopaedic Trauma Association.

PubMed

Gans, Itai; Jain, Amit; Sirisreetreerux, Norachart; Haut, Elliott R; Hasenboehler, Erik A

2017-01-01

The risk of postoperative surgical site infection after long bone fracture fixation can be decreased with appropriate antibiotic use. However, there is no agreement on the superiority of a single- or multiple-dose perioperative regimen of antibiotic prophylaxis. The purpose of this study is to determine the following: 1) What are the current practice patterns of orthopaedic trauma surgeons in using perioperative antibiotics for closed long bone fractures? 2) What is the current knowledge of published antibiotic prophylaxis guidelines among orthopaedic trauma surgeons? 3) Are orthopaedic surgeons willing to change their current practices? A questionnaire was distributed via email between September and December 2015 to 955 Orthopaedic Trauma Association members, of whom 297 (31%) responded. Most surgeons (96%) use cefazolin as first-line infection prophylaxis. Fifty-nine percent used a multiple-dose antibiotic regimen, 39% used a single-dose regimen, and 2% varied this decision according to patient factors. Thirty-six percent said they were unfamiliar with Centers for Disease Control and Prevention (CDC) antibiotic prophylaxis guidelines; only 30% were able to select the correct CDC recommendation from a multiple-choice list. However, 44% of surgeons said they followed CDC recommendations. Fifty-six percent answered that a single-dose antibiotic prophylaxis regimen was not inferior to a multiple-dose regimen. If a level-I study comparing a single preoperative dose versus multiple perioperative antibiotic dosing regimen for treatment of closed long bone fractures were published, most respondents (64%) said they would fully follow these guidelines, and 22% said they would partially change their practice to follow these guidelines. There is heterogeneity in the use of single- versus multiple-dose antibiotic prophylaxis for surgical repair of closed long bone fractures. Many surgeons were unsure of current evidence-based recommendations regarding perioperative antibiotic use. Most respondents indicated they would be receptive to high-level evidence regarding the single- versus multiple-dose perioperative prophylactic antibiotics for the treatment of closed long bone fractures.

The application of a sparse, distributed memory to the detection, identification and manipulation of physical objects

NASA Technical Reports Server (NTRS)

Kanerva, P.

1986-01-01

To determine the relation of the sparse, distributed memory to other architectures, a broad review of the literature was made. The memory is called a pattern memory because they work with large patterns of features (high-dimensional vectors). A pattern is stored in a pattern memory by distributing it over a large number of storage elements and by superimposing it over other stored patterns. A pattern is retrieved by mathematical or statistical reconstruction from the distributed elements. Three pattern memories are discussed.

Correspondence model-based 4D VMAT dose simulation for analysis of local metastasis recurrence after extracranial SBRT

NASA Astrophysics Data System (ADS)

Sothmann, T.; Gauer, T.; Wilms, M.; Werner, R.

2017-12-01

The purpose of this study is to introduce a novel approach to incorporate patient-specific breathing variability information into 4D dose simulation of volumetric arc therapy (VMAT)-based stereotactic body radiotherapy (SBRT) of extracranial metastases. Feasibility of the approach is illustrated by application to treatment planning and motion data of lung and liver metastasis patients. The novel 4D dose simulation approach makes use of a regression-based correspondence model that allows representing patient motion variability by breathing signal-steered interpolation and extrapolation of deformable image registration motion fields. To predict the internal patient motion during treatment with only external breathing signal measurements being available, the patients’ internal motion information and external breathing signals acquired during 4D CT imaging were correlated. Combining the correspondence model, patient-specific breathing signal measurements during treatment and time-resolved information about dose delivery, reconstruction of a motion variability-affected dose becomes possible. As a proof of concept, the proposed approach is illustrated by a retrospective 4D simulation of VMAT-based SBRT treatment of ten patients with 15 treated lung and liver metastases and known clinical endpoints for the individual metastases (local metastasis recurrence yes/no). Resulting 4D-simulated dose distributions were compared to motion-affected dose distributions estimated by standard 4D CT-only dose accumulation and the originally (i.e. statically) planned dose distributions by means of GTV D98 indices (dose to 98% of the GTV volume). A potential linkage of metastasis-specific endpoints to differences between GTV D98 indices of planned and 4D-simulated dose distributions was analyzed.

Impact of treatment planning with deformable image registration on dose distribution for carbon-ion beam lung treatment using a fixed irradiation port and rotating couch.

PubMed

Kumagai, M; Mori, S; Yamamoto, N

2015-06-01

When using a fixed irradiation port, treatment couch rotation is necessary to increase beam angle selection. We evaluated dose variations associated with positional morphological changes to organs. We retrospectively chose the data sets of ten patients with lung cancer who underwent respiratory-gated CT at three different couch rotation angles (0°, 20° and -20°). The respective CT data sets are referred to as CT0, CT20 and CT-20. Three treatment plans were generated as follows: in Plan 1, all compensating bolus designs and dose distributions were calculated using CT0. To evaluate the rotation effect without considering morphology changes, in Plan 2, the compensating boli designed using CT0 were applied to the CT±20 images. Plan 3 involved compensating boli designed using the CT±20 images. The accumulated dose distributions were calculated using deformable image registration (DIR). A sufficient prescribed dose was calculated for the planning target volume (PTV) in Plan 1 [minimum dose received by a volume ≥95% (D95) > 95.8%]. By contrast, Plan 2 showed degraded dose conformation to the PTV (D95 > 90%) owing to mismatch of the bolus design to the morphological positional changes in the respective CT. The dose assessment results of Plan 3 were very close to those of Plan 1. Dose distribution is significantly affected by whether or not positional organ morphology changes are factored into dose planning. In treatment planning using multiple CT scans with different couch positions, it is mandatory to calculate the accumulated dose using DIR.

Inverse Planning Approach for 3-D MRI-Based Pulse-Dose Rate Intracavitary Brachytherapy in Cervix Cancer

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

Chajon, Enrique; Dumas, Isabelle; Touleimat, Mahmoud B.Sc.

2007-11-01

Purpose: The purpose of this study was to evaluate the inverse planning simulated annealing (IPSA) software for the optimization of dose distribution in patients with cervix carcinoma treated with MRI-based pulsed-dose rate intracavitary brachytherapy. Methods and Materials: Thirty patients treated with a technique using a customized vaginal mold were selected. Dose-volume parameters obtained using the IPSA method were compared with the classic manual optimization method (MOM). Target volumes and organs at risk were delineated according to the Gynecological Brachytherapy Group/European Society for Therapeutic Radiology and Oncology recommendations. Because the pulsed dose rate program was based on clinical experience with lowmore » dose rate, dwell time values were required to be as homogeneous as possible. To achieve this goal, different modifications of the IPSA program were applied. Results: The first dose distribution calculated by the IPSA algorithm proposed a heterogeneous distribution of dwell time positions. The mean D90, D100, and V100 calculated with both methods did not differ significantly when the constraints were applied. For the bladder, doses calculated at the ICRU reference point derived from the MOM differed significantly from the doses calculated by the IPSA method (mean, 58.4 vs. 55 Gy respectively; p = 0.0001). For the rectum, the doses calculated at the ICRU reference point were also significantly lower with the IPSA method. Conclusions: The inverse planning method provided fast and automatic solutions for the optimization of dose distribution. However, the straightforward use of IPSA generated significant heterogeneity in dwell time values. Caution is therefore recommended in the use of inverse optimization tools with clinical relevance study of new dosimetric rules.« 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

Development of an irradiation method with lateral modulation of SOBP width using a cone-type filter for carbon ion beams.

PubMed

Ishizaki, Azusa; Ishii, Keizo; Kanematsu, Nobuyuki; Kanai, Tatsuaki; Yonai, Shunsuke; Kase, Yuki; Takei, Yuka; Komori, Masataka

2009-06-01

Passive irradiation methods deliver an extra dose to normal tissues upstream of the target tumor, while in dynamic irradiation methods, interplay effects between dynamic beam delivery and target motion induced by breathing or respiration distort the dose distributions. To solve the problems of those two irradiation methods, the authors have developed a new method that laterally modulates the spread-out Bragg peak (SOBP) width. By reducing scanning in the depth direction, they expect to reduce the interplay effects. They have examined this new irradiation method experimentally. In this system, they used a cone-type filter that consisted of 400 cones in a grid of 20 cones by 20 cones. There were five kinds of cones with different SOBP widths arranged on the frame two dimensionally to realize lateral SOBP modulation. To reduce the number of steps of cones, they used a wheel-type filter to make minipeaks. The scanning intensity was modulated for each SOBP width with a pair of scanning magnets. In this experiment, a stepwise dose distribution and spherical dose distribution of 60 mm in diameter were formed. The nonflatness of the stepwise dose distribution was 5.7% and that of the spherical dose distribution was 3.8%. A 2 mm misalignment of the cone-type filter resulted in a nonflatness of more than 5%. Lateral SOBP modulation with a cone-type filter and a scanned carbon ion beam successfully formed conformal dose distribution with nonflatness of 3.8% for the spherical case. The cone-type filter had to be set to within 1 mm accuracy to maintain nonflatness within 5%. This method will be useful to treat targets moving during breathing and targets in proximity to important organs.

A measurement-based generalized source model for Monte Carlo dose simulations of CT scans

PubMed Central

Ming, Xin; Feng, Yuanming; Liu, Ransheng; Yang, Chengwen; Zhou, Li; Zhai, Hezheng; Deng, Jun

2018-01-01

The goal of this study is to develop a generalized source model (GSM) for accurate Monte Carlo dose simulations of CT scans based solely on the measurement data without a priori knowledge of scanner specifications. The proposed generalized source model consists of an extended circular source located at x-ray target level with its energy spectrum, source distribution and fluence distribution derived from a set of measurement data conveniently available in the clinic. Specifically, the central axis percent depth dose (PDD) curves measured in water and the cone output factors measured in air were used to derive the energy spectrum and the source distribution respectively with a Levenberg-Marquardt algorithm. The in-air film measurement of fan-beam dose profiles at fixed gantry was back-projected to generate the fluence distribution of the source model. A benchmarked Monte Carlo user code was used to simulate the dose distributions in water with the developed source model as beam input. The feasibility and accuracy of the proposed source model was tested on a GE LightSpeed and a Philips Brilliance Big Bore multi-detector CT (MDCT) scanners available in our clinic. In general, the Monte Carlo simulations of the PDDs in water and dose profiles along lateral and longitudinal directions agreed with the measurements within 4%/1mm for both CT scanners. The absolute dose comparison using two CTDI phantoms (16 cm and 32 cm in diameters) indicated a better than 5% agreement between the Monte Carlo-simulated and the ion chamber-measured doses at a variety of locations for the two scanners. Overall, this study demonstrated that a generalized source model can be constructed based only on a set of measurement data and used for accurate Monte Carlo dose simulations of patients’ CT scans, which would facilitate patient-specific CT organ dose estimation and cancer risk management in the diagnostic and therapeutic radiology. PMID:28079526

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

A measurement-based generalized source model for Monte Carlo dose simulations of CT scans

NASA Astrophysics Data System (ADS)

Ming, Xin; Feng, Yuanming; Liu, Ransheng; Yang, Chengwen; Zhou, Li; Zhai, Hezheng; Deng, Jun

2017-03-01

The goal of this study is to develop a generalized source model for accurate Monte Carlo dose simulations of CT scans based solely on the measurement data without a priori knowledge of scanner specifications. The proposed generalized source model consists of an extended circular source located at x-ray target level with its energy spectrum, source distribution and fluence distribution derived from a set of measurement data conveniently available in the clinic. Specifically, the central axis percent depth dose (PDD) curves measured in water and the cone output factors measured in air were used to derive the energy spectrum and the source distribution respectively with a Levenberg-Marquardt algorithm. The in-air film measurement of fan-beam dose profiles at fixed gantry was back-projected to generate the fluence distribution of the source model. A benchmarked Monte Carlo user code was used to simulate the dose distributions in water with the developed source model as beam input. The feasibility and accuracy of the proposed source model was tested on a GE LightSpeed and a Philips Brilliance Big Bore multi-detector CT (MDCT) scanners available in our clinic. In general, the Monte Carlo simulations of the PDDs in water and dose profiles along lateral and longitudinal directions agreed with the measurements within 4%/1 mm for both CT scanners. The absolute dose comparison using two CTDI phantoms (16 cm and 32 cm in diameters) indicated a better than 5% agreement between the Monte Carlo-simulated and the ion chamber-measured doses at a variety of locations for the two scanners. Overall, this study demonstrated that a generalized source model can be constructed based only on a set of measurement data and used for accurate Monte Carlo dose simulations of patients’ CT scans, which would facilitate patient-specific CT organ dose estimation and cancer risk management in the diagnostic and therapeutic radiology.

Measurement of the secondary neutron dose distribution from the LET spectrum of recoils using the CR-39 plastic nuclear track detector in 10 MV X-ray medical radiation fields

NASA Astrophysics Data System (ADS)

Fujibuchi, Toshioh; Kodaira, Satoshi; Sawaguchi, Fumiya; Abe, Yasuyuki; Obara, Satoshi; Yamaguchi, Masae; Kawashima, Hajime; Kitamura, Hisashi; Kurano, Mieko; Uchihori, Yukio; Yasuda, Nakahiro; Koguchi, Yasuhiro; Nakajima, Masaru; Kitamura, Nozomi; Sato, Tomoharu

2015-04-01

We measured the recoil charged particles from secondary neutrons produced by the photonuclear reaction in a water phantom from a 10-MV photon beam from medical linacs. The absorbed dose and the dose equivalent were evaluated from the linear energy transfer (LET) spectrum of recoils using the CR-39 plastic nuclear track detector (PNTD) based on well-established methods in the field of space radiation dosimetry. The contributions and spatial distributions of these in the phantom on nominal photon exposures were verified as the secondary neutron dose and neutron dose equivalent. The neutron dose equivalent normalized to the photon-absorbed dose was 0.261 mSv/100 MU at source to chamber distance 90 cm. The dose equivalent at the surface gave the highest value, and was attenuated to less than 10% at 5 cm from the surface. The dose contribution of the high LET component of ⩾100 keV/μm increased with the depth in water, resulting in an increase of the quality factor. The CR-39 PNTD is a powerful tool that can be used to systematically measure secondary neutron dose distributions in a water phantom from an in-field to out-of-field high-intensity photon beam.

Estimation Of Organ Doses From Solar Particle Events For Future Space Exploration Missions

NASA Technical Reports Server (NTRS)

Kim, Myung-Hee; Cucinotta, Francis A.

2006-01-01

Radiation protection practices define the effective dose as a weighted sum of equivalent dose over major organ sites for radiation cancer risks. Since a crew personnel dosimeter does not make direct measurement of the effective dose, it has been estimated with skin-dose measurements and radiation transport codes for ISS and STS missions. If sufficient protection is not provided near solar maximum, the radiation risk can be significant due to exposure to sporadic solar particle events (SPEs) as well as to the continuous galactic cosmic radiation (GCR) on future exploratory-class and long-duration missions. For accurate estimates of overall fatal cancer risks from SPEs, the specific doses at various blood forming organs (BFOs) were considered, because proton fluences and doses vary considerably across marrow regions. Previous estimates of BFO doses from SPEs have used an average body-shielding distribution for the bone marrow based on the computerized anatomical man model (CAM). With the development of an 82-point body-shielding distribution at BFOs, the mean and variance of SPE doses in the major active marrow regions (head and neck, chest, abdomen, pelvis and thighs) will be presented. Consideration of the detailed distribution of bone marrow sites is one of many requirements to improve the estimation of effective doses for radiation cancer risks.

Analytical modeling of relative luminescence efficiency of Al2O3:C optically stimulated luminescence detectors exposed to high-energy heavy charged particles.

PubMed

Sawakuchi, Gabriel O; Yukihara, Eduardo G

2012-01-21

The objective of this work is to test analytical models to calculate the luminescence efficiency of Al(2)O(3):C optically stimulated luminescence detectors (OSLDs) exposed to heavy charged particles with energies relevant to space dosimetry and particle therapy. We used the track structure model to obtain an analytical expression for the relative luminescence efficiency based on the average radial dose distribution produced by the heavy charged particle. We compared the relative luminescence efficiency calculated using seven different radial dose distribution models, including a modified model introduced in this work, with experimental data. The results obtained using the modified radial dose distribution function agreed within 20% with experimental data from Al(2)O(3):C OSLDs relative luminescence efficiency for particles with atomic number ranging from 1 to 54 and linear energy transfer in water from 0.2 up to 1368 keV µm(-1). In spite of the significant improvement over other radial dose distribution models, understanding of the underlying physical processes associated with these radial dose distribution models remain elusive and may represent a limitation of the track structure model.

Enhancement of Structured Reporting - an Integration Reporting Module with Radiation Dose Collection Supporting.

PubMed

Lee, Ming-Che; Chuang, Kei-Shih; Hsu, Tien-Cheng; Lee, Chien-Ding

2016-11-01

Collection of radiation dose derived from radiological examination is necessary not only for radiation protection, but also for fulfillment of structured reports. However, the material regarding of radiation dose cannot be directly utilized by the Radiological Information System (RIS) since it is generated and only stored in the Picture Archiving and Communication System (PACS). In this paper, an integration reporting module is proposed to facilitate handling of dose information and structured reporting by providing two functionalities. First, a gateway is established to automatically collect the related information from PACS for further analyzing and monitoring the accumulated radiation. Second, the designated structured reporting patterns with corresponding radiation dose measurements can be acquired by radiologists as necessary. In the design, the radiation dose collection gateway and the well-established pattern are collocated to achieve that there is no need to do manual entry for structured reporting, thus increasing productivity and medical quality.

SU-E-T-541: Bolus Effect of Thermoplastic Masks in IMRT and VMAT Head and Neck Treatments

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

Zhen, H; Nedzi, L; Chen, S

2014-06-01

Purpose: To quantitatively evaluate the bolus effect of thermoplalstic mask on patient skin dose during multi-field IMRT and VMAT treatment. Methods: The clinically approved target contours for five head and neck patients were deformably registered to an anthropomorphic Rando phantom. Two plans: Multifield IMRT plan with 7-9 beams and VMAT plan with 2-4 arcs were created for each patient following same dose constraints. 3mm skin was excluded from PTVs but not constrained during optimization. The prescription dose was 200-220 cGy/fraction. A thermoplastic head and shoulder mask was customized for the Rando phantom. Each plan was delivered to the phantom twicemore » with and without mask. During each delivery, two rectangular strips of EBT3 films (1cm x 6.8cm) were placed across the anterior upper and lower neck near PTVs to measure the surface dose. For consistency films were positioned at same locations for same patient. A total of 8 film strips were obtained for each patient. Film dose was calibrated in the range of 0-400cGy on the day of plan delivery. For dose comparison 3 regions of interests (ROIs) of 1×1 cm{sup 2} were selected at left, right and middle part of each film, resulting in 6 point doses at each plan delivery. Results: The films without mask show relatively uniform dose distribution while those with mask clearly show mesh pattern of mask, usually indicating an increase in skin dose. On average the increase in skin dose over all ROIs with mask was 31.9%(±14.8%) with a range of 11.4%- 58.4%. There is no statistically significant difference (p=0.44) between skin dose increase in VMAT (30.8%±15.3%) and IMRT delivery (33.0%±14.9%). Conclusion: Thermoplastic immobilization masks increase surface dose for HN patient by around 30%. The magnitude is comparable between multi-field IMRT and VMAT. Radiochromic EBT3 film serves as an effective tool to quantify bolus effect.« less

Flexible meal-related dosing with repaglinide facilitates glycemic control in therapy-naive type 2 diabetes.

PubMed

Moses, R G; Gomis, R; Frandsen, K B; Schlienger, J L; Dedov, I

2001-01-01

This double-blind randomized placebo-controlled parallel group study assessed the efficacy and safety (with particular regard to body weight and hypoglycemia) of repaglinide when used in a flexible mealtime dosing regimen in a situation close to everyday clinical practice. A total of 408 patients with type 2 diabetes considered poorly controlled by diet, but without a history of previous antidiabetic medication, were randomized to receive 0.5 mg repaglinide at mealtimes (increased to 1 mg after 4 weeks depending on blood glucose response) or placebo for 16 weeks. Patients were free to choose a flexible meal pattern, adjusting the dosing schedule from two to four preprandial doses per day in accordance with a "one meal, one dose; no meal, no dose" principle. Additional snacks were not a requirement of the treatment schedule. Treatment with repaglinide significantly improved glycemic control with respect to baseline and placebo, reducing HbA1c by 1.14% from baseline and fasting plasma glucose by 1.8 mmol/l. Improvement in glycemic control was independent of the meal pattern adopted by patients, including those most commonly taking two or four meals daily, with no correlation between meal pattern and risk of hypoglycemia. The improvement in glycemic control was also independent of degree of obesity and age < or =65 or >65 years. There was no significant body weight increase in the repaglinide group. Mealtime dosing with repaglinide is effective in improving overall glycemic control in type 2 diabetic patients for which control is suboptimal using diet alone. Patients are able to vary their meal pattern from a conventional regimen of three meals daily without compromising control or increasing the risk of adverse events.

Inherent and environmental patterns in biomass allocation and allometry among higher plants

NASA Astrophysics Data System (ADS)

Poorter, Hendrik

2017-04-01

It is well-known that plants may adjust the distribution of biomass over leaves, stems and roots depending on environmental conditions. It is also clear that size is an important factor as well. However, good quantitative insights are lacking. In this talk I analyse biomass allocation patterns to leaves, stems and roots of herbs and woody species. A database was compiled with 11.000 records of leaf, stem and root biomass for 1200 species. First, I'll derive general dose-response curves that describe the relationship between biomass allocation and the 12 most important a-biotic environmental factors and compare them with the changes in leaf, stem and root morphology. Second, I'll focus on allometric relationships between the various organs and test to what extent they comply with models like that for Metabolic Scaling Theory, where the slope of the log-log relationship between leaf and root biomass is expected to have a value of ¾. Third, I analyse how leaf, stem and root mass fractions change as a function of total plant size. This offers a great opportunity to test to what extent there are systematic differences in allocation patterns related to phylogeny (e.g. Gymnosperms vs. Angiosperms, grasses vs. herbaceous dicots) and functional group (e.g. deciduous vs. evergreens). Poorter et al. (2012) Biomass allocation to leaves, stems and roots: meta-analyses of interspecific variation and environmental control. New Phytol. 193: 30-50. Poorter & Sack (2012) Pitfalls and possibilities in the analysis of biomass allocation patterns in plants. Front. Plant Sci. 3: 259. Poorter et al. (2015) How does biomass distribution change with size and differ among species? New Phytol. 208: 736-749

Dose rate estimation around a 60Co gamma-ray irradiation source by means of 115mIn photoactivation.

PubMed

Murataka, Ayanori; Endo, Satoru; Kojima, Yasuaki; Shizuma, Kiyoshi

2010-01-01

Photoactivation of nuclear isomer (115m)In with a halflife of 4.48 h occurs by (60)Co gamma-ray irradiation. This is because the resonance gamma-ray absorption occurs at 1078 keV level for stable (115)In, and that energy gamma-rays are produced by Compton scattering of (60)Co primary gamma-rays. In this work, photoactivation of (115m)In was applied to estimate the dose rate distribution around a (60)Co irradiation source utilizing a standard dose rate taken by alanine dosimeter. The (115m)In photoactivation was measured at 10 to 160 cm from the (60)Co source. The derived dose rate distribution shows a good agreement with both alanine dosimeter data and Monte Carlo simulation. It is found that angular distribution of the dose rate along a circumference at radius 2.8 cm from the central axis shows +/- 10% periodical variation reflecting the radioactive strength of the source rods, but less periodic distribution at radius 10 and 20 cm. The (115m)In photoactivation along the vertical direction in the central irradiation port strongly depends on the height and radius as indicated by Monte Carlo simulation. It is demonstrated that (115m)In photoactivation is a convenient method to estimate the dose rate distribution around a (60)Co source.

SU-F-19A-05: Experimental and Monte Carlo Characterization of the 1 Cm CivaString 103Pd Brachytherapy Source

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

Reed, J; Micka, J; Culberson, W

Purpose: To determine the in-air azimuthal anisotropy and in-water dose distribution for the 1 cm length of the CivaString {sup 103}Pd brachytherapy source through measurements and Monte Carlo (MC) simulations. American Association of Physicists in Medicine Task Group No. 43 (TG-43) dosimetry parameters were also determined for this source. Methods: The in-air azimuthal anisotropy of the source was measured with a NaI scintillation detector and simulated with the MCNP5 radiation transport code. Measured and simulated results were normalized to their respective mean values and compared. The TG-43 dose-rate constant, line-source radial dose function, and 2D anisotropy function for this sourcemore » were determined from LiF:Mg,Ti thermoluminescent dosimeter (TLD) measurements and MC simulations. The impact of {sup 103}Pd well-loading variability on the in-water dose distribution was investigated using MC simulations by comparing the dose distribution for a source model with four wells of equal strength to that for a source model with strengths increased by 1% for two of the four wells. Results: NaI scintillation detector measurements and MC simulations of the in-air azimuthal anisotropy showed that ≥95% of the normalized data were within 1.2% of the mean value. TLD measurements and MC simulations of the TG-43 dose-rate constant, line-source radial dose function, and 2D anisotropy function agreed to within the experimental TLD uncertainties (k=2). MC simulations showed that a 1% variability in {sup 103}Pd well-loading resulted in changes of <0.1%, <0.1%, and <0.3% in the TG-43 dose-rate constant, radial dose distribution, and polar dose distribution, respectively. Conclusion: The CivaString source has a high degree of azimuthal symmetry as indicated by the NaI scintillation detector measurements and MC simulations of the in-air azimuthal anisotropy. TG-43 dosimetry parameters for this source were determined from TLD measurements and MC simulations. {sup 103}Pd well-loading variability results in minimal variations in the in-water dose distribution according to MC simulations. This work was partially supported by CivaTech Oncology, Inc. through an educational grant for Joshua Reed, John Micka, Wesley Culberson, and Larry DeWerd and through research support for Mark Rivard.« less

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

Li, Xinhua; Zhang, Da; Liu, Bob, E-mail: bliu7@mgh.harvard.edu

Purpose: The knowledge of longitudinal dose distribution provides the most direct view of the accumulated dose in computed tomography (CT) scanning. The purpose of this work was to perform a comprehensive study of dose distribution width and energy absorption with a wide range of subject sizes and beam irradiated lengths. Methods: Cumulative dose distribution along the z-axis was calculated based on the previously published CT dose equilibration data by Li, Zhang, and Liu [Med. Phys. 40, 031903 (10pp.) (2013)] and a mechanism for computing dose on axial lines by Li, Zhang, and Liu [Med. Phys. 39, 5347–5352 (2012)]. Full widthmore » at half maximum (FWHM), full width at tenth maximum (FWTM), the total energy (E) absorbed in a small cylinder of unit mass per centimeter square about the central or peripheral axis, and the energy (E{sub in}) absorbed inside irradiated length (L) were subsequently extracted from the dose distribution. Results: Extensive results of FWHM, FWTM, and E{sub in}/E were presented on the central and peripheral axes of infinitely long PMMA (diameters 6–50 cm) and water (diameters 6–55 cm) cylinders with L < 100 cm. FWHM was greater than the primary beam width only on the central axes of large phantoms and also with L ranging from a few centimeter to about 33 cm. FWTM generally increased with phantom diameter, and could be up to 32 cm longer than irradiated length, depending on L, phantom diameter and axis, but was insensitive to phantom material (PMMA or water). E{sub in}/E increased with L and asymptotically approached unity for large L. As phantom diameter increased, E{sub in}/E generally decreased, but asymptotically approached constant levels on the peripheral axes of large phantoms. A heuristic explanation of dose distribution width results was presented. Conclusions: This study enables the reader to gain a comprehensive view of dose distribution width and energy absorption and provides useful data for estimating doses to organs inside or beyond the irradiated region. The dose length product (DLP) presented by CT scanners is equal to neither E nor E{sub in}. Both E and E{sub in} can be evaluated using the equations and results presented in this paper and are robust with both constant and variable tube current scanning techniques.« less

Systematic evaluation of four-dimensional hybrid depth scanning for carbon-ion lung therapy

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

Mori, Shinichiro; Furukawa, Takuji; Inaniwa, Taku

2013-03-15

Purpose: Irradiation of a moving target with a scanning beam requires a comprehensive understanding of organ motion as well as a robust dose error mitigation technique. The authors studied the effects of intrafractional respiratory motion for carbon-ion pencil beam scanning with phase-controlled rescanning on dose distributions for lung tumors. To address density variations, they used 4DCT data. Methods: Dose distributions for various rescanning methods, such as simple layer rescanning (LR), volumetric rescanning, and phase-controlled rescanning (PCR), were calculated for a lung phantom and a lung patient studies. To ensure realism, they set the scanning parameters such as scanning velocity andmore » energy variation time to be similar to those used at our institution. Evaluation metrics were determined with regard to clinical relevance, and consisted of (i) phase-controlled rescanning, (ii) sweep direction, (iii) target motion (direction and amplitude), (iv) respiratory cycle, and (v) prescribed dose. Spot weight maps were calculated by using a beam field-specific target volume, which takes account of range variations for respective respiratory phases. To emphasize the impact of intrafractional motion on the dose distribution, respiratory gating was not used. The accumulated dose was calculated by applying a B-spline-based deformable image registration, and the results for phase-controlled layered rescanning (PCR{sub L}) and phase-controlled volumetric rescanning (PCR{sub V}) were compared. Results: For the phantom study, simple LR was unable to improve the dose distributions for an increased number of rescannings. The phase-controlled technique without rescanning (1 Multiplication-Sign PCR{sub L} and 1 Multiplication-Sign PCR{sub V}) degraded dose conformity significantly due to a reduced scan velocity. In contrast, 4 Multiplication-Sign PCR{sub L} or more significantly and consistently improved dose distribution. PCR{sub V} showed interference effects, but in general also improved dose homogeneity with higher numbers of rescannings. Dose distributions with single PCR{sub L}/PCR{sub V} with a sweep direction perpendicular to motion direction showed large hot/cold spots; however, this effect vanished with higher numbers of rescannings for both methods. Similar observations were obtained for the other dose metrics, such as target motion (SI/AP), amplitude (6-22 mm peak-to-peak) and respiratory period (3.0-5.0 s). For four or more rescannings, both methods showed significantly better results, albeit that volumetric PCR was more affected by interference effects, which lead to severe degradation of a few dose distributions. The clinical example showed the same tendencies as the phantom study. Dose assessment metrics (D95, Dmax/Dmin, homogeneity index) were improved with an increasing number of PCR{sub L}/PCR{sub V}, but with PCR{sub L} being more robust. Conclusions: PCR{sub L} requires a longer treatment time than PCR{sub V} for high numbers of rescannings in the NIRS scanning system but is more robust. Although four or more rescans provided good dose homogeneity and conformity, the authors prefer to use more rescannings for clinical cases to further minimize dose degradation effects due to organ motion.« less

SU-E-T-50: Automatic Validation of Megavoltage Beams Modeled for Clinical Use in Radiation Therapy

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

Melchior, M; Salinas Aranda, F; 21st Century Oncology, Ft. Myers, FL

2014-06-01

Purpose: To automatically validate megavoltage beams modeled in XiO™ 4.50 (Elekta, Stockholm, Sweden) and Varian Eclipse™ Treatment Planning Systems (TPS) (Varian Associates, Palo Alto, CA, USA), reducing validation time before beam-on for clinical use. Methods: A software application that can automatically read and analyze DICOM RT Dose and W2CAD files was developed using MatLab integrated development environment.TPS calculated dose distributions, in DICOM RT Dose format, and dose values measured in different Varian Clinac beams, in W2CAD format, were compared. Experimental beam data used were those acquired for beam commissioning, collected on a water phantom with a 2D automatic beam scanningmore » system.Two methods were chosen to evaluate dose distributions fitting: gamma analysis and point tests described in Appendix E of IAEA TECDOC-1583. Depth dose curves and beam profiles were evaluated for both open and wedged beams. Tolerance parameters chosen for gamma analysis are 3% and 3 mm dose and distance, respectively.Absolute dose was measured independently at points proposed in Appendix E of TECDOC-1583 to validate software results. Results: TPS calculated depth dose distributions agree with measured beam data under fixed precision values at all depths analyzed. Measured beam dose profiles match TPS calculated doses with high accuracy in both open and wedged beams. Depth and profile dose distributions fitting analysis show gamma values < 1. Relative errors at points proposed in Appendix E of TECDOC-1583 meet therein recommended tolerances.Independent absolute dose measurements at points proposed in Appendix E of TECDOC-1583 confirm software results. Conclusion: Automatic validation of megavoltage beams modeled for their use in the clinic was accomplished. The software tool developed proved efficient, giving users a convenient and reliable environment to decide whether to accept or not a beam model for clinical use. Validation time before beam-on for clinical use was reduced to a few hours.« less

Monte Carlo MCNP-4B-based absorbed dose distribution estimates for patient-specific dosimetry.

PubMed

Yoriyaz, H; Stabin, M G; dos Santos, A

2001-04-01

This study was intended to verify the capability of the Monte Carlo MCNP-4B code to evaluate spatial dose distribution based on information gathered from CT or SPECT. A new three-dimensional (3D) dose calculation approach for internal emitter use in radioimmunotherapy (RIT) was developed using the Monte Carlo MCNP-4B code as the photon and electron transport engine. It was shown that the MCNP-4B computer code can be used with voxel-based anatomic and physiologic data to provide 3D dose distributions. This study showed that the MCNP-4B code can be used to develop a treatment planning system that will provide such information in a time manner, if dose reporting is suitably optimized. If each organ is divided into small regions where the average energy deposition is calculated with a typical volume of 0.4 cm(3), regional dose distributions can be provided with reasonable central processing unit times (on the order of 12-24 h on a 200-MHz personal computer or modest workstation). Further efforts to provide semiautomated region identification (segmentation) and improvement of marrow dose calculations are needed to supply a complete system for RIT. It is envisioned that all such efforts will continue to develop and that internal dose calculations may soon be brought to a similar level of accuracy, detail, and robustness as is commonly expected in external dose treatment planning. For this study we developed a code with a user-friendly interface that works on several nuclear medicine imaging platforms and provides timely patient-specific dose information to the physician and medical physicist. Future therapy with internal emitters should use a 3D dose calculation approach, which represents a significant advance over dose information provided by the standard geometric phantoms used for more than 20 y (which permit reporting of only average organ doses for certain standardized individuals)

Dosimetric characterizations of GZP6 60Co high dose rate brachytherapy sources: application of superimposition method

PubMed Central

Bahreyni Toossi, Mohammad Taghi; Ghorbani, Mahdi; Mowlavi, Ali Asghar; Meigooni, Ali Soleimani

2012-01-01

Background Dosimetric characteristics of a high dose rate (HDR) GZP6 Co-60 brachytherapy source have been evaluated following American Association of Physicists in MedicineTask Group 43U1 (AAPM TG-43U1) recommendations for their clinical applications. Materials and methods MCNP-4C and MCNPX Monte Carlo codes were utilized to calculate dose rate constant, two dimensional (2D) dose distribution, radial dose function and 2D anisotropy function of the source. These parameters of this source are compared with the available data for Ralstron 60Co and microSelectron192Ir sources. Besides, a superimposition method was developed to extend the obtained results for the GZP6 source No. 3 to other GZP6 sources. Results The simulated value for dose rate constant for GZP6 source was 1.104±0.03 cGyh-1U-1. The graphical and tabulated radial dose function and 2D anisotropy function of this source are presented here. The results of these investigations show that the dosimetric parameters of GZP6 source are comparable to those for the Ralstron source. While dose rate constant for the two 60Co sources are similar to that for the microSelectron192Ir source, there are differences between radial dose function and anisotropy functions. Radial dose function of the 192Ir source is less steep than both 60Co source models. In addition, the 60Co sources are showing more isotropic dose distribution than the 192Ir source. Conclusions The superimposition method is applicable to produce dose distributions for other source arrangements from the dose distribution of a single source. The calculated dosimetric quantities of this new source can be introduced as input data to the GZP6 treatment planning system (TPS) and to validate the performance of the TPS. PMID:23077455

Identification of Morphological Character and Esterase Isozyme Pattern in Second-Generation Black Rice Plant Irradiated to Gamma Rays

NASA Astrophysics Data System (ADS)

Hartanti, R. S.; Putri, T. A. N.; Zulfa, F.; Sutarno; Suranto

2017-04-01

Black rice is one of the functional foods due to its high anthocyanin content. Black rice grain was irradiated by gamma rays with a dose of 200 Gy and 300 Gy. The main purpose of this irradiation is to induce mutation to the black rice plant in order to achieve the improved organism. This study was undertaken to elucidate the morphological character and esterase isozyme pattern of black rice plant after irradiated by gamma rays. There were morphological differences on leaves, stems and grains between irradiated and non irradiated black rice plant. Gamma radiation dose of 200 Gy showed the significant influence of the length of the stem, number of internodes, and length of leaves. The radiation dose of 300 Gy showed the significant influence of the decrease value of diameter of 3rd internodes, number of branches and width of leaves. Flowering time is getting faster as increasing radiation dose. At the age of 74 days after planting there are 9.15% plants of 200 Gy radiation dose that have flowered faster than normal plants. This value increased into 11.45% at the dose of radiation 300 Gy. There were differences in the esterase banding pattern between radiation dose of 200 Gy and 300 Gy than the control plants, indicated that randomly mutation has occurred.

Methamphetamine blood concentrations in human abusers: application to pharmacokinetic modeling.

PubMed

Melega, William P; Cho, Arthur K; Harvey, Dennis; Laćan, Goran

2007-04-01

Characterization of methamphetamine's (METH) dose-dependent effects on brain neurochemistry may represent a critical component for better understanding the range of resultant behavioral pathologies. Most human studies, however, have assessed only the effects of long term, high dose METH abuse (e.g., greater than 1000 mg/day) in individuals meeting DSM-IV criteria for METH dependence. Yet, for the majority of METH abusers, their patterns of METH exposure that consist of lower doses remain less well-characterized. In this study, blood samples were obtained from 105 individuals detained by police for possible criminal activity and testing positive for stimulants by EMIT assay. METH blood concentrations were subsequently quantified by GC-MS and were predominantly in the low micromolar range (0.1-11.1 microM), with median and mean values of 1.3 microM (0.19 mg/l) and 2 microM (0.3 mg/l), respectively. Pharmacokinetic calculations based on these measured values were used to estimate initial METH body burdens, the median value being 52 mg. Modeling a 52 mg dose for a 4 day-METH maintenance exposure pattern of 4 doses/day at 4 h intervals showed that blood concentrations remained between 1 and 4 microM during this period. Collectively, these data present evidence for a METH exposure pattern distinct from high dose-METH abuse and provide the rationale for assessing potential brain pathology associated with such lower dose-METH exposure.

A Comparison of Four Indices for Combining Distance and Dose Differences

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

Thomas, Simon J., E-mail: simon.thomas@addenbrookes.nhs.uk; Cowley, Ian R.

2012-04-01

Purpose: When one is comparing two dose distributions, a number of methods have been published to combine dose difference and distance to agreement into a single measure. Some have been defined as pass/fail indices and some as numeric indices. We show that the pass/fail indices can all be used to derive numeric indices, and we compare the results of using these indices to evaluate one-dimensional (1D) and three-dimensional (3D) dose distributions, with the aim of selecting the most appropriate index for use in different circumstances. Methods and Materials: The indices compared are the gamma index, the kappa index, the indexmore » in International Commission on Radiation Units and Measurements Report 83, and a box index. Comparisons are made for 1D and 3D distributions. The 1D distribution is chosen to have a variety of dose gradients. The 3D distribution is taken from a clinical treatment plan. The effect of offsetting distributions by known distances and doses is studied. Results: The International Commission on Radiation Units and Measurements Report 83 index causes large discontinuities unless the dose gradient cutoff is set to equal the ratio of the dose tolerance to the distance tolerance. If it is so set, it returns identical results to the kappa index. Where the gradient is very high or very low, all the indices studied in this article give similar results for the same tolerance values. For moderate gradients, they differ, with the box index being the least strict, followed by the gamma index, and with the kappa index being the most strict. Conclusions: If the clinical tolerances are much greater than the uncertainties of the measuring system, the kappa index should be used, with tolerance values determined by the clinical tolerances. In cases where the uncertainties of the measuring system dominate, the box index will be best able to determine errors in the delivery system.« 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

SU-E-T-422: Fast Analytical Beamlet Optimization for Volumetric Intensity-Modulated Arc Therapy

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

Chan, Kenny S K; Lee, Louis K Y; Xing, L

2015-06-15

Purpose: To implement a fast optimization algorithm on CPU/GPU heterogeneous computing platform and to obtain an optimal fluence for a given target dose distribution from the pre-calculated beamlets in an analytical approach. Methods: The 2D target dose distribution was modeled as an n-dimensional vector and estimated by a linear combination of independent basis vectors. The basis set was composed of the pre-calculated beamlet dose distributions at every 6 degrees of gantry angle and the cost function was set as the magnitude square of the vector difference between the target and the estimated dose distribution. The optimal weighting of the basis,more » which corresponds to the optimal fluence, was obtained analytically by the least square method. Those basis vectors with a positive weighting were selected for entering into the next level of optimization. Totally, 7 levels of optimization were implemented in the study.Ten head-and-neck and ten prostate carcinoma cases were selected for the study and mapped to a round water phantom with a diameter of 20cm. The Matlab computation was performed in a heterogeneous programming environment with Intel i7 CPU and NVIDIA Geforce 840M GPU. Results: In all selected cases, the estimated dose distribution was in a good agreement with the given target dose distribution and their correlation coefficients were found to be in the range of 0.9992 to 0.9997. Their root-mean-square error was monotonically decreasing and converging after 7 cycles of optimization. The computation took only about 10 seconds and the optimal fluence maps at each gantry angle throughout an arc were quickly obtained. Conclusion: An analytical approach is derived for finding the optimal fluence for a given target dose distribution and a fast optimization algorithm implemented on the CPU/GPU heterogeneous computing environment greatly reduces the optimization time.« less

Practical dose point-based methods to characterize dose distribution in a stationary elliptical body phantom for a cone-beam C-arm CT system

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

Choi, Jang-Hwan, E-mail: jhchoi21@stanford.edu; Constantin, Dragos; Ganguly, Arundhuti

2015-08-15

Purpose: To propose new dose point measurement-based metrics to characterize the dose distributions and the mean dose from a single partial rotation of an automatic exposure control-enabled, C-arm-based, wide cone angle computed tomography system over a stationary, large, body-shaped phantom. Methods: A small 0.6 cm{sup 3} ion chamber (IC) was used to measure the radiation dose in an elliptical body-shaped phantom made of tissue-equivalent material. The IC was placed at 23 well-distributed holes in the central and peripheral regions of the phantom and dose was recorded for six acquisition protocols with different combinations of minimum kVp (109 and 125 kVp)more » and z-collimator aperture (full: 22.2 cm; medium: 14.0 cm; small: 8.4 cm). Monte Carlo (MC) simulations were carried out to generate complete 2D dose distributions in the central plane (z = 0). The MC model was validated at the 23 dose points against IC experimental data. The planar dose distributions were then estimated using subsets of the point dose measurements using two proposed methods: (1) the proximity-based weighting method (method 1) and (2) the dose point surface fitting method (method 2). Twenty-eight different dose point distributions with six different point number cases (4, 5, 6, 7, 14, and 23 dose points) were evaluated to determine the optimal number of dose points and their placement in the phantom. The performances of the methods were determined by comparing their results with those of the validated MC simulations. The performances of the methods in the presence of measurement uncertainties were evaluated. Results: The 5-, 6-, and 7-point cases had differences below 2%, ranging from 1.0% to 1.7% for both methods, which is a performance comparable to that of the methods with a relatively large number of points, i.e., the 14- and 23-point cases. However, with the 4-point case, the performances of the two methods decreased sharply. Among the 4-, 5-, 6-, and 7-point cases, the 7-point case (1.0% [±0.6%] difference) and the 6-point case (0.7% [±0.6%] difference) performed best for method 1 and method 2, respectively. Moreover, method 2 demonstrated high-fidelity surface reconstruction with as few as 5 points, showing pixelwise absolute differences of 3.80 mGy (±0.32 mGy). Although the performance was shown to be sensitive to the phantom displacement from the isocenter, the performance changed by less than 2% for shifts up to 2 cm in the x- and y-axes in the central phantom plane. Conclusions: With as few as five points, method 1 and method 2 were able to compute the mean dose with reasonable accuracy, demonstrating differences of 1.7% (±1.2%) and 1.3% (±1.0%), respectively. A larger number of points do not necessarily guarantee better performance of the methods; optimal choice of point placement is necessary. The performance of the methods is sensitive to the alignment of the center of the body phantom relative to the isocenter. In body applications where dose distributions are important, method 2 is a better choice than method 1, as it reconstructs the dose surface with high fidelity, using as few as five points.« less

Dose-distance metric that predicts late rectal bleeding in patients receiving radical prostate external-beam radiotherapy

NASA Astrophysics Data System (ADS)

Lee, Richard; Chan, Elisa K.; Kosztyla, Robert; Liu, Mitchell; Moiseenko, Vitali

2012-12-01

The relationship between rectal dose distribution and the incidence of late rectal complications following external-beam radiotherapy has been previously studied using dose-volume histograms or dose-surface histograms. However, they do not account for the spatial dose distribution. This study proposes a metric based on both surface dose and distance that can predict the incidence of rectal bleeding in prostate cancer patients treated with radical radiotherapy. One hundred and forty-four patients treated with radical radiotherapy for prostate cancer were prospectively followed to record the incidence of grade ≥2 rectal bleeding. Radiotherapy plans were used to evaluate a dose-distance metric that accounts for the dose and its spatial distribution on the rectal surface, characterized by a logistic weighting function with slope a and inflection point d0. This was compared to the effective dose obtained from dose-surface histograms, characterized by the parameter n which describes sensitivity to hot spots. The log-rank test was used to determine statistically significant (p < 0.05) cut-off values for the dose-distance metric and effective dose that predict for the occurrence of rectal bleeding. For the dose-distance metric, only d0 = 25 and 30 mm combined with a > 5 led to statistical significant cut-offs. For the effective dose metric, only values of n in the range 0.07-0.35 led to statistically significant cut-offs. The proposed dose-distance metric is a predictor of rectal bleeding in prostate cancer patients treated with radiotherapy. Both the dose-distance metric and the effective dose metric indicate that the incidence of grade ≥2 rectal bleeding is sensitive to localized damage to the rectal surface.

The dose distribution of low dose rate Cs-137 in intracavitary brachytherapy: comparison of Monte Carlo simulation, treatment planning calculation and polymer gel measurement

NASA Astrophysics Data System (ADS)

Fragoso, M.; Love, P. A.; Verhaegen, F.; Nalder, C.; Bidmead, A. M.; Leach, M.; Webb, S.

2004-12-01

In this study, the dose distribution delivered by low dose rate Cs-137 brachytherapy sources was investigated using Monte Carlo (MC) techniques and polymer gel dosimetry. The results obtained were compared with a commercial treatment planning system (TPS). The 20 mm and the 30 mm diameter Selectron vaginal applicator set (Nucletron) were used for this study. A homogeneous and a heterogeneous—with an air cavity—polymer gel phantom was used to measure the dose distribution from these sources. The same geometrical set-up was used for the MC calculations. Beyond the applicator tip, differences in dose as large as 20% were found between the MC and TPS. This is attributed to the presence of stainless steel in the applicator and source set, which are not considered by the TPS calculations. Beyond the air cavity, differences in dose of around 5% were noted, due to the TPS assuming a homogeneous water medium. The polymer gel results were in good agreement with the MC calculations for all the cases investigated.

Direct nano-patterning of graphene with helium ion beams

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

Naitou, Y., E-mail: yu-naitou@aist.go.jp; Iijima, T.; Ogawa, S.

2015-01-19

Helium ion microscopy (HIM) was used for direct nano-patterning of single-layer graphene (SLG) on SiO{sub 2}/Si substrates. This technique involves irradiation of the sample with accelerated helium ions (He{sup +}). Doses of 2.0 × 10{sup 16 }He{sup + }cm{sup −2} from a 30 kV beam induced a metal-insulator transition in the SLG. The resolution of HIM patterning on SLG was investigated by fabricating nanoribbons and nanostructures. Analysis of scanning capacitance microscopy measurements revealed that the spatial resolution of HIM patterning depended on the dosage of He{sup +} in a non-monotonic fashion. Increasing the dose from 2.0 × 10{sup 16} to 5.0 × 10{sup 16 }He{sup + }cm{sup −2} improved the spatialmore » resolution to several tens of nanometers. However, doses greater than 1.0 × 10{sup 17 }He{sup + }cm{sup −2} degraded the patterning characteristics. Direct patterning using HIM is a versatile approach to graphene fabrication and can be applied to graphene-based devices.« less

Precise and Arbitrary Deposition of Biomolecules onto Biomimetic Fibrous Matrices for Spatially Controlled Cell Distribution and Functions.

PubMed

Jia, Chao; Luo, Bowen; Wang, Haoyu; Bian, Yongqian; Li, Xueyong; Li, Shaohua; Wang, Hongjun

2017-09-01

Advances in nano-/microfabrication allow the fabrication of biomimetic substrates for various biomedical applications. In particular, it would be beneficial to control the distribution of cells and relevant biomolecules on an extracellular matrix (ECM)-like substrate with arbitrary micropatterns. In this regard, the possibilities of patterning biomolecules and cells on nanofibrous matrices are explored here by combining inkjet printing and electrospinning. Upon investigation of key parameters for patterning accuracy and reproducibility, three independent studies are performed to demonstrate the potential of this platform for: i) transforming growth factor (TGF)-β1-induced spatial differentiation of fibroblasts, ii) spatiotemporal interactions between breast cancer cells and stromal cells, and iii) cancer-regulated angiogenesis. The results show that TGF-β1 induces local fibroblast-to-myofibroblast differentiation in a dose-dependent fashion, and breast cancer clusters recruit activated stromal cells and guide the sprouting of endothelial cells in a spatially resolved manner. The established platform not only provides strategies to fabricate ECM-like interfaces for medical devices, but also offers the capability of spatially controlling cell organization for fundamental studies, and for high-throughput screening of various biomolecules for stem cell differentiation and cancer therapeutics. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Development of a facility for high-precision irradiation of cells with carbon ions.

PubMed

van Goethem, Marc-Jan; Niemantsverdriet, Maarten; Brandenburg, Sytze; Langendijk, Johannes A; Coppes, Robert P; van Luijk, Peter

2011-01-01

Compared to photons, using particle radiation in radiotherapy reduces the dose and irradiated volume of normal tissues, potentially reducing side effects. The biological effect of dose deposited by particles such as carbon ions, however, differs from that of dose deposited by photons. The inaccuracy in models to estimate the biological effects of particle radiation remains the most important source of uncertainties in particle therapy. Improving this requires high-precision studies on biological effects of particle radiation. Therefore, the authors aimed to develop a facility for reproducible and high-precision carbon-ion irradiation of cells in culture. The combined dose nonuniformity in the lateral and longitudinal direction should not exceed +/-1.5%. Dose to the cells from particles than other carbon ions should not exceed 5%. A uniform lateral dose distribution was realized using a single scatter foil and quadrupole magnets. A modulator wheel was used to create a uniform longitudinal dose distribution. The choice of beam energy and the optimal design of these components was determined using GEANT4 and SRIM Monte Carlo simulations. Verification of the uniformity of the dose distribution was performed using a scintillating screen (lateral) and a water phantom (longitudinal). The reproducibility of dose delivery between experiments was assessed by repeated measurements of the spatial dose distribution. Moreover, the reproducibility of dose-response measurements was tested by measuring the survival of irradiated HEK293 cells in three independent experiments. The relative contribution of dose from nuclear reaction fragments to the sample was found to be <5% when using 90 MeV/u carbon ions. This energy still allows accurate dosimetry conforming to the IAEA Report TRS-398, facilitating comparison to dose-effect data obtained with other radiation qualities. A 1.3 mm long spread-out Bragg peak with a diameter of 30 mm was created, allowing the irradiation of cell samples with the specified accuracy. Measurements of the transverse and longitudinal dose distribution showed that the dose variation over the sample volume was +/-0.8% and +/-0.7% in the lateral and longitudinal directions, respectively. The track-averaged LET of 132 +/- 10 keV/microm and dose-averaged LET of 189 +/- 15 keV/microm at the position of the sample were obtained from a GEANT4 simulation, which was validated experimentally. Three separately measured cell-survival curves yielded nearly identical results. With the new facility, high-precision carbon-ion irradiations of biological samples can be performed with highly reproducible results.

Scattered radiation from dental metallic crowns in head and neck radiotherapy.

PubMed

Shimozato, T; Igarashi, Y; Itoh, Y; Yamamoto, N; Okudaira, K; Tabushi, K; Obata, Y; Komori, M; Naganawa, S; Ueda, M

2011-09-07

We aimed to estimate the scattered radiation from dental metallic crowns during head and neck radiotherapy by irradiating a jaw phantom with external photon beams. The phantom was composed of a dental metallic plate and hydroxyapatite embedded in polymethyl methacrylate. We used radiochromic film measurement and Monte Carlo simulation to calculate the radiation dose and dose distribution inside the phantom. To estimate dose variations in scattered radiation under different clinical situations, we altered the incident energy, field size, plate thickness, plate depth and plate material. The simulation results indicated that the dose at the incident side of the metallic dental plate was approximately 140% of that without the plate. The differences between dose distributions calculated with the radiation treatment-planning system (TPS) algorithms and the data simulation, except around the dental metallic plate, were 3% for a 4 MV photon beam. Therefore, we should carefully consider the dose distribution around dental metallic crowns determined by a TPS.

Scattered radiation from dental metallic crowns in head and neck radiotherapy

NASA Astrophysics Data System (ADS)

Shimozato, T.; Igarashi, Y.; Itoh, Y.; Yamamoto, N.; Okudaira, K.; Tabushi, K.; Obata, Y.; Komori, M.; Naganawa, S.; Ueda, M.

2011-09-01

We aimed to estimate the scattered radiation from dental metallic crowns during head and neck radiotherapy by irradiating a jaw phantom with external photon beams. The phantom was composed of a dental metallic plate and hydroxyapatite embedded in polymethyl methacrylate. We used radiochromic film measurement and Monte Carlo simulation to calculate the radiation dose and dose distribution inside the phantom. To estimate dose variations in scattered radiation under different clinical situations, we altered the incident energy, field size, plate thickness, plate depth and plate material. The simulation results indicated that the dose at the incident side of the metallic dental plate was approximately 140% of that without the plate. The differences between dose distributions calculated with the radiation treatment-planning system (TPS) algorithms and the data simulation, except around the dental metallic plate, were 3% for a 4 MV photon beam. Therefore, we should carefully consider the dose distribution around dental metallic crowns determined by a TPS.

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

Experimental determination of particle range and dose distribution in thick targets through fragmentation reactions of stable heavy ions.

PubMed

Inaniwa, Taku; Kohno, Toshiyuki; Tomitani, Takehiro; Urakabe, Eriko; Sato, Shinji; Kanazawa, Mitsutaka; Kanai, Tatsuaki

2006-09-07

In radiation therapy with highly energetic heavy ions, the conformal irradiation of a tumour can be achieved by using their advantageous features such as the good dose localization and the high relative biological effectiveness around their mean range. For effective utilization of such properties, it is necessary to evaluate the range of incident ions and the deposited dose distribution in a patient's body. Several methods have been proposed to derive such physical quantities; one of them uses positron emitters generated through projectile fragmentation reactions of incident ions with target nuclei. We have proposed the application of the maximum likelihood estimation (MLE) method to a detected annihilation gamma-ray distribution for determination of the range of incident ions in a target and we have demonstrated the effectiveness of the method with computer simulations. In this paper, a water, a polyethylene and a polymethyl methacrylate target were each irradiated with stable (12)C, (14)N, (16)O and (20)Ne beams. Except for a few combinations of incident beams and targets, the MLE method could determine the range of incident ions R(MLE) with a difference between R(MLE) and the experimental range of less than 2.0 mm under the circumstance that the measurement of annihilation gamma rays was started just after the irradiation of 61.4 s and lasted for 500 s. In the process of evaluating the range of incident ions with the MLE method, we must calculate many physical quantities such as the fluence and the energy of both primary ions and fragments as a function of depth in a target. Consequently, by using them we can obtain the dose distribution. Thus, when the mean range of incident ions is determined with the MLE method, the annihilation gamma-ray distribution and the deposited dose distribution can be derived simultaneously. The derived dose distributions in water for the mono-energetic heavy-ion beams of four species were compared with those measured with an ionization chamber. The good agreement between the derived and the measured distributions implies that the deposited dose distribution in a target can be estimated from the detected annihilation gamma-ray distribution with a positron camera.

PRECLINICAL PHARMACOKINETIC ANALYSIS OF (E)-METHYL-4-ARYL-4-OXABUT-2-ENOATE, A NOVEL SER/THR PROTEIN KINASE B INIBITOR, IN RATS.

PubMed

Zhai, Qian-Qian; Pang, Jing; Li, Guo-Qing; Li, Cong-Ran; Wang, Yu-Cheng; Yu, Li-Yan; Li, Jian; YOUm, Xue-Fu

2017-01-01

(E)-Methyl-4-aryl-4-oxabut-2-enoate, designated YH-8, is a novel Serflhr protein kinase B (PknB) inhibitor, which is designed for the treatment of tuberculosis. The aim of this study was to investigate the pharmacokinetics, bioavailability, tissue distribution and excretion characteristics of YH-8 in rats and study its plasma protein binding in vitro. The pharmacokinetic properties were examined after intravenously injected YH-8 at 10 and 20 mg/kg and oral administrated YH-8 at 50, 100 and 200 mg/kg to rats. The concentrations of YH-8 in plasma were determined with LC-MS/MS, with a liquid-liquid extraction. The tissue distribution and urinary, fecal and -biliary excretion patterns of YH-8 were investigated following a single oral dosing of 100 mg/kg. The plasma protein binding rates of YH-8 were determined using ultra-filtration method. After intra- venous and oral administration, YH-8 showed dose-independent pharmacokinetic characteristics, with T(1/2) of approximately 5.5 h and 7.1 h, respectively. The oral absolute bioavailability of YH-8 was relatively low (about 12%). YH-8 was widely distributed in various tissues and showed substantial deposition in intestine, stomach, liver, lung and kidney. The drug was mainly eliminated via fecal excretion and its binding rate with plasma protein was concentration-dependent. In conclusion, this study as first provided the full pharmacokinetic characteristics of YH-8, which would be helpful for its further development and clinical application.

Interpretation of sucrose gradient sedimentation pattern of deoxyribonucleic acid fragments resulting from random breaks.

PubMed

Litwin, S; Shahn, E; Kozinski, A W

1969-07-01

Mass distribution in a sucrose gradient of deoxyribonucleic acid (DNA) fragments arising as a result of random breaks is predicted by analytical means from which computer evaluations are plotted. The analytical results are compared with the results of verifying experiments: (i) a Monte Carlo computer experiment in which simulated molecules of DNA were individuals of unit length subjected to random "breaks" applied by a random number generator, and (ii) an in vitro experiment in which molecules of T4 DNA, highly labeled with (32)P, were stored in liquid nitrogen for variable periods of time during which a precisely known number of (32)P atoms decayed, causing single-stranded breaks. The distribution of sizes of the resulting fragments was measured in an alkaline sucrose gradient. The profiles obtained in this fashion were compared with the mathematical predictions. Both experiments agree with the analytical approach and thus permit the use of the graphs obtained from the latter as a means of determining the average number of random breaks in DNA from distributions obtained experimentally in a sucrose gradient. An example of the application of this procedure to a previously unresolved problem is provided in the case of DNA from ultraviolet-irradiated phage which undergoes a dose-dependent intracellular breakdown. The relationship between the number of lethal hits and the number of single-stranded breaks was not previously established. A comparison of the calculated number of nicks per strand of DNA with the known dose in phage-lethal hits reveals a relationship closely approximating one lethal hit to one single-stranded break.

Fully automated treatment planning for head and neck radiotherapy using a voxel-based dose prediction and dose mimicking method

NASA Astrophysics Data System (ADS)

McIntosh, Chris; Welch, Mattea; McNiven, Andrea; Jaffray, David A.; Purdie, Thomas G.

2017-08-01

Recent works in automated radiotherapy treatment planning have used machine learning based on historical treatment plans to infer the spatial dose distribution for a novel patient directly from the planning image. We present a probabilistic, atlas-based approach which predicts the dose for novel patients using a set of automatically selected most similar patients (atlases). The output is a spatial dose objective, which specifies the desired dose-per-voxel, and therefore replaces the need to specify and tune dose-volume objectives. Voxel-based dose mimicking optimization then converts the predicted dose distribution to a complete treatment plan with dose calculation using a collapsed cone convolution dose engine. In this study, we investigated automated planning for right-sided oropharaynx head and neck patients treated with IMRT and VMAT. We compare four versions of our dose prediction pipeline using a database of 54 training and 12 independent testing patients by evaluating 14 clinical dose evaluation criteria. Our preliminary results are promising and demonstrate that automated methods can generate comparable dose distributions to clinical. Overall, automated plans achieved an average of 0.6% higher dose for target coverage evaluation criteria, and 2.4% lower dose at the organs at risk criteria levels evaluated compared with clinical. There was no statistically significant difference detected in high-dose conformity between automated and clinical plans as measured by the conformation number. Automated plans achieved nine more unique criteria than clinical across the 12 patients tested and automated plans scored a significantly higher dose at the evaluation limit for two high-risk target coverage criteria and a significantly lower dose in one critical organ maximum dose. The novel dose prediction method with dose mimicking can generate complete treatment plans in 12-13 min without user interaction. It is a promising approach for fully automated treatment planning and can be readily applied to different treatment sites and modalities.

Fully automated treatment planning for head and neck radiotherapy using a voxel-based dose prediction and dose mimicking method.

PubMed

McIntosh, Chris; Welch, Mattea; McNiven, Andrea; Jaffray, David A; Purdie, Thomas G

2017-07-06

Recent works in automated radiotherapy treatment planning have used machine learning based on historical treatment plans to infer the spatial dose distribution for a novel patient directly from the planning image. We present a probabilistic, atlas-based approach which predicts the dose for novel patients using a set of automatically selected most similar patients (atlases). The output is a spatial dose objective, which specifies the desired dose-per-voxel, and therefore replaces the need to specify and tune dose-volume objectives. Voxel-based dose mimicking optimization then converts the predicted dose distribution to a complete treatment plan with dose calculation using a collapsed cone convolution dose engine. In this study, we investigated automated planning for right-sided oropharaynx head and neck patients treated with IMRT and VMAT. We compare four versions of our dose prediction pipeline using a database of 54 training and 12 independent testing patients by evaluating 14 clinical dose evaluation criteria. Our preliminary results are promising and demonstrate that automated methods can generate comparable dose distributions to clinical. Overall, automated plans achieved an average of 0.6% higher dose for target coverage evaluation criteria, and 2.4% lower dose at the organs at risk criteria levels evaluated compared with clinical. There was no statistically significant difference detected in high-dose conformity between automated and clinical plans as measured by the conformation number. Automated plans achieved nine more unique criteria than clinical across the 12 patients tested and automated plans scored a significantly higher dose at the evaluation limit for two high-risk target coverage criteria and a significantly lower dose in one critical organ maximum dose. The novel dose prediction method with dose mimicking can generate complete treatment plans in 12-13 min without user interaction. It is a promising approach for fully automated treatment planning and can be readily applied to different treatment sites and modalities.

SU-E-T-409: Evaluation of Tissue Composition Effect On Dose Distribution in Radiotherapy with 6 MV Photon Beam of a Medical Linac

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

Ghorbani, M; Tabatabaei, Z; Noghreiyan, A Vejdani

Purpose: The aim of this study is to evaluate soft tissue composition effect on dose distribution for various soft tissues and various depths in radiotherapy with 6 MV photon beam of a medical linac. Methods: A phantom and Siemens Primus linear accelerator were simulated using MCNPX Monte Carlo code. In a homogeneous cubic phantom, six types of soft tissue and three types of tissue-equivalent materials were defined separately. The soft tissues were muscle (skeletal), adipose tissue, blood (whole), breast tissue, soft tissue (9-component) and soft tissue (4-component). The tissue-equivalent materials included: water, A-150 tissue-equivalent plastic and perspex. Photon dose relativemore » to dose in 9-component soft tissue at various depths on the beam’s central axis was determined for the 6 MV photon beam. The relative dose was also calculated and compared for various MCNPX tallies including,F8, F6 and,F4. Results: The results of the relative photon dose in various materials relative to dose in 9-component soft tissue and using different tallies are reported in the form of tabulated data. Minor differences between dose distributions in various soft tissues and tissue-equivalent materials were observed. The results from F6 and F4 were practically the same but different with,F8 tally. Conclusion: Based on the calculations performed, the differences in dose distributions in various soft tissues and tissue-equivalent materials are minor but they could be corrected in radiotherapy calculations to upgrade the accuracy of the dosimetric calculations.« less

Three-dimensional radiochromic film dosimetry for volumetric modulated arc therapy using a spiral water phantom.

PubMed

Tanooka, Masao; Doi, Hiroshi; Miura, Hideharu; Inoue, Hiroyuki; Niwa, Yasue; Takada, Yasuhiro; Fujiwara, Masayuki; Sakai, Toshiyuki; Sakamoto, Kiyoshi; Kamikonya, Norihiko; Hirota, Shozo

2013-11-01

We validated 3D radiochromic film dosimetry for volumetric modulated arc therapy (VMAT) using a newly developed spiral water phantom. The phantom consists of a main body and an insert box, each of which has an acrylic wall thickness of 3 mm and is filled with water. The insert box includes a spiral film box used for dose-distribution measurement, and a film holder for positioning a radiochromic film. The film holder has two parallel walls whose facing inner surfaces are equipped with spiral grooves in a mirrored configuration. The film is inserted into the spiral grooves by its side edges and runs along them to be positioned on a spiral plane. Dose calculation was performed by applying clinical VMAT plans to the spiral water phantom using a commercial Monte Carlo-based treatment-planning system, Monaco, whereas dose was measured by delivering the VMAT beams to the phantom. The calculated dose distributions were resampled on the spiral plane, and the dose distributions recorded on the film were scanned. Comparisons between the calculated and measured dose distributions yielded an average gamma-index pass rate of 87.0% (range, 91.2-84.6%) in nine prostate VMAT plans under 3 mm/3% criteria with a dose-calculation grid size of 2 mm. The pass rates were increased beyond 90% (average, 91.1%; range, 90.1-92.0%) when the dose-calculation grid size was decreased to 1 mm. We have confirmed that 3D radiochromic film dosimetry using the spiral water phantom is a simple and cost-effective approach to VMAT dose verification.

Monte Carlo investigation of backscatter point spread function for x-ray imaging examinations

NASA Astrophysics Data System (ADS)

Xiong, Zhenyu; Vijayan, Sarath; Rudin, Stephen; Bednarek, Daniel R.

2017-03-01

X-ray imaging examinations, especially complex interventions, may result in relatively high doses to the patient's skin inducing skin injuries. A method was developed to determine the skin-dose distribution for non-uniform x-ray beams by convolving the backscatter point-spread-function (PSF) with the primary-dose distribution to generate the backscatter distribution that, when added to the primary dose, gives the total-dose distribution. This technique was incorporated in the dose-tracking system (DTS), which provides a real-time color-coded 3D-mapping of skin dose during fluoroscopic procedures. The aim of this work is to investigate the variation of the backscatter PSF with different parameters. A backscatter PSF of a 1-mm x-ray beam was generated by EGSnrc Monte-Carlo code for different x-ray beam energies, different soft-tissue thickness above bone, different bone thickness and different entrance-beam angles, as well as for different locations on the SK-150 anthropomorphic head phantom. The results show a reduction of the peak scatter to primary dose ratio of 48% when X-ray beam voltage is increased from 40 keV to 120 keV. The backscatter dose was reduced when bone was beneath the soft tissue layer and this reduction increased with thinner soft tissue and thicker bone layers. The backscatter factor increased about 21% as the angle of incidence of the beam with the entrance surface decreased from 90° (perpendicular) to 30°. The backscatter PSF differed for different locations on the SK-150 phantom by up to 15%. The results of this study can be used to improve the accuracy of dose calculation when using PSF convolution in the DTS.

Assessing dose rate distributions in VMAT plans

NASA Astrophysics Data System (ADS)

Mackeprang, P.-H.; Volken, W.; Terribilini, D.; Frauchiger, D.; Zaugg, K.; Aebersold, D. M.; Fix, M. K.; Manser, P.

2016-04-01

Dose rate is an essential factor in radiobiology. As modern radiotherapy delivery techniques such as volumetric modulated arc therapy (VMAT) introduce dynamic modulation of the dose rate, it is important to assess the changes in dose rate. Both the rate of monitor units per minute (MU rate) and collimation are varied over the course of a fraction, leading to different dose rates in every voxel of the calculation volume at any point in time during dose delivery. Given the radiotherapy plan and machine specific limitations, a VMAT treatment plan can be split into arc sectors between Digital Imaging and Communications in Medicine control points (CPs) of constant and known MU rate. By calculating dose distributions in each of these arc sectors independently and multiplying them with the MU rate, the dose rate in every single voxel at every time point during the fraction can be calculated. Independently calculated and then summed dose distributions per arc sector were compared to the whole arc dose calculation for validation. Dose measurements and video analysis were performed to validate the calculated datasets. A clinical head and neck, cranial and liver case were analyzed using the tool developed. Measurement validation of synthetic test cases showed linac agreement to precalculated arc sector times within  ±0.4 s and doses  ±0.1 MU (one standard deviation). Two methods for the visualization of dose rate datasets were developed: the first method plots a two-dimensional (2D) histogram of the number of voxels receiving a given dose rate over the course of the arc treatment delivery. In similarity to treatment planning system display of dose, the second method displays the dose rate as color wash on top of the corresponding computed tomography image, allowing the user to scroll through the variation over time. Examining clinical cases showed dose rates spread over a continuous spectrum, with mean dose rates hardly exceeding 100 cGy min-1 for conventional fractionation. A tool to analyze dose rate distributions in VMAT plans with sub-second accuracy was successfully developed and validated. Dose rates encountered in clinical VMAT test cases show a continuous spectrum with a mean less than or near 100 cGy min-1 for conventional fractionation.

Geometric parameter analysis to predetermine optimal radiosurgery technique for the treatment of arteriovenous malformation

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

Mestrovic, Ante; Clark, Brenda G.; Department of Medical Physics, British Columbia Cancer Agency, Vancouver, British Columbia

2005-11-01

Purpose: To develop a method of predicting the values of dose distribution parameters of different radiosurgery techniques for treatment of arteriovenous malformation (AVM) based on internal geometric parameters. Methods and Materials: For each of 18 previously treated AVM patients, four treatment plans were created: circular collimator arcs, dynamic conformal arcs, fixed conformal fields, and intensity-modulated radiosurgery. An algorithm was developed to characterize the target and critical structure shape complexity and the position of the critical structures with respect to the target. Multiple regression was employed to establish the correlation between the internal geometric parameters and the dose distribution for differentmore » treatment techniques. The results from the model were applied to predict the dosimetric outcomes of different radiosurgery techniques and select the optimal radiosurgery technique for a number of AVM patients. Results: Several internal geometric parameters showing statistically significant correlation (p < 0.05) with the treatment planning results for each technique were identified. The target volume and the average minimum distance between the target and the critical structures were the most effective predictors for normal tissue dose distribution. The structure overlap volume with the target and the mean distance between the target and the critical structure were the most effective predictors for critical structure dose distribution. The predicted values of dose distribution parameters of different radiosurgery techniques were in close agreement with the original data. Conclusions: A statistical model has been described that successfully predicts the values of dose distribution parameters of different radiosurgery techniques and may be used to predetermine the optimal technique on a patient-to-patient basis.« less

[Polymer Gel Dosimeter].

PubMed

Hayashi, Shin-Ichiro

2017-01-01

With rapid advances being made in radiotherapy treatment, three-dimensional (3D) dose measurement techniques of great precision are required more than ever before. It is expected that 3D polymer gel dosimeters will satisfy clinical needs for an effective detector that can measure the complex 3D dose distributions. Polymer gel dosimeters are devices that utilize the radiation-induced polymerization reactions of vinyl monomers in a gel to store information about radiation dose. The 3D absorbed dose distribution can be deduced from the resulting polymer distribution using several imaging modalities, such as MRI, X-ray and optical CTs. In this article, the fundamental characteristics of polymer gel dosimeter are reviewed and some challenging keys are also suggested for the widely spread in clinical use.

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

Multiparametric Determination of Radiation Risk

NASA Technical Reports Server (NTRS)

Richmond, Robert C.

2003-01-01

Predicting risk of human cancer following exposure to ionizing space radiation is challenging in part because of uncertainties of low-dose distribution amongst cells, of unknown potentially synergistic effects of microgravity upon cellular protein-expression, and of processing dose-related damage within cells to produce rare and late-appearing malignant transformation, degrade the confidence of cancer risk-estimates. The NASA- specific responsibility to estimate the risks of radiogenic cancer in a limited number of astronauts is not amenable to epidemiologic study, thereby increasing this challenge. Developing adequately sensitive cellular biodosimeters that simultaneously report 1) the quantity of absorbed close after exposure to ionizing radiation, 2) the quality of radiation delivering that dose, and 3) the risk of developing malignant transformation by the cells absorbing that dose could be useful for resolving these challenges. Use of a multiparametric cellular biodosimeter is suggested using analyses of gene-expression and protein-expression whereby large datasets of cellular response to radiation-induced damage are obtained and analyzed for expression-profiles correlated with established end points and molecular markers predictive for cancer-risk. Analytical techniques of genomics and proteomics may be used to establish dose-dependency of multiple gene- and protein- expressions resulting from radiation-induced cellular damage. Furthermore, gene- and protein-expression from cells in microgravity are known to be altered relative to cells grown on the ground at 1g. Therefore, hypotheses are proposed that 1) macromolecular expression caused by radiation-induced damage in cells in microgravity may be different than on the ground, and 2) different patterns of macromolecular expression in microgravity may alter human radiogenic cancer risk relative to radiation exposure on Earth. A new paradigm is accordingly suggested as a national database wherein genomic and proteomic datasets are registered and interrogated in order to provide statistically significant dose-dependent risk estimation of radiogenic cancer in astronauts.

Dosimetric comparison of lung stereotactic body radiotherapy treatment plans using averaged computed tomography and end-exhalation computed tomography images: Evaluation of the effect of different dose-calculation algorithms and prescription methods

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

Mitsuyoshi, Takamasa; Nakamura, Mitsuhiro, E-mail: m_nkmr@kuhp.kyoto-u.ac.jp; Matsuo, Yukinori

The purpose of this article is to quantitatively evaluate differences in dose distributions calculated using various computed tomography (CT) datasets, dose-calculation algorithms, and prescription methods in stereotactic body radiotherapy (SBRT) for patients with early-stage lung cancer. Data on 29 patients with early-stage lung cancer treated with SBRT were retrospectively analyzed. Averaged CT (Ave-CT) and expiratory CT (Ex-CT) images were reconstructed for each patient using 4-dimensional CT data. Dose distributions were initially calculated using the Ave-CT images and recalculated (in the same monitor units [MUs]) by employing Ex-CT images with the same beam arrangements. The dose-volume parameters, including D{sub 95}, D{submore » 90}, D{sub 50}, and D{sub 2} of the planning target volume (PTV), were compared between the 2 image sets. To explore the influence of dose-calculation algorithms and prescription methods on the differences in dose distributions evident between Ave-CT and Ex-CT images, we calculated dose distributions using the following 3 different algorithms: x-ray Voxel Monte Carlo (XVMC), Acuros XB (AXB), and the anisotropic analytical algorithm (AAA). We also used 2 different dose-prescription methods; the isocenter prescription and the PTV periphery prescription methods. All differences in PTV dose-volume parameters calculated using Ave-CT and Ex-CT data were within 3 percentage points (%pts) employing the isocenter prescription method, and within 1.5%pts using the PTV periphery prescription method, irrespective of which of the 3 algorithms (XVMC, AXB, and AAA) was employed. The frequencies of dose-volume parameters differing by >1%pt when the XVMC and AXB were used were greater than those associated with the use of the AAA, regardless of the dose-prescription method employed. All differences in PTV dose-volume parameters calculated using Ave-CT and Ex-CT data on patients who underwent lung SBRT were within 3%pts, regardless of the dose-calculation algorithm or the dose-prescription method employed.« less

SU-F-T-563: Delivered Dose Reconstruction of Moving Targets for Gated Volumetric Modulated Arc Therapy (VMAT)

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

Chung, H; Cho, S; Jeong, C

2016-06-15

Purpose: Actual delivered dose of moving tumors treated with gated volumetric arc therapy (VMAT) may significantly differ from the planned dose assuming static target. In this study, we developed a method which reconstructs actual delivered dose distribution of moving target by taking into account both tumor motion and dynamic beam delivery of gated VMAT, and applied to abdominal tumors. Methods: Fifteen dual-arc VMAT plans (Eclipse, Varian Medical Systems) for 5 lung, 5 pancreatic, and 5 liver cancer patients treated with gated VMAT stereotactic body radiotherapy (SBRT) were studied. For reconstruction of the delivered dose distribution, we divided each original arcmore » beam into control-point-wise sub-beams, and applied beam isocenter shifting to each sub-beam to reflect the tumor motion. The tumor positions as a function of beam delivery were estimated by synchronizing the beam delivery with the respiratory signal which acquired during treatment. For this purpose, an in-house program (MATLAB, Mathworks) was developed to convert the original DICOM plan data into motion-involved treatment plan. The motion-involved DICOM plan was imported into Eclipse for dose calculation. The reconstructed delivered dose was compared to the plan dose using the dose coverage of gross tumor volume (GTV) and dose distribution of organs at risk (OAR). Results: The mean GTV dose coverage difference between the reconstructed delivered dose and the plan dose was 0.2 % in lung and pancreas cases, and no difference in liver cases. Mean D1000cc of ipsilateral lungs was reduced (0.8 ± 1.4cGy). Conclusion: We successfully developed a method of delivered dose reconstruction taking into account both respiratory tumor motion and dynamic beam delivery, and applied it to abdominal tumors treated with gated VAMT. No significant deterioration of delivered dose distribution indicates that interplay effect would be minimal even in the case of gated SBRT. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2015038710)« less

Gold-implanted shallow conducting layers in polymethylmethacrylate

NASA Astrophysics Data System (ADS)

Teixeira, F. S.; Salvadori, M. C.; Cattani, M.; Brown, I. G.

2009-03-01

PMMA (polymethylmethacrylate) was ion implanted with gold at very low energy and over a range of different doses using a filtered cathodic arc metal plasma system. A nanometer scale conducting layer was formed, fully buried below the polymer surface at low implantation dose, and evolving to include a gold surface layer as the dose was increased. Depth profiles of the implanted material were calculated using the Dynamic TRIM computer simulation program. The electrical conductivity of the gold-implanted PMMA was measured in situ as a function of dose. Samples formed at a number of different doses were subsequently characterized by Rutherford backscattering spectrometry, and test patterns were formed on the polymer by electron beam lithography. Lithographic patterns were imaged by atomic force microscopy and demonstrated that the contrast properties of the lithography were well maintained in the surface-modified PMMA.

Improvement of sub-20nm pattern quality with dose modulation technique for NIL template production

NASA Astrophysics Data System (ADS)

Yagawa, Keisuke; Ugajin, Kunihiro; Suenaga, Machiko; Kanamitsu, Shingo; Motokawa, Takeharu; Hagihara, Kazuki; Arisawa, Yukiyasu; Kobayashi, Sachiko; Saito, Masato; Ito, Masamitsu

2016-04-01

Nanoimprint lithography (NIL) technology is in the spotlight as a next-generation semiconductor manufacturing technique for integrated circuits at 22 nm and beyond. NIL is the unmagnified lithography technique using template which is replicated from master templates. On the other hand, master templates are currently fabricated by electron-beam (EB) lithography[1]. In near future, finer patterns less than 15nm will be required on master template and EB data volume increases exponentially. So, we confront with a difficult challenge. A higher resolution EB mask writer and a high performance fabrication process will be required. In our previous study, we investigated a potential of photomask fabrication process for finer patterning and achieved 15.5nm line and space (L/S) pattern on template by using VSB (Variable Shaped Beam) type EB mask writer and chemically amplified resist. In contrast, we found that a contrast loss by backscattering decreases the performance of finer patterning. For semiconductor devices manufacturing, we must fabricate complicated patterns which includes high and low density simultaneously except for consecutive L/S pattern. Then it's quite important to develop a technique to make various size or coverage patterns all at once. In this study, a small feature pattern was experimentally formed on master template with dose modulation technique. This technique makes it possible to apply the appropriate exposure dose for each pattern size. As a result, we succeed to improve the performance of finer patterning in bright field area. These results show that the performance of current EB lithography process have a potential to fabricate NIL template.

Calculation of Dose Deposition in 3D Voxels by Heavy Ions

NASA Technical Reports Server (NTRS)

Plante, Ianik; Cucinotta, Francis A.

2010-01-01

The biological response to high-LET radiation is very different from low-LET radiation, and can be partly attributed to the energy deposition by the radiation. Several experiments, notably detection of gamma-H2AX foci by immunofluorescence, has revealed important differences in the nature and in the spatial distribution of double-strand breaks (DSB) induced by low- and high-LET radiations. Many calculations, most of which are based on amorphous track models with radial dose, have been combined with chromosome models to calculate the number and distribution of DSB within nuclei and chromosome aberrations. In this work, the Monte-Carlo track structure simulation code RITRACKS have been used to calculate directly the energy deposition in voxels (3D pixels). A cubic volume of 5 micrometers of side was irradiated by 1) 450 (1)H+ ions of 300 MeV (LET is approximately 0.3 keV/micrometer) and 2) by 1 (56)Fe26+ ion of 1 GeV/amu (LET is approximately 150 keV/micrometer). In both cases, the dose deposited in the volume is approximately 1 Gy. All energy deposition events are recorded and dose is calculated in voxels of 20 micrometers of side. The voxels are then visualized in 3D by using a color scale to represent the intensity of the dose in a voxel. This simple approach has revealed several important points which may help understand experimental observations. In both simulations, voxels which receive low dose are the most numerous, and those corresponding to electron track ends received a dose which is in the higher range. The dose voxels are distributed randomly and scattered uniformly within the volume irradiated by low-LET radiation. The distribution of the voxels shows major differences for the (56)Fe26+ ion. The track structure can still be seen, and voxels with much higher dose are found in the region corresponding to the track "core". These high-dose voxels are not found in the low-LET irradiation simulation and may be responsible for DSB that are more difficult to repair. By applying a threshold on the dose visualization, voxels corresponding to electron track ends are evidenced and the spatial distribution of voxels is very similar to the distribution of DSB observed in gamma H2AX experiments, even if no chromosomes have been included in the simulation. Furthermore, this work has shown that a significant dose is deposited in voxels corresponding to electron track ends. Since some delta-rays from iron ion can travel several millimeters, they may also be of radiobiological importance.

A correction scheme for a simplified analytical random walk model algorithm of proton dose calculation in distal Bragg peak regions

NASA Astrophysics Data System (ADS)

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

2016-10-01

The lateral homogeneity assumption is used in most analytical algorithms for proton dose, such as the pencil-beam algorithms and our simplified analytical random walk model. To improve the dose calculation in the distal fall-off region in heterogeneous media, we analyzed primary proton fluence near heterogeneous media and propose to calculate the lateral fluence with voxel-specific Gaussian distributions. The lateral fluence from a beamlet is no longer expressed by a single Gaussian for all the lateral voxels, but by a specific Gaussian for each lateral voxel. The voxel-specific Gaussian for the beamlet of interest is calculated by re-initializing the fluence deviation on an effective surface where the proton energies of the beamlet of interest and the beamlet passing the voxel are the same. The dose improvement from the correction scheme was demonstrated by the dose distributions in two sets of heterogeneous phantoms consisting of cortical bone, lung, and water and by evaluating distributions in example patients with a head-and-neck tumor and metal spinal implants. The dose distributions from Monte Carlo simulations were used as the reference. The correction scheme effectively improved the dose calculation accuracy in the distal fall-off region and increased the gamma test pass rate. The extra computation for the correction was about 20% of that for the original algorithm but is dependent upon patient geometry.

Stochastic Modeling of Radioactive Material Releases

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

Andrus, Jason; Pope, Chad

2015-09-01

Nonreactor nuclear facilities operated under the approval authority of the U.S. Department of Energy use unmitigated hazard evaluations to determine if potential radiological doses associated with design basis events challenge or exceed dose evaluation guidelines. Unmitigated design basis events that sufficiently challenge dose evaluation guidelines or exceed the guidelines for members of the public or workers, merit selection of safety structures, systems, or components or other controls to prevent or mitigate the hazard. Idaho State University, in collaboration with Idaho National Laboratory, has developed a portable and simple to use software application called SODA (Stochastic Objective Decision-Aide) that stochastically calculatesmore » the radiation dose associated with hypothetical radiological material release scenarios. Rather than producing a point estimate of the dose, SODA produces a dose distribution result to allow a deeper understanding of the dose potential. SODA allows users to select the distribution type and parameter values for all of the input variables used to perform the dose calculation. SODA then randomly samples each distribution input variable and calculates the overall resulting dose distribution. In cases where an input variable distribution is unknown, a traditional single point value can be used. SODA was developed using the MATLAB coding framework. The software application has a graphical user input. SODA can be installed on both Windows and Mac computers and does not require MATLAB to function. SODA provides improved risk understanding leading to better informed decision making associated with establishing nuclear facility material-at-risk limits and safety structure, system, or component selection. It is important to note that SODA does not replace or compete with codes such as MACCS or RSAC, rather it is viewed as an easy to use supplemental tool to help improve risk understanding and support better informed decisions. The work was funded through a grant from the DOE Nuclear Safety Research and Development Program.« less

SU-C-BRD-07: Three-Dimensional Dose Reconstruction in the Presence of Inhomogeneities Using Fast EPID-Based Back-Projection Method

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

Ren, Q; Cao, R; Pei, X

2015-06-15

Purpose: Three-dimensional dose verification can detect errors introduced by the treatment planning system (TPS) or differences between planned and delivered dose distribution during the treatment. The aim of the study is to extend a previous in-house developed three-dimensional dose reconstructed model in homogeneous phantom to situtions in which tissue inhomogeneities are present. Methods: The method was based on the portal grey images from an electronic portal imaging device (EPID) and the relationship between beamlets and grey-scoring voxels at the position of the EPID. The relationship was expressed in the form of grey response matrix that was quantified using thickness-dependence scattermore » kernels determined by series of experiments. From the portal grey-value distribution information measured by the EPID the two-dimensional incident fluence distribution was reconstructed based on the grey response matrix using a fast iterative algorithm. The accuracy of this approach was verified using a four-field intensity-modulated radiotherapy (IMRT) plan for the treatment of lung cancer in anthopomorphic phantom. Each field had between twenty and twenty-eight segments and was evaluated by comparing the reconstructed dose distribution with the measured dose. Results: The gamma-evaluation method was used with various evaluation criteria of dose difference and distance-to-agreement: 3%/3mm and 2%/2 mm. The dose comparison for all irradiated fields showed a pass rate of 100% with the criterion of 3%/3mm, and a pass rate of higher than 92% with the criterion of 2%/2mm. Conclusion: Our experimental results demonstrate that our method is capable of accurately reconstructing three-dimensional dose distribution in the presence of inhomogeneities. Using the method, the combined planning and treatment delivery process is verified, offing an easy-to-use tool for the verification of complex treatments.« less

TU-H-CAMPUS-TeP3-03: Dose Enhancement by Gold Nanoparticles Around the Bragg Peak of Proton Beams

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

Kwon, J; Sutherland, K; Hashimoto, T

2016-06-15

Purpose: To make clear the spatial distribution of dose enhancement around gold nanoparticles (GNPs) located near the proton Bragg peak, and to evaluate the potential of GNPs as a radio sensitizer. Methods: The dose enhancement by electrons emitted from GNPs under proton irradiation was estimated by Geant4 Monte Carlo simulation toolkit in two steps. In an initial macroscopic step, 100 and 195 MeV proton beams were incident on a water cube, 30 cm on a side. Energy distributions of protons were calculated at four depths, 50% and 75% proximal to the Bragg peak, 100% peak, and 75% distal to themore » peak (P50, P75, Peak, and D75, respectively). In a subsequent microscopic step, protons with the energy distribution calculated above were incident on a 20 nm diameter GNP in a nanometer-size water box and the spatial distribution of dose around the GNP was determined for each energy distribution. The dose enhancement factor (DEF) was also deduced. Results: The dose enhancement effect was spread to several tens of nanometers in the both depth and radial directions. The enhancement area increased in the order of P50, P75, Peak, and D75 for both cases with 100 and 195 MeV protons. In every position around the Bragg peak, the 100 MeV beam resulted in a higher dose enhancement than the 195 MeV beam. At P75, the average and maximum DEF were 3.9 and 17.0 for 100 MeV, and 3.5 and 16.2 for 195 MeV, respectively. These results indicate that lower energy protons caused higher dose enhancement in this incident proton energy range. Conclusion: The dose enhancement around GNPs spread as the position in the Bragg peak region becomes deeper and depends on proton energy. It is expected that GNPs can be used as a radio sensitizer with consideration of the location and proton beam energy.« 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

Predicting pneumonitis risk: a dosimetric alternative to mean lung dose.

PubMed

Tucker, Susan L; Mohan, Radhe; Liengsawangwong, Raweewan; Martel, Mary K; Liao, Zhongxing

2013-02-01

To determine whether the association between mean lung dose (MLD) and risk of severe (grade ≥3) radiation pneumonitis (RP) depends on the dose distribution pattern to normal lung among patients receiving 3-dimensional conformal radiation therapy for non-small-cell lung cancer. Three cohorts treated with different beam arrangements were identified. One cohort (2-field boost [2FB]) received 2 parallel-opposed (anteroposterior-posteroanterior) fields per fraction initially, followed by a sequential boost delivered using 2 oblique beams. The other 2 cohorts received 3 or 4 straight fields (3FS and 4FS, respectively), ie, all fields were irradiated every day. The incidence of severe RP was plotted against MLD in each cohort, and data were analyzed using the Lyman-Kutcher-Burman (LKB) model. The incidence of grade ≥3 RP rose more steeply as a function of MLD in the 2FB cohort (N=120) than in the 4FS cohort (N=138), with an intermediate slope for the 3FS group (N=99). The estimated volume parameter from the LKB model was n=0.41 (95% confidence interval, 0.15-1.0) and led to a significant improvement in fit (P=.05) compared to a fit with volume parameter fixed at n=1 (the MLD model). Unlike the MLD model, the LKB model with n=0.41 provided a consistent description of the risk of severe RP in all three cohorts (2FB, 3FS, 4FS) simultaneously. When predicting risk of grade ≥3 RP, the mean lung dose does not adequately take into account the effects of high doses. Instead, the effective dose, computed from the LKB model using volume parameter n=0.41, may provide a better dosimetric parameter for predicting RP risk. If confirmed, these findings support the conclusion that for the same MLD, high doses to small lung volumes ("a lot to a little") are worse than low doses to large volumes ("a little to a lot"). Copyright © 2013 Elsevier Inc. All rights reserved.

Comparison of internal dose estimates obtained using organ-level, voxel S value, and Monte Carlo techniques

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

Grimes, Joshua, E-mail: grimes.joshua@mayo.edu; Celler, Anna

2014-09-15

Purpose: The authors’ objective was to compare internal dose estimates obtained using the Organ Level Dose Assessment with Exponential Modeling (OLINDA/EXM) software, the voxel S value technique, and Monte Carlo simulation. Monte Carlo dose estimates were used as the reference standard to assess the impact of patient-specific anatomy on the final dose estimate. Methods: Six patients injected with{sup 99m}Tc-hydrazinonicotinamide-Tyr{sup 3}-octreotide were included in this study. A hybrid planar/SPECT imaging protocol was used to estimate {sup 99m}Tc time-integrated activity coefficients (TIACs) for kidneys, liver, spleen, and tumors. Additionally, TIACs were predicted for {sup 131}I, {sup 177}Lu, and {sup 90}Y assuming themore » same biological half-lives as the {sup 99m}Tc labeled tracer. The TIACs were used as input for OLINDA/EXM for organ-level dose calculation and voxel level dosimetry was performed using the voxel S value method and Monte Carlo simulation. Dose estimates for {sup 99m}Tc, {sup 131}I, {sup 177}Lu, and {sup 90}Y distributions were evaluated by comparing (i) organ-level S values corresponding to each method, (ii) total tumor and organ doses, (iii) differences in right and left kidney doses, and (iv) voxelized dose distributions calculated by Monte Carlo and the voxel S value technique. Results: The S values for all investigated radionuclides used by OLINDA/EXM and the corresponding patient-specific S values calculated by Monte Carlo agreed within 2.3% on average for self-irradiation, and differed by as much as 105% for cross-organ irradiation. Total organ doses calculated by OLINDA/EXM and the voxel S value technique agreed with Monte Carlo results within approximately ±7%. Differences between right and left kidney doses determined by Monte Carlo were as high as 73%. Comparison of the Monte Carlo and voxel S value dose distributions showed that each method produced similar dose volume histograms with a minimum dose covering 90% of the volume (D90) agreeing within ±3%, on average. Conclusions: Several aspects of OLINDA/EXM dose calculation were compared with patient-specific dose estimates obtained using Monte Carlo. Differences in patient anatomy led to large differences in cross-organ doses. However, total organ doses were still in good agreement since most of the deposited dose is due to self-irradiation. Comparison of voxelized doses calculated by Monte Carlo and the voxel S value technique showed that the 3D dose distributions produced by the respective methods are nearly identical.« less

Skin dosimetry of patients during interventional cardiology procedures in the Czech Republic

NASA Astrophysics Data System (ADS)

Sukupova, Lucie; Novak, Leos

2008-01-01

The aim of the study is to determine distribution of air kerma-area product, fluoro time and number of frames values for the two most frequent procedures in the interventional cardiology, to reconstruct skin dose distributions for some patients undergoing coronarography and percutaneous transluminal coronary angioplasty procedures. Patient dose data were obtained from X-ray unit dose monitoring software report from one hospital and the reconstructions were performed in MATLAB. Dependence of maximum skin dose on air kerma-area product, fluoro time and number of frames was determined to assess trigger levels of these quantities, which can indicate possible exceeding of the 2 Gy skin dose threshold.

Medical dosimetry in Hungary

NASA Astrophysics Data System (ADS)

Turák, O.; Osvay, M.; Ballay, L.

2012-09-01

Radiation exposure of medical staff during cardiological and radiological procedures was investigated. The exposure of medical staff is directly connected to patient exposure. The aim of this study was to determine the distribution of doses on uncovered part of body of medical staff using LiF thermoluminescent (TL) dosimeters in seven locations. Individual Kodak film dosimeters (as authorized dosimetry system) were used for the assessment of medical staff's effective dose. Results achieved on dose distribution measurements confirm that wearing only one film badge under the lead apron does not provide enough information on the personal dose. The value of estimated annual doses on eye lens and extremities (fingers) were in good correlation with international publications.

Recent skyshine calculations at Jefferson Lab

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

Degtyarenko, P.

1997-12-01

New calculations of the skyshine dose distribution of neutrons and secondary photons have been performed at Jefferson Lab using the Monte Carlo method. The dose dependence on neutron energy, distance to the neutron source, polar angle of a source neutron, and azimuthal angle between the observation point and the momentum direction of a source neutron have been studied. The azimuthally asymmetric term in the skyshine dose distribution is shown to be important in the dose calculations around high-energy accelerator facilities. A parameterization formula and corresponding computer code have been developed which can be used for detailed calculations of the skyshinemore » dose maps.« less

Optimal shield mass distribution for space radiation protection

NASA Technical Reports Server (NTRS)

Billings, M. P.

1972-01-01

Computational methods have been developed and successfully used for determining the optimum distribution of space radiation shielding on geometrically complex space vehicles. These methods have been incorporated in computer program SWORD for dose evaluation in complex geometry, and iteratively calculating the optimum distribution for (minimum) shield mass satisfying multiple acute and protected dose constraints associated with each of several body organs.

Distributional properties of relative phase in bimanual coordination.

PubMed

James, Eric; Layne, Charles S; Newell, Karl M

2010-10-01

Studies of bimanual coordination have typically estimated the stability of coordination patterns through the use of the circular standard deviation of relative phase. The interpretation of this statistic depends upon the assumption of a von Mises distribution. The present study tested this assumption by examining the distributional properties of relative phase in three bimanual coordination patterns. There were significant deviations from the von Mises distribution due to differences in the kurtosis of distributions. The kurtosis depended upon the relative phase pattern performed, with leptokurtic distributions occurring in the in-phase and antiphase patterns and platykurtic distributions occurring in the 30° pattern. Thus, the distributional assumptions needed to validly and reliably use the standard deviation are not necessarily present in relative phase data though they are qualitatively consistent with the landscape properties of the intrinsic dynamics.

Maximizing the biological effect of proton dose delivered with scanned beams via inhomogeneous daily dose distributions

PubMed Central

Zeng, Chuan; Giantsoudi, Drosoula; Grassberger, Clemens; Goldberg, Saveli; Niemierko, Andrzej; Paganetti, Harald; Efstathiou, Jason A.; Trofimov, Alexei

2013-01-01

Purpose: Biological effect of radiation can be enhanced with hypofractionation, localized dose escalation, and, in particle therapy, with optimized distribution of linear energy transfer (LET). The authors describe a method to construct inhomogeneous fractional dose (IFD) distributions, and evaluate the potential gain in the therapeutic effect from their delivery in proton therapy delivered by pencil beam scanning. Methods: For 13 cases of prostate cancer, the authors considered hypofractionated courses of 60 Gy delivered in 20 fractions. (All doses denoted in Gy include the proton's mean relative biological effectiveness (RBE) of 1.1.) Two types of plans were optimized using two opposed lateral beams to deliver a uniform dose of 3 Gy per fraction to the target by scanning: (1) in conventional full-target plans (FTP), each beam irradiated the entire gland, (2) in split-target plans (STP), beams irradiated only the respective proximal hemispheres (prostate split sagittally). Inverse planning yielded intensity maps, in which discrete position control points of the scanned beam (spots) were assigned optimized intensity values. FTP plans preferentially required a higher intensity of spots in the distal part of the target, while STP, by design, employed proximal spots. To evaluate the utility of IFD delivery, IFD plans were generated by rearranging the spot intensities from FTP or STP intensity maps, separately as well as combined using a variety of mixing weights. IFD courses were designed so that, in alternating fractions, one of the hemispheres of the prostate would receive a dose boost and the other receive a lower dose, while the total physical dose from the IFD course was roughly uniform across the prostate. IFD plans were normalized so that the equivalent uniform dose (EUD) of rectum and bladder did not increase, compared to the baseline FTP plan, which irradiated the prostate uniformly in every fraction. An EUD-based model was then applied to estimate tumor control probability (TCP) and normal tissue complication probability (NTCP). To assess potential local RBE variations, LET distributions were calculated with Monte Carlo, and compared for different plans. The results were assessed in terms of their sensitivity to uncertainties in model parameters and delivery. Results: IFD courses included equal number of fractions boosting either hemisphere, thus, the combined physical dose was close to uniform throughout the prostate. However, for the entire course, the prostate EUD in IFD was higher than in conventional FTP by up to 14%, corresponding to the estimated increase in TCP to 96% from 88%. The extent of gain depended on the mixing factor, i.e., relative weights used to combine FTP and STP spot weights. Increased weighting of STP typically yielded a higher target EUD, but also led to increased sensitivity of dose to variations in the proton's range. Rectal and bladder EUD were same or lower (per normalization), and the NTCP for both remained below 1%. The LET distributions in IFD also depended strongly on the mixing weights: plans using higher weight of STP spots yielded higher LET, indicating a potentially higher local RBE. Conclusions: In proton therapy delivered by pencil beam scanning, improved therapeutic outcome can potentially be expected with delivery of IFD distributions, while administering the prescribed quasi-uniform dose to the target over the entire course. The biological effectiveness of IFD may be further enhanced by optimizing the LET distributions. IFD distributions are characterized by a dose gradient located in proximity of the prostate's midplane, thus, the fidelity of delivery would depend crucially on the precision with which the proton range could be controlled. PMID:23635256

Maximizing the biological effect of proton dose delivered with scanned beams via inhomogeneous daily dose distributions.

PubMed

Zeng, Chuan; Giantsoudi, Drosoula; Grassberger, Clemens; Goldberg, Saveli; Niemierko, Andrzej; Paganetti, Harald; Efstathiou, Jason A; Trofimov, Alexei

2013-05-01

Biological effect of radiation can be enhanced with hypofractionation, localized dose escalation, and, in particle therapy, with optimized distribution of linear energy transfer (LET). The authors describe a method to construct inhomogeneous fractional dose (IFD) distributions, and evaluate the potential gain in the therapeutic effect from their delivery in proton therapy delivered by pencil beam scanning. For 13 cases of prostate cancer, the authors considered hypofractionated courses of 60 Gy delivered in 20 fractions. (All doses denoted in Gy include the proton's mean relative biological effectiveness (RBE) of 1.1.) Two types of plans were optimized using two opposed lateral beams to deliver a uniform dose of 3 Gy per fraction to the target by scanning: (1) in conventional full-target plans (FTP), each beam irradiated the entire gland, (2) in split-target plans (STP), beams irradiated only the respective proximal hemispheres (prostate split sagittally). Inverse planning yielded intensity maps, in which discrete position control points of the scanned beam (spots) were assigned optimized intensity values. FTP plans preferentially required a higher intensity of spots in the distal part of the target, while STP, by design, employed proximal spots. To evaluate the utility of IFD delivery, IFD plans were generated by rearranging the spot intensities from FTP or STP intensity maps, separately as well as combined using a variety of mixing weights. IFD courses were designed so that, in alternating fractions, one of the hemispheres of the prostate would receive a dose boost and the other receive a lower dose, while the total physical dose from the IFD course was roughly uniform across the prostate. IFD plans were normalized so that the equivalent uniform dose (EUD) of rectum and bladder did not increase, compared to the baseline FTP plan, which irradiated the prostate uniformly in every fraction. An EUD-based model was then applied to estimate tumor control probability (TCP) and normal tissue complication probability (NTCP). To assess potential local RBE variations, LET distributions were calculated with Monte Carlo, and compared for different plans. The results were assessed in terms of their sensitivity to uncertainties in model parameters and delivery. IFD courses included equal number of fractions boosting either hemisphere, thus, the combined physical dose was close to uniform throughout the prostate. However, for the entire course, the prostate EUD in IFD was higher than in conventional FTP by up to 14%, corresponding to the estimated increase in TCP to 96% from 88%. The extent of gain depended on the mixing factor, i.e., relative weights used to combine FTP and STP spot weights. Increased weighting of STP typically yielded a higher target EUD, but also led to increased sensitivity of dose to variations in the proton's range. Rectal and bladder EUD were same or lower (per normalization), and the NTCP for both remained below 1%. The LET distributions in IFD also depended strongly on the mixing weights: plans using higher weight of STP spots yielded higher LET, indicating a potentially higher local RBE. In proton therapy delivered by pencil beam scanning, improved therapeutic outcome can potentially be expected with delivery of IFD distributions, while administering the prescribed quasi-uniform dose to the target over the entire course. The biological effectiveness of IFD may be further enhanced by optimizing the LET distributions. IFD distributions are characterized by a dose gradient located in proximity of the prostate's midplane, thus, the fidelity of delivery would depend crucially on the precision with which the proton range could be controlled.

Microdistribution of fluorescently-labeled monoclonal antibody in a peritoneal dissemination model of ovarian cancer

NASA Astrophysics Data System (ADS)

Kosaka, Nobuyuki; Ogawa, Mikako; Paik, David S.; Paik, Chang H.; Choyke, Peter L.; Kobayashi, Hisataka

2010-02-01

The microdistribution of therapeutic monoclonal antibodies within a tumor is important for determining clinical response. Nonuniform microdistribution predicts therapy failure. Herein, we developed a semiquantitative method for measuring microdistribution of an antibody within a tumor using in situ fluorescence microscopy and sought to modulate the microdistribution by altering the route and timing of antibody dosing. The microdistribution of a fluorescently-labeled antibody, trastuzumab (50-μg and 150-μg intraperitoneal injection (i.p.), and 100-μg intravenous injection (i.v.)) was evaluated in a peritoneal dissemination mouse model of ovarian cancer. In addition, we evaluated the microdistribution of concurrently-injected (30-μg i.p. and 100-μg i.v.) or serial (two doses of 30-μg i.p.) trastuzumab using in situ multicolor fluorescence microscopy. After the administration of 50-μg i.p. and 100-μg i.v. trastuzumab fluorescence imaging showed no significant difference in the central to peripheral signal ratio (C/P ratio) and demonstrated a peripheral-dominant accumulation, whereas administration of 150-μg i.p. trastuzumab showed relatively uniform, central dominant accumulation. With concurrent-i.p.-i.v. injections trastuzumab showed slightly higher C/P ratio than concurrently-injected i.p. trastuzumab. Moreover, in the serial injection study, the second injection of trastuzumab distributed more centrally than the first injection, while no difference was observed in the control group. Our results suggest that injection routes do not affect the microdistribution pattern of antibody in small peritoneal disseminations. However, increasing the dose results in a more uniform antibody distribution within peritoneal nodules. Furthermore, the serial i.p. injection of antibody can modify the microdistribution within tumor nodules. This work has implications for the optimal delivery of antibody based cancer therapies.

Dose rate evaluation of workers on the operation floor in Fukushima-Daiichi Unit 3

NASA Astrophysics Data System (ADS)

Matsushita, Kaoru; Kurosawa, Masahiko; Shirai, Keisuke; Matsuoka, Ippei; Mukaida, Naoki

2017-09-01

At Fukushima Daiichi Nuclear Power Plant Unit 3, installation of a fuel handling machine is planned to support the removal of spent fuel. The dose rates at the workplace were calculated based on the source distribution measured using a collimator in order to confirm that the dose rates on the operation floor were within a manageable range. It was confirmed that the accuracy of the source distribution was C/M = 1.0-2.4. These dose rates were then used to plan the work on the operation floor.

Using a conformal water bolus to adjust heating patterns of microwave waveguide applicators

NASA Astrophysics Data System (ADS)

Stauffer, Paul R.; Rodrigues, Dario B.; Sinahon, Randolf; Sbarro, Lyndsey; Beckhoff, Valeria; Hurwitz, Mark D.

2017-02-01

Background: Hyperthermia, i.e., raising tissue temperature to 40-45°C for 60 min, has been demonstrated to increase the effectiveness of radiation and chemotherapy for cancer. Although multi-element conformal heat applicators are under development to provide more adjustable heating of contoured anatomy, to date the most often used applicator to heat superficial disease is the simple microwave waveguide. With only a single power input, the operator must be resourceful to adjust heat treatment to accommodate variable size and shape tumors spreading across contoured anatomy. Methods: We used multiphysics simulation software that couples electromagnetic, thermal and fluid dynamics physics to simulate heating patterns in superficial tumors from commercially available microwave waveguide applicators. Temperature distributions were calculated inside homogenous muscle and layered skin-fat-muscle-tumor-bone tissue loads for a typical range of applicator coupling configurations and size of waterbolus. Variable thickness waterbolus was simulated as necessary to accommodate contoured anatomy. Physical models of several treatment configurations were constructed for comparison of simulation results with experimental specific absorption rate (SAR) measurements in homogenous muscle phantom. Results: Accuracy of the simulation model was confirmed with experimental SAR measurements of three unique applicator setups. Simulations demonstrated the ability to generate a wide range of power deposition patterns with commercially available waveguide antennas by controllably varying size and thickness of the waterbolus layer. Conclusion: Heating characteristics of 915 MHz waveguide antennas can be varied over a wide range by controlled adjustment of microwave power, coupling configuration, and waterbolus lateral size and thickness. The uniformity of thermal dose delivered to superficial tumors can be improved by cyclic switching of waterbolus thickness during treatment to proactively shift heat peaks and nulls around under the aperture, thereby reducing patient pain while increasing minimum thermal dose by end of treatment.

Suppression of transient enhanced diffusion in sub-micron patterned silicon template by dislocation loops formation

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

Hu, Kuan-Kan; Woon, Wei Yen; Chang, Ruey-Dar

We investigate the evolution of two dimensional transient enhanced diffusion (TED) of phosphorus in sub-micron scale patterned silicon template. Samples doped with low dose phosphorus with and without high dose silicon self-implantation, were annealed for various durations. Dopant diffusion is probed with plane-view scanning capacitance microscopy. The measurement revealed two phases of TED. Significant suppression in the second phase TED is observed for samples with high dose self-implantation. Transmission electron microscopy suggests the suppressed TED is related to the evolution of end of range defect formed around ion implantation sidewalls.

Suppression of transient enhanced diffusion in sub-micron patterned silicon template by dislocation loops formation

NASA Astrophysics Data System (ADS)

Hu, Kuan-Kan; Chang, Ruey-Dar; Woon, Wei Yen

2015-10-01

We investigate the evolution of two dimensional transient enhanced diffusion (TED) of phosphorus in sub-micron scale patterned silicon template. Samples doped with low dose phosphorus with and without high dose silicon self-implantation, were annealed for various durations. Dopant diffusion is probed with plane-view scanning capacitance microscopy. The measurement revealed two phases of TED. Significant suppression in the second phase TED is observed for samples with high dose self-implantation. Transmission electron microscopy suggests the suppressed TED is related to the evolution of end of range defect formed around ion implantation sidewalls.

Lifelong Exercise Patterns and Cardiovascular Health.

PubMed

Maessen, Martijn F H; Verbeek, André L M; Bakker, Esmée A; Thompson, Paul D; Hopman, Maria T E; Eijsvogels, Thijs M H

2016-06-01

To determine the relationship between lifelong exercise dose and the prevalence of cardiovascular morbidity. From June 1, 2011, through December 31, 2014, 21,266 individuals completed an online questionnaire regarding their lifelong exercise patterns and cardiovascular health status. Cardiovascular disease (CVD) was defined as a diagnosis of myocardial infarction, stroke, or heart failure, and cardiovascular risk factors (CVRFs) were defined as hypertension, hypercholesterolemia, or type 2 diabetes. Lifelong exercise patterns were measured over a median of 32 years for 405 patients with CVD, 1379 patients with CVRFs, and 10,656 controls. Participants were categorized into nonexercisers and quintiles (Q1-Q5) of exercise dose (metabolic equivalent task [MET] minutes per week). The CVD/CVRF prevalence was lower for each exercise quintile compared with nonexercisers (CVD: nonexercisers, 9.6% vs Q1: 4.4%, Q2: 2.8%, Q3: 2.4%, Q4: 3.6%, Q5: 3.9%; P<.001; CVRF: nonexercisers, 24.6% vs Q1: 13.8%, Q2: 10.2%, Q3: 9.0%, Q4: 9.4%, Q5: 12.0%; P<.001). The lowest exercise dose (Q1) significantly reduced CVD and CVRF prevalence, but the largest reductions were found at 764 to 1091 MET-min/wk for CVD (adjusted odds ratio=0.31; 95% CI, 0.20-0.48) and CVRFs (adjusted odds ratio=0.36; 95% CI, 0.28-0.47). The CVD/CVRF prevalence did not further decrease in higher exercise dose groups. Exercise intensity did not influence the relationship between exercise patterns and CVD or CVRFs. These findings demonstrate a curvilinear relationship between lifelong exercise patterns and cardiovascular morbidity. Low exercise doses can effectively reduce CVD/CVRF prevalence, but engagement in exercise for 764 to 1091 MET-min/wk is associated with the lowest CVD/CVRF prevalence. Higher exercise doses do not yield additional benefits. Copyright © 2016 Mayo Foundation for Medical Education and Research. Published by Elsevier Inc. All rights reserved.

Fieldable computer system for determining gamma-ray pulse-height distributions, flux spectra, and dose rates from Little Boy

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

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

1984-01-01

Our system consists of a LeCroy 3500 data acquisition system with a built-in CAMAC crate and eight bismuth-germanate detectors 7.62 cm in diameter and 7.62 cm long. Gamma-ray pulse-height distributions are acquired simultaneously for up to eight positions. The system was very carefully calibrated and characterized from 0.1 to 8.3 MeV using gamma-ray spectra from a variety of radioactive sources. By fitting the pulse-height distributions from the sources with a function containing 17 parameters, we determined theoretical repsonse functions. We use these response functions to unfold the distributions to obtain flux spectra. A flux-to-dose-rate conversion curve based on the workmore » of Dimbylow and Francis is then used to obtain dose rates. Direct use of measured spectra and flux-to-dose-rate curves to obtain dose rates avoids the errors that can arise from spectrum dependence in simple gamma-ray dosimeter instruments. We present some gamma-ray doses for the Little Boy assembly operated at low power. These results can be used to determine the exposures of the Hiroshima survivors and thus aid in the establishment of radation exposure limits for the nuclear industry.« less

Spatiotemporal radiotherapy planning using a global optimization approach

NASA Astrophysics Data System (ADS)

Adibi, Ali; Salari, Ehsan

2018-02-01

This paper aims at quantifying the extent of potential therapeutic gain, measured using biologically effective dose (BED), that can be achieved by altering the radiation dose distribution over treatment sessions in fractionated radiotherapy. To that end, a spatiotemporally integrated planning approach is developed, where the spatial and temporal dose modulations are optimized simultaneously. The concept of equivalent uniform BED (EUBED) is used to quantify and compare the clinical quality of spatiotemporally heterogeneous dose distributions in target and critical structures. This gives rise to a large-scale non-convex treatment-plan optimization problem, which is solved using global optimization techniques. The proposed spatiotemporal planning approach is tested on two stylized cancer cases resembling two different tumor sites and sensitivity analysis is performed for radio-biological and EUBED parameters. Numerical results validate that spatiotemporal plans are capable of delivering a larger BED to the target volume without increasing the BED in critical structures compared to conventional time-invariant plans. In particular, this additional gain is attributed to the irradiation of different regions of the target volume at different treatment sessions. Additionally, the trade-off between the potential therapeutic gain and the number of distinct dose distributions is quantified, which suggests a diminishing marginal gain as the number of dose distributions increases.

Preliminary investigations on the determination of three-dimensional dose distributions using scintillator blocks and optical tomography

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

Kroll, Florian; Karsch, Leonhard; Pawelke, Jörg

2013-08-15

Purpose: Clinical QA in teletherapy as well as the characterization of experimental radiation sources for future medical applications requires effective methods for measuring three-dimensional (3D) dose distributions generated in a water-equivalent medium. Current dosimeters based on ionization chambers, diodes, thermoluminescence detectors, radiochromic films, or polymer gels exhibit various drawbacks: High quality 3D dose determination is either very sophisticated and expensive or requires high amounts of effort and time for the preparation or read out. New detectors based on scintillator blocks in combination with optical tomography are studied, since they have the potential to facilitate the desired cost-effective, transportable, and long-termmore » stable dosimetry system that is able to determine 3D dose distributions with high spatial resolution in a short time.Methods: A portable detector prototype was set up based on a plastic scintillator block and four digital cameras. During irradiation the scintillator emits light, which is detected by the fixed cameras. The light distribution is then reconstructed by optical tomography, using maximum-likelihood expectation maximization. The result of the reconstruction approximates the 3D dose distribution. First performance tests of the prototype using laser light were carried out. Irradiation experiments were performed with ionizing radiation, i.e., bremsstrahlung (6 to 21 MV), electrons (6 to 21 MeV), and protons (68 MeV), provided by clinical and research accelerators.Results: Laser experiments show that the current imaging properties differ from the design specifications: The imaging scale of the optical systems is position dependent, ranging from 0.185 mm/pixel to 0.225 mm/pixel. Nevertheless, the developed dosimetry method is proven to be functional for electron and proton beams. Induced radiation doses of 50 mGy or more made 3D dose reconstructions possible. Taking the imaging properties into account, determined dose profiles are in agreement with reference measurements. An inherent drawback of the scintillator is the nonlinear light output for high stopping-power radiation due to the quenching effect. It impacts the depth dose curves measured with the dosimeter. For single Bragg peak distributions this leads to a peak to plateau ratio of 2.8 instead of 4.5 for the reference ionization chamber measurement. Furthermore, the transmission of the clinical bremsstrahlung beams through the scintillator leads to the saturation of one camera, making dose reconstructions in that case presently not feasible.Conclusions: It is shown that distributions of scintillation light generated by proton or electron beams can be reconstructed by the dosimetry system within minutes. The quenching apparent for proton irradiation, and the yet not precisely determined position dependency of the imaging scale, require further investigation and corrections. Upgrading the prototype with larger or inorganic scintillators would increase the detectable proton and electron energy range. The presented results show that the determination of 3D dose distributions using scintillator blocks and optical tomography is a promising dosimetry method.« less

Preliminary investigations on the determination of three-dimensional dose distributions using scintillator blocks and optical tomography.

PubMed

Kroll, Florian; Pawelke, Jörg; Karsch, Leonhard

2013-08-01

Clinical QA in teletherapy as well as the characterization of experimental radiation sources for future medical applications requires effective methods for measuring three-dimensional (3D) dose distributions generated in a water-equivalent medium. Current dosimeters based on ionization chambers, diodes, thermoluminescence detectors, radiochromic films, or polymer gels exhibit various drawbacks: High quality 3D dose determination is either very sophisticated and expensive or requires high amounts of effort and time for the preparation or read out. New detectors based on scintillator blocks in combination with optical tomography are studied, since they have the potential to facilitate the desired cost-effective, transportable, and long-term stable dosimetry system that is able to determine 3D dose distributions with high spatial resolution in a short time. A portable detector prototype was set up based on a plastic scintillator block and four digital cameras. During irradiation the scintillator emits light, which is detected by the fixed cameras. The light distribution is then reconstructed by optical tomography, using maximum-likelihood expectation maximization. The result of the reconstruction approximates the 3D dose distribution. First performance tests of the prototype using laser light were carried out. Irradiation experiments were performed with ionizing radiation, i.e., bremsstrahlung (6 to 21 MV), electrons (6 to 21 MeV), and protons (68 MeV), provided by clinical and research accelerators. Laser experiments show that the current imaging properties differ from the design specifications: The imaging scale of the optical systems is position dependent, ranging from 0.185 mm/pixel to 0.225 mm/pixel. Nevertheless, the developed dosimetry method is proven to be functional for electron and proton beams. Induced radiation doses of 50 mGy or more made 3D dose reconstructions possible. Taking the imaging properties into account, determined dose profiles are in agreement with reference measurements. An inherent drawback of the scintillator is the nonlinear light output for high stopping-power radiation due to the quenching effect. It impacts the depth dose curves measured with the dosimeter. For single Bragg peak distributions this leads to a peak to plateau ratio of 2.8 instead of 4.5 for the reference ionization chamber measurement. Furthermore, the transmission of the clinical bremsstrahlung beams through the scintillator leads to the saturation of one camera, making dose reconstructions in that case presently not feasible. It is shown that distributions of scintillation light generated by proton or electron beams can be reconstructed by the dosimetry system within minutes. The quenching apparent for proton irradiation, and the yet not precisely determined position dependency of the imaging scale, require further investigation and corrections. Upgrading the prototype with larger or inorganic scintillators would increase the detectable proton and electron energy range. The presented results show that the determination of 3D dose distributions using scintillator blocks and optical tomography is a promising dosimetry method.

Analysis of the NAEG model of transuranic radionuclide transport and dose

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

Kercher, J.R.; Anspaugh, L.R.

We analyze the model for estimating the dose from /sup 239/Pu developed for the Nevada Applied Ecology Group (NAEG) by using sensitivity analysis and uncertainty analysis. Sensitivity analysis results suggest that the air pathway is the critical pathway for the organs receiving the highest dose. Soil concentration and the factors controlling air concentration are the most important parameters. The only organ whose dose is sensitive to parameters in the ingestion pathway is the GI tract. The air pathway accounts for 100% of the dose to lung, upper respiratory tract, and thoracic lymph nodes; and 95% of its dose via ingestion.more » Leafy vegetable ingestion accounts for 70% of the dose from the ingestion pathway regardless of organ, peeled vegetables 20%; accidental soil ingestion 5%; ingestion of beef liver 4%; beef muscle 1%. Only a handful of model parameters control the dose for any one organ. The number of important parameters is usually less than 10. Uncertainty analysis indicates that choosing a uniform distribution for the input parameters produces a lognormal distribution of the dose. The ratio of the square root of the variance to the mean is three times greater for the doses than it is for the individual parameters. As found by the sensitivity analysis, the uncertainty analysis suggests that only a few parameters control the dose for each organ. All organs have similar distributions and variance to mean ratios except for the lymph modes. 16 references, 9 figures, 13 tables.« less

Concentration rather than dose defines the local brain toxicity of agents that are effectively distributed by convection-enhanced delivery.

PubMed

Zhang, Rong; Saito, Ryuta; Mano, Yui; Kanamori, Masayuki; Sonoda, Yukihiko; Kumabe, Toshihiro; Tominaga, Teiji

2014-01-30

Convection-enhanced delivery (CED) has been developed as a potentially effective drug-delivery strategy into the central nervous system. In contrast to systemic intravenous administration, local delivery achieves high concentration and prolonged retention in the local tissue, with increased chance of local toxicity, especially with toxic agents such as chemotherapeutic agents. Therefore, the factors that affect local toxicity should be extensively studied. With the assumption that concentration-oriented evaluation of toxicity is important for local CED, we evaluated the appearance of local toxicity among different agents after delivery with CED and studied if it is dose dependent or concentration dependent. Local toxicity profile of chemotherapeutic agents delivered via CED indicates BCNU was dose-dependent, whereas that of ACNU was concentration-dependent. On the other hand, local toxicity for doxorubicin, which is not distributed effectively by CED, was dose-dependent. Local toxicity for PLD, which is extensively distributed by CED, was concentration-dependent. Traditional evaluation of drug induced toxicity was dose-oriented. This is true for systemic intravascular delivery. However, with local CED, toxicity of several drugs exacerbated in concentration-dependent manner. From our study, local toxicity of drugs that are likely to distribute effectively tended to be concentration-dependent. Concentration rather than dose may be more important for the toxicity of agents that are effectively distributed by CED. Concentration-oriented evaluation of toxicity is more important for CED. Copyright © 2013 Elsevier B.V. All rights reserved.

Potential benefits of dosimetric VMAT tracking verified with 3D film measurements.

PubMed

Crijns, Wouter; Defraene, Gilles; Van Herck, Hans; Depuydt, Tom; Haustermans, Karin; Maes, Frederik; Van den Heuvel, Frank

2016-05-01

To evaluate three different plan adaptation strategies using 3D film-stack dose measurements of both focal boost and hypofractionated prostate VMAT treatments. The adaptation strategies (a couch shift, geometric tracking, and dosimetric tracking) were applied for three realistic intrafraction prostate motions. A focal boost (35 × 2.2 and 35 × 2.7 Gy) and a hypofractionated (5 × 7.25 Gy) prostate VMAT plan were created for a heterogeneous phantom that allows for internal prostate motion. For these plans geometric tracking and dosimetric tracking were evaluated by ionization chamber (IC) point dose measurements (zero-D) and measurements using a stack of EBT3 films (3D). The geometric tracking applied translations, rotations, and scaling of the MLC aperture in response to realistic prostate motions. The dosimetric tracking additionally corrected the monitor units to resolve variations due to difference in depth, tissue heterogeneity, and MLC-aperture. The tracking was based on the positions of four fiducial points only. The film measurements were compared to the gold standard (i.e., IC measurements) and the planned dose distribution. Additionally, the 3D measurements were converted to dose volume histograms, tumor control probability, and normal tissue complication probability parameters (DVH/TCP/NTCP) as a direct estimate of clinical relevance of the proposed tracking. Compared to the planned dose distribution, measurements without prostate motion and tracking showed already a reduced homogeneity of the dose distribution. Adding prostate motion further blurs the DVHs for all treatment approaches. The clinical practice (no tracking) delivered the dose distribution inside the PTV but off target (CTV), resulting in boost dose errors up to 10%. The geometric and dosimetric tracking corrected the dose distribution's position. Moreover, the dosimetric tracking could achieve the planned boost DVH, but not the DVH of the more homogeneously irradiated prostate. A drawback of both the geometric and dosimetric tracking was a reduced MLC blocking caused by the rotational component of the MLC aperture corrections. Because of the used CTV to PTV margins and the high doses in the considered fractionation schemes, the TCP differed less than 0.02 from the planned value for all targets and all correction methods. The rectal NTCP constraints, however, could not be realized using any of these methods. The geometric and dosimetric tracking use only a limited input, but they deposit the dose distribution with higher geometric accuracy than the clinical practice. The latter case has boost dose errors up to 10%. The increased accuracy has a modest impact [Δ(NT)CP < 0.02] because of the applied margins and the high dose levels used. To allow further margin reduction tracking methods are vital. The proposed methodology could further be improved by implementing a rotational correction using collimator rotations.

Poster - Thur Eve - 69: Electron beam dosimetry in heterogeneous phantoms using the MAGIC normoxic polymer gel.

PubMed

Nedaie, H A; Ghahraman, A R; Bolouri, B; Arbabi, A

2012-07-01

Recently, radiation sensitive polymer gels are being used as a reliable dosimetry method for three-dimensional (3D) verification of radiation doses in clinical use. Some properties of gel dosimeters have made them useful in verifying complex situations in electron therapy. The aim of this study was to experimentally evaluate the influence of tissue inhomogeneities on electron beam dose distributions by use of polymer gel dosimetry. Another purpose was to evaluate the appropriateness of polymer gels for electron beam dosimetry applications. A cylindrical phantom filled with MAGIC polymer gel with a polyacrilic wall (ρ = 1.18 g.cm -3 ) was placed in a Perspex water-filled tank exactly underneath the bone inhomogeneity region .Then, the slab phantom was irradiated with a dose of 5Gy of 8MeV electrons to measure the dose distribution beyond the heterogeneity region. Afterwards, another cylindrical gel phantom similar to the above was used and irradiated with the same dose of 15 MeV electrons to measure the dose distribution beyond the same heterogeneity region. The same mentioned setup was repeated for measurement of the dose distribution beneath the air heterogeneity and homogenous phantom. The results of gel dosimetry under bone inhomogeneity have shown a reduction in dose. This is related to the high mass stopping and mass scattering powers of bone tissue. In addition, dose enhancement is seen laterally near the bone-tissue interface, due to increased side scattering of electrons. Hot and cold scatter lobes under heterogeneity regions are other effects that can be seen. The results of gel dosimetry under the air inhomogeneity have shown an increase in dose. This is related to the low mass stopping and mass scattering powers of the air cavity. When a high energy beam passes through a low-density medium or an air cavity, electronic equilibrium is lost along the central axis of the beam .The dose rebuild up is a consequence of this electronic disequilibrium. An overall good agreement was found between measurements with gel and with a diode detector for the single beam experiment. Electron dose distributions are significantly altered in the presence of tissue inhomogeneities such as bone and air cavities which are related to mass stopping and mass scattering powers of heterogeneous materials. © 2012 American Association of Physicists in Medicine.

Latent uncertainties of the precalculated track Monte Carlo method

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

Renaud, Marc-André; Seuntjens, Jan; Roberge, David

Purpose: While significant progress has been made in speeding up Monte Carlo (MC) dose calculation methods, they remain too time-consuming for the purpose of inverse planning. To achieve clinically usable calculation speeds, a precalculated Monte Carlo (PMC) algorithm for proton and electron transport was developed to run on graphics processing units (GPUs). The algorithm utilizes pregenerated particle track data from conventional MC codes for different materials such as water, bone, and lung to produce dose distributions in voxelized phantoms. While PMC methods have been described in the past, an explicit quantification of the latent uncertainty arising from the limited numbermore » of unique tracks in the pregenerated track bank is missing from the paper. With a proper uncertainty analysis, an optimal number of tracks in the pregenerated track bank can be selected for a desired dose calculation uncertainty. Methods: Particle tracks were pregenerated for electrons and protons using EGSnrc and GEANT4 and saved in a database. The PMC algorithm for track selection, rotation, and transport was implemented on the Compute Unified Device Architecture (CUDA) 4.0 programming framework. PMC dose distributions were calculated in a variety of media and compared to benchmark dose distributions simulated from the corresponding general-purpose MC codes in the same conditions. A latent uncertainty metric was defined and analysis was performed by varying the pregenerated track bank size and the number of simulated primary particle histories and comparing dose values to a “ground truth” benchmark dose distribution calculated to 0.04% average uncertainty in voxels with dose greater than 20% of D{sub max}. Efficiency metrics were calculated against benchmark MC codes on a single CPU core with no variance reduction. Results: Dose distributions generated using PMC and benchmark MC codes were compared and found to be within 2% of each other in voxels with dose values greater than 20% of the maximum dose. In proton calculations, a small (≤1 mm) distance-to-agreement error was observed at the Bragg peak. Latent uncertainty was characterized for electrons and found to follow a Poisson distribution with the number of unique tracks per energy. A track bank of 12 energies and 60000 unique tracks per pregenerated energy in water had a size of 2.4 GB and achieved a latent uncertainty of approximately 1% at an optimal efficiency gain over DOSXYZnrc. Larger track banks produced a lower latent uncertainty at the cost of increased memory consumption. Using an NVIDIA GTX 590, efficiency analysis showed a 807 × efficiency increase over DOSXYZnrc for 16 MeV electrons in water and 508 × for 16 MeV electrons in bone. Conclusions: The PMC method can calculate dose distributions for electrons and protons to a statistical uncertainty of 1% with a large efficiency gain over conventional MC codes. Before performing clinical dose calculations, models to calculate dose contributions from uncharged particles must be implemented. Following the successful implementation of these models, the PMC method will be evaluated as a candidate for inverse planning of modulated electron radiation therapy and scanned proton beams.« less

Latent uncertainties of the precalculated track Monte Carlo method.

PubMed

Renaud, Marc-André; Roberge, David; Seuntjens, Jan

2015-01-01

While significant progress has been made in speeding up Monte Carlo (MC) dose calculation methods, they remain too time-consuming for the purpose of inverse planning. To achieve clinically usable calculation speeds, a precalculated Monte Carlo (PMC) algorithm for proton and electron transport was developed to run on graphics processing units (GPUs). The algorithm utilizes pregenerated particle track data from conventional MC codes for different materials such as water, bone, and lung to produce dose distributions in voxelized phantoms. While PMC methods have been described in the past, an explicit quantification of the latent uncertainty arising from the limited number of unique tracks in the pregenerated track bank is missing from the paper. With a proper uncertainty analysis, an optimal number of tracks in the pregenerated track bank can be selected for a desired dose calculation uncertainty. Particle tracks were pregenerated for electrons and protons using EGSnrc and geant4 and saved in a database. The PMC algorithm for track selection, rotation, and transport was implemented on the Compute Unified Device Architecture (cuda) 4.0 programming framework. PMC dose distributions were calculated in a variety of media and compared to benchmark dose distributions simulated from the corresponding general-purpose MC codes in the same conditions. A latent uncertainty metric was defined and analysis was performed by varying the pregenerated track bank size and the number of simulated primary particle histories and comparing dose values to a "ground truth" benchmark dose distribution calculated to 0.04% average uncertainty in voxels with dose greater than 20% of Dmax. Efficiency metrics were calculated against benchmark MC codes on a single CPU core with no variance reduction. Dose distributions generated using PMC and benchmark MC codes were compared and found to be within 2% of each other in voxels with dose values greater than 20% of the maximum dose. In proton calculations, a small (≤ 1 mm) distance-to-agreement error was observed at the Bragg peak. Latent uncertainty was characterized for electrons and found to follow a Poisson distribution with the number of unique tracks per energy. A track bank of 12 energies and 60000 unique tracks per pregenerated energy in water had a size of 2.4 GB and achieved a latent uncertainty of approximately 1% at an optimal efficiency gain over DOSXYZnrc. Larger track banks produced a lower latent uncertainty at the cost of increased memory consumption. Using an NVIDIA GTX 590, efficiency analysis showed a 807 × efficiency increase over DOSXYZnrc for 16 MeV electrons in water and 508 × for 16 MeV electrons in bone. The PMC method can calculate dose distributions for electrons and protons to a statistical uncertainty of 1% with a large efficiency gain over conventional MC codes. Before performing clinical dose calculations, models to calculate dose contributions from uncharged particles must be implemented. Following the successful implementation of these models, the PMC method will be evaluated as a candidate for inverse planning of modulated electron radiation therapy and scanned proton beams.

Evaluation of material heterogeneity dosimetric effects using radiochromic film for COMS eye plaques loaded with {sup 125}I seeds (model I25.S16)

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

Acar, Hilal; Chiu-Tsao, Sou-Tung; Oezbay, Ismail

Purpose: (1) To measure absolute dose distributions in eye phantom for COMS eye plaques with {sup 125}I seeds (model I25.S16) using radiochromic EBT film dosimetry. (2) To determine the dose correction function for calculations involving the TG-43 formalism to account for the presence of the COMS eye plaque using Monte Carlo (MC) method specific to this seed model. (3) To test the heterogeneous dose calculation accuracy of the new version of Plaque Simulator (v5.3.9) against the EBT film data for this seed model. Methods: Using EBT film, absolute doses were measured for {sup 125}I seeds (model I25.S16) in COMS eyemore » plaques (1) along the plaque's central axis for (a) uniformly loaded plaques (14-20 mm in diameter) and (b) a 20 mm plaque with single seed, and (2) in off-axis direction at depths of 5 and 12 mm for all four plaque sizes. The EBT film calibration was performed at {sup 125}I photon energy. MC calculations using MCNP5 code for a single seed at the center of a 20 mm plaque in homogeneous water and polystyrene medium were performed. The heterogeneity dose correction function was determined from the MC calculations. These function values at various depths were entered into PS software (v5.3.9) to calculate the heterogeneous dose distributions for the uniformly loaded plaques (of all four sizes). The dose distributions with homogeneous water assumptions were also calculated using PS for comparison. The EBT film measured absolute dose rate values (film) were compared with those calculated using PS with homogeneous assumption (PS Homo) and heterogeneity correction (PS Hetero). The values of dose ratio (film/PS Homo) and (film/PS Hetero) were obtained. Results: The central axis depth dose rate values for a single seed in 20 mm plaque measured using EBT film and calculated with MCNP5 code (both in ploystyrene phantom) were compared, and agreement within 9% was found. The dose ratio (film/PS Homo) values were substantially lower than unity (mostly between 0.8 and 0.9) for all four plaque sizes, indicating dose reduction by COMS plaque compared with homogeneous assumption. The dose ratio (film/PS Hetero) values were close to unity, indicating the PS Hetero calculations agree with those from the film study. Conclusions: Substantial heterogeneity effect on the {sup 125}I dose distributions in an eye phantom for COMS plaques was verified using radiochromic EBT film dosimetry. The calculated doses for uniformly loaded plaques using PS with heterogeneity correction option enabled were corroborated by the EBT film measurement data. Radiochromic EBT film dosimetry is feasible in measuring absolute dose distributions in eye phantom for COMS eye plaques loaded with single or multiple {sup 125}I seeds. Plaque Simulator is a viable tool for the calculation of dose distributions if one understands its limitations and uses the proper heterogeneity correction feature.« less

Inputs and spatial distribution patterns of Cr in Jiaozhou Bay

NASA Astrophysics Data System (ADS)

Yang, Dongfang; Miao, Zhenqing; Huang, Xinmin; Wei, Linzhen; Feng, Ming

2018-03-01

Cr pollution in marine bays has been one of the critical environmental issues, and understanding the input and spatial distribution patterns is essential to pollution control. In according to the source strengths of the major pollution sources, the input patterns of pollutants to marine bay include slight, moderate and heavy, and the spatial distribution are corresponding to three block models respectively. This paper analyzed input patterns and distributions of Cr in Jiaozhou Bay, eastern China based on investigation on Cr in surface waters during 1979-1983. Results showed that the input strengths of Cr in Jiaozhou Bay could be classified as moderate input and slight input, and the input strengths were 32.32-112.30 μg L-1 and 4.17-19.76 μg L-1, respectively. The input patterns of Cr included two patterns of moderate input and slight input, and the horizontal distributions could be defined by means of Block Model 2 and Block Model 3, respectively. In case of moderate input pattern via overland runoff, Cr contents were decreasing from the estuaries to the bay mouth, and the distribution pattern was parallel. In case of moderate input pattern via marine current, Cr contents were decreasing from the bay mouth to the bay, and the distribution pattern was parallel to circular. The Block Models were able to reveal the transferring process of various pollutants, and were helpful to understand the distributions of pollutants in marine bay.

MRI-based treatment planning with pseudo CT generated through atlas registration.

PubMed

Uh, Jinsoo; Merchant, Thomas E; Li, Yimei; Li, Xingyu; Hua, Chiaho

2014-05-01

To evaluate the feasibility and accuracy of magnetic resonance imaging (MRI)-based treatment planning using pseudo CTs generated through atlas registration. A pseudo CT, providing electron density information for dose calculation, was generated by deforming atlas CT images previously acquired on other patients. The authors tested 4 schemes of synthesizing a pseudo CT from single or multiple deformed atlas images: use of a single arbitrarily selected atlas, arithmetic mean process using 6 atlases, and pattern recognition with Gaussian process (PRGP) using 6 or 12 atlases. The required deformation for atlas CT images was derived from a nonlinear registration of conjugated atlas MR images to that of the patient of interest. The contrasts of atlas MR images were adjusted by histogram matching to reduce the effect of different sets of acquisition parameters. For comparison, the authors also tested a simple scheme assigning the Hounsfield unit of water to the entire patient volume. All pseudo CT generating schemes were applied to 14 patients with common pediatric brain tumors. The image similarity of real patient-specific CT and pseudo CTs constructed by different schemes was compared. Differences in computation times were also calculated. The real CT in the treatment planning system was replaced with the pseudo CT, and the dose distribution was recalculated to determine the difference. The atlas approach generally performed better than assigning a bulk CT number to the entire patient volume. Comparing atlas-based schemes, those using multiple atlases outperformed the single atlas scheme. For multiple atlas schemes, the pseudo CTs were similar to the real CTs (correlation coefficient, 0.787-0.819). The calculated dose distribution was in close agreement with the original dose. Nearly the entire patient volume (98.3%-98.7%) satisfied the criteria of chi-evaluation (<2% maximum dose and 2 mm range). The dose to 95% of the volume and the percentage of volume receiving at least 95% of the prescription dose in the planning target volume differed from the original values by less than 2% of the prescription dose (root-mean-square, RMS < 1%). The PRGP scheme did not perform better than the arithmetic mean process with the same number of atlases. Increasing the number of atlases from 6 to 12 often resulted in improvements, but statistical significance was not always found. MRI-based treatment planning with pseudo CTs generated through atlas registration is feasible for pediatric brain tumor patients. The doses calculated from pseudo CTs agreed well with those from real CTs, showing dosimetric accuracy within 2% for the PTV when multiple atlases were used. The arithmetic mean process may be a reasonable choice over PRGP for the synthesis scheme considering performance and computational costs.

MRI-based treatment planning with pseudo CT generated through atlas registration

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

Uh, Jinsoo, E-mail: jinsoo.uh@stjude.org; Merchant, Thomas E.; Hua, Chiaho

2014-05-15

Purpose: To evaluate the feasibility and accuracy of magnetic resonance imaging (MRI)-based treatment planning using pseudo CTs generated through atlas registration. Methods: A pseudo CT, providing electron density information for dose calculation, was generated by deforming atlas CT images previously acquired on other patients. The authors tested 4 schemes of synthesizing a pseudo CT from single or multiple deformed atlas images: use of a single arbitrarily selected atlas, arithmetic mean process using 6 atlases, and pattern recognition with Gaussian process (PRGP) using 6 or 12 atlases. The required deformation for atlas CT images was derived from a nonlinear registration ofmore » conjugated atlas MR images to that of the patient of interest. The contrasts of atlas MR images were adjusted by histogram matching to reduce the effect of different sets of acquisition parameters. For comparison, the authors also tested a simple scheme assigning the Hounsfield unit of water to the entire patient volume. All pseudo CT generating schemes were applied to 14 patients with common pediatric brain tumors. The image similarity of real patient-specific CT and pseudo CTs constructed by different schemes was compared. Differences in computation times were also calculated. The real CT in the treatment planning system was replaced with the pseudo CT, and the dose distribution was recalculated to determine the difference. Results: The atlas approach generally performed better than assigning a bulk CT number to the entire patient volume. Comparing atlas-based schemes, those using multiple atlases outperformed the single atlas scheme. For multiple atlas schemes, the pseudo CTs were similar to the real CTs (correlation coefficient, 0.787–0.819). The calculated dose distribution was in close agreement with the original dose. Nearly the entire patient volume (98.3%–98.7%) satisfied the criteria of chi-evaluation (<2% maximum dose and 2 mm range). The dose to 95% of the volume and the percentage of volume receiving at least 95% of the prescription dose in the planning target volume differed from the original values by less than 2% of the prescription dose (root-mean-square, RMS < 1%). The PRGP scheme did not perform better than the arithmetic mean process with the same number of atlases. Increasing the number of atlases from 6 to 12 often resulted in improvements, but statistical significance was not always found. Conclusions: MRI-based treatment planning with pseudo CTs generated through atlas registration is feasible for pediatric brain tumor patients. The doses calculated from pseudo CTs agreed well with those from real CTs, showing dosimetric accuracy within 2% for the PTV when multiple atlases were used. The arithmetic mean process may be a reasonable choice over PRGP for the synthesis scheme considering performance and computational costs.« less

MRI-based treatment planning with pseudo CT generated through atlas registration

PubMed Central

Uh, Jinsoo; Merchant, Thomas E.; Li, Yimei; Li, Xingyu; Hua, Chiaho

2014-01-01

Purpose: To evaluate the feasibility and accuracy of magnetic resonance imaging (MRI)-based treatment planning using pseudo CTs generated through atlas registration. Methods: A pseudo CT, providing electron density information for dose calculation, was generated by deforming atlas CT images previously acquired on other patients. The authors tested 4 schemes of synthesizing a pseudo CT from single or multiple deformed atlas images: use of a single arbitrarily selected atlas, arithmetic mean process using 6 atlases, and pattern recognition with Gaussian process (PRGP) using 6 or 12 atlases. The required deformation for atlas CT images was derived from a nonlinear registration of conjugated atlas MR images to that of the patient of interest. The contrasts of atlas MR images were adjusted by histogram matching to reduce the effect of different sets of acquisition parameters. For comparison, the authors also tested a simple scheme assigning the Hounsfield unit of water to the entire patient volume. All pseudo CT generating schemes were applied to 14 patients with common pediatric brain tumors. The image similarity of real patient-specific CT and pseudo CTs constructed by different schemes was compared. Differences in computation times were also calculated. The real CT in the treatment planning system was replaced with the pseudo CT, and the dose distribution was recalculated to determine the difference. Results: The atlas approach generally performed better than assigning a bulk CT number to the entire patient volume. Comparing atlas-based schemes, those using multiple atlases outperformed the single atlas scheme. For multiple atlas schemes, the pseudo CTs were similar to the real CTs (correlation coefficient, 0.787–0.819). The calculated dose distribution was in close agreement with the original dose. Nearly the entire patient volume (98.3%–98.7%) satisfied the criteria of chi-evaluation (<2% maximum dose and 2 mm range). The dose to 95% of the volume and the percentage of volume receiving at least 95% of the prescription dose in the planning target volume differed from the original values by less than 2% of the prescription dose (root-mean-square, RMS < 1%). The PRGP scheme did not perform better than the arithmetic mean process with the same number of atlases. Increasing the number of atlases from 6 to 12 often resulted in improvements, but statistical significance was not always found. Conclusions: MRI-based treatment planning with pseudo CTs generated through atlas registration is feasible for pediatric brain tumor patients. The doses calculated from pseudo CTs agreed well with those from real CTs, showing dosimetric accuracy within 2% for the PTV when multiple atlases were used. The arithmetic mean process may be a reasonable choice over PRGP for the synthesis scheme considering performance and computational costs. PMID:24784377

Evaluation of the effect of patient dose from cone beam computed tomography on prostate IMRT using Monte Carlo simulation.

PubMed

Chow, James C L; Leung, Michael K K; Islam, Mohammad K; Norrlinger, Bernhard D; Jaffray, David A

2008-01-01

The aim of this study is to evaluate the impact of the patient dose due to the kilovoltage cone beam computed tomography (kV-CBCT) in a prostate intensity-modulated radiation therapy (IMRT). The dose distributions for the five prostate IMRTs were calculated using the Pinnacle treatment planning system. To calculate the patient dose from CBCT, phase-space beams of a CBCT head based on the ELEKTA x-ray volume imaging system were generated using the Monte Carlo BEAMnr code for 100, 120, 130, and 140 kVp energies. An in-house graphical user interface called DOSCTP (DOSXYZnrc-based) developed using MATLAB was used to calculate the dose distributions due to a 360 degrees photon arc from the CBCT beam with the same patient CT image sets as used in Pinnacle. The two calculated dose distributions were added together by setting the CBCT doses equal to 1%, 1.5%, 2%, and 2.5% of the prescription dose of the prostate IMRT. The prostate plan and the summed dose distributions were then processed in the CERR platform to determine the dose-volume histograms (DVHs) of the regions of interest. Moreover, dose profiles along the x- and y-axes crossing the isocenter with and without addition of the CBCT dose were determined. It was found that the added doses due to CBCT are most significant at the femur heads. Higher doses were found at the bones for a relatively low energy CBCT beam such as 100 kVp. Apart from the bones, the CBCT dose was observed to be most concentrated on the anterior and posterior side of the patient anatomy. Analysis of the DVHs for the prostate and other critical tissues showed that they vary only slightly with the added CBCT dose at different beam energies. On the other hand, the changes of the DVHs for the femur heads due to the CBCT dose and beam energy were more significant than those of rectal and bladder wall. By analyzing the vertical and horizontal dose profiles crossing the femur heads and isocenter, with and without the CBCT dose equal to 2% of the prescribed dose, it was found that there is about a 5% increase of dose at the femur head. Still, such an increase in the femur head dose is well below the dose limit of the bone in our IMRT plans. Therefore, under these dose fractionation conditions, it is concluded that, though CBCT causes a higher dose deposited at the bones, there may be no significant effect in the DVHs of critical tissues in the prostate IMRT.

High resolution digital autoradiographic and dosimetric analysis of heterogeneous radioactivity distribution in xenografted prostate tumors.

PubMed

Timmermand, Oskar V; Nilsson, Jenny; Strand, Sven-Erik; Elgqvist, Jörgen

2016-12-01

The first main aim of this study was to illustrate the absorbed dose rate distribution from 177 Lu in sections of xenografted prostate cancer (PCa) tumors using high resolution digital autoradiography (DAR) and compare it with hypothetical identical radioactivity distributions of 90 Y or 7 MeV alpha-particles. Three dosimetry models based on either dose point kernels or Monte Carlo simulations were used and evaluated. The second and overlapping aim, was to perform DAR imaging and dosimetric analysis of the distribution of radioactivity, and hence the absorbed dose rate, in tumor sections at an early time point after injection during radioimmunotherapy using 177 Lu-h11B6, directed against the human kallikrein 2 antigen. Male immunodeficient BALB/c nude mice, aged 6-8 w, were inoculated by subcutaneous injection of ∼10 7 LNCaP cells in a 200 μl suspension of a 1:1 mixture of medium and Matrigel. The antibody h11B6 was conjugated with the chelator CHX-A″-DTPA after which conjugated h11B6 was mixed with 177 LuCl 3 . The incubation was performed at room temperature for 2 h, after which the labeling was terminated and the solution was purified on a NAP-5 column. About 20 MBq 177 Lu-h11B6 was injected intravenously in the tail vein. At approximately 10 h postinjection (hpi), the mice were sacrificed and one tumor was collected from each of the five animals and cryosectioned into 10 μm thick slices. The tumor slices were measured and imaged using the DAR MicroImager system and the M3Vision software. Then the absorbed dose rate was calculated using a dose point kernel generated with the Monte Carlo code gate v7.0. The DAR system produced high resolution images of the radioactivity distribution, close to the resolution of single PCa cells. The DAR images revealed a pronounced heterogeneous radioactivity distribution, i.e., count rate per area, in the tumors, indicated by the normalized intensity variations along cross sections as mean ± SD: 0.15 ± 0.15, 0.20 ± 0.18, 0.12 ± 0.17, 0.15 ± 0.16, and 0.23 ± 0.22, for each tumor section, respectively. The absorbed dose rate distribution for 177 Lu at the time of dissection 10 hpi showed a maximum value of 2.9 ± 0.4 Gy/h (mean ± SD), compared to 6.0 ± 0.9 and 159 ± 25 Gy/h for the hypothetical 90 Y and 7 MeV alpha-particle cases assuming the same count rate densities. Mean absorbed dose rate values were 0.13, 0.53, and 6.43 Gy/h for 177 Lu, 90 Y, and alpha-particles, respectively. The initial uptake of 177 Lu-h11B6 produces a high absorbed dose rate, which is important for a successful therapeutic outcome. The hypothetical 90 Y case indicates a less heterogeneous absorbed dose rate distribution and a higher mean absorbed dose rate compared to 177 Lu, although with a potentially increased irradiation of surrounding healthy tissue. The hypothetical alpha-particle case indicates the possibility of a higher maximum absorbed dose rate, although with a more heterogeneous absorbed dose rate distribution.

Stochastic rat lung dosimetry for inhaled radon progeny: a surrogate for the human lung for lung cancer risk assessment.

PubMed

Winkler-Heil, R; Hussain, M; Hofmann, W

2015-05-01

Laboratory rats are frequently used in inhalation studies as a surrogate for human exposures. The objective of the present study was therefore to develop a stochastic dosimetry model for inhaled radon progeny in the rat lung, to predict bronchial dose distributions and to compare them with corresponding dose distributions in the human lung. The most significant difference between human and rat lungs is the branching structure of the bronchial tree, which is relatively symmetric in the human lung, but monopodial in the rat lung. Radon progeny aerosol characteristics used in the present study encompass conditions typical for PNNL and COGEMA rat inhalation studies, as well as uranium miners and human indoor exposure conditions. It is shown here that depending on exposure conditions and modeling assumptions, average bronchial doses in the rat lung ranged from 5.4 to 7.3 mGy WLM(-1). If plotted as a function of airway generation, bronchial dose distributions exhibit a significant maximum in large bronchial airways. If, however, plotted as a function of airway diameter, then bronchial doses are much more uniformly distributed throughout the bronchial tree. Comparisons between human and rat exposures indicate that rat bronchial doses are slightly higher than human bronchial doses by about a factor of 1.3, while lung doses, averaged over the bronchial (BB), bronchiolar (bb) and alveolar-interstitial (AI) regions, are higher by about a factor of about 1.6. This supports the current view that the rat lung is indeed an appropriate surrogate for the human lung in case of radon-induced lung cancers. Furthermore, airway diameter seems to be a more appropriate morphometric parameter than airway generations to relate bronchial doses to bronchial carcinomas.

SU-F-18C-11: Diameter Dependency of the Radial Dose Distribution in a Long Polyethylene Cylinder

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

Bakalyar, D; McKenney, S; Feng, W

Purpose: The radial dose distribution in the central plane of a long cylinder following a long CT scan depends upon the diameter and composition of the cylinder. An understanding of this behavior is required for determining the spatial average of the dose in the central plane. Polyethylene, the material for construction of the TG200/ICRU phantom (30 cm in diameter) was used for this study. Size effects are germane to the principles incorporated in size specific dose estimates (SSDE); thus diameter dependency was explored as well. Method: ssuming a uniform cylinder and cylindrically symmetric conditions of irradiation, the dose distribution canmore » be described using a radial function. This function must be an even function of the radial distance due to the conditions of symmetry. Two effects are accounted for: The direct beam makes its weakest contribution at the center while the contribution due to scatter is strongest at the center and drops off abruptly at the outer radius. An analytic function incorporating these features was fit to Monte Carlo results determined for infinite polyethylene cylinders of various diameters. A further feature of this function is that it is integrable. Results: Symmetry and continuity dictate a local extremum at the center which is a minimum for the larger sizes. The competing effects described above can Resultin an absolute maximum occurring between the center and outer edge of the cylinders. For the smallest cylinders, the maximum dose may occur at the center. Conclusion: An integrable, analytic function can be used to characterize the radial dependency of dose for cylindrical CT phantoms of various sizes. One use for this is to help determine average dose distribution over the central cylinder plane when equilibrium dose has been reached.« less

Water-filled balloon in the postoperative resection cavity improves dose distribution to target volumes in radiotherapy of maxillary sinus carcinoma.

PubMed

Zhang, Qun; Lin, Shi-Rong; He, Fang; Kang, De-Hua; Chen, Guo-Zhang; Luo, Wei

2011-11-01

Postoperative radiotherapy is a major treatment for patients with maxillary sinus carcinoma. However, the irregular resection cavity poses a technical difficulty for this treatment, causing uneven dose distribution to target volumes. In this study, we evaluated the dose distribution to target volumes and normal tissues in postoperative intensity-modulated radiotherapy (IMRT) after placing a water-filled balloon into the resection cavity. Three postoperative patients with advanced maxillary sinus carcinoma were selected in this trial. Water-filled balloons and supporting dental stents were fabricated according to the size of the maxillary resection cavity. Simulation CT scans were performed with or without water-filled balloons, IMRT treatment plans were established, and dose distribution to target volumes and organs at risk were evaluated. Compared to those in the treatment plan without balloons, the dose (D98) delivered to 98% of the gross tumor volume (GTV) increased by 2.1 Gy (P = 0.009), homogeneity index (HI) improved by 2.3% (P = 0.001), and target volume conformity index (TCI) of 68 Gy increased by 18.5% (P = 0.011) in the plan with balloons. Dosimetry endpoints of normal tissues around target regions in both plans were not significantly different (P > 0.05) except for the optic chiasm. In the plan without balloons, 68 Gy high-dose regions did not entirely cover target volumes in the ethmoid sinus, posteromedial wall of the maxillary sinus, or surgical margin of the hard palate. In contrast, 68 Gy high-dose regions entirely covered the GTV in the plan with balloons. These results suggest that placing a water-filled balloon in the resection cavity for postoperative IMRT of maxillary sinus carcinoma can reduce low-dose regions and markedly and simultaneously increase dose homogeneity and conformity of target volumes.

Dosimetric verification for intensity-modulated arc therapy plans by use of 2D diode array, radiochromic film and radiosensitive polymer gel.

PubMed

Hayashi, Naoki; Malmin, Ryan L; Watanabe, Yoichi

2014-05-01

Several tools are used for the dosimetric verification of intensity-modulated arc therapy (IMAT) treatment delivery. However, limited information is available for composite on-line evaluation of these tools. The purpose of this study was to evaluate the dosimetric verification of IMAT treatment plans using a 2D diode array detector (2D array), radiochromic film (RCF) and radiosensitive polymer gel dosimeter (RPGD). The specific verification plans were created for IMAT for two prostate cancer patients by use of the clinical treatment plans. Accordingly, the IMAT deliveries were performed with the 2D array on a gantry-mounting device, RCF in a cylindrical acrylic phantom, and the RPGD in two cylindrical phantoms. After the irradiation, the planar dose distributions from the 2D array and the RCFs, and the 3D dose distributions from the RPGD measurements were compared with the calculated dose distributions using the gamma analysis method (3% dose difference and 3-mm distance-to-agreement criterion), dose-dependent dose difference diagrams, dose difference histograms, and isodose distributions. The gamma passing rates of 2D array, RCFs and RPGD for one patient were 99.5%, 96.5% and 93.7%, respectively; the corresponding values for the second patient were 97.5%, 92.6% and 92.9%. Mean percentage differences between the RPGD measured and calculated doses in 3D volumes containing PTVs were -0.29 ± 7.1% and 0.97 ± 7.6% for the two patients, respectively. In conclusion, IMAT prostate plans can be delivered with high accuracy, although the 3D measurements indicated less satisfactory agreement with the treatment plans, mainly due to the dosimetric inaccuracy in low-dose regions of the RPGD measurements.

Three-dimensional radiochromic film dosimetry for volumetric modulated arc therapy using a spiral water phantom

PubMed Central

Tanooka, Masao; Doi, Hiroshi; Miura, Hideharu; Inoue, Hiroyuki; Niwa, Yasue; Takada, Yasuhiro; Fujiwara, Masayuki; Sakai, Toshiyuki; Sakamoto, Kiyoshi; Kamikonya, Norihiko; Hirota, Shozo

2013-01-01

We validated 3D radiochromic film dosimetry for volumetric modulated arc therapy (VMAT) using a newly developed spiral water phantom. The phantom consists of a main body and an insert box, each of which has an acrylic wall thickness of 3 mm and is filled with water. The insert box includes a spiral film box used for dose-distribution measurement, and a film holder for positioning a radiochromic film. The film holder has two parallel walls whose facing inner surfaces are equipped with spiral grooves in a mirrored configuration. The film is inserted into the spiral grooves by its side edges and runs along them to be positioned on a spiral plane. Dose calculation was performed by applying clinical VMAT plans to the spiral water phantom using a commercial Monte Carlo-based treatment-planning system, Monaco, whereas dose was measured by delivering the VMAT beams to the phantom. The calculated dose distributions were resampled on the spiral plane, and the dose distributions recorded on the film were scanned. Comparisons between the calculated and measured dose distributions yielded an average gamma-index pass rate of 87.0% (range, 91.2–84.6%) in nine prostate VMAT plans under 3 mm/3% criteria with a dose-calculation grid size of 2 mm. The pass rates were increased beyond 90% (average, 91.1%; range, 90.1–92.0%) when the dose-calculation grid size was decreased to 1 mm. We have confirmed that 3D radiochromic film dosimetry using the spiral water phantom is a simple and cost-effective approach to VMAT dose verification. PMID:23685667

SU-F-T-442: Dose Distribution Comparison for Post-Laryngectomy Stoma Area Between Conventional AP and VMAT Plans with Or Without Bolus

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

Lee, B; Zhang, J; Cho-Lim, J

Purpose: To compare dose distributions of conventional AP vs. VMAT treatment plans with or without bolus around post-laryngectomy stoma. Methods: Radiation dose coverage for post-laryngectomy stoma was analyzed using a set of real-case CT-simulation images. After meticulous contouring of the catheter cuff, stoma lumen, peri-stoma skin and subclinical tumor bed at the larynx, the resulting dosimetry plans were analyzed with or without a 5 mm bolus placement. Wet gauze was used to minimize the effect of any air gap. Four plans were generated: AP superclavicular (SCV) plan with or without bolus, and VMAT plan with or without bolus. A dosemore » of 60Gy in 30 fractions was prescribed at 3 cm depth for AP SCV plan, and to 95% of the PTV volume for VMAT plan. Results: For the conventional AP SCV plan, the peri-stoma skin dose is sensitive to bolus placement as well as air gap compensation by wetted gauze (V95% of 20.7%, 33.0% and 94.8% for no bolus, bolus without and with air gap compensation, respectively). For stoma lumen, the dose drops off rapidly in depth. The catheter cuff may have certain dose-buildup effect, but air gap around it and under the bolus placed can pose a more serious problem. The dose distributions of the two VMAT plans are moderately different for peri-stoma skin (V95% of 95.0% with bolus and air gap compensation, and 82.3% without bolus), but nearly identical for stoma lumen (V95% of 91.5% and 92.0%, respectively). VMAT allows beamlets with different angles of incidence that helped achieve such dose distribution around the stoma even without bolus placement. Conclusion: Overall, the dose coverage around the stoma in the VMAT plan is better than the conventional AP SCV plan. To achieve optimal dose distribution, it is still recommended to place physical bolus and reduce the air gaps.« less

SU-E-T-586: Optimal Determination of Tolerance Level for Radiation Dose Delivery Verification in An in Vivo Dosimetry System

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

Chen, Y; Souri, S; Gill, G

Purpose: To statistically determine the optimal tolerance level in the verification of delivery dose compared to the planned dose in an in vivo dosimetry system in radiotherapy. Methods: The LANDAUER MicroSTARii dosimetry system with screened nanoDots (optically stimulated luminescence dosimeters) was used for in vivo dose measurements. Ideally, the measured dose should match with the planned dose and falls within a normal distribution. Any deviation from the normal distribution may be redeemed as a mismatch, therefore a potential sign of the dose misadministration. Randomly mis-positioned nanoDots can yield a continuum background distribution. A percentage difference of the measured dose tomore » its corresponding planned dose (ΔD) can be used to analyze combined data sets for different patients. A model of a Gaussian plus a flat function was used to fit the ΔD distribution. Results: Total 434 nanoDot measurements for breast cancer patients were collected across a period of three months. The fit yields a Gaussian mean of 2.9% and a standard deviation (SD) of 5.3%. The observed shift of the mean from zero is attributed to the machine output bias and calibration of the dosimetry system. A pass interval of −2SD to +2SD was applied and a mismatch background was estimated to be 4.8%. With such a tolerance level, one can expect that 99.99% of patients should pass the verification and at most 0.011% might have a potential dose misadministration that may not be detected after 3 times of repeated measurements. After implementation, a number of new start breast cancer patients were monitored and the measured pass rate is consistent with the model prediction. Conclusion: It is feasible to implement an optimal tolerance level in order to maintain a low limit of potential dose misadministration while still to keep a relatively high pass rate in radiotherapy delivery verification.« less

A new approach to pattern metrology

NASA Astrophysics Data System (ADS)

Ausschnitt, Christopher P.

2004-05-01

We describe an approach to pattern metrology that enables the simultaneous determination of critical dimensions, overlay and film thickness. A single optical system captures nonzero- and zero-order diffracted signals from illuminated grating targets, as well as unpatterned regions of the surrounding substrate. Differential targets provide in situ dimensional calibration. CD target signals are analyzed to determine average dimension, profile attributes, and effective dose and defocus. In turn, effective dose and defocus determines all CDs pre-correlated to the dose and focus settings of the exposure tool. Overlay target signals are analyzed to determine the relative reflectivity of the layer pair and the overlay error between them. Compared to commercially available pattern metrology (SEM, optical microscopy, AFM, scatterometry and schnitzlometry), our approach promises improved signal-to-noise, higher throughput and smaller targets. We have dubbed this optical chimera MOXIE (Metrology Of eXtremely Irrational Exuberance).

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

Poster — Thur Eve — 11: Validation of the orthopedic metallic artifact reduction tool for CT simulations at the Ottawa Hospital Cancer Centre

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

Sutherland, J; Foottit, C

Metallic implants in patients can produce image artifacts in kilovoltage CT simulation images which can introduce noise and inaccuracies in CT number, affecting anatomical segmentation and dose distributions. The commercial orthopedic metal artifact reduction algorithm (O-MAR) (Philips Healthcare System) was recently made available on CT simulation scanners at our institution. This study validated the clinical use of O-MAR by investigating its effects on CT number and dose distributions. O-MAR corrected and uncorrected images were acquired with a Philips Brilliance Big Bore CT simulator of a cylindrical solid water phantom that contained various plugs (including metal) of known density. CT numbermore » accuracy was investigated by determining the mean and standard deviation in regions of interest (ROI) within each plug for uncorrected and O-MAR corrected images and comparing with no-metal image values. Dose distributions were calculated using the Monaco treatment planning system. Seven open fields were equally spaced about the phantom around a ROI near the center of the phantom. These were compared to a “correct” dose distribution calculated by overriding electron densities a no-metal phantom image to produce an image containing metal but no artifacts. An overall improvement in CT number and dose distribution accuracy was achieved by applying the O-MAR correction. Mean CT numbers and standard deviations were found to be generally improved. Exceptions included lung equivalent media, which is consistent with vendor specified contraindications. Dose profiles were found to vary by ±4% between uncorrected or O-MAR corrected images with O-MAR producing doses closer to ground truth.« less

Dose distribution verification for GYN brachytherapy using EBT Gafchromic film and TG-43 calculation.

PubMed

Gholami, Somayeh; Mirzaei, Hamid Reza; Jabbary Arfaee, Ali; Jaberi, Ramin; Nedaie, Hassan Ali; Rabi Mahdavi, Seied; Rajab Bolookat, Eftekhar; Meigooni, Ali S

2016-01-01

Verification of dose distributions for gynecological (GYN) brachytherapy implants using EBT Gafchromic film. One major challenge in brachytherapy is to verify the accuracy of dose distributions calculated by a treatment planning system. A new phantom was designed and fabricated using 90 slabs of 18 cm × 16 cm × 0.2 cm Perspex to accommodate a tandem and Ovoid assembly, which is normally used for GYN brachytherapy treatment. This phantom design allows the use of EBT Gafchromic films for dosimetric verification of GYN implants with a cobalt-60 HDR system or a LDR Cs-137 system. Gafchromic films were exposed using a plan that was designed to deliver 1.5 Gy of dose to 0.5 cm distance from the lateral surface of ovoids from a pair of ovoid assembly that was used for treatment vaginal cuff. For a quantitative analysis of the results for both LDR and HDR systems, the measured dose values at several points of interests were compared with the calculated data from a commercially available treatment planning system. This planning system was utilizing the TG-43 formalism and parameters for calculation of dose distributions around a brachytherapy implant. The results of these investigations indicated that the differences between the calculated and measured data at different points were ranging from 2.4% to 3.8% for the LDR Cs-137 and HDR Co-60 systems, respectively. The EBT Gafchromic films combined with the newly designed phantom could be utilized for verification of the dose distributions around different GYN implants treated with either LDR or HDR brachytherapy procedures.

Reevaluation of the AAPM TG-43 brachytherapy dosimetry parameters for an 125I seed, and the influence of eye plaque design on dose distributions and dose-volume histograms

NASA Astrophysics Data System (ADS)

Aryal, Prakash

The TG-43 dosimetry parameters of the Advantage(TM) 125I model IAI-125A brachytherapy seed were studied. An investigation using modern MCNP radiation transport code with updated cross-section libraries was performed. Twelve different simulation conditions were studied for a single seed by varying the coating thickness, mass density, photon energy spectrum and cross-section library. The dose rate was found to be 6.3% lower at 1 cm in comparison to published results. New TG-43 dosimetry parameters are proposed. The dose distribution for a brachytherapy eye plaque, model EP917, was investigated, including the effects of collimation from high-Z slots. Dose distributions for 26 slot designs were determined using Monte Carlo methods and compared between the published literature, a clinical treatment planning system, and physical measurements. The dosimetric effect of the composition and mass density of the gold backing was shown to be less than 3%. Slot depth, width, and length changed the central axis (CAX) dose distributions by < 1% per 0.1 mm in design variation. Seed shifts in the slot towards the eye and shifts of the 125I-laden silver rod within the seed had the greatest impact on the CAX dose distribution, changing it by 14%, 9%, 4.3%, and 2.7% at 1, 2, 5, and 10 mm, respectively, from the inner scleral surface. The measured, full plaque slot geometry delivered 2.4% +/- 1.1% higher dose along the plaque's CAX than the geometry provided by the manufacturer and 2.2%+/-2.3% higher than Plaque Simulator(TM) (PS) treatment planning software (version 5.7.6). The D10 for the simulated tumor, inner sclera, and outer sclera for the measured slot plaque to manufacturer provided slot design was 9%, 10%, and 19% higher, respectively. In comparison to the measured plaque design, a theoretical plaque having narrow and deep slots delivered 30%, 37%, and 62% lower D 10 doses to the tumor, inner sclera, and outer sclera, respectively. CAX doses at --1, 0, 1, and 2 mm were also lower by a factor of 2.6, 1.72, 1.50, and 1.39, respectively. The study identified substantial sensitivity of the EP917 plaque dose distributions to slot design. KEYWORDS: Monte Carlo methods, dosimetry, 125I, TG-43, eye plaque brachytherapy.

Leaf position optimization for step-and-shoot IMRT.

PubMed

De Gersem, W; Claus, F; De Wagter, C; Van Duyse, B; De Neve, W

2001-12-01

To describe the theoretical basis, the algorithm, and implementation of a tool that optimizes segment shapes and weights for step-and-shoot intensity-modulated radiation therapy delivered by multileaf collimators. The tool, called SOWAT (Segment Outline and Weight Adapting Tool) is applied to a set of segments, segment weights, and corresponding dose distribution, computed by an external dose computation engine. SOWAT evaluates the effects of changing the position of each collimating leaf of each segment on an objective function, as follows. Changing a leaf position causes a change in the segment-specific dose matrix, which is calculated by a fast dose computation algorithm. A weighted sum of all segment-specific dose matrices provides the dose distribution and allows computation of the value of the objective function. Only leaf position changes that comply with the multileaf collimator constraints are evaluated. Leaf position changes that tend to decrease the value of the objective function are retained. After several possible positions have been evaluated for all collimating leaves of all segments, an external dose engine recomputes the dose distribution, based on the adapted leaf positions and weights. The plan is evaluated. If the plan is accepted, a segment sequencer is used to make the prescription files for the treatment machine. Otherwise, the user can restart SOWAT using the new set of segments, segment weights, and corresponding dose distribution. The implementation was illustrated using two example cases. The first example is a T1N0M0 supraglottic cancer case that was distributed as a multicenter planning exercise by investigators from Rotterdam, The Netherlands. The exercise involved a two-phase plan. Phase 1 involved the delivery of 46 Gy to a concave-shaped planning target volume (PTV) consisting of the primary tumor volume and the elective lymph nodal regions II-IV on both sides of the neck. Phase 2 involved a boost of 24 Gy to the primary tumor region only. SOWAT was applied to the Phase 1 plan. Parotid sparing was a planning goal. The second implementation example is an ethmoid sinus cancer case, planned with the intent of bilateral visus sparing. The median PTV prescription dose was 70 Gy with a maximum dose constraint to the optic pathway structures of 60 Gy. The initial set of segments, segment weights, and corresponding dose distribution were obtained, respectively, by an anatomy-based segmentation tool, a segment weight optimization tool, and a differential scatter-air ratio dose computation algorithm as external dose engine. For the supraglottic case, this resulted in a plan that proved to be comparable to the plans obtained at the other institutes by forward or inverse planning techniques. After using SOWAT, the minimum PTV dose and PTV dose homogeneity increased; the maximum dose to the spinal cord decreased from 38 Gy to 32 Gy. The left parotid mean dose decreased from 22 Gy to 19 Gy and the right parotid mean dose from 20 to 18 Gy. For the ethmoid sinus case, the target homogeneity increased by leaf position optimization, together with a better sparing of the optical tracts. By using SOWAT, the plans improved with respect to all plan evaluation end points. Compliance with the multileaf collimator constraints is guaranteed. The treatment delivery time remains almost unchanged, because no additional segments are created.

In vivo dosimetry using Gafchromic films during pelvic intraoperative electron radiation therapy (IOERT)

PubMed Central

Costa, Filipa; Gomes, Dora; Magalhães, Helena; Arrais, Rosário; Moreira, Graciete; Cruz, Maria Fátima; Silva, José Pedro; Santos, Lúcio; Sousa, Olga

2016-01-01

Objective: To characterize in vivo dose distributions during pelvic intraoperative electron radiation therapy (IOERT) for rectal cancer and to assess the alterations introduced by irregular irradiation surfaces in the presence of bevelled applicators. Methods: In vivo measurements were performed with Gafchromic films during 32 IOERT procedures. 1 film per procedure was used for the first 20 procedures. The methodology was then optimized for the remaining 12 procedures by using a set of 3 films. Both the average dose and two-dimensional dose distributions for each film were determined. Phantom measurements were performed for comparison. Results: For flat and concave surfaces, the doses measured in vivo agree with expected values. For concave surfaces with step-like irregularities, measured doses tend to be higher than expected doses. Results obtained with three films per procedure show a large variability along the irradiated surface, with important differences from expected profiles. These results are consistent with the presence of surface hotspots, such as those observed in phantoms in the presence of step-like irregularities, as well as fluid build-up. Conclusion: Clinical dose distributions in the IOERT of rectal cancer are often different from the references used for prescription. Further studies are necessary to assess the impact of these differences on treatment outcomes. In vivo measurements are important, but need to be accompanied by accurate imaging of positioning and irradiated surfaces. Advances in knowledge: These results confirm that surface irregularities occur frequently in rectal cancer IOERT and have a measurable effect on the dose distribution. PMID:27188847

A revision of the gamma-evaluation concept for the comparison of dose distributions.

PubMed

Bakai, Annemarie; Alber, Markus; Nüsslin, Fridtjof

2003-11-07

A method for the quantitative four-dimensional (4D) evaluation of discrete dose data based on gradient-dependent local acceptance thresholds is presented. The method takes into account the local dose gradients of a reference distribution for critical appraisal of misalignment and collimation errors. These contribute to the maximum tolerable dose error at each evaluation point to which the local dose differences between comparison and reference data are compared. As shown, the presented concept is analogous to the gamma-concept of Low et al (1998a Med. Phys. 25 656-61) if extended to (3+1) dimensions. The pointwise dose comparisons of the reformulated concept are easier to perform and speed up the evaluation process considerably, especially for fine-grid evaluations of 3D dose distributions. The occurrences of false negative indications due to the discrete nature of the data are reduced with the method. The presented method was applied to film-measured, clinical data and compared with gamma-evaluations. 4D and 3D evaluations were performed. Comparisons prove that 4D evaluations have to be given priority, especially if complex treatment situations are verified, e.g., non-coplanar beam configurations.

Preliminary evaluation of the dosimetric accuracy of cone-beam computed tomography for cases with respiratory motion

NASA Astrophysics Data System (ADS)

Kim, Dong Wook; Bae, Sunhyun; Chung, Weon Kuu; Lee, Yoonhee

2014-04-01

Cone-beam computed tomography (CBCT) images are currently used for patient positioning and adaptive dose calculation; however, the degree of CBCT uncertainty in cases of respiratory motion remains an interesting issue. This study evaluated the uncertainty of CBCT-based dose calculations for a moving target. Using a phantom, we estimated differences in the geometries and the Hounsfield units (HU) between CT and CBCT. The calculated dose distributions based on CT and CBCT images were also compared using a radiation treatment planning system, and the comparison included cases with respiratory motion. The geometrical uncertainties of the CT and the CBCT images were less than 0.15 cm. The HU differences between CT and CBCT images for standard-dose-head, high-quality-head, normal-pelvis, and low-dose-thorax modes were 31, 36, 23, and 33 HU, respectively. The gamma (3%, 0.3 cm)-dose distribution between CT and CBCT was greater than 1 in 99% of the area. The gamma-dose distribution between CT and CBCT during respiratory motion was also greater than 1 in 99% of the area. The uncertainty of the CBCT-based dose calculation was evaluated for cases with respiratory motion. In conclusion, image distortion due to motion did not significantly influence dosimetric parameters.

A novel approach to EPID-based 3D volumetric dosimetry for IMRT and VMAT QA

NASA Astrophysics Data System (ADS)

Alhazmi, Abdulaziz; Gianoli, Chiara; Neppl, Sebastian; Martins, Juliana; Veloza, Stella; Podesta, Mark; Verhaegen, Frank; Reiner, Michael; Belka, Claus; Parodi, Katia

2018-06-01

Intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) are relatively complex treatment delivery techniques and require quality assurance (QA) procedures. Pre-treatment dosimetric verification represents a fundamental QA procedure in daily clinical routine in radiation therapy. The purpose of this study is to develop an EPID-based approach to reconstruct a 3D dose distribution as imparted to a virtual cylindrical water phantom to be used for plan-specific pre-treatment dosimetric verification for IMRT and VMAT plans. For each depth, the planar 2D dose distributions acquired in air were back-projected and convolved by depth-specific scatter and attenuation kernels. The kernels were obtained by making use of scatter and attenuation models to iteratively estimate the parameters from a set of reference measurements. The derived parameters served as a look-up table for reconstruction of arbitrary measurements. The summation of the reconstructed 3D dose distributions resulted in the integrated 3D dose distribution of the treatment delivery. The accuracy of the proposed approach was validated in clinical IMRT and VMAT plans by means of gamma evaluation, comparing the reconstructed 3D dose distributions with Octavius measurement. The comparison was carried out using (3%, 3 mm) criteria scoring 99% and 96% passing rates for IMRT and VMAT, respectively. An accuracy comparable to the one of the commercial device for 3D volumetric dosimetry was demonstrated. In addition, five IMRT and five VMAT were validated against the 3D dose calculation performed by the TPS in a water phantom using the same passing rate criteria. The median passing rates within the ten treatment plans was 97.3%, whereas the lowest was 95%. Besides, the reconstructed 3D distribution is obtained without predictions relying on forward dose calculation and without external phantom or dosimetric devices. Thus, the approach provides a fully automated, fast and easy QA procedure for plan-specific pre-treatment dosimetric verification.

Escalating dose, multiple binge methamphetamine regimen does not impair recognition memory in rats.

PubMed

Clark, Robert E; Kuczenski, Ronald; Segal, David S

2007-07-01

Rats exposed to methamphetamine (METH) in an acute high dose "binge" pattern have been reported to exhibit a persistent deficit in a novel object recognition (NOR) task, which may suggest a potential risk for human METH abusers. However, most high dose METH abusers initially use lower doses before progressively increasing the dose, only eventually engaging in multiple daily administrations. To simulate this pattern of METH exposure, we administered progressively increasing doses of METH to rats over a 14 day interval, then treated them with daily METH binges for 11 days. This treatment resulted in a persistent deficit in striatal dopamine (DA) levels of approximately 20%. We then tested them in a NOR task under a variety of conditions. We could not detect a deficit in their performance in the NOR task under any of the testing conditions. These results suggest that mechanisms other than or additional to the decrement in striatal DA associated with an acute METH binge are responsible for the deficit in the NOR task, and that neuroadaptations consequential to prolonged escalating dose METH pretreatment mitigate against these mechanisms.

Genetic epidemiology of pharmacogenetic variations in CYP2C9, CYP4F2 and VKORC1 genes associated with warfarin dosage in the Indian population.

PubMed

Giri, Anil K; Khan, Nazir M; Grover, Sandeep; Kaur, Ismeet; Basu, Analabha; Tandon, Nikhil; Scaria, Vinod; Kukreti, Ritushree; Brahmachari, Samir K; Bharadwaj, Dwaipayan

2014-07-01

Warfarin, a widely used anticoagulant, exhibits large interindividual variability in dose requirements. CYP2C9 and VKORC1 polymorphisms in various ethnic groups have been extensively studied as genetic markers associated with variable drug response. However, allele frequencies of these variants have not been assessed in major ethnic groups in the Indian population. To study the functional variants known to affect warfarin dosing, we reanalyzed genotype microarray datasets generated as a part of genome-wide association studies as well as data from the Indian Genome Variation database. We examined data from 2680 individuals across 24 ethnically diverse Indian subpopulations. Allelic distribution of VKORC1 (-1639G>A) showed a greater degree of variation across Indian subpopulations, with frequencies as low as 6.5% in an out-group subpopulation to >70% in Tibeto-Burmans. Risk allele frequency of CYP4F2*3 (V433M) was higher in north Indians (0.30-0.44), as compared with other world populations, such as African-American (0.12), Caucasian (0.34) and Hispanic (0.23). TheVKORC1 variant (-1639A) was shown to be prevalent amongst Tibeto-Burmans, whereas CYP2C9 (R144C, I359L) and CYP4F2 (V433M) variants were observed in considerable variability amongst Indo-Europeans. The frequency of CYP2C9*3 (I359L) in north Indians was found to be higher than in most Asian populations. Furthermore, geographical distribution patterns of these variants in north India showed an increased trend of warfarin extensive metabolizers from the Himalayan to Gangetic region. Combined allele frequency (CYP2C9*3 and CYP4F2*3) data suggest that poor metabolizers varied in the range of 0.38-1.85% in Indo-Europeans. Based on genotypic distribution, the majority of the Indian subpopulation might require higher doses for stable anticoagulation, whereas careful assessment is required for Tibeto-Burmans who are expected to have intermediate dose requirement. This is the largest global genetic epidemiological study examining variants associated with warfarin that could potentially be valuable to clinicians in optimizing dosage strategies.

Space radiation absorbed dose distribution in a human phantom

NASA Technical Reports Server (NTRS)

Badhwar, G. D.; Atwell, W.; Badavi, F. F.; Yang, T. C.; Cleghorn, T. F.

2002-01-01

The radiation risk to astronauts has always been based on measurements using passive thermoluminescent dosimeters (TLDs). The skin dose is converted to dose equivalent using an average radiation quality factor based on model calculations. The radiological risk estimates, however, are based on organ and tissue doses. This paper describes results from the first space flight (STS-91, 51.65 degrees inclination and approximately 380 km altitude) of a fully instrumented Alderson Rando phantom torso (with head) to relate the skin dose to organ doses. Spatial distributions of absorbed dose in 34 1-inch-thick sections measured using TLDs are described. There is about a 30% change in dose as one moves from the front to the back of the phantom body. Small active dosimeters were developed specifically to provide time-resolved measurements of absorbed dose rates and quality factors at five organ locations (brain, thyroid, heart/lung, stomach and colon) inside the phantom. Using these dosimeters, it was possible to separate the trapped-proton and the galactic cosmic radiation components of the doses. A tissue-equivalent proportional counter (TEPC) and a charged-particle directional spectrometer (CPDS) were flown next to the phantom torso to provide data on the incident internal radiation environment. Accurate models of the shielding distributions at the site of the TEPC, the CPDS and a scalable Computerized Anatomical Male (CAM) model of the phantom torso were developed. These measurements provided a comprehensive data set to map the dose distribution inside a human phantom, and to assess the accuracy and validity of radiation transport models throughout the human body. The results show that for the conditions in the International Space Station (ISS) orbit during periods near the solar minimum, the ratio of the blood-forming organ dose rate to the skin absorbed dose rate is about 80%, and the ratio of the dose equivalents is almost one. The results show that the GCR model dose-rate predictions are 20% lower than the observations. Assuming that the trapped-belt models lead to a correct orbit-averaged energy spectrum, the measurements of dose rates inside the phantom cannot be fully understood. Passive measurements using 6Li- and 7Li-based detectors on the astronauts and inside the brain and thyroid of the phantom show the presence of a significant contribution due to thermal neutrons, an area requiring additional study.

Dissipation and adsorption of isoproturon, tebuconazole, chlorpyrifos and their main transformation products under laboratory and field conditions.

PubMed

Papadopoulou, Evangelia S; Karas, Panagiotis A; Nikolaki, Sofia; Storck, Veronika; Ferrari, Federico; Trevisan, Marco; Tsiamis, George; Martin-Laurent, Fabrice; Karpouzas, Dimitrios G

2016-11-01

Assessment of dissipation constitutes an integral part of pesticides risk assessment since it provides an estimate of the level and the duration of exposure of the terrestrial ecosystem to pesticides. Within the frame of an overall assessment of the soil microbial toxicity of pesticides, we investigated the dissipation of a range of dose rates of three model pesticides, isoproturon (IPU), tebuconazole (TCZ), and chlorpyrifos (CHL), and the formation and dissipation of their main transformation products following a tiered lab-to-field approach. The adsorption of pesticides and their transformation products was also determined. IPU was the least persistent pesticide showing a dose-dependent increase in its persistence in both laboratory and field studies. CHL dissipation showed a dose-dependent increase under laboratory conditions and an exact opposite trend in the field. TCZ was the most persistent pesticide under lab conditions showing a dose-dependent decrease in its dissipation, whereas in the field TCZ exhibited a biphasic dissipation pattern with extrapolated DT90s ranging from 198 to 603.4days in the ×1 and ×2 dose rates, respectively. IPU was demethylated to mono- (MD-IPU) and di-desmethyl-isoproturon (DD-IPU) which dissipated following a similar pattern with the parent compound. CHL was hydrolyzed to 3,5,6-trichloro-2-pyridinol (TCP) which dissipated showing a reverse dose-dependent pattern compared to CHL. Pesticides adsorption affinity increased in the order IPU

Using spatial information about recurrence risk for robust optimization of dose-painting prescription functions

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

Bender, Edward T.

Purpose: To develop a robust method for deriving dose-painting prescription functions using spatial information about the risk for disease recurrence. Methods: Spatial distributions of radiobiological model parameters are derived from distributions of recurrence risk after uniform irradiation. These model parameters are then used to derive optimal dose-painting prescription functions given a constant mean biologically effective dose. Results: An estimate for the optimal dose distribution can be derived based on spatial information about recurrence risk. Dose painting based on imaging markers that are moderately or poorly correlated with recurrence risk are predicted to potentially result in inferior disease control when comparedmore » the same mean biologically effective dose delivered uniformly. A robust optimization approach may partially mitigate this issue. Conclusions: The methods described here can be used to derive an estimate for a robust, patient-specific prescription function for use in dose painting. Two approximate scaling relationships were observed: First, the optimal choice for the maximum dose differential when using either a linear or two-compartment prescription function is proportional to R, where R is the Pearson correlation coefficient between a given imaging marker and recurrence risk after uniform irradiation. Second, the predicted maximum possible gain in tumor control probability for any robust optimization technique is nearly proportional to the square of R.« less

A case study of radiotherapy planning for Intensity Modulation Radiation Therapy for the whole scalp with matching electron treatment

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

Sponseller, Patricia, E-mail: sponselp@uw.edu; Department of Radiation Oncology, University of Washington Medical Center, Seattle, WA; Paravathaneni, Upendra

2013-07-01

The purpose of this report is to communicate a technique to match an electron field to the dose distribution of an Intensity-Modulated Radiation Therapy (IMRT) plan. A patient with multiple areas of squamous cell carcinoma over the scalp was treated using 60 Gy in 2.0-Gy fractions to the entire scalp and first echelon nodes with multiple 6-MV photon fields. To deliver an adequate dose to the scalp, a custom 1.0-cm bolus helmet was fashioned using a solid piece of aquaplast. Along with the IMRT scalp treatment, a left zygoma area was treated with electrons matching the anterior border of themore » IMRT dose distribution. The border was matched by creating a left lateral field with the multileaf collimator shaped to the IMRT dose distribution. The result indicated an adequate dose to the skin match between the IMRT plan and the electron field. Results were confirmed using optically stimulated luminescence placed at the skin match area, so that the dose matched the prescription within 10%.« less

A method for the assessment of specific energy distribution in a model tumor system

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

Noska, M.A.

1996-12-31

Due to the short range of alpha particles in tissue, the calculation of dose from internally deposited alpha emitters requires a detailed analysis of the microscopic distribution of the radionuclide in order to determine the spatial distribution of energy emission events and, from this, the spatial distribution of dose. In the present study, the authors used quantitative autoradiography (QAR) to assess the microdistribution of a radiolabeled monoclonal antibody (MAb) fragment in human glioma xenografts in mice.

A survival model for fractionated radiotherapy with an application to prostate cancer

NASA Astrophysics Data System (ADS)

Zaider, Marco; Zelefsky, Michael J.; Hanin, Leonid G.; Tsodikov, Alexander D.; Yakovlev, Andrei Y.; Leibel, Steven A.

2001-10-01

This paper explores the applicability of a mechanistic survival model, based on the distribution of clonogens surviving a course of fractionated radiation therapy, to clinical data on patients with prostate cancer. The study was carried out using data on 1100 patients with clinically localized prostate cancer who were treated with three-dimensional conformal radiation therapy. The patients were stratified by radiation dose (group 1: <67.5 Gy; group 2: 67.5-72.5 Gy; group 3: 72.5-77.5 Gy; group 4: 77.5-87.5 Gy) and prognosis category (favourable, intermediate and unfavourable as defined by pre-treatment PSA and Gleason score). A relapse was recorded when tumour recurrence was diagnosed or when three successive prostate specific antigen (PSA) elevations were observed from a post-treatment nadir PSA level. PSA relapse-free survival was used as the primary end point. The model, which is based on an iterated Yule process, is specified in terms of three parameters: the mean number of tumour clonogens that survive the treatment, the mean of the progression time of post-treatment tumour development and its standard deviation. The model parameters were estimated by the maximum likelihood method. The fact that the proposed model provides an excellent description both of the survivor function and of the hazard rate is prima facie evidence of the validity of the model because closeness of the two survivor functions (empirical and model-based) does not generally imply closeness of the corresponding hazard rates. The estimated cure probabilities for the favourable group are 0.80, 0.74 and 0.87 (for dose groups 1-3, respectively); for the intermediate group: 0.25, 0.51, 0.58 and 0.78 (for dose groups 1-4, respectively) and for the unfavourable group: 0.0, 0.27, 0.33 and 0.64 (for dose groups 1-4, respectively). The distribution of progression time to tumour relapse was found to be independent of prognosis group but dependent on dose. As the dose increases the mean progression time decreases (41, 28.5, 26.2 and 14.7 months for dose groups 1-4, respectively). This analysis confirms that, in terms of cure rate, dose escalation has a significant positive effect only in the intermediate and unfavourable groups. It was found that progression time is inversely proportional to dose, which means that patients recurring in higher dose groups have shorter recurrence times, yet these groups have better survival, particularly long-term. The explanation for this seemingly illogical observation lies in the fact that less aggressive tumours, potentially recurring after a long period of time, are cured by higher doses and do not contribute to the recurrence pattern. As a result, patients in higher dose groups are less likely to recur; however, if they do, they tend to recur earlier. The estimated hazard rates for prostate cancer pass through a clear-cut maximum, thus revealing a time period with especially high values of instantaneous cancer-specific risk; the estimates appear to be nonproportional across dose strata.