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Sample records for models dosimetric properties

  1. SU-E-T-111: An Iterative Approach to Modelling Dosimetric Properties of a Varian MLC

    SciTech Connect

    DiCostanzo, D

    2015-06-15

    Purpose: In effort to efficiently and accurately model MLC parameters for use in Varian Eclipse treatment planning system (TPS), an iterative technique for characterizing the dosimetric properties of MLCs has been developed. Methods: The initial characterization of the dosimetric leaf gap (DLG) and MLC transmission was performed using varied sizes of moving gaps and transmission measurements through central axis of the radiation beam. These values were determined during the initial data collection. After the initial values were determined and entered into the TPS, two plans were calculated to test the veracity of DLG and transmission independently. The plan used to determine the DLG has openings of varied sizes which are affected differently by the DLG. A large field uniform fluence that required a MLC carriage shift was used to determine the transmission value independent of DLG. After characterizing the dosimetric properties of the MLC independently, clinical IMRT plans were tested and used to tweak the final values. Results: This approach to modelling MLC dosimetric properties was employed for: standard 120 leaf MLC (SDMLC) and 120 leaf high definition MLC (HDMLC). Both types were successfully commissioned, tested, and approved for clinical use on 4 SDMLC machines and 2 HDMLC machines. The pass rate of clinical IMRT plans was 96.9% for 6MV and 98.3% for 10MV for SDMLC and 96.3% for 6MV, 96.5% for 6FFF, and 97.5% for 10FFF for HDMLCs using MapCheck2 with gamma analysis of 2%/2mm and 10% threshold. The final DLG and transmission parameters for 6X were 0.5mm and 0.01, and 1.35mm and 0.02 for HD and SD MLCs respectively. Conclusion: This iterative approach of determining dosimetric properties of MLCs is viable for both SDMLC and HDMLC and multiple energies. This approach accurately and efficiently determines the values needed for commissioning MLCs when they are employed for modulated therapies.

  2. Practical simplifications for radioimmunotherapy dosimetric models

    SciTech Connect

    Shen, S.; DeNardo, G.L.; O`Donnell, R.T.; Yuan, A.; DeNardo, D.A.; Macey, D.J.; DeNardo, S.J.

    1999-01-01

    Radiation dosimetry is potentially useful for assessment and prediction of efficacy and toxicity for radionuclide therapy. The usefulness of these dose estimates relies on the establishment of a dose-response model using accurate pharmacokinetic data and a radiation dosimetric model. Due to the complexity in radiation dose estimation, many practical simplifications have been introduced in the dosimetric modeling for clinical trials of radioimmunotherapy. Although research efforts are generally needed to improve the simplifications used at each stage of model development, practical simplifications are often possible for specific applications without significant consequences to the dose-response model. In the development of dosimetric methods for radioimmunotherapy, practical simplifications in the dosimetric models were introduced. This study evaluated the magnitude of uncertainty associated with practical simplifications for: (1) organ mass of the MIRD phantom; (2) radiation contribution from target alone; (3) interpolation of S value; (4) macroscopic tumor uniformity; and (5) fit of tumor pharmacokinetic data.

  3. Optical and dosimetric properties of zircon.

    PubMed

    Kristianpoller, N; Weiss, D; Chen, R

    2006-01-01

    Irradiation effects were investigated in zircon crystals by methods of optical absorption and luminescence. Special attention was given to the effects of vacuum ultraviolet (VUV) radiation. The same main thermoluminescence (TL) peaks with the same thermal activation energies appeared after VUV as after X- or beta irradiation, indicating that the same traps were induced by the different irradiations. TL excitation spectra in the VUV showed an increase <220 nm and maxima near 190 and 140 nm. Excitation spectra of phototransferred TL (PTTL) and optically stimulated luminescence (OSL) were also measured. Most TL emission bands also appeared in the X-luminescence, PTTL and OSL. Dosimetric properties such as the TL radiation sensitivity, thermal stability of radiation-induced defects and TL dose dependence were also investigated. The radiation sensitivity of zircon was by an order of magnitude lower than that of TLD-100. The 355 K TL peak showed linear dose dependence only up to approximately 500 Gy and the 520 K peak up to approximately 1800 Gy.

  4. Monte carlo investigation of the dosimetric properties of the new 103Pd BrachySeedPd-103 Model Pd-1 source.

    PubMed

    Chan, Gordon H; Prestwich, William V

    2002-09-01

    Recently, 103Pd brachytherapy sources have been increasingly used for interstitial implants as an alternative to 125I sources. The BrachySeedPd-103 Model Pd-1 seed is one of the latest in a series of new brachytherapy sources that have become available commercially. The dosimetric properties of the seed were investigated by Monte Carlo simulation, which was performed using the Integrated Tiger Series CYLTRAN code. Following the AAPM Task Group 43 formalism, the dose rate constant, radial dose function, and anisotropy parameters were determined. The dose rate constant, A, was calculated to be 0.613 +/- 3% cGy h(-1) U(-1). This air kerma strength was derived from Monte Carlo simulation using the point extrapolation method. The radial dose function, g(r), was computed at distances from 0.15 to 10 cm. The anisotropy function, F(r,theta), and anisotropy factor, phi(an)(r), were calculated at distances from 0.5 to 7 cm. The anisotropy constant, phi(an), was determined to be 0.978, which is closer to unity than most other 103Pd seeds, indicating a high degree of uniformity in dose distribution. The dose rate constant and the radial dose function were also investigated by analytical modeling, which served as an independent evaluation of the Monte Carlo data, and found to be in good agreement with the Monte Carlo results.

  5. Dosimetric properties of a flattening filter-free 6-MV photon beam: a Monte Carlo study.

    PubMed

    Mesbahi, Asghar; Mehnati, Parinaz; Keshtkar, Ahmad; Farajollahi, Alireza

    2007-08-01

    The dosimetric features of an unflattened 6-MV photon beam of an Elekta SL-25 linac was calculated by the Monte Carlo (MC) method. The head of the Elekta SL-25 linac was simulated using the MCNP4C MC code. The accuracy of the model was evaluated using measured dosimetric features, including depth dose values and dose profiles in a water phantom. The flattening filter was then removed, and beam dosimetric properties were calculated by the MC method and compared with those of the flattened photon beam. Our results showed a significant (twofold) increase in the dose rate for all field sizes. Also, the photon beam spectra for an unflattened beam were softer, which led to a steeper reduction in depth doses. The decrease in the out-of-field dose and increase in the contamination electrons and a buildup region dose were the other consequences of removing the flattening filter. Our study revealed that, for recent radiotherapy techniques, the use of multileaf collimators for beam shaping removing the flattening filter could offer some advantages, including an increased dose rate and decreased out-of-field dose.

  6. Dosimetric properties of dysprosium doped calcium magnesium borate glass subjected to Co-60 gamma ray

    SciTech Connect

    Omar, R. S. Wagiran, H. Saeed, M. A.

    2016-01-22

    Thermoluminescence (TL) dosimetric properties of dysprosium doped calcium magnesium borate (CMB:Dy) glass are presented. This study is deemed to understand the application of calcium as the modifier in magnesium borate glass with the presence of dysprosium as the activator to be performed as TL dosimeter (TLD). The study provides fundamental knowledge of a glass system that may lead to perform new TL glass dosimetry application in future research. Calcium magnesium borate glass systems of (70-y) B{sub 2}O{sub 3} − 20 CaO – 10 MgO-(y) Dy{sub 2}O{sub 3} with 0.05  mol % ≤ y ≤ 0.7  mol % of dyprosium were prepared by melt-quenching technique. The amorphous structure and TL properties of the prepared samples were determined using powder X-ray diffraction (XRD) and TL reader; model Harshaw 4500 respectively. The samples were irradiated to Co-60 gamma source at a dose of 50 Gy. Dosimetric properties such as annealing procedure, time temperature profile (TTP) setting, optimization of Dy{sub 2}O{sub 3} concentration of 0.5 mol % were determined for thermoluminescence dosimeter (TLD) reader used.

  7. A biokinetic and dosimetric model for ionic indium in humans

    NASA Astrophysics Data System (ADS)

    Andersson, Martin; Mattsson, Sören; Johansson, Lennart; Leide-Svegborn, Sigrid

    2017-08-01

    This paper reviews biokinetic data for ionic indium, and proposes a biokinetic model for systemic indium in adult humans. The development of parameter values focuses on human data and indium in the form of ionic indium(III), as indium chloride and indium arsenide. The model presented for systemic indium is defined by five different pools: plasma, bone marrow, liver, kidneys and other soft tissues. The model is based on two subsystems: one corresponding to indium bound to transferrin and one where indium is transported back to the plasma, binds to red blood cell transferrin and is then excreted through the kidneys to the urinary bladder. Absorbed doses to several organs and the effective dose are calculated for 111In- and 113mIn-ions. The proposed biokinetic model is compared with previously published biokinetic indium models published by the ICRP. The absorbed doses are calculated using the ICRP/ICRU adult reference phantoms and the effective dose is estimated according to ICRP Publication 103. The effective doses for 111In and 113mIn are 0.25 mSv MBq-1 and 0.013 mSv MBq-1 respectively. The updated biokinetic and dosimetric models presented in this paper take into account human data and new animal data, which represent more detailed and presumably more accurate dosimetric data than that underlying previous models for indium.

  8. Biologic data, models, and dosimetric methods for internal emitters

    SciTech Connect

    Weber, D.A.

    1990-01-01

    The absorbed radiation dose from internal emitters has been and will remain a pivotal factor in assessing risk and therapeutic utility in selecting radiopharmaceuticals for diagnosis and treatment. Although direct measurements of absorbed dose and dose distributions in vivo have been and will continue to be made in limited situations, the measurement of the biodistribution and clearance of radiopharmaceuticals in human subjects and the use of this data is likely to remain the primary means to approach the calculation and estimation of absorbed dose from internal emitters over the next decade. Since several approximations are used in these schema to calculate dose, attention must be given to inspecting and improving the application of this dosimetric method as better techniques are developed to assay body activity and as more experience is gained in applying these schema to calculating absorbed dose. Discussion of the need for considering small scale dosimetry to calculate absorbed dose at the cellular level will be presented in this paper. Other topics include dose estimates for internal emitters, biologic data mathematical models and dosimetric methods employed. 44 refs.

  9. Study of the thermoluminescence dosimetric properties of window glass

    NASA Astrophysics Data System (ADS)

    Engin, Birol; Aydaş, Canan; Demirtaş, Hayrünnisa

    2010-01-01

    This paper presents the main thermoluminescence (TL) dosimetric characteristics of commercial Turkish transparent window glass. The structure of the glow curves, including the number of peaks, was found to be dose-dependent. A low-temperature glow peak that at 160 °C shifts to higher temperatures was also observed with increasing storage time at room temperature. This result suggests that this TL glow peak is actually made up of two or more overlapping peaks. These we have attributed to the glow peaks at lower temperatures, which decay faster than the ones at higher temperatures with storage time. The thermal fading of the window glass sample at room temperature showed a relatively sharp decay of about 60% occurring over a period of 28 days, after which the decay rate is small for a measured period of 250 days. In order to the improve the post-irradiation stability of the glow curve, the glass samples were heated after irradiation. To remove the unstable TL peaks responsible for the initial rapid fading, post-irradiation heating at 160 °C for 10 min was found to be the most suitable procedure. The dosimetric characteristics of the post-irradiation heated window glass examined in this study include fading, gamma photon dose-response, reproducibility, batch sensitivity, humidity influence, a dose-rate effect and photon energy response. Dose-response was found to be appropriate for dosimetry in the range 5 Gy to 10 kGy. The post-irradiation heating procedure did not affect the main dosimetric characteristics of the window glass samples. The results in this work suggest that the materials could, by using the TL technique, be a suitable candidate for alternative dose measurements in radiation processing, provided that a judicious choice of the post-irradiation heat temperature is made to minimize fading.

  10. Study of the dosimetric properties of an unflattened 6-MV photon beam by using the BEAMnrc code

    NASA Astrophysics Data System (ADS)

    Kajaria, Ankit; Sharma, Neeraj; Sharma, Shiru; Pradhan, Satyajit; Mandal, Abhijit; Aggarwal, Lalit. M.

    2016-08-01

    This study investigated the basic dosimetric properties of a Flattening-filter-free 6-MV photon beam based on the unique performance model of the Varian Clinic 600 linac operated with and without a flattening filter. Dosimetric features, including the central-axis absorbed dose, the beam profiles and the photon and electron fluences were calculated for the flattened and unflattened cases separately by using Monte Carlo simulations. We observe that the dosimetric field size and penumbra were slightly smaller for the unflattened beam, but the beam's non-flatness is unlikely to present a problem for treatments with small fields. Absolute depth dose calculations showed an increase in the dose rate by a factor of more than 2.4 for the unflattened 6-MV beam which depended on the depth. These results suggest that the removal of the filter could result in higher central-axis dose rates and hence, shorter beam delivery times for treatments. Surface doses were found to be higher for the unflattened beam due to more contamination electrons and low-energy photons being present in the beam. The total scatter factor, SCP, varies less with the field sizes, indicating that removing the filter from the beam line can reduce significantly the amount of head scatter photons and therefore, doses to normal tissues and organs.

  11. Analysis of superficial fluorescence patterns in nonmelanoma skin cancer during photodynamic therapy by a dosimetric model

    NASA Astrophysics Data System (ADS)

    Salas-García, I.; Fanjul-Vélez, F.; Arce-Diego, J. L.

    2016-03-01

    In this work the superficial fluorescence patterns in different nonmelanoma skin cancers and their photodynamic treatment response are analysed by a fluorescence based dosimetric model. Results show differences of even more than 50% in the fluorescence patterns as photodynamic therapy progresses depending on the malignant tissue type. They demonstrate the great relevance of the biological media as an additional dosimetric factor and contribute to the development of a future customized therapy with the assistance of dosimetric tools to interpret the fluorescence images obtained during the treatment monitoring and the differential photodiagnosis.

  12. A comprehensive approach to age-dependent dosimetric modeling

    SciTech Connect

    Leggett, R.W.; Cristy, M.; Eckerman, K.F.

    1986-01-01

    In the absence of age-specific biokinetic models, current retention models of the International Commission on Radiological Protection (ICRP) frequently are used as a point of departure for evaluation of exposures to the general population. These models were designed and intended for estimation of long-term integrated doses to the adult worker. Their format and empirical basis preclude incorporation of much valuable physiological information and physiologically reasonable assumptions that could be used in characterizing the age-specific behavior of radioelements in humans. In this paper we discuss a comprehensive approach to age-dependent dosimetric modeling in which consideration is given not only to changes with age in masses and relative geometries of body organs and tissues but also to best available physiological and radiobiological information relating to the age-specific biobehavior of radionuclides. This approach is useful in obtaining more accurate estimates of long-term dose commitments as a function of age at intake, but it may be particularly valuable in establishing more accurate estimates of dose rate as a function of age. Age-specific dose rates are needed for a proper analysis of the potential effects on estimates or risk of elevated dose rates per unit intake in certain stages of life, elevated response per unit dose received during some stages of life, and age-specific non-radiogenic competing risks.

  13. Dosimetric properties of high energy current (HEC) detector in keV x-ray beams

    NASA Astrophysics Data System (ADS)

    Zygmanski, Piotr; Shrestha, Suman; Elshahat, Bassem; Karellas, Andrew; Sajo, Erno

    2015-04-01

    We introduce a new x-ray radiation detector. The detector employs high-energy current (HEC) formed by secondary electrons consisting predominantly of photoelectrons and Auger electrons, to directly convert x-ray energy to detector signal without externally applied power and without amplification. The HEC detector is a multilayer structure composed of thin conducting layers separated by dielectric layers with an overall thickness of less than a millimeter. It can be cut to any size and shape, formed into curvilinear surfaces, and thus can be designed for a variety of QA applications. We present basic dosimetric properties of the detector as function of x-ray energy, depth in the medium, area and aspect ratio of the detector, as well as other parameters. The prototype detectors show similar dosimetric properties to those of a thimble ionization chamber, which operates at high voltage. The initial results obtained for kilovoltage x-rays merit further research and development towards specific medical applications.

  14. Dosimetric property of mineral extracted from calamari and exposed to gamma rays

    NASA Astrophysics Data System (ADS)

    Cruz-Zaragoza, E.; Roman-Lopez, J.; Cruz, L. Pérez; Furetta, C.; Chiaravalle, E.; Mangiacotti, M.; Marchesani, G.

    2013-07-01

    Dosimetric property of polymineral fraction, quartz mainly, obtained from calamari was investigated. The commercial calamari samples from China and Sud Africa were collected in the markets of Italy. All polymineral debris were extracted and isolated from the whole body of calamari. The surface of the polymineral samples was analyzed by using the Scanning Electron Microscopy (SEM) and their chemical composition was determined using Energy Dispersive Spectroscopy (EDS). The polymineral was exposed to gamma rays (60Co) at different doses (0.5-80 Gy) to determine dosimetric property. Thermoluminescent (TL) glow curves showed two peaks centered at around 98-100 °C and 128-138 °C temperature range. The glow curves have been analyzed by using a deconvolution program. A linear dose response between 0.5 to 20 Gy was observed. The TL response of the samples as a function of the time storage, fading, presented a reduction of about 36-40 % at the end of 24 h. The reproducibility of the TL response after ten cycles of irradiation-readout showed an acceptable standard deviation in dosimetry. The polimineral fraction obtained from calamari shows an interesting dosimetric property and it may be useful for dosimetry in gamma radiation field.

  15. Dosimetric property of mineral extracted from calamari and exposed to gamma rays

    SciTech Connect

    Cruz-Zaragoza, E.; Roman-Lopez, J.; Cruz, L. Perez; Furetta, C.; Chiaravalle, E.; Mangiacotti, M.; Marchesani, G.

    2013-07-03

    Dosimetric property of polymineral fraction, quartz mainly, obtained from calamari was investigated. The commercial calamari samples from China and Sud Africa were collected in the markets of Italy. All polymineral debris were extracted and isolated from the whole body of calamari. The surface of the polymineral samples was analyzed by using the Scanning Electron Microscopy (SEM) and their chemical composition was determined using Energy Dispersive Spectroscopy (EDS). The polymineral was exposed to gamma rays ({sup 60}Co) at different doses (0.5-80 Gy) to determine dosimetric property. Thermoluminescent (TL) glow curves showed two peaks centered at around 98-100 Degree-Sign C and 128-138 Degree-Sign C temperature range. The glow curves have been analyzed by using a deconvolution program. A linear dose response between 0.5 to 20 Gy was observed. The TL response of the samples as a function of the time storage, fading, presented a reduction of about 36-40 % at the end of 24 h. The reproducibility of the TL response after ten cycles of irradiation-readout showed an acceptable standard deviation in dosimetry. The polimineral fraction obtained from calamari shows an interesting dosimetric property and it may be useful for dosimetry in gamma radiation field.

  16. Dosimetric analysis of 123I, 125I and 131I in thyroid follicle models

    PubMed Central

    2014-01-01

    Background Radioiodine is routinely used or proposed for diagnostic and therapeutic purposes: 123I, 125I and 131I for diagnostics and 125I and 131I for therapy. When radioiodine-labelled pharmaceuticals are administered to the body, radioiodide might be released into the circulation and taken up by the thyroid gland, which may then be an organ at risk. The aim of this study was to compare dosimetric properties for 123I, 125I and 131I in previously developed thyroid models for man, rat and mouse. Methods Dosimetric calculations were performed using the Monte Carlo code MCNPX 2.6.0 and nuclear decay data from ICRP 107. Only the non-radiative transitions in the decays were considered. The S value was determined for the cell nuclei in species-specific thyroid follicle models for mouse, rat and man for different spatial distributions of radioiodine. Results For the species-specific single follicle models with radioiodine homogeneously within the follicle lumen, the highest S value came from 131I, with the largest contribution from the β particles. When radioiodine was homogeneously distributed within the follicle cells or the follicle cell nucleus, the highest contribution originated from 125I, about two times higher than 123I, with the largest contribution from the Auger electrons. The mean absorbed dose calculated for our human thyroid multiple follicle model, assuming homogenous distribution of for 123I, 125I, or 131I within the follicle lumens and follicle cells, was 9%, 18% and 4% higher, respectively, compared with the mean absorbed dose according to Medical Internal Radiation Dose (MIRD) formalism and nuclear decay data. When radioiodine was homogeneously distributed in the follicle lumens, our calculations gave up to 90% lower mean absorbed dose for 125I compared to MIRD (20% lower for 123I, and 2% lower for 131I). Conclusions This study clearly demonstrates the importance of using more detailed dosimetric methods and models than MIRD formalism for radioiodine

  17. Dosimetric properties of a proton beamline dedicated to the treatment of ocular disease

    SciTech Connect

    Slopsema, R. L. Mamalui, M.; Yeung, D.; Malyapa, R.; Li, Z.; Zhao, T.

    2014-01-15

    Purpose: A commercial proton eyeline has been developed to treat ocular disease. Radiotherapy of intraocular lesions (e.g., uveal melanoma, age-related macular degeneration) requires sharp dose gradients to avoid critical structures like the macula and optic disc. A high dose rate is needed to limit patient gazing times during delivery of large fractional dose. Dose delivery needs to be accurate and predictable, not in the least because current treatment planning algorithms have limited dose modeling capabilities. The purpose of this paper is to determine the dosimetric properties of a new proton eyeline. These properties are compared to those of existing systems and evaluated in the context of the specific clinical requirements of ocular treatments. Methods: The eyeline is part of a high-energy, cyclotron-based proton therapy system. The energy at the entrance of the eyeline is 105 MeV. A range modulator (RM) wheel generates the spread-out Bragg peak, while a variable range shifter system adjusts the range and spreads the beam laterally. The range can be adjusted from 0.5 up to 3.4 g/cm{sup 2}; the modulation width can be varied in steps of 0.3 g/cm{sup 2} or less. Maximum field diameter is 2.5 cm. All fields can be delivered with a dose rate of 30 Gy/min or more. The eyeline is calibrated according to the IAEA TRS-398 protocol using a cylindrical ionization chamber. Depth dose distributions and dose/MU are measured with a parallel-plate ionization chamber; lateral profiles with radiochromic film. The dose/MU is modeled as a function of range, modulation width, and instantaneous MU rate with fit parameters determined per option (RM wheel). Results: The distal fall-off of the spread-out Bragg peak is 0.3 g/cm{sup 2}, larger than for most existing systems. The lateral penumbra varies between 0.9 and 1.4 mm, except for fully modulated fields that have a larger penumbra at skin. The source-to-axis distance is found to be 169 cm. The dose/MU shows a strong dependence

  18. An investigation of the dosimetric and kinetic properties of sand using ESR and TL techniques.

    PubMed

    Aydaş, Canan; Aydın, Talat

    2015-07-01

    In this research, the general dosimetric and kinetic properties of sand from a beach in southern Turkey were investigated using electron spin resonance (ESR) and thermoluminescence (TL) techniques. The ESR dose response curve presents linear behaviour in the dose range of 250-1000 Gy followed by sublinear behaviour in the dose range of 2-8 kGy. Kinetic behaviors and activation energy of the free radical were also calculated using the data obtained from annealing studies performed at four different temperatures (220, 240, 260 and 280°C). The activation energy value was calculated as 1.47 eV. The long-term fading of the ESR signal at room temperature turned out to be best described by a second-order kinetic decay function. The presence of measurable ESR signal intensity even after a storage period of 90 days was considered as providing an opportunity in the dose estimation of irradiated sand sample. Although the TL glow curve of the natural (unirradiated) sand sample only has a single broad peak at 317°C, the glow curve of the irradiated sample has four glow peaks located at ~115°C, ~156°C, ~231°C and ~308°C and their intensity tends to be increased with absorbed dose.Tmax-Tstop and glow curve fitting results showed that presence of at least five peaks located at ∼116°C, 149°C, 228°C, 306°C and 360°C. This result suggests that the apparently single glow peak D may consist of two or more overlapping glow peaks. According to the thermal fading of the sand sample at room temperature, the TL signal intensities (23°C and 308°C) were found to be quite large after 30 days of storage this allows a more accurate measurement of the glow peak intensity. The additive dose method, variable heating rate method (VHRM), Tmax-Tstop and glow curve fitting method were used to number of peaks, dosimetric properties and kinetic parameters. This study shows that ESR and TL techniques could be successfully used to investigate the kinetics and dosimetric properties of sand

  19. Dosimetric properties of an amorphous silicon EPID for verification of modulated electron radiotherapy

    SciTech Connect

    Chatelain, Cecile; Vetterli, Daniel; Henzen, Dominik; Favre, Pascal; Fix, Michael K.; Manser, Peter; Morf, Daniel; Scheib, Stefan

    2013-06-15

    Purpose: To investigate the dosimetric properties of an electronic portal imaging device (EPID) for electron beam detection and to evaluate its potential for quality assurance (QA) of modulated electron radiotherapy (MERT). Methods: A commercially available EPID was used to detect electron beams shaped by a photon multileaf collimator (MLC) at a source-surface distance of 70 cm. The fundamental dosimetric properties such as reproducibility, dose linearity, field size response, energy response, and saturation were investigated for electron beams. A new method to acquire the flood-field for the EPID calibration was tested. For validation purpose, profiles of open fields and various MLC fields (square and irregular) were measured with a diode in water and compared to the EPID measurements. Finally, in order to use the EPID for QA of MERT delivery, a method was developed to reconstruct EPID two-dimensional (2D) dose distributions in a water-equivalent depth of 1.5 cm. Comparisons were performed with film measurement for static and dynamic monoenergy fields as well as for multienergy fields composed by several segments of different electron energies. Results: The advantageous EPID dosimetric properties already known for photons as reproducibility, linearity with dose, and dose rate were found to be identical for electron detection. The flood-field calibration method was proven to be effective and the EPID was capable to accurately reproduce the dose measured in water at 1.0 cm depth for 6 MeV, 1.3 cm for 9 MeV, and 1.5 cm for 12, 15, and 18 MeV. The deviations between the output factors measured with EPID and in water at these depths were within {+-}1.2% for all the energies with a mean deviation of 0.1%. The average gamma pass rate (criteria: 1.5%, 1.5 mm) for profile comparison between EPID and measurements in water was better than 99% for all the energies considered in this study. When comparing the reconstructed EPID 2D dose distributions at 1.5 cm depth to film

  20. Dosimetric treatment course simulation based on a statistical model of deformable organ motion.

    PubMed

    Söhn, M; Sobotta, B; Alber, M

    2012-06-21

    We present a method of modeling dosimetric consequences of organ deformation and correlated motion of adjacent organ structures in radiotherapy. Based on a few organ geometry samples and the respective deformation fields as determined by deformable registration, principal component analysis (PCA) is used to create a low-dimensional parametric statistical organ deformation model (Söhn et al 2005 Phys. Med. Biol. 50 5893-908). PCA determines the most important geometric variability in terms of eigenmodes, which represent 3D vector fields of correlated organ deformations around the mean geometry. Weighted sums of a few dominating eigenmodes can be used to simulate synthetic geometries, which are statistically meaningful inter- and extrapolations of the input geometries, and predict their probability of occurrence. We present the use of PCA as a versatile treatment simulation tool, which allows comprehensive dosimetric assessment of the detrimental effects that deformable geometric uncertainties can have on a planned dose distribution. For this, a set of random synthetic geometries is generated by a PCA model for each simulated treatment course, and the dose of a given treatment plan is accumulated in the moving tissue elements via dose warping. This enables the calculation of average voxel doses, local dose variability, dose-volume histogram uncertainties, marginal as well as joint probability distributions of organ equivalent uniform doses and thus of TCP and NTCP, and other dosimetric and biologic endpoints. The method is applied to the example of deformable motion of prostate/bladder/rectum in prostate IMRT. Applications include dosimetric assessment of the adequacy of margin recipes, adaptation schemes, etc, as well as prospective 'virtual' evaluation of the possible benefits of new radiotherapy schemes.

  1. Dosimetric properties of radiophotoluminescent glass detector in low-energy photon beams.

    PubMed

    Kadoya, Noriyuki; Shimomura, Kouhei; Kitou, Satoshi; Shiota, Yasuo; Fujita, Yukio; Dobashi, Suguru; Takeda, Ken; Jingu, Keiichi; Matsushita, Haruo; Namito, Yoshihito; Ban, Syuichi; Koyama, Syuji; Tabushi, Katsuyoshi

    2012-10-01

    A radiophotoluminescent glass rod dosimeter (RGD) has recently become commercially available. It is being increasingly used for dosimetry in radiotherapy to measure the absorbed dose including scattered low-energy photons on the body surface of a patient and for postal dosimetry audit. In this article, the dosimetric properties of the RGD, including energy dependence of the dose response, reproducibly, variation in data obtained by the RGD for each energy, and angular dependence in low-energy photons, are discussed. An RGD (GD-301, Asahi Techno Glass Corporation, Shizuoka, Japan) was irradiated with monochromatic low-energy photon beams generated by synchrotron radiation at Photon Factory, High Energy Accelerator Research Organization (KEK). The size of GD-301 was 1.5 mm in diameter and 8.5 mm in length and the active dose readout volume being 1 mm diameter and 0.6 mm depth located 0.7 mm from the end of the detector. The energy dependence of the dose response and reproducibility and variation were investigated for RGDs irradiated with a plastic holder and those irradiated without the plastic holder. Response of the RGD was obtained by not only conventional single field irradiation but also bilateral irradiation. Angular dependence of the RGD was measured in the range of 0°-90° for 13, 17, 40, and 80 keV photon beams by conventional single field irradiation. The dose responses had a peak at around 40 keV. For the energy range of less than 25 keV, all dose response curves steeply decreased in comparison with the ratio of mass energy absorption coefficient of the RGD to that of air. As for the reproducibility and variation in data obtained by the RGD, the coefficient of variance increased with decrease in photon energy. Furthermore, the variation for bilateral irradiation was less than that for single field irradiation. Regarding angular dependence of the RGD, for energies of 13 and 17 keV, the response decreased with increase in the irradiation angle, and the

  2. The revised International Commission on Radiological Protection (ICRP) dosimetric model for the human respiratory tract

    SciTech Connect

    Bair, W.J.

    1992-05-01

    A task group has revised the dosimetric model of the respiratory tract used to calculate annual limits on intake of radionuclides. The revised model can be used to project respiratory tract doses for workers and members of the public from airborne radionuclides and to assess past exposures. Doses calculated for specific extrathoracic and thoracic tissues can be adjusted to account for differences in radiosensitivity and summed to yield two values of dose for the respiratory tract that are applicable to the ICRP tissue weighted dosimetry system.

  3. Revision of the ICRP dosimetric model for the human respiratory tract

    SciTech Connect

    Bair, W.J.

    1990-12-01

    Although the dosimetric model of the respiratory tract used in ICRP Publication 30 had not been shown to be seriously deficient for the purpose of calculating Annual Limits on Intake (ALIs) for workers, the availability of new information led the ICRP in 1984 to create a special Task Group to review the dosimetric model of the respiratory tract and, if justified, propose revisions or a new model. The Task Group directed its efforts toward improving the model used in Publication 30 rather than developing a completely new model. The objective was a model that would facilitate calculation of biologically meaningful doses; be consistent with morphological, physiological, and radiobiological characteristics of the respiratory tract; incorporate current knowledge; meet all radiation protection needs; be user friendly by not being unnecessarily sophisticated; be adaptable to development of computer software for calculation of relevant radiation doses from knowledge of a few readily measured exposure parameters; be equally useful for assessment purposes as for calculating ALIs; be applicable to all members of the world population; and consider the influence of smoking, air pollutants, and diseases of the inhalation, deposition, and clearance of radioactive particles from the respiratory tract. The model provides for calculation of a committed dose equivalent for each region, adjusted for the relative cancer sensitivity of that region, and for the summing of these to yield a committed dose equivalent for the entire respiratory tract. 3 figs.

  4. A Combined Tissue Kinetics and Dosimetric Model of Respiratory Tissue Exposed to Radiation

    SciTech Connect

    John R. Ford

    2005-11-01

    Existing dosimetric models of the radiation response of tissues are essentially static. Consideration of changes in the cell populations over time has not been addressed realistically. For a single acute dose this is not a concern, but for modeling chronic exposures or fractionated acute exposures, the natural turnover and progression of cells could have a significant impact on a variety of endpoints. This proposal addresses the shortcomings of current methods by combining current dose-based calculation techniques with information on the cell turnover for a model tissue. The proposed model will examine effects at the single-cell level for an exposure of a section of human bronchiole. The cell model will be combined with Monte Carlo calculations of doses to cells and cell nuclei due to varying dose-rates of different radiation qualities. Predictions from the model of effects on survival, apoptosis rates, and changes in the number of cycling and differentiating cells will be tested experimentally. The availability of dynamic dosimetric models of tissues at the single-cell level will be useful for analysis of low-level radiation exposures and in the development of new radiotherapy protocols.

  5. Americium in the beagle dog: biokinetic and dosimetric model.

    PubMed

    Luciani, A; Polig, E; Lloyd, R D; Miller, S C

    2006-05-01

    A biokinetic model of the systemic distribution of americium in the beagle dog is presented. The model is based on a previous biokinetic model of plutonium. The data sets used for the development of the model were the measurements of excreted activity (urine and feces) and organ burdens (skeleton, liver, and other soft tissues) for different levels of initial injected activity. In developing the model, the compartmental structure of the skeleton of the plutonium model was adopted, and only the numerical values of parameters were adapted. The model well describes the fractions of americium in the skeleton, liver, and soft tissues and the total fraction excreted in urine and feces. The tuning of the liver clearance parameter provides a realistic description of the change in the partitioning between liver and skeleton for different injection levels. The most significant features of the biokinetics and dosimetry of americium and plutonium in beagles are compared. The total fractions of the clearance to the skeleton and the liver are roughly equal to the value for plutonium, but the partitioning of americium between these organs is reversed with respect to the partitioning of plutonium. 241Am doses to liver and skeleton are similar to 239Pu doses, owing to some counteracting factors. For the highest injection level, the liver mass is dependent on the time post injection. For the skeletal tissues, the dose to the cortical endosteum by far exceeds the dose to the trabecular endosteum and the red marrow. The model provides the basis for statistical survival analyses and risk estimates.

  6. PROSPECTIVE ASSESSMENT OF DOSIMETRIC/PHYSIOLOGIC-BASED MODELS FOR PREDICTING RADIATION PNEUMONITIS

    PubMed Central

    Kocak, Zafer; Borst, Gerben R.; Zeng, Jing; Zhou, Sumin; Hollis, Donna R.; Zhang, Junan; Evans, Elizabeth S.; Folz, Rodney J.; Wong, Terrence; Kahn, Daniel; Belderbos, Jose S. A.; Lebesque, Joos V.; Marks, Lawrence B.

    2007-01-01

    Purpose Clinical and 3D dosimetric parameters are associated with symptomatic radiation pneumonitis rates in retrospective studies. Such parameters include: mean lung dose (MLD), radiation (RT) dose to perfused lung (via SPECT), and pre-RT lung function. Based on prior publications, we defined pre-RT criteria hypothesized to be predictive for later development of pneumonitis. We herein prospectively test the predictive abilities of these dosimetric/functional parameters on two cohorts of patients from Duke and the Netherlands Cancer Institute (NKI). Methods and Materials For the Duke cohort, 55 eligible patients treated between 1999-2005 on a prospective IRB-approved study to monitor RT-induced lung injury were analyzed. A similar group of patients treated at the NKI between 1996-2002 were identified. Patients believed to be at high and low risk for pneumonitis were defined based on: a) MLD; b) OpRP (sum of predicted perfusion reduction based on regional dose response curve); and c) pre-RT DLCO. All doses reflected tissue density heterogeneity. The rates of grade ≥2 pneumonitis in the “presumed” high and low risk groups were compared using Fisher’s exact test. Results In the Duke group, pneumonitis rates in patients prospectively deemed to be at “high” vs. “low” risk are 7/20 and 9/35, respectively; p=0.33 one tailed Fisher’s. Similarly, comparable rates for the NKI group are 4/21 and 6/44, respectively, p=0.41 one-tailed Fisher’s. Conclusion The prospective model is unable to accurately segregate patients into high vs. low risk groups. However, considered retrospectively, these data are consistent with prior studies suggesting that dosimetric (e.g. MLD) and functional (e.g. PFTs or SPECT) parameters are predictive for RT-induced pneumonitis. Additional work is needed to better identify, and prospectively assess, predictors of RT-induced lung injury. PMID:17189069

  7. Evaluation of the dosimetric properties of a synthetic single crystal diamond detector in high energy clinical proton beams

    SciTech Connect

    Mandapaka, A. K.; Ghebremedhin, A.; Patyal, B.; Marinelli, Marco; Prestopino, G.; Verona, C.; Verona-Rinati, G.

    2013-12-15

    Purpose: To investigate the dosimetric properties of a synthetic single crystal diamond Schottky diode for accurate relative dose measurements in large and small field high-energy clinical proton beams.Methods: The dosimetric properties of a synthetic single crystal diamond detector were assessed by comparison with a reference Markus parallel plate ionization chamber, an Exradin A16 microionization chamber, and Exradin T1a ion chamber. The diamond detector was operated at zero bias voltage at all times. Comparative dose distribution measurements were performed by means of Fractional depth dose curves and lateral beam profiles in clinical proton beams of energies 155 and 250 MeV for a 14 cm square cerrobend aperture and 126 MeV for 3, 2, and 1 cm diameter circular brass collimators. ICRU Report No. 78 recommended beam parameters were used to compare fractional depth dose curves and beam profiles obtained using the diamond detector and the reference ionization chamber. Warm-up/stability of the detector response and linearity with dose were evaluated in a 250 MeV proton beam and dose rate dependence was evaluated in a 126 MeV proton beam. Stem effect and the azimuthal angle dependence of the diode response were also evaluated.Results: A maximum deviation in diamond detector signal from the average reading of less than 0.5% was found during the warm-up irradiation procedure. The detector response showed a good linear behavior as a function of dose with observed deviations below 0.5% over a dose range from 50 to 500 cGy. The detector response was dose rate independent, with deviations below 0.5% in the investigated dose rates ranging from 85 to 300 cGy/min. Stem effect and azimuthal angle dependence of the diode signal were within 0.5%. Fractional depth dose curves and lateral beam profiles obtained with the diamond detector were in good agreement with those measured using reference dosimeters.Conclusions: The observed dosimetric properties of the synthetic single

  8. Evaluation of the dosimetric properties of a synthetic single crystal diamond detector in high energy clinical proton beams.

    PubMed

    Mandapaka, A K; Ghebremedhin, A; Patyal, B; Marinelli, Marco; Prestopino, G; Verona, C; Verona-Rinati, G

    2013-12-01

    To investigate the dosimetric properties of a synthetic single crystal diamond Schottky diode for accurate relative dose measurements in large and small field high-energy clinical proton beams. The dosimetric properties of a synthetic single crystal diamond detector were assessed by comparison with a reference Markus parallel plate ionization chamber, an Exradin A16 microionization chamber, and Exradin T1a ion chamber. The diamond detector was operated at zero bias voltage at all times. Comparative dose distribution measurements were performed by means of Fractional depth dose curves and lateral beam profiles in clinical proton beams of energies 155 and 250 MeV for a 14 cm square cerrobend aperture and 126 MeV for 3, 2, and 1 cm diameter circular brass collimators. ICRU Report No. 78 recommended beam parameters were used to compare fractional depth dose curves and beam profiles obtained using the diamond detector and the reference ionization chamber. Warm-up∕stability of the detector response and linearity with dose were evaluated in a 250 MeV proton beam and dose rate dependence was evaluated in a 126 MeV proton beam. Stem effect and the azimuthal angle dependence of the diode response were also evaluated. A maximum deviation in diamond detector signal from the average reading of less than 0.5% was found during the warm-up irradiation procedure. The detector response showed a good linear behavior as a function of dose with observed deviations below 0.5% over a dose range from 50 to 500 cGy. The detector response was dose rate independent, with deviations below 0.5% in the investigated dose rates ranging from 85 to 300 cGy∕min. Stem effect and azimuthal angle dependence of the diode signal were within 0.5%. Fractional depth dose curves and lateral beam profiles obtained with the diamond detector were in good agreement with those measured using reference dosimeters. The observed dosimetric properties of the synthetic single crystal diamond detector indicate that

  9. SU-E-T-135: Dosimetric Properties of the OCTAVIUS Detector 1500

    SciTech Connect

    Stelljes, T; Looe, H; Chofor, N; Poppe, B; Harmeyer, A; Reuter, J; Harder, D

    2014-06-01

    Purpose: In this study the dosimetric properties of the Octavius Detector 1500 array (PTW-Freiburg-Germany) are investigated. Methods: The chambers of the array, each with an entrance window of 4.4 × 4.4 cm{sup 2}, are arranged in a checkerboard pattern in a measurement area of 27 × 27 cm{sup 2} with a sampling frequency of 0.1 mm{sup −1} along each row which can be doubled by merging two measurements shifted by 5 mm. Linearity, stability and output factors were measured with either a Semiflex 31013 or 31010 as a reference detector. Output factors were additionally measured with a Diode 60012. The effective point of measurement was determined by comparing TPR curves of the array with Roos chamber 34001 measurements. The lateral dose response function of a single chamber was determined by comparison with a high resolution diode. An IMRT field verification was carried out with a merged OD1500 measurement. Results: The OD1500 was stable within ±0.15 %. Deviations in linearity did not exceed 1% from 5 to 1000 MU. The effective point of measurement was 8.2 mm below the surface. Deviations in output factors were below 0.77 % from 5 × 5 to 27 × 27 cm{sup 2}. As expected for the smallest field of 1 × 1 cm{sup 2}, the deviation from the diode was significant. The widths of the lateral dose response functions were σ{sup 6} = (2.07 ± 0.03) mm and σ{sup 15} = (2.09 ± 0.03) mm. Gamma Index passing rates for typical IMRT and VMAT plans were above 90 % compared to film and TPS calculations for a local 3 mm / 3 % criterion. Conclusion: The first measurements with the OD1500 array show the excellent applicability of the array for clinical dosimetry. The response of the array to the mean photon energy and dose per pulse are under investigation.

  10. Dosimetric effects on small-field beam-modeling for stereotactic body radiation therapy

    NASA Astrophysics Data System (ADS)

    Cho, Woong; Kim, Suzy; Kim, Jung-In; Wu, Hong-Gyun; Jung, Joo-Young; Kim, Min-Joo; Suh, Tae-Suk; Kim, Jin-Young; Kim, Jong Won

    2015-02-01

    The treatment planning of stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) requires high accuracy of dosimetric data for small radiation fields. The dosimetric effects on the beam-modeling process of a treatment planning system (TPS) were investigated using different measured small-field data sets. We performed small-field dosimetry with three detectors: a CC13 ion chamber, a CC01 ion chamber, and an edge detector. Percentage depth doses (PDDs) and dose profiles for field sizes given by 3 × 3 cm2, 2 × 2 cm2, and 1 × 1 cm2 were obtained for 6 MV and 15 MV photon beams. Each measured data set was used as data input for a TPS, in which a beam-modeling process was implemented using the collapsed cone convolution (CCC) algorithm for dose calculation. The measured data were used to generate six beam-models based on each combination of detector type and photon energy, which were then used to calculate the corresponding PDDs and dose profiles for various depths and field sizes. Root mean square differences (RMSDs) between the calculated and the measured doses were evaluated for the PDDs and the dose profiles. The RMSDs of PDDs beyond the maximum dose depth were within an accuracy of 0.2-0.6%, being clinically acceptable. The RMSDs of the dose profiles corresponding to the CC13, the CC01, and the edge detector were 2.80%, 1.49%, and 1.46% for a beam energy of 6 MV and 2.34%, 1.15%, and 1.44% for a beam energy of 15 MV, respectively. The calculated results for the CC13 ion chamber showed the most discrepancy compared to the measured data, due to the relatively large sensitive volume of this detector. However, the calculated dose profiles for the detectors were not significantly different from another. The physical algorithm used in the beam-modeling process did not seem to be sensitive to blurred data measured with detectors with large sensitive volumes. Each beam-model was used to clinically evaluate lung and lymphatic node SBRT plans

  11. Monte Carlo modelling the dosimetric effects of electrode material on diamond detectors.

    PubMed

    Baluti, Florentina; Deloar, Hossain M; Lansley, Stuart P; Meyer, Juergen

    2015-03-01

    Diamond detectors for radiation dosimetry were modelled using the EGSnrc Monte Carlo code to investigate the influence of electrode material and detector orientation on the absorbed dose. The small dimensions of the electrode/diamond/electrode detector structure required very thin voxels and the use of non-standard DOSXYZnrc Monte Carlo model parameters. The interface phenomena was investigated by simulating a 6 MV beam and detectors with different electrode materials, namely Al, Ag, Cu and Au, with thickens of 0.1 µm for the electrodes and 0.1 mm for the diamond, in both perpendicular and parallel detector orientation with regards to the incident beam. The smallest perturbations were observed for the parallel detector orientation and Al electrodes (Z = 13). In summary, EGSnrc Monte Carlo code is well suited for modelling small detector geometries. The Monte Carlo model developed is a useful tool to investigate the dosimetric effects caused by different electrode materials. To minimise perturbations cause by the detector electrodes, it is recommended that the electrodes should be made from a low-atomic number material and placed parallel to the beam direction.

  12. Dosimetric properties of plasma density effects on laser-accelerated VHEE beams using a sharp density-transition scheme

    NASA Astrophysics Data System (ADS)

    Yoo, Seung Hoon; Min, Byung Jun; Cho, Sungho; Kim, Eun Ho; Park, Jeong Hoon; Jung, Won-Gyun; Kim, Geun Beom; Kim, Kum Bae; Kim, Jaehoon; Jeong, Hojin; Lee, Kitae; Park, Sung Yong

    2017-01-01

    In this paper, the effects of the plasma density on laser-accelerated electron beams for radiation therapy with a sharp density transition are investigated. In the sharp density-transition scheme for electron injection, the crucial issue is finding the optimum density conditions under which electrons injected only during the first period of the laser wake wave are accelerated further. In this paper, we report particle-in-cell simulation results for the effects of both the scale length and the densitytransition ratio on the generation of a quasi-mono-energetic electron bunch. The effects of both the transverse parabolic channel and the plasma length on the electron-beam's quality are investigated. Also, we show the experimental results for the feasibility of a sharp density-transition structure. The dosimetric properties of these very high-energy electron beams are calculated using Monte Carlo simulations.

  13. Evaluation of the Positional Accuracy and Dosimetric Properties of a Three-dimensional Printed Device for Head and Neck Immobilization.

    PubMed

    Sato, Kiyokazu; Takeda, Ken; Dobashi, Suguru; Kadoya, Noriyuki; Ito, Kengo; Chiba, Mizuki; Kishi, Kazuma; Yanagawa, Isao; Jingu, Keiichi

    2017-01-01

    Our aim was to investigate the feasibility of a three-dimensional (3D) -printed head-and-neck (HN) immobilization device by comparing its positional accuracy and dosimetric properties with those of a conventional immobilization device (CID). We prepared a 3D-printed immobilization device (3DID) consisting of a mask and headrest with acrylonitrile-butadiene-styrene resin developed from the computed tomography data obtained by imaging a HN phantom. For comparison, a CID comprising a thermoplastic mask and headrest was prepared using the same HN phantom. We measured the setup error using the ExacTrac X-ray image system. Furthermore, using the ionization chamber and the water-equivalent phantom, we measured the changes in the dose due to the difference in the immobilization device material from the photon of 4 MV and 6 MV. The positional accuracy of the two devices were almost similar in each direction except in the vertical, lateral, and pitch directions (t-test, p<0.0001), and the maximum difference was 1 mm, and 1°. The standard deviations were not statistically different in each direction except in the longitudinal (F-test, p=0.034) and roll directions (F-test, p<0.0001). When the thickness was the same, the dose difference was almost similar at a 50 mm depth. At a 1 mm depth, the 3DID-plate had a 2.9-4.2% lower dose than the CID-plate. This study suggested that the positional accuracy and dosimetric properties of 3DID were almost similar to those of CID.

  14. TG-43 U1 based dosimetric characterization of model 67-6520 Cs-137 brachytherapy source

    SciTech Connect

    Meigooni, Ali S.; Wright, Clarissa; Koona, Rafiq A.; Awan, Shahid B.; Granero, Domingo; Perez-Calatayud, Jose; Ballester, Facundo

    2009-10-15

    Purpose: Brachytherapy treatment has been a cornerstone for management of various cancer sites, particularly for the treatment of gynecological malignancies. In low dose rate brachytherapy treatments, {sup 137}Cs sources have been used for several decades. A new {sup 137}Cs source design has been introduced (model 67-6520, source B3-561) by Isotope Products Laboratories (IPL) for clinical application. The goal of the present work is to implement the TG-43 U1 protocol in the characterization of the aforementioned {sup 137}Cs source. Methods: The dosimetric characteristics of the IPL {sup 137}Cs source are measured using LiF thermoluminescent dosimeters in a Solid Water phantom material and calculated using Monte Carlo simulations with the GEANT4 code in Solid Water and liquid water. The dose rate constant, radial dose function, and two-dimensional anisotropy function of this source model were obtained following the TG-43 U1 recommendations. In addition, the primary and scatter dose separation (PSS) formalism that could be used in convolution/superposition methods to calculate dose distributions around brachytherapy sources in heterogeneous media was studied. Results: The measured and calculated dose rate constants of the IPL {sup 137}Cs source in Solid Water were found to be 0.930({+-}7.3%) and 0.928({+-}2.6%) cGy h{sup -1} U{sup -1}, respectively. The agreement between these two methods was within our experimental uncertainties. The Monte Carlo calculated value in liquid water of the dose rate constant was {Lambda}=0.948({+-}2.6%) cGy h{sup -1} U{sup -1}. Similarly, the agreement between measured and calculated radial dose functions and the anisotropy functions was found to be within {+-}5%. In addition, the tabulated data that are required to characterize the source using the PSS formalism were derived. Conclusions: In this article the complete dosimetry of the newly designed {sup 137}Cs IPL source following the AAPM TG-43 U1 dosimetric protocol and the PSS

  15. Preliminary investigation of the dosimetric properties of ClearView™ dosimeter

    NASA Astrophysics Data System (ADS)

    Huet, C.; Colnot, J.; Clairand, I.

    2017-05-01

    ClearView™ is a single-use radiochromic 3D dosimeter designed by Modus Medical Devices Inc. Some of the dosimetric characteristics of this gel, such as response as a function of dose and as a function of energy were investigated. Moreover, a 400 mL jar was irradiated with a 1x1 cm2 field and PDD and cross-profiles were compared to those obtained with active detectors. Small volumes of gels were found to exhibit a linear response to dose in the dose range 10-80 Gy. Promising PDD and cross profiles were obtained. Artefacts obtained in high resolution for the PDD are suspected to come from small inhomogeneities in the gel.

  16. Dosimetric Significance of the ICRP's Updated Guidance and Models, 1989-2003, and Implications for U.S. Federal Guidance

    SciTech Connect

    Leggett, R.W.

    2003-09-10

    Over the past two decades the U.S. Environmental Protection Agency (EPA) has issued a series of Federal guidance documents for the purpose of providing the Federal and State agencies with technical information to assist their implementation of radiation protection programs. Currently recommended dose conversion factors, annual limits on intake, and derived air concentrations for intake of radionuclides are tabulated in Federal Guidance Report No. 11 (FGR 11), published in 1988. The tabulations in FGR 11 were based on dosimetric quantities and biokinetic and dosimetric models of the International Commission on Radiological Protection (ICRP) developed for application to occupational exposures. Since the publication of FGR 11 the ICRP has revised some of its dosimetric quantities and its models for workers and has also developed age-specific models and dose conversion factors for intake of radionuclides by members of the public. This report examines the extent of the changes in the inhalation and ingestion dose coefficients of FGR 11 implied by the updated recommendations of the ICRP, both for workers and members of the public.

  17. Biokinetic and dosimetric modelling in the estimation of radiation risks from internal emitters.

    PubMed

    Harrison, John

    2009-06-01

    The International Commission on Radiological Protection (ICRP) has developed biokinetic and dosimetric models that enable the calculation of organ and tissue doses for a wide range of radionuclides. These are used to calculate equivalent and effective dose coefficients (dose in Sv Bq(-1) intake), considering occupational and environmental exposures. Dose coefficients have also been given for a range of radiopharmaceuticals used in diagnostic medicine. Using equivalent and effective dose, exposures from external sources and from different radionuclides can be summed for comparison with dose limits, constraints and reference levels that relate to risks from whole-body radiation exposure. Risk estimates are derived largely from follow-up studies of the survivors of the atomic bombings at Hiroshima and Nagasaki in 1945. New dose coefficients will be required following the publication in 2007 of new ICRP recommendations. ICRP biokinetic and dosimetric models are subject to continuing review and improvement, although it is arguable that the degree of sophistication of some of the most recent models is greater than required for the calculation of effective dose to a reference person for the purposes of regulatory control. However, the models are also used in the calculation of best estimates of doses and risks to individuals, in epidemiological studies and to determine probability of cancer causation. Models are then adjusted to best fit the characteristics of the individuals and population under consideration. For example, doses resulting from massive discharges of strontium-90 and other radionuclides to the Techa River from the Russian Mayak plutonium plant in the early years of its operation are being estimated using models adapted to take account of measurements on local residents and other population-specific data. Best estimates of doses to haemopoietic bone marrow, in utero and postnatally, are being used in epidemiological studies of radiation-induced leukaemia

  18. Reliability of Current Biokinetic and Dosimetric Models for Radionuclides: A Pilot Study

    SciTech Connect

    Leggett, Richard Wayne; Eckerman, Keith F; Meck, Robert A.

    2008-10-01

    This report describes the results of a pilot study of the reliability of the biokinetic and dosimetric models currently used by the U.S. Nuclear Regulatory Commission (NRC) as predictors of dose per unit internal or external exposure to radionuclides. The study examines the feasibility of critically evaluating the accuracy of these models for a comprehensive set of radionuclides of concern to the NRC. Each critical evaluation would include: identification of discrepancies between the models and current databases; characterization of uncertainties in model predictions of dose per unit intake or unit external exposure; characterization of variability in dose per unit intake or unit external exposure; and evaluation of prospects for development of more accurate models. Uncertainty refers here to the level of knowledge of a central value for a population, and variability refers to quantitative differences between different members of a population. This pilot study provides a critical assessment of models for selected radionuclides representing different levels of knowledge of dose per unit exposure. The main conclusions of this study are as follows: (1) To optimize the use of available NRC resources, the full study should focus on radionuclides most frequently encountered in the workplace or environment. A list of 50 radionuclides is proposed. (2) The reliability of a dose coefficient for inhalation or ingestion of a radionuclide (i.e., an estimate of dose per unit intake) may depend strongly on the specific application. Multiple characterizations of the uncertainty in a dose coefficient for inhalation or ingestion of a radionuclide may be needed for different forms of the radionuclide and different levels of information of that form available to the dose analyst. (3) A meaningful characterization of variability in dose per unit intake of a radionuclide requires detailed information on the biokinetics of the radionuclide and hence is not feasible for many infrequently

  19. Theoretical and experimental determination of dosimetric characteristics for brachyseed Pd-103, model Pd-1, source.

    PubMed

    Meigooni, Ali S; Zhang, Hualin; Perry, Candace; Dini, Sharifeh A; Koona, Rafiq A

    2003-05-01

    Dosimetric characteristics of the BrachySeed Pd-103, Model Pd-1 source have been determined using both theoretical and experimental methods. Dose rate constant, radial dose function, and anisotropy functions of the source have been obtained following the TG-43 recommendations. Derivation of the dose rate constant was based on recent NIST WAFAC calibration performed in accordance with their 1999 Standard. Measurements were performed in Solid Water using LiF TLD chips. Theoretical simulation calculations were performed in both Solid Water and water phantom materials using MCNP4C2 Monte Carlo code using DLC-200 interaction data. The results of the Monte Carlo simulation indicated a dose rate constant of 0.65 cGyh(-1)U(-1) and 0.61 cGyh (-1)U(-1) in water and Solid Water, respectively. The measured dose rate constant in Solid Water was found to be 0.63+/-7% cGyh (-1)U(-1), which is within the experimental uncertainty of the Monte-Carlo simulated results. The anisotropy functions of the source were calculated in both water and in Solid Water at the radial distances of 1 to 7 cm. Measurements were made in Solid Water at distances of 2, 3, 5, and 7 cm. The Monte-Carlo calculated anisotropy constant of the new source was found to be 0.98 in water. The tabulated data and 5th order polynomial fit coefficients for the radial dose function along with the dose rate constant and anisotropy functions are provided to support clinical use of this source.

  20. A Dosimetric Model of Duodenal Toxicity After Stereotactic Body Radiotherapy for Pancreatic Cancer

    SciTech Connect

    Murphy, James D.; Christman-Skieller, Claudia; Kim, Jeff; Dieterich, Sonja; Chang, Daniel T.; Koong, Albert C.

    2010-12-01

    Introduction: Dose escalation for pancreas cancer is limited by the tolerance of adjacent normal tissues, especially with stereotactic body radiotherapy (SBRT). The duodenum is generally considered to be the organ at greatest risk. This study reports on the dosimetric determinants of duodenal toxicity with single-fraction SBRT. Methods and Materials: Seventy-three patients with locally advanced unresectable pancreatic adenocarcinoma received 25 Gy in a single fraction. Dose-volume histogram (DVH) endpoints evaluated include V{sub 5} (volume of duodenum that received 5 Gy), V{sub 10}, V{sub 15}, V{sub 20}, V{sub 25}, and D{sub max} (maximum dose to 1 cm{sup 3}). Normal tissue complication probability (NTCP) was evaluated with a Lyman model. Univariate and multivariate analyses were conducted with Kaplan-Meier and Cox regression models. Results: The median time to Grade 2-4 duodenal toxicity was 6.3 months (range, 1.6-11.8 months). The 6- and 12-month actuarial rates of toxicity were 11% and 29%, respectively. V{sub 10}-V{sub 25} and D{sub max} all correlated significantly with duodenal toxicity (p < 0.05). In particular, V{sub 15} {>=} 9.1 cm{sup 3} and V{sub 15} < 9.1 cm{sup 3} yielded duodenal toxicity rates of 52% and 11%, respectively (p = 0.002); V{sub 20} {>=} 3.3 cm{sup 3} and V{sub 20} < 3.3 cm{sup 3} gave toxicity rates of 52% and 11%, respectively (p = 0.002); and D{sub max} {>=} 23 Gy and D{sub max} < 23 Gy gave toxicity rates of 49% and 12%, respectively (p = 0.004). Lyman NTCP model optimization generated the coefficients m = 0.23, n = 0.12, and TD{sub 50} = 24.6 Gy. Only the Lyman NTCP model remained significant in multivariate analysis (p = 0.001). Conclusions: Multiple DVH endpoints and a Lyman NTCP model are strongly predictive of duodenal toxicity after SBRT for pancreatic cancer. These dose constraints will be valuable in future abdominal SBRT studies.

  1. An innovative dosimetric model for formulating a semi-analytical solution for the activity-volume relationship in prostate implants

    SciTech Connect

    Lee, Plato C.; Parks, Eric K.; Moran, Brian J

    2003-12-31

    An innovative (and yet simple) dosimetric model is proposed that provides a semi-analytical solution to the total activity-volume relationship in ultrasound-guided transperineal prostate implant. This dosimetric model is based on 4 simple assumptions. First, the prostate target volume is approximated as a sphere. Second, the urethra is presumed to transverse through the center of the prostate target volume. Third, peripheral loading is applied as the seed-loading technique. Fourth, as the major innovation of the proposed model, the radial dose function of the Iodine-125 {sup 125}I seed is forced to fit a simple power function of the distance r. Pursuant to the third assumption, the peripherally-loaded seeds also define a spherical volume defined as the loading volume w. Also pursuant to the fourth assumption, the radial dose function is expressed as 1.139*r{sup -0.474} for r = 1.5 to 2.5 cm. Thereafter, a simple analytical power-law equation, A = 1.630* w{sup 0.825}, for the relationship between the total activity A in mCi and the loading volume w in cc is derived for {sup 125}I monotherapy. Isodose plans for loading volumes corresponding to r = 1.5, 1.8, 2.2, and 2.5 cm were performed. The maximal isodose coverage volume {sub max}V100 was calculated for each case and was found to be on the average 65% larger than the loading volume w. Matching prostate target volume V to the loading volume w therefore yields a generous implant (with a margin of approximately 3.3 mm). Conversely, matching the prostate target volume V to the {sub max}V100 yields a tight implant (with 0.0 mm or no margin). Matching the prostate target volume V to a midpoint between the loading volume w and {sub max}V100 yields a moderate implant (with approximately 1- to 2-mm margin). Three individual equations are derived for each type of implants: A = 1.630* V{sup 0.825}, A = 1.288* V{sup 0.825}, or A = 1.078 V{sup 0.825} for generous, tight, or moderate implants, respectively. Patient data at the

  2. Evaluation of the dosimetric properties of a diode detector for small field proton radiosurgery.

    PubMed

    McAuley, Grant A; Teran, Anthony V; Slater, Jerry D; Slater, James M; Wroe, Andrew J

    2015-11-08

    The small fields and sharp gradients typically encountered in proton radiosurgery require high spatial resolution dosimetric measurements, especially below 1-2 cm diameters. Radiochromic film provides high resolution, but requires postprocessing and special handling. Promising alternatives are diode detectors with small sensitive volumes (SV) that are capable of high resolution and real-time dose acquisition. In this study we evaluated the PTW PR60020 proton dosimetry diode using radiation fields and beam energies relevant to radiosurgery applications. Energies of 127 and 157 MeV (9.7 to 15 cm range) and initial diameters of 8, 10, 12, and 20mm were delivered using single-stage scattering and four modulations (0, 15, 30, and 60mm) to a water tank in our treatment room. Depth dose and beam profile data were compared with PTW Markus N23343 ionization chamber, EBT2 Gafchromic film, and Monte Carlo simulations. Transverse dose profiles were measured using the diode in "edge-on" orientation or EBT2 film. Diode response was linear with respect to dose, uniform with dose rate, and showed an orientation-dependent (i.e., beam parallel to, or perpendicular to, detector axis) response of less than 1%. Diodevs. Markus depth-dose profiles, as well as Markus relative dose ratio vs. simulated dose-weighted average lineal energy plots, suggest that any LET-dependent diode response is negligible from particle entrance up to the very distal portion of the SOBP for the energies tested. Finally, while not possible with the ionization chamber due to partial volume effects, accurate diode depth-dose measurements of 8, 10, and 12 mm diameter beams were obtained compared to Monte Carlo simulations. Because of the small SV that allows measurements without partial volume effects and the capability of submillimeter resolution (in edge-on orientation) that is crucial for small fields and high-dose gradients (e.g., penumbra, distal edge), as well as negligible LET dependence over nearly the

  3. Image quality & dosimetric property of an investigational imaging beam line MV-CBCT.

    PubMed

    Beltran, Chris; Lukose, Renin; Gangadharan, B; Bani-Hashemi, A; Faddegon, Bruce A

    2009-06-17

    To measure and compare the contrast to noise ratio (CNR) as a function of dose for the CBCTs produced by the mega-voltage (MV) imaging beam line (IBL) and the treatment beam line (TBL), and to compare the dose to target and various critical structures of pediatric patients for the IBL CBCT versus standard TBL orthogonal port films. Two Siemens Oncor linear accelerators were modified at our institution such that the MV-CBCT would operate under an investigational IBL rather than the standard 6MV TBL. Prior to the modification, several CBCTs of an electron density phantom were acquired with the TBL at various dose values. After the modification, another set of CBCTs of the electron density phantom were acquired for various doses using the IBL. The Contrast to Noise Ratio (CNR) for each tissue equivalent insert was calculated. In addition, a dosimetric study of pediatric patients was conducted comparing the 1 cGy IBL CBCT and conventional TBL orthogonal pair port films. The CNR for eight tissue equivalent inserts at five different dose settings for each type of CBCT was measured. The CNR of the muscle insert was 0.8 for a 5 cGy TBL CBCT, 1.1 for a 1.5 cGy IBL CBCT and 2.8 for a conventional CT. The CNR of the trabecular bone insert was 2.9 for a 5 cGy TBL CBCT, 5.5 for a 1.5 cGy IBL CBCT and 14.8 for a conventional CT. The IBL CBCT delivered approximately one-fourth the dose to the target and critical structures of the patients as compared to the TBL orthogonal pair port films. The IBL CBCT improves image quality while simultaneously reducing the dose to the patient as compared to the TBL CBCT. A 1 cGy IBL CBCT, which is used for boney anatomy localization, delivers one-fourth the dose as compared to conventional ortho-pair films.

  4. Evaluation of the dosimetric properties of a diode detector for small field proton radiosurgery.

    PubMed

    McAuley, Grant A; Teran, Anthony V; Slater, Jerry D; Slater, James M; Wroe, Andrew J

    2015-11-01

    The small fields and sharp gradients typically encountered in proton radiosurgery require high spatial resolution dosimetric measurements, especially below 1-2 cm diameters. Radiochromic film provides high resolution, but requires postprocessing and special handling. Promising alternatives are diode detectors with small sensitive volumes (SV) that are capable of high resolution and real-time dose acquisition. In this study we evaluated the PTW PR60020 proton dosimetry diode using radiation fields and beam energies relevant to radiosurgery applications. Energies of 127 and 157 MeV (9.7 to 15 cm range) and initial diameters of 8, 10, 12, and 20 mm were delivered using single-stage scattering and four modulations (0, 15, 30, and 60 mm) to a water tank in our treatment room. Depth dose and beam profile data were compared with PTW Markus N23343 ionization chamber, EBT2 Gafchromic film, and Monte Carlo simulations. Transverse dose profiles were measured using the diode in "edge-on" orientation or EBT2 film. Diode response was linear with respect to dose, uniform with dose rate, and showed an orientation-dependent (i.e., beam parallel to, or perpendicular to, detector axis) response of less than 1%. Diode vs. Markus depth-dose profiles, as well as Markus relative dose ratio vs. simulated dose-weighted average lineal energy plots, suggest that any LET-dependent diode response is negligible from particle entrance up to the very distal portion of the SOBP for the energies tested. Finally, while not possible with the ionization chamber due to partial volume effects, accurate diode depth-dose measurements of 8, 10, and 12 mm diameter beams were obtained compared to Monte Carlo simulations. Because of the small SV that allows measurements without partial volume effects and the capability of submillimeter resolution (in edge-on orientation) that is crucial for small fields and high-dose gradients (e.g., penumbra, distal edge), as well as negligible LET dependence over nearly the

  5. Dosimetric sensing and optical properties of ZnO-SnO2 nanocomposites synthesized by co-precipitation method

    NASA Astrophysics Data System (ADS)

    Baitha, Pankaj Kr.; Pal, Partha P.; Manam, J.

    2014-05-01

    In this study an effort has been made to investigate the dosimetric sensing and optical properties of ZnO-SnO2 nanocomposites at different pH values. The nanocomposites samples are irradiated by X-ray and then thermoluminescence (TL) analysis is carried out to investigate the response. The structural details of nanocomposites are characterized by Scanning Electron microscope, X-Ray Powder Diffraction and Fourier Transform Infrared Spectroscopy. Similarly, optical properties were characterized by UV-vis spectroscopy and Photoluminescence spectroscopy. The XRD studies revealed good crystallnity of samples with presence of both phases, ZnO as well as SnO2 simultaneously. The SEM image revealed nanoflakes and nanoflower shape of ZnO-SnO2 nanocomposite for sample synthesized at pH 7. Also, nanocube and nanosphere can be seen at higher pH value of 9. The room temperature photoluminescence spectra of ZnO-SnO2 nanocomposite contain multi peaks at 398 nm, 410 nm, 451 nm, 469 nm, 484 nm, 493 nm and 545 nm at an excitation wavelength of 225 nm, which arises mainly due to oxygen and zinc related defects. The TL glow curve shows intense glow peaks at 346°, 261°, 209° and 153° for the samples synthesized at pH 3, pH 5, pH 7 and pH 9 respectively. The peaks are found to be increased with higher pH values. The peaks are found to be shifted towards lower temperature with higher pH values. The study shows that the ZnO-SnO2 nano-composite is more developed material than singly ZnO compound or SnO2 with enhanced opto-electronic and thermal properties and great applications in thermal dosimetry.

  6. Model-based versus specific dosimetry in diagnostic context: Comparison of three dosimetric approaches

    SciTech Connect

    Marcatili, S. Villoing, D.; Mauxion, T.; Bardiès, M.; McParland, B. J.

    2015-03-15

    Purpose: The dosimetric assessment of novel radiotracers represents a legal requirement in most countries. While the techniques for the computation of internal absorbed dose in a therapeutic context have made huge progresses in recent years, in a diagnostic scenario the absorbed dose is usually extracted from model-based lookup tables, most often derived from International Commission on Radiological Protection (ICRP) or Medical Internal Radiation Dose (MIRD) Committee models. The level of approximation introduced by these models may impact the resulting dosimetry. The aim of this work is to establish whether a more refined approach to dosimetry can be implemented in nuclear medicine diagnostics, by analyzing a specific case. Methods: The authors calculated absorbed doses to various organs in six healthy volunteers administered with flutemetamol ({sup 18}F) injection. Each patient underwent from 8 to 10 whole body 3D PET/CT scans. This dataset was analyzed using a Monte Carlo (MC) application developed in-house using the toolkit GATE that is capable to take into account patient-specific anatomy and radiotracer distribution at the voxel level. They compared the absorbed doses obtained with GATE to those calculated with two commercially available software: OLINDA/EXM and STRATOS implementing a dose voxel kernel convolution approach. Results: Absorbed doses calculated with GATE were higher than those calculated with OLINDA. The average ratio between GATE absorbed doses and OLINDA’s was 1.38 ± 0.34 σ (from 0.93 to 2.23). The discrepancy was particularly high for the thyroid, with an average GATE/OLINDA ratio of 1.97 ± 0.83 σ for the six patients. Differences between STRATOS and GATE were found to be higher. The average ratio between GATE and STRATOS absorbed doses was 2.51 ± 1.21 σ (from 1.09 to 6.06). Conclusions: This study demonstrates how the choice of the absorbed dose calculation algorithm may introduce a bias when gamma radiations are of importance, as is

  7. Dosimetric properties of equivalent-quality flattening filter-free (FFF) and flattened photon beams of Versa HD linear accelerator.

    PubMed

    Meshram, Mukesh N; Pramanik, Srimanta; Ranjith, C P; Gopal, Saravana K; Dobhal, Rishabh

    2016-05-08

    This study presents the basic dosimetric properties of photon beams of a Versa HD linear accelerator (linac), which is capable of delivering flattening filter-free (FFF) beams with a beam quality equivalent to the corresponding flattened beams based on comprehensive beam data measurement. The analyzed data included the PDDs, profiles, penumbra, out-of-field doses, surface doses, output factors, head and phantom scatter factors, and MLC transmissions for both FFF and flattened beams of 6 MV and 10 MV energy from an Elekta Versa HD linac. The 6MVFFF and 10MVFFF beams had an equivalent mean energy to the flattened beams and showed less PDD variations with the field sizes. Compared with their corresponding flattened beams, Dmax was deeper for FFF beams for all field sizes; the ionization ratio variations with the field size were lower for FFF beams; the out-of-field doses were lower and the penumbras were sharper for the FFF beams; the off-axis profile variations with the depths were lesser for the FFF beams. Further, the 6MVFFF and 10MVFFF beams had 35.7% and 40.9% less variations in output factor with the field size, respectively. The collimator exchange effect was reduced in the FFF mode. The head scatter factor showed 59.1% and 73.6% less variations, on average, for the 6MVFFF and 10MVFFF beams, respectively; the variations in the phantom scatter factor were also smaller. The surface doses for all beams increased linearly with the field size. The 6MVFFF and 10MVFFF beams had higher surface doses than the corresponding flattened beams for field sizes of up to 10 ×10cm2 but had lower surface doses for larger fields. Both FFF beams had lower average MLC transmissions than the flattened beams. The finding that the FFF beams were of equivalent quality to the corresponding flattened beams indicates a significant dif-ference from the data on unmatched FFF beams.

  8. Dosimetric characteristics of a newly designed grid block for megavoltage photon radiation and its therapeutic advantage using a linear quadratic model

    SciTech Connect

    Meigooni, Ali S.; Dou Kai; Meigooni, Navid J.; Gnaster, Michael; Awan, Shahid; Dini, Sharifeh; Johnson, Ellis L.

    2006-09-15

    Grid radiation therapy with megavoltage x-ray beam has been proven to be an effective technique for management of large, bulky malignant tumors. The clinical advantage of GRID therapy, combined with conventional radiation therapy, has been demonstrated using a prototype GRID block [Mohiuddin, Curtis, Grizos, and Komarnicky, Cancer 66, 114-118 (1990)]. Recently, a new GRID block design with improved dosimetric properties has become commercially available from Radiation Product Design, Inc. (Albertive, MN). This GRID collimator consists of an array of focused apertures in a cerrobend block arranged in a hexagonal pattern having a circular cross-section with a diameter and center-to-center spacing of 14.3 and 21.1 mm, respectively, in the plane of isocenter. In this project, dosimetric characteristics of the newly redesigned GRID block have been investigated for a Varian 21EX linear accelerator (Varian Associates, Palo Alto, CA). These determinations were performed using radiographic films, thermoluminescent dosimeters in Solid Water trade mark sign phantom materials, and an ionization chamber in water. The output factor, percentage depth dose, beam profiles, and isodose distributions of the GRID radiation as a function of field size and beam energy have been measured using both 6 and 18 MV x-ray beams. In addition, the therapeutic advantage obtained from this treatment modality with the new GRID block design for a high, single fraction of dose has been calculated using the linear quadratic model with {alpha}/{beta} ratios for typical tumor and normal cells. These biological characteristics of the new GRID block design will also be presented.

  9. DOSIMETRIC PROPERTIES OF THE NEW TLD ALBEDO NEUTRON DOSEMETER AWST-TL-GD 04.

    PubMed

    Haninger, T; Henniger, J

    2016-09-01

    A new official albedo dosemeter based on thermoluminescent detectors has been introduced in 2015 by the individual monitoring service of the Helmholtz Zentrum München for monitoring persons who are exposed occupationally against photon and neutron radiation. To enhance the sensitivity for fast neutrons, a new badge with an enlarged albedo window has been developed at TU Dresden. The properties of the new albedo dosemeter are discussed, and the results of official intercomparisons and field calibrations are shown.

  10. Dosimetric properties of an amorphous-silicon EPID used in continuous acquisition mode for application to dynamic and arc IMRT

    SciTech Connect

    McCurdy, B. M. C.; Greer, P. B.

    2009-07-15

    Dosimetric properties of an amorphous-silicon electronic portal imaging device (EPID) operated in a real-time acquisition mode were investigated. This mode will be essential for time-resolved dose verification of dynamic (sliding window) intensity modulated radiation therapy (IMRT) and intensity modulated arc radiation therapy (arc-IMRT). The EPID was used in continuous acquisition mode (i.e., ''cine'' mode) where individual sequential image frames are acquired in real time. The properties studied include dose linearity, reproducibility of response, and image stability. Results of using the continuous acquisition mode with several example treatments including dynamic IMRT, arc treatment, and single-arc-IMRT are compared to results using the well-studied integrated acquisition mode (i.e., ''frame averaging'' or ''IMRT'' mode). Real-time EPID response was also compared to real-time ion-chamber data for selected points in the deliveries. The example treatment deliveries in both continuous and integrated acquisition modes were converted to arbitrary EPID dose units via a calibration field. The summation of all acquired continuous mode images was compared using percentage dose difference to the single image acquired in the integrated mode using in-field pixels only (defined as those pixels >10% of maximum, in-field signal). Using the continuous acquisition mode, the EPID response was not linear with dose. It was found that the continuous mode dose response corresponded approximately to dropping one image per acquisition session. Reproducibility of EPID response to low monitor units (MUs) was found to be poor but greatly improved with increasing MU. Open field profiles were found to be stable in the cross-plane direction but required several frames to become stable in the in-plane direction. However, both of these issues are clinically insignificant due to arc-IMRT deliveries requiring relatively large monitor units (>100 MU). Analysis of the five IMRT, arc, and arc

  11. Melt-compounded composites of ethylene vinyl acetate with magnesium sulfate as flexible EPR dosimeters: Mechanical properties, manufacturing process feasibility and dosimetric characteristics.

    PubMed

    Suman, S K; Kadam, R M; Mondal, R K; Murali, S; Dubey, K A; Bhardwaj, Y K; Natarajan, V

    2017-03-01

    Novel polymeric composites for radiation dosimetry were developed. The composites were prepared by solvent-free melt compounding of ethylene vinyl acetate (EVA) (40% vinyl) and magnesium sulfate (MgSO4). Mechanical properties, melt flow characteristics and dosimetric properties were investigated. The composites with up to 50% (wt) of MgSO4 were flexible and capable of flow. The dose response of the EPR signal of the composites was studied in the dose range 3Gy-4kGy and found to be linear between 18Gy and 4kGy. The reproducibility of dose measurements was good. The signal fading rate and the energy dependence of the dose response were found to be acceptable.

  12. Dosimetric model for antibody targeted radionuclide therapy of tumor cells in cerebrospinal fluid

    SciTech Connect

    Millar, W.T.; Barrett, A. )

    1990-02-01

    Although encouraging results have been obtained using systemic radioimmunotherapy in the treatment of cancer, it is likely that regional applications may prove more effective. One such strategy is the treatment of central nervous system leukemia in children by intrathecal instillation of targeting or nontargeting beta particle emitting radionuclide carriers. The beta particle dosimetry of the spine is assessed, assuming that the spinal cord and the cerebrospinal fluid compartment can be adequately represented by a cylindrical annulus. The radionuclides investigated were {sup 90}Y, {sup 131}I, {sup 67}Cu, and {sup 199}Au. It is shown that the radiation dose to the cord can be significantly reduced using short range beta particle emitters and that there is little advantage in using targeting carriers with these radionuclides. {sup 199}Au and {sup 67}Cu also have the advantage of having a suitable gamma emission for imaging, permitting pretherapy imaging and dosimetric calculations to be undertaken prior to therapy. If these methods prove successful, it may be possible to replace the external beam component used in the treatment of central nervous system leukemia in children by intrathecal radionuclide therapy, thus reducing or avoiding side effects such as growth and intellectual impairment.

  13. Dosimetric models of the eye and lens of the eye and their use in assessing dose coefficients for ocular exposures.

    PubMed

    Bolch, W E; Dietze, G; Petoussi-Henss, N; Zankl, M

    2015-06-01

    Based upon recent epidemiological studies of ocular exposure, the Main Commission of the International Commission on Radiological Protection (ICRP) in ICRP Publication 118 states that the threshold dose for radiation-induced cataracts is now considered to be approximately 0.5 Gy for both acute and fractionated exposures. Consequently, a reduction was also recommended for the occupational annual equivalent dose to the lens of the eye from 150 mSv to 20 mSv, averaged over defined periods of 5 years. To support ocular dose assessment and optimisation, Committee 2 included Annex F within ICRP Publication 116 . Annex F provides dose coefficients - absorbed dose per particle fluence - for photon, electron, and neutron irradiation of the eye and lens of the eye using two dosimetric models. The first approach uses the reference adult male and female voxel phantoms of ICRP Publication 110. The second approach uses the stylised eye model of Behrens et al., which itself is based on ocular dimensional data given in Charles and Brown. This article will review the data and models of Annex F with particular emphasis on how these models treat tissue regions thought to be associated with stem cells at risk.

  14. MAX meets ADAM: a dosimetric comparison between a voxel-based and a mathematical model for external exposure to photons.

    PubMed

    Kramer, R; Vieira, J W; Khoury, H J; de Andrade Lima, F

    2004-03-21

    The International Commission on Radiological Protection intends to revise the organ and tissue equivalent dose conversion coefficients published in various reports. For this purpose the mathematical human medical internal radiation dose (MIRD) phantoms, actually in use, have to be replaced by recently developed voxel-based phantoms. This study investigates the dosimetric consequences, especially with respect to the effective male dose, if not only a MIRD phantom is replaced by a voxel phantom, but also if the tissue compositions and the radiation transport codes are changed. This task will be resolved by systematically replacing in the mathematical ADAM/GSF exposure model, first the radiation transport code, then the tissue composition and finally the phantom anatomy, in order to arrive at the voxel-based MAX/EGS4 exposure model. The results show that the combined effect of these replacements can decrease the effective male dose by up to 25% for external exposures to photons for incident energies above 30 keV for different field geometries, mainly because of increased shielding by a heterogeneous skeleton and by the overlying adipose and muscle tissue, and also because of the positions internal organs have in a realistically designed human body compared to their positions in the mathematically constructed phantom.

  15. MAX meets ADAM: a dosimetric comparison between a voxel-based and a mathematical model for external exposure to photons

    NASA Astrophysics Data System (ADS)

    Kramer, R.; Vieira, J. W.; Khoury, H. J.; Lima, F. de Andrade

    2004-03-01

    The International Commission on Radiological Protection intends to revise the organ and tissue equivalent dose conversion coefficients published in various reports. For this purpose the mathematical human medical internal radiation dose (MIRD) phantoms, actually in use, have to be replaced by recently developed voxel-based phantoms. This study investigates the dosimetric consequences, especially with respect to the effective male dose, if not only a MIRD phantom is replaced by a voxel phantom, but also if the tissue compositions and the radiation transport codes are changed. This task will be resolved by systematically replacing in the mathematical ADAM/GSF exposure model, first the radiation transport code, then the tissue composition and finally the phantom anatomy, in order to arrive at the voxel-based MAX/EGS4 exposure model. The results show that the combined effect of these replacements can decrease the effective male dose by up to 25% for external exposures to photons for incident energies above 30 keV for different field geometries, mainly because of increased shielding by a heterogeneous skeleton and by the overlying adipose and muscle tissue, and also because of the positions internal organs have in a realistically designed human body compared to their positions in the mathematically constructed phantom.

  16. SU-D-BRE-03: Dosimetric Impact of In-Air Spot Size Variations for Commissioning a Room-Matched Beam Model for Pencil Beam Scanning Proton Therapy

    SciTech Connect

    Zhang, Y; Giebeler, A; Mascia, A; Piskulich, F; Perles, L; Lepage, R; Dong, L

    2014-06-01

    Purpose: To quantitatively evaluate dosimetric consequence of spot size variations and validate beam-matching criteria for commissioning a pencil beam model for multiple treatment rooms. Methods: A planning study was first conducted by simulating spot size variations to systematically evaluate dosimetric impact of spot size variations in selected cases, which was used to establish the in-air spot size tolerance for beam matching specifications. A beam model in treatment planning system was created using in-air spot profiles acquired in one treatment room. These spot profiles were also acquired from another treatment room for assessing the actual spot size variations between the two treatment rooms. We created twenty five test plans with targets of different sizes at different depths, and performed dose measurement along the entrance, proximal and distal target regions. The absolute doses at those locations were measured using ionization chambers at both treatment rooms, and were compared against the calculated doses by the beam model. Fifteen additional patient plans were also measured and included in our validation. Results: The beam model is relatively insensitive to spot size variations. With an average of less than 15% measured in-air spot size variations between two treatment rooms, the average dose difference was −0.15% with a standard deviation of 0.40% for 55 measurement points within target region; but the differences increased to 1.4%±1.1% in the entrance regions, which are more affected by in-air spot size variations. Overall, our single-room based beam model in the treatment planning system agreed with measurements in both rooms < 0.5% within the target region. For fifteen patient cases, the agreement was within 1%. Conclusion: We have demonstrated that dosimetrically equivalent machines can be established when in-air spot size variations are within 15% between the two treatment rooms.

  17. SU-E-T-446: Evaluation of the Dosimetric Properties of a Diode Detector to Proton Radiosurgery

    SciTech Connect

    Teran, A; McAuley, G; Slater, J M; Slater, J D; Wroe, A

    2014-06-01

    Purpose: To test the PTW PR60020 proton dosimetry diode in radiation fields relevant to proton radiosurgery applications and evaluate its suitability as a high resolution, real time dosimetry device. Methods: Data was collected using our standard nominal radiosurgery energies of 126 MeV and 155 MeV through a single stage scattering system, corresponding to a range of 9.7 and 15 cm in water respectively. Various beam modulations were tested as part of this study. Depth dose and beam profile measurements were completed with the PTW PR60020 dosimetry diode with comparative measurements using a PTW Markus ionization chamber and EBT2 Gafchromic film. Monte Carlo simulations were also completed for comparison. Results: The single 1 mm{sup 2} by 20 μm thick sensitive volume allowed for high spatial resolution measurements while maintaining sufficient sensitive volume to ensure that measurements could be completed without excessive beam delivery. Depth dose profiles exhibited negligible LET dependence which typically impacts film and other solid state dosimetry devices, while beam ranges measured with the PTW diode were within 1 mm of ion chamber data. In an edge on arrangement beam profiles were also measured within 0.5 mm full-width at half-maximum at various depths as compared to film and simulation data. Conclusion: The PTW PR60020 proved to be a very useful radiation metrology apparatus for proton radiosurgery applications. Its waterproof and rugged construction allowed for easy deployment in phantoms or water tanks that are commonly used in proton radiosurgery QA. Dosimetrically, the diode exhibited negligible LET dependence as a function of depth, while in edge on arrangement to the incident proton beam it facilitated the measurement of beam profiles with a spatial resolution comparable to both Monte Carlo and film measurements. This project was sponsored in part by funding from the Department of Defense (DOD# W81XWH-BAA-10-1)

  18. The Revised International Commission on Radiological Protection (ICRP) dosimetric model for the human respiratory tract

    SciTech Connect

    Bair, W.J.

    1991-09-01

    The new respiratory tract model is based on the premise that the large differences in radiation sensitivity of respiratory tract tissues, and the wide range of doses they receive, argue for calculating specific tissue doses rather than average lung doses for radiation protection purposes. The new model is more complex than the current lung model because it describes deposition of inhaled radioactive material in the clearance from several tissues and regions of the respiratory tract and is applicable to the worldwide population of both workers and the public. 2 refs., 2 figs.

  19. SU-E-T-360: End-To-End Dosimetric Testing of a Versa HD Linear Accelerator with the Agility Head Modeled in Pinnacle3

    SciTech Connect

    Saenz, D; Narayanasamy, G; Cruz, W; Papanikolaou, N; Stathakis, S

    2015-06-15

    Purpose: The Versa HD incorporates a variety of upgrades, primarily including the Agility head. The distinct dosimetric properties of the head from its predecessors combined with flattening-filter-free (FFF) beams require a new investigation of modeling in planning systems and verification of modeling accuracy. Methods: A model was created in Pinnacle{sup 3} v9.8 with commissioned beam data. Leaf transmission was modeled as <0.5% with maximum leaf speed of 3 cm/s. Photon spectra were tuned for FFF beams, for which profiles were modeled with arbitrary profiles rather than with cones. For verification, a variety of plans with varied parameters were devised, and point dose measurements were compared to calculated values. A phantom of several plastic water and Styrofoam slabs was scanned and imported into Pinnacle{sup 3}. Beams of different field sizes, SSD, wedges, and gantry angles were created. All available photon energies (6 MV, 10 MV, 18 MV, 6 FFF, 10 FFF) as well four clinical electron energies (6, 9, 12, and 15 MeV) were investigated. The plans were verified at a calculation point (8 cm deep for photons, variable for electrons) by measurement with a PTW Semiflex ionization chamber. In addition, IMRT testing was performed with three standard plans (step and shoot IMRT, small and large field VMAT plans). The plans were delivered on the Delta4 IMRT QA phantom (ScandiDos, Uppsala, Sweden). Results: Homogeneous point dose measurement agreed within 2% for all photon and electron beams. Open field photon measurements along the central axis at 100 cm SSD passed within 1%. Gamma passing rates were >99.5% for all plans with a 3%/3mm tolerance criteria. The IMRT QA results for the first 23 patients yielded gamma passing rates of 97.4±2.3%. Conclusion: The end-to-end testing ensured confidence in the ability of Pinnacle{sup 3} to model photon and electron beams with the Agility head.

  20. Study of Dosimetric and Thermal Properties of a Newly Developed Thermo-brachytherapy Seed for Treatment of Solid Tumors

    NASA Astrophysics Data System (ADS)

    Gautam, Bhoj R.

    Studies on the curative effects of hyperthermia and radiation therapy on treatment of cancer show strong evidence of synergistic enhancement when both radiation and hyperthermia treatment modalities are applied simultaneously. A variety of tissue heating approaches developed to date still fail to overcome essential limitations such as inadequate temperature control, temperature non-uniformity, and prolonged time delay between hyperthermia and radiation treatments. We propose a new self-regulating Thermo-brachytherapy (TB) seed, which serves as a source of both radiation and heat for concurrent administration of brachytherapy and hyperthermia. The proposed seed is based on the BestRTM Iodine-125 seed model 2301, where the tungsten marker core and the air gap are replaced with ferromagnetic material. The ferromagnetic core produces heat when subjected to an alternating electromagnetic (EM) field and effectively shuts off after reaching the Curie temperature (TC) of the ferromagnetic material, thus establishing temperature self-regulation. The seed has a ferromagnetic Ni-Cu alloy core having a Curie transition at a temperature of 52 °C. This study summarizes the design and development of the self regulating ferromagnetic core TB seed for the concurrent hyperthermia and brachytherapy treatments. An experimental study of the magnetic properties of the Ni1-xCu x (0.28≤ x ≤0.3) alloys, and the simulation studies of radiation and thermal distribution properties of the seed have been performed. A preliminary experiment for the ferromagnetic induction heating of Ni-Cu needles has been carried out to ensure the practical feasibility of the induction heating. Radiation dose characterizing parameters (dose rate constant and other TG-43 factors) were calculated using the Monte Carlo method. For the thermal characteristics, we studied a model consisting of single or multiple seeds placed in the central region of a cylindrical phantom using a finite-element analysis method

  1. Development of a three-dimensional model of the human respiratory system for dosimetric use

    PubMed Central

    2013-01-01

    Background Determining the fate of inhaled contaminants in the human respiratory system has challenged scientists for years. Human and animal studies have provided some data, but there is a paucity of data for toxic contaminants and sensitive populations (such as children, elderly, diseased). Methods Three-dimensional modeling programs and publicly available human physiology data have been used to develop a comprehensive model of the human respiratory system. Results The in silico human respiratory system model, which includes the extrathoracic region (nasal, oral, pharyngeal, and laryngeal passages), the upper airways (trachea and main bronchi), the tracheobronchial tree, and branching networks through alveolar region, allows for virtually any variation of airway geometries and disease states. The model allows for parameterization of variables that define the subject’s airways by integrating morphological changes created by disease, age, etc. with a dynamic morphology. Conclusions The model can be used for studies of sensitive populations and the homeland security community, in cases where inhalation studies on humans cannot be conducted with toxic contaminants of interest. PMID:23634755

  2. A dosimetric model for the heterogeneous delivery of radioactive nanoparticles In vivo: a feasibility study.

    PubMed

    Satterlee, Andrew B; Attayek, Peter; Midkiff, Bentley; Huang, Leaf

    2017-03-17

    ᅟ: Accurate and quantitative dosimetry for internal radiation therapy can be especially challenging, given the heterogeneity of patient anatomy, tumor anatomy, and source deposition. Internal radiotherapy sources such as nanoparticles and monoclonal antibodies require high resolution imaging to accurately model the heterogeneous distribution of these sources in the tumor. The resolution of nuclear imaging modalities is not high enough to measure the heterogeneity of intratumoral nanoparticle deposition or intratumoral regions, and mathematical models do not represent the actual heterogeneous dose or dose response. To help answer questions at the interface of tumor dosimetry and tumor biology, we have modeled the actual 3-dimensional dose distribution of heterogeneously delivered radioactive nanoparticles in a tumor after systemic injection.

  3. On using the dosimetric leaf gap to model the rounded leaf ends in VMAT/RapidArc plans.

    PubMed

    Szpala, Stanislaw; Cao, Fred; Kohli, Kirpal

    2014-03-06

    Partial transmission through rounded leaf ends of Varian multileaf collimators (MLC) is accounted for with a parameter called the dosimetric leaf gap (DLG). Verification of the value of the DLG is needed when the dose delivery is accompanied by gantry rotation in VMAT plans. We compared the doses measured with GAFCHROMIC film and an ionization chamber to treatment planning system (TPS) calculations to identify the optimum values of the DLG in clinical plans of the whole brain with metastases transferred to a phantom. We noticed the absence of a single value of the DLG that properly models all VMAT plans in our cohort (the optimum DLG varied between 0.93 ± 0.15 mm and 2.2 ± 0.2 mm). The former value is considerably different from the optimum DLG in sliding window plans (about 2.0 mm) that approximate IMRT plans. We further found that a single-value DLG model cannot accurately reproduce the measured dose profile even of a uniform static slit at a fixed gantry, which is the simplest MLC-delimited field. The calculation overestimates the measurement in the proximal penumbra, while it underestimates in the distal penumbra. This prompted us to expand the DLG parameter from a plan-specific number to a mathematical concept of the DLG being a function of the distance in the beam's eye view (BEV) between the dose point and the leaf ends. Such function compensates for the difference between the penumbras in a beam delimited with a rounded leaf MLC and delimited with solid jaws. Utilization of this concept allowed us generating a pair of step-and-shoot MLC plans for which we could qualitatively predict the value of the DLG providing best match to ionization chamber measurements. The plan for which the leafs stayed predominantly at positions requiring low values of the DLG (as seen in the profiles of 1D slits) yielded the combined DLG of 1.1 ± 0.2 mm, while the plan with leafs staying at positions requiring larger values of the DLG yielded the DLG 2.4 ± 0.2 mm. Considering

  4. Pu-239 organ specific dosimetric model applied to non-human biota

    NASA Astrophysics Data System (ADS)

    Kaspar, Matthew Jason

    There are few locations throughout the world, like the Maralinga nuclear test site located in south western Australia, where sufficient plutonium contaminate concentration levels exist that they can be utilized for studies of the long-term radionuclide accumulation in non-human biota. The information obtained will be useful for the potential human users of the site while also keeping with international efforts to better understand doses to non-human biota. In particular, this study focuses primarily on a rabbit sample set collected from the population located within the site. Our approach is intended to employ the same dose and dose rate methods selected by the International Commission on Radiological Protection and adapted by the scientific community for similar research questions. These models rely on a series of simplifying assumptions on biota and their geometry; in particular; organisms are treated as spherical and ellipsoidal representations displaying the animal mass and volume. These simplifications assume homogeneity of all animal tissues. In collaborative efforts between Colorado State University and the Australian Nuclear Science and Technology Organisation (ANSTO), we are expanding current knowledge on radionuclide accumulation in specific organs causing organ-specific dose rates, such as Pu-239 accumulating in bone, liver, and lungs. Organ-specific dose models have been developed for humans; however, little has been developed for the dose assessment to biota, in particular rabbits. This study will determine if it is scientifically valid to use standard software, in particular ERICA Tool, as a means to determine organ-specific dosimetry due to Pu-239 accumulation in organs. ERICA Tool is normally applied to whole organisms as a means to determine radiological risk to whole ecosystems. We will focus on the aquatic model within ERICA Tool, as animal organs, like aquatic organisms, can be assumed to lie within an infinite uniform medium. This model would

  5. Independent dosimetric assessment of the model EP917 episcleral brachytherapy plaque

    SciTech Connect

    Aryal, Prakash; Molloy, Janelle A.; Rivard, Mark J.

    2014-09-15

    Purpose: To investigate the influence of slot design on dose distributions and dose-volume histograms (DVHs) for the model EP917 plaque for episcleral brachytherapy. Methods: Dimensions and orientations of the slots were measured for three model EP917 plaques and compared to data in the Plaque Simulator (PS) treatment planning software (version 5.7.6). These independently determined coordinates were incorporated into the MCNP Monte Carlo simulation environment to obtain dose from the plaques in a water environment and in a clinical environment with ocular structures. A tumor volume was simulated as 5 mm in apical height and 11 mm in basal diameter. Variations in plaque mass density and composition; slot length, width, and depth; seed positioning; and Ag-marker rod positioning were simulated to examine their influence on plaque central axis (CAX) and planar dose distributions, and DVHs. Results: Seed shifts in a single slot toward the eye and shifts of the{sup 125}I-coated Ag rod within the capsule had the greatest impact on CAX dose distribution. A shift of 0.0994 mm toward the eye increased dose by 14%, 9%, 4.3%, and 2.7% at 1, 2, 5, and 10 mm, respectively, from the inner sclera. When examining the fully-modeled plaque in the ocular geometry, the largest dose variations were caused by shifting the Ag rods toward the sclera and shifting the seeds away from the globe when the slots were made 0.51 mm deeper, causing +34.3% and −69.4% dose changes to the outer sclera, respectively. At points along the CAX, dose from the full plaque geometry using the measured slot design was 2.4% ± 1.1% higher than the manufacturer-provided slot design and 2.2% ± 2.3% higher than the homogeneous calculation of PS treatment planning results. The ratio of D{sub 10} values for the measured slot design to the D{sub 10} values for the manufacturer-provided slot design was higher by 9%, 10%, and 19% for the tumor, inner sclera, and outer sclera, respectively. In comparison to the

  6. A review of dosimetric and toxicity modeling of proton versus photon craniospinal irradiation for pediatrics medulloblastoma.

    PubMed

    Ho, Evangeline S Q; Barrett, Sarah A; Mullaney, Laura M

    2017-08-01

    Craniospinal irradiation (CSI) is the standard radiation therapy treatment for medulloblastoma. Conventional CSI photon therapy (Photon-CSI) delivers significant dose to surrounding normal tissue (NT). Research into pediatric CSI with proton therapy (Proton-CSI) has increased, with the aim of exploiting the potential to reduce NT dose and associated post-treatment complications. This review aims to compare treatment outcomes of pediatric medulloblastoma patients between Proton- and Photon-CSI treatments. A search and review of studies published between 1990 and 2016 comparing pediatric (2-18 years) medulloblastoma Proton- and Photon-CSI in three aspects - normal organ sparing and target coverage; normal organ dysfunction and second malignancy risks - was completed. Fifteen studies were selected for review and the results were directly compared. Proton-CSI reported improved out-of-field organ sparing while target coverage improvements were inconsistent. Normal organ dysfunction risks were predicted to be lower following Proton-CSI. Secondary malignancy risks (SMRs) were generally lower with Proton-CSI based on several different risk models. Proton-CSI conferred better treatment outcomes than Photon-CSI for pediatric medulloblastoma patients. This review serves to compare the current literature in the absence of long-term data from prospective studies.

  7. Calibrated Properties Model

    SciTech Connect

    C. Ahlers; H. Liu

    2000-03-12

    The purpose of this Analysis/Model Report (AMR) is to document the Calibrated Properties Model that provides calibrated parameter sets for unsaturated zone (UZ) flow and transport process models for the Yucca Mountain Site Characterization Project (YMP). This work was performed in accordance with the ''AMR Development Plan for U0035 Calibrated Properties Model REV00. These calibrated property sets include matrix and fracture parameters for the UZ Flow and Transport Model (UZ Model), drift seepage models, drift-scale and mountain-scale coupled-processes models, and Total System Performance Assessment (TSPA) models as well as Performance Assessment (PA) and other participating national laboratories and government agencies. These process models provide the necessary framework to test conceptual hypotheses of flow and transport at different scales and predict flow and transport behavior under a variety of climatic and thermal-loading conditions.

  8. Dosimetric audit in brachytherapy

    PubMed Central

    Bradley, D A; Nisbet, A

    2014-01-01

    Dosimetric audit is required for the improvement of patient safety in radiotherapy and to aid optimization of treatment. The reassurance that treatment is being delivered in line with accepted standards, that delivered doses are as prescribed and that quality improvement is enabled is as essential for brachytherapy as it is for the more commonly audited external beam radiotherapy. Dose measurement in brachytherapy is challenging owing to steep dose gradients and small scales, especially in the context of an audit. Several different approaches have been taken for audit measurement to date: thimble and well-type ionization chambers, thermoluminescent detectors, optically stimulated luminescence detectors, radiochromic film and alanine. In this work, we review all of the dosimetric brachytherapy audits that have been conducted in recent years, look at current audits in progress and propose required directions for brachytherapy dosimetric audit in the future. The concern over accurate source strength measurement may be essentially resolved with modern equipment and calibration methods, but brachytherapy is a rapidly developing field and dosimetric audit must keep pace. PMID:24807068

  9. Dosimetric properties of radiophotoluminescent glass rod detector in high-energy photon beams from a linear accelerator and cyber-knife.

    PubMed

    Arakia, Fujio; Moribe, Nobuyuki; Shimonobou, Toshiaki; Yamashita, Yasuyuki

    2004-07-01

    A fully automatic radiophotoluminescent glass rod dosimeter (GRD) system has recently become commercially available. This article discusses the dosimetric properties of the GRD including uniformity and reproducibility of signal, dose linearity, and energy and directional dependence in high-energy photon beams. In addition, energy response is measured in electron beams. The uniformity and reproducibility of the signal from 50 GRDs using a 60Co beam are both +/- 1.1% (one standard deviation). Good dose linearity of the GRD is maintained for doses ranging from 0.5 to 30 Gy, the lower and upper limits of this study, respectively. The GRD response is found to show little energy dependence in photon energies of a 60Co beam, 4 MV (TPR20(10)=0.617) and 10 MV (TPR(20)10=0.744) x-ray beams. However, the GRD responses for 9 MeV (mean energy, Ez = 3.6 MeV) and 16 MeV (Ez = 10.4 MeV) electron beams are 4%-5% lower than that for a 60Co beam in the beam quality dependence. The measured angular dependence of GRD, ranging from 0 degrees (along the long axis of GRD) to 120 degrees is within 1.5% for a 4 MV x-ray beam. As applications, a linear accelerator-based radiosurgery system and Cyber-Knife output factors are measured by a GRD and compared with those from various detectors including a p-type silicon diode detector, a diamond detector, and an ion chamber. It is found that the GRD is a very useful detector for small field dosimetry, in particular, below 10 mm circular fields.

  10. Calibrated Properties Model

    SciTech Connect

    T. Ghezzehej

    2004-10-04

    The purpose of this model report is to document the calibrated properties model that provides calibrated property sets for unsaturated zone (UZ) flow and transport process models (UZ models). The calibration of the property sets is performed through inverse modeling. This work followed, and was planned in, ''Technical Work Plan (TWP) for: Unsaturated Zone Flow Analysis and Model Report Integration'' (BSC 2004 [DIRS 169654], Sections 1.2.6 and 2.1.1.6). Direct inputs to this model report were derived from the following upstream analysis and model reports: ''Analysis of Hydrologic Properties Data'' (BSC 2004 [DIRS 170038]); ''Development of Numerical Grids for UZ Flow and Transport Modeling'' (BSC 2004 [DIRS 169855]); ''Simulation of Net Infiltration for Present-Day and Potential Future Climates'' (BSC 2004 [DIRS 170007]); ''Geologic Framework Model'' (GFM2000) (BSC 2004 [DIRS 170029]). Additionally, this model report incorporates errata of the previous version and closure of the Key Technical Issue agreement TSPAI 3.26 (Section 6.2.2 and Appendix B), and it is revised for improved transparency.

  11. Dosimetric and thermal properties of a newly developed thermobrachytherapy seed with ferromagnetic core for treatment of solid tumors

    SciTech Connect

    Gautam, Bhoj; Parsai, E. Ishmael; Shvydka, Diana; Feldmeier, John; Subramanian, Manny

    2012-04-15

    Purpose: Studies of the curative effects of hyperthermia and radiation therapy on treatment of cancer show a strong evidence of a synergistic enhancement when both radiation and hyperthermia modalities are applied simultaneously. Varieties of tissue heating approaches developed up to date still fail to overcome such essential limitations as an inadequate temperature control, temperature nonuniformity, and prolonged time delay between hyperthermia and radiation treatments. The authors propose a new self-regulating thermobrachytherapy seed, which serves as a source of both radiation and heat for concurrent administration of brachytherapy and hyperthermia. Methods: The proposed seed is based on the BEST Medical, Inc., Seed Model 2301-I{sup 125}, where tungsten marker core and the air gap are replaced with a ferromagnetic material. The ferromagnetic core produces heat when subjected to alternating electromagnetic (EM) field and effectively shuts off after reaching the Curie temperature (T{sub C}) of the ferromagnetic material thus realizing the temperature self-regulation. The authors present a Monte Carlo study of the dose rate constant and other TG-43 factors for the proposed seed. For the thermal characteristics, the authors studied a model consisting of 16 seeds placed in the central region of a cylindrical water phantom using a finite-element partial differential equation solver package ''COMSOL Multiphysics.''Results: The modification of the internal structure of the seed slightly changes dose rate and other TG-43 factors characterizing radiation distribution. The thermal modeling results show that the temperature of the thermoseed surface rises rapidly and stays constant around T{sub C} of the ferromagnetic material. The amount of heat produced by the ferromagnetic core is sufficient to raise the temperature of the surrounding phantom to the therapeutic range. The phantom volume reaching the therapeutic temperature range increases with increase in frequency or

  12. SU-E-T-336: Dosimetric Properties of a New Solid Water High Equivalency Phantom for High-Energy Photon Beams

    SciTech Connect

    Araki, F; Ohno, T; Onitsuka, R; Shimohigashi, Y

    2015-06-15

    Purpose: To investigate dosimetric properties in high-energy photon beams for a Solid Water High Equivalency (SWHE, SW557) phantom (Gammex) which was newly developed as water mimicking material. Methods: The mass density of SWHE and SWHE/water electron density ratio are 1.032 g/cm{sup 3} and 1.005 according to the manufacturer information, respectively. SWHE is more water equivalent material in physical characteristics and uniformity than conventional SW457. This study calculated the relative ionization ratio of water and SWHE as a function of depth from the cavity dose in PTW30013 and Exradin A19 Farmer-type ionization chambers using Monte Caro simulations. The simulation was performed with a 10 x 10 cm{sup 2} field at SAD of 100 cm for 4, 6, 10, 15, and 18 MV photons. The ionization ratio was also measured with the PTW30013 chamber for 6 and 15 MV photons. In addition, the overall perturbation factor of both chambers was calculated for both phantoms. Results: The relative ionization ratio curves for water and SWHE was in good agreement for all photon energies. The ionization ratio of water/SWHE for both chambers was 0.999–1.002, 0.999–1.002, 1.001–1.004, 1.004–1.007, and 1.006–1.010 at depths of over the buildup region for 4, 6, 10, 15, and 18 MV photons, respectively. The ionization ratio of water/SWHE increased up to 1% with increasing the photon energy. The measured ionization ratio of water/SWHE for 6 and 15 MV photons agreed well with calculated values. The overall perturbation factor for both chambers was 0.983–0.988 and 0.978–0.983 for water and SWHE, respectively, in a range from 4 MV to 18 MV. Conclusion: The depth scaling factor of water/SWHE was equal to unity for all photon energies. The ionization ratio of water/SWHE at a reference depth was equal to unity for 4 and 6 MV and larger up to 0.7% than unity for 18 MV.

  13. Rock Properties Model

    SciTech Connect

    C. Lum

    2004-09-16

    The purpose of this model report is to document the Rock Properties Model version 3.1 with regard to input data, model methods, assumptions, uncertainties and limitations of model results, and qualification status of the model. The report also documents the differences between the current and previous versions and validation of the model. The rock properties model provides mean matrix and lithophysae porosity, and the cross-correlated mean bulk density as direct input to the ''Saturated Zone Flow and Transport Model Abstraction'', MDL-NBS-HS-000021, REV 02 (BSC 2004 [DIRS 170042]). The constraints, caveats, and limitations associated with this model are discussed in Section 6.6 and 8.2. Model validation accomplished by corroboration with data not cited as direct input is discussed in Section 7. The revision of this model report was performed as part of activities being conducted under the ''Technical Work Plan for: The Integrated Site Model, Revision 05'' (BSC 2004 [DIRS 169635]). The purpose of this revision is to bring the report up to current procedural requirements and address the Regulatory Integration Team evaluation comments. The work plan describes the scope, objectives, tasks, methodology, and procedures for this process.

  14. Evaluation of dosimetric properties of 6 MV & 10 MV photon beams from a linear accelerator with no flattening filter

    NASA Astrophysics Data System (ADS)

    Pearson, David

    A linear accelerator manufactured by Elekta, equipped with a multi leaf collimation (MLC) system has been modelled using Monte Carlo simulations with the photon flattening filter removed. The purpose of this investigation was to show that more efficient and more accurate Intensity Modulated Radiation Therapy (IMRT) treatments can be delivered from a standard linear accelerator with the flattening filter removed from the beam. A range of simulations of 6 MV and 10 MV photon were studied and compared to a model of a standard accelerator which included the flattening filter for those beams. Measurements using a scanning water phantom were also performed after the flattening filter had been removed. We show here that with the flattening filter removed, an increase to the dose on the central axis by a factor of 2.35 and 4.18 is achieved for 6 MV and 10 MV photon beams respectively using a standard 10x 10cm2 field size. A comparison of the dose at points at the field edges led to the result that, removal of the flattening filter reduced the dose at these points by approximately 10% for the 6 MV beam over the clinical range of field sizes. A further consequence of removing the flattening filter was the softening of the photon energy spectrum leading to a steeper reduction in dose at depths greater than dmax. Also studied was the electron contamination brought about by the removal of the filter. To reduce this electron contamination and thus reduce the skin dose to the patient we consider the use of an electron scattering foil in the beam path. The electron scattering foil had very little effect on dmax. From simulations of a standard 6MV beam, a filter-free beam and a filter-free beam with electron scattering foil, we deduce that the proportion of electrons in the photon beam is 0.35%, 0.28% and 0.27%, consecutively. In short, higher dose rates will result in decreased treatment times and the reduced dose outside of the field is indicative of reducing the dose to the

  15. Calibrated Properties Model

    SciTech Connect

    H. H. Liu

    2003-02-14

    This report has documented the methodologies and the data used for developing rock property sets for three infiltration maps. Model calibration is necessary to obtain parameter values appropriate for the scale of the process being modeled. Although some hydrogeologic property data (prior information) are available, these data cannot be directly used to predict flow and transport processes because they were measured on scales smaller than those characterizing property distributions in models used for the prediction. Since model calibrations were done directly on the scales of interest, the upscaling issue was automatically considered. On the other hand, joint use of data and the prior information in inversions can further increase the reliability of the developed parameters compared with those for the prior information. Rock parameter sets were developed for both the mountain and drift scales because of the scale-dependent behavior of fracture permeability. Note that these parameter sets, except those for faults, were determined using the 1-D simulations. Therefore, they cannot be directly used for modeling lateral flow because of perched water in the unsaturated zone (UZ) of Yucca Mountain. Further calibration may be needed for two- and three-dimensional modeling studies. As discussed above in Section 6.4, uncertainties for these calibrated properties are difficult to accurately determine, because of the inaccuracy of simplified methods for this complex problem or the extremely large computational expense of more rigorous methods. One estimate of uncertainty that may be useful to investigators using these properties is the uncertainty used for the prior information. In most cases, the inversions did not change the properties very much with respect to the prior information. The Output DTNs (including the input and output files for all runs) from this study are given in Section 9.4.

  16. Dosimetric accuracy of a deterministic radiation transport based {sup 192}Ir brachytherapy treatment planning system. Part III. Comparison to Monte Carlo simulation in voxelized anatomical computational models

    SciTech Connect

    Zourari, K.; Pantelis, E.; Moutsatsos, A.; Sakelliou, L.; Georgiou, E.; Karaiskos, P.; Papagiannis, P.

    2013-01-15

    Purpose: To compare TG43-based and Acuros deterministic radiation transport-based calculations of the BrachyVision treatment planning system (TPS) with corresponding Monte Carlo (MC) simulation results in heterogeneous patient geometries, in order to validate Acuros and quantify the accuracy improvement it marks relative to TG43. Methods: Dosimetric comparisons in the form of isodose lines, percentage dose difference maps, and dose volume histogram results were performed for two voxelized mathematical models resembling an esophageal and a breast brachytherapy patient, as well as an actual breast brachytherapy patient model. The mathematical models were converted to digital imaging and communications in medicine (DICOM) image series for input to the TPS. The MCNP5 v.1.40 general-purpose simulation code input files for each model were prepared using information derived from the corresponding DICOM RT exports from the TPS. Results: Comparisons of MC and TG43 results in all models showed significant differences, as reported previously in the literature and expected from the inability of the TG43 based algorithm to account for heterogeneities and model specific scatter conditions. A close agreement was observed between MC and Acuros results in all models except for a limited number of points that lay in the penumbra of perfectly shaped structures in the esophageal model, or at distances very close to the catheters in all models. Conclusions: Acuros marks a significant dosimetry improvement relative to TG43. The assessment of the clinical significance of this accuracy improvement requires further work. Mathematical patient equivalent models and models prepared from actual patient CT series are useful complementary tools in the methodology outlined in this series of works for the benchmarking of any advanced dose calculation algorithm beyond TG43.

  17. A revised dosimetric characterization of the model S700 electronic brachytherapy source containing an anode-centering plastic insert and other components not included in the 2006 model

    SciTech Connect

    Hiatt, Jessica R.; Davis, Stephen D.; Rivard, Mark J.

    2015-06-15

    Purpose: The model S700 Axxent electronic brachytherapy source by Xoft, Inc., was characterized by Rivard et al. in 2006. Since then, the source design was modified to include a new insert at the source tip. Current study objectives were to establish an accurate source model for simulation purposes, dosimetrically characterize the new source and obtain its TG-43 brachytherapy dosimetry parameters, and determine dose differences between the original simulation model and the current model S700 source design. Methods: Design information from measurements of dissected model S700 sources and from vendor-supplied CAD drawings was used to aid establishment of an updated Monte Carlo source model, which included the complex-shaped plastic source-centering insert intended to promote water flow for cooling the source anode. These data were used to create a model for subsequent radiation transport simulations in a water phantom. Compared to the 2006 simulation geometry, the influence of volume averaging close to the source was substantially reduced. A track-length estimator was used to evaluate collision kerma as a function of radial distance and polar angle for determination of TG-43 dosimetry parameters. Results for the 50 kV source were determined every 0.1 cm from 0.3 to 15 cm and every 1° from 0° to 180°. Photon spectra in water with 0.1 keV resolution were also obtained from 0.5 to 15 cm and polar angles from 0° to 165°. Simulations were run for 10{sup 10} histories, resulting in statistical uncertainties on the transverse plane of 0.04% at r = 1 cm and 0.06% at r = 5 cm. Results: The dose-rate distribution ratio for the model S700 source as compared to the 2006 model exceeded unity by more than 5% for roughly one quarter of the solid angle surrounding the source, i.e., θ ≥ 120°. The radial dose function diminished in a similar manner as for an {sup 125}I seed, with values of 1.434, 0.636, 0.283, and 0.0975 at 0.5, 2, 5, and 10 cm, respectively. The radial dose

  18. Creation and application of voxelised dosimetric models, and a comparison with the current methodology as used for the International Commission on Radiological Protection's Reference Animals and Plants.

    PubMed

    Higley, K; Ruedig, E; Gomez-Fernandez, M; Caffrey, E; Jia, J; Comolli, M; Hess, C

    2015-06-01

    Over the past decade, the International Commission on Radiological Protection (ICRP) has developed a comprehensive approach to environmental protection that includes the use of Reference Animals and Plants (RAPs) to assess radiological impacts on the environment. For the purposes of calculating radiation dose, the RAPs are approximated as simple shapes that contain homogeneous distributions of radionuclides. As uncertainties in environmental dose effects are larger than uncertainties in radiation dose calculation, some have argued against more realistic dose calculation methodologies. However, due to the complexity of organism morphology, internal structure, and density, dose rates calculated via a homogenous model may be too simplistic. The purpose of this study is to examine the benefits of a voxelised phantom compared with simple shapes for organism modelling. Both methods typically use Monte Carlo methods to calculate absorbed dose, but voxelised modelling uses an exact three-dimensional replica of an organism with accurate tissue composition and radionuclide source distribution. It is a multi-stage procedure that couples imaging modalities and processing software with Monte Carlo N-Particle. These features increase dosimetric accuracy, and may reduce uncertainty in non-human biota dose-effect studies by providing mechanistic answers regarding where and how population-level dose effects arise. © The International Society for Prosthetics and Orthotics Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

  19. Dosimetric data for the fetus derived from an anatomical model of its mother at the end of the first trimester

    SciTech Connect

    Davis, J.L.; Stabin, M.G.; Cristy, M.; Ryman, J.C.

    1986-01-01

    We discuss a study of the radiation transport of monoenergetic photons within a mathematical phantom of the pregnant female at the end of the first trimester. This phantom was developed from the adult female member of the ORNL phantom series with modifications reflecting anatomical changes at this stage of pregnancy. This geometry was incorporated into the ALGAMP Monte Carlo radiation transport code used at ORNL with the phantom series. For internal sources of radiation the emission of 60,000 monoenergetic photons at each of 12 energies within 30 organs of the body was simulated. Energy deposition within 158 regions of the body, including uterine wall, uterine contents, and 12 subregions within the contents, was tabulated. The results are presented in terms of the specific absorbed fraction, i.e., the fraction of the photon energy emitted within a source organ that is absorbed per unit mass of the target region. The specific absorbed fraction data are commonly used to evaluate the dose associated with internal emitters, e.g., from administered radiopharmaceuticals. Additional calculations have been performed for a uniform, isotropic field of photons incident on the surface of the phantom; these data provide information on the shielding of the fetus by the mother and are of interest in evaluation of doses from external radiation fields. In this study we have provided dosimetric information useful in making quantitative risk estimates for the developing fetus. Our investigations demonstrate that even at this early stage in pregnancy the effective dose equivalent to the mother cannot be used as an index of the dose equivalent to the fetus. Further efforts will be directed to consideration of later stages in fetal development and consideration of irradiation by external neutron fields.

  20. SU-E-T-328: The Volume Effect Correction of Probe-Type Dosimetric Detectors Derived From the Convolution Model

    SciTech Connect

    Looe, HK; Poppe, B; Harder, D

    2014-06-01

    Purpose: To derive and introduce a new correction factor kV, the “volume effect correction factor”, that accounts for not only the dose averaging over the detector's sensitive volume but also the secondary electron generation and transport inclusive of the disturbance of the field of secondary electrons within the detector. Materials and Methods: Mathematical convolutions and Fourier's convolution theorem have been used. Monte Carlo simulations of photon pencil beams were performed using EGSnrc. Detector constructions were adapted from manufacturers' information. Results: For the calculation of kV, the three basic convolution kernels have to be taken into account: the dose deposition kernel KD(x) (fluence to dose), the photon fluence response kernel KM(x) (photon fluence to detector signal) and the “dose response kernel” K(x) (dose to detector signal). K(x) is calculated from FT[K(x)] = [1/sqrt(2”)]FT[KM(x)]/FT[KD(x)], where the magnitude of kV(x) can be thereby calculated for arbitrary photon beam profiles and the areanormalized K(x). Conclusions: n order to take into account for the dimensions of dosimetric detectors in narrow photon beams, the “volume effect correction factor” kV has been introduced into the fundamental equation of probe-type dosimetry, and the convolution method has proven to be a method for the derivation of its numerical values. For narrow photon beams, whose width is comparable to the secondary electron ranges, kV can reach very high values, but it can be shown that the signals of small diamond detectors are well representing the absorbed dose to water averaged over the detector volume.

  1. MO-G-17A-04: Internal Dosimetric Calculations for Pediatric Nuclear Imaging Applications, Using Monte Carlo Simulations and High-Resolution Pediatric Computational Models

    SciTech Connect

    Papadimitroulas, P; Kagadis, GC; Loudos, G

    2014-06-15

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

  2. On the use of advanced numerical models for the evaluation of dosimetric parameters and the verification of exposure limits at workplaces.

    PubMed

    Catarinucci, L; Tarricone, L

    2009-12-01

    With the next transposition of the 2004/40/EC Directive, employers will become responsible for the electromagnetic field level at the workplace. To make this task easier, the scientific community is compiling practical guidelines to be followed. This work aims at enriching such guidelines, especially for the dosimetric issues. More specifically, some critical aspects related to the application of numerical dosimetric techniques for the verification of the safety limit compliance have been highlighted. In particular, three different aspects have been considered: the dosimetric parameter dependence on the shape and the inner characterisation of the exposed subject as well as on the numerical algorithm used, and the correlation between reference limits and basic restriction. Results and discussions demonstrate how, even by using sophisticated numerical techniques, in some cases a complex interpretation of the result is mandatory.

  3. Pinnacle3 modeling and end-to-end dosimetric testing of a Versa HD linear accelerator with the Agility head and flattening filter-free modes.

    PubMed

    Saenz, Daniel L; Narayanasamy, Ganesh; Cruz, Wilbert; Papanikolaou, Nikos; Stathakis, Sotirios

    2016-01-08

    The Elekta Versa HD incorporates a variety of upgrades to the line of Elekta linear accelerators, primarily including the Agility head and flattening filter-free (FFF) photon beam delivery. The completely distinct dosimetric output of the head from its predecessors, combined with the FFF beams, requires a new investigation of modeling in treatment planning systems. A model was created in Pinnacle3 v9.8 with the commissioned beam data. A phantom consisting of several plastic water and Styrofoam slabs was scanned and imported into Pinnacle3, where beams of different field sizes, source-to-surface distances (SSDs), wedges, and gantry angles were devised. Beams included all of the available photon energies (6, 10, 18, 6FFF, and 10 FFF MV), as well as the four electron energies commissioned for clinical use (6, 9, 12, and 15 MeV). The plans were verified at calculation points by measurement with a calibrated ionization chamber. Homogeneous and hetero-geneous point-dose measurements agreed within 2% relative to maximum dose for all photon and electron beams. AP photon open field measurements along the central axis at 100 cm SSD passed within 1%. In addition, IMRT testing was also performed with three standard plans (step and shoot IMRT, as well as a small- and large-field VMAT plan). The IMRT plans were delivered on the Delta4 IMRT QA phantom, for which a gamma passing rate was > 99.5% for all plans with a 3% dose deviation, 3 mm distance-to-agreement, and 10% dose threshold. The IMRT QA results for the first 23 patients yielded gamma passing rates of 97.4% ± 2.3%. Such testing ensures confidence in the ability of Pinnacle3 to model photon and electron beams with the Agility head.

  4. SU-D-BRE-06: Modeling the Dosimetric Effects of Volumetric and Layer-Based Repainting Strategies in Spot Scanning Proton Treatment Plans

    SciTech Connect

    Johnson, J E; Beltran, C; Herman, M G; Kruse, J J

    2014-06-01

    Purpose: To compare multiple repainting techniques as strategies for mitigating the interplay effect in free-breathing, spot scanning proton plans. Methods: An analytic routine modeled three-dimensional dose distributions of pencil-beam proton plans delivered to a moving target. The interplay effect was studied in subsequent calculations by modeling proton delivery from a clinical synchrotron based spot scanning system and respiratory target motion, patterned from surrogate breathing traces from clinical 4DCT scans and normalized to nominal 0.5 and 1 cm amplitudes. Two distinct repainting strategies were modeled. In idealized volumetric repainting, the plan is divided up and delivered multiple times successively, with each instance only delivering a fraction of the total MU. Maximum-MU repainting involves delivering a fixed number of MU per spot and repeating a given energy layer until the prescribed MU are reached. For each of 13 patient breathing traces, the dose was computed for up to four volumetric repaints and an array of maximum-MU values. Delivery strategies were inter-compared based on target coverage, dose homogeneity, and delivery time. Results: Increasing levels of repainting generally improved plan quality and reduced dosimetric variability at the expense of longer delivery time. Motion orthogonal to the scan direction yielded substantially greater dose deviations than motion parallel to the scan direction. For a fixed delivery time, maximum-MU repainting was most effective relative to idealized volumetric repainting at small maximum-MU values. For 1 cm amplitude motion orthogonal to the scan direction, the average homogeneity metric (D5 – D95)[%] of 23.4% was reduced to 7.6% with a 168 s delivery using volumetric repainting compared with 8.7% in 157.2 s for maximum-MU repainting. The associated static target homogeneity metric was 2.5%. Conclusion: Maximum-MU repainting can provide a reasonably effective alternative to volumetric repainting for

  5. TL and OSL dose response and stability properties of various commercially glass samples obtained from Turkey for dosimetric purposes in the UV emission spectral region.

    PubMed

    Şahiner, Eren

    2017-10-01

    This paper reports Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) dose response characteristics of ten different commercial glass samples collected from Turkey. Nowadays, glass samples are widely used mostly in objects of everyday life. The study focuses to both TL and OSL dose responses, through a dose region within 1 and 512Gy. Lowest detectable dose limit (LDDL) as well as the respective linearity features of the corresponding dose response curves were studied for both TL and OSL. Moreover, signal reproducibility and fading behaviors have also been studied in detail. For specific samples, the lowest detectable dose was yielded at 2Gy, making thus these samples appropriate for retrospective dosimetry applications. Nevertheless, based on the features reported in the present study, the majority of the samples could be possibly used effectively for dosimetric applications of higher doses in the UV region emission. Copyright © 2017 Elsevier Ltd. All rights reserved.

  6. Computational modeling of properties

    NASA Technical Reports Server (NTRS)

    Franz, Judy R.

    1994-01-01

    A simple model was developed to calculate the electronic transport parameters in disordered semiconductors in strong scattered regime. The calculation is based on a Green function solution to Kubo equation for the energy-dependent conductivity. This solution together with a rigorous calculation of the temperature-dependent chemical potential allows the determination of the dc conductivity and the thermopower. For wise-gap semiconductors with single defect bands, these transport properties are investigated as a function of defect concentration, defect energy, Fermi level, and temperature. Under certain conditions the calculated conductivity is quite similar to the measured conductivity in liquid II-VI semiconductors in that two distinct temperature regimes are found. Under different conditions the conductivity is found to decrease with temperature; this result agrees with measurements in amorphous Si. Finally the calculated thermopower can be positive or negative and may change sign with temperature or defect concentration.

  7. Clinical Digital Breast Tomosynthesis System: Dosimetric Characterization

    PubMed Central

    Feng, Steve Si Jia

    2012-01-01

    Purpose: To comprehensively characterize the dosimetric properties of a clinical digital breast tomosynthesis (DBT) system for the acquisition of mammographic and tomosynthesis images. Materials and Methods: Compressible water-oil mixture phantoms were created and imaged by using the automatic exposure control (AEC) of the Selenia Dimensions system (Hologic, Bedford, Mass) in both DBT and full-field digital mammography (FFDM) mode. Empirical measurements of the x-ray tube output were performed with a dosimeter to measure the air kerma for the range of tube current–exposure time product settings and to develop models of the automatically selected x-ray spectra. A Monte Carlo simulation of the system was developed and used in conjunction with the AEC-chosen settings and spectra models to compute and compare the mean glandular dose (MGD) resulting from both imaging modalities for breasts of varying sizes and glandular compositions. Results: Acquisition of a single craniocaudal view resulted in an MGD ranging from 0.309 to 5.26 mGy in FFDM mode and from 0.657 to 3.52 mGy in DBT mode. For a breast with a compressed thickness of 5.0 cm and a 50% glandular fraction, a DBT acquisition resulted in an only 8% higher MGD than an FFDM acquisition (1.30 and 1.20 mGy, respectively). For a breast with a compressed thickness of 6.0 cm and a 14.3% glandular fraction, a DBT acquisition resulted in an 83% higher MGD than an FFDM acquisition (2.12 and 1.16 mGy, respectively). Conclusion: For two-dimensional–three-dimensional fusion imaging with the Selenia Dimensions system, the MGD for a 5-cm-thick 50% glandular breast is 2.50 mGy, which is less than the Mammography Quality Standards Act limit for a two-view screening mammography study. © RSNA, 2012 PMID:22332070

  8. An Improved Model for Predicting Radiation Pneumonitis Incorporating Clinical and Dosimetric Variables;Lung cancer; Radiation pneumonitis; Dose-volume histogram; Angiotensin converting enzyme inhibitor

    SciTech Connect

    Jenkins, Peter; Watts, Joanne

    2011-07-15

    Purpose: Single dose-volume metrics are of limited value for the prediction of radiation pneumonitis (RP) in day-to-day clinical practice. We investigated whether multiparametric models that incorporate clinical and physiologic factors might have improved accuracy. Methods and Materials: The records of 160 patients who received radiation therapy for non-small-cell lung cancer were reviewed. All patients were treated to the same dose and with an identical technique. Dosimetric, pulmonary function, and clinical parameters were analyzed to determine their ability to predict for the subsequent development of RP. Results: Twenty-seven patients (17%) developed RP. On univariate analysis, the following factors were significantly correlated with the risk of pneumonitis: fractional volume of lung receiving >5-20 Gy, absolute volume of lung spared from receiving >5-15 Gy, mean lung dose, craniocaudal position of the isocenter, transfer coefficient for carbon monoxide (KCOc), total lung capacity, coadministration of angiotensin converting enzyme inhibitors, and coadministration of angiotensin receptor antagonists. By combining the absolute volume of lung spared from receiving >5 Gy with the KCOc, we defined a new parameter termed Transfer Factor Spared from receiving >5 Gy (TFS{sub 5}). The area under the receiver operator characteristic curve for TFS{sub 5} was 0.778, increasing to 0.846 if patients receiving modulators of the renin-angiotensin system were excluded from the analysis. Patients with a TFS{sub 5} <2.17 mmol/min/kPa had a risk of RP of 30% compared with 5% for the group with a TFS{sub 5} {>=}2.17. Conclusions: TFS{sub 5} represents a simple parameter that can be used in routine clinical practice to more accurately segregate patients into high- and low-risk groups for developing RP.

  9. SU-E-T-650: Quantification and Modeling of the Dosimetric Impact of the IBEAM Evo Treatment Couchtop EP (Elekta) in VMAT

    SciTech Connect

    Zhang, R; Bai, W; Fleckenstein, J

    2015-06-15

    Purpose: quantification and modelling of the dosimetric impact of the treatment couch in Monaco Treatment Planning System. Methods: The attenuation characteristics of couchtop EP was evaluated for two different photon acceleration potentials (6MV and 10MV) for a field size of (10×10) cm2. Phantom positions in A-B direction: on the left half, in the center and on the right half of the couch. Dose measurements of couch attenuation were performed at gantry angles from 180° to 122°, using a 0.125cc semiflex ionization chamber isocentrically placed in the center of a homogeneous cylindric sliced RW3 phantom. Each experimental setup was first measured on the LINAC and then reproduced in the TPS. By adjusting the relative-to-water electron density (ED) values of the couch, the measured attenuation was replicated. The simulated results were evaluated by comparing the measurements and simulations. Results: Without the couch model included the maximum difference between measured and calculated dose was 5.5% (5.1%) and 6.6% (6.1%) for 2 mm and 5 mm voxel size, when the phantom was positioned on the left (center). The couch model was included in the TPS with a uniform ED of 0.18 or a 2 component model with a fiber ED= 0.6 and foam core ED= 0.1. After including the treatment couch, the mean dose attenuation was reduced from 2.8% without couch included to (0.0, 0.8, −0.2, 0.6)%. The 4 different values represent the 1 and 2 components model and 2 and 5 mm voxel grid size. Conclusion: For a uniform relative-to-water couch electron density of 0.18 a good agreement between measured and calculated dose distributions was obtained for all different energies, voxel grid spacings and gantry angles. Therefore, we conclude that the Monaco couch model accurately describes the dose perturbations due to the presence of the patient couch and should therefore be used during treatment planning. This project is supported by Technology Foundation for Selected Overseas Chinese Scholar

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

    SciTech Connect

    Kostou, T; Papadimitroulas, P; Kagadis, GC; Loudos, G

    2014-06-15

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

  11. SU-E-T-459: Dosimetric Consequences of Rotated Elliptical Proton Spots in Modeling In-Air Proton Fluence for Calculating Doses in Water of Proton Pencil Beams

    SciTech Connect

    Matysiak, W; Yeung, D; Hsi, W

    2014-06-01

    Purpose: We present a study of dosimetric consequences on doses in water in modeling in-air proton fluence independently along principle axes for rotated elliptical spots. Methods: Phase-space parameters for modeling in-air fluence are the position sigma for the spatial distribution, the angle sigma for the angular distribution, and the correlation between position and angle distributions. Proton spots of the McLaren proton therapy system were measured at five locations near the isocenter for the energies of 180 MeV and 250 MeV. An elongated elliptical spot rotated with respect to the principle axes was observed for the 180 MeV, while a circular-like spot was observed for the 250 MeV. In the first approach, the phase-space parameters were derived in the principle axes without rotation. In the second approach, the phase space parameters were derived in the reference frame with axes rotated to coincide with the major axes of the elliptical spot. Monte-Carlo simulations with derived phase-space parameters using both approaches to tally doses in water were performed and analyzed. Results: For the rotated elliptical 180 MeV spots, the position sigmas were 3.6 mm and 3.2 mm in principle axes, but were 4.3 mm and 2.0 mm when the reference frame was rotated. Measured spots fitted poorly the uncorrelated 2D Gaussian, but the quality of fit was significantly improved after the reference frame was rotated. As a Result, phase space parameters in the rotated frame were more appropriate for modeling in-air proton fluence of 180 MeV protons. Considerable differences were observed in Monte Carlo simulated dose distributions in water with phase-space parameters obtained with the two approaches. Conclusion: For rotated elliptical proton spots, phase-space parameters obtained in the rotated reference frame are better for modeling in-air proton fluence, and can be introduced into treatment planning systems.

  12. SU-C-303-03: Dosimetric Model of the Beagle Needed for Pre-Clinical Testing of Radiopharmaceuticals

    SciTech Connect

    Shang, M; Sands, M; Bolch, W

    2015-06-15

    Purpose: Large animal models, most popularly beagles, have been crucial surrogates to humans in determining radiation safety levels of radiopharmaceuticals. This study aims to develop a detailed beagle phantom to accurately approximate organ absorbed doses for therapy nuclear medicine preclinical studies. Methods: A 3D NURBS model was created subordinate to a whole body CT of an adult beagle. Bones were harvested and CT imaged to offer macroscopic skeletal detail. Samples of trabecular spongiosa were cored and imaged to offer microscopic skeletal detail for bone trabeculae and marrow volume fractions. Results: Organ masses in the model are typical of an adult beagle. Trends in volume fractions for skeletal dosimetry are fundamentally similar to those found in existing models of other canine species. Conclusion: This work warrants its use in further investigations of radiation transport calculation for electron and photon dosimetry. This model accurately represents the anatomy of a beagle, and can be directly translated into a useable geometry for a voxel-based Monte Carlo radiation transport program such as MCNP6. Work supported by a grant from the Hyundai Hope on Wheels Foundation for Pediatric Cancer Research.

  13. HUMTRN and EFFECTS: Age and sex specific dosimetric and physiological human population dynamics models for dose assessment

    SciTech Connect

    Gallegos, A.F.; Wenzel, W.J. )

    1989-01-01

    A human simulation model called HUMTRN and a population risk assessment model called EFFECTS were developed at Los Alamos National Laboratory as a major component of the BIOTRAN environmental risk assessment model. HUMTRN simulates growth using dietary and physiological characteristics and kinetics of radionuclides to predict radiation doses to selected organs of both sexes in different age groups. The model called EFFECTS was interfaced with output from HUMTRN to predict cancer risks in a dynamic human population. EFFECTS is based on the National Research Council Committee on the Biological Effects of Ionizing Radiation (BEIR)-III radiation cancer mortality estimates from the U.S. population mortality and natality estimates for both sexes between the ages of 1 and 70. These models track radiation intake from air, water, and food, calculate uptake in major growing organs, and estimate cancer mortality risks. This report documents the use of an IBM Personal Computer AT to run HUMTRN and EFFECTS. Air, water, and food contaminant concentrations are provided as input to HUMTRN, which then provides input for EFFECTS. The limitations of this approach are also discussed.

  14. Dosimetric Characteristics for Brachytherapy Sources

    SciTech Connect

    DeWerd, Larry A.; Davis, Stephen D.

    2011-05-05

    Brachytherapy sources are characterized by the dosimetric parameters in a protocol such as the American Association of Physicists in Medicine Task Group 43. The air-kerma strength is measured and traceable to a primary standard. Then the parameters such as dose-rate constant, radial dose function, and anisotropy function are measured and related back to the primary standard. This is normally accomplished with thermoluminescent dosimeters (TLDs). Since radial dose function and anisotropy function are relative parameters, some of the dosimetric corrections are negligible. For the dose-rate constant, parameters such as the energy dependence compared with a calibration beam such as {sup 60}Co need to be accounted for. A description of the primary standard measurements and TLD measurements will be discussed.

  15. Modeling skull electrical properties

    PubMed Central

    Sadleir, R. J.; Argibay, A.

    2008-01-01

    Accurate representations and measurements of skull electrical conductivity are essential in developing appropriate forward models for applications such as inverse EEG or Electrical Impedance Tomography of the head. Because of its layered structure, it is often assumed that skull is anisotropic, with an anisotropy ratio around 10. However, no detailed investigation of skull anisotropy has been performed. In this paper we investigate four-electrode measurements of conductivities and their relation to tissue anisotropy ratio (ratio of tangential to radial conductivity) in layered or anisotropic biological samples similar to bone. It is shown here that typical values for the thicknesses and radial conductivities of individual skull layers produce tissue with much smaller anisotropy ratios than 10. Moreover, we show that there are very significant differences between the field patterns formed in a three-layered isotropic structure plausible for bone, and those formed assuming that bone is homogeneous and anisotropic.We performed a measurement of conductivity using an electrode configuration sensitive to the distinction between three-layered and homogeneous anisotropic composition and found results consistent with the sample being three-layered. We recommend that the skull be more appropriately represented as three isotropic layers than as homogeneous and anisotropic. PMID:17629793

  16. Modeling skull electrical properties.

    PubMed

    Sadleir, R J; Argibay, A

    2007-10-01

    Accurate representations and measurements of skull electrical conductivity are essential in developing appropriate forward models for applications such as inverse EEG or Electrical Impedance Tomography of the head. Because of its layered structure, it is often assumed that skull is anisotropic, with an anisotropy ratio around 10. However, no detailed investigation of skull anisotropy has been performed. In this paper we investigate four-electrode measurements of conductivities and their relation to tissue anisotropy ratio (ratio of tangential to radial conductivity) in layered or anisotropic biological samples similar to bone. It is shown here that typical values for the thicknesses and radial conductivities of individual skull layers produce tissue with much smaller anisotropy ratios than 10. Moreover, we show that there are very significant differences between the field patterns formed in a three-layered isotropic structure plausible for bone, and those formed assuming that bone is homogeneous and anisotropic. We performed a measurement of conductivity using an electrode configuration sensitive to the distinction between three-layered and homogeneous anisotropic composition and found results consistent with the sample being three-layered. We recommend that the skull be more appropriately represented as three isotropic layers than as homogeneous and anisotropic.

  17. Elaboration d'un dosimetre a fibres scintillantes

    NASA Astrophysics Data System (ADS)

    Archambault, Louis

    adapte pour l'evaluation precise et rapide de patrons de doses. Meme si un modele abordable de camera CCD a ete utilise, il a ete possible de developper un dosimetre precis, reproductible et de haute resolution spatiale possedant les excellentes proprietes des scintillateurs plastiques.

  18. ROCK PROPERTIES MODEL ANALYSIS MODEL REPORT

    SciTech Connect

    Clinton Lum

    2002-02-04

    The purpose of this Analysis and Model Report (AMR) is to document Rock Properties Model (RPM) 3.1 with regard to input data, model methods, assumptions, uncertainties and limitations of model results, and qualification status of the model. The report also documents the differences between the current and previous versions and validation of the model. The rock properties models are intended principally for use as input to numerical physical-process modeling, such as of ground-water flow and/or radionuclide transport. The constraints, caveats, and limitations associated with this model are discussed in the appropriate text sections that follow. This work was conducted in accordance with the following planning documents: WA-0344, ''3-D Rock Properties Modeling for FY 1998'' (SNL 1997, WA-0358), ''3-D Rock Properties Modeling for FY 1999'' (SNL 1999), and the technical development plan, Rock Properties Model Version 3.1, (CRWMS M&O 1999c). The Interim Change Notice (ICNs), ICN 02 and ICN 03, of this AMR were prepared as part of activities being conducted under the Technical Work Plan, TWP-NBS-GS-000003, ''Technical Work Plan for the Integrated Site Model, Process Model Report, Revision 01'' (CRWMS M&O 2000b). The purpose of ICN 03 is to record changes in data input status due to data qualification and verification activities. These work plans describe the scope, objectives, tasks, methodology, and implementing procedures for model construction. The constraints, caveats, and limitations associated with this model are discussed in the appropriate text sections that follow. The work scope for this activity consists of the following: (1) Conversion of the input data (laboratory measured porosity data, x-ray diffraction mineralogy, petrophysical calculations of bound water, and petrophysical calculations of porosity) for each borehole into stratigraphic coordinates; (2) Re-sampling and merging of data sets; (3) Development of geostatistical simulations of porosity; (4

  19. Dosimetric characterization of model Cs-1 Rev2 cesium-131 brachytherapy source in water phantoms and human tissues with MCNP5 Monte Carlo simulation.

    PubMed

    Wang, Jianhua; Zhang, Hualin

    2008-04-01

    A recently developed alternative brachytherapy seed, Cs-1 Rev2 cesium-131, has begun to be used in clinical practice. The dosimetric characteristics of this source in various media, particularly in human tissues, have not been fully evaluated. The aim of this study was to calculate the dosimetric parameters for the Cs-1 Rev2 cesium-131 seed following the recommendations of the AAPM TG-43U1 report [Rivard et al., Med. Phys. 31, 633-674 (2004)] for new sources in brachytherapy applications. Dose rate constants, radial dose functions, and anisotropy functions of the source in water, Virtual Water, and relevant human soft tissues were calculated using MCNP5 Monte Carlo simulations following the TG-43U1 formalism. The results yielded dose rate constants of 1.048, 1.024, 1.041, and 1.044 cGy h(-1) U(-1) in water, Virtual Water, muscle, and prostate tissue, respectively. The conversion factor for this new source between water and Virtual Water was 1.02, between muscle and water was 1.006, and between prostate and water was 1.004. The authors' calculation of anisotropy functions in a Virtual Water phantom agreed closely with Murphy's measurements [Murphy et al., Med. Phys. 31, 1529-1538 (2004)]. Our calculations of the radial dose function in water and Virtual Water have good agreement with those in previous experimental and Monte Carlo studies. The TG-43U1 parameters for clinical applications in water, muscle, and prostate tissue are presented in this work.

  20. Standardization of individual dosimetric systems

    NASA Astrophysics Data System (ADS)

    Cavallini, A.

    1983-10-01

    The activities of an Italian operating group for the standardization of individual dosimeters are discussed. Intercalibration was performed for about 10,000 individual dosimeters in order to analyze systematic and random measuring errors. The validity of normalized inspection procedures was examined and the necessity of periodic checks was considered. Legislation is proposed including a technical inspection prior to authorization to start a dosimetry center and a norm for periodic controls of dosimetry services. The creation of a dosimetric data bank is also suggested.

  1. Dosimetric methodology of the ICRP

    SciTech Connect

    Eckerman, K.F.

    1994-12-31

    Establishment of guidance for the protection of workers and members of the public from radiation exposures necessitates estimation of the radiation dose to tissues of the body at risk. The dosimetric methodology formulated by the International Commission on Radiological Protection (ICRP) is intended to be responsive to this need. While developed for radiation protection, elements of the methodology are often applied in addressing other radiation issues; e.g., risk assessment. This chapter provides an overview of the methodology, discusses its recent extension to age-dependent considerations, and illustrates specific aspects of the methodology through a number of numerical examples.

  2. Mass transport analysis: inhalation rfc methods framework for interspecies dosimetric adjustment.

    PubMed

    Hanna, L M; Lou, S R; Su, S; Jarabek, A M

    2001-05-01

    In 1994, the U.S. Environmental Protection Agency introduced dosimetry modeling into the methods used to derive an inhalation reference concentration (RfC). The type of dosimetric adjustment factor (DAF) applied had to span the range of physicochemical characteristics of the gases listed on the Clean Air Act Amendments in 1991 as hazardous air pollutants (HAPs) and accommodate differences in available data with respect to their toxicokinetic properties. A framework was proposed that allowed for a hierarchy of dosimetry model structures, from optimal to rudimentary, and a category scheme that provided for limiting model structures based on physicochemical and toxicokinetic properties. These limiting cases were developed from restricting consideration to specific properties relying on an understanding of the generalized system based on mass transport theory. Physiochemical characteristics included the solubility and reactivity (e.g., propensity to dissociate, oxidize, or serve as a metabolic substrate) of the gas and were used as major determinants of absorption. Dosimetric adjustments were developed to evaluate portal of entry (POE) effects as well as remote (systemic) effects relevant to the toxicokinetic properties of the gas of interest. The gas categorization scheme consisted of defining three gas categories: (1) gases that are highly soluble and/or reactive, absorbing primarily in the extrathoracic airways; (2) gases that are moderately soluble and/or reactive, absorbing throughout the airways, as well as accumulating in the bloodstream; and (3) gases that have a low water solubility and are lipid soluble such that they are primarily absorbed in the pulmonary region and likely to act systemically. This article presents the framework and the mass transport theory behind the RfC method. Comparison to compartmental approaches and considerations for future development are also discussed.

  3. IPIP: A new approach to inverse planning for HDR brachytherapy by directly optimizing dosimetric indices

    SciTech Connect

    Siauw, Timmy; Cunha, Adam; Atamtuerk, Alper; Hsu, I-Chow; Pouliot, Jean; Goldberg, Ken

    2011-07-15

    Purpose: Many planning methods for high dose rate (HDR) brachytherapy require an iterative approach. A set of computational parameters are hypothesized that will give a dose plan that meets dosimetric criteria. A dose plan is computed using these parameters, and if any dosimetric criteria are not met, the process is iterated until a suitable dose plan is found. In this way, the dose distribution is controlled by abstract parameters. The purpose of this study is to develop a new approach for HDR brachytherapy by directly optimizing the dose distribution based on dosimetric criteria. Methods: The authors developed inverse planning by integer program (IPIP), an optimization model for computing HDR brachytherapy dose plans and a fast heuristic for it. They used their heuristic to compute dose plans for 20 anonymized prostate cancer image data sets from patients previously treated at their clinic database. Dosimetry was evaluated and compared to dosimetric criteria. Results: Dose plans computed from IPIP satisfied all given dosimetric criteria for the target and healthy tissue after a single iteration. The average target coverage was 95%. The average computation time for IPIP was 30.1 s on an Intel(R) Core{sup TM}2 Duo CPU 1.67 GHz processor with 3 Gib RAM. Conclusions: IPIP is an HDR brachytherapy planning system that directly incorporates dosimetric criteria. The authors have demonstrated that IPIP has clinically acceptable performance for the prostate cases and dosimetric criteria used in this study, in both dosimetry and runtime. Further study is required to determine if IPIP performs well for a more general group of patients and dosimetric criteria, including other cancer sites such as GYN.

  4. Dosimetric Predictors of Laryngeal Edema

    SciTech Connect

    Sanguineti, Giuseppe . E-mail: gisangui@utmb.edu; Adapala, Prashanth; Endres, Eugene J. C; Brack, Collin; Fiorino, Claudio; Sormani, Maria Pia; Parker, Brent

    2007-07-01

    Purpose: To investigate dosimetric predictors of laryngeal edema after radiotherapy (RT). Methods and Materials: A total of 66 patients were selected who had squamous cell carcinoma of the head and neck with grossly uninvolved larynx at the time of RT, no prior major surgical operation except for neck dissection and tonsillectomy, treatment planning data available for analysis, and at least one fiberoptic examination of the larynx within 2 years from RT performed by a single observer. Both the biologically equivalent mean dose at 2 Gy per fraction and the cumulative biologic dose-volume histogram of the larynx were extracted for each patient. Laryngeal edema was prospectively scored after treatment. Time to endpoint, moderate or worse laryngeal edema (Radiation Therapy Oncology Group Grade 2+), was calculated with log rank test from the date of treatment end. Results: At a median follow-up of 17.1 months (range, 0.4- 50.0 months), the risk of Grade 2+ edema was 58.9% {+-} 7%. Mean dose to the larynx, V30, V40, V50, V60, and V70 were significantly correlated with Grade 2+ edema at univariate analysis. At multivariate analysis, mean laryngeal dose (continuum, hazard ratio, 1.11; 95% confidence interval, 1.06-1.15; p < 0.001), and positive neck stage at RT (N0-x vs. N +, hazard ratio, 3.66; 95% confidence interval, 1.40-9.58; p = 0.008) were the only independent predictors. Further stratification showed that, to minimize the risk of Grade 2+ edema, the mean dose to the larynx has to be kept {<=}43.5 Gy at 2 Gy per fraction. Conclusion: Laryngeal edema is strictly correlated with various dosimetric parameters; mean dose to the larynx should be kept {<=}43.5 Gy.

  5. Reevaluations of dosimetric factors: Hiroshima and Nagasaki

    SciTech Connect

    Bond, V.P.; Thiessen, J.W.

    1982-01-01

    Separate abstracts were prepared for the 13 papers in this proceedings of a symposium on the reevaluation of dosimetric factors for Hiroshima and Nagasaki. A summary and general discussion are included at the end of the proceedings. (KRM)

  6. Transport Properties for Combustion Modeling

    SciTech Connect

    Brown, N.J.; Bastein, L.; Price, P.N.

    2010-02-19

    This review examines current approximations and approaches that underlie the evaluation of transport properties for combustion modeling applications. Discussed in the review are: the intermolecular potential and its descriptive molecular parameters; various approaches to evaluating collision integrals; supporting data required for the evaluation of transport properties; commonly used computer programs for predicting transport properties; the quality of experimental measurements and their importance for validating or rejecting approximations to property estimation; the interpretation of corresponding states; combination rules that yield pair molecular potential parameters for unlike species from like species parameters; and mixture approximations. The insensitivity of transport properties to intermolecular forces is noted, especially the non-uniqueness of the supporting potential parameters. Viscosity experiments of pure substances and binary mixtures measured post 1970 are used to evaluate a number of approximations; the intermediate temperature range 1 < T* < 10, where T* is kT/{var_epsilon}, is emphasized since this is where rich data sets are available. When suitable potential parameters are used, errors in transport property predictions for pure substances and binary mixtures are less than 5 %, when they are calculated using the approaches of Kee et al.; Mason, Kestin, and Uribe; Paul and Warnatz; or Ern and Giovangigli. Recommendations stemming from the review include (1) revisiting the supporting data required by the various computational approaches, and updating the data sets with accurate potential parameters, dipole moments, and polarizabilities; (2) characterizing the range of parameter space over which the fit to experimental data is good, rather than the current practice of reporting only the parameter set that best fits the data; (3) looking for improved combining rules, since existing rules were found to under-predict the viscosity in most cases; (4

  7. Dosimetric Characteristics of 6 MV Modified Beams by Physical Wedges of a Siemens Linear Accelerator.

    PubMed

    Zabihzadeh, Mansour; Birgani, Mohammad Javad Tahmasebi; Hoseini-Ghahfarokhi, Mojtaba; Arvandi, Sholeh; Hoseini, Seyed Mohammad; Fadaei, Mahbube

    2016-01-01

    Physical wedges still can be used as missing tissue compensators or filters to alter the shape of isodose curves in a target volume to reach an optimal radiotherapy plan without creating a hotspot. The aim of this study was to investigate the dosimetric properties of physical wedges filters such as off-axis photon fluence, photon spectrum, output factor and half value layer. The photon beam quality of a 6 MV Primus Siemens modified by 150 and 450 physical wedges was studied with BEAMnrc Monte Carlo (MC) code. The calculated present depth dose and dose profile curves for open and wedged photon beam were in good agreement with the measurements. Increase of wedge angle increased the beam hardening and this effect was more pronounced at the heal region. Using such an accurate MC model to determine of wedge factors and implementation of it as a calculation algorithm in the future treatment planning systems is recommended.

  8. Electron spin resonance dosimetric properties of bone

    SciTech Connect

    Caracelli, I.; Terrile, M.C.; Mascarenhas, S.

    1986-02-01

    The characteristics of electron spin resonance (ESR) dosimetry using bovine bone samples are described. The number of paramagnetic centers created by gamma radiation in the inorganic bone matrix was measured as a function of absorbed dose. The minimum detectable dose was 0.5 Gy for 60Co gamma rays. The response was linear up to the maximum dose studied (30 Gy) and independent of dose rate up to the maximum dose rate used (1.67 Gy min-1). For different bone samples the reproducibility was 5%. This method may be valuable for nuclear accident dosimetry.

  9. Modeling Magnetic Properties in EZTB

    NASA Technical Reports Server (NTRS)

    Lee, Seungwon; vonAllmen, Paul

    2007-01-01

    A software module that calculates magnetic properties of a semiconducting material has been written for incorporation into, and execution within, the Easy (Modular) Tight-Binding (EZTB) software infrastructure. [EZTB is designed to model the electronic structures of semiconductor devices ranging from bulk semiconductors, to quantum wells, quantum wires, and quantum dots. EZTB implements an empirical tight-binding mathematical model of the underlying physics.] This module can model the effect of a magnetic field applied along any direction and does not require any adjustment of model parameters. The module has thus far been applied to study the performances of silicon-based quantum computers in the presence of magnetic fields and of miscut angles in quantum wells. The module is expected to assist experimentalists in fabricating a spin qubit in a Si/SiGe quantum dot. This software can be executed in almost any Unix operating system, utilizes parallel computing, can be run as a Web-portal application program. The module has been validated by comparison of its predictions with experimental data available in the literature.

  10. SU-C-204-01: A Dosimetric Investigation Into the Effects of Yttrium-90 Radioembolization On the GI Tract: In-Vivo and Histological Analysis in An Animal Model

    SciTech Connect

    Pasciak, A; Nodit, L; Bourgeois, A; Bradley, Y; Paxton, B; Arepally, A

    2016-06-15

    Purpose: In Yttrium-90 (90Y) radioembolization, non-target embolization (NTE) to the stomach or small bowel can result in ulceration, a rare but difficult to manage clinical complication. However, dosimetric thresholds for toxicity to these tissues from radioembolization have never been evaluated in a controlled setting. We performed an analysis of the effect of 90Y radioembolization in a porcine model at different absorbed-dose endpoints. Methods: Under approval of the University of Tennessee IACUC, 6 female pigs were included in this study. Animals underwent transfemoral angiography and infusion of calibrated dosages of 90Y resin microspheres into arteries supplying part of the gastric wall. A 99mTc-MAA simulation study was performed first to determine perfused tissue volume for treatment planning along with contrast-enhanced CT. The pigs were monitored for side effects for 9 weeks, after which time they were euthanized and their upper gastrointestinal tracts were harvested for analysis. Results: 90Y radioembolization was infused resulting in average absorbed doses of between 35.5 and 91.9 Gy to the gastric wall. No animal exhibited any signs of pain or gastrointestinal distress through the duration of the study. Excised tissue showed 1–2 small (<3.0 cm2) healed or healing superficial gastric lesions in 5 out of 6 animals. Histologic analysis demonstrated that lesion location was superficial to areas of abnormally high microsphere deposition. An analysis of microsphere deposition patterns within the gastric wall indicated a high preference for submucosal deposition. Dosimetric evaluation at the luminal mucosa performed based on microsphere deposition patterns confirmed that 90Y dosimetry techniques conventionally used in hepatic dosimetry provide a reasonable estimate of absorbed dose. Conclusion: The upper gastrointestinal tract may be less sensitive to 90Y radioembolization than previously thought. Lack of charged-particle equilibrium at the luminal mucosa

  11. Dosimetric assessment of the PRESAGE dosimeter for a proton pencil beam

    NASA Astrophysics Data System (ADS)

    Wuu, C.-S.; Xu, Y.; Qian, X.; Adamovics, J.; Cascio, E.; Lu, H.-M.

    2013-06-01

    The objective of this study is to assess the feasibility of using PRESAGE dosimeters for proton pencil beam dosimetry. Two different formulations of phantom materials were tested for their suitability in characterizing a single proton pencil beam. The dosimetric response of PRESAGE was found to be linear up to 4Gy. First-generation optical CT scanner, OCTOPUSTM was used to implement dose distributions for proton pencil beams since it provides most accurate readout. Percentage depth dose curves and beam profiles for two proton energy, 110 MeV, and 93 MeV, were used to evaluate the dosimetric performance of two PRESAGE phantom formulas. The findings from this study show that the dosimetric properties of the phantom materials match with basic physics of proton beams.

  12. A generalized definition of dosimetric quantities.

    PubMed

    Kellerer, A M; Rossi, H H

    1990-04-01

    The current definitions of microdosimetric and dosimetric quantities use the notion of 'ionizing radiation'. However, this notion is not rigorously defined, and its definition would require the somewhat arbitrary choice of specified energy cut-off values for different types of particles. Instead of choosing fixed cut-off values one can extend the system of definitions by admitting the free selection of a category of types and energies of particles that are taken to be part of the field. In this way one extends the system of dosimetric quantities. Kerma and absorbed dose appear then as special cases of a more general dosimetric quantity, and an analogue to kerma can be obtained for charged particle fields; it is termed cema. A modification that is suitable for electron fields is termed reduced cema.

  13. Dosimetric comparison of Acuros XB deterministic radiation transport method with Monte Carlo and model-based convolution methods in heterogeneous media

    PubMed Central

    Han, Tao; Mikell, Justin K.; Salehpour, Mohammad; Mourtada, Firas

    2011-01-01

    Purpose: The deterministic Acuros XB (AXB) algorithm was recently implemented in the Eclipse treatment planning system. The goal of this study was to compare AXB performance to Monte Carlo (MC) and two standard clinical convolution methods: the anisotropic analytical algorithm (AAA) and the collapsed-cone convolution (CCC) method. Methods: Homogeneous water and multilayer slab virtual phantoms were used for this study. The multilayer slab phantom had three different materials, representing soft tissue, bone, and lung. Depth dose and lateral dose profiles from AXB v10 in Eclipse were compared to AAA v10 in Eclipse, CCC in Pinnacle3, and EGSnrc MC simulations for 6 and 18 MV photon beams with open fields for both phantoms. In order to further reveal the dosimetric differences between AXB and AAA or CCC, three-dimensional (3D) gamma index analyses were conducted in slab regions and subregions defined by AAPM Task Group 53. Results: The AXB calculations were found to be closer to MC than both AAA and CCC for all the investigated plans, especially in bone and lung regions. The average differences of depth dose profiles between MC and AXB, AAA, or CCC was within 1.1, 4.4, and 2.2%, respectively, for all fields and energies. More specifically, those differences in bone region were up to 1.1, 6.4, and 1.6%; in lung region were up to 0.9, 11.6, and 4.5% for AXB, AAA, and CCC, respectively. AXB was also found to have better dose predictions than AAA and CCC at the tissue interfaces where backscatter occurs. 3D gamma index analyses (percent of dose voxels passing a 2%∕2 mm criterion) showed that the dose differences between AAA and AXB are significant (under 60% passed) in the bone region for all field sizes of 6 MV and in the lung region for most of field sizes of both energies. The difference between AXB and CCC was generally small (over 90% passed) except in the lung region for 18 MV 10 × 10 cm2 fields (over 26% passed) and in the bone region for 5 × 5 and 10

  14. Dosimetric characteristics of the Siemens IGRT carbon fiber tabletop.

    PubMed

    Spezi, Emiliano; Ferri, Andrea

    2007-01-01

    In this work, the dosimetric characteristics of a new commercial carbon fiber treatment table are investigated. The photon beam attenuation properties of the Siemens image-guided radiation therapy (IGRT) tabletop were studied in detail. Two sets of dosimetric measurements were performed. In the first experiment a polystyrene slab phantom was used: the central axis attenuation and the skin-sparing detriment were investigated. In the second experiment, the off-axis treatment table transmission was investigated using a polystyrene cylindrical phantom. Measurements were taken at the isocenter for a 360 degrees rotation of the radiation beam. Our results show that the photon beam attenuation of the Siemens IGRT carbon fiber tabletop varies from a minimum of 2.1% (central axis) to a maximum of 4.6% (120 degrees and 240 degrees beam incidence). The beam entrance dose increases from 82% to 97% of the dose at the depth of maximum for a clinical 6-MV radiation field. The depth of maximum also decreases by 0.4 cm. Despite the wedge cross section of the table the beam attenuation properties of the IGRT tabletop remain constant along the longitudinal direction. American Association of Medical Dosimetrists.

  15. Dosimetric Characteristics of the Siemens IGRT Carbon Fiber Tabletop

    SciTech Connect

    Spezi, Emiliano; Ferri, Andrea

    2007-01-01

    In this work, the dosimetric characteristics of a new commercial carbon fiber treatment table are investigated. The photon beam attenuation properties of the Siemens image-guided radiation therapy (IGRT) tabletop were studied in detail. Two sets of dosimetric measurements were performed. In the first experiment a polystyrene slab phantom was used: the central axis attenuation and the skin-sparing detriment were investigated. In the second experiment, the off-axis treatment table transmission was investigated using a polystyrene cylindrical phantom. Measurements were taken at the isocenter for a 360 deg. rotation of the radiation beam. Our results show that the photon beam attenuation of the Siemens IGRT carbon fiber tabletop varies from a minimum of 2.1% (central axis) to a maximum of 4.6% (120 deg. and 240 deg. beam incidence). The beam entrance dose increases from 82% to 97% of the dose at the depth of maximum for a clinical 6-MV radiation field. The depth of maximum also decreases by 0.4 cm. Despite the wedge cross section of the table the beam attenuation properties of the IGRT tabletop remain constant along the longitudinal direction. American Association of Medical Dosimetrists.

  16. The trinucleons: Physical observables and model properties

    SciTech Connect

    Gibson, B.F.

    1992-01-01

    Our progress in understanding the properties of {sup 3}H and {sup 3}He in terms of a nonrelativistic Hamiltonian picture employing realistic nuclear forces is reviewed. Trinucleon model properties are summarized for a number of contemporary force models, and predictions for physical observables are presented. Disagreement between theoretical model results and experimental results are highlighted.

  17. The trinucleons: Physical observables and model properties

    SciTech Connect

    Gibson, B.F.

    1992-05-01

    Our progress in understanding the properties of {sup 3}H and {sup 3}He in terms of a nonrelativistic Hamiltonian picture employing realistic nuclear forces is reviewed. Trinucleon model properties are summarized for a number of contemporary force models, and predictions for physical observables are presented. Disagreement between theoretical model results and experimental results are highlighted.

  18. Dosimetric study of the new Intersource125 iodine seed.

    PubMed

    Reniers, B; Vynckier, S; Scalliet, P

    2001-11-01

    The use of low energy photon emitters for brachytherapy applications, as in the treatment of the prostate or of eye tumors, has significantly increased these last few years. New seed models for 125I have been recently introduced. The aim of this study is to determine the dosimetric parameters as recommended by the AAPM in the TG43 formalism for a new iodine seed design: the InterSource125 (Furnished by IBt, Seneffe, Belgium). Measurements are made with LiF thermoluminescent dosimeters (size of 1 mm3) in solid water phantoms to obtain the dose constant, the radial dose function, and the anisotropy function. The TLDs were calibrated at 6 MV and an energy correction factor of 1.41 has been applied. The same dose parameters are also obtained by Monte Carlo calculations (MCNP4B) in solid water and in liquid water. The radial function was measured at 1, 1.5, 2, 3, 4, 5, 6, and 7 cm and calculated between 0.3 and 7 cm. The anisotropy functions were measured at 2, 3, and 5 cm and calculated between 0.3 and 7 cm. The calculated and the measured TG43 functions for solid water are in excellent agreement. We have then calculated these functions in liquid water to obtain the dosimetric information for clinical applications as per TG43 recommendations. In WTI, the calculated dose rate constant is 0.98+/-1% and the measured value is 1.03 +/- 7 %. The calculated value for water is 1.02+/- 1 %. In conclusion, the dosimetric functions for the new iodine seed InterSource125 have been determined. They are quite different from the data of the well-known model 6711 from Amersham due to the absence of silver in the new seed. The characteristics are very similar to those of model 6702.

  19. Preparation, thermoluminescence, photoluminescence and dosimetric characteristics of LiF:Mg,Cu,P,B phosphor

    NASA Astrophysics Data System (ADS)

    Preto, Prince D.; Vidyavathy, B.; Dhabekar, Bhushan S.

    2017-01-01

    This paper presents the preparation, thermoluminescence, thermoluminescence (TL) emission, photoluminescence (PL) emission and dosimetric properties of a new LiF:Mg,Cu,P,B (MCPB) phosphor. This phosphor shows an enhanced sensitivity and is 27 times more sensitive than LiF:Mg,Ti and 1.15 times more sensitive than LiF:Mg,Cu,P (MCP). The position and shape of the glow curve of MCPB is very much similar to that of MCP, but the intensity of the main dosimetric peak increases, reaches a maximum at a concentration of about 0.025 mol% and then decreases slowly upon further addition of boron. The main dosimetric peak of the phosphor appears at 220 °C and is linear up to 10 Gy with a minimum detectable dose of about 10 μGy. MCPB phosphor can be reused up to 10 cycles at an annealing temperature of 260 °C for 10 min without loss in TL sensitivity. MCPB exhibits a very low residual signal (0.42 %) when compared to that of GR-200A and GR-200P reported in the literature. The structural and morphological characteristics of the phosphor have been studied using X-ray diffraction method and scanning electron microscope. Both the TL and PL emission spectrum are recorded and analyzed. The various other dosimetric properties like annealing temperature, fading, reusability and residual signal are also presented in this study.

  20. Dosimetric accuracy of proton therapy for chordoma patients with titanium implants

    PubMed Central

    Verburg, Joost M.; Seco, Joao

    2013-01-01

    Purpose: To investigate dosimetric errors in proton therapy treatment planning due to titanium implants, and to determine how these affect postoperative passively scattered proton therapy for chordoma patients with orthopedic hardware. Methods: The presence of titanium hardware near the tumor may affect the dosimetric accuracy of proton therapy. Artifacts in the computed tomography (CT) scan can cause errors in the proton stopping powers used for dose calculation, which are derived from CT numbers. Also, clinical dose calculation algorithms may not accurately simulate proton beam transport through the implants, which have very different properties as compared to human tissue. The authors first evaluated the impact of these two main issues. Dose errors introduced by metal artifacts were studied using phantoms with and without titanium inserts, and patient scans on which a metal artifact reduction method was applied. Pencil-beam dose calculations were compared to models of nuclear interactions in titanium and Monte Carlo simulations. Then, to assess the overall impact on treatment plans for chordoma, the authors compared the original clinical treatment plans to recalculated dose distributions employing both metal artifact reduction and Monte Carlo methods. Results: Dose recalculations of clinical proton fields showed that metal artifacts cause range errors up to 6 mm distal to regions affected by CT artifacts. Monte Carlo simulations revealed dose differences >10% in the high-dose area, and range differences up to 10 mm. Since these errors are mostly local in nature, the large number of fields limits the impact on target coverage in the chordoma treatment plans to a small decrease of dose homogeneity. Conclusions: In the presence of titanium implants, CT metal artifacts and the approximations of pencil-beam dose calculations cause considerable errors in proton dose calculation. The spatial distribution of the errors however limits the overall impact on passively

  1. Models of the optical properties of solids

    NASA Astrophysics Data System (ADS)

    Tropf, William J.; Thomas, Michael E.

    1992-12-01

    Physically-based optical property models of solids are a convenient means of representing the complex index of refraction as a function of frequency and temperature. This modeling approach is especially convenient considering the wide spread use of personal computers and the uncomplicated mathematical form of the models. Models provide a convenient method of cataloging measurements and interpolated between measurements. Several useful models covering absorption and scattering phenomena are presented. Together, these models allow prediction of optical properties over the spectral range from microwaves to the electronic band gap. Temperature dependence of the optical properties cover a more restricted range, but some models predict optical properties from liquid helium to melting temperatures. We have developed an optical properties code incorporating the following models: the classical (one- phonon) oscillator model, our multi-phonon model, the Urbach tail and weak absorption tail models, free-carrier model, and an empirical scatter model. These models require measured parameters which are given for common materials. Comparisons of model calculations of the refractive index, the absorption coefficient, and scattering coefficient to experimental data are presented.

  2. Dosimetric calculations for uranium miners for epidemiological studies.

    PubMed

    Marsh, J W; Blanchardon, E; Gregoratto, D; Hofmann, W; Karcher, K; Nosske, D; Tomásek, L

    2012-05-01

    Epidemiological studies on uranium miners are being carried out to quantify the risk of cancer based on organ dose calculations. Mathematical models have been applied to calculate the annual absorbed doses to regions of the lung, red bone marrow, liver, kidney and stomach for each individual miner arising from exposure to radon gas, radon progeny and long-lived radionuclides (LLR) present in the uranium ore dust and to external gamma radiation. The methodology and dosimetric models used to calculate these organ doses are described and the resulting doses for unit exposure to each source (radon gas, radon progeny and LLR) are presented. The results of dosimetric calculations for a typical German miner are also given. For this miner, the absorbed dose to the central regions of the lung is dominated by the dose arising from exposure to radon progeny, whereas the absorbed dose to the red bone marrow is dominated by the external gamma dose. The uncertainties in the absorbed dose to regions of the lung arising from unit exposure to radon progeny are also discussed. These dose estimates are being used in epidemiological studies of cancer in uranium miners.

  3. Thermophysical property models for lunar regolith

    NASA Astrophysics Data System (ADS)

    Schreiner, Samuel S.; Dominguez, Jesus A.; Sibille, Laurent; Hoffman, Jeffrey A.

    2016-03-01

    We present a set of thermophysical property models for lunar regolith. Data from over 25 sources in the literature are integrated and fit with regression models for the following properties: composition, density, specific heat, latent heat of melting/fusion, thermal conductivity, electrical conductivity, optical absorption length, Gibbs Free Energy and Enthalpy of Formation. The models are based on data from Apollo samples and high-temperature molten regolith simulants, extending significantly beyond existing models in the literature. Furthermore, separate regression models are presented for Mare and Highlands regolith to demonstrate the effect of composition and to allow the models to be tailored to a wide range of applications. These models can enable more consistent, informed analysis and design of lunar regolith processing hardware and can also support lunar geological simulations. In addition to regression models for each material property, the raw data are presented to allow for further interpretation and fitting as necessary.

  4. NOTE: The Virtual Family—development of surface-based anatomical models of two adults and two children for dosimetric simulations

    NASA Astrophysics Data System (ADS)

    Christ, Andreas; Kainz, Wolfgang; Hahn, Eckhart G.; Honegger, Katharina; Zefferer, Marcel; Neufeld, Esra; Rascher, Wolfgang; Janka, Rolf; Bautz, Werner; Chen, Ji; Kiefer, Berthold; Schmitt, Peter; Hollenbach, Hans-Peter; Shen, Jianxiang; Oberle, Michael; Szczerba, Dominik; Kam, Anthony; Guag, Joshua W.; Kuster, Niels

    2010-01-01

    The objective of this study was to develop anatomically correct whole body human models of an adult male (34 years old), an adult female (26 years old) and two children (an 11-year-old girl and a six-year-old boy) for the optimized evaluation of electromagnetic exposure. These four models are referred to as the Virtual Family. They are based on high resolution magnetic resonance (MR) images of healthy volunteers. More than 80 different tissue types were distinguished during the segmentation. To improve the accuracy and the effectiveness of the segmentation, a novel semi-automated tool was used to analyze and segment the data. All tissues and organs were reconstructed as three-dimensional (3D) unstructured triangulated surface objects, yielding high precision images of individual features of the body. This greatly enhances the meshing flexibility and the accuracy with respect to thin tissue layers and small organs in comparison with the traditional voxel-based representation of anatomical models. Conformal computational techniques were also applied. The techniques and tools developed in this study can be used to more effectively develop future models and further improve the accuracy of the models for various applications. For research purposes, the four models are provided for free to the scientific community.

  5. Invariance Properties for General Diagnostic Classification Models

    ERIC Educational Resources Information Center

    Bradshaw, Laine P.; Madison, Matthew J.

    2016-01-01

    In item response theory (IRT), the invariance property states that item parameter estimates are independent of the examinee sample, and examinee ability estimates are independent of the test items. While this property has long been established and understood by the measurement community for IRT models, the same cannot be said for diagnostic…

  6. Invariance Properties for General Diagnostic Classification Models

    ERIC Educational Resources Information Center

    Bradshaw, Laine P.; Madison, Matthew J.

    2016-01-01

    In item response theory (IRT), the invariance property states that item parameter estimates are independent of the examinee sample, and examinee ability estimates are independent of the test items. While this property has long been established and understood by the measurement community for IRT models, the same cannot be said for diagnostic…

  7. Thermophysical Property Models for Lunar Regolith

    NASA Technical Reports Server (NTRS)

    Schreiner, Samuel S.; Dominguez, Jesus A.; Sibille, Laurent; Hoffman, Jeffrey A.

    2015-01-01

    We present a set of models for a wide range of lunar regolith material properties. Data from the literature are t with regression models for the following regolith properties: composition, density, specific heat, thermal conductivity, electrical conductivity, optical absorption length, and latent heat of melting/fusion. These models contain both temperature and composition dependencies so that they can be tailored for a range of applications. These models can enable more consistent, informed analysis and design of lunar regolith processing hardware. Furthermore, these models can be utilized to further inform lunar geological simulations. In addition to regression models for each material property, the raw data is also presented to allow for further interpretation and fitting as necessary.

  8. Validation of mathematical models for the prediction of organs-at-risk dosimetric metrics in high-dose-rate gynecologic interstitial brachytherapy

    SciTech Connect

    Damato, Antonio L.; Viswanathan, Akila N.; Cormack, Robert A.

    2013-10-15

    Purpose: Given the complicated nature of an interstitial gynecologic brachytherapy treatment plan, the use of a quantitative tool to evaluate the quality of the achieved metrics compared to clinical practice would be advantageous. For this purpose, predictive mathematical models to predict the D{sub 2cc} of rectum and bladder in interstitial gynecologic brachytherapy are discussed and validated.Methods: Previous plans were used to establish the relationship between D2cc and the overlapping volume of the organ at risk with the targeted area (C0) or a 1-cm expansion of the target area (C1). Three mathematical models were evaluated: D{sub 2cc}=α*C{sub 1}+β (LIN); D{sub 2cc}=α– exp(–β*C{sub 0}) (EXP); and a mixed approach (MIX), where both C{sub 0} and C{sub 1} were inputs of the model. The parameters of the models were optimized on a training set of patient data, and the predictive error of each model (predicted D{sub 2cc}− real D{sub 2cc}) was calculated on a validation set of patient data. The data of 20 patients were used to perform a K-fold cross validation analysis, with K = 2, 4, 6, 8, 10, and 20.Results: MIX was associated with the smallest mean prediction error <6.4% for an 18-patient training set; LIN had an error <8.5%; EXP had an error <8.3%. Best case scenario analysis shows that an error ≤5% can be achieved for a ten-patient training set with MIX, an error ≤7.4% for LIN, and an error ≤6.9% for EXP. The error decreases with the increase in training set size, with the most marked decrease observed for MIX.Conclusions: The MIX model can predict the D{sub 2cc} of the organs at risk with an error lower than 5% with a training set of ten patients or greater. The model can be used in the development of quality assurance tools to identify treatment plans with suboptimal sparing of the organs at risk. It can also be used to improve preplanning and in the development of real-time intraoperative planning tools.

  9. Properties of Vector Preisach Models

    NASA Technical Reports Server (NTRS)

    Kahler, Gary R.; Patel, Umesh D.; Torre, Edward Della

    2004-01-01

    This paper discusses rotational anisotropy and rotational accommodation of magnetic particle tape. These effects have a performance impact during the reading and writing of the recording process. We introduce the reduced vector model as the basis for the computations. Rotational magnetization models must accurately compute the anisotropic characteristics of ellipsoidally magnetizable media. An ellipticity factor is derived for these media that computes the two-dimensional magnetization trajectory for all applied fields. An orientation correction must be applied to the computed rotational magnetization. For isotropic materials, an orientation correction has been developed and presented. For anisotropic materials, an orientation correction is introduced.

  10. Dosimetric aspects of radiolabeled antibodies for tumor therapy

    SciTech Connect

    Humm, J.L.

    1986-09-01

    Radioimmunotherapy (RIT) is rapidly attracting interest as a potential new weapon in the arsenal for cancer therapy. This article concentrates on some of the dosimetric aspects affecting the potential success of RIT, and examines factors which influence the choice of a radiolabel for RIT. No radionuclide is likely to give an optimum tumor/nontumor insult for all tumor types; therefore, the concept of matching the source to tumor morphology is introduced. Lists of candidate radionuclides are given, classified according to the type of decay, range, and energy of the emission. The article examines how the choice of radionuclide for radiolabeling the antibody affects the local energy deposition in the tumor. Both the effect of tumor size on the energy absorbed fraction and the problem of antibody binding heterogeneity are discussed. The approach to RIT is to relate the choice of radionuclide to the physical properties of the tumor. 26 references.

  11. Patient feature based dosimetric Pareto front prediction in esophageal cancer radiotherapy

    SciTech Connect

    Wang, Jiazhou; Zhao, Kuaike; Peng, Jiayuan; Xie, Jiang; Chen, Junchao; Zhang, Zhen; Hu, Weigang; Jin, Xiance; Studenski, Matthew

    2015-02-15

    Purpose: To investigate the feasibility of the dosimetric Pareto front (PF) prediction based on patient’s anatomic and dosimetric parameters for esophageal cancer patients. Methods: Eighty esophagus patients in the authors’ institution were enrolled in this study. A total of 2928 intensity-modulated radiotherapy plans were obtained and used to generate PF for each patient. On average, each patient had 36.6 plans. The anatomic and dosimetric features were extracted from these plans. The mean lung dose (MLD), mean heart dose (MHD), spinal cord max dose, and PTV homogeneity index were recorded for each plan. Principal component analysis was used to extract overlap volume histogram (OVH) features between PTV and other organs at risk. The full dataset was separated into two parts; a training dataset and a validation dataset. The prediction outcomes were the MHD and MLD. The spearman’s rank correlation coefficient was used to evaluate the correlation between the anatomical features and dosimetric features. The stepwise multiple regression method was used to fit the PF. The cross validation method was used to evaluate the model. Results: With 1000 repetitions, the mean prediction error of the MHD was 469 cGy. The most correlated factor was the first principal components of the OVH between heart and PTV and the overlap between heart and PTV in Z-axis. The mean prediction error of the MLD was 284 cGy. The most correlated factors were the first principal components of the OVH between heart and PTV and the overlap between lung and PTV in Z-axis. Conclusions: It is feasible to use patients’ anatomic and dosimetric features to generate a predicted Pareto front. Additional samples and further studies are required improve the prediction model.

  12. Evaluation of material heterogeneity dosimetric effects using radiochromic film for COMS eye plaques loaded with {sup 125}I seeds (model I25.S16)

    SciTech Connect

    Acar, Hilal; Chiu-Tsao, Sou-Tung; Oezbay, Ismail; Kemikler, Goenuel; Tuncer, Samuray

    2013-01-15

    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 eye 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

  13. Dosimetric impact of an {sup 192}Ir brachytherapy source cable length modeled using a grid-based Boltzmann transport equation solver

    SciTech Connect

    Mikell, Justin K.; Mourtada, Firas

    2010-09-15

    Purpose: To evaluate the dose distributions of an {sup 192}Ir source (model VS2000) in homogeneous water geometry calculated using a deterministic grid-based Boltzmann transport equation solver (GBBS) in the commercial treatment planning system (TPS) (BRACHYVISION-ACUROS v8.8). Methods: Using percent dose differences (%{Delta}D), the GBBS (BV-ACUROS) was compared to the (1) published TG-43 data, (2) MCNPX Monte Carlo (MC) simulations of the {sup 192}Ir source centered in a 15 cm radius water sphere, and (3) TG-43 output from the TPS using vendor supplied (BV-TG43-vendor) and user extended (BV-TG43-extended) 2D anisotropy functions F(r,{theta}). BV-ACUROS assumes 1 mm of NiTi cable, while the TPS TG-43 algorithm uses data based on a 15 cm cable. MC models of various cable lengths were simulated. Results: The MC simulations resulted in >20% dose deviations along the cable for 1, 2, and 3 mm cable lengths relative to 15 cm. BV-ACUROS comparisons with BV-TG43-vendor and BV-TG43-extended yielded magnitude of differences, consistent with those seen in MC simulations. However, differences >20% extended further ({theta}{<=}10 deg.) when using the vendor supplied anisotropy function F{sub ven}(r,{theta}). These differences were also seen in comparisons of F(r,{theta}) derived from the TPS output. Conclusions: The results suggest that %{Delta}D near the cable region is larger than previously estimated. The spatial distribution of the dose deviation is highly dependent on the reference TG-43 data used to compare to GBBS. The differences observed, while important to realize, should not have an impact on clinical dosimetry in homogeneous water.

  14. Modeling hygroelastic properties of genetically modified aspen

    Treesearch

    Laszlo Horvath; Perry Peralta; Ilona Peszlen; Levente Csoka; Balazs Horvath; Joseph Jakes

    2012-01-01

    Numerical and three-dimensional finite element models were developed to improve understanding of major factors affecting hygroelastic wood properties. Effects of chemical composition, microfibril angle, crystallinity, structure of microfibrils, moisture content, and hydrophilicity of the cell wall were included in the model. Wood from wild-type and decreased-lignin...

  15. Dosimetric characteristic of a new 125I brachytherapy source.

    PubMed

    Sadeghi, Mahdi; Khanmohammadi, Zahra

    2011-11-01

    A new brachytherapy (125)I source has been investigated at Iranian Agricultural, Medical and Industrial Research School. Dosimetric characteristics [dose-rate constant Λ, radial dose function g(l)(r) and anisotropy function F(r,)] of IRA-(125)I were theoretically determined in terms of the updated AAPM task group 43 (TG-43U1) recommendations. Versions 5 and 4C of the Monte Carlo radiation transport code were used to calculate the dosimetry parameters around the source. The Monte Carlo calculated dose-rate constant of the (125)I source in water was found to be 92×10(-4) Gy h(-1) U(-1) with an approximate uncertainty of ±3 %. Brachytherapy seed model, 6711-(125)I, carrying (125)I radionuclides, was modelled and benchmarked against previously published values. Finally, the calculated results were compared with the published results of those of other source manufacturers.

  16. Glass rod detectors for small field, stereotactic radiosurgery dosimetric audit.

    PubMed

    Perks, J; Gao, M; Smith, V; Skubic, S; Goetsch, S

    2005-03-01

    This paper demonstrates the feasibility of using glass rod detectors for quality assurance audit of radiosurgery units. Five radiosurgery units (3 Gamma Knife model C, 1 Gamma Knife model U and 1 Cyberknife) located in California participated in the study. At each center glass rod detectors were used to measure a number of dosimetric parameters including relative collimator output factor and absolute dose rate. The Gamma Knife data obtained is in excellent agreement with the commissioning data generated by the manufacturer for each unit and the Cyberknife data is in general agreement with the data published by other centers. In particular the output factor of the 4 mm Gamma Knife helmet factor, a subject of abundant debate, was measured in the range 0.863-0.872 with an accuracy of better than 1% across the four participating centers. It is hoped that this pilot study will facilitate a nationwide postal audit of stereotactic radiosurgery units.

  17. Capillary Properties of Model Pores.

    NASA Astrophysics Data System (ADS)

    Walsh, Tim J.

    Available from UMI in association with The British Library. Liquid menisci in small pores exhibit a curved surface across which there is a significant pressure difference. In the past it has been difficult to calculate the curvatures, of this class of menisci. Some recent studies have shown that a relatively straightforward, but hitherto neglected, method originated by Mayer & Stowe (1965) and Princen (1969a) can be applied to analyse wedging menisci. However, the method has lacked a comprehensive experimental verification. This investigation follows on from the previously limited studies. A standardised method for the application of the analysis is described, the results from which are compared to observations made using modified experimental procedures. The behaviour of the capillary surfaces formed in several model pores are analysed with the method. The model systems studied are rectangular ducts, the pores formed by a rod in an angled corner, by two contacting rods and a plate and the space between a rod and a plate. For the latter two shapes the analysis is extended to include systems of mixed wettability which have a particular bearing on enhanced oil recovery operations. Experiments in which curvatures are inferred from observations of capillary rise, are performed using two comparative techniques. An involved procedure confirms predictions of meniscus curvature to within 0.3%. Use of a more straightforward, through less accurate, technique enables variations of curvature with tube shape or contact angle(s) to be conveniently studied. Results obtained are excellent and confirm the theory within the determined experimental errors. (Abstract shortened by UMI.).

  18. Effect of blood activity on dosimetric calculations for radiopharmaceuticals

    NASA Astrophysics Data System (ADS)

    Zvereva, Alexandra; Petoussi-Henss, Nina; Li, Wei Bo; Schlattl, Helmut; Oeh, Uwe; Zankl, Maria; Graner, Frank Philipp; Hoeschen, Christoph; Nekolla, Stephan G.; Parodi, Katia; Schwaiger, Markus

    2016-11-01

    The objective of this work was to investigate the influence of the definition of blood as a distinct source on organ doses, associated with the administration of a novel radiopharmaceutical for positron emission tomography-computed tomography (PET/CT) imaging—(S)-4-(3-18F-fluoropropyl)-L-glutamic acid (18F-FSPG). Personalised pharmacokinetic models were constructed based on clinical PET/CT images from five healthy volunteers and blood samples from four of them. Following an identifiability analysis of the developed compartmental models, person-specific model parameters were estimated using the commercial program SAAM II. Organ doses were calculated in accordance to the formalism promulgated by the Committee on Medical Internal Radiation Dose (MIRD) and the International Commission on Radiological Protection (ICRP) using specific absorbed fractions for photons and electrons previously derived for the ICRP reference adult computational voxel phantoms. Organ doses for two concepts were compared: source organ activities in organs parenchyma with blood as a separate source (concept-1); aggregate activities in perfused source organs without blood as a distinct source (concept-2). Aggregate activities comprise the activities of organs parenchyma and the activity in the regional blood volumes (RBV). Concept-1 resulted in notably higher absorbed doses for most organs, especially non-source organs with substantial blood contents, e.g. lungs (92% maximum difference). Consequently, effective doses increased in concept-1 compared to concept-2 by 3-10%. Not considering the blood as a distinct source region leads to an underestimation of the organ absorbed doses and effective doses. The pronounced influence of the blood even for a radiopharmaceutical with a rapid clearance from the blood, such as 18F-FSPG, suggests that blood should be introduced as a separate compartment in most compartmental pharmacokinetic models and blood should be considered as a distinct source in

  19. Modelling Observable Properties of Rapidly Rotating Stars

    NASA Astrophysics Data System (ADS)

    Castañeda, D.; Deupree, R. G.; Aufdenberg, J.

    2016-11-01

    To fully understand the Be star phenomenon, one must have a reasonable degree of knowledge about the star beneath the disk, which is often found to be rapidly rotating. Rapid rotation complicates modelling because fundamental properties like the stellar luminosity and effective temperature require knowledge of the angle of inclination at which the star is observed. Furthermore our knowledge of the structure of rapidly rotating stars is on a less sure foundation than for non-rotating stars. The uncertainties in the inclination and the surface properties of a few rapidly rotating stars have been substantially reduced by interferometric observations over the last decade, and these stars can be used as tests of rotating stellar models, even if those stars themselves may not be Be stars. Vega, as an MK standard, is historically a very important star because it is used for calibration purposes. However, several studies have suggested that Vega is a rapidly rotating star viewed at a very low inclination angle, raising questions as to how well we really know its properties. Appropriate modelling has been challenging and there is still room for debate over the actual properties of Vega, as opposed to its observed properties. We have previously shown that under certain conditions both the stellar surface properties and the deduced surface properties scale from one model to another with the same surface shape. We used this scaling algorithm with realistic 2D models to compute high-resolution spectral energy distributions and interferometric visibilities to determine the best rotating model fit to Vega. Detailed comparisons between the computed and observed data will be presented.

  20. Dosimetric verification in water of a Monte Carlo treatment planning tool for proton, helium, carbon and oxygen ion beams at the Heidelberg Ion Beam Therapy Center

    NASA Astrophysics Data System (ADS)

    Tessonnier, T.; Böhlen, T. T.; Ceruti, F.; Ferrari, A.; Sala, P.; Brons, S.; Haberer, T.; Debus, J.; Parodi, K.; Mairani, A.

    2017-08-01

    The introduction of ‘new’ ion species in particle therapy needs to be supported by a thorough assessment of their dosimetric properties and by treatment planning comparisons with clinically used proton and carbon ion beams. In addition to the latter two ions, helium and oxygen ion beams are foreseen at the Heidelberg Ion Beam Therapy Center (HIT) as potential assets for improving clinical outcomes in the near future. We present in this study a dosimetric validation of a FLUKA-based Monte Carlo treatment planning tool (MCTP) for protons, helium, carbon and oxygen ions for spread-out Bragg peaks in water. The comparisons between the ions show the dosimetric advantages of helium and heavier ion beams in terms of their distal and lateral fall-offs with respect to protons, reducing the lateral size of the region receiving 50% of the planned dose up to 12 mm. However, carbon and oxygen ions showed significant doses beyond the target due to the higher fragmentation tail compared to lighter ions (p and He), up to 25%. The Monte Carlo predictions were found to be in excellent geometrical agreement with the measurements, with deviations below 1 mm for all parameters investigated such as target and lateral size as well as distal fall-offs. Measured and simulated absolute dose values agreed within about 2.5% on the overall dose distributions. The MCTP tool, which supports the usage of multiple state-of-the-art relative biological effectiveness models, will provide a solid engine for treatment planning comparisons at HIT.

  1. Dosimetric verification in water of a Monte Carlo treatment planning tool for proton, helium, carbon and oxygen ion beams at the Heidelberg Ion Beam Therapy Center.

    PubMed

    Tessonnier, T; Böhlen, T T; Ceruti, F; Ferrari, A; Sala, P; Brons, S; Haberer, T; Debus, J; Parodi, K; Mairani, A

    2017-07-31

    The introduction of 'new' ion species in particle therapy needs to be supported by a thorough assessment of their dosimetric properties and by treatment planning comparisons with clinically used proton and carbon ion beams. In addition to the latter two ions, helium and oxygen ion beams are foreseen at the Heidelberg Ion Beam Therapy Center (HIT) as potential assets for improving clinical outcomes in the near future. We present in this study a dosimetric validation of a FLUKA-based Monte Carlo treatment planning tool (MCTP) for protons, helium, carbon and oxygen ions for spread-out Bragg peaks in water. The comparisons between the ions show the dosimetric advantages of helium and heavier ion beams in terms of their distal and lateral fall-offs with respect to protons, reducing the lateral size of the region receiving 50% of the planned dose up to 12 mm. However, carbon and oxygen ions showed significant doses beyond the target due to the higher fragmentation tail compared to lighter ions (p and He), up to 25%. The Monte Carlo predictions were found to be in excellent geometrical agreement with the measurements, with deviations below 1 mm for all parameters investigated such as target and lateral size as well as distal fall-offs. Measured and simulated absolute dose values agreed within about 2.5% on the overall dose distributions. The MCTP tool, which supports the usage of multiple state-of-the-art relative biological effectiveness models, will provide a solid engine for treatment planning comparisons at HIT.

  2. Dosimetric comparison between two MLC systems commonly used for stereotactic radiosurgery and radiotherapy: a Monte Carlo and experimental study.

    PubMed

    Asnaashari, K; Chow, James C L; Heydarian, Mostafa

    2013-06-01

    In this work dosimetric parameters of two multi-leaf collimator (MLC) systems, namely the beam modulator (BM), which is the MLC commercial name for Elekta "Synergy S" linear accelerator and Radionics micro-MLC (MMLC), are compared using measurements and Monte Carlo simulations. Dosimetric parameters, such as percentage depth doses (PDDs), in-plane and cross-plane dose profiles, and penumbras for different depths and field sizes of the 6 MV photon beams were measured using ionization chamber and a water tank. The collimator leakages were measured using radiographic films. MMLC and BM were modeled using the EGSnrc-based BEAMnrc Monte Carlo code and above dosimetric parameters were calculated. The energy fluence spectra for the two MLCs were also determined using the BEAMnrc and BEAMDP. Dosimetric parameters of the two MLCs were similar, except for penumbras. Leaf-side and leaf-end 80-20% dose penumbras at 10 cm depth for a 10×10 cm(2) field size were 4.8 and 5.1mm for MMLC and 5.3 mm and 6.3 mm for BM, respectively. Both Radionics MMLC and Elekta BM can be used effectively based on their dosimetric characteristics for stereotactic radiosurgery and radiotherapy, although the former showed slightly sharper dose penumbra especially in the leaf-end direction. Copyright © 2012 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

  3. Dosimetric characteristics of Novalis shaped beam surgery unit.

    PubMed

    Yin, Fang-Fang; Zhu, Jingeng; Yan, Hui; Gaun, Haiqun; Hammoud, Rabih; Ryu, Samuel; Kim, Jae H

    2002-08-01

    The dosimetric characteristics of a new dedicated radiosurgical treatment unit are systematically measured in terms of its percent depth dose, beam profile, and relative scatter factor. High-resolution diode detector, mini-ion-chamber detector, and conventional Kodak XV films are used to measure dosimetric data for a range of field sizes from 6x6 mm to 100x100 mm. The effects of collimator size, micro-multileaf collimator shape, and detector type on the dosimetric data are investigated. Results indicate that, with careful design, accurate dosimetric data could be acquired using either a dedicated diode detector or a mini-ion-chamber detector, and film detector. Special attention is required when measuring dosimetric data for small field sizes such as 6x6 mm.

  4. Critical properties of random Potts models

    NASA Astrophysics Data System (ADS)

    Kinzel, Wolfgang; Domany, Eytan

    1981-04-01

    The critical properties of Potts models with random bonds are considered in two dimensions. A position-space renormalization-group procedure, based on the Migdal-Kadanoff method, is developed. While all previous position-space calculations satisfied the Harris criterion and the resulting scaling relation only approximately, we found conditions under which these relations are exactly satisfied, and constructed our renormalization-group procedure accordingly. Numerical results for phase diagrams and thermodynamic functions for various random-bond Potts models are presented. In addition, some exact results obtained using a duality transformation, as well as an heuristic derivation of scaling properties that correspond to the percolation problem are given.

  5. Dosimetric adaptive IMRT driven by fiducial points

    SciTech Connect

    Crijns, Wouter; Van Herck, Hans; Defraene, Gilles; Van den Bergh, Laura; Haustermans, Karin; Slagmolen, Pieter; Maes, Frederik; Van den Heuvel, Frank

    2014-06-15

    Purpose: Intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy have become standard treatments but are more sensitive to anatomical variations than 3D conformal techniques. To correct for inter- and intrafraction anatomical variations, fast and easy to implement methods are needed. Here, the authors propose a full dosimetric IMRT correction that finds a compromise in-between basic repositioning (the current clinical practice) and full replanning. It simplifies replanning by avoiding a recontouring step and a full dose calculation. It surpasses repositioning by updating the preoptimized fluence and monitor units (MU) using a limited number of fiducial points and a pretreatment (CB)CT. To adapt the fluence the fiducial points were projected in the beam's eye view (BEV). To adapt the MUs, point dose calculation towards the same fiducial points were performed. The proposed method is intrinsically fast and robust, and simple to understand for operators, because of the use of only four fiducial points and the beam data based point dose calculations. Methods: To perform our dosimetric adaptation, two fluence corrections in the BEV are combined with two MU correction steps along the beam's path. (1) A transformation of the fluence map such that it is realigned with the current target geometry. (2) A correction for an unintended scaling of the penumbra margin when the treatment beams scale to the current target size. (3) A correction for the target depth relative to the body contour and (4) a correction for the target distance to the source. The impact of the correction strategy and its individual components was evaluated by simulations on a virtual prostate phantom. This heterogeneous reference phantom was systematically subjected to population based prostate transformations to simulate interfraction variations. Additionally, a patient example illustrated the clinical practice. The correction strategy was evaluated using both dosimetric (CTV mean

  6. [Dosimetric evaluation of conformal radiotherapy: conformity factor].

    PubMed

    Oozeer, R; Chauvet, B; Garcia, R; Berger, C; Felix-Faure, C; Reboul, F

    2000-01-01

    The aim of three-dimensional conformal therapy (3DCRT) is to treat the Planning Target Volume (PTV) to the prescribed dose while reducing doses to normal tissues and critical structures, in order to increase local control and reduce toxicity. The evaluation tools used for optimizing treatment techniques are three-dimensional visualization of dose distributions, dose-volume histograms, tumor control probabilities (TCP) and normal tissue complication probabilities (NTCP). These tools, however, do not fully quantify the conformity of dose distributions to the PTV. Specific tools were introduced to measure this conformity for a given dose level. We have extended those definitions to different dose levels, using a conformity index (CI). CI is based on the relative volumes of PTV and outside the PTV receiving more than a given dose. This parameter has been evaluated by a clinical study including 82 patients treated for lung cancer and 82 patients treated for prostate cancer. The CI was low for lung dosimetric studies (0.35 at the prescribed dose 66 Gy) due to build-up around the GTV and to spinal cord sparing. For prostate dosimetric studies, the CI was higher (0.57 at the prescribed dose 70 Gy). The CI has been used to compare treatment plans for lung 3DCRT (2 vs 3 beams) and prostate 3DCRT (4 vs 7 beams). The variation of CI with dose can be used to optimize dose prescription.

  7. Viscoelastic modelling of tennis ball properties

    NASA Astrophysics Data System (ADS)

    Sissler, L.; Jones, R.; Leaney, P. G.; Harland, A.

    2010-06-01

    An explicit finite element (FE) tennis ball model which illustrates the effects of the viscoelastic materials of a tennis ball on ball deformation and bounce during normal impacts is presented. A tennis ball is composed of a rubber core and a fabric cover comprised of a wool-nylon mix which exhibit non-linear strain rate properties during high velocity impacts. The rubber core model was developed and validated using low strain rate tensile tests on rubber samples as well as high velocity normal impacts of pressurised cores at velocities ranging from 15 m/s to 50 m/s. The impacts were recorded using a high speed video (HSV) camera to determine deformation, impact time and coefficient of restitution (COR). The material properties of the core model were tuned to match the HSV results. A two component anisotropic fabric model was created which included artificial Rayleigh damping to account for hysteresis effects, and the core model 'tuning' process was used to refine the cloth layer. The ball model's parameters were in good agreement with experimental data at all velocities for both cores and complete balls, and a time sequenced comparison of HSV ball motion and FE model confirmed the validity of the model.

  8. Dynamical properties of the Rabi model

    NASA Astrophysics Data System (ADS)

    Hu, Binglu; Zhou, Huili; Chen, Shujie; Xianlong, Gao; Wang, Kelin

    2017-02-01

    We study the dynamical properties of the quantum Rabi model using a systematic expansion method. Based on the observation that the parity symmetry of the Rabi model is kept during evolution of the states, we decompose the initial state and the time-dependent one into positive and negative parity parts expanded by superposition of the coherent states. The evolutions of the corresponding positive and the negative parities are obtained, in which the expansion coefficients in the dynamical equations are known from the derived recurrence relation.

  9. Dosimetric measurements of an n-butyl cyanoacrylate embolization material for arteriovenous malformations

    SciTech Connect

    Labby, Zacariah E.; Chaudhary, Neeraj; Gemmete, Joseph J.; Pandey, Aditya S.; Roberts, Donald A.

    2015-04-15

    Purpose: The therapeutic regimen for cranial arteriovenous malformations often involves both stereotactic radiosurgery and endovascular embolization. Embolization agents may contain tantalum or other contrast agents to assist the neurointerventionalists, leading to concerns regarding the dosimetric effects of these agents. This study investigated dosimetric properties of n-butyl cyanoacrylate (n-BCA) plus lipiodol with and without tantalum powder. Methods: The embolization agents were provided cured from the manufacturer with and without added tantalum. Attenuation measurements were made for the samples and compared to the attenuation of a solid water substitute using a 6 MV photon beam. Effective linear attenuation coefficients (ELAC) were derived from attenuation measurements made using a portal imager and derived sample thickness maps projected in an identical geometry. Probable dosimetric errors for calculations in which the embolized regions are overridden with the properties of water were calculated using the ELAC values. Interface effects were investigated using a parallel plate ion chamber placed at set distances below fixed samples. Finally, Hounsfield units (HU) were measured using a stereotactic radiosurgery CT protocol, and more appropriate HU values were derived from the ELAC results and the CT scanner’s HU calibration curve. Results: The ELAC was 0.0516 ± 0.0063 cm{sup −1} and 0.0580 ± 0.0091 cm{sup −1} for n-BCA without and with tantalum, respectively, compared to 0.0487 ± 0.0009 cm{sup −1} for the water substitute. Dose calculations with the embolized region set to be water equivalent in the treatment planning system would result in errors of −0.29% and −0.93% per cm thickness of n-BCA without and with tantalum, respectively. Interface effects compared to water were small in magnitude and limited in distance for both embolization materials. CT values at 120 kVp were 2082 and 2358 HU for n-BCA without and with tantalum, respectively

  10. Material modeling of biofilm mechanical properties.

    PubMed

    Laspidou, C S; Spyrou, L A; Aravas, N; Rittmann, B E

    2014-05-01

    A biofilm material model and a procedure for numerical integration are developed in this article. They enable calculation of a composite Young's modulus that varies in the biofilm and evolves with deformation. The biofilm-material model makes it possible to introduce a modeling example, produced by the Unified Multi-Component Cellular Automaton model, into the general-purpose finite-element code ABAQUS. Compressive, tensile, and shear loads are imposed, and the way the biofilm mechanical properties evolve is assessed. Results show that the local values of Young's modulus increase under compressive loading, since compression results in the voids "closing," thus making the material stiffer. For the opposite reason, biofilm stiffness decreases when tensile loads are imposed. Furthermore, the biofilm is more compliant in shear than in compression or tension due to the how the elastic shear modulus relates to Young's modulus. Copyright © 2014 Elsevier Inc. All rights reserved.

  11. The dosimetric impact of control point spacing for sliding gap MLC fields.

    PubMed

    Zwan, Benjamin J; Hindmarsh, Jonathan; Seymour, Erin; Kandasamy, Kankean; Sloan, Kirbie; David, Rajesakar; Lee, Christopher

    2016-11-08

    Dynamic sliding gap multileaf collimator (MLC) fields are used to model MLC properties within the treatment planning system (TPS) for dynamic treatments. One of the key MLC properties in the Eclipse TPS is the dosimetric leaf gap (DLG) and precise determination of this parameter is paramount to ensuring accurate dose delivery. In this investigation, we report on how the spacing between control points (CPs) for sliding gap fields impacts the dose delivery, MLC positioning accuracy, and measurement of the DLG. The central axis dose was measured for sliding gap MLC fields with gap widths ranging from 2 to 40 mm. It was found that for deliveries containing two CPs, the central axis dose was underestimated by the TPS for all gap widths, with the maximum difference being 8% for a 2 mm gap field. For the same sliding gap fields containing 50 CPs, the measured dose was always within ± 2% of the TPS dose. By directly measuring the MLC trajectories we show that this dose difference is due to a systematic MLC gap error for fields containing two CPs, and that the cause of this error is due to the leaf position offset table which is incorrectly applied when the spacing between CPs is too large. This MLC gap error resulted in an increase in the measured DLG of 0.5 mm for both 6MV and 10 MV, when using fields with 2 CPs compared to 50 CPs. Furthermore, this change in DLG was shown to decrease the mean TPS-calculated dose to the target volume by 2.6% for a clinical IMRT test plan. This work has shown that systematic MLC positioning errors occur for sliding gap MLC fields containing two CPs and that using these fields to model critical TPS parameters, such as the DLG, may result in clinically significant systematic dose calculation errors during subsequent dynamic MLC treatments.

  12. The dosimetric impact of control point spacing for sliding gap MLC fields.

    PubMed

    Zwan, Benjamin J; Hindmarsh, Jonathan; Seymour, Erin; Kandasamy, Kankean; Sloan, Kirbie; David, Rajesakar; Lee, Christopher

    2016-11-01

    Dynamic sliding gap multileaf collimator (MLC) fields are used to model MLC properties within the treatment planning system (TPS) for dynamic treatments. One of the key MLC properties in the Eclipse TPS is the dosimetric leaf gap (DLG) and precise determination of this parameter is paramount to ensuring accurate dose delivery. In this investigation, we report on how the spacing between control points (CPs) for sliding gap fields impacts the dose delivery, MLC positioning accuracy, and measurement of the DLG. The central axis dose was measured for sliding gap MLC fields with gap widths ranging from 2 to 40 mm. It was found that for deliveries containing two CPs, the central axis dose was underestimated by the TPS for all gap widths, with the maximum difference being 8% for a 2 mm gap field. For the same sliding gap fields containing 50 CPs, the measured dose was always within ±2% of the TPS dose. By directly measuring the MLC trajectories we show that this dose difference is due to a systematic MLC gap error for fields containing two CPs, and that the cause of this error is due to the leaf position offset table which is incorrectly applied when the spacing between CPs is too large. This MLC gap error resulted in an increase in the measured DLG of 0.5 mm for both 6 MV and 10 MV, when using fields with 2 CPs compared to 50 CPs. Furthermore, this change in DLG was shown to decrease the mean TPS-calculated dose to the target volume by 2.6% for a clinical IMRT test plan. This work has shown that systematic MLC positioning errors occur for sliding gap MLC fields containing two CPs and that using these fields to model critical TPS parameters, such as the DLG, may result in clinically significant systematic dose calculation errors during subsequent dynamic MLC treatments. PACS number(s): 87.56.nk.

  13. Patient-specific dosimetric endpoints based treatment plan quality control in radiotherapy.

    PubMed

    Song, Ting; Staub, David; Chen, Mingli; Lu, Weiguo; Tian, Zhen; Jia, Xun; Li, Yongbao; Zhou, Linghong; Jiang, Steve B; Gu, Xuejun

    2015-11-07

    In intensity modulated radiotherapy (IMRT), the optimal plan for each patient is specific due to unique patient anatomy. To achieve such a plan, patient-specific dosimetric goals reflecting each patient's unique anatomy should be defined and adopted in the treatment planning procedure for plan quality control. This study is to develop such a personalized treatment plan quality control tool by predicting patient-specific dosimetric endpoints (DEs). The incorporation of patient specific DEs is realized by a multi-OAR geometry-dosimetry model, capable of predicting optimal DEs based on the individual patient's geometry. The overall quality of a treatment plan is then judged with a numerical treatment plan quality indicator and characterized as optimal or suboptimal. Taking advantage of clinically available prostate volumetric modulated arc therapy (VMAT) treatment plans, we built and evaluated our proposed plan quality control tool. Using our developed tool, six of twenty evaluated plans were identified as sub-optimal plans. After plan re-optimization, these suboptimal plans achieved better OAR dose sparing without sacrificing the PTV coverage, and the dosimetric endpoints of the re-optimized plans agreed well with the model predicted values, which validate the predictability of the proposed tool. In conclusion, the developed tool is able to accurately predict optimally achievable DEs of multiple OARs, identify suboptimal plans, and guide plan optimization. It is a useful tool for achieving patient-specific treatment plan quality control.

  14. Patient-specific dosimetric endpoints based treatment plan quality control in radiotherapy

    NASA Astrophysics Data System (ADS)

    Song, Ting; Staub, David; Chen, Mingli; Lu, Weiguo; Tian, Zhen; Jia, Xun; Li, Yongbao; Zhou, Linghong; Jiang, Steve B.; Gu, Xuejun

    2015-11-01

    In intensity modulated radiotherapy (IMRT), the optimal plan for each patient is specific due to unique patient anatomy. To achieve such a plan, patient-specific dosimetric goals reflecting each patient’s unique anatomy should be defined and adopted in the treatment planning procedure for plan quality control. This study is to develop such a personalized treatment plan quality control tool by predicting patient-specific dosimetric endpoints (DEs). The incorporation of patient specific DEs is realized by a multi-OAR geometry-dosimetry model, capable of predicting optimal DEs based on the individual patient’s geometry. The overall quality of a treatment plan is then judged with a numerical treatment plan quality indicator and characterized as optimal or suboptimal. Taking advantage of clinically available prostate volumetric modulated arc therapy (VMAT) treatment plans, we built and evaluated our proposed plan quality control tool. Using our developed tool, six of twenty evaluated plans were identified as sub-optimal plans. After plan re-optimization, these suboptimal plans achieved better OAR dose sparing without sacrificing the PTV coverage, and the dosimetric endpoints of the re-optimized plans agreed well with the model predicted values, which validate the predictability of the proposed tool. In conclusion, the developed tool is able to accurately predict optimally achievable DEs of multiple OARs, identify suboptimal plans, and guide plan optimization. It is a useful tool for achieving patient-specific treatment plan quality control.

  15. Investigating the dosimetric and tumor control consequences of prostate seed loss and migration

    SciTech Connect

    Knaup, Courtney; Mavroidis, Panayiotis; Esquivel, Carlos; Stathakis, Sotirios; Swanson, Gregory; Baltas, Dimos; Papanikolaou, Nikos

    2012-06-15

    Purpose: Low dose-rate brachytherapy is commonly used to treat prostate cancer. However, once implanted, the seeds are vulnerable to loss and movement. The goal of this work is to investigate the dosimetric and radiobiological effects of the types of seed loss and migration commonly seen in prostate brachytherapy. Methods: Five patients were used in this study. For each patient three treatment plans were created using Iodine-125, Palladium-103, and Cesium-131 seeds. The three seeds that were closest to the urethra were identified and modeled as the seeds lost through the urethra. The three seeds closest to the exterior of prostatic capsule were identified and modeled as those lost from the prostate periphery. The seed locations and organ contours were exported from Prowess and used by in-house software to perform the dosimetric and radiobiological evaluation. Seed loss was simulated by simultaneously removing 1, 2, or 3 seeds near the urethra 0, 2, or 4 days after the implant or removing seeds near the exterior of the prostate 14, 21, or 28 days after the implant. Results: Loss of one, two or three seeds through the urethra results in a D{sub 90} reduction of 2%, 5%, and 7% loss, respectively. Due to delayed loss of peripheral seeds, the dosimetric effects are less severe than for loss through the urethra. However, while the dose reduction is modest for multiple lost seeds, the reduction in tumor control probability was minimal. Conclusions: The goal of this work was to investigate the dosimetric and radiobiological effects of the types of seed loss and migration commonly seen in prostate brachytherapy. The results presented show that loss of multiple seeds can cause a substantial reduction of D{sub 90} coverage. However, for the patients in this study the dose reduction was not seen to reduce tumor control probability.

  16. Dosimetric investigations on Mars-96 mission.

    PubMed

    Semkova, J; Dachev, T s; Matviichuk, Y u; Koleva, R; Tomov, B; Baynov, P; Petrov, V; Nguyen, V; Siegrist, M; Chene, J; d'Uston, C; Cotin, F

    1994-10-01

    The dosimetric experiments Dose-M and Liulin as part of the more complex French-German-Bulgarian-Russian experiments for the investigation of the radiation environment for Mars-96 mission are described. The experiments will be realized with dosemeter-radiometer instruments, measuring absorbed dose in semiconductor detectors and the particle flux. Two detectors will be mounted on board the Mars-96 orbiter. Another detector will be on the guiderope of the Mars-96 Aerostate station. The scientific aims of Dose-M and Liulin experiments are: Analysis of the absorbed dose and the flux on the path and around Mars behind different shielding. Study of the shielding characteristics of the Martian atmosphere from galactic and solar cosmic rays including solar proton events. Together with the French gamma-spectrometer and the German neutron detectors the investigation of the radiation environment on the surface of Mars and in the atmosphere up to 4000 m altitude will be conducted.

  17. Leaf sequencing and dosimetric verification in intensity-modulated radiotherapy

    NASA Astrophysics Data System (ADS)

    Agazaryan, Nzhde

    Although sophisticated means to calculate and deliver intensity modulated radiotherapy (IMRT) have been developed by many groups, methods to verify the delivery, as well as definitions of acceptability of a treatment in terms of these measurements are the most problematic at this stage of advancement of IMRT. Present intensity modulated radiotherapy systems fail to account for many dosimetric characteristics of the delivery system. In this dissertation, a dosimetrically based leaf sequencing algorithm is developed and implemented for multileaf collimated intensity modulated radiotherapy. The dosimetric considerations are investigated and are shown to significantly improve the outcome in terms of an agreement between desired and delivered radiation dose distributions. Subsequently, a system for determining the desirability of a produced intensity modulated radiotherapy plan in terms of deliverability of calculated profiles with the use of a multileaf collimator is developed. Three deliverability scoring indices are defined to evaluate the deliverability of the profiles. Gradient Index (GI) is a measure of the complexity of the profile in terms of gradients. Baseline Index (BI) is the fraction of the profile that is planned to get lower than the minimum level of transmission radiation. Cumulative Monitor Unit Index (CMUI) is the ratio of the cumulative monitor units (CMU) required for obtaining the desired profile to an average dose level in the profile. The dosimetric investigations of the deliverability scoring indices are presented, showing a clear correlation between scoring indices and dosimetric accuracy. Finally, materials and methods are developed for verification of intensity modulated radiotherapy. Dosimetric verification starts from investigations of the developed leaf sequencing algorithm, then extends to dosimetric verification in terms of deliverability, and lastly, dosimetric verification of complete clinical IMRT plans is performed.

  18. Shape Models and Physical Properties of Asteroids

    NASA Astrophysics Data System (ADS)

    Santana-Ros, T.; Dudziński, G.; Bartczak, P.

    Despite the large amount of high quality data generated in recent space encounters with asteroids, the majority of our knowledge about these objects comes from ground based observations. Asteroids travelling in orbits that are potentially hazardous for the Earth form an especially interesting group to be studied. In order to predict their orbital evolution, it is necessary to investigate their physical properties. This paper briefly describes the data requirements and different techniques used to solve the lightcurve inversion problem. Although photometry is the most abundant type of observational data, models of asteroids can be obtained using various data types and techniques. We describe the potential of radar imaging and stellar occultation timings to be combined with disk-integrated photometry in order to reveal information about physical properties of asteroids.

  19. Baryon properties in the relativistic quark model

    NASA Astrophysics Data System (ADS)

    Ebert, D.; Faustov, R. N.; Galkin, V. O.

    2017-09-01

    Properties of heavy and strange baryons are investigated in the framework of the relativistic quark-diquark picture. It is based on the relativistic quark model of hadrons, which was previously successfully applied for the calculation of meson properties. It is assumed that two quarks in a baryon form a diquark and baryon is considered as the bound quark-diquark system. The relativistic effects and diquark internal structure are consistently taken into account. Calculations are performed up to rather high orbital and radial excitations of heavy and strange baryons. On this basis the Regge trajectories are constructed. The rates of semileptonic decays of heavy baryons are calculated. The obtained results agree well with available experimental data.

  20. Using measurable dosimetric quantities to characterize the inter-structural tradeoff in inverse planning

    NASA Astrophysics Data System (ADS)

    Liu, Hongcheng; Dong, Peng; Xing, Lei

    2017-08-01

    Traditional inverse planning relies on the use of weighting factors to balance the conflicting requirements of different structures. Manual trial-and-error determination of weighting factors has long been recognized as a time-consuming part of treatment planning. The purpose of this work is to develop an inverse planning framework that parameterizes the dosimetric tradeoff among the structures with physically meaningful quantities to simplify the search for clinically sensible plans. In this formalism, instead of using weighting factors, the permissible variation range of the prescription dose or dose volume histogram (DVH) of the involved structures are used to characterize the ‘importance’ of the structures. The inverse planning is then formulated into a convex feasibility problem, called the dosimetric variation-controlled model (DVCM), whose goal is to generate plans with dosimetric or DVH variations of the structures consistent with the pre-specified values. For simplicity, the dosimetric variation range for a structure is extracted from a library of previous cases which possess similar anatomy and prescription. A two-phase procedure (TPP) is designed to solve the model. The first phase identifies a physically feasible plan to satisfy the prescribed dosimetric variation, and the second phase automatically improves the plan in case there is room for further improvement. The proposed technique is applied to plan two prostate cases and two head-and-neck cases and the results are compared with those obtained using a conventional CVaR approach and with a moment-based optimization scheme. Our results show that the strategy is able to generate clinically sensible plans with little trial and error. In all cases, the TPP generates a very competitive plan as compared to those obtained using the alternative approaches. Particularly, in the planning of one of the head-and-neck cases, the TPP leads to a non-trivial improvement in the resultant dose distribution

  1. Medical linear accelerator mounted mini-beam collimator: design, fabrication and dosimetric characterization.

    PubMed

    Cranmer-Sargison, G; Crewson, C; Davis, W M; Sidhu, N P; Kundapur, V

    2015-09-07

    The goal of this work was to design, build and experimentally characterize a linear accelerator mounted mini-beam collimator for use at a nominal 6 MV beam energy. Monte Carlo simulation was used in the design and dosimetric characterization of a compact mini-beam collimator assembly mounted to a medical linear accelerator. After fabrication, experimental mini-beam dose profiles and central axis relative output were measured and the results used to validate the simulation data. The simulation data was then used to establish traceability back to an established dosimetric code of practice. The Monte Carlo simulation work revealed that changes in collimator blade width have a greater influence on the valley-to-peak dose ratio than do changes in blade height. There was good agreement between the modeled and measured profile data, with the exception of small differences on either side of the central peak dose. These differences were found to be systematic across all depths and result from limitations associated with the collimator fabrication. Experimental mini-beam relative output and simulation data agreed to better than ± 2.0%, which is well within the level of uncertainty required for dosimetric traceability of non-standard field geometries. A mini-beam collimator has now been designed, built and experimentally characterized for use with a commercial linear accelerator operated at a nominal 6 MV beam energy.

  2. Dosimetric characterization of a bi-directional micromultileaf collimator for stereotactic applications.

    PubMed

    Bucciolini, M; Russo, S; Banci Buonamici, F; Pini, S; Silli, P

    2002-07-01

    A 6 MV photon beam from Linac SL75-5 has been collimated with a new micromultileaf device that is able to shape the field in the two orthogonal directions with four banks of leaves. This is the first clinical installation of the collimator and in this paper the dosimetric characterization of the system is reported. The dosimetric parameters required by the treatment planning system used for the dose calculation in the patient are: tissue maximum ratios, output factors, transmission and leakage of the leaves, penumbra values. Ionization chambers, silicon diode, radiographic films, and LiF thermoluminescent dosimeters have been employed for measurements of absolute dose and beam dosimetric data. Measurements with different dosimeters supply results in reasonable agreement among them and consistent with data available in literature for other models of micromultileaf collimator; that permits the use of the measured parameters for clinical applications. The discrepancies between results obtained with the different detectors (around 2%) for the analyzed parameters can be considered an indication of the accuracy that can be reached by current stereotactic dosimetry.

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

    PubMed Central

    Ghorbani, Mahdi; Davenport, David

    2016-01-01

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

  4. Monte Carlo dosimetric study of the medium dose rate CSM40 source.

    PubMed

    Vijande, J; Granero, D; Perez-Calatayud, J; Ballester, F

    2013-12-01

    The (137)Cs medium dose rate (MDR) CSM40 source model (Eckert & Ziegler BEBIG, Germany) is in clinical use but no dosimetric dataset has been published. This study aims to obtain dosimetric data for the CSM40 source for its use in clinical practice as required by the American Association of Physicists in Medicine (AAPM) and the European Society for Radiotherapy and Oncology (ESTRO). Penelope2008 and Geant4 Monte Carlo codes were used to characterize this source dosimetrically. It was located in an unbounded water phantom with composition and mass density as recommended by AAPM and ESTRO. Due to the low photon energies of (137)Cs, absorbed dose was approximated by collisional kerma. Additional simulations were performed to obtain the air-kerma strength, sK. Mass-energy absorption coefficients in water and air were consistently derived and used to calculate collisional kerma. Results performed with both radiation transport codes showed agreement typically within 0.05%. Dose rate constant, radial dose function and anisotropy function are provided for the CSM40 and compared with published data for other commercially available (137)Cs sources. An uncertainty analysis has been performed. The data provided by this study can be used as input data and verification in the treatment planning systems.

  5. Tantalum powder consolidation, modeling and properties

    SciTech Connect

    Bingert, S.R.; Vargas, V.D.; Sheinberg, H.C.

    1996-10-01

    A systematic approach was taken to investigate the consolidation of tantalum powders. The effects of sinter time, temperature and ramp rate; hot isostatic pressing (HIP) temperature and time; and powder oxygen content on consolidation density, kinetics, microstructure, crystallographic texture, and mechanical properties have been evaluated. In general, higher temperatures and longer hold times resulted in higher density compacts with larger grain sizes for both sintering and HIP`ing. HIP`ed compacts were consistently higher in density than sintered products. The higher oxygen content powders resulted in finer grained, higher density HIP`ed products than the low oxygen powders. Texture analysis showed that the isostatically processed powder products demonstrated a near random texture. This resulted in isotropic properties in the final product. Mechanical testing results showed that the HIP`ed powder products had consistently higher flow stresses than conventionally produced plates, and the sintered compacts were comparable to the plate material. A micromechanics model (Ashby HIP model) has been employed to predict the mechanisms active in the consolidation processes of cold isostatic pressing (CIP), HIP and sintering. This model also predicts the density of the end product and whether grain growth should be expected under the applied processing conditions.

  6. Some Divergence Properties of Asset Price Models

    NASA Astrophysics Data System (ADS)

    Stummer, Wolfgang

    2001-12-01

    We consider asset price processes Xt which are weak solutions of one-dimensional stochastic differential equations of the form (equation (2)) Such price models can be interpreted as non-lognormally-distributed generalizations of the geometric Brownian motion. We study properties of the Iα-divergence between the law of the solution Xt and the corresponding drift-less measure (the special case α=1 is the relative entropy). This will be applied to some context in statistical information theory as well as to arbitrage theory and contingent claim valuation. For instance, the seminal option pricing theorems of Black-Scholes and Merton appear as a special case.

  7. TU-D-9A-01: TG176: Dosimetric Effects of Couch Tops and Immobilization Devices

    SciTech Connect

    Olch, A

    2014-06-15

    The dosimetric impact from devices external to the patient is a complex combination of increased skin dose, reduced tumor dose, and altered dose distribution. Although small monitor unit or dose corrections are routinely made for blocking trays, ion chamber correction factors, or tissue inhomogeneities, the dose perturbation of the treatment couch top or immobilization devices are often overlooked. These devices also increase surface dose, an effect which is also often ignored or underestimated. These concerns have grown recently due to the increased use of monolithic carbon fiber couch tops which are optimal for imaging for patient position verification but cause attenuation and increased surface dose compared to the ‘tennis racket’ style couch top they often replace. Also, arc delivery techniques have replaced stationary gantry techniques which cause a greater fraction of the dose to be delivered from posterior angles. A host of immobilization devices are available and used to increase patient positioning reproducibility, and these also have attenuation and skin dose implications which are often ignored. This report of Task Group 176 serves to present a survey of published data that illustrates the magnitude of the dosimetric effects of a wide range of devices external to the patient. The report also provides methods for modeling couch tops in treatment planning systems so the physicist can accurately compute the dosimetric effects for indexed patient treatments. Both photon and proton beams are considered. A discussion on avoidance of high density structures during beam planning is also provided. An important aspect of this report are the recommendations we make to clinical physicists, treatment planning system vendors, and device vendors on how to make measurements of skin dose and attenuation, how to report these values, and for the vendors, an appeal is made to work together to provide accurate couch top models in planning systems. Learning Objectives

  8. Modeling of carbon fiber couch attenuation properties with a commercial treatment planning system.

    PubMed

    Mihaylov, I B; Corry, P; Yan, Y; Ratanatharathorn, V; Moros, E G

    2008-11-01

    The purpose of this work is to evaluate the modeling of carbon fiber couch attenuation properties with a commercial treatment planning system (TPS, Pinnacle3, v8.0d). A carbon fiber couch (Brain-Lab) was incorporated into the TPS by automatic contouring of all transverse CT slices. The couch shape and dimensions were set according to the vendor specifications. The couch composition was realized by assigning appropriate densities to the delineated contours. The couch modeling by the TPS was validated by absolute dosimetric measurements. A phantom consisting of several solid water slabs was CT scanned, the CT data set was imported into the TPS, and the carbon fiber couch was auto-contoured. Open (unblocked) field plans for different gantry angles and field sizes were generated. The doses to a point at 3 cm depth, placed at the linac isocenter, were computed. The phantom was irradiated according to the dose calculation setup and doses were measured with an ion chamber. In addition, percent depth dose (PDD) curves were computed as well as measured with radiographic film. The calculated and measured doses, transmissions, and PDDs were cross-compared. Doses for several posterior fields (0 degree, 30 degrees, 50 degrees, 75 degrees, 83 degrees) were calculated for 6 and 18 MV photon beams. For model validation a nominal field size of 10 x 10 cm2 was chosen and 100 MU were delivered for each portal. The largest difference between computed and measured doses for those posterior fields was within 1.7%. A comparison between computed and measured transmissions for the aforementioned fields was performed and the results were found to agree within 1.1%. The differences between computed and measured doses for different field sizes, ranging from 5 x 5 cm2 to 25 x 25 cm2 in 5 cm increments, were within 2%. Measured and computed PDD curves with and without the couch agree from the surface up to 30 cm depth. The PDDs indicate a surface dose increase resulting from the carbon fiber

  9. Dosimetric variability of the rats' exposure to electromagnetic pulses.

    PubMed

    Li, Congsheng; Yang, Lei; Li, Chung-huan; Xie, Yi; Wu, Tongning

    2015-01-01

    Rats' exposure to electromagnetic pulses (EMPs) has been conducted using an EMP simulator for various biological endpoints. In contrast, information about the EMP energy distribution and its variability in rats is lacking. EMPs are signals with spectrum concentrating in several hundred MHz, leading to EM absorption patterns different from those obtained at high frequencies. In this study, two anatomical models of rats (a male and a female) were reconstructed from magnetic resonance imaging. The models had the same posture as in the exposure experiments. Realistic EMPs were acquired directly from the EMP simulator and applied to the simulations. The interaction of the EMP with the rat was analyzed through the finite-difference time-domain method. Two approaches were utilized to calculate the energy absorption at the tissue and whole-body levels. Dosimetric variability due to incident directions, polarizations, exposure signals simplification, and rat separation was evaluated in this study. The variability result differed substantially from that of the non-constrained rats' exposure experiments. The result sensitivity to frequency and amplitude was discussed as well. The work can be used as a basis to determine the uncertainty and to formulate a standard experimental protocol for this type of experiment.

  10. Top Quark Properties in Little Higgs Models

    SciTech Connect

    Berger, C.F.; Perelstein, M.; Petriello, F.; /Wisconsin U., Madison

    2005-12-08

    Identifying the mechanism which breaks electroweak symmetry and generates fermion masses is one of the main physics goals for both the LHC and the ILC. Studies of the top quark have the potential to illuminate this issue; since it is the heaviest of the Standard Model (SM) fermions, the top is expected to couple strongly to the symmetry-breaking sector. Consequently, the structure of that sector can have significant, potentially observable effects on the properties of the top. for example, it is well known that the vector and axial t{bar t}Z form factors receive large corrections (of order 5-10%) in certain models of dynamical electroweak symmetry breaking [1]. At future colliders such as the LHC and the ILC, we will be able to pursue a program of precision top physics, similar to the program studying the Z at LEP and SLC. In this manuscript, they study the corrections to the top quark properties in ''Little Higgs'' models of electroweak symmetry breaking [2], and compare the expected deviations from the SM predictions with expected sensitivities of experiments at the LHC and the ILC. In the Little Higgs models, electroweak symmetry is driven by the radiative effects from the top sector, including the SM-like top and its heavy counterpart, a TeV-scale ''heavy top'' T. Probing this structure experimentally is quite difficult. While the LHC should be able to discover the T quark, its potential for studying its couplings is limited [3,4]. Direct production of the T will likely be beyond the kinematic reach of the ILC. However, we will show below that the corrections to the gauge couplings of the SM top, induced by its mixing with the T, will be observable at the ILC throughout the parameter range consistent with naturalness. Measuring these corrections will provide a unique window on the top sector of the Little Higgs. Many Little Higgs models have been proposed in the literature. We will consider two examples in this study, the ''Littlest Higgs'' model [5], and its

  11. TU-C-17A-10: Patient Features Based Dosimetric Pareto Front Prediction In Esophagus Cancer Radiotherapy

    SciTech Connect

    Wang, J; Zhao, K; Peng, J; Hu, W; Jin, X

    2014-06-15

    Purpose: The purpose of this study is to study the feasibility of the dosimetric pareto front (PF) prediction based on patient anatomic and dosimetric parameters for esophagus cancer patients. Methods: Sixty esophagus patients in our institution were enrolled in this study. A total 2920 IMRT plans were created to generated PF for each patient. On average, each patient had 48 plans. The anatomic and dosimetric features were extracted from those plans. The mean lung dose (MLD), mean heart dose (MHD), spinal cord max dose and PTV homogeneous index (PTVHI) were recorded for each plan. The principal component analysis (PCA) was used to extract overlap volume histogram (OVH) features between PTV and other critical organs. The full dataset was separated into two parts include the training dataset and the validation dataset. The prediction outcomes were the MHD and MLD for the current study. The spearman rank correlation coefficient was used to evaluate the correlation between the anatomical features and dosimetric features. The PF was fit by the the stepwise multiple regression method. The cross-validation method was used to evaluation the model. Results: The mean prediction error of the MHD was 465 cGy with 100 repetitions. The most correlated factors were the first principal components of the OVH between heart and PTV, and the overlap between heart and PTV in Z-axis. The mean prediction error of the MLD was 195 cGy. The most correlated factors were the first principal components of the OVH between lung and PTV, and the overlap between lung and PTV in Z-axis. Conclusion: It is feasible to use patients anatomic and dosimetric features to generate a predicted PF. Additional samples and further studies were required to get a better prediction model.

  12. Dosimetric characterization of two radium sources for retrospective dosimetry studies

    SciTech Connect

    Candela-Juan, C.; Karlsson, M.; Lundell, M.; Ballester, F.; Tedgren, Å. Carlsson

    2015-05-15

    Purpose: During the first part of the 20th century, {sup 226}Ra was the most used radionuclide for brachytherapy. Retrospective accurate dosimetry, coupled with patient follow up, is important for advancing knowledge on long-term radiation effects. The purpose of this work was to dosimetrically characterize two {sup 226}Ra sources, commonly used in Sweden during the first half of the 20th century, for retrospective dose–effect studies. Methods: An 8 mg {sup 226}Ra tube and a 10 mg {sup 226}Ra needle, used at Radiumhemmet (Karolinska University Hospital, Stockholm, Sweden), from 1925 to the 1960s, were modeled in two independent Monte Carlo (MC) radiation transport codes: GEANT4 and MCNP5. Absorbed dose and collision kerma around the two sources were obtained, from which the TG-43 parameters were derived for the secular equilibrium state. Furthermore, results from this dosimetric formalism were compared with results from a MC simulation with a superficial mould constituted by five needles inside a glass casing, placed over a water phantom, trying to mimic a typical clinical setup. Calculated absorbed doses using the TG-43 formalism were also compared with previously reported measurements and calculations based on the Sievert integral. Finally, the dose rate at large distances from a {sup 226}Ra point-like-source placed in the center of 1 m radius water sphere was calculated with GEANT4. Results: TG-43 parameters [including g{sub L}(r), F(r, θ), Λ, and s{sub K}] have been uploaded in spreadsheets as additional material, and the fitting parameters of a mathematical curve that provides the dose rate between 10 and 60 cm from the source have been provided. Results from TG-43 formalism are consistent within the treatment volume with those of a MC simulation of a typical clinical scenario. Comparisons with reported measurements made with thermoluminescent dosimeters show differences up to 13% along the transverse axis of the radium needle. It has been estimated that

  13. Dosimetric characterization of two radium sources for retrospective dosimetry studies.

    PubMed

    Candela-Juan, C; Karlsson, M; Lundell, M; Ballester, F; Tedgren, Å Carlsson

    2015-05-01

    During the first part of the 20th century, (226)Ra was the most used radionuclide for brachytherapy. Retrospective accurate dosimetry, coupled with patient follow up, is important for advancing knowledge on long-term radiation effects. The purpose of this work was to dosimetrically characterize two (226)Ra sources, commonly used in Sweden during the first half of the 20th century, for retrospective dose-effect studies. An 8 mg (226)Ra tube and a 10 mg (226)Ra needle, used at Radiumhemmet (Karolinska University Hospital, Stockholm, Sweden), from 1925 to the 1960s, were modeled in two independent Monte Carlo (MC) radiation transport codes: geant4 and mcnp5. Absorbed dose and collision kerma around the two sources were obtained, from which the TG-43 parameters were derived for the secular equilibrium state. Furthermore, results from this dosimetric formalism were compared with results from a MC simulation with a superficial mould constituted by five needles inside a glass casing, placed over a water phantom, trying to mimic a typical clinical setup. Calculated absorbed doses using the TG-43 formalism were also compared with previously reported measurements and calculations based on the Sievert integral. Finally, the dose rate at large distances from a (226)Ra point-like-source placed in the center of 1 m radius water sphere was calculated with geant4. TG-43 parameters [including gL(r), F(r, θ), Λ, and sK] have been uploaded in spreadsheets as additional material, and the fitting parameters of a mathematical curve that provides the dose rate between 10 and 60 cm from the source have been provided. Results from TG-43 formalism are consistent within the treatment volume with those of a MC simulation of a typical clinical scenario. Comparisons with reported measurements made with thermoluminescent dosimeters show differences up to 13% along the transverse axis of the radium needle. It has been estimated that the uncertainty associated to the absorbed dose within the

  14. The importance of properties in modeling

    NASA Technical Reports Server (NTRS)

    Giamei, A. F.

    1993-01-01

    thermal conductivity (for liquid and solid), viscosity, surface tension, thermal expansion, mechanical properties, etc. Preliminary data is frequently gathered from the literature; however, this is often not available for modern alloys. If additional data are required, measurements can be used; however, these are costly, time consuming and can be erroneous due to a lack of testing standards or impure materials. Microstructural predictors can be extracted from thermal information, e.g. cooling rate and thermal gradient; the prediction of microstructure is dependent on solidus and liquidus temperature, mushy zone permeability, the solidification curve, volume changes, phase transformations, alloying effects (such as surface tension or viscosity), mold/metal reactions, metal/environment reactions, etc. Defect maps may be needed to predict the onset of shrinkage, hot cracking or 'freckling'. Constants may be needed for stress relaxation, dendrite coarsening, vaporization, etc. Visualization was used as a tool to better comprehend complex data sets associated with the analysis of directional solidification (including crystal growth) and welding. Examples include not only isotherms, but also cooling rate, growth rate and thermal gradient. The latter two are not single valued scalars, but rather time and space dependent vector fields. Efficient models were developed for both casting and welding to predict heat flow and the relationship to dendrite and grain growth. These codes include many of the non-linear effects, e.g. radiation, which dominate these processes. The home-built FDM code(s) were designed to be useful not only to the scientist, but also to the process engineer. Special output can be requested to compare directly to experimental data. Visualization procedures were developed to visualize critical results, e.g. fusion zone width at the surface opposite that where the arc is applied ('penetration'). Both elaborate and simplified distortion analyses were carried out

  15. A high sensitive phosphor for dosimetric applications

    SciTech Connect

    Kore, Bhushan P. Dhoble, S. J.; Dhoble, N. S.; Lochab, S. P.

    2015-06-24

    In this study a novel TL phosphor CaMg{sub 3}(SO{sub 4}){sub 4}:Dy{sup 3+} was prepared by acid distillation method. The TL response of this phosphor towards γ-rays and carbon ion beam was tested. Good dosimetric glow curve was observed which is stable against both the type of radiations. The CaMg{sub 3}(SO{sub 4}){sub 4}:Dy{sup 3+} phosphor doped with 0.2 mol% of Dy{sup 3+}, irradiated with γ-ray shows nearly equal sensitivity to that of commercially available CaSO{sub 4}:Dy TLD phosphor whereas 3.5 times more sensitivity than CaSO{sub 4}:Dy, when irradiated with carbon ion beam. The change in glow peak intensities and glow peak temperature with variation in irradiation species and energy of ion beam is discussed here. The effect of these on trapping parameters is also illustrated.

  16. Gamma Putty dosimetric studies in electron beam

    PubMed Central

    Gloi, Aime M.

    2016-01-01

    Traditionally, lead has been used for field shaping in megavoltage electron beams in radiation therapy. In this study, we analyze the dosimetric parameters of a nontoxic, high atomic number (Z = 83), bismuth-loaded material called Gamma Putty that is malleable and can be easily molded to any desired shape. First, we placed an ionization chamber at different depths in a solid water phantom under a Gamma Putty shield of thickness (t = 0, 3, 5, 10, 15, 20, and 25 mm, respectively) and measured the ionizing radiation on the central axis (CAX) for electron beam ranging in energies from 6 to 20 MeV. Next, we investigated the relationship between the relative ionization (RI) measured at a fixed depth for several Gamma Putty shield at different cutout diameters ranging from 2 to 5 cm for various beam energies and derived an exponential fitting equation for clinical purposes. The dose profiles along the CAX show that bremsstrahlung dominates for Gamma Putty thickness >15 mm. For high-energy beams (12–20 MeV) and all Gamma Putty thicknesses up to 25 mm, RI below 5% could not be achieved due to the strong bremsstrahlung component. However, Gamma Putty is a very suitable material for reducing the transmission factor below 5% and protecting underlying normal tissues for low-energy electron beams (6–9 MeV). PMID:27651563

  17. Dosimetric characteristics of the Elekta Beam Modulator.

    PubMed

    Patel, I; Glendinning, A G; Kirby, M C

    2005-12-07

    The dosimetric characteristics of a production pilot multi-leaf collimator (Elekta Beam Modulator, Elekta Oncology Systems, Crawley, UK) having a 4 mm leaf width (at isocentre) have been investigated. Characteristics explored included leaf bank set-up, penumbra width (80-20%) as a function of leaf position, leaf positioning reproducibility, interleaf leakage and leaf transmission. The penumbra values for leaf ends were measured to be between 4.2 and 4.8 mm for various large rectangular fields studied using Kodak X-omat V film at isocentre (1.5 cm deep). Similar films were taken with a standard 1 cm width multi-leaf collimator (MLC) and the penumbra for leaf ends was found to range from 4.3 to 5.2 mm. Other results showed that the rounded leaf tip provided tight control of the penumbra across the leaves' full range of travel. The positioning of the leaves was within a 0.5 mm range when approaching from the same direction. The maximum interleaf leakage was found to be 1.7% and the average leaf transmission less than 1.0%. No major differences were observed in leakage and transmission with changing gantry angle.

  18. SU-E-T-123: Dosimetric Comparison Between Portrait and Landscape Orientations in Radiochromic Film Dosimetry

    SciTech Connect

    Kakinohana, Y; Toita, T; Kasuya, G; Ariga, T; Heianna, J; Murayama, S

    2014-06-01

    Purpose: To compare the dosimetric properties of radiochromic films with different orientation. Methods: A sheet of EBT3 film was cut into eight pieces with the following sizes: 15×15 cm2 (one piece), 5x15 cm{sup 2} (two) and 4×5 cm{sup 2} (five). A set of two EBT3 sheets was used at each dose level. Two sets were used changing the delivered doses (1 and 2 Gy). The 5×15 cm{sup 2} pieces were rotated by 90 degrees in relation to each other, such that one had landscape orientation and the other had portrait orientation. All 5×15 cm2 pieces were irradiated with their long side aligned with the x-axis of the radiation field. The 15×15 cm{sup 2} pieces were irradiated rotated at 90 degrees to each other. Five pieces, (a total of ten from two sheets) were used to obtain a calibration curve. The irradiated films were scanned using an Epson ES-2200 scanner and were analyzed using ImageJ software. In this study, no correction was applied for the nonuniform scanner signal that is evident in the direction of the scanner lamp. Each film piece was scanned both in portrait and landscape orientations. Dosimetric comparisons of the beam profiles were made in terms of the film orientations (portrait and landscape) and scanner bed directions (perpendicular and parallel to the scanner movement). Results: In general, portrait orientation exhibited higher noise than landscape and was adversely affected to a great extent by the nonuniformity in the direction of the scanner lamp. A significant difference in the measured field widths between the perpendicular and parallel directions was found for both orientations. Conclusion: Without correction for the nonuniform scanner signal in the direction of the scanner lamp, a landscape orientation is preferable. A more detailed investigation is planned to evaluate quantitatively the effect of orientation on the dosimetric properties of a film.

  19. Modeling Statistical Properties of Written Text

    PubMed Central

    2009-01-01

    Written text is one of the fundamental manifestations of human language, and the study of its universal regularities can give clues about how our brains process information and how we, as a society, organize and share it. Among these regularities, only Zipf's law has been explored in depth. Other basic properties, such as the existence of bursts of rare words in specific documents, have only been studied independently of each other and mainly by descriptive models. As a consequence, there is a lack of understanding of linguistic processes as complex emergent phenomena. Beyond Zipf's law for word frequencies, here we focus on burstiness, Heaps' law describing the sublinear growth of vocabulary size with the length of a document, and the topicality of document collections, which encode correlations within and across documents absent in random null models. We introduce and validate a generative model that explains the simultaneous emergence of all these patterns from simple rules. As a result, we find a connection between the bursty nature of rare words and the topical organization of texts and identify dynamic word ranking and memory across documents as key mechanisms explaining the non trivial organization of written text. Our research can have broad implications and practical applications in computer science, cognitive science and linguistics. PMID:19401762

  20. Models of electromagnetic properties of composite media

    NASA Astrophysics Data System (ADS)

    Liu, Jin

    Electromagnetic composite materials have attracted much interest in recent years, due to their desirable microwave and optical applications. One class of these is negative refractive index materials, or double negative materials, in which both permittivity and permeability of materials are simultaneously negative. Many exciting potential applications of double negative materials have been proposed, such as the perfect lens and the cloaking device. Here, a simple-cubic lattice of identical, homogeneous or coated non-metallic spherical particles embedded in a matrix is analyzed. One contribution of this work is the derivation of an analytical formula for the threshold dielectric loss angle of spherical inclusions, above which DNG behavior of the system is extinguished. In addition, analytical formulas are derived from which double negative bandwidth of a simple-cubic lattice of identical, magnetodielectric homogeneous or coated spheres can be determined. Another case of interest is nanocomposites, which commonly consist of nanoparticles embedded in a polymer matrix. These materials show superior dielectric or mechanical performance by taking advantage of the merits of their individual non-hybrid components. In one manifestation, diblock copolymers can be utilized to spatially separate nanoparticles by incorporating them in one block, preferentially, to form a long-range ordered structure. By designing this structure, the electromagnetic properties can be tailored for potential applications in novel devices. Here, molecular dynamics of polymer matrices and nanocomposites is analyzed by parametric modeling of their dielectric spectra, supporting design of a composite with desired electromagnetic properties.

  1. Dynamical Properties of Polymers: Computational Modeling

    SciTech Connect

    CURRO, JOHN G.; ROTTACH, DANA; MCCOY, JOHN D.

    2001-01-01

    The free volume distribution has been a qualitatively useful concept by which dynamical properties of polymers, such as the penetrant diffusion constant, viscosity, and glass transition temperature, could be correlated with static properties. In an effort to put this on a more quantitative footing, we define the free volume distribution as the probability of finding a spherical cavity of radius R in a polymer liquid. This is identical to the insertion probability in scaled particle theory, and is related to the chemical potential of hard spheres of radius R in a polymer in the Henry's law limit. We used the Polymer Reference Interaction Site Model (PRISM) theory to compute the free volume distribution of semiflexible polymer melts as a function of chain stiffness. Good agreement was found with the corresponding free volume distributions obtained from MD simulations. Surprisingly, the free volume distribution was insensitive to the chain stiffness, even though the single chain structure and the intermolecular pair correlation functions showed a strong dependence on chain stiffness. We also calculated the free volume distributions of polyisobutylene (PIB) and polyethylene (PE) at 298K and at elevated temperatures from PRISM theory. We found that PIB has more of its free volume distributed in smaller size cavities than for PE at the same temperature.

  2. Bifurcation properties of a stratospheric vacillation model

    NASA Technical Reports Server (NTRS)

    Yoden, Shigeo

    1987-01-01

    Nonlinear properties of the stratospheric vacillation model of Holton and Mass (1976) are studied numerically using bifurcation theory. Severe truncation and vertical differencing are used to obtain 81 nonlinear ordinary differential equations with time-dependent variables. Three branches of the steady solutions are determined using Powell's hybrid method and the pseudoarclength continuation method, and a multiplicity of stable steady-state solutions with different vertical structures are found to exist in some range of the bifurcation parameter. Periodic solutions are found which branch off from a steady solution by a Hopf bifurcation. It is suggested that the interannual variability of the stratospheric circulation in the middle and high latitudes during winter may be explained by the multiplicity of steady and periodic stable solutions.

  3. Dosimetric Analysis of Radiation-Induced Gastric Bleeding

    PubMed Central

    Feng, Mary; Normolle, Daniel; Pan, Charlie C.; Dawson, Laura A.; Amarnath, Sudha; Ensminger, William D.; Lawrence, Theodore S.; Ten Haken, Randall K.

    2012-01-01

    Purpose Radiation-induced gastric bleeding has been poorly understood. In this study, we describe dosimetric predictors for gastric bleeding after fractionated radiotherapy and compare several predictive models. Materials & Methods The records of 139 sequential patients treated with 3-dimensional conformal radiotherapy (3D-CRT) for intrahepatic malignancies between January 1999 and April 2002 were reviewed. Median follow-up was 7.4 months. Logistic regression and Lyman normal tissue complication probability (NTCP) models for the occurrence of ≥ grade 3 gastric bleed were fit to the data. The principle of maximum likelihood was used to estimate parameters for all models. Results Sixteen of 116 evaluable patients (14%) developed gastric bleeds, at a median time of 4.0 months (mean 6.5 months, range 2.1–28.3 months) following completion of RT. The median and mean of the maximum doses to the stomach were 61 and 63 Gy (range 46 Gy–86 Gy), respectively, after bio-correction to equivalent 2 Gy daily fractions. The Lyman NTCP model with parameters adjusted for cirrhosis was most predictive of gastric bleed (AUROC=0.92). Best fit Lyman NTCP model parameters were n =0.10, and m =0.21, with TD50(normal) =56 Gy and TD50(cirrhosis) = 22 Gy. The low n value is consistent with the importance of maximum dose; a lower TD50 value for the cirrhosis patients points out their greater sensitivity. Conclusion This study demonstrates that the Lyman NTCP model has utility for predicting gastric bleeding, and that the presence of cirrhosis greatly increases this risk. These findings should facilitate the design of future clinical trials involving high-dose upper abdominal radiation. PMID:22541965

  4. Dosimetric Analysis of Radiation-induced Gastric Bleeding

    SciTech Connect

    Feng, Mary; Normolle, Daniel; Pan, Charlie C.; Dawson, Laura A.; Amarnath, Sudha; Ensminger, William D.; Lawrence, Theodore S.; Ten Haken, Randall K.

    2012-09-01

    Purpose: Radiation-induced gastric bleeding has been poorly understood. In this study, we described dosimetric predictors for gastric bleeding after fractionated radiation therapy. Methods and Materials: The records of 139 sequential patients treated with 3-dimensional conformal radiation therapy (3D-CRT) for intrahepatic malignancies were reviewed. Median follow-up was 7.4 months. The parameters of a Lyman normal tissue complication probability (NTCP) model for the occurrence of {>=}grade 3 gastric bleed, adjusted for cirrhosis, were fitted to the data. The principle of maximum likelihood was used to estimate parameters for NTCP models. Results: Sixteen of 116 evaluable patients (14%) developed gastric bleeds at a median time of 4.0 months (mean, 6.5 months; range, 2.1-28.3 months) following completion of RT. The median and mean maximum doses to the stomach were 61 and 63 Gy (range, 46-86 Gy), respectively, after biocorrection of each part of the 3D dose distributions to equivalent 2-Gy daily fractions. The Lyman NTCP model with parameters adjusted for cirrhosis predicted gastric bleed. Best-fit Lyman NTCP model parameters were n=0.10 and m=0.21 and with TD{sub 50} (normal) = 56 Gy and TD{sub 50} (cirrhosis) = 22 Gy. The low n value is consistent with the importance of maximum dose; a lower TD{sub 50} value for the cirrhosis patients points out their greater sensitivity. Conclusions: This study demonstrates that the Lyman NTCP model has utility for predicting gastric bleeding and that the presence of cirrhosis greatly increases this risk. These findings should facilitate the design of future clinical trials involving high-dose upper abdominal radiation.

  5. Design and dosimetric considerations of a modified COMS plaque: The reusable 'seed-guide' insert

    SciTech Connect

    Astrahan, Melvin A.; Szechter, Andrzej; Finger, Paul T.

    2005-08-15

    is modeled and the dosimetric impact discussed. Another unintended consequence of water equivalency is that some fluorescent x rays emitted from the gold backing can now reach the eye. These very low energy x rays were virtually eliminated by absorption in Silastic. When loaded with {sup 125}I seeds the modified plaque appears to produce dose distributions that are almost the same as those of the original COMS plaque and the maximum dosimetric uncertainty introduced by an air bubble is about 2%. Dose distributions calculated for a modified plaque loaded with {sup 103}Pd seeds show that dose to healthy ocular structures distal to the tumor apex can be reduced compared to {sup 125}I. Clearly, it is faster and easier to glue seeds into the reusable gold seed-guide insert than it is to load the COMS-Silastic carrier.

  6. Percolation properties in a traffic model

    NASA Astrophysics Data System (ADS)

    Wang, Feilong; Li, Daqing; Xu, Xiaoyun; Wu, Ruoqian; Havlin, Shlomo

    2015-11-01

    As a dynamical complex system, traffic is characterized by a transition from free flow to congestions, which is mostly studied in highways. However, despite its importance in developing congestion mitigation strategies, the understanding of this common traffic phenomenon in a city scale is still missing. An open question is how the traffic in the network collapses from a global efficient traffic to isolated local flows in small clusters, i.e. the question of traffic percolation. Here we study the traffic percolation properties on a lattice by simulation of an agent-based model for traffic. A critical traffic volume in this model distinguishes the free state from the congested state of traffic. Our results show that the threshold of traffic percolation decreases with increasing traffic volume and reaches a minimum value at the critical traffic volume. We show that this minimal threshold is the result of longest spatial correlation between traffic flows at the critical traffic volume. These findings may help to develop congestion mitigation strategies in a network view.

  7. Advanced optical techniques for monitoring dosimetric parameters in photodynamic therapy

    NASA Astrophysics Data System (ADS)

    Li, Buhong; Qiu, Zhihai; Huang, Zheng

    2012-12-01

    Photodynamic therapy (PDT) is based on the generation of highly reactive singlet oxygen through interactions of photosensitizer, light and molecular oxygen. PDT has become a clinically approved, minimally invasive therapeutic modality for a wide variety of malignant and nonmalignant diseases. The main dosimetric parameters for predicting the PDT efficacy include the delivered light dose, the quantification and photobleaching of the administrated photosensitizer, the tissue oxygen concentration, the amount of singlet oxygen generation and the resulting biological responses. This review article presents the emerging optical techniques that in use or under development for monitoring dosimetric parameters during PDT treatment. Moreover, the main challenges in developing real-time and noninvasive optical techniques for monitoring dosimetric parameters in PDT will be described.

  8. Dosimetric accuracy of a staged radiosurgery treatment

    NASA Astrophysics Data System (ADS)

    Cernica, George; de Boer, Steven F.; Diaz, Aidnag; Fenstermaker, Robert A.; Podgorsak, Matthew B.

    2005-05-01

    For large cerebral arteriovenous malformations (AVMs), the efficacy of radiosurgery is limited since the large doses necessary to produce obliteration may increase the risk of radiation necrosis to unacceptable levels. An alternative is to stage the radiosurgery procedure over multiple stages (usually two), effectively irradiating a smaller volume of the AVM nidus with a therapeutic dose during each session. The difference between coordinate systems defined by sequential stereotactic frame placements can be represented by a translation and a rotation. A unique transformation can be determined based on the coordinates of several fiducial markers fixed to the skull and imaged in each stereotactic coordinate system. Using this transformation matrix, isocentre coordinates from the first stage can be displayed in the coordinate system of subsequent stages allowing computation of a combined dose distribution covering the entire AVM. The accuracy of this approach was tested on an anthropomorphic head phantom and was verified dosimetrically. Subtle defects in the phantom were used as control points, and 2 mm diameter steel balls attached to the surface were used as fiducial markers and reference points. CT images (2 mm thick) were acquired. Using a transformation matrix developed with two frame placements, the predicted locations of control and reference points had an average error of 0.6 mm near the fiducial markers and 1.0 mm near the control points. Dose distributions in a staged treatment approach were accurately calculated using the transformation matrix. This approach is simple, fast and accurate. Errors were small and clinically acceptable for Gamma Knife radiosurgery. Accuracy can be improved by reducing the CT slice thickness.

  9. FBX aqueous chemical dosimeter for measurement of dosimetric parameters.

    PubMed

    Moussous, O; Medjadj, T; Benguerba, M

    2011-02-01

    We investigated the ferrous sulphate-benzoic acid-xylenol orange (FBX) aqueous chemical dosimeter for measurement of dosimetric parameters such as the output factor, backscatter factor and lateral beam profiles for different square fields sizes for (60)Co γ-rays. A water phantom was employed to measure these parameters. An ionization chamber (IC) was used for calibration and comparison. A comparison of the resulting measurements with an ionization chamber's measured parameters showed good agreement. We thus believe that the tissue equivalent FBX dosimetry system can measure the dosimetric parameters for (60)Co with reasonable accuracy.

  10. The Potosi Reservoir Model 2013c, Property Modeling Update

    SciTech Connect

    Adushita, Yasmin; Smith, Valerie; Leetaru, Hannes

    2014-09-30

    property modeling workflows and layering. This model was retained as the base case. In the preceding Task [1], the Potosi reservoir model was updated to take into account the new data from the Verification Well #2 (VW2) which was drilled in 2012. The porosity and permeability modeling was revised to take into account the log data from the new well. Revisions of the 2010 modeling assumptions were also done on relative permeability, capillary pressures, formation water salinity, and the maximum allowable well bottomhole pressure. Dynamic simulations were run using the injection target of 3.5 million tons per annum (3.2 MTPA) for 30 years. This dynamic model was named Potosi Dynamic Model 2013b. In this Task, a new property modeling workflow was applied, where seismic inversion data guided the porosity mapping and geobody extraction. The static reservoir model was fully guided by PorosityCube interpretations and derivations coupled with petrophysical logs from three wells. The two main assumptions are: porosity features in the PorosityCube that correlate with lost circulation zones represent vugular zones, and that these vugular zones are laterally continuous. Extrapolation was done carefully to populate the vugular facies and their corresponding properties outside the seismic footprint up to the boundary of the 30 by 30 mi (48 by 48 km) model. Dynamic simulations were also run using the injection target of 3.5 million tons per annum (3.2 MTPA) for 30 years. This new dynamic model was named Potosi Dynamic Model 2013c. Reservoir simulation with the latest model gives a cumulative injection of 43 million tons (39 MT) in 30 years with a single well, which corresponds to 40% of the injection target. The injection rate is approx. 3.2 MTPA in the first six months as the well is injecting into the surrounding vugs, and declines rapidly to 1.8 million tons per annum (1.6 MTPA) in year 3 once the surrounding vugs are full and the CO2 start to reach the matrix. After, the injection

  11. Dosimetric effects caused by couch tops and immobilization devices: Report of AAPM Task Group 176

    SciTech Connect

    Olch, Arthur J.; Gerig, Lee; Li, Heng; Mihaylov, Ivaylo; Morgan, Andrew

    2014-06-15

    The dosimetric impact from devices external to the patient is a complex combination of increased skin dose, reduced tumor dose, and altered dose distribution. Although small monitor unit or dose corrections are routinely made for blocking trays, ion chamber correction factors, e.g., accounting for temperature and pressure, or tissue inhomogeneities, the dose perturbation of the treatment couch top or immobilization devices is often overlooked. These devices also increase skin dose, an effect which is also often ignored or underestimated. These concerns have grown recently due to the increased use of monolithic carbon fiber couch tops which are optimal for imaging for patient position verification but cause attenuation and increased skin dose compared to the “tennis racket” style couch top they often replace. Also, arc delivery techniques have replaced stationary gantry techniques which cause a greater fraction of the dose to be delivered from posterior angles. A host of immobilization devices are available and used to increase patient positioning reproducibility, and these also have attenuation and skin dose implications which are often ignored. This report of Task Group 176 serves to present a survey of published data that illustrates the magnitude of the dosimetric effects of a wide range of devices external to the patient. The report also provides methods for modeling couch tops in treatment planning systems so the physicist can accurately compute the dosimetric effects for indexed patient treatments. Both photon and proton beams are considered. A discussion on avoidance of high density structures during beam planning is also provided. An important aspect of this report are the recommendations the authors make to clinical physicists, treatment planning system vendors, and device vendors on how to make measurements of surface dose and attenuation and how to report these values. For the vendors, an appeal is made to work together to provide accurate couch top

  12. Radioembolization of Hepatic Lesions from a Radiobiology and Dosimetric Perspective

    PubMed Central

    Cremonesi, Marta; Chiesa, Carlo; Strigari, Lidia; Ferrari, Mahila; Botta, Francesca; Guerriero, Francesco; De Cicco, Concetta; Bonomo, Guido; Orsi, Franco; Bodei, Lisa; Di Dia, Amalia; Grana, Chiara Maria; Orecchia, Roberto

    2014-01-01

    Radioembolization (RE) of liver cancer with 90Y-microspheres has been applied in the last two decades with notable responses and acceptable toxicity. Two types of microspheres are available, glass and resin, the main difference being the activity/sphere. Generally, administered activities are established by empirical methods and differ for the two types. Treatment planning based on dosimetry is a prerogative of few centers, but has notably gained interest, with evidence of predictive power of dosimetry on toxicity, lesion response, and overall survival (OS). Radiobiological correlations between absorbed doses and toxicity to organs at risk, and tumor response, have been obtained in many clinical studies. Dosimetry methods have evolved from the macroscopic approach at the organ level to voxel analysis, providing absorbed dose spatial distributions and dose–volume histograms (DVH). The well-known effects of the external beam radiation therapy (EBRT), such as the volume effect, underlying disease influence, cumulative damage in parallel organs, and different tolerability of re-treatment, have been observed also in RE, identifying in EBRT a foremost reference to compare with. The radiobiological models – normal tissue complication probability and tumor control probability – and/or the style (DVH concepts) used in EBRT are introduced in RE. Moreover, attention has been paid to the intrinsic different activity distribution of resin and glass spheres at the microscopic scale, with dosimetric and radiobiological consequences. Dedicated studies and mathematical models have developed this issue and explain some clinical evidences, e.g., the shift of dose to higher toxicity thresholds using glass as compared to resin spheres. This paper offers a comprehensive review of the literature incident to dosimetry and radiobiological issues in RE, with the aim to summarize the results and to identify the most useful methods and information that should accompany future studies

  13. Dosimetric characterization and organ dose assessment in digital breast tomosynthesis: Measurements and Monte Carlo simulations using voxel phantoms

    SciTech Connect

    Baptista, Mariana Di Maria, Salvatore; Barros, Sílvia; Vaz, Pedro; Figueira, Catarina; Sarmento, Marta; Orvalho, Lurdes

    2015-07-15

    Purpose: Due to its capability to more accurately detect deep lesions inside the breast by removing the effect of overlying anatomy, digital breast tomosynthesis (DBT) has the potential to replace the standard mammography technique in clinical screening exams. However, the European Guidelines for DBT dosimetry are still a work in progress and there are little data available on organ doses other than to the breast. It is, therefore, of great importance to assess the dosimetric performance of DBT with respect to the one obtained with standard digital mammography (DM) systems. The aim of this work is twofold: (i) to study the dosimetric properties of a combined DBT/DM system (MAMMOMAT Inspiration Siemens{sup ®}) for a tungsten/rhodium (W/Rh) anode/filter combination and (ii) to evaluate organs doses during a DBT examination. Methods: For the first task, measurements were performed in manual and automatic exposure control (AEC) modes, using two homogeneous breast phantoms: a PMMA slab phantom and a 4 cm thick breast-shaped rigid phantom, with 50% of glandular tissue in its composition. Monte Carlo (MC) simulations were performed using Monte Carlo N-Particle eXtended v.2.7.0. A MC model was implemented to mimic DM and DBT acquisitions for a wide range of x-ray spectra (24 –34 kV). This was used to calculate mean glandular dose (MGD) and to compute series of backscatter factors (BSFs) that could be inserted into the DBT dosimetric formalism proposed by Dance et al. Regarding the second aim of the study, the implemented MC model of the clinical equipment, together with a female voxel phantom (“Laura”), was used to calculate organ doses considering a typical DBT acquisition. Results were compared with a standard two-view mammography craniocaudal (CC) acquisition. Results: Considering the AEC mode, the acquisition of a single CC view results in a MGD ranging from 0.53 ± 0.07 mGy to 2.41 ± 0.31 mGy in DM mode and from 0.77 ± 0.11 mGy to 2.28 ± 0.32 mGy in DBT mode

  14. Sea Level Rise National Coastal Property Model

    EPA Science Inventory

    The impact of sea level rise on coastal properties depends critically on the human response to the threat, which in turn depends on several factors, including the immediacy of the risk, the magnitude of property value at risk, options for adapting to the threat and the cost of th...

  15. Sea Level Rise National Coastal Property Model

    EPA Science Inventory

    The impact of sea level rise on coastal properties depends critically on the human response to the threat, which in turn depends on several factors, including the immediacy of the risk, the magnitude of property value at risk, options for adapting to the threat and the cost of th...

  16. Neuropharmacological properties of farnesol in Murine model

    PubMed Central

    Shahnouri, M.; Abouhosseini Tabari, M.; Araghi, A.

    2016-01-01

    Research on new compounds of therapeutic value for behavioral disorders has progressed recently. Several studies have reported neuropharmacological activities of plant derived terpenes. Farnesol is a sesquiterpene whose most popular source is fruits but the anxiolytic activity for farnesol is still unknown. The present study was conducted on 32 male Swiss Albino mice (8 in each group) to evaluate the neuropharmacological properties of farnesol and its effects on plasma cortisol levels. Farnesol was administered intraperitoneally at single doses of 50 and 100 mg/kg, while diazepam 2 mg/kg was used as standard anxiolytic. Thirty minutes after injections, open field test (OFT), elevated plus maze (EPM), a forced swimming test (FST), and a hot plate test (HPT) were performed for evaluation of anxiety-like behavior, depression and nociception. In OFT, farnesol at the dose of 100 mg/kg led to significant decrease in locomotor activity (P<0.01). In EPM, only farnesol 100 mg/kg led to significant increase in the number of entries to the open arms and the time spent in open arms (P<0.01). Increase in immobility time in FST was seen in farnesol 50 and 100 mg/kg (P<0.001). Farnesol 100 mg/kg exerts significant prolongation in the latency of responses to noxious heat stimuli in HPT. Like diazepam, farnesol decreased plasma levels of cortisol. Results revealed that farnesol had anxiolytic, anti-nociceptive and depressant effects in murine models. The present study provides pharmacological evidence supporting the use of farnesol as a sedative for anxiety disorders. PMID:28224010

  17. Dose escalation in permanent brachytherapy for prostate cancer: dosimetric and biological considerations

    NASA Astrophysics Data System (ADS)

    Li, X. Allen; Wang, Jian Z.; Stewart, Robert D.; Di Biase, Steven J.

    2003-09-01

    No prospective dose escalation study for prostate brachytherapy (PB) with permanent implants has been reported. In this work, we have performed a dosimetric and biological analysis to explore the implications of dose escalation in PB using 125I and 103Pd implants. The concept of equivalent uniform dose (EUD), proposed originally for external-beam radiotherapy (EBRT), is applied to low dose rate brachytherapy. For a given 125I or 103Pd PB, the EUD for tumour that corresponds to a dose distribution delivered by EBRT is calculated based on the linear quadratic model. The EUD calculation is based on the dose volume histogram (DVH) obtained retrospectively from representative actual patient data. Tumour control probabilities (TCPs) are also determined in order to compare the relative effectiveness of different dose levels. The EUD for normal tissue is computed using the Lyman model. A commercial inverse treatment planning algorithm is used to investigate the feasibility of escalating the dose to prostate with acceptable dose increases in the rectum and urethra. The dosimetric calculation is performed for five representative patients with different prostate sizes. A series of PB dose levels are considered for each patient using 125I and 103Pd seeds. It is found that the PB prescribed doses (minimum peripheral dose) that give an equivalent EBRT dose of 64.8, 70.2, 75.6 and 81 Gy with a fraction size of 1.8 Gy are 129, 139, 150 and 161 Gy for 125I and 103, 112, 122 and 132 Gy for 103Pd implants, respectively. Estimates of the EUD and TCP for a series of possible prescribed dose levels (e.g., 145, 160, 170 and 180 Gy for 125I and 125, 135, 145 and 155 for 103Pd implants) are tabulated. The EUD calculation was found to depend strongly on DVHs and radiobiological parameters. The dosimetric calculations suggest that the dose to prostate can be escalated without a substantial increase in both rectal and urethral dose. For example, increasing the PB prescribed dose from 145 to

  18. Dosimetric impact of an air passage on intraluminal brachytherapy for bronchus cancer

    PubMed Central

    Okamoto, Hiroyuki; Wakita, Akihisa; Nakamura, Satoshi; Nishioka, Shie; Aikawa, Ako; Kato, Toru; Abe, Yoshihisa; Kobayashi, Kazuma; Inaba, Koji; Murakami, Naoya; Itami, Jun

    2016-01-01

    The brachytherapy dose calculations used in treatment planning systems (TPSs) have conventionally been performed assuming homogeneous water. Using measurements and a Monte Carlo simulation, we evaluated the dosimetric impact of an air passage on brachytherapy for bronchus cancer. To obtain the geometrical characteristics of an air passage, we analyzed the anatomical information from CT images of patients who underwent intraluminal brachytherapy using a high-dose-rate 192Ir source (MicroSelectron V2r®, Nucletron). Using an ionization chamber, we developed a measurement system capable of measuring the peripheral dose with or without an air cavity surrounding the catheter. Air cavities of five different radii (0.3, 0.5, 0.75, 1.25 and 1.5 cm) were modeled by cylindrical tubes surrounding the catheter. A Monte Carlo code (GEANT4) was also used to evaluate the dosimetric impact of the air cavity. Compared with dose calculations in homogeneous water, the measurements and GEANT4 indicated a maximum overdose of 5–8% near the surface of the air cavity (with the maximum radius of 1.5 cm). Conversely, they indicated a minimum overdose of ~1% in the region 3–5 cm from the cavity surface for the smallest radius of 0.3 cm. The dosimetric impact depended on the size and the distance of the air passage, as well as the length of the treatment region. Based on dose calculations in water, the TPS for intraluminal brachytherapy for bronchus cancer had an unexpected overdose of 3–5% for a mean radius of 0.75 cm. This study indicates the need for improvement in dose calculation accuracy with respect to intraluminal brachytherapy for bronchus cancer. PMID:27605630

  19. Synthesis and characterization of CaF{sub 2}:Dy nanophosphor for dosimetric application

    SciTech Connect

    Bhadane, Mahesh S.; Dahiwale, S. S.; Bhoraskar, V. N.; Dhole, S. D.; Patil, B. J.; Kulkarni, M. S.; Bhatt, B. C.

    2015-06-24

    In this work, nanoparticles (NPs) of dysprosium doped calcium fluoride (CaF{sub 2}:Dy) 1 mol % has been prepared using simple chemical co-precipitation method and its thermoluminescence (TL) dosimetric properties were studied. The synthesized nanoparticle sample was characterized by X-ray diffraction (XRD) and the particle size of face centered cubic phase NPs was found around 30 nm. The shape, morphology and size were also observed by scanning electron microscopy (SEM). From gamma irradiated CaF{sub 2}:Dy TL curves, it was observed that the total areas of all the glow peak intensities are dramatically changed with increase in annealing temperature. Further, TL glow curve of the CaF{sub 2}:Dy at 183 °C annealed at 400 °C, showed very sharp linear response in the dose range from 1 Gy to 750 Gy. This linear response of CaF{sub 2}:Dy nanophosphor as a function of gamma dose is very useful from radiation dosimetric point of view.

  20. Dosimetric characteristics of fabricated silica fibre for postal radiotherapy dose audits

    NASA Astrophysics Data System (ADS)

    Fadzil, M. S. Ahmad; Ramli, N. N. H.; Jusoh, M. A.; Kadni, T.; Bradley, D. A.; Ung, N. M.; Suhairul, H.; Mohd Noor, N.

    2014-11-01

    Present investigation aims to establish the dosimetric characteristics of a novel fabricated flat fibre TLD system for postal radiotherapy dose audits. Various thermoluminescence (TL) properties have been investigated for five sizes of 6 mol% Ge-doped optical fibres. Key dosimetric characteristics including reproducibility, linearity, fading and energy dependence have been established. Irradiations were carried out using a linear accelerator (linac) and a Cobalt-60 machine. For doses from 0.5 Gy up to 10 Gy, Ge-doped flat fibres exhibit linearity between TL yield and dose, reproducible to better than 8% standard deviation (SD) following repeat measurements (n = 3). For photons generated at potentials from 1.25 MeV to 10 MV an energy-dependent response is noted, with a coefficient of variation (CV) of less than 40% over the range of energies investigated. For 6.0 mm length flat fibres 100 μm thick × 350 pm wide, the TL fading loss following 30 days of storage at room temperature was < 8%. The Ge-doped flat fibre system represents a viable basis for use in postal radiotherapy dose audits, corrections being made for the various factors influencing the TL yield.

  1. Comparison of dosimetric characteristics of Siemens virtual and physical wedges for ONCOR linear accelerator.

    PubMed

    Attalla, Ehab M; Abo-Elenein, H S; Ammar, H; El-Desoky, Ismail

    2010-07-01

    Dosimetric properties of virtual wedge (VW) and physical wedge (PW) in 6- and 10-MV photon beams from a Siemens ONCOR linear accelerator, including wedge factors, depth doses, dose profiles, peripheral doses, are compared. While there is a great difference in absolute values of wedge factors, VW factors (VWFs) and PW factors (PWFs) have a similar trend as a function of field size. PWFs have stronger depth dependence than VWF due to beam hardening in PW fields. VW dose profiles in the wedge direction, in general, match very well with those of PW, except in the toe area of large wedge angles with large field sizes. Dose profiles in the nonwedge direction show a significant reduction in PW fields due to off-axis beam softening and oblique filtration. PW fields have significantly higher peripheral doses than open and VW fields. VW fields have similar surface doses as the open fields, while PW fields have lower surface doses. Surface doses for both VW and PW increase with field size and slightly with wedge angle. For VW fields with wedge angles 45° and less, the initial gap up to 3 cm is dosimetrically acceptable when compared to dose profiles of PW. VW fields in general use less monitor units than PW fields.

  2. [Mathematical simulation support to the dosimetric monitoring on the Russian segment of the International Space Station].

    PubMed

    Mitrikas, V G

    2014-01-01

    To ensure radiation safety of cosmonauts, it is necessary not only to predict, but also to reconstruct absorbed dose dynamics with the knowledge of how long cosmonauts stay in specific space vehicle compartments with different shielding properties and lacking equipment for dosimetric monitoring. In this situation, calculating is one and only way to make a correct estimate of radiation exposure of cosmonaut's organism as a whole (tissue-average dose) and of separate systems and organs. The paper addresses the issues of mathematical simulation of epy radiation environment of standard dosimetric instruments in the Russian segments of the International Space Station (ISS RS). Results of comparing the simulation and experimental data for the complement of dosimeters including ionization chamber-based radiometer R-16, DB8 dosimeters composed of semiconductor detectors, and Pille dosimeters composed of thermoluminescent detectors evidence that the current methods of simulation in support of the ISS RS radiation monitoring provide a sufficiently good agreement between the calculated and experimental data.

  3. Modeling Electronic Properties of Complex Oxides

    NASA Astrophysics Data System (ADS)

    Krishnaswamy, Karthik

    Complex oxides are a class of materials that have recently emerged as potential candidates for electronic applications owing to their interesting electronic properties. The goal of this dissertation is to develop a fundamental understanding of these electronic properties using a combination of first-principles approaches based on density functional theory (DFT), and Schr odinger-Poisson (SP) simulation (Abstract shortened by ProQuest.

  4. SU-E-T-411: Dosimetric Comparison Between Two Multileaf Collimator Systems for Stereotactic Radiosurgery and Radiotherapy.

    PubMed

    Asnaashari, K; Chow, J; Heydarian, M

    2012-06-01

    This aim of this study is to compare the dosimetric parameters of two multileaf collimator (MLC) systems: (1) the beam modulator (BM), which is the MLC commercial name for Elekta 'Synergy S' linear accelerator; and (2) Radionics micro-MLC (MMLC). Dosimetric parameters of percentage depth dose (PDD), in-plane and cross-plane beam profile, penumbra, MLC leakage and transmission for a 6 MV photon beam with different field sizes and depths were measured using ionization chamber, film, solid water phantom and water tank. At the same time, the BM and MMLC were modeled using the BEAMnrc code and the above dosimetric parameters were calculated using Monte Carlo simulations. Energy fluence spectra for the two MLC were determined using the BEAMnrc and BEAMDP. We found that dosimetric parameters (PDD, beam profile, energy fluence spectra, leakage and transmission) of the two MLC were similar, except for penumbra. The leaf-side and leaf-end 20%-80% penumbras at 10 cm depth for a 10×10 cm(2) field were 4.8 and 5.1 mm for the MMLC and 5.3 mm and 6.3 mm for the BM, respectively. The maximum percentage of the leakage for the BM and MMLC are 1.3% and 1.2%, while the average percentage of leakage for the BM and MMLC are 0.9% and 1%. Based on their dosimetric characteristics for stereotactic radiosurgery and radiotherapy, it can be concluded that both the BM and MMLC can be used effectively, though the latter showed slightly sharper dose penumbra especially in the leaf-end direction. However, the BM has the advantages of producing considerably larger field at isocenter and having a greater isocenter clearance compared to the MMLC. The dosimetric data in this study should help radiotherapy staff to appreciate dependence of dosimetry on the MLC design and configuration for stereotactic radiosurgery and radiotherapy. Actual or potential conflicts of interest do not exist. © 2012 American Association of Physicists in Medicine.

  5. Modeling Non-Linear Material Properties in Composite Materials

    DTIC Science & Technology

    2016-06-28

    Technical Report ARWSB-TR-16013 MODELING NON-LINEAR MATERIAL PROPERTIES IN COMPOSITE MATERIALS Michael F. Macri Andrew G...REPORT TYPE Technical 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE MODELING NON-LINEAR MATERIAL PROPERTIES IN COMPOSITE MATERIALS ...systems are increasingly incorporating composite materials into their design. Many of these systems subject the composites to environmental conditions

  6. Modeling of Mechanical Properties of Advanced Nanostructured Ceramic Composites

    DTIC Science & Technology

    2010-03-15

    technical report 3. DATES COVERED (From - To) From Ol-Jan-2007 to 31 -Dec-2009 4. TITLE AND SUBTITLE Modeling of Mechanical Properties of Advanced ...for puj^Ux^ r^Wse_- dC5+rvioockd>v^ <JMT4MTLC4<JSI . 13. SUPPLEMENTARY NOTES 14. ABSTRACT Mechanical properties of advanced nanostructured...Modeling of Mechanical Properties of Advanced Nanostructured Ceramic Composites Program Officer: Larry Kabacoff CO-PI Information Number of Co-PIs

  7. Dosimetric effects of rotational output variation and x-ray target degradation on helical tomotherapy plans.

    PubMed

    Staton, Robert J; Langen, Katja M; Kupelian, Patrick A; Meeks, Sanford L

    2009-07-01

    In this study, two potential sources of IMRT delivery error have been identified for helical tomotherapy delivery using the HiART system (TomoTherapy, Inc., Madison, WI): Rotational output variation and target degradation. The HiArt system is known to have output variation, typically about +/- 2%, due to the absence of a dose servo system. On the HiArt system, x-ray target replacement is required approximately every 10-12 months due to target degradation. Near the end of target life, the target thins and causes a decrease in the beam energy and a softening of the beam profile at the lateral edges of the beam. The purpose of this study is to evaluate the dosimetric effects of rotational output variation and target degradation by modeling their effects and incorporating them into recalculated treatment plans for three clinical scenarios: Head and neck, partial breast, and prostate. Models were created to emulate both potential sources of error. For output variation, a model was created using a sine function to match the amplitude (+/- 2%), frequency, and phase of the measured rotational output variation data. A second model with a hypothetical variation of +/- 7% was also created to represent the largest variation that could exist without violating the allowable dose window in the delivery system. A measured beam profile near the end of target life was used to create a modified beam profile model for the target degradation. These models were then incorporated into the treatment plan by modifying the leaf opening times in the delivery sinogram. A new beam model was also created to mimic the change in beam energy seen near the end of target life. The plans were then calculated using a research version of the PLANNED ADAPTIVE treatment planning software from TomoTherapy, Inc. Three plans were evaluated in this study: Head and neck, partial breast, and prostate. The D50 of organs at risk, the D95 for planning target volumes (PTVs), and the local dose difference were used

  8. The work of the ICRP dose calculational task group: Issues in implementation of the ICRP dosimetric methodology

    SciTech Connect

    Eckerman, K.F.

    1999-01-01

    Committee 2 of the International Commission on Radiological Protection (ICRP) has had efforts underway to provide the radiation protection community with age-dependent dose coefficients, i.e.g, the dose per unit intake. The Task Group on Dose Calculations, chaired by the author, is responsible for the computation of these coefficients. The Task Group, formed in 1974 to produce ICRP Publication 30, is now international in its membership and its work load has been distributed among the institutions represented on the task group. This paper discusses: (1) recent advances in biokinetic modeling; (2) the recent changes in the dosimetric methodology; (3) the novel computational problems with some of the ICRP quantities; and (4) quality assurance issues which the Task Group has encountered. Potential future developments of the dosimetric framework which might strengthen the relationships with the emerging understanding of radiation risk will also be discussed.

  9. Predicting Pneumonitis Risk: A Dosimetric Alternative to Mean Lung Dose

    SciTech Connect

    Tucker, Susan L.; Mohan, Radhe; Liengsawangwong, Raweewan; Martel, Mary K.; Liao Zhongxing

    2013-02-01

    Purpose: 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. Methods and Materials: 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. Results: 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. Conclusions: 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').

  10. Modeling and parameterization of horizontally inhomogeneous cloud radiative properties

    NASA Technical Reports Server (NTRS)

    Welch, R. M.

    1995-01-01

    One of the fundamental difficulties in modeling cloud fields is the large variability of cloud optical properties (liquid water content, reflectance, emissivity). The stratocumulus and cirrus clouds, under special consideration for FIRE, exhibit spatial variability on scales of 1 km or less. While it is impractical to model individual cloud elements, the research direction is to model a statistical ensembles of cloud elements with mean-cloud properties specified. The major areas of this investigation are: (1) analysis of cloud field properties; (2) intercomparison of cloud radiative model results with satellite observations; (3) radiative parameterization of cloud fields; and (4) development of improved cloud classification algorithms.

  11. Modeling thermal properties of plutonium mononitride

    NASA Astrophysics Data System (ADS)

    Yu, H. L.; Huang, H.; Li, G.; Li, H. B.; Meng, D. Q.

    2015-06-01

    The thermal properties of plutonium mononitride (PuN) were investigated by molecular dynamics method. The interatomic potentials of PuN were fitted by using Chen-Möbius multiple lattice inversion technique. Based on these interatomic potentials, the lattice constant, bulk modulus, compressibility, cohesive energy and heat capacity of PuN were obtained and the results are well consistent with experimental data and previous reports. It indicates that the potentials we build in this study are effective for studying thermal properties of PuN.

  12. Multi-institutional dosimetric and geometric commissioning of image-guided small animal irradiators

    SciTech Connect

    Lindsay, P. E.; Granton, P. V.; Hoof, S. van; Hermans, J.; Gasparini, A.; Jelveh, S.; Clarkson, R.; Kaas, J.; Wittkamper, F.; Sonke, J.-J.; Verhaegen, F.; Jaffray, D. A.

    2014-03-15

    Purpose: To compare the dosimetric and geometric properties of a commercial x-ray based image-guided small animal irradiation system, installed at three institutions and to establish a complete and broadly accessible commissioning procedure. Methods: The system consists of a 225 kVp x-ray tube with fixed field size collimators ranging from 1 to 44 mm equivalent diameter. The x-ray tube is mounted opposite a flat-panel imaging detector, on a C-arm gantry with 360° coplanar rotation. Each institution performed a full commissioning of their system, including half-value layer, absolute dosimetry, relative dosimetry (profiles, percent depth dose, and relative output factors), and characterization of the system geometry and mechanical flex of the x-ray tube and detector. Dosimetric measurements were made using Farmer-type ionization chambers, small volume air and liquid ionization chambers, and radiochromic film. The results between the three institutions were compared. Results: At 225 kVp, with 0.3 mm Cu added filtration, the first half value layer ranged from 0.9 to 1.0 mm Cu. The dose-rate in-air for a 40 × 40 mm{sup 2} field size, at a source-to-axis distance of 30 cm, ranged from 3.5 to 3.9 Gy/min between the three institutions. For field sizes between 2.5 mm diameter and 40 × 40 mm{sup 2}, the differences between percent depth dose curves up to depths of 3.5 cm were between 1% and 4% on average, with the maximum difference being 7%. The profiles agreed very well for fields >5 mm diameter. The relative output factors differed by up to 6% for fields larger than 10 mm diameter, but differed by up to 49% for fields ≤5 mm diameter. The mechanical characteristics of the system (source-to-axis and source-to-detector distances) were consistent between all three institutions. There were substantial differences in the flex of each system. Conclusions: With the exception of the half-value layer, and mechanical properties, there were significant differences between the

  13. Modelling the scaling properties of human mobility

    NASA Astrophysics Data System (ADS)

    Song, Chaoming; Koren, Tal; Wang, Pu; Barabási, Albert-László

    2010-10-01

    Individual human trajectories are characterized by fat-tailed distributions of jump sizes and waiting times, suggesting the relevance of continuous-time random-walk (CTRW) models for human mobility. However, human traces are barely random. Given the importance of human mobility, from epidemic modelling to traffic prediction and urban planning, we need quantitative models that can account for the statistical characteristics of individual human trajectories. Here we use empirical data on human mobility, captured by mobile-phone traces, to show that the predictions of the CTRW models are in systematic conflict with the empirical results. We introduce two principles that govern human trajectories, allowing us to build a statistically self-consistent microscopic model for individual human mobility. The model accounts for the empirically observed scaling laws, but also allows us to analytically predict most of the pertinent scaling exponents.

  14. Modeling adsorption: Investigating adsorbate and adsorbent properties

    NASA Astrophysics Data System (ADS)

    Webster, Charles Edwin

    1999-12-01

    Surface catalyzed reactions play a major role in current chemical production technology. Currently, 90% of all chemicals are produced by heterogeneously catalyzed reactions. Most of these catalyzed reactions involve adsorption, concentrating the substrate(s) (the adsorbate) on the surface of the solid (the adsorbent). Pore volumes, accessible surface areas, and the thermodynamics of adsorption are essential in the understanding of solid surface characteristics fundamental to catalyst and adsorbent screening and selection. Molecular properties such as molecular volumes and projected molecular areas are needed in order to convert moles adsorbed to surface volumes and areas. Generally, these molecular properties have been estimated from bulk properties, but many assumptions are required. As a result, different literature values are employed for these essential molecular properties. Calculated molar volumes and excluded molecular areas are determined and tabulated for a variety of molecules. Molecular dimensions of molecules are important in the understanding of molecular exclusion as well as size and shape selectivity, diffusion, and adsorbent selection. Molecular dimensions can also be used in the determination of the effective catalytic pore size of a catalyst. Adsorption isotherms, on zeolites, (crystalline mineral oxides) and amorphous solids, can be analyzed with the Multiple Equilibrium Analysis (MEA) description of adsorption. The MEA produces equilibrium constants (Ki), capacities (ni), and thermodynamic parameters (enthalpies, ΔHi, and entropies, ΔSi) of adsorption for each process. Pore volumes and accessible surface areas are calculated from the process capacities. Adsorption isotherms can also be predicted for existing and new adsorbate-adsorbent systems with the MEA. The results show that MEA has the potential of becoming a standard characterization method for microporous solids that will lead to an increased understanding of their behavior in gas

  15. Validation of a personalized dosimetric evaluation tool (Oedipe) for targeted radiotherapy based on the Monte Carlo MCNPX code.

    PubMed

    Chiavassa, S; Aubineau-Lanièce, I; Bitar, A; Lisbona, A; Barbet, J; Franck, D; Jourdain, J R; Bardiès, M

    2006-02-07

    Dosimetric studies are necessary for all patients treated with targeted radiotherapy. In order to attain the precision required, we have developed Oedipe, a dosimetric tool based on the MCNPX Monte Carlo code. The anatomy of each patient is considered in the form of a voxel-based geometry created using computed tomography (CT) images or magnetic resonance imaging (MRI). Oedipe enables dosimetry studies to be carried out at the voxel scale. Validation of the results obtained by comparison with existing methods is complex because there are multiple sources of variation: calculation methods (different Monte Carlo codes, point kernel), patient representations (model or specific) and geometry definitions (mathematical or voxel-based). In this paper, we validate Oedipe by taking each of these parameters into account independently. Monte Carlo methodology requires long calculation times, particularly in the case of voxel-based geometries, and this is one of the limits of personalized dosimetric methods. However, our results show that the use of voxel-based geometry as opposed to a mathematically defined geometry decreases the calculation time two-fold, due to an optimization of the MCNPX2.5e code. It is therefore possible to envisage the use of Oedipe for personalized dosimetry in the clinical context of targeted radiotherapy.

  16. Dosimetric measurements of Onyx embolization material for stereotactic radiosurgery

    SciTech Connect

    Roberts, Donald A.; Balter, James M.; Chaudhary, Neeraj; Gemmete, Joseph J.; Pandey, Aditya S.

    2012-11-15

    Purpose: Arteriovenous malformations are often treated with a combination of embolization and stereotactic radiosurgery. Concern has been expressed in the past regarding the dosimetric properties of materials used in embolization and the effects that the introduction of these materials into the brain may have on the quality of the radiosurgery plan. To quantify these effects, the authors have taken large volumes of Onyx 34 and Onyx 18 (ethylene-vinyl alcohol copolymer doped with tantalum) and measured the attenuation and interface effects of these embolization materials. Methods: The manufacturer provided large cured volumes ({approx}28 cc) of both Onyx materials. These samples were 8.5 cm in diameter with a nominal thickness of 5 mm. The samples were placed on a block tray above a stack of solid water with an Attix chamber at a depth of 5 cm within the stack. The Attix chamber was used to measure the attenuation. These measurements were made for both 6 and 16 MV beams. Placing the sample directly on the solid water stack and varying the thickness of solid water between the sample and the Attix chamber measured the interface effects. The computed tomography (CT) numbers for bulk material were measured in a phantom using a wide bore CT scanner. Results: The transmission through the Onyx materials relative to solid water was approximately 98% and 97% for 16 and 6 MV beams, respectively. The interface effect shows an enhancement of approximately 2% and 1% downstream for 16 and 6 MV beams. CT numbers of approximately 2600-3000 were measured for both materials, which corresponded to an apparent relative electron density (RED) {rho}{sub e}{sup w} to water of approximately 2.7-2.9 if calculated from the commissioning data of the CT scanner. Conclusions: We performed direct measurements of attenuation and interface effects of Onyx 34 and Onyx 18 embolization materials with large samples. The introduction of embolization materials affects the dose distribution of a MV

  17. Estimating Energy Conversion Efficiency of Thermoelectric Materials: Constant Property Versus Average Property Models

    NASA Astrophysics Data System (ADS)

    Armstrong, Hannah; Boese, Matthew; Carmichael, Cody; Dimich, Hannah; Seay, Dylan; Sheppard, Nathan; Beekman, Matt

    2017-01-01

    Maximum thermoelectric energy conversion efficiencies are calculated using the conventional "constant property" model and the recently proposed "cumulative/average property" model (Kim et al. in Proc Natl Acad Sci USA 112:8205, 2015) for 18 high-performance thermoelectric materials. We find that the constant property model generally predicts higher energy conversion efficiency for nearly all materials and temperature differences studied. Although significant deviations are observed in some cases, on average the constant property model predicts an efficiency that is a factor of 1.16 larger than that predicted by the average property model, with even lower deviations for temperature differences typical of energy harvesting applications. Based on our analysis, we conclude that the conventional dimensionless figure of merit ZT obtained from the constant property model, while not applicable for some materials with strongly temperature-dependent thermoelectric properties, remains a simple yet useful metric for initial evaluation and/or comparison of thermoelectric materials, provided the ZT at the average temperature of projected operation, not the peak ZT, is used.

  18. Properties of the Bayesian Knowledge Tracing Model

    ERIC Educational Resources Information Center

    van de Sande, Brett

    2013-01-01

    Bayesian Knowledge Tracing is used very widely to model student learning. It comes in two different forms: The first form is the Bayesian Knowledge Tracing "hidden Markov model" which predicts the probability of correct application of a skill as a function of the number of previous opportunities to apply that skill and the model…

  19. Properties of the Bayesian Knowledge Tracing Model

    ERIC Educational Resources Information Center

    van de Sande, Brett

    2013-01-01

    Bayesian Knowledge Tracing is used very widely to model student learning. It comes in two different forms: The first form is the Bayesian Knowledge Tracing "hidden Markov model" which predicts the probability of correct application of a skill as a function of the number of previous opportunities to apply that skill and the model…

  20. Constitutive Modeling of the Mechanical Properties of Optical Fibers

    NASA Technical Reports Server (NTRS)

    Moeti, L.; Moghazy, S.; Veazie, D.; Cuddihy, E.

    1998-01-01

    Micromechanical modeling of the composite mechanical properties of optical fibers was conducted. Good agreement was obtained between the values of Young's modulus obtained by micromechanics modeling and those determined experimentally for a single mode optical fiber where the wave guide and the jacket are physically coupled. The modeling was also attempted on a polarization-maintaining optical fiber (PANDA) where the wave guide and the jacket are physically decoupled, and found not to applicable since the modeling required perfect bonding at the interface. The modeling utilized constituent physical properties such as the Young's modulus, Poisson's ratio, and shear modulus to establish bounds on the macroscopic behavior of the fiber.

  1. Constitutive Modeling of the Mechanical Properties of Optical Fibers

    NASA Technical Reports Server (NTRS)

    Moeti, L.; Moghazy, S.; Veazie, D.; Cuddihy, E.

    1998-01-01

    Micromechanical modeling of the composite mechanical properties of optical fibers was conducted. Good agreement was obtained between the values of Young's modulus obtained by micromechanics modeling and those determined experimentally for a single mode optical fiber where the wave guide and the jacket are physically coupled. The modeling was also attempted on a polarization-maintaining optical fiber (PANDA) where the wave guide and the jacket are physically decoupled, and found not to applicable since the modeling required perfect bonding at the interface. The modeling utilized constituent physical properties such as the Young's modulus, Poisson's ratio, and shear modulus to establish bounds on the macroscopic behavior of the fiber.

  2. Dosimetric characterization of a 2D polycrystalline CVD diamond detector

    NASA Astrophysics Data System (ADS)

    Bartoli, A.; Cupparo, I.; Baldi, A.; Scaringella, M.; Pasquini, A.; Pallotta, S.; Talamonti, C.; Bruzzi, M.

    2017-03-01

    A bidimensional pixelated dosimeter composed of two polycrystalline Chemical Vapour Deposited diamond films, 2.5 × 2.5 cm2 each placed aside, has been manufactured so as to obtain a detector with a 2 mm pitch over a total active area of 5.0 × 2.5 cm2. We performed the dosimetric characterization of the detector with an Elekta Synergy linear accelerator using a 6 MV photon beam. Uniformity maps, rise and fall times, signal repeatability, dependence on dose rate, linearity with dose and sensitivity show that the device is suitable for dosimetric evaluations in Intensity Modulated Radiation Therapy and Volumetric Modulated Arc Therapy (VMAT) treatments. Then, a first quantitative evaluation of the dose distribution in a lung VMAT treatment plan has been carried out, by comparing data from our device with Treatment Planning Sistem values by means of a Γ test, with promising results.

  3. Developing and improving a scanning system for dosimetric applications

    SciTech Connect

    Perez, P.; Galvan, V.; Castellanoa, G.; Valente, M.

    2010-08-04

    Radiotherapy is nowadays one of the most used techniques for the treatment of different pathologies, particularly cancer diseases. The accuracy regarding the application of these treatments, which are planned according to patient information, depends mainly on the dosimetric measurements of absorbed dose within irradiated tissues. The present work is devoted to the study, design and construction of an original device capable of performing visible light transmission measurements in order to analyze Fricke gel dosimeters. Furthermore, a suitable bi-dimensional positioning system along with a dedicated control system and image processing software has been adapted to the dosimetric device in order to perform 2D dose mapping. The obtained results confirm the feasibility of the proposed method, therefore suggesting its potentiality for clinical applications.

  4. [Improved program maintenance of the CIRCIS dosimetric planning system].

    PubMed

    Sevast'ianov, A I; Liutova, N A; Ratner, T G

    1983-03-01

    A special computer complex CIRCIS (Informatique, France) is used in the All-Union Cancer Research Center, USSR AMS, for the dosimetric planning of radiotherapy on 5 gamma-beam units and electron accelerator. Mathematical maintenance of the complex includes programs of the calculation of dose distribution for gamma-, inhibition and electron radiation but has no program of the calculation of the time of irradiation. The authors have devised and introduced into the complex such a program in the Fortran language that makes it possible to calculate within 2-3 min the time of irradiation for multifield rotation therapy using several units as a time, thus expediting the dosimetric planning for patients' irradiation.

  5. [Dosimetric verification of the intensity modulated radiation therapy].

    PubMed

    Zhang, Yuhai; Gao, Yang

    2010-05-01

    To research the method of dosimetric verification of the intensity modulated radiation therapy (IMRT). The IMRT treatment plans were designed by Eclipse TPS and were implemented in Varian ClinacIX LA with 6MV X-ray. The absolute point doses were measured using a PTW 0.6 cc ion chamber with UNIDOS E dosimeter and the planes dose distributions were measured using PTW 2D-Array ion chamber in the phantom. The error between the measured dose and calculated dose in the interesting points was less than 3%. The points passed ratio was more than 90% in gamma analysis method (3 mm 13%) about the plane dose distribution verification. The method of dosimetric verification of IMRT is reliable and efficient in the implementation.

  6. Integrative Modeling of Electrical Properties of Pacemaker Cardiac Cells

    NASA Astrophysics Data System (ADS)

    Grigoriev, M.; Babich, L.

    2016-06-01

    This work represents modeling of electrical properties of pacemaker (sinus) cardiac cells. Special attention is paid to electrical potential arising from transmembrane current of Na+, K+ and Ca2+ ions. This potential is calculated using the NaCaX model. In this respect, molar concentration of ions in the intercellular space which is calculated on the basis of the GENTEX model is essential. Combined use of two different models allows referring this approach to integrative modeling.

  7. An Overview of Intellectual Property and Intangible Asset Valuation Models

    ERIC Educational Resources Information Center

    Matsuura, Jeffrey H.

    2004-01-01

    This paper reviews the economic models most commonly applied to estimate the value of intellectual property and other forms of intangible assets. It highlights the key strengths and weaknesses of these models. One of the apparent weaknesses of the most commonly used valuation models is the failure to incorporate legal rights into their…

  8. Modeling of rheological properties for entangled polymer systems

    NASA Astrophysics Data System (ADS)

    Banerjee, Nilanjana

    The study of entangled polymer rheology both in the field of medicine and polymer processing has their major importance. Mechanical properties of biomolecules are studied in order to better understand cellular behavior. Similarly, industrial processing of polymers needs thorough understanding of rheology so as to improve process techniques. Work in this dissertation has been organized into three major sections. Firstly, numerical/analytical models are reviewed for describing rheological properties and mechanical behaviors of cytoskeleton. The cytoskeleton models are classified into categories according to the length scales of the phenomena of interest. The main principles and characteristics of each model are summarized and discussed by comparison with each other, thus providing a systematic understanding of biopolymer network modeling. Secondly, a new constitutive "toy" Mead-Banerjee-Park (MBP) model is developed for monodisperse entangled polymer systems, by introducing the idea of a configuration dependent friction coefficient (CDFC) and entanglement dynamics (ED) into the MLD "toy" model. The model is tested against experimental data in steady and transient extensional and shear flows. The model simultaneously captures the monotonic thinning of the extensional flow curve of polystyrene (PS) melts and the extension hardening found in PS solutions. Thirdly, the monodisperse MBP model is accordingly modified into polydisperse MBP "toy" constitutive model to predict the nonlinear viscoelastic material properties of model polydisperse systems. The polydisperse MBP toy model accurately predicts the material properties in the forward direction for transient uniaxial extension and transient shear flow.

  9. CALCULATION OF PHYSICOCHEMICAL PROPERTIES FOR ENVIRONMENTAL MODELING

    EPA Science Inventory

    Recent trends in environmental regulatory strategies dictate that EPA will rely heavily on predictive modeling to carry out the increasingly complex array of exposure and risk assessments necessary to develop scientifically defensible regulations. In response to this need, resea...

  10. CALCULATION OF PHYSICOCHEMICAL PROPERTIES FOR ENVIRONMENTAL MODELING

    EPA Science Inventory

    Recent trends in environmental regulatory strategies dictate that EPA will rely heavily on predictive modeling to carry out the increasingly complex array of exposure and risk assessments necessary to develop scientifically defensible regulations. In response to this need, resea...

  11. Monte Carlo simulation and dosimetric verification of radiotherapy beam modifiers

    NASA Astrophysics Data System (ADS)

    Spezi, E.; Lewis, D. G.; Smith, C. W.

    2001-11-01

    Monte Carlo simulation of beam modifiers such as physical wedges and compensating filters has been performed with a rectilinear voxel geometry module. A modified version of the EGS4/DOSXYZ code has been developed for this purpose. The new implementations have been validated against the BEAM Monte Carlo code using its standard component modules (CMs) in several geometrical conditions. No significant disagreements were found within the statistical errors of 0.5% for photons and 2% for electrons. The clinical applicability and flexibility of the new version of the code has been assessed through an extensive verification versus dosimetric data. Both Varian multi-leaf collimator (MLC) wedges and standard wedges have been simulated and compared against experiments for 6 MV photon beams and different field sizes. Good agreement was found between calculated and measured depth doses and lateral dose profiles along both wedged and unwedged directions for different depths and focus-to-surface distances. Furthermore, Monte Carlo-generated output factors for both open and wedged fields agreed with linac commissioning beam data within statistical uncertainties of the calculations (<3% at largest depths). Compensating filters of both low-density and high-density materials have also been successfully simulated. As a demonstration, a wax compensating filter with a complex three-dimensional concave and convex geometry has been modelled through a CT scan import. Calculated depth doses and lateral dose profiles for different field sizes agreed well with experiments. The code was used to investigate the performance of a commercial treatment planning system in designing compensators. Dose distributions in a heterogeneous water phantom emulating the head and neck region were calculated with the convolution-superposition method (pencil beam and collapsed cone implementations) and compared against those from the MC code developed herein. The new technique presented in this work is

  12. Asymptotic properties of mathematical models of excitability.

    PubMed

    Biktasheva, I V; Simitev, R D; Suckley, R; Biktashev, V N

    2006-05-15

    We analyse small parameters in selected models of biological excitability, including Hodgkin-Huxley (Hodgkin & Huxley 1952 J. Physiol.117, 500-544) model of nerve axon, Noble (Noble 1962 J. Physiol.160, 317-352) model of heart Purkinje fibres and Courtemanche et al. (Courtemanche et al. 1998 Am. J. Physiol.275, H301-H321) model of human atrial cells. Some of the small parameters are responsible for differences in the characteristic time-scales of dynamic variables, as in the traditional singular perturbation approaches. Others appear in a way which makes the standard approaches inapplicable. We apply this analysis to study the behaviour of fronts of excitation waves in spatially extended cardiac models. Suppressing the excitability of the tissue leads to a decrease in the propagation speed, but only to a certain limit; further suppression blocks active propagation and leads to a passive diffusive spread of voltage. Such a dissipation may happen if a front propagates into a tissue recovering after a previous wave, e.g. re-entry. A dissipated front does not recover even when the excitability restores. This has no analogy in FitzHugh-Nagumo model and its variants, where fronts can stop and then start again. In two spatial dimensions, dissipation accounts for breakups and self-termination of re-entrant waves in excitable media with Courtemanche et al. kinetics.

  13. Gamma dosimetric parameters in some skeletal muscle relaxants

    NASA Astrophysics Data System (ADS)

    Manjunatha, H. C.

    2017-09-01

    We have studied the attenuation of gamma radiation of energy ranging from 84 keV to 1330 keV (^{170}Tm, ^{22}Na,^{137}Cs, and ^{60}Co) in some commonly used skeletal muscle relaxants such as tubocurarine chloride, gallamine triethiodide, pancuronium bromide, suxamethonium bromide and mephenesin. The mass attenuation coefficient is measured from the attenuation experiment. In the present work, we have also proposed the direct relation between mass attenuation coefficient (μ /ρ ) and mass energy absorption coefficient (μ _{en}/ρ ) based on the nonlinear fitting procedure. The gamma dosimetric parameters such as mass energy absorption coefficient (μ _{en}/ρ ), effective atomic number (Z_{eff}), effective electron density (N_{el}), specific γ-ray constant, air kerma strength and dose rate are evaluated from the measured mass attentuation coefficient. These measured gamma dosimetric parameters are compared with the theoretical values. The measured values agree with the theoretical values. The studied gamma dosimetric values for the relaxants are useful in medical physics and radiation medicine.

  14. Proton Radiotherapy for Liver Tumors: Dosimetric Advantages Over Photon Plans

    SciTech Connect

    Wang Xiaochun Krishnan, Sunil; Zhang Xiaodong; Dong Lei; Briere, Tina; Crane, Christopher H.; Martel, Mary; Gillin, Michael; Mohan, Radhe; Beddar, Sam

    2008-01-01

    The purpose of the study is to dosimetrically investigate the advantages of proton radiotherapy over photon radiotherapy for liver tumors. The proton plan and the photon plan were designed using commercial treatment planning systems. The treatment target dose conformity and heterogeneity and dose-volume analyses of normal structures were compared between proton and photon radiotherapy for 9 patients with liver tumors. Proton radiotherapy delivered a more conformal target dose with slightly less homogeneity when compared with photon radiotherapy. Protons significantly reduced the fractional volume of liver receiving dose greater or equal to 30 Gy (V{sub 30}) and the mean liver dose. The stomach and duodenal V{sub 45} were significantly lower with the use of proton radiotherapy. The V{sub 40} and V{sub 50} of the heart and the maximum spinal cord dose were also significantly lower with the use of proton radiotherapy. Protons were better able to spare one kidney completely and deliver less dose to one (generally the left) kidney than photons. The mean dose to the total body and most critical structures was significantly decreased using protons when compared to corresponding photon plans. In conclusion, our study suggests the dosimetric benefits of proton radiotherapy over photon radiotherapy. These dosimetric advantages of proton plans may permit further dose escalation with lower risk of complications.

  15. Effective atomic numbers and electron density of dosimetric material

    PubMed Central

    Kaginelli, S. B.; Rajeshwari, T.; Sharanabasappa; Kerur, B. R.; Kumar, Anil S.

    2009-01-01

    A novel method for determination of mass attenuation coefficient of x-rays employing NaI (Tl) detector system and radioactive sources is described.in this paper. A rigid geometry arrangement and gating of the spectrometer at FWHM position and selection of absorber foils are all done following detailed investigation, to minimize the effect of small angle scattering and multiple scattering on the mass attenuation coefficient, μ/ρ, value. Firstly, for standardization purposes the mass attenuation coefficients of elemental foils such as Aluminum, Copper, Molybdenum, Tantalum and Lead are measured and then, this method is utilized for dosimetric interested material (sulfates). The experimental mass attenuation coefficient values are compared with the theoretical values to find good agreement between the theory and experiment within one to two per cent. The effective atomic numbers of the biological substitute material are calculated by sum rule and from the graph. The electron density of dosimetric material is calculated using the effective atomic number. The study has discussed in detail the attenuation coefficient, effective atomic number and electron density of dosimetric material/biological substitutes. PMID:20098566

  16. Nano-QSPR Modelling of Carbon-Based Nanomaterials Properties.

    PubMed

    Salahinejad, Maryam

    2015-01-01

    Evaluation of chemical and physical properties of nanomaterials is of critical importance in a broad variety of nanotechnology researches. There is an increasing interest in computational methods capable of predicting properties of new and modified nanomaterials in the absence of time-consuming and costly experimental studies. Quantitative Structure- Property Relationship (QSPR) approaches are progressive tools in modelling and prediction of many physicochemical properties of nanomaterials, which are also known as nano-QSPR. This review provides insight into the concepts, challenges and applications of QSPR modelling of carbon-based nanomaterials. First, we try to provide a general overview of QSPR implications, by focusing on the difficulties and limitations on each step of the QSPR modelling of nanomaterials. Then follows with the most significant achievements of QSPR methods in modelling of carbon-based nanomaterials properties and their recent applications to generate predictive models. This review specifically addresses the QSPR modelling of physicochemical properties of carbon-based nanomaterials including fullerenes, single-walled carbon nanotube (SWNT), multi-walled carbon nanotube (MWNT) and graphene.

  17. Polymer gel dosimetry for the TG-43 dosimetric characterization of a new 125I interstitial brachytherapy seed.

    PubMed

    Papagiannis, P; Pantelis, E; Georgiou, E; Karaiskos, P; Angelopoulos, A; Sakelliou, L; Stiliaris, S; Baltas, D; Seimenis, I

    2006-04-21

    In this work, a polymer gel-magnetic resonance (MR) imaging method is employed for the dosimetric characterization of a new 125I low dose rate seed (IsoSeed model I25.S17). Two vials filled with PABIG gel were prepared in-house and one new seed as well as one commercially available 125I seed of similar dose rate and well-known dosimetric parameters (IsoSeed model I25.S06) were positioned in each vial. Both seeds in each vial were MR scanned simultaneously on days 11 and 26 after implantation. The data obtained from the known seed in each vial are used to calibrate the gel dose response which, for the prolonged irradiation duration necessitated by the investigated dose rates, depends on the overall irradiation time. Data for this study are presented according to the AAPM TG-43 dosimetric formalism. Polymer gel results concerning the new seed are compared to corresponding, published dosimetric results obtained, for the purpose of the new seed clinical implementation, by our group using the established methods of Monte Carlo (MC) simulation and thermo-luminescence dosimetry (TLD). Polymer gel dosimetry yields an average dose rate constant value of lambda = (0.921 +/- 0.031) cGy h(-1) U(-1) relative to (MC)lambda = (0.929 +/- 0.014) cGy h(-1) U(-1), (TLD)lambda = (0.951 +/- 0.044) cGy h(-1) U(-1) and the average value of Lambda = (0.940 +/- 0.051) cGy h(-1) U(-1) proposed for the clinical implementation of the new seed. Results for radial dose function, g(L)(r), and anisotropy function, F(r, theta), also agree with corresponding MC calculations within experimental uncertainties which are smaller for the polymer gel method compared to TLD. It is concluded that the proposed polymer gel-magnetic resonance imaging methodology could be used at least as a supplement to the established techniques for the dosimetric characterization of new low energy and low dose rate interstitial brachytherapy seeds.

  18. Electronic properties of fractal-glass models

    NASA Astrophysics Data System (ADS)

    Schwalm, William A.; Schwalm, Mizuho K.

    1989-06-01

    Analytic results are presented for four new fractal lattices. A basic similarity between fractals and homogeneous glassy networks is the fluctuating environments of the lattice sites. The fractals are classified in terms of their local bonding geometry by comparison with glassy networks: (1) amorphous graphite, (2) two-dimensional and (3) three-dimensional Zachariasen glasses of two components, and (4) a three-component, infinitely ramified glass model with fractal dimension d¯~=3 and spectral dimension d¯¯>2.5. Localization and size scaling of corner-to-corner propagation are investigated, and it is found that there is a transition from power-law to exponential dependence in the case of model (1) at a correlation length λ~=64. Edge states appear to play an important role in propagation over distances longer than λ. Effects of ring closure and site variety are studied by making two modifications to model (1). In the first, branch cuts unroll the ring structure into a Bethe lattice. In the second, the rings are severed, resulting in a fractal tree. Results suggest that noncontinuum spectral structure is more closely related to site variety than to connectedness or ring closure in these fractal-glass models. This is similar to Anderson localization in the homogeneous random case.

  19. Renormalization of aperiodic model lattices: spectral properties

    NASA Astrophysics Data System (ADS)

    Kroon, Lars; Riklund, Rolf

    2003-04-01

    Many of the published results for one-dimensional deterministic aperiodic systems treat rather simplified electron models with either a constant site energy or a constant hopping integral. Here we present some rigorous results for more realistic mixed tight-binding systems with both the site energies and the hopping integrals having an aperiodic spatial variation. It is shown that the mixed Thue-Morse, period-doubling and Rudin-Shapiro lattices can be transformed to on-site models on renormalized lattices maintaining the individual order between the site energies. The character of the energy spectra for these mixed models is therefore the same as for the corresponding on-site models. Furthermore, since the study of electrons on a lattice governed by the Schrödinger tight-binding equation maps onto the study of elastic vibrations on a harmonic chain, we have proved that the vibrational spectra of aperiodic harmonic chains with distributions of masses determined by the Thue-Morse sequence and the period-doubling sequence are purely singular continuous.

  20. Benchmarking Dosimetric Quality Assessment of Prostate Intensity-Modulated Radiotherapy

    SciTech Connect

    Senthi, Sashendra; Gill, Suki S.; Haworth, Annette; Kron, Tomas; Cramb, Jim; Rolfo, Aldo; Thomas, Jessica; Duchesne, Gillian M.; Hamilton, Christopher H.; Joon, Daryl Lim; Bowden, Patrick; Foroudi, Farshad

    2012-02-01

    Purpose: To benchmark the dosimetric quality assessment of prostate intensity-modulated radiotherapy and determine whether the quality is influenced by disease or treatment factors. Patients and Methods: We retrospectively analyzed the data from 155 consecutive men treated radically for prostate cancer using intensity-modulated radiotherapy to 78 Gy between January 2007 and March 2009 across six radiotherapy treatment centers. The plan quality was determined by the measures of coverage, homogeneity, and conformity. Tumor coverage was measured using the planning target volume (PTV) receiving 95% and 100% of the prescribed dose (V{sub 95%} and V{sub 100%}, respectively) and the clinical target volume (CTV) receiving 95% and 100% of the prescribed dose. Homogeneity was measured using the sigma index of the PTV and CTV. Conformity was measured using the lesion coverage factor, healthy tissue conformity index, and the conformity number. Multivariate regression models were created to determine the relationship between these and T stage, risk status, androgen deprivation therapy use, treatment center, planning system, and treatment date. Results: The largest discriminatory measurements of coverage, homogeneity, and conformity were the PTV V{sub 95%}, PTV sigma index, and conformity number. The mean PTV V{sub 95%} was 92.5% (95% confidence interval, 91.3-93.7%). The mean PTV sigma index was 2.10 Gy (95% confidence interval, 1.90-2.20). The mean conformity number was 0.78 (95% confidence interval, 0.76-0.79). The treatment center independently influenced the coverage, homogeneity, and conformity (all p < .0001). The planning system independently influenced homogeneity (p = .038) and conformity (p = .021). The treatment date independently influenced the PTV V{sub 95%} only, with it being better at the start (p = .013). Risk status, T stage, and the use of androgen deprivation therapy did not influence any aspect of plan quality. Conclusion: Our study has benchmarked measures

  1. Benchmarking dosimetric quality assessment of prostate intensity-modulated radiotherapy.

    PubMed

    Senthi, Sashendra; Gill, Suki S; Haworth, Annette; Kron, Tomas; Cramb, Jim; Rolfo, Aldo; Thomas, Jessica; Duchesne, Gillian M; Hamilton, Christopher H; Joon, Daryl Lim; Bowden, Patrick; Foroudi, Farshad

    2012-02-01

    To benchmark the dosimetric quality assessment of prostate intensity-modulated radiotherapy and determine whether the quality is influenced by disease or treatment factors. We retrospectively analyzed the data from 155 consecutive men treated radically for prostate cancer using intensity-modulated radiotherapy to 78 Gy between January 2007 and March 2009 across six radiotherapy treatment centers. The plan quality was determined by the measures of coverage, homogeneity, and conformity. Tumor coverage was measured using the planning target volume (PTV) receiving 95% and 100% of the prescribed dose (V(95%) and V(100%), respectively) and the clinical target volume (CTV) receiving 95% and 100% of the prescribed dose. Homogeneity was measured using the sigma index of the PTV and CTV. Conformity was measured using the lesion coverage factor, healthy tissue conformity index, and the conformity number. Multivariate regression models were created to determine the relationship between these and T stage, risk status, androgen deprivation therapy use, treatment center, planning system, and treatment date. The largest discriminatory measurements of coverage, homogeneity, and conformity were the PTV V(95%), PTV sigma index, and conformity number. The mean PTV V(95%) was 92.5% (95% confidence interval, 91.3-93.7%). The mean PTV sigma index was 2.10 Gy (95% confidence interval, 1.90-2.20). The mean conformity number was 0.78 (95% confidence interval, 0.76-0.79). The treatment center independently influenced the coverage, homogeneity, and conformity (all p < .0001). The planning system independently influenced homogeneity (p = .038) and conformity (p = .021). The treatment date independently influenced the PTV V(95%) only, with it being better at the start (p = .013). Risk status, T stage, and the use of androgen deprivation therapy did not influence any aspect of plan quality. Our study has benchmarked measures of coverage, homogeneity, and conformity for the treatment of prostate

  2. Modelling nifedipine photodegradation, photostability and actinometric properties.

    PubMed

    Maafi, Wassila; Maafi, Mounir

    2013-11-01

    The photodegradation of drugs obeying unimolecular mechanisms such as that of nifedipine (NIF) were usually characterised in the literature by zero-, first- and second-order kinetics. This approach has been met with varying success. This paper addresses this issue and proposes a novel approach for unimolecular photodegradation kinetics. The photodegradation of the cardiovascular drug nifedipine is investigated within this framework. Experimental kinetic data of nifedipine photodegradation were obtained by continuous monochromatic irradiation and DAD analysis. Fourth-order Runge-Kutta calculated kinetic data served for the validation of the new semi-empirical integrated rate-law model proposed in this study. A new model equation has been developed and proposed which faithfully describes the kinetic behaviour of NIF in solution for non-isosbestic irradiations at wavelengths where both NIF and its photoproduct absorb. NIF absolute quantum yield values were determined and found to increase with irradiation wavelength according to a defined sigmoid relationship. The effects of increasing NIF or excipients' concentrations on NIF kinetics were successfully modelled and found to improve NIF photostability. The potential of NIF for actinometry has been explored and evaluated. A new reaction order (the so-called Φ-order) has been identified and specifically proposed for unimolecular photodegradation reactions. The semi-empirical and integrated rate-law models facilitated reliable kinetic studies of NIF photodegradation as an example of AB(1Φ) unimolecular reactions. It allowed filling a gap in kinetic studies of drugs since, thus far, thermal first-order or a combination of first- and zero- order kinetic equations were generally applied for drug photoreactions in the literature. Also, a new reaction order, the "Φ-order", has been evidenced and proposed as a specific alternative for photodegradation kinetics. Copyright © 2013 Elsevier B.V. All rights reserved.

  3. Beam properties and stability of a flattening-filter free 7 MV beam--An overview

    SciTech Connect

    Dzierma, Yvonne; Licht, Norbert; Nuesken, Frank; Ruebe, Christian

    2012-05-15

    Purpose: Several works have recently focused on flattening-filter-free (FFF) beams of linear accelerators of various companies (in particular, Varian and Elekta), but no overview as yet exists for the flattening-filter free 7XU beam (Siemens Artiste). Methods: Dosimetric properties of the 7XU beam were measured in May and September 2011. We present depth dose curves and beam profiles, output factors, and MLC transmission and assess the stability of the measurements. The 7XU beam was commissioned in the Pinnacle Superscript-Three treatment planning system (TPS), and modeling results including the spectrum are presented. Results: The percent depth dose curve of the 7XU beam is similar to the flat 6X beam line, with a slightly smaller surface dose. The beam profiles show the characteristic shape of flattening-filter free beams, with deviations between measurements of generally less than 1%. The output factors of the 7XU beam decrease more slowly than for the 6X beam. The MLC transmission is comparable but slightly less for the 7XU beam. The 7XU beam can be adequately modeled by the Pinnacle Superscript-Three TPS, with successful dosimetric verification. The spectrum of the 7XU beam has lower photon fluence up to approximately 2.5 MeV and higher fluence beyond, with a slightly higher mean energy. Conclusions: The 7XU beam has been commissioned for clinical use after successful modeling, stability checks, and dosimetric verification.

  4. Beam properties and stability of a flattening-filter free 7 MV beam-an overview.

    PubMed

    Dzierma, Yvonne; Licht, Norbert; Nuesken, Frank; Ruebe, Christian

    2012-05-01

    Several works have recently focused on flattening-filter-free (FFF) beams of linear accelerators of various companies (in particular, Varian and Elekta), but no overview as yet exists for the flattening-filter free 7XU beam (Siemens Artiste). Dosimetric properties of the 7XU beam were measured in May and September 2011. We present depth dose curves and beam profiles, output factors, and MLC transmission and assess the stability of the measurements. The 7XU beam was commissioned in the Pinnacle[superscript three] treatment planning system (TPS), and modeling results including the spectrum are presented. The percent depth dose curve of the 7XU beam is similar to the flat 6X beam line, with a slightly smaller surface dose. The beam profiles show the characteristic shape of flattening-filter free beams, with deviations between measurements of generally less than 1%. The output factors of the 7XU beam decrease more slowly than for the 6X beam. The MLC transmission is comparable but slightly less for the 7XU beam. The 7XU beam can be adequately modeled by the Pinnacle[superscript three] TPS, with successful dosimetric verification. The spectrum of the 7XU beam has lower photon fluence up to approximately 2.5 MeV and higher fluence beyond, with a slightly higher mean energy. The 7XU beam has been commissioned for clinical use after successful modeling, stability checks, and dosimetric verification.

  5. Desert Dust Properties, Modelling, and Monitoring

    NASA Technical Reports Server (NTRS)

    Kaskaoutis, Dimitris G.; Kahn, Ralph A.; Gupta, Pawan; Jayaraman, Achuthan; Bartzokas, Aristides

    2013-01-01

    This paper is just the three-page introduction to a Special Issue of Advances in Meteorology focusing on desert dust. It provides a paragraph each on 13 accepted papers, most relating to the used of satellite data to assess attributes or distribution of airborne desert dust. As guest Associate Editors of this issue, we organized the papers into a systematic whole, beginning with large-scale transport and seasonal behavior, then to regional dust transport, transport history, and climate impacts, first in the Mediterranean region, then India and central Asia, and finally focusing on transport model assessment and the use of lidar as a technique to constrain dust spatial-temporal distribution.

  6. Desert Dust Properties, Modelling, and Monitoring

    NASA Technical Reports Server (NTRS)

    Kaskaoutis, Dimitris G.; Kahn, Ralph A.; Gupta, Pawan; Jayaraman, Achuthan; Bartzokas, Aristides

    2013-01-01

    This paper is just the three-page introduction to a Special Issue of Advances in Meteorology focusing on desert dust. It provides a paragraph each on 13 accepted papers, most relating to the used of satellite data to assess attributes or distribution of airborne desert dust. As guest Associate Editors of this issue, we organized the papers into a systematic whole, beginning with large-scale transport and seasonal behavior, then to regional dust transport, transport history, and climate impacts, first in the Mediterranean region, then India and central Asia, and finally focusing on transport model assessment and the use of lidar as a technique to constrain dust spatial-temporal distribution.

  7. Poster - Thur Eve - 25: In vivo dosimetric verification of intensity-modulated radiation therapy.

    PubMed

    Chytyk-Praznik, K; Van Uytven, E; Van Beek, T; McCurdy, Bmc

    2012-07-01

    Dosimetric verification of patient treatment plans has become increasingly important due to the widespread use of complicated delivery techniques. IMRT and VMAT treatments are typically verified prior to start of the patient's course of treatment, using a point dose and/or a film measurement. Pre-treatment verification will not detect patient or machine-related errors; therefore, in vivo dosimetric verification is the only way to determine if the patient's treatment was delivered correctly. Portal images were acquired throughout the course of five prostate and six head-and-neck patient IMRT treatments. The corresponding predicted images were calculated using a previously developed portal dose image prediction algorithm, which combines a versatile fluence model with a patient scatter and EPID dose prediction model. The prostate patient image agreement was found to vary day-to-day due to rectal gas pockets and the effect of adjustable support rails on the patient couch. The head-and-neck patient images were observed to be more consistent daily, but an increased measured dose was evident at the periphery of the patient, likely due to patient weight loss. The majority of the fields agreed within 3% and 3 mm for greater than 90% of the pixels, as established by the χ-comparison. This work demonstrates the changes in patient anatomy that are detectable with the portal dose image prediction model. Prior to clinical implementation, the effect of the couch must be incorporated into the model, the image acquisition must be automatically scheduled and routine EPID QA must be undertaken to ensure the collection of high-quality EPID images. © 2012 American Association of Physicists in Medicine.

  8. Some bivariate distributions for modeling the strength properties of lumber

    Treesearch

    Richard A. Johnson; James W. Evans; David W. Green

    Accurate modeling of the joint stochastic nature of the strength properties of dimension lumber is essential to the determination of reliability-based design safety factors. This report reviews the major techniques for obtaining bivariate distributions and then discusses bivariate distributions whose marginal distributions suggest they might be useful for modeling the...

  9. Learning to Apply Models of Materials While Explaining Their Properties

    ERIC Educational Resources Information Center

    Karpin, Tiia; Juuti, Kalle; Lavonen, Jari

    2014-01-01

    Background: Applying structural models is important to chemistry education at the upper secondary level, but it is considered one of the most difficult topics to learn. Purpose: This study analyses to what extent in designed lessons students learned to apply structural models in explaining the properties and behaviours of various materials.…

  10. Predicting Plywood Properties with Wood-based Composite Models

    Treesearch

    Christopher Adam Senalik; Robert J. Ross

    2015-01-01

    Previous research revealed that stress wave nondestructive testing techniques could be used to evaluate the tensile and flexural properties of wood-based composite materials. Regression models were developed that related stress wave transmission characteristics (velocity and attenuation) to modulus of elasticity and strength. The developed regression models accounted...

  11. Thermodynamic properties of a hard/soft-magnetic bilayer model

    SciTech Connect

    Taaev, T. A. Khizriev, K. Sh.; Murtazaev, A. K.

    2016-05-15

    A model for describing the thermodynamic properties of a hard/soft-magnetic bilayer is proposed and thoroughly studied using the Monte Carlo method. Temperature dependences of the heat capacity, total magnetization, magnetizations of the hard- and soft-magnetic layers, total magnetic susceptibility, and susceptibilities of the hard- and soft-magnetic layers have been calculated by this method in the framework of the proposed model. The obtained temperature dependences of the heat capacity and magnetic susceptibility display double maxima that result from the two phase transitions that take place in the system. The influence of system dimensions on the thermodynamic properties of the model has been considered.

  12. An optical model for the microwave properties of sea ice

    NASA Technical Reports Server (NTRS)

    Gloersen, P.; Larabee, J. K.

    1981-01-01

    The complex refractive index of sea ice is modeled and used to predict the microwave signatures of various sea ice types. Results are shown to correspond well with the observed values of the complex index inferred from dielectic constant and dielectric loss measurements performed in the field, and with observed microwave signatures of sea ice. The success of this modeling procedure vis a vis modeling of the dielectric properties of sea ice constituents used earlier by several others is explained. Multiple layer radiative transfer calculations are used to predict the microwave properties of first-year sea ice with and without snow, and multiyear sea ice.

  13. Approximate Model Checking of PCTL Involving Unbounded Path Properties

    NASA Astrophysics Data System (ADS)

    Basu, Samik; Ghosh, Arka P.; He, Ru

    We study the problem of applying statistical methods for approximate model checking of probabilistic systems against properties encoded as PCTL formulas. Such approximate methods have been proposed primarily to deal with state-space explosion that makes the exact model checking by numerical methods practically infeasible for large systems. However, the existing statistical methods either consider a restricted subset of PCTL, specifically, the subset that can only express bounded until properties; or rely on user-specified finite bound on the sample path length. We propose a new method that does not have such restrictions and can be effectively used to reason about unbounded until properties. We approximate probabilistic characteristics of an unbounded until property by that of a bounded until property for a suitably chosen value of the bound. In essence, our method is a two-phase process: (a) the first phase is concerned with identifying the bound k 0; (b) the second phase computes the probability of satisfying the k 0-bounded until property as an estimate for the probability of satisfying the corresponding unbounded until property. In both phases, it is sufficient to verify bounded until properties which can be effectively done using existing statistical techniques. We prove the correctness of our technique and present its prototype implementations. We empirically show the practical applicability of our method by considering different case studies including a simple infinite-state model, and large finite-state models such as IPv4 zeroconf protocol and dining philosopher protocol modeled as Discrete Time Markov chains.

  14. Using JMatPro to model materials properties and behavior

    NASA Astrophysics Data System (ADS)

    Saunders, N.; Guo, U. K. Z.; Li, X.; Miodownik, A. P.; Schillé, J.-Ph.

    2003-12-01

    This article describes the development of a new multi-platform software program called JMatPro for calculating the properties and behavior of multi-component alloys. These properties are wide ranging, including thermophysical and physical properties (from room temperature to the liquid state), time-temperature-transformation/continuous-cooling transformation diagrams, stress/strain diagrams, proof and tensile stress, hardness, coarsening of γ' and γ″, and creep. A feature of the new program is that the calculations are based on sound physical principles rather than purely statistical methods. Thus, many of the shortcomings of methods such as regression analysis can be overcome. With this program, sensitivity to microstructure can be included for many of the properties and the true inter-relationship between properties can be developed, for example in the modeling of creep and precipitation hardening.

  15. SU-E-T-09: A Dosimetric Analysis of Various Clinically Used Bolus Materials

    SciTech Connect

    Stowe, M; Yeager, C; Zhou, F; Hand, C

    2014-06-01

    Purpose: To evaluate the dosimetric effect of various clinically used bolus materials. Methods: Materials investigated include solid water, superflab, wet gauze, wet sheets, Play-Doh{sup ™}, and gauze embedded with petroleum jelly. Each bolusing material was scanned in a Philips CT to determine the Hounsfield unit (HU) and to verify uniformity throughout the material. Using the corresponding HU, boluses of 0.5 cm and 1.0 cm thicknesses were created in the Eclipse treatment planning system (TPS) on a solid water phantom. Dose was calculated at various depths for beam energies 6 MV, 6 MeV, 9 MeV, and 12 MeV to determine the effects of each material on deposition of dose. In addition, linac-based measurements at these energies were made using a farmer chamber in solid water. Wet sheets and wet gauze were measured with various water content to quantify the effects on dose. Results: Preliminary CT scans find a range in HU of bolus materials from −120 to almost 300. There is a trend in the dose at depth based on the HU of the material; however inconsistencies are found when the bolus materials have a negative HU value. The measured data indicates that there is a linear relationship between the mass of water in a material and the dose reading, the slope of which is material dependent. Conclusion: Due to the variation in HU of the bolus materials studied, it is recommended that any new bolus be evaluated before clinical use to determine physical and dosimetric properties. If possible, patients should have bolus included in their CT scans; or if the bolus is created in the TPS, the HU should correspond to the material used. For water-soaked materials, once the bolus material is selected (gauze or sheet), the bolusing effect is only dependent on the amount of water applied to the material.

  16. Dosimetric characterization of the M-15 high-dose-rate Iridium-192 brachytherapy source using the AAPM and ESTRO formalism.

    PubMed

    Ho Than, Minh-Tri; Munro Iii, John J; Medich, David C

    2015-05-08

    The Source Production & Equipment Co. (SPEC) model M-15 is a new Iridium-192 brachytherapy source model intended for use as a temporary high-dose-rate (HDR) brachytherapy source for the Nucletron microSelectron Classic afterloading system. The purpose of this study is to characterize this HDR source for clinical application by obtaining a complete set of Monte Carlo calculated dosimetric parameters for the M-15, as recommended by AAPM and ESTRO, for isotopes with average energies greater than 50 keV. This was accomplished by using the MCNP6 Monte Carlo code to simulate the resulting source dosimetry at various points within a pseudoinfinite water phantom. These dosimetric values next were converted into the AAPM and ESTRO dosimetry parameters and the respective statistical uncertainty in each parameter also calculated and presented. The M-15 source was modeled in an MCNP6 Monte Carlo environment using the physical source specifications provided by the manufacturer. Iridium-192 photons were uniformly generated inside the iridium core of the model M-15 with photon and secondary electron transport replicated using photoatomic cross-sectional tables supplied with MCNP6. Simulations were performed for both water and air/vacuum computer models with a total of 4 × 109 sources photon history for each simulation and the in-air photon spectrum filtered to remove low-energy photons belowδ = 10 keV. Dosimetric data, including D·(r,θ), gL(r), F(r,θ), φan(r), and φ-an, and their statistical uncertainty were calculated from the output of an MCNP model consisting of an M-15 source placed at the center of a spherical water phantom of 100 cm diameter. The air kerma strength in free space, SK, and dose rate constant, Λ, also was computed from a MCNP model with M-15 Iridium-192 source, was centered at the origin of an evacuated phantom in which a critical volume containing air at STP was added 100 cm from the source center. The reference dose rate, D·(r0,θ0) ≡ D· (1cm

  17. Modeling adsorption properties of structurally deformed metal-organic frameworks using structure-property map.

    PubMed

    Jeong, WooSeok; Lim, Dae-Woon; Kim, Sungjune; Harale, Aadesh; Yoon, Minyoung; Suh, Myunghyun Paik; Kim, Jihan

    2017-07-25

    Structural deformation and collapse in metal-organic frameworks (MOFs) can lead to loss of long-range order, making it a challenge to model these amorphous materials using conventional computational methods. In this work, we show that a structure-property map consisting of simulated data for crystalline MOFs can be used to indirectly obtain adsorption properties of structurally deformed MOFs. The structure-property map (with dimensions such as Henry coefficient, heat of adsorption, and pore volume) was constructed using a large data set of over 12000 crystalline MOFs from molecular simulations. By mapping the experimental data points of deformed SNU-200, MOF-5, and Ni-MOF-74 onto this structure-property map, we show that the experimentally deformed MOFs share similar adsorption properties with their nearest neighbor crystalline structures. Once the nearest neighbor crystalline MOFs for a deformed MOF are selected from a structure-property map at a specific condition, then the adsorption properties of these MOFs can be successfully transformed onto the degraded MOFs, leading to a new way to obtain properties of materials whose structural information is lost.

  18. Spatial Modeling of Geometallurgical Properties: Techniques and a Case Study

    SciTech Connect

    Deutsch, Jared L.; Palmer, Kevin; Deutsch, Clayton V.; Szymanski, Jozef; Etsell, Thomas H.

    2016-06-15

    High-resolution spatial numerical models of metallurgical properties constrained by geological controls and more extensively by measured grade and geomechanical properties constitute an important part of geometallurgy. Geostatistical and other numerical techniques are adapted and developed to construct these high-resolution models accounting for all available data. Important issues that must be addressed include unequal sampling of the metallurgical properties versus grade assays, measurements at different scale, and complex nonlinear averaging of many metallurgical parameters. This paper establishes techniques to address each of these issues with the required implementation details and also demonstrates geometallurgical mineral deposit characterization for a copper–molybdenum deposit in South America. High-resolution models of grades and comminution indices are constructed, checked, and are rigorously validated. The workflow demonstrated in this case study is applicable to many other deposit types.

  19. CURRENT STATUS OF INDIVIDUAL DOSIMETRIC MONITORING IN UKRAINE.

    PubMed

    Chumak, V; Deniachenko, N; Makarovska, O; Mihailescu, L-C; Prykhodko, A; Voloskyi, V; Vanhavere, F

    2016-09-01

    About 50 000 workers are being occupationally exposed to radiation in Ukraine. Individual dosimetric monitoring (IDM) is provided by 77 dosimetry services and laboratories of very different scale with a number of monitored workers ranging from several persons to ∼9000. In the present work, the current status of personal dosimetry in Ukraine was studied. The First National Intercomparison (FNI) of the IDM labs was accompanied by a survey of the laboratory operation in terms of coverage, types of dosimetry provided, instrumentation and methodologies used, metrological support, data recording, etc. Totally, 34 laboratories responded to the FNI call, and 18 services with 19 different personal dosimetry systems took part in the intercomparison exercise providing 24 dosimeters each for blind irradiation to photons of 6 different qualities (ISO N-series X-rays, S-Cs and S-Co sources) in a dose range of 5-60 mSv. Performance of the dosimetry labs was evaluated according to ISO 14146 criteria of matching trumpet curves with H0 = 0.2 mSv. The test revealed that 8 of the 19 systems meet ISO 14146 criteria in full, 5 other labs show marginal performance and 6 laboratories demonstrated catastrophic quality of dosimetric results. Altogether, 18 participating labs provide dosimetric monitoring to 37 477 workers (about three-fourths of all occupationally exposed workers), usually on monthly (nuclear industry) or quarterly (rest of applications) basis. Of this number, 20 664 persons (55 %) receive completely adequate individual monitoring, and the number of personnel receiving IDM of inadequate quality counts 3054 persons. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  20. Dosimetric Characteristics of a Two-Dimensional Diode Array Detector Irradiated with Passively Scattered Proton Beams

    PubMed Central

    Liengsawangwong, Praimakorn; Sahoo, Nanayan; Ding, Xiaoning; Lii, MingFwu; Gillin, Michale T.; Zhu, Xiaorong Ronald

    2015-01-01

    Purpose: To evaluate the dosimetric characteristics of a two-dimensional (2D) diode array detector irradiated with passively scattered proton beams. Materials and Methods: A diode array detector, MapCHECK (Model 1175, Sun Nuclear, Melbourne, FL, USA) was characterized in passive-scattered proton beams. The relative sensitivity of the diodes and absolute dose calibration were determined using a 250 MeV beam. The pristine Bragg curves (PBCs) measured by MapCHECK diodes were compared with those of an ion chamber using a range shift method. The water-equivalent thickness (WET) of the diode array detector’s intrinsic buildup also was determined. The inverse square dependence, linearity, and other proton dosimetric quantities measured by MapCHECK were also compared with those of the ion chambers. The change in the absolute dose response of the MapCHECK as a function of accumulated radiation dose was used as an indicator of radiation damage to the diodes. 2D dose distribution with and without the compensator were measured and compared with the treatment planning system (TPS) calculations. Results: The WET of the MapCHECK diode’s buildup was determined to be 1.7 cm. The MapCHECK-measured PBC were virtually identical to those measured by a parallel-plate ion chamber for 160, 180, and 250 MeV proton beams. The inverse square results of the MapCHECK were within ±0.4% of the ion chamber results. The linearity of MapCHECK results was within 1% of those from the ion chamber as measured in the range between 10 and 300 MU. All other dosimetric quantities were within 1.3% of the ion chamber results. The 2D dose distributions for non-clinical fields without compensator and the patient treatment fields with the compensator were consistent with the TPS results. The absolute dose response of the MapCHECK was changed by 7.4% after an accumulated dose increased by 170 Gy. Conclusions: The MapCHECK is a convenient and useful tool for 2D dose distribution measurements using passively

  1. Poster - Thur Eve - 12: Dosimetric manifestation of harmonic mode imaging for seed implant brachytherapy.

    PubMed

    Sandhu, G; Angyalfi, S; Dunscombe, P; Khan, R

    2012-07-01

    To demonstrate the dosimetric effects of observer variability in defining the prostate and critical organs, using Tissue Harmonic (H) ultrasound imaging mode for permanent seed implant brachytherapy. Images were acquired using a B -K medical 8848 probe with Brightness (B) and H mode for ten prostate brachytherapy patients. The prostate, rectum and urethra were contoured independently by five observers. The clinically used treatment plans based on B mode imaging fulfilling the dosimetric criteria were applied on these contours. Dosimetric parameters (prostate: D90, V100 and V200; rectum: V100; urethra: V140, V150 and V160) were computed using SPOT PRO™ planning system. Interobserver variability in dosimetric parameters was tested using standard deviations as percentages of means. Two-factor analysis of variances showed significant (p<0.05) interobserver variability in all dosimetric parameters for both modes. Interobserver agreement in dosimetric parameters improves in H mode due to improved interobserver consistency in contouring these organs on H mode images compared to B mode. There is no significant difference observed (paired student t test, p>0.05) in the mean values of dosimetric parameters in H and B mode for prostate and critical organs. H mode due to its better image quality helped to improve the interobserver agreement in contouring the prostate and critical organs and hence better interobserver consistency in all dosimetric parameter. Because the difference in the mean value of dosimetric parameters between two imaging modes is not statistically significant, H mode does not appear to offer any clinical advantages in terms of improving the dosimetric outcome. © 2012 American Association of Physicists in Medicine.

  2. Patient doses and dosimetric evaluations in interventional cardiology.

    PubMed

    Bor, Dogan; Olğar, Turan; Toklu, Türkay; Cağlan, Ayça; Onal, Elif; Padovani, Renato

    2009-03-01

    Interventional cardiological examinations may be associated with excessive radiation exposures which may cause skin injuries and higher probabilities of stochastic effects. Dose-area product (DAP) and skin doses of 325 patients were measured using alternative dosimetric techniques for different cardiological examinations. Data were collected from five different systems with the involvement of 11 cardiologists. All these dosimetric information has been collected separately for each of 10 projections together with the exposure parameters of X-ray systems. Mean DAP values measured with a transparent ion chamber were 49.1 Gy cm(2), 66.8 Gy cm(2), 106.9 Gy cm(2) and 124.7 Gy cm(2), respectively, for coronary angiography (CA), percutaneous transluminal coronary angioplasty (PTCA) or stent (PT-SI), coronary angiography and/or PTCA and/or stent (CA-PT-SI), and ablation examinations. Radiochromic films, thermoluminescent dosimeters (TLD) and point measurement of air kerma (AK) were carried out for skin dose assessments. Skin doses of 23 patients measured with radiochromic films were found to be between 2 Gy and 6 Gy. Although the complexity of the procedures was the major reason for these excessive doses, considerable contributions of high X-ray output of some fluoroscopy units were also noticed. In addition to the direct measurement of DAP, alternative DAP values were also determined from the skin dose measurement techniques; exposed areas were summed on digitized radiochromic films in one technique, The product of AK reading with X-ray field size measured at the patient entrance using slow X-ray films was taken as another DAP. Good correlations were found among the DAP results and also between the entrance skin doses calculated from AK measurements and direct DAP readings (R(2)=0.91). A trigger DAP value of 130 Gy cm(2) for the 2 Gy of skin doses was derived from this relationship. Collection of dosimetric data for each projection was also investigated regarding a

  3. Analytical model for nanoscale viscoelastic properties characterization using dynamic nanoindentation

    NASA Astrophysics Data System (ADS)

    Yuya, Philip A.; Patel, Nimitt G.

    2014-08-01

    In the last few decades, nanoindentation has gained widespread acceptance as a technique for materials properties characterization at micron and submicron length scales. Accurate and precise characterization of material properties with a nanoindenter is critically dependent on the ability to correctly model the response of the test equipment in contact with the material. In dynamic nanoindention analysis, a simple Kelvin-Voigt model is commonly used to capture the viscoelastic response. However, this model oversimplifies the response of real viscoelastic materials such as polymers. A model is developed that captures the dynamic nanoindentation response of a viscoelastic material. Indenter tip-sample contact forces are modelled using a generalized Maxwell model. The results on a silicon elastomer were analysed using conventional two element Kelvin-Voigt model and contrasted to analysis done using the Maxwell model. The results show that conventional Kelvin-Voigt model overestimates the storage modulus of the silicone elastomer by ~30%. Maxwell model represents a significant improvement in capturing the viscoelastic material behaviour over the Voigt model.

  4. Surface properties of native human plasma lipoproteins and lipoprotein models.

    PubMed Central

    Massey, J B; Pownall, H J

    1998-01-01

    Plasma lipoprotein surface properties are important but poorly understood determinants of lipoprotein catabolism. To elucidate the relation between surface properties and surface reactivity, the physical properties of surface monolayers of native lipoproteins and lipoprotein models were investigated by fluorescent probes of surface lipid fluidity, surface lateral diffusion, and interfacial polarity, and by their reactivity to Naja melanoleuca phospholipase A2 (PLA2). Native lipoproteins were human very low, low-, and subclass 3 high-density lipoproteins (VLDL, LDL, and HDL3); models were 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) or its ether analog in single-bilayer vesicles, large and small microemulsions of POPC and triolein, and reassembled HDL (apolipoprotein A-I plus phospholipid). Among lipoproteins, surface lipid fluidity increased in the order HDL3 < LDL < VLDL, varying inversely with their (protein + cholesterol)/phospholipid ratios. Models resembled VLDL in fluidity. Both lateral mobility in the surface monolayer and polarity of the interfacial region were lower in native lipoproteins than in models. Among native lipoproteins and models, increased fluidity in the surface monolayer was associated with increased reactivity to PLA2. Addition of cholesterol (up to 20 mol%) to models had little effect on PLA2 activity, whereas the addition of apolipoprotein C-III stimulated it. Single-bilayer vesicles, phospholipid-triolein microemulsions, and VLDL have surface monolayers that are quantitatively similar, and distinct from those of LDL and HDL3. Surface property and enzymatic reactivity differences between lipoproteins and models were associated with differences in surface monolayer protein and cholesterol contents. Thus differences in the surface properties that regulate lipolytic reactivity are a predictable function of surface composition. PMID:9533698

  5. Properties Preservation in Distributed Execution of Petri Nets Models

    NASA Astrophysics Data System (ADS)

    Costa, Anikó; Barbosa, Paulo; Gomes, Luís; Ramalho, Franklin; Figueiredo, Jorge; Junior, Antônio

    Model-based development for embedded system design has been used to support the increase of system's complexity. Several modeling formalisms are well matched for usage within this area. One of the goals of this work is to contribute to the usage of Petri nets as system specification language within model-based development of embedded systems having MDA proposals as a reference for the development flow. Distributed execution of the Petri net model is achieved through model partitioning into sub-modules. System decomposition is obtained through net splitting operation. Two types of implementation platforms were considered: compliant and non-compliant with zero time delay for communication between modules. Using model-checking techniques, properties associated with the execution of the distributed models in both types of platforms were compared with the execution of the initial (centralized) Petri net model.

  6. Dosimetric considerations of interstitial photodynamic therapy of the canine prostate mediated by intra-arterially administered hypocrellin derivative

    NASA Astrophysics Data System (ADS)

    Liu, Weiyang; Dickey, Dwayne J.; Xiao, Zhengwen; Moore, Ronald B.; Tulip, John

    2008-02-01

    Interstitial photodynamic therapy (iPDT) is a promising minimally invasive treatment modality for locally confined prostate cancer. Therapeutically excited at 635nm, the photophysical properties of SL-052 (a novel hypocrellin derivative photosensitizer) lend themselves uniquely to iPDT, facilitating real-time monitoring. Under 635nm excitation, SL-052 exhibits near infrared fluorescence, allowing both photosensitizer fluorescence and tissue transmissivity to be continuously monitored. The absorption and fluorescence characteristics of SL-052 in vivo and in vitro are first illustrated. SL-052 mediated iPDT of canine prostate was performed with a novel switched light delivery system and novel intra-arterial drug delivery method. A preliminary examination of the dosimetric properties of intra-arterial iPDT is presented, focusing on transmissivity dynamics. Spectrofluorimetry results relating specifically to the unique photophysical properties of SL-052 iPDT are also included.

  7. Spatiotemporal properties of microsaccades: Model predictions and experimental tests

    NASA Astrophysics Data System (ADS)

    Zhou, Jian-Fang; Yuan, Wu-Jie; Zhou, Zhao

    2016-10-01

    Microsaccades are involuntary and very small eye movements during fixation. Recently, the microsaccade-related neural dynamics have been extensively investigated both in experiments and by constructing neural network models. Experimentally, microsaccades also exhibit many behavioral properties. It’s well known that the behavior properties imply the underlying neural dynamical mechanisms, and so are determined by neural dynamics. The behavioral properties resulted from neural responses to microsaccades, however, are not yet understood and are rarely studied theoretically. Linking neural dynamics to behavior is one of the central goals of neuroscience. In this paper, we provide behavior predictions on spatiotemporal properties of microsaccades according to microsaccade-induced neural dynamics in a cascading network model, which includes both retinal adaptation and short-term depression (STD) at thalamocortical synapses. We also successfully give experimental tests in the statistical sense. Our results provide the first behavior description of microsaccades based on neural dynamics induced by behaving activity, and so firstly link neural dynamics to behavior of microsaccades. These results indicate strongly that the cascading adaptations play an important role in the study of microsaccades. Our work may be useful for further investigations of the microsaccadic behavioral properties and of the underlying neural dynamical mechanisms responsible for the behavioral properties.

  8. Database and Interim Glass Property Models for Hanford HLW Glasses

    SciTech Connect

    Hrma, Pavel R.; Piepel, Gregory F.; Vienna, John D.; Cooley, Scott K.; Kim, Dong-Sang; Russell, Renee L.

    2001-07-24

    The purpose of this report is to provide a methodology for an increase in the efficiency and a decrease in the cost of vitrifying high-level waste (HLW) by optimizing HLW glass formulation. This methodology consists in collecting and generating a database of glass properties that determine HLW glass processability and acceptability and relating these properties to glass composition. The report explains how the property-composition models are developed, fitted to data, used for glass formulation optimization, and continuously updated in response to changes in HLW composition estimates and changes in glass processing technology. Further, the report reviews the glass property-composition literature data and presents their preliminary critical evaluation and screening. Finally the report provides interim property-composition models for melt viscosity, for liquidus temperature (with spinel and zircon primary crystalline phases), and for the product consistency test normalized releases of B, Na, and Li. Models were fitted to a subset of the screened database deemed most relevant for the current HLW composition region.

  9. Modeling anisotropic Maxwell-Jüttner distributions: derivation and properties

    NASA Astrophysics Data System (ADS)

    Livadiotis, George

    2016-12-01

    In this paper we develop a model for the anisotropic Maxwell-Jüttner distribution and examine its properties. First, we provide the characteristic conditions that the modeling of consistent and well-defined anisotropic Maxwell-Jüttner distributions needs to fulfill. Then, we examine several models, showing their possible advantages and/or failures in accordance to these conditions. We derive a consistent model, and examine its properties and its connection with thermodynamics. We show that the temperature equals the average of the directional temperature-like components, as it holds for the classical, anisotropic Maxwell distribution. We also derive the internal energy and Boltzmann-Gibbs entropy, where we show that both are maximized for zero anisotropy, that is, the isotropic Maxwell-Jüttner distribution.

  10. Modeling multidomain hydraulic properties of shrink-swell soils

    NASA Astrophysics Data System (ADS)

    Stewart, Ryan D.; Abou Najm, Majdi R.; Rupp, David E.; Selker, John S.

    2016-10-01

    Shrink-swell soils crack and become compacted as they dry, changing properties such as bulk density and hydraulic conductivity. Multidomain models divide soil into independent realms that allow soil cracks to be incorporated into classical flow and transport models. Incongruously, most applications of multidomain models assume that the porosity distributions, bulk density, and effective saturated hydraulic conductivity of the soil are constant. This study builds on a recently derived soil shrinkage model to develop a new multidomain, dual-permeability model that can accurately predict variations in soil hydraulic properties due to dynamic changes in crack size and connectivity. The model only requires estimates of soil gravimetric water content and a minimal set of parameters, all of which can be determined using laboratory and/or field measurements. We apply the model to eight clayey soils, and demonstrate its ability to quantify variations in volumetric water content (as can be determined during measurement of a soil water characteristic curve) and transient saturated hydraulic conductivity, Ks (as can be measured using infiltration tests). The proposed model is able to capture observed variations in Ks of one to more than two orders of magnitude. In contrast, other dual-permeability models assume that Ks is constant, resulting in the potential for large error when predicting water movement through shrink-swell soils. Overall, the multidomain model presented here successfully quantifies fluctuations in the hydraulic properties of shrink-swell soil matrices, and are suitable for use in physical flow and transport models based on Darcy's Law, the Richards Equation, and the advection-dispersion equation.

  11. Cement-aggregate compatibility and structure property relationships including modelling

    SciTech Connect

    Jennings, H.M.; Xi, Y.

    1993-07-15

    The role of aggregate, and its interface with cement paste, is discussed with a view toward establishing models that relate structure to properties. Both short (nm) and long (mm) range structure must be considered. The short range structure of the interface depends not only on the physical distribution of the various phases, but also on moisture content and reactivity of aggregate. Changes that occur on drying, i.e. shrinkage, may alter the structure which, in turn, feeds back to alter further drying and shrinkage. The interaction is dynamic, even without further hydration of cement paste, and the dynamic characteristic must be considered in order to fully understand and model its contribution to properties. Microstructure and properties are two subjects which have been pursued somewhat separately. This review discusses both disciplines with a view toward finding common research goals in the future. Finally, comment is made on possible chemical reactions which may occur between aggregate and cement paste.

  12. Mechanical Properties of Nanostructured Materials Determined Through Molecular Modeling Techniques

    NASA Technical Reports Server (NTRS)

    Clancy, Thomas C.; Gates, Thomas S.

    2005-01-01

    The potential for gains in material properties over conventional materials has motivated an effort to develop novel nanostructured materials for aerospace applications. These novel materials typically consist of a polymer matrix reinforced with particles on the nanometer length scale. In this study, molecular modeling is used to construct fully atomistic models of a carbon nanotube embedded in an epoxy polymer matrix. Functionalization of the nanotube which consists of the introduction of direct chemical bonding between the polymer matrix and the nanotube, hence providing a load transfer mechanism, is systematically varied. The relative effectiveness of functionalization in a nanostructured material may depend on a variety of factors related to the details of the chemical bonding and the polymer structure at the nanotube-polymer interface. The objective of this modeling is to determine what influence the details of functionalization of the carbon nanotube with the polymer matrix has on the resulting mechanical properties. By considering a range of degree of functionalization, the structure-property relationships of these materials is examined and mechanical properties of these models are calculated using standard techniques.

  13. A Chemical Properties Simulator to Support Integrated Environmental Modeling

    EPA Science Inventory

    Users of Integrated Environmental Modeling (IEM) systems are responsible for defining individual chemicals and their properties, a process that is time-consuming at best and overwhelming at worst, especially for new chemicals with new structures. A software tool is needed to allo...

  14. A Chemical Properties Simulator to Support Integrated Environmental Modeling (proceeding)

    EPA Science Inventory

    Users of Integrated Environmental Modeling (IEM) systems are responsible for defining individual chemicals and their properties, a process that is time-consuming at best and overwhelming at worst, especially for new chemicals with new structures. A software tool is needed to allo...

  15. A Chemical Properties Simulator to Support Integrated Environmental Modeling

    EPA Science Inventory

    Users of Integrated Environmental Modeling (IEM) systems are responsible for defining individual chemicals and their properties, a process that is time-consuming at best and overwhelming at worst, especially for new chemicals with new structures. A software tool is needed to allo...

  16. A Chemical Properties Simulator to Support Integrated Environmental Modeling (proceeding)

    EPA Science Inventory

    Users of Integrated Environmental Modeling (IEM) systems are responsible for defining individual chemicals and their properties, a process that is time-consuming at best and overwhelming at worst, especially for new chemicals with new structures. A software tool is needed to allo...

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

    SciTech Connect

    Wu, L; Huang, B; Rowedder, B; Ma, B; Kuang, Y

    2014-06-15

    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 delivered 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

  18. The dosimetric impact of gadolinium-based contrast media in GBM brain patient plans for a MRI-Linac

    NASA Astrophysics Data System (ADS)

    Bilal Ahmad, Syed; Paudel, Moti Raj; Sarfehnia, Arman; Kim, Anthony; Pang, Geordi; Ruschin, Mark; Sahgal, Arjun; Keller, Brian M.

    2017-08-01

    Dosimetric effects of gadolinium based contrast media (Gadovist) were evaluated for the Elekta MRI linear accelerator using the research version of the Monaco treatment planning system (TPS). In order to represent a gadolinium uptake, the contrast was manually assigned to a phantom as well as to the gross tumour volume (GTV) of 6 glioblastoma multiforme (GBM) patients. A preliminary estimate of the dose enhancement, due to gadolinium, was performed using the phantom irradiated with a single beam. A more complicated assessment was performed for the GBM patients using a 7 field IMRT technique. The material table in Monaco was modified in order to identify the presence of a non-biological material. The dose distribution was modelled using GPUMCD (MC algorithm in Monaco) for an unmodified (or default) material table (DMT) as well as for a modified (or custom) material table (CMT) for both the phantom and patients. Various concentrations ranging between 8 and 157 mg ml-1 were used to represent the gadolinium uptake in the patient’s GTV. It was assumed that the gadolinium concentration remained the same for the entire course of radiation treatment. Results showed that at the tissue-Gadovist interface, inside the phantom, dose scored using the DMT was 7% lower compared to that using the CMT for 157 mg ml-1 concentration of gadolinium. Dosimetric differences in the case of the patient study were measured using the DVH parameters. D 50% was higher by 6% when the DMT was used compared to the CMT for dose modelling for a gadolinium concentration of 157 mg ml-1. This difference decreased gradually with decreasing concentration of gadolinium. It was concluded that dosimetric differences can be quantified in Monaco if the tumour-gadolinium concentration is more than 23 mg ml-1. If the gadolinium concentration is lower than 23 mg ml-1, then a correction for the presence of gadolinium may not be necessary in the TPS.

  19. Lifelong modelling of properties for materials with technological memory

    NASA Astrophysics Data System (ADS)

    Falaleev, AP; Meshkov, VV; Vetrogon, AA; Ogrizkov, SV; Shymchenko, AV

    2016-10-01

    An investigation of real automobile parts produced from dual phase steel during standard periods of life cycle is presented, which considers such processes as stamping, exploitation, automobile accident, and further repair. The development of the phenomenological model of the mechanical properties of such parts was based on the two surface plastic theory of Chaboche. As a consequence of the composite structure of dual phase steel, it was shown that local mechanical properties of parts produced from this material change significantly their during their life cycle, depending on accumulated plastic deformations and thermal treatments. Such mechanical property changes have a considerable impact on the accuracy of the computer modelling of automobile behaviour. The most significant errors of modelling were obtained at the critical operating conditions, such as crashes and accidents. The model developed takes into account the kinematics (Bauschinger effect), isotropic hardening, non-linear elastic steel behaviour and changes caused by the thermal treatment. Using finite element analysis, the model allows the evaluation of the passive safety of a repaired car body, and enables increased restoration accuracy following an accident. The model was confirmed experimentally for parts produced from dual phase steel DP780.

  20. Comprehensive Australasian multicentre dosimetric intercomparison: issues, logistics and recommendations.

    PubMed

    Ebert, M A; Harrison, K M; Cornes, D; Howlett, S J; Joseph, D J; Kron, T; Hamilton, C S; Denham, J W

    2009-02-01

    The present paper describes the logistics of the 2004-2008 Australasian Level III Dosimetry Intercomparison. Dosimetric intercomparisons (or 'audits') can be used in radiotherapy to evaluate the accuracy and quality of radiation delivery. An intercomparison was undertaken in New Zealand and Australia to evaluate the feasibility and logistics of ongoing dosimetric intercomparisons that evaluate all steps in the radiotherapy treatment process, known as a 'Level III' intercomparison. The study commenced in 2002 with the establishment of a study team, definition of the study protocol, acquisition of appropriate equipment and recruitment of participating radiotherapy centres. Measurements were undertaken between October 2004 and March 2008, and included collation of data on time, costs and logistics of the study. Forty independent Australian and New Zealand radiotherapy centres agreed to participate. Measurement visits were made to 37 of these centres. Data is presented on the costs of the study and the level of support required. The study involved the participation of 16 staff at the study centre who invested over 4000 hours in the study, and of over 200 professionals at participating centres. Recommendations are provided for future phantom-based intercomparisons. It is hoped that the present paper will be of benefit to any centres or groups contemplating similar activities by identifying the processes involved in establishing the study, the potential hazards and pitfalls, and expected resource requirements.

  1. Determination of dosimetric quantities in pediatric abdominal computed tomography scans*

    PubMed Central

    Jornada, Tiago da Silva; da Silva, Teógenes Augusto

    2014-01-01

    Objective Aiming at contributing to the knowledge on doses in computed tomography (CT), this study has the objective of determining dosimetric quantities associated with pediatric abdominal CT scans, comparing the data with diagnostic reference levels (DRL). Materials and methods The study was developed with a Toshiba Asteion single-slice CT scanner and a GE BrightSpeed multi-slice CT unit in two hospitals. Measurements were performed with a pencil-type ionization chamber and a 16 cm-diameter polymethylmethacrylate trunk phantom. Results No significant difference was observed in the values for weighted air kerma index (CW), but the differences were relevant in values for volumetric air kerma index (CVOL), air kerma-length product (PKL,CT) and effective dose. Conclusion Only the CW values were lower than the DRL, suggesting that dose optimization might not be necessary. However, PKL,CT and effective dose values stressed that there still is room for reducing pediatric radiation doses. The present study emphasizes the importance of determining all dosimetric quantities associated with CT scans. PMID:25741103

  2. Dosimetric characteristics of LKB:Cu,P solid TL detector

    NASA Astrophysics Data System (ADS)

    Hashim, S.; Alajerami, Y. S. M.; Ghoshal, S. K.; Saleh, M. A.; Saripan, M. I.; Kadir, A. B. A.; Bradley, D. A.; Alzimami, K.

    2014-11-01

    The dosimetric characteristics of newly developed borate glass dosimeter modified with lithium and potassium carbonate (LKB) and co-doped with CuO and NH4H2PO4 are reported. Broad peaks in the absence of any sharp peak confirms the amorphous nature of the prepared glass. A simple glow curve of Cu doped sample is observed with a single prominent peak (Tm) at 220 °C. The TL intensity response shows an enhancement of ~100 times due to the addition of CuO (0.1 mol%) to LKB compound. A further enhancement of the intensity by a factor of 3 from the addition of 0.25 mol% NH4H2PO4 as a co-dopant impurity is attributed to the creation of extra electron traps with consequent increase in energy transfer of radiation recombination centers. The TL yield performance of LKB:Cu,P with Zeff ≈8.92 is approximately seventeen times less sensitive compared to LiF:Mg,Ti (TLD-100). The proposed dosimeter shows good linearity up to 103 Gy, minimal fading and photon energy independence. These attractive features offered by our dosimeter is expected to pave the way towards dosimetric applications.

  3. Dosimetric precision of an ion beam tracking system

    PubMed Central

    2010-01-01

    Background Scanned ion beam therapy of intra-fractionally moving tumors requires motion mitigation. GSI proposed beam tracking and performed several experimental studies to analyse the dosimetric precision of the system for scanned carbon beams. Methods A beam tracking system has been developed and integrated in the scanned carbon ion beam therapy unit at GSI. The system adapts pencil beam positions and beam energy according to target motion. Motion compensation performance of the beam tracking system was assessed by measurements with radiographic films, a range telescope, a 3D array of 24 ionization chambers, and cell samples for biological dosimetry. Measurements were performed for stationary detectors and moving detectors using the beam tracking system. Results All detector systems showed comparable data for a moving setup when using beam tracking and the corresponding stationary setup. Within the target volume the mean relative differences of ionization chamber measurements were 0.3% (1.5% standard deviation, 3.7% maximum). Film responses demonstrated preserved lateral dose gradients. Measurements with the range telescope showed agreement of Bragg peak depth under motion induced range variations. Cell survival experiments showed a mean relative difference of -5% (-3%) between measurements and calculations within the target volume for beam tracking (stationary) measurements. Conclusions The beam tracking system has been successfully integrated. Full functionality has been validated dosimetrically in experiments with several detector types including biological cell systems. PMID:20591160

  4. Dosimetric algorithm to reproduce isodose curves obtained from a LINAC.

    PubMed

    Estrada Espinosa, Julio Cesar; Martínez Ovalle, Segundo Agustín; Pereira Benavides, Cinthia Kotzian

    2014-01-01

    In this work isodose curves are obtained by the use of a new dosimetric algorithm using numerical data from percentage depth dose (PDD) and the maximum absorbed dose profile, calculated by Monte Carlo in a 18 MV LINAC. The software allows reproducing the absorbed dose percentage in the whole irradiated volume quickly and with a good approximation. To validate results an 18 MV LINAC with a whole geometry and a water phantom were constructed. On this construction, the distinct simulations were processed by the MCNPX code and then obtained the PDD and profiles for the whole depths of the radiation beam. The results data were used by the code to produce the dose percentages in any point of the irradiated volume. The absorbed dose for any voxel's size was also reproduced at any point of the irradiated volume, even when the voxels are considered to be of a pixel's size. The dosimetric algorithm is able to reproduce the absorbed dose induced by a radiation beam over a water phantom, considering PDD and profiles, whose maximum percent value is in the build-up region. Calculation time for the algorithm is only a few seconds, compared with the days taken when it is carried out by Monte Carlo.

  5. Dosimetric Algorithm to Reproduce Isodose Curves Obtained from a LINAC

    PubMed Central

    Estrada Espinosa, Julio Cesar; Martínez Ovalle, Segundo Agustín; Pereira Benavides, Cinthia Kotzian

    2014-01-01

    In this work isodose curves are obtained by the use of a new dosimetric algorithm using numerical data from percentage depth dose (PDD) and the maximum absorbed dose profile, calculated by Monte Carlo in a 18 MV LINAC. The software allows reproducing the absorbed dose percentage in the whole irradiated volume quickly and with a good approximation. To validate results an 18 MV LINAC with a whole geometry and a water phantom were constructed. On this construction, the distinct simulations were processed by the MCNPX code and then obtained the PDD and profiles for the whole depths of the radiation beam. The results data were used by the code to produce the dose percentages in any point of the irradiated volume. The absorbed dose for any voxel's size was also reproduced at any point of the irradiated volume, even when the voxels are considered to be of a pixel's size. The dosimetric algorithm is able to reproduce the absorbed dose induced by a radiation beam over a water phantom, considering PDD and profiles, whose maximum percent value is in the build-up region. Calculation time for the algorithm is only a few seconds, compared with the days taken when it is carried out by Monte Carlo. PMID:25045398

  6. Multicellular dosimetric chain for molecular radiotherapy exemplified with dose simulations on 3D cell spheroids.

    PubMed

    Reijonen, Vappu; Kanninen, Liisa K; Hippeläinen, Eero; Lou, Yan-Ru; Salli, Eero; Sofiev, Alexey; Malinen, Melina; Paasonen, Timo; Yliperttula, Marjo; Kuronen, Antti; Savolainen, Sauli

    2017-08-01

    Absorbed radiation dose-response relationships are not clear in molecular radiotherapy (MRT). Here, we propose a voxel-based dose calculation system for multicellular dosimetry in MRT. We applied confocal microscope images of a spherical cell aggregate i.e. a spheroid, to examine the computation of dose distribution within a tissue from the distribution of radiopharmaceuticals. A confocal microscope Z-stack of a human hepatocellular carcinoma HepG2 spheroid was segmented using a support-vector machine algorithm and a watershed function. Heterogeneity in activity uptake was simulated by selecting a varying amount of the cell nuclei to contain (111)In, (125)I, or (177)Lu. Absorbed dose simulations were carried out using vxlPen, a software application based on the Monte Carlo code PENELOPE. We developed a schema for radiopharmaceutical dosimetry. The schema utilizes a partially supervised segmentation method for cell-level image data together with a novel main program for voxel-based radiation dose simulations. We observed that for (177)Lu, radiation cross-fire enabled full dose coverage even if the radiopharmaceutical had accumulated to only 60% of the spheroid cells. This effect was not found with (111)In and (125)I. Using these Auger/internal conversion electron emitters seemed to guarantee that only the cells with a high enough activity uptake will accumulate a lethal amount of dose, while neighboring cells are spared. We computed absorbed radiation dose distributions in a 3D-cultured cell spheroid with a novel multicellular dosimetric chain. Combined with pharmacological studies in different tissue models, our cell-level dosimetric calculation method can clarify dose-response relationships for radiopharmaceuticals used in MRT. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

  7. Determination of dosimetric parameters for shielded 153Gd source in prostate cancer brachytherapy

    PubMed Central

    Ghorbani, Mahdi; Ghatei, Najmeh; Mehrpouyan, Mohammad; Meigooni, Ali S.; Shahraini, Ramin

    2017-01-01

    Abstract Background Interstitial rotating shield brachytherapy (I-RSBT) is a recently developed method for treatment of prostate cancer. In the present study TG-43 dosimetric parameters of a 153Gd source were obtained for use in I-RSBT. Materials and methods A 153Gd source located inside a needle including a Pt shield and an aluminum window was simulated using MCNPX Monte Carlo code. Dosimetric parameters of this source model, including air kerma strength, dose rate constant, radial dose function and 2D anisotropy function, with and without the shields were calculated according to the TG-43 report. Results The air kerma strength was found to be 6.71 U for the non-shielded source with 1 GBq activity. This value was found to be 0.04 U and 6.19 U for the Pt shield and Al window cases, respectively. Dose rate constant for the non-shielded source was found to be 1.20 cGy/(hU). However, for a shielded source with Pt and aluminum window, dose rate constants were found to be 0.07 cGy/(hU) and 0.96 cGy/(hU), on the shielded and window sides, respectively. The values of radial dose function and anisotropy function were tabulated for these sources. Additionally, isodose curves were drawn for sources with and without shield, in order to evaluate the effect of shield on dose distribution. Conclusions Existence of the Pt shield may greatly reduce the dose to organs at risk and normal tissues which are located toward the shielded side. The calculated air kerma strength, dose rate constant, radial dose function and 2D anisotropy function data for the 153Gd source for the non-shielded and the shielded sources can be used in the treatment planning system (TPS). PMID:28265239

  8. Dosimetric implications of the infiltrated injection

    SciTech Connect

    Castronovo, F.P.; McKusick, K.A.; Strauss, H.W.

    1984-01-01

    Following inadvertent infiltration of a radiopharmaceutical, there is variable and uncertain uptake in target tissue. Concomitantly, there is also a concern for the radiation dose to the infiltrated site. This investigation determined the clearance and radiation burdens from various radiopharmaceutical infiltrates in a rat model. Nine separate sites were studied for: Tc-99m microspheres; Tc-99m MDP; Ga-67 citrate; and Tl-201 chloride. Following sc injection on the shaven posteriors of anesthetized adult male Sprague-Dawley rats, gamma camera and computer data were collected up to 24 hours. The resulting data were expressed semilogarithmically as the mean (N = 9) of the ''% retained at site'' as a f(time) after injection. Nonparticulate agents showed a tri-exponential release pattern from each site, whereas the microspheres remained for an extended period of time. Using these pharma-cokinetic curves, the % remaining at each site for various times, and rems/mCi per lcc infiltrate was determined.

  9. Effects of model layer simplification using composite hydraulic properties

    USGS Publications Warehouse

    Kuniansky, Eve L.; Sepulveda, Nicasio; Elango, Lakshmanan

    2011-01-01

    Groundwater provides much of the fresh drinking water to more than 1.5 billion people in the world (Clarke et al., 1996) and in the United States more that 50 percent of citizens rely on groundwater for drinking water (Solley et al., 1998). As aquifer systems are developed for water supply, the hydrologic system is changed. Water pumped from the aquifer system initially can come from some combination of inducing more recharge, water permanently removed from storage, and decreased groundwater discharge. Once a new equilibrium is achieved, all of the pumpage must come from induced recharge and decreased discharge (Alley et al., 1999). Further development of groundwater resources may result in reductions of surface water runoff and base flows. Competing demands for groundwater resources require good management. Adequate data to characterize the aquifers and confining units of the system, like hydrologic boundaries, groundwater levels, streamflow, and groundwater pumping and climatic data for recharge estimation are to be collected in order to quantify the effects of groundwater withdrawals on wetlands, streams, and lakes. Once collected, three-dimensional (3D) groundwater flow models can be developed and calibrated and used as a tool for groundwater management. The main hydraulic parameters that comprise a regional or subregional model of an aquifer system are the hydraulic conductivity and storage properties of the aquifers and confining units (hydrogeologic units) that confine the system. Many 3D groundwater flow models used to help assess groundwater/surface-water interactions require calculating ?effective? or composite hydraulic properties of multilayered lithologic units within a hydrogeologic unit. The calculation of composite hydraulic properties stems from the need to characterize groundwater flow using coarse model layering in order to reduce simulation times while still representing the flow through the system accurately. The accuracy of flow models with

  10. Analytic Thermoelectric Couple Modeling: Variable Material Properties and Transient Operation

    NASA Technical Reports Server (NTRS)

    Mackey, Jonathan A.; Sehirlioglu, Alp; Dynys, Fred

    2015-01-01

    To gain a deeper understanding of the operation of a thermoelectric couple a set of analytic solutions have been derived for a variable material property couple and a transient couple. Using an analytic approach, as opposed to commonly used numerical techniques, results in a set of useful design guidelines. These guidelines can serve as useful starting conditions for further numerical studies, or can serve as design rules for lab built couples. The analytic modeling considers two cases and accounts for 1) material properties which vary with temperature and 2) transient operation of a couple. The variable material property case was handled by means of an asymptotic expansion, which allows for insight into the influence of temperature dependence on different material properties. The variable property work demonstrated the important fact that materials with identical average Figure of Merits can lead to different conversion efficiencies due to temperature dependence of the properties. The transient couple was investigated through a Greens function approach; several transient boundary conditions were investigated. The transient work introduces several new design considerations which are not captured by the classic steady state analysis. The work helps to assist in designing couples for optimal performance, and also helps assist in material selection.

  11. Modeling silica aerogel optical performance by determining its radiative properties

    NASA Astrophysics Data System (ADS)

    Zhao, Lin; Yang, Sungwoo; Bhatia, Bikram; Strobach, Elise; Wang, Evelyn N.

    2016-02-01

    Silica aerogel has been known as a promising candidate for high performance transparent insulation material (TIM). Optical transparency is a crucial metric for silica aerogels in many solar related applications. Both scattering and absorption can reduce the amount of light transmitted through an aerogel slab. Due to multiple scattering, the transmittance deviates from the Beer-Lambert law (exponential attenuation). To better understand its optical performance, we decoupled and quantified the extinction contributions of absorption and scattering separately by identifying two sets of radiative properties. The radiative properties are deduced from the measured total transmittance and reflectance spectra (from 250 nm to 2500 nm) of synthesized aerogel samples by solving the inverse problem of the 1-D Radiative Transfer Equation (RTE). The obtained radiative properties are found to be independent of the sample geometry and can be considered intrinsic material properties, which originate from the aerogel's microstructure. This finding allows for these properties to be directly compared between different samples. We also demonstrate that by using the obtained radiative properties, we can model the photon transport in aerogels of arbitrary shapes, where an analytical solution is difficult to obtain.

  12. Uncertainty of mantle geophysical properties computed from phase equilibrium models

    NASA Astrophysics Data System (ADS)

    Connolly, J. A. D.; Khan, A.

    2016-05-01

    Phase equilibrium models are used routinely to predict geophysically relevant mantle properties. A limitation of this approach is that nonlinearity of the phase equilibrium problem precludes direct assessment of the resultant uncertainties. To overcome this obstacle, we stochastically assess uncertainties along self-consistent mantle adiabats for pyrolitic and basaltic bulk compositions to 2000 km depth. The dominant components of the uncertainty are the identity, composition and elastic properties of the minerals. For P wave speed and density, the latter components vary little, whereas the first is confined to the upper mantle. Consequently, P wave speeds, densities, and adiabatic temperatures and pressures predicted by phase equilibrium models are more uncertain in the upper mantle than in the lower mantle. In contrast, uncertainties in S wave speeds are dominated by the uncertainty in shear moduli and are approximately constant throughout the model depth range.

  13. Contura Multi-Lumen Balloon Breast Brachytherapy Catheter: Comparative Dosimetric Findings of a Phase 4 Trial

    SciTech Connect

    Arthur, Douglas W.; Vicini, Frank A.; Julian, Thomas B.; Cuttino, Laurie W.; Mukhopadhyay, Nitai D.

    2013-06-01

    Purpose: Final dosimetric findings of a completed, multi-institutional phase 4 registry trial using the Contura Multi-Lumen Balloon (MLB) breast brachytherapy catheter to deliver accelerated partial breast irradiation (APBI) in patients with early-stage breast cancer are presented. Methods and Materials: Three dosimetric plans with identical target coverage were generated for each patient for comparison: multilumen multidwell (MLMD); central-lumen multidwell (CLMD); and central-lumen single-dwell (CLSD) loading of the Contura catheter. For this study, a successful treatment plan achieved ideal dosimetric goals and included the following: ≥95% of the prescribed dose (PD) covering ≥95% of the target volume (TV); maximum skin dose ≤125% of the PD; maximum rib dose ≤145% of the PD; and V150 ≤50 cc and V200 ≤10 cc. Results: Between January 2008 and February 2011, 23 institutions participated. A total of 318 patients were available for dosimetric review. Using the Contura MLB, all dosimetric criteria were met in 78.93% of cases planned with MLMD versus 55.38% with the CLMD versus 37.66% with the CLSD (P≤.0001). Evaluating all patients with the full range of skin to balloon distance represented, median maximum skin dose was reduced by 12% and median maximum rib dose by 13.9% when using MLMD-based dosimetric plans compared to CLSD. The dosimetric benefit of MLMD was further demonstrated in the subgroup of patients where skin thickness was <5 mm, where MLMD use allowed a 38% reduction in median maximum skin dose over CLSD. For patients with rib distance <5 mm, the median maximum rib dose reduction was 27%. Conclusions: Use of the Contura MLB catheter produced statistically significant improvements in dosimetric capabilities between CLSD and CLMD treatments. This device approach demonstrates the ability not only to overcome the barriers of limited skin thickness and close rib proximity, but to consistently achieve a higher standard of dosimetric planning goals.

  14. Realistic modeling of the electronic properties of doped amorphous silicon

    SciTech Connect

    Hack, M.; Street, R.A.

    1988-09-19

    In this letter we describe a fundamental approach to calculating the electronic properties of doped amorphous silicon which takes into account the thermal history of the material. Above the equilibrium temperature, the material is in a thermodynamically stable state, and this is derived by minimizing the free energy using a simple density of states model. The calculations are based on the defect compensation model of doping, introducing distributions of formation energies for neutral dangling bonds and fourfold dopant atoms while preserving charge neutrality. Our results are in good agreement with experimental data providing a realistic model for use in device simulation programs.

  15. Nonlinear reduced-order modeling with monotonicity property

    NASA Astrophysics Data System (ADS)

    Chaturantabut, Saifon

    2016-10-01

    This work proposes a general form of nonlinear model reduction approach that preserves the monotonicity property of the original full-order model, which can be used to guarantee the existence and uniqueness of the solution. The derivation of the proposed methodology is based on using basis from proper orthogonal decomposition method and modifying an interpolatory projection approach, called discrete empirical interpolation method, by enforcing a symmetric structure of the approximation. The efficiency and accuracy of the proposed method are illustrated through the numerical tests on a nonlinear model describing reaction diffusion problems.

  16. Tensile Properties and Viscoelastic Model of a Polyimide Film

    NASA Astrophysics Data System (ADS)

    Zhang, Shengde; Mori, Syuhei; Sakane, Masao; Nagasawa, Tadashi; Kobayashi, Kaoru

    This paper presents tensile properties of a polyimide thin film used in electronic devices. Tensile tests were performed to determine Young's modulus, proportional limit, yield stress, ultimate tensile strength and elongation of the polyimide film. Effects of strain rate and temperature on the tensile properties were discussed. There was a little effect of strain rate on Young's modulus but proportional limit, yield stress and ultimate tensile strength increased with increasing strain rate. Only elongation decreased with strain rate. Young's modulus, proportional limit, yield stress and ultimate tensile strength decreased with increasing temperature, but elongation increased. Applicability of a viscoelastic model for describing the stress-strain curves of the polyimide film was discussed.

  17. Structure and physical properties of biomembranes and model membranes

    NASA Astrophysics Data System (ADS)

    Hianik, T.

    2006-12-01

    Biomembranes belong to the most important structures of the cell and the cell organels. They play not only structural role of the barrier separating the external and internal part of the membrane but contain also various functional molecules, like receptors, ionic channels, carriers and enzymes. The cell membrane also preserves non-equillibrium state in a cell which is crucial for maintaining its excitability and other signaling functions. The growing interest to the biomembranes is also due to their unique physical properties. From physical point of view the biomembranes, that are composed of lipid bilayer into which are incorporated integral proteins and on their surface are anchored peripheral proteins and polysaccharides, represent liquid scrystal of smectic type. The biomembranes are characterized by anisotropy of structural and physical properties. The complex structure of biomembranes makes the study of their physical properties rather difficult. Therefore several model systems that mimic the structure of biomembranes were developed. Among them the lipid monolayers at an air-water interphase, bilayer lipid membranes (BLM), supported bilayer lipid membranes (sBLM) and liposomes are most known. This work is focused on the introduction into the "physical word" of the biomembranes and their models. After introduction to the membrane structure and the history of its establishment, the physical properties of the biomembranes and their models areare stepwise presented. The most focus is on the properties of lipid monolayers, BLM, sBLM and liposomes that were most detailed studied. This contribution has tutorial character that may be usefull for undergraduate and graduate students in the area of biophysics, biochemistry, molecular biology and bioengineering, however it contains also original work of the author and his co-worker and PhD students, that may be usefull also for specialists working in the field of biomembranes and model membranes.

  18. Dosimetric and late radiation toxicity comparison between iodine-125 brachytherapy and stereotactic radiation therapy for juxtapapillary choroidal melanoma.

    PubMed

    Krema, Hatem; Heydarian, Mostafa; Beiki-Ardakani, Akbar; Weisbrod, Daniel; Xu, Wei; Laperriere, Normand J; Sahgal, Arjun

    2013-07-01

    To compare the dose distributions and late radiation toxicities for (125)I brachytherapy (IBT) and stereotactic radiation therapy (SRT) in the treatment of juxtapapillary choroidal melanoma. Ninety-four consecutive patients with juxtapapillary melanoma were reviewed: 30 have been treated with IBT and 64 with SRT. Iodine-125 brachytherapy cases were modeled with plaque simulator software for dosimetric analysis. The SRT dosimetric data were obtained from the Radionics XKnife RT3 software. Mean doses at predetermined intraocular points were calculated. Kaplan-Meier estimates determined the actuarial rates of late toxicities, and the log-rank test compared the estimates. The median follow-up was 46 months in both cohorts. The 2 cohorts were balanced with respect to pretreatment clinical and tumor characteristics. Comparisons of radiation toxicity rates between the IBT and SRT cohorts yielded actuarial rates at 50 months for cataracts of 62% and 75% (P=.1), for neovascular glaucoma 8% and 47% (P=.002), for radiation retinopathy 59% and 89% (P=.0001), and for radiation papillopathy 39% and 74% (P=.003), respectively. Dosimetric comparisons between the IBT and SRT cohorts yielded mean doses of 12.8 and 14.1 Gy (P=.56) for the lens center, 17.6 and 19.7 Gy (P=.44) for the lens posterior pole, 13.9 and 10.8 Gy (P=.30) for the ciliary body, 61.9 and 69.7 Gy (P=.03) for optic disc center, and 48.9 and 60.1 Gy (P<.0001) for retina at 5-mm distance from tumor margin, respectively. Late radiation-induced toxicities were greater with SRT, which is secondary to the high-dose exposure inherent to the technique as compared with IBT. When technically feasible, IBT is preferred to treat juxtapapillary choroidal melanoma. Copyright © 2013 Elsevier Inc. All rights reserved.

  19. Volumetric modulated arc radiotherapy sparing the thyroid gland for early-stage glottic cancer: A dosimetrical analysis.

    PubMed

    Kim, Eun Seok; Yeo, Seung-Gu

    2014-06-01

    Previous studies on advanced radiotherapy (RT) techniques for early stage glottic cancer have focused on sparing the carotid artery. However, the aim of the present study was to evaluate the dosimetric advantages of volumetric modulated arc therapy (VMAT) in terms of sparing the thyroid gland in early-stage glottic cancer patients. In total, 15 cT1N0M0 glottic cancer patients treated with definitive RT using VMAT were selected, and for dosimetric comparison, a conventional RT plan comprising opposed-lateral wedged fields was generated for each patient. The carotid artery, thyroid gland and spinal cord were considered organs at risk. The prescription dose was 63 Gy at 2.25 Gy per fraction. For the thyroid gland and carotid artery, all compared parameters were significantly lower with VMAT compared with conventional RT. For the thyroid gland, the median reduction rates of the mean dose (Dmean), the volume receiving ≥30% of the prescription dose (V30) and the V50 were 32.6, 40.9 and 46.0%, respectively. The Dmean was 14.7±2.6 Gy when using VMAT compared with 22.2±3.9 Gy when using conventional RT. The differences between the techniques in terms of planning target volume coverage and dose homogeneity were not significant. When considering a recent normal tissue complication probability model, which indicated the mean thyroid gland dose as the most significant predictor of radiation-induced hypothyroidism, the dosimetric advantage shown in this study may be valuable in reducing hypothyroidism following RT for early stage glottic cancer patients.

  20. Volumetric modulated arc radiotherapy sparing the thyroid gland for early-stage glottic cancer: A dosimetrical analysis

    PubMed Central

    KIM, EUN SEOK; YEO, SEUNG-GU

    2014-01-01

    Previous studies on advanced radiotherapy (RT) techniques for early stage glottic cancer have focused on sparing the carotid artery. However, the aim of the present study was to evaluate the dosimetric advantages of volumetric modulated arc therapy (VMAT) in terms of sparing the thyroid gland in early-stage glottic cancer patients. In total, 15 cT1N0M0 glottic cancer patients treated with definitive RT using VMAT were selected, and for dosimetric comparison, a conventional RT plan comprising opposed-lateral wedged fields was generated for each patient. The carotid artery, thyroid gland and spinal cord were considered organs at risk. The prescription dose was 63 Gy at 2.25 Gy per fraction. For the thyroid gland and carotid artery, all compared parameters were significantly lower with VMAT compared with conventional RT. For the thyroid gland, the median reduction rates of the mean dose (Dmean), the volume receiving ≥30% of the prescription dose (V30) and the V50 were 32.6, 40.9 and 46.0%, respectively. The Dmean was 14.7±2.6 Gy when using VMAT compared with 22.2±3.9 Gy when using conventional RT. The differences between the techniques in terms of planning target volume coverage and dose homogeneity were not significant. When considering a recent normal tissue complication probability model, which indicated the mean thyroid gland dose as the most significant predictor of radiation-induced hypothyroidism, the dosimetric advantage shown in this study may be valuable in reducing hypothyroidism following RT for early stage glottic cancer patients. PMID:24932276

  1. Dosimetric and Late Radiation Toxicity Comparison Between Iodine-125 Brachytherapy and Stereotactic Radiation Therapy for Juxtapapillary Choroidal Melanoma

    SciTech Connect

    Krema, Hatem

    2013-07-01

    Purpose: To compare the dose distributions and late radiation toxicities for {sup 125}I brachytherapy (IBT) and stereotactic radiation therapy (SRT) in the treatment of juxtapapillary choroidal melanoma. Methods: Ninety-four consecutive patients with juxtapapillary melanoma were reviewed: 30 have been treated with IBT and 64 with SRT. Iodine-125 brachytherapy cases were modeled with plaque simulator software for dosimetric analysis. The SRT dosimetric data were obtained from the Radionics XKnife RT3 software. Mean doses at predetermined intraocular points were calculated. Kaplan-Meier estimates determined the actuarial rates of late toxicities, and the log–rank test compared the estimates. Results: The median follow-up was 46 months in both cohorts. The 2 cohorts were balanced with respect to pretreatment clinical and tumor characteristics. Comparisons of radiation toxicity rates between the IBT and SRT cohorts yielded actuarial rates at 50 months for cataracts of 62% and 75% (P=.1), for neovascular glaucoma 8% and 47% (P=.002), for radiation retinopathy 59% and 89% (P=.0001), and for radiation papillopathy 39% and 74% (P=.003), respectively. Dosimetric comparisons between the IBT and SRT cohorts yielded mean doses of 12.8 and 14.1 Gy (P=.56) for the lens center, 17.6 and 19.7 Gy (P=.44) for the lens posterior pole, 13.9 and 10.8 Gy (P=.30) for the ciliary body, 61.9 and 69.7 Gy (P=.03) for optic disc center, and 48.9 and 60.1 Gy (P<.0001) for retina at 5-mm distance from tumor margin, respectively. Conclusions: Late radiation-induced toxicities were greater with SRT, which is secondary to the high-dose exposure inherent to the technique as compared with IBT. When technically feasible, IBT is preferred to treat juxtapapillary choroidal melanoma.

  2. SU-F-BRE-04: Construction of 3D Printed Patient Specific Phantoms for Dosimetric Verification Measurements

    SciTech Connect

    Ehler, E; Higgins, P; Dusenbery, K

    2014-06-15

    Purpose: To validate a method to create per patient phantoms for dosimetric verification measurements. Methods: Using a RANDO phantom as a substitute for an actual patient, a model of the external features of the head and neck region of the phantom was created. A phantom was used instead of a human for two reasons: to allow for dosimetric measurements that would not be possible in-vivo and to avoid patient privacy issues. Using acrylonitrile butadiene styrene thermoplastic as the building material, a hollow replica was created using the 3D printer filled with a custom tissue equivalent mixture of paraffin wax, magnesium oxide, and calcium carbonate. A traditional parallel-opposed head and neck plan was constructed. Measurements were performed with thermoluminescent dosimeters in both the RANDO phantom and in the 3D printed phantom. Calculated and measured dose was compared at 17 points phantoms including regions in high and low dose regions and at the field edges. On-board cone beam CT was used to localize both phantoms within 1mm and 1° prior to radiation. Results: The maximum difference in calculated dose between phantoms was 1.8% of the planned dose (180 cGy). The mean difference between calculated and measured dose in the anthropomorphic phantom and the 3D printed phantom was 1.9% ± 2.8% and −0.1% ± 4.9%, respectively. The difference between measured and calculated dose was determined in the RANDO and 3D printed phantoms. The differences between measured and calculated dose in each respective phantom was within 2% for 12 of 17 points. The overlap of the RANDO and 3D printed phantom was 0.956 (Jaccard Index). Conclusion: A custom phantom was created using a 3D printer. Dosimetric calculations and measurements showed good agreement between the dose in the RANDO phantom (patient substitute) and the 3D printed phantom.

  3. A breathing thorax phantom with independently programmable 6D tumour motion for dosimetric measurements in radiation therapy

    NASA Astrophysics Data System (ADS)

    Steidl, P.; Richter, D.; Schuy, C.; Schubert, E.; Haberer, Th; Durante, M.; Bert, C.

    2012-04-01

    Irradiation of moving targets using a scanned ion beam can cause clinically intolerable under- and overdosages within the target volume due to the interplay effect. Several motion mitigation techniques such as gating, beam tracking and rescanning are currently investigated to overcome this restriction. To enable detailed experimental studies of potential mitigation techniques a complex thorax phantom was developed. The phantom consists of an artificial thorax with ribs to introduce density changes. The contraction of the thorax can be controlled by a stepping motor. A robotic driven detector head positioned inside the thorax mimics e.g. a lung tumour. The detector head comprises 20 ionization chambers and 5 radiographic films for target dose measurements. The phantom’s breathing as well as the 6D tumour motion (3D translation, 3D rotation) can be programmed independently and adjusted online. This flexibility allows studying the dosimetric effects of correlation mismatches between internal and external motions, irregular breathing, or baseline drifts to name a few. Commercial motion detection systems, e.g. VisionRT or Anzai belt, can be mounted as they would be mounted in a patient case. They are used to control the 4D treatment delivery and to generate data for 4D dose calculation. To evaluate the phantom’s properties, measurements addressing reproducibility, stability, temporal behaviour and performance of dedicated breathing manoeuvres were performed. In addition, initial dosimetric tests for treatment with a scanned carbon beam are reported.

  4. Dosimetric comparison of four new design {sup 103}Pd brachytherapy sources: Optimal design using silver and copper rod cores

    SciTech Connect

    Hosseini, S. Hamed; Sadeghi, Mahdi; Ataeinia, Vahideh

    2009-07-15

    Four new brachytherapy sources, IRA1-{sup 103}Pd, IRA2-{sup 103}Pd, IRA3-{sup 103}Pd, and IRA4-{sup 103}Pd, have been developed at Agricultural, Medical, and Industrial Research School and are designed for permanent implant application. With the goal of determining an optimal design for a {sup 103}Pd source, this article compares the dosimetric properties of these sources with reference to the authors' earlier IRA-{sup 103}Pd source. The four new sources differ in end cap configuration and thickness and in the core material, silver or copper, that carries the adsorbed {sup 103}Pd. Dosimetric data derived from the authors' Monte Carlo simulation results are reported in accordance with the updated AAPM Task Group No. 43 report (TG-43U1). For each source, the authors obtained detailed results for the dose rate constant {Lambda}, the radial dose function g(r), the anisotropy function F(r,{theta}), and the anisotropy factor {phi}{sub an}(r). In this study, the optimal source IRA3-{sup 103}Pd provides the most isotropic dose distribution in water with the dose rate constant of 0.678({+-}0.1%) cGy h{sup -1} U{sup -1}. The IRA3-{sup 103}Pd design has a silver rod core combined with thin-wall, concave end caps. Finally, the authors compared the results for their optimal source with published results for those of other source manufacturers.

  5. Dosimetric differences between intraoperative and postoperative plans using Cs-131 in transrectal ultrasound–guided brachytherapy for prostatic carcinoma

    SciTech Connect

    Jones, Andrew; Treas, Jared; Yavoich, Brian; Dean, Douglas; Danella, John; Yumen, Omar

    2014-01-01

    The aim of the study was to investigate the differences between intraoperative and postoperative dosimetry for transrectal ultrasound–guided transperineal prostate implants using cesium-131 ({sup 131}Cs). Between 2006 and 2010, 166 patients implanted with {sup 131}Cs had both intraoperative and postoperative dosimetry studies. All cases were monotherapy and doses of 115 were prescribed to the prostate. The dosimetric properties (D{sub 90}, V{sub 150}, and V{sub 100} for the prostate) of the studies were compared. Two conformity indices were also calculated and compared. Finally, the prostate was automatically sectioned into 6 sectors (anterior and posterior sectors at the base, midgland, and apex) and the intraoperative and postoperative dosimetry was compared in each individual sector. Postoperative dosimetry showed statistically significant changes (p < 0.01) in every dosimetric value except V{sub 150}. In each significant case, the postoperative plans showed lower dose coverage. The conformity indexes also showed a bimodal frequency distribution with the index indicating poorer dose conformity in the postoperative plans. Sector analysis revealed less dose coverage postoperatively in the base and apex sectors with an increase in dose to the posterior midgland sector. Postoperative dosimetry overall and in specific sectors of the prostate differs significantly from intraoperative planning. Care must be taken during the intraoperative planning stage to ensure complete dose coverage of the prostate with the understanding that the final postoperative dosimetry will show less dose coverage.

  6. A breathing thorax phantom with independently programmable 6D tumour motion for dosimetric measurements in radiation therapy.

    PubMed

    Steidl, P; Richter, D; Schuy, C; Schubert, E; Haberer, Th; Durante, M; Bert, C

    2012-04-21

    Irradiation of moving targets using a scanned ion beam can cause clinically intolerable under- and overdosages within the target volume due to the interplay effect. Several motion mitigation techniques such as gating, beam tracking and rescanning are currently investigated to overcome this restriction. To enable detailed experimental studies of potential mitigation techniques a complex thorax phantom was developed. The phantom consists of an artificial thorax with ribs to introduce density changes. The contraction of the thorax can be controlled by a stepping motor. A robotic driven detector head positioned inside the thorax mimics e.g. a lung tumour. The detector head comprises 20 ionization chambers and 5 radiographic films for target dose measurements. The phantom's breathing as well as the 6D tumour motion (3D translation, 3D rotation) can be programmed independently and adjusted online. This flexibility allows studying the dosimetric effects of correlation mismatches between internal and external motions, irregular breathing, or baseline drifts to name a few. Commercial motion detection systems, e.g. VisionRT or Anzai belt, can be mounted as they would be mounted in a patient case. They are used to control the 4D treatment delivery and to generate data for 4D dose calculation. To evaluate the phantom's properties, measurements addressing reproducibility, stability, temporal behaviour and performance of dedicated breathing manoeuvres were performed. In addition, initial dosimetric tests for treatment with a scanned carbon beam are reported.

  7. Micromagnetic modeling of the shielding properties of nanoscale ferromagnetic layers

    NASA Astrophysics Data System (ADS)

    Iskandarova, I. M.; Knizhnik, A. A.; Popkov, A. F.; Potapkin, B. V.; Stainer, Q.; Lombard, L.; Mackay, K.

    2016-09-01

    Ferromagnetic shields are widely used to concentrate magnetic fields in a target region of space. Such shields are also used in spintronic nanodevices such as magnetic random access memory and magnetic logic devices. However, the shielding properties of nanostructured shields can differ considerably from those of macroscopic samples. In this work, we investigate the shielding properties of nanostructured NiFe layers around a current line using a finite element micromagnetic model. We find that thin ferromagnetic layers demonstrate saturation of magnetization under an external magnetic field, which reduces the shielding efficiency. Moreover, we show that the shielding properties of nanoscale ferromagnetic layers strongly depend on the uniformity of the layer thickness. Magnetic anisotropy in ultrathin ferromagnetic layers can also influence their shielding efficiency. In addition, we show that domain walls in nanoscale ferromagnetic shields can induce large increases and decreases in the generated magnetic field. Therefore, ferromagnetic shields for spintronic nanodevices require careful design and precise fabrication.

  8. Composition dependence of fluid thermophysical properties: Theory and modeling

    SciTech Connect

    Ely, J.F.

    1993-03-29

    Objectives are studies of equilibrium/nonequilibrium properties of asymmetric fluid mixtures through computer simulation (CS), development of predictive theories of mixture equilibrium properties, development and application of selection algorithm methodology for mixture equations of state, and use of theory to develop new engineering design models for fluid mixtures. Kirwood charging method CS of Lennard-Jones mixtures with large size ratios verified the Kirkwood-Buff/Baxter method of calculating chemical potentials. CS of n-butane showed that the rheology is not a function of system size. A modified stepwise regression algorithm was developed and applied to HFC R134a. An analytical expression was developed for conformal solution size correction for mixtures. The extended corresponding states theory (ECST) can be applied to systems having large polarity differences; an accurate representation was developed of bulk phase properties of water-hydrocarbon systems. It was found how to force ECST to reach the correct virial limit.

  9. Modeling the photosensitizing properties of thiolate-protected gold nanoclusters.

    PubMed

    Azarias, Cloé; Adamo, Carlo; Perrier, Aurélie

    2016-03-21

    An accurate computational strategy for studying the structural, redox and optical properties of thiolated gold nanoclusters (GNCs) using (Time-Dependent) Density Functional Theory is proposed. The influence of the pseudopotential/basis set, solvent description and the choice of the functional has been investigated to model the structural and electronic properties of the Au25(SR)18(-) system, with R being an organic ligand. This study aims to describe with a comparable precision both the GNC and the organic ligands and rationalize the effect of coating on different GNC properties. Two differently coated GNCs have been considered: the system with R = CH2CH2Ph and the GNC coated with 17 alkyl chains (C6H13) and functionalized by one fluorophore pyrene derivative (CH2CH2(NH)(CO)Py). The computational protocol we propose should then be used to design more efficient metal cluster-sensitized solar cells.

  10. Langmuir films of asphaltene model compounds and their fluorescent properties.

    PubMed

    Nordgård, Erland L; Landsem, Eva; Sjöblom, Johan

    2008-08-19

    The relationship between the physicochemical properties of asphaltenes and asphaltene structure is an issue of increasing focus. Surface pressure-area isotherms of asphaltene model compounds have been investigated to gain more knowledge of their arrangement at an aqueous surface. Variations in interfacial activity have been correlated to proposed arrangements. The presence of a carboxylic acid has shown to be crucial for their interfacial activity and film properties. The acid group directs the molecules normal to the surface, forming a stable monolayer film. The high stability was absent when no acidic groups were present. Fluorescence spectra of deposited Langmuir-Blodgett films showed only the presence of the excimer emission for thin films of acidic model compounds, indicating a close face-to-face arrangement of the molecules. Time-correlated single photon counting (TCSPC) of the model compounds in toluene indicated the presence of aggregates for two of four compounds at low concentrations. However, a sudden drop of interfacial tension observed could not be correlated to the aggregation. Instead, aggregation induced by addition of a "poor" solvent showed decreased interfacial activity when aggregated due to decrease of monomers in bulk. The findings regarding these asphaltene model compounds and their structural differences show the great effect an acidic group has on their physicochemical properties.

  11. A relatively simple model for percolation properties of real networks

    NASA Astrophysics Data System (ADS)

    Fu, Tao; Zou, Liling; Li, Chenguang; Zhao, Junbo

    2017-08-01

    Analyzing percolation rules of real networks has some great realistic significance. In this paper, we develop a relatively simple model based on generating function method to study percolation properties of real networks. We construct our model for both site and bond percolation, compare its estimates with those of the message passing algorithm and simulation results on computer-generated networks as well as practical networks, and discuss causes of the inaccuracy. The conclusions show that the accuracy of our model could be accepted though it is lower than that of the message passing algorithm and the discrepancies between the estimates of our model and the simulation values mainly come from the disagreement of those real networks with the model hypotheses.

  12. Mathematical properties of models of the reaction-diffusion type

    NASA Astrophysics Data System (ADS)

    Beccaria, M.; Soliani, G.

    Nonlinear systems of the reaction-diffusion (RD) type, including Gierer-Meinhardt models of autocatalysis, are studied using Lie algebras coming from their prolongation structure. Depending on the form of the functions of the fields characterizing the reactions among them, we consider both quadratic and cubic RD equations. On the basis of the prolongation algebra associated with a given RD model, we distinguish the model as a completely linearizable or a partially linearizable system. In this classification a crucial role is played by the relative sign of the diffusion coefficients, which strongly influence the properties of the system. In correspondence to the above situations, different algebraic characterizations, together with exact and approximate solutions, are found. Interesting examples are the quadratic RD model, which admits an exact solution in terms of the elliptic Weierstrass function, and the cubic Gierer-Meinhardt model, whose prolongation algebra leads to the similitude group in the plane.

  13. Thermodynamic properties of lattice hard-sphere models.

    PubMed

    Panagiotopoulos, A Z

    2005-09-08

    Thermodynamic properties of several lattice hard-sphere models were obtained from grand canonical histogram- reweighting Monte Carlo simulations. Sphere centers occupy positions on a simple cubic lattice of unit spacing and exclude neighboring sites up to a distance sigma. The nearestneighbor exclusion model, sigma = radical2, was previously found to have a second-order transition. Models with integer values of sigma = 1 or 2 do not have any transitions. Models with sigma = radical3 and sigma = 3 have weak first-order fluid-solid transitions while those with sigma = 2 radical2, 2 radical3, and 3 radical2 have strong fluid-solid transitions. Pressure, chemical potential, and density are reported for all models and compared to the results for the continuum, theoretical predictions, and prior simulations when available.

  14. Potential application of metal nanoparticles for dosimetric systems: Concepts and perspectives

    SciTech Connect

    Guidelli, Eder José Baffa, Oswaldo

    2014-11-07

    Metallic nanoparticles increase the delivered dose and consequently enhance tissue radio sensitization during radiation therapy of cancer. The Dose Enhancement Factor (DEF) corresponds to the ratio between the dose deposited on a tissue containing nanoparticles, and the dose deposited on a tissue without nanoparticles. In this sense, we have used electron spin resonance spectroscopy (ESR) to investigate how silver and gold nanoparticles affect the dose deposition in alanine dosimeters, which act as a surrogate of soft tissue. Besides optimizing radiation absorption by the dosimeter, the optical properties of these metal nanoparticles could also improve light emission from materials employed as radiation detectors. Therefore, we have also examined how the plasmonic properties of noble metal nanoparticles could enhance radiation detection using optically stimulated luminescence (OSL) dosimetry. This work will show results on how the use of gold and silver nanoparticles are beneficial for the ESR and OSL dosimetric techniques, and will describe the difficulties we have been facing, the challenges to overcome, and the perspectives.

  15. Potential application of metal nanoparticles for dosimetric systems: Concepts and perspectives

    NASA Astrophysics Data System (ADS)

    Guidelli, Eder José; Baffa, Oswaldo

    2014-11-01

    Metallic nanoparticles increase the delivered dose and consequently enhance tissue radio sensitization during radiation therapy of cancer. The Dose Enhancement Factor (DEF) corresponds to the ratio between the dose deposited on a tissue containing nanoparticles, and the dose deposited on a tissue without nanoparticles. In this sense, we have used electron spin resonance spectroscopy (ESR) to investigate how silver and gold nanoparticles affect the dose deposition in alanine dosimeters, which act as a surrogate of soft tissue. Besides optimizing radiation absorption by the dosimeter, the optical properties of these metal nanoparticles could also improve light emission from materials employed as radiation detectors. Therefore, we have also examined how the plasmonic properties of noble metal nanoparticles could enhance radiation detection using optically stimulated luminescence (OSL) dosimetry. This work will show results on how the use of gold and silver nanoparticles are beneficial for the ESR and OSL dosimetric techniques, and will describe the difficulties we have been facing, the challenges to overcome, and the perspectives.

  16. Modeling the Hydrodynamical Properties of the QGP at RHIC

    NASA Astrophysics Data System (ADS)

    Garishvili, Irakli; Soltz, Ron; Pratt, Scott; Cheng, Micael; Glenn, Andrew; Newby, Jason; Linden-Levy, Loren; Abelev, Betty

    2010-11-01

    Comparisons of the RHIC data to various theoretical models suggest that the evolution of the QGP, a state of matter believed to be created in early stages of heavy ion collisions at RHIC, is qualitatively well described by hydrodynamics. However, the key properties of the QGP, such as initial temperature, Tinit, and the ratio of shear viscosity to entropy density of matter, η/s, are not precisely known. To constrain these properties we have developed a multi-stage hydrodynamics/hadron cascade model of heavy ion collisions which incorporates Glauber initial state conditions, pre-equilibrium flow, the UVH2+1 viscous hydro model, Cooper-Frye freezeout, and the UrQMD hadronic cascade model. To test the sensitivity of the observables to the equation of state (EoS), we use several different EoS in the hydrodynamic evolution, including those derived from the hadron resonance gas model and lattice QCD. This framework has an ability to predict key QGP observables, such as, elliptic flow, spectra, and HBT radii for various particle species. For each set of model's input parameters (Tinit, η/s and initial flow) we perform a simultaneous comparison to spectra, elliptic flow, and HBT measured at RHIC. Based on this analysis the determinations of Tinit and η/s will be presented.

  17. An FE model of a cellular polypropylene: exploring mechanical properties

    NASA Astrophysics Data System (ADS)

    Sgardelis, Pavlos; Pozzi, Michele

    2017-05-01

    Several analytical models have been suggested to describe the changes in the electromechanical properties of Cellular Polypropylene (Cell-PP) due to charging. However, there is a limited number of studies considering the non-linear dependence of the piezoelectric coefficient d33 on the mechanical load applied. One of the main reasons for this nonlinearity is the stiffness of the film that increases proportionally to the applied mechanical load. Moreover the size and shape distribution of the enclosed voids is an important determinant of the electromechanical properties. In this work, the geometry of a 3D model of Cell-PP is designed on the basis of analytical Splines. Both the manufacturing procedure of Cell-PP films (bi-axial stretching) and the pressure expansion treatment were simulated in order to account for a realistic void distribution. The FEA is done on a 2D cross-section of the modelled film. The modelled mechanical response is analysed based on increasing mechanical load applied. The load-deflection curves obtained from the analysis are then compared to the experimental results acquired via Dynamical Mechanical Analyzer (DMA) to validate the model. Four types of Cell-PP films, expanded at different pressures, were used in this validation. The aim is to develop a model that describes the effect of morphological parameters on the stiffness of the films by simulating the manufacturing procedure.

  18. Modelling agronomic properties of Technosols constructed with urban wastes.

    PubMed

    Rokia, S; Séré, G; Schwartz, C; Deeb, M; Fournier, F; Nehls, T; Damas, O; Vidal-Beaudet, L

    2014-11-01

    The greening of urban and suburban areas requires large amounts of arable earth that is a non-renewable resource. However, concentration of population in cities leads to the production of high amounts of wastes and by-products that are nowadays partly recycled as a resource and quite systematically exported out of urban areas. To preserve natural soil resources, a strategy of waste recycling as fertile substitutes is proposed. Eleven wastes are selected for their environmental harmlessness and their contrasted physico-chemical properties for their potential use in pedological engineering. The aim is (i) to demonstrate the feasibility of the formulation of fertile substrates exclusively with wastes and (ii) to model their physico-chemical properties following various types, number and proportions of constitutive wastes. Twenty-five binary and ternary combinations are tested at different ratios for total carbon, Olsen available phosphorus, cation exchange capacity, water pH, water retention capacity and bulk density. Dose-response curves describe the variation of physico-chemical properties of mixtures depending on the type and ratio of selected wastes. If these mixtures mainly mimic natural soils, some of them present more extreme urban soil features, especially for pH and P(Olsen). The fertility of the new substrates is modelled by multilinear regressions for the main soil properties.

  19. Effects of model layer simplification using composite hydraulic properties

    USGS Publications Warehouse

    Sepulveda, Nicasio; Kuniansky, Eve L.

    2010-01-01

    The effects of simplifying hydraulic property layering within an unconfined aquifer and the underlying confining unit were assessed. The hydraulic properties of lithologic units within the unconfined aquifer and confining unit were computed by analyzing the aquifer-test data using radial, axisymmetric two-dimensional (2D) flow. Time-varying recharge to the unconfined aquifer and pumping from the confined Upper Floridan aquifer (USA) were simulated using 3D flow. Conceptual flow models were developed by gradually reducing the number of lithologic units in the unconfined aquifer and confining unit by calculating composite hydraulic properties for the simplified lithologic units. Composite hydraulic properties were calculated using either thickness-weighted averages or inverse modeling using regression-based parameter estimation. No significant residuals were simulated when all lithologic units comprising the unconfined aquifer were simulated as one layer. The largest residuals occurred when the unconfined aquifer and confining unit were aggregated into a single layer (quasi-3D), with residuals over 100% for the leakage rates to the confined aquifer and the heads in the confining unit. Residuals increased with contrasts in vertical hydraulic conductivity between the unconfined aquifer and confining unit. Residuals increased when the constant-head boundary at the bottom of the Upper Floridan aquifer was replaced with a no-flow boundary.

  20. Mathematical Modeling of Subthreshold Resonant Properties in Pyloric Dilator Neurons

    PubMed Central

    Vazifehkhah Ghaffari, Babak; Kouhnavard, Mojgan; Aihara, Takeshi; Kitajima, Tatsuo

    2015-01-01

    Various types of neurons exhibit subthreshold resonance oscillation (preferred frequency response) to fluctuating sinusoidal input currents. This phenomenon is well known to influence the synaptic plasticity and frequency of neural network oscillation. This study evaluates the resonant properties of pacemaker pyloric dilator (PD) neurons in the central pattern generator network through mathematical modeling. From the pharmacological point of view, calcium currents cannot be blocked in PD neurons without removing the calcium-dependent potassium current. Thus, the effects of calcium (ICa) and calcium-dependent potassium (IKCa) currents on resonant properties remain unclear. By taking advantage of Hodgkin-Huxley-type model of neuron and its equivalent RLC circuit, we examine the effects of changing resting membrane potential and those ionic currents on the resonance. Results show that changing the resting membrane potential influences the amplitude and frequency of resonance so that the strength of resonance (Q-value) increases by both depolarization and hyperpolarization of the resting membrane potential. Moreover, hyperpolarization-activated inward current (Ih) and ICa (in association with IKCa) are dominant factors on resonant properties at hyperpolarized and depolarized potentials, respectively. Through mathematical analysis, results indicate that Ih and IKCa affect the resonant properties of PD neurons. However, ICa only has an amplifying effect on the resonance amplitude of these neurons. PMID:25960999

  1. Mathematical modeling of subthreshold resonant properties in pyloric dilator neurons.

    PubMed

    Vazifehkhah Ghaffari, Babak; Kouhnavard, Mojgan; Aihara, Takeshi; Kitajima, Tatsuo

    2015-01-01

    Various types of neurons exhibit subthreshold resonance oscillation (preferred frequency response) to fluctuating sinusoidal input currents. This phenomenon is well known to influence the synaptic plasticity and frequency of neural network oscillation. This study evaluates the resonant properties of pacemaker pyloric dilator (PD) neurons in the central pattern generator network through mathematical modeling. From the pharmacological point of view, calcium currents cannot be blocked in PD neurons without removing the calcium-dependent potassium current. Thus, the effects of calcium (I(Ca)) and calcium-dependent potassium (I(KCa)) currents on resonant properties remain unclear. By taking advantage of Hodgkin-Huxley-type model of neuron and its equivalent RLC circuit, we examine the effects of changing resting membrane potential and those ionic currents on the resonance. Results show that changing the resting membrane potential influences the amplitude and frequency of resonance so that the strength of resonance (Q-value) increases by both depolarization and hyperpolarization of the resting membrane potential. Moreover, hyperpolarization-activated inward current (I(h)) and I(Ca) (in association with I(KCa)) are dominant factors on resonant properties at hyperpolarized and depolarized potentials, respectively. Through mathematical analysis, results indicate that I h and I(KCa) affect the resonant properties of PD neurons. However, I(Ca) only has an amplifying effect on the resonance amplitude of these neurons.

  2. Modeling Material Properties of Lead-Free Solder Alloys

    NASA Astrophysics Data System (ADS)

    Guo, Zhanli; Saunders, Nigel; Miodownik, Peter; Schillé, Jean-Philippe

    2008-01-01

    A full set of physical and thermophysical properties for lead-free solder (LFS) alloys have been calculated, including liquidus/solidus temperatures, fraction solid, density, coefficient of thermal expansion, thermal conductivity, Young’s modulus, viscosity, and liquid surface tension, all as a function of composition and temperature (extending into the liquid state). The results have been extensively validated against data available in the literature. A detailed comparison of the properties of two LFS alloys Sn-20In-2.8Ag and Sn-5.5Zn-4.5In-3.5Bi with Sn-37Pb has been made to show the utility and need for calculations that cover a wide range of properties, including the need to consider the effect of nonequilibrium cooling. The modeling of many of these properties follows well-established procedures previously used in JMatPro software for a range of structural alloys. This paper describes an additional procedure for the calculation of the liquid surface tension for multicomponent systems, based on the Butler equation. Future software developments are reviewed, including the addition of mechanical properties, but the present calculations can already make a useful contribution to the selection of appropriate new LFS alloys.

  3. Dosimetric studies of cadmium free alloy used in compensator based intensity modulated radiotherapy

    NASA Astrophysics Data System (ADS)

    Kaushik, Sandeep; Punia, Rajesh; Tyagi, Atul; Singh, Mann P.

    2017-10-01

    Aim of this study was to investigate dosimetric properties of cadmium free alloy which is used in compensator based intensity modulated radiotherapy (cIMRT). A mixture of lead, bismuth and tin was used to prepare the alloy whose melting point is 90-95 °C. Slabs of different thicknesses ranging from 0.71 cm to 6.14 cm were prepared. Density of alloy was measured by Archimedes' principle using water. For six megavolt (6 MV) photon beam energy transmission, linear effective attenuation coefficient (μeff), tissue phantom ratio (TPR1020), beam hardening, surface dose (Ds), percentage depth dose (PDD) and effect of scatter has been measured and analyzed for different field sizes and different thickness of compensator. Effect of extended source to detector distance (SDD) on transmissions and μeff was measured. The density of alloy was found to be 9.5456 g/cm3. At SDD of 100 cm, μeff was observed 0.4253 cm-1 for a field size of 10×10 cm 2. Calculated TPR1020 was found to be within 3% of experimental TPR1020 . It was found to be increasing with increasing thickness of compensator. Ds was found to decrease with thickness of compensator and increase with wider collimator opening due to increased scattered dose. Compensator slabs of 1 cm, 1.98 cm and 4.16 cm decreased surface dose by 4.2%, 6.1% and 9.5% respectively for a field size of 10×10 cm2 at 100 cm SDD. For small field size of 3×3 cm2 and 5×5 cm2 PDDs are increased from 3.0% to 5.5% of open beam PDDs as compensator thickness increased from 1 cm to 6.14 cm at a depth of 10 cm in water while variation in PDD is insignificant in for larger field sizes 10×10 cm2 to 20×20 cm2. A high degree of intensity modulation is essential in cIMRT and it can be achieved with this compensator material. Dosimetric properties analyzed in this study establish this alloy as a reliable, reusable, optimally dense and cost effective compensator material.

  4. Modeling transport properties of inhomogeneous superconductor-metal composites

    SciTech Connect

    Borroto, A.; Altshuler, E.; Del Río, L.; Arronte, M.; Johansen, T. H.

    2014-11-17

    We propose a model for a superconductor-metal composite that allows to derive intrinsic transport properties of the superconducting phase based on 2D images of its cross section, and a minimal set of parameters. The method is tested experimentally by using, as model composite, a “transversal bridge” made on a Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10+x} (BSCCO)-Ag multi-filamentary tape. It is shown that the approach allows to predict the measured I−〈E〉 curves of the filaments. In addition, one can determine the critical current anisotropy between the longitudinal and transverse directions of the Ag-BSCCO tape, and also of its superconducting filaments separately, which emphasizes the role of the morphology of the composite in the transport properties.

  5. Modeling hydrodynamic properties of open-cell metal foams

    NASA Astrophysics Data System (ADS)

    De Jaeger, P.; De Schampheleire, S.; Huisseune, H.; Ameel, B.; T'Joen, C.; De Paepe, M.

    2012-11-01

    Modeling the hydrodynamics of open-cell aluminum foam still is a challenging task because of the large range of length-scales, own to the physical phenomena which occur in the complex structure. Upscaling the classical conservation equations is a promising approach, but introduces the problem of modeling closure terms. This is dealt with via the well-known porous properties, i.e., permeability and inertial loss factor. Derivation of these properties is commonly done by linking pressure drop data to velocity via a second order interpolation. This, however, introduces significant deviation between the available data set, up to anorder of magnitude, which in turn results in difficulties to predict pressure drop during desing the desing phase of an applicaiton. As the closure terms have a well-defined physical meaning, it should be possible to compute them with better accuracy. This forms the topic of this paper.

  6. 2014 Enhanced LAW Glass Property-Composition Models, Phase 2

    SciTech Connect

    Muller, Isabelle; Pegg, Ian L.; Joseph, Innocent; Gilbo, Konstantin

    2015-10-28

    This report describes the results of testing specified by the Enhanced LAW Glass Property-Composition Models, VSL-13T3050-1, Rev. 0 Test Plan. The work was performed in compliance with the quality assurance requirements specified in the Test Plan. Results required by the Test Plan are reported. The te4st results and this report have been reviewed for correctness, technical adequacy, completeness, and accuracy.

  7. Influence of saturation properties on shell-model calculations

    NASA Astrophysics Data System (ADS)

    Abzouzi, A.; Caurier, E.; Zuker, A. P.

    1991-03-01

    It is shown that the nuclear Hamiltonian scrH separates rigorously into a monopole field scrHm and a multipole part scrHm. scrHm is entirely responsible for saturation properties and can be treated phenomenologically with few parameters. When realistic interactions are used for scrHM in regions from the p shell to the N=82 isotones, shell-model calculations yield excellent spectroscopy and demand nuclear radii very close to the observed ones.

  8. Modeling of Impact Properties of Auxetic Materials Phase 2

    DTIC Science & Technology

    2014-03-01

    Modeling of Impact Properties of Auxetic Materials – Phase 2 Lei Jiang, Dustin Pearson, Tim Dunbar Martec Limited Prepared By: Martec Limited 400...Manager: Lei Jiang, 902-425-5101 PWGSC Contract Number: W7707-135609/001/HAL CSA: Dr. Jeff Szabo, Defence Scientist, 902-427-3427 The scientific or...specifies the in-plane integration rule for 4-node shell elements. With IRQUAD = 2, “2×2 Gauss quadrature integration is employed”. The

  9. SU-E-T-342: Use of Patient Geometry Measurements to Predict Dosimetric Gain with VMAT Over 3D for Chestwall and Regional Nodal Radiation

    SciTech Connect

    Dumane, V; Knoll, M; Green, S; Bakst, R; Hunt, M; Steinberger, E

    2014-06-01

    Purpose: To predict the dosimetric gain of VMAT over 3D for the treatment ofchestwall/IMN/supraclavicular nodes using geometric parameters acquired during simulation Methods: CT scans for 20 left and 20 right sided patients were retrospectively analyzed toobtain percent ipsilateral lung volume included in the PWT and supraclavicular fields, central lung depth (CLD), maximum lung depth (MLD), separation, chestwall concavity (defined here as the product of CLD and separation) and the maximum heart depth (MHD). VMAT, PWT and P/E plans were done for each case. The ipsilateral lung V20 Gy and mean, total lung V20 Gy and mean, heart V25 Gy and mean were noted for each plan. Correlation coefficients were obtained and linear regression models were built using data from the above training set of patients and then tested on 4 new patients. Results: The decrease in ipsilateral lung V20 Gy, total lung V20 Gy, ipsilateral lung mean and total lung mean with VMAT over PWT significantly (p<0.05) correlated with the percent volume of ipsilateral lung included in the PWT and supraclavicular fields with correlation coefficient values of r = 0.83, r = 0.77, r = 0.78 and r = 0.75 respectively. Significant correlations were also found between MHD and the decrease in heart V25 Gy and mean of r = 0.77 and r = 0.67 respectively. Dosimetric improvement with VMAT over P/E plans showed no correlation to any of the geometric parameters investigated in this study. The dosimetric gain predicted for the 4 test cases by the linear regression models given their respective percent ipsilateral lung volumes fell within the 95% confidence intervals around the best regression fit. Conclusion: The percent ipsilateral lung volume appears to be a strong predictor of the dosimetric gain on using VMAT over PWT apriori.

  10. Spectroscopic properties of vitamin E models in solution

    NASA Astrophysics Data System (ADS)

    Oliveira, L. B. A.; Colherinhas, G.; Fonseca, T. L.; Castro, M. A.

    2015-05-01

    We investigate the first absorption band and the 13C and 17O magnetic shieldings of vitamin E models in chloroform and in water using the S-MC/QM methodology in combination with the TD-DFT and GIAO approaches. The results show that the solvent effects on these spectroscopic properties are small but a proper description of the solvent shift for 17O magnetic shielding of the hydroxyl group in water requires the use of explicit solute-solvent hydrogen bonds. In addition, the effect of the replacement of hydrogen atoms by methyl groups in the vitamin E models only affects magnetic shieldings.

  11. Potential ocular damage from microwave exposure during electrosurgery: dosimetric survey

    SciTech Connect

    Paz, J.D.; Milliken, R.; Ingram, W.T.; Frank, A.; Atkin, A.

    1987-07-01

    A dosimetric survey of microwave radiation emitted by electrosurgical units used in operating rooms indicated that surgeons expose themselves to levels that may be hazardous, and that ocular exposures are especially high: 20 cm from the active lead, electric field strength at the eye/forehead position was 9.0 X 10(6) V2/M2 for the monopolar unit; and magnetic field strength at this position reached a magnitude of 3.5 A2/M2. These electric and magnetic fields exceeded the TLVs of the American National Standards Institute. The authors concluded that the high levels of microwave radiation generated by electrosurgery devices should receive immediate attention to assess health effects associated with such exposures.

  12. Diagnostics techniques and dosimetric evaluations for environmental radioactivity investigations

    NASA Astrophysics Data System (ADS)

    Caridi, F.; D'Agostino, M.; Belvedere, A.; Marguccio, S.; Belmusto, G.; Gatto, M. F.

    2016-10-01

    A comprehensive study was conducted about the investigation of the natural/anthropo-genic radioactivity of various environmental matrices. Different diagnostics techniques were employed: high resolution HpGe gamma spectrometry, to quantify the activity concentration of radionuclides that emit gamma photons; alpha spectrometry, for the determination of the specific activity of α -emitters radioisotopes; liquid scintillation, to measure the activity concentration of tritium, radon and total alpha/beta in liquid samples; alpha spectrometry through the Rad7 setup, to estimate the gas radon activity concentration in air, water and soil; total alpha/beta counter, for the activity concentration quantification of radionuclides, in solid samples, emitting alpha/beta particles. From the dosimetric point of view, knowledge of the radioactivity level in the environmental matrices allows to evaluate any possible radiological hazard for the population, through the calculation of the appropriate parameters of radioprotection and their comparison with the safety limits reported by the literature.

  13. Bremsstrahlung dosimetric parameters of beta-emitting therapeutic radionuclides

    NASA Astrophysics Data System (ADS)

    Manjunatha, H. C.

    2016-03-01

    Dosimetric parameters such as efficiency of bremsstrahlung, probability of energy loss of beta during bremsstrahlung production, intensity and dose rate of high, medium and low-energy beta-emitting therapeutic radionuclides in different tissues of human organs are computed. These parameters are lower in adipose tissue than all other studied tissues. The efficiency, intensity and dose rate of bremsstrahlung increases with maximum energy of the beta nuclide (Emax) and modified atomic number (Zmod) of the target tissue. The estimated bremsstrahlung efficiency, intensity and dose rate are useful in the calculations of photon track-length distributions. These parameters are useful to determine the quality and quantity of the bremsstrahlung radiation (known as the source term). Precise estimation of this source term is very important in planning for radiotherapy and diagnosis.

  14. Studies on photon buildup for some thermoluminescent dosimetric compounds

    NASA Astrophysics Data System (ADS)

    Singh, V. P.; Badiger, N. M.

    2016-03-01

    Photon buildup for some SrSO4, BaSO4, MgSO4, MnSO4, FeSO4 and ZnSO4 thermoluminescent dosimetric (TLD) compounds was investigated in the present work. Photon energy absorption buildup factors and photon exposure build factors were computed for the TLD compounds using the five-parameter geometric progression fitting method in energy range 0.015-15 MeV for penetration depths up to 40 mean free path. The buildup factors were studied as a function of photon energy, penetration depth and chemical compositions. Effective atomic numbers and air-kerma for the TLD compounds were calculated and ICRU standard tissue equivalence was discussed.

  15. EFFECTIVE DOSIMETRIC HALF LIFE OF CESIUM 137 SOIL CONTAMINATION

    SciTech Connect

    Jannik, T; P Fledderman, P; Michael Paller, M

    2008-01-09

    In the early 1960s, an area of privately-owned swamp adjacent to the US Department of Energy's Savannah River Site (SRS), known as Creek Plantation, was contaminated by site operations. Studies conducted in 1974 estimated that approximately 925 GBq of {sup 137}Cs was deposited in the swamp. Subsequently, a series of surveys--composed of 52 monitoring locations--was initiated to characterize and trend the contaminated environment. The annual, potential, maximum doses to a hypothetical hunter were estimated by conservatively using the maximum {sup 137}Cs concentrations measured in the soil. The purpose of this report is to calculate an 'effective dosimetric' half-life for {sup 137}Cs in soil (based on the maximum concentrations) and compare it to the effective environmental half-life (based on the geometric mean concentrations).

  16. Mechanical properties characterization and modeling of active polymer gels

    NASA Astrophysics Data System (ADS)

    Marra, Steven Paul

    Active polymer gels expand and contract in response to certain environmental stimuli, such as the application of an electric field or a change in the pH level of the surroundings. This ability to achieve large, reversible deformations with no external mechanical loading has generated much interest in the use of these gels as actuators and "artificial muscles." While much work has been done to study the behavior and properties of these gels, little information is available regarding the full constitutive description of the mechanical and actuation properties. This work focuses on developing a means of characterizing the mechanical properties of active polymer gels and describing how these properties evolve as the gel actuates. Poly(vinyl alcohol)-poly(acrylic acid) (PVA-PAA) gel was chosen as the model material for this work because it is relatively simple and safe to both fabricate and actuate. PVA-PAA gels are fabricated on-site using a solvent-casting technique. These gels expand when moved from acidic to basic solutions, and contract when moved from basic to acidic solutions. Citric acid and sodium bicarbonate were used as the testing solutions for this work. The mechanical properties of the gel were characterized by conducting uniaxial and biaxial tests on thin PVA-PAA gel films. A biaxial testing system has been developed which can measure stresses and deformations of these films in a variety of liquid environments. The experimental results on PVA-PAA gels show these materials to be relatively compliant, and slightly viscoelastic and compressible. These gels are also capable of large recoverable deformations in both acidic and basic environments. A thermodynamically consistent finite-elastic constitutive model was developed to describe the mechanical and actuation behaviors of active polymer gels. The mechanical properties of the gel are characterized by a free-energy function, and the model utilizes an evolving internal variable to describe the actuation

  17. Loss of accuracy using smeared properties in composite beam modeling

    NASA Astrophysics Data System (ADS)

    Liu, Ning

    Advanced composite materials have broad, proven applications in many engineering systems ranging from sports equipment sectors to components on the space shuttle because of their lightweight characteristics and significantly high stiffness. Together with this merit of composite materials is the challenge of improving computational simulation process for composites analysis. Composite structures, particularly composite laminates, usually consist of many layers with different lay-up angles. The anisotropic and heterogeneous features render 3D finite element analysis (FEA) computationally expensive in terms of the computational time and the computing power. At the constituent level, composite materials are heterogeneous. But quite often one homogenizes each layer of composites, i.e. lamina, and uses the homogenized material properties as averaged (smeared) values of those constituent materials for analysis. This is an approach extensively used in design and analysis of composite laminates. Furthermore, many industries tempted to use smeared properties at the laminate level to further reduce the model of composite structures. At this scale, smeared properties are averaged material properties that are weighted by the layer thickness. Although this approach has the advantage of saving computational time and cost of modeling significantly, the prediction of the structural responses may not be accurate, particularly the pointwise stress distribution. Therefore, it is important to quantify the loss of accuracy when one uses smeared properties. In this paper, several different benchmark problems are carefully investigated in order to exemplify the effect of the smeared properties on the global behavior and pointwise stress distribution of the composite beam. In the classical beam theory, both Newtonian method and variational method include several ad hoc assumptions to construct the model, however, these assumptions are avoided if one uses variational asymptotic method. VABS

  18. Outer hair cell electromechanical properties in a nonlinear piezoelectric model

    PubMed Central

    Liu, Yi-Wen; Neely, Stephen T.

    2009-01-01

    A nonlinear piezoelectric circuit is proposed to model electromechanical properties of the outer hair cell (OHC) in mammalian cochleae. The circuit model predicts (a) that the nonlinear capacitance decreases as the stiffness of the load increases, and (b) that the axial compliance of the cell reaches a maximum at the same membrane potential for peak capacitance. The model was also designed to be integrated into macro-mechanical models to simulate cochlear wave propagation. Analytic expressions of the cochlear-partition shunt admittance and the wave propagation function are derived in terms of OHC electro-mechanical parameters. Small-signal analyses indicate that, to achieve cochlear amplification, (1) nonlinear capacitance must be sufficiently high and (2) the OHC receptor current must be sensitive to the velocity of the reticular lamina. PMID:19640041

  19. Outer hair cell electromechanical properties in a nonlinear piezoelectric model.

    PubMed

    Liu, Yi-Wen; Neely, Stephen T

    2009-08-01

    A nonlinear piezoelectric circuit is proposed to model electromechanical properties of the outer hair cell (OHC) in mammalian cochleae. The circuit model predicts (a) that the nonlinear capacitance decreases as the stiffness of the load increases, and (b) that the axial compliance of the cell reaches a maximum at the same membrane potential for peak capacitance. The model was also designed to be integrated into macro-mechanical models to simulate cochlear wave propagation. Analytic expressions of the cochlear-partition shunt admittance and the wave propagation function are derived in terms of OHC electro-mechanical parameters. Small-signal analyses indicate that, to achieve cochlear amplification, (1) nonlinear capacitance must be sufficiently high and (2) the OHC receptor current must be sensitive to the velocity of the reticular lamina.

  20. Representing the dosimetric impact of deformable image registration errors

    NASA Astrophysics Data System (ADS)

    Vickress, Jason; Battista, Jerry; Barnett, Rob; Yartsev, Slav

    2017-09-01

    Deformable image registration (DIR) is emerging as a tool in radiation therapy for calculating the cumulative dose distribution across multiple fractions of treatment. Unfortunately, due to the variable nature of DIR algorithms and dependence of performance on image quality, registration errors can result in dose accumulation errors. In this study, landmarked images were used to characterize the DIR error throughout an image space and determine its impact on dosimetric analysis. Ten thoracic 4DCT images with 300 landmarks per image study matching the end-inspiration and end-expiration phases were obtained from ‘dir-labs’. DIR was performed using commercial software MIM Maestro. The range of dose uncertainty (RDU) was calculated at each landmark pair as the maximum and minimum of the doses within a sphere around the landmark in the end-expiration phase. The radius of the sphere was defined by a measure of DIR error which included either the actual DIR error, mean DIR error per study, constant errors of 2 or 5 mm, inverse consistency error, transitivity error or the distance discordance metric (DDM). The RDUs were evaluated using the magnitude of dose uncertainty (MDU) and inclusion rate (IR) of actual error lying within the predicted RDU. The RDU was calculated for 300 landmark pairs on each 4DCT study for all measures of DIR error. The most representative RDU was determined using the actual DIR error with a MDU of 2.5 Gy and IR of 97%. Across all other measures of DIR error, the DDM was most predictive with a MDU of 2.5 Gy and IR of 86%, closest to the actual DIR error. The proposed method represents the range of dosimetric uncertainty of DIR error using either landmarks at specific voxels or measures of registration accuracy throughout the volume.

  1. Electron radiotherapy: a study on dosimetric uncertainty using small cutouts.

    PubMed

    Chow, James C L; Grigorov, Grigor N

    2007-01-07

    This note investigated the dosimetric uncertainties due to the positional error when centring a small cutout to the machine central beam axis (CAX) in electron radiotherapy. A group of six circular cutouts with 4 cm diameter were made with their centres shifting 0, 2, 4, 6, 8 and 10 mm from the machine CAX for the 6 x 6 cm(2) applicator. The per cent depth doses, beam profiles and output factors were measured using the 4, 9 and 16 MeV clinical electron beams produced by a Varian 21 EX linear accelerator. The 2D isodose distributions in the z-x (or cross-line) and z-y (or in-line) plane were calculated by Monte Carlo simulation using the EGSnrc system. When the cutout centre was shifted away from the machine CAX for the 4 MeV beam, the d(m), R(80) and R(90) at the machine CAX had no significant change (<0.1 mm). For higher energies of 9 and 16 MeV beams, the d(m) was reduced by 0.45 and 1.63 mm per mm, between the cutout centre and the machine CAX with off-axis shift <6 mm respectively. R(80) and R(90) were reduced by more than 0.3 mm per mm off-axis shift for both energies. The isodose coverage of the in-line axis beam profile was reduced when the cutout centre was shifted away from machine CAX. It is important for oncology staff to note such dosimetric changes in the clinical electron radiotherapy, particularly when a high energy electron beam is used for small cutout. Such positional uncertainty is unavoidable in fabricating an electron cutout in the mould room.

  2. SU-E-T-134: Dosimetric Implications From Organ Segmentation

    SciTech Connect

    Wu, Z; Turian, J; Chu, J

    2014-06-01

    Purpose: To evaluate the dosimetric implications resulting from organ segmentation performed by different clinical experts Methods: Twelve patients received SBRT treatment to thoracic region within the past year were selected for this study. Three physicians contoured a set of organs following RTOG guideline. DVHs of all contours were generated from the approved plans used for treatment, and were compared to those produced during planning. Most OARs were evaluated on their max dose, some, such as heart and chest wall, were also evaluated on metrics such as max dose to 4cc of volume, or 30Gy volume dose. Results: In general, there is a greater dosimetric difference between the RTOG contour sets and clinical contour sets than among the three RTOG contour sets themselves for each patient. For example, there was no difference in esophagus max dose between the RTOG contour sets for ten patients. However, they showed an average of 2.3% higher max dose than the clinical contour set, with a standard deviation of 6.6%. The proximal bronchial tree (PBT) showed a similar behavior. The average difference of PBT max dose for seven patients is 0% between the three RTOG contour sets, with standard deviation of 1%. They showed an average of 16.1% higher max dose than the clinical contour set, with a standard deviation of 126%. Conclusion: This study shows that using RTOG contouring standards improves segmentation consistency between different physicians; most of the contours examined showed less than 1% dose difference. When RTOG contour sets were compared to the clinical contour set, the differences are much more significant. Thus it is important to standardize contouring guidelines in radiation therapy treatment planning. This will reduce uncertainties in clinical outcome analysis and research studies.

  3. A model for evaluating physico-chemical substance properties required by consequence analysis models.

    PubMed

    Nikmo, Juha; Kukkonen, Jaakko; Riikonen, Kari

    2002-04-26

    Modeling systems for analyzing the consequences of chemical emergencies require as input values a number of physico-chemical substance properties, commonly as a function of temperature at atmospheric pressure. This paper presents a mathematical model "CHEMIC", which can be used for evaluating such substance properties, assuming that six basic constant quantities are available (molecular weight, freezing or melting point, normal boiling point, critical temperature, critical pressure and critical volume). The model has been designed to yield reasonably accurate numerical predictions, while at the same time keeping the amount of input data to a minimum. The model is based on molecular theory or thermodynamics, together with empirical corrections. Mostly, model equations are based on the so-called law of corresponding states. The model evaluates substance properties as a function of temperature at atmospheric pressure. These include seven properties commonly required by consequence analysis and heavy gas dispersion modeling systems: vapor pressure, vapor and liquid densities, heat of vaporization, vapor and liquid viscosities and binary diffusion coefficient. The model predictions for vapor pressure, vapor and liquid densities and heat of vaporization have been evaluated by using the Clausius-Clapeyron equation. We have also compared the predictions of the CHEMIC model with those of the DATABANK database (developed by the AEA Technology, UK), which includes detailed semi-empirical correlations. The computer program CHEMIC could be easily introduced into consequence analysis modeling systems in order to extend their performance to address a wider selection of substances.

  4. Microwave measurement and modeling of the dielectric properties of vegetation

    NASA Astrophysics Data System (ADS)

    Shrestha, Bijay Lal

    Some of the important applications of microwaves in the industrial, scientific and medical sectors include processing and treatment of various materials, and determining their physical properties. The dielectric properties of the materials of interest are paramount irrespective of the applications, hence, a wide range of materials covering food products, building materials, ores and fuels, and biological materials have been investigated for their dielectric properties. However, very few studies have been conducted towards the measurement of dielectric properties of green vegetations, including commercially important plant crops such as alfalfa. Because of its high nutritional value, there is a huge demand for this plant and its processed products in national and international markets, and an investigation into the possibility of applying microwaves to improve both the net yield and quality of the crop can be beneficial. Therefore, a dielectric measurement system based upon the probe reflection technique has been set up to measure dielectric properties of green plants over a frequency range from 300 MHz to 18 GHz, moisture contents from 12%, wet basis to 79%, wet basis, and temperatures from -15°C to 30°C. Dielectric properties of chopped alfalfa were measured with this system over frequency range of 300 MHz to 18 GHz, moisture content from 11.5%, wet basis, to 73%, wet basis, and density over the range from 139 kg m-3 to 716 kg m-3 at 23°C. The system accuracy was found to be +/-6% and +/-10% in measuring the dielectric constant and loss factor respectively. Empirical, semi empirical and theoretical models that require only moisture content and operating frequency were determined to represent the dielectric properties of both leaves and stems of alfalfa at 22°C. The empirical models fitted the measured dielectric data extremely well. The root mean square error (RMSE) and the coefficient of determination (r2) for dielectric constant and loss factor of leaves

  5. Properties of Ideal Point Classification Models for Bivariate Binary Data.

    PubMed

    Worku, Hailemichael M; De Rooij, Mark

    2017-06-01

    The ideal point classification (IPC) model was originally proposed for analysing multinomial data in the presence of predictors. In this paper, we studied properties of the IPC model for analysing bivariate binary data with a specific focus on three quantities: (1) the marginal probabilities; (2) the association structure between the two binary responses; and (3) the joint probabilities. We found that the IPC model with a specific class point configuration represents either the marginal probabilities or the association structure. However, the IPC model is not able to represent both quantities at the same time. We then derived a new parametrization of the model, the bivariate IPC (BIPC) model, which is able to represent both the marginal probabilities and the association structure. Like the standard IPC model, the results of the BIPC model can be displayed in a biplot, from which the effects of predictors on the binary responses and on their association can be read. We will illustrate our findings with a psychological example relating personality traits to depression and anxiety disorders.

  6. The Computational Properties of a Simplified Cortical Column Model.

    PubMed

    Cain, Nicholas; Iyer, Ramakrishnan; Koch, Christof; Mihalas, Stefan

    2016-09-01

    The mammalian neocortex has a repetitious, laminar structure and performs functions integral to higher cognitive processes, including sensory perception, memory, and coordinated motor output. What computations does this circuitry subserve that link these unique structural elements to their function? Potjans and Diesmann (2014) parameterized a four-layer, two cell type (i.e. excitatory and inhibitory) model of a cortical column with homogeneous populations and cell type dependent connection probabilities. We implement a version of their model using a displacement integro-partial differential equation (DiPDE) population density model. This approach, exact in the limit of large homogeneous populations, provides a fast numerical method to solve equations describing the full probability density distribution of neuronal membrane potentials. It lends itself to quickly analyzing the mean response properties of population-scale firing rate dynamics. We use this strategy to examine the input-output relationship of the Potjans and Diesmann cortical column model to understand its computational properties. When inputs are constrained to jointly and equally target excitatory and inhibitory neurons, we find a large linear regime where the effect of a multi-layer input signal can be reduced to a linear combination of component signals. One of these, a simple subtractive operation, can act as an error signal passed between hierarchical processing stages.

  7. The Computational Properties of a Simplified Cortical Column Model

    PubMed Central

    Iyer, Ramakrishnan; Koch, Christof; Mihalas, Stefan

    2016-01-01

    The mammalian neocortex has a repetitious, laminar structure and performs functions integral to higher cognitive processes, including sensory perception, memory, and coordinated motor output. What computations does this circuitry subserve that link these unique structural elements to their function? Potjans and Diesmann (2014) parameterized a four-layer, two cell type (i.e. excitatory and inhibitory) model of a cortical column with homogeneous populations and cell type dependent connection probabilities. We implement a version of their model using a displacement integro-partial differential equation (DiPDE) population density model. This approach, exact in the limit of large homogeneous populations, provides a fast numerical method to solve equations describing the full probability density distribution of neuronal membrane potentials. It lends itself to quickly analyzing the mean response properties of population-scale firing rate dynamics. We use this strategy to examine the input-output relationship of the Potjans and Diesmann cortical column model to understand its computational properties. When inputs are constrained to jointly and equally target excitatory and inhibitory neurons, we find a large linear regime where the effect of a multi-layer input signal can be reduced to a linear combination of component signals. One of these, a simple subtractive operation, can act as an error signal passed between hierarchical processing stages. PMID:27617444

  8. Semiclassical model and properties of resonant tunneling diode

    NASA Astrophysics Data System (ADS)

    Sheng, H.

    1991-12-01

    A semiclassical model involving the semiclassical transport theory is developed for the double barrier resonant tunneling diode (RTD). In the transport theory, a correlation function which accounts for the phase coherence is introduced. By means of a simple multiple scattering theory, the correlation function can be analytically expressed. Based on the semiclassical transport theory, the DC and AC small signal models are built. DC properties, such as current, quantum well charge density, voltage distribution, accumulation layer current, capacitance as well as conductance are analyzed and calculated in detail. Fabrication and measurement of RTD are also carried out and the experimental and the theoretical results agree well. An improved design, the graded spacer layer resonant tunneling diode, is proposed. This new design promises to greatly increase the peak-to-valley current ratio. In the AC small signal model, the cutoff frequency is calculated and an expression for the recently found inductance in the equivalent circuit is derived. Also the high frequency oscillations associated with the transit time resonance are obtained. Also, this infrared resonance property is analyzed by a quantum model.

  9. Modeling of Manganese Ferroalloy Slag Properties and Flow During Tapping

    NASA Astrophysics Data System (ADS)

    Muller, Jacques; Zietsman, Johannes Hendrik; Pistorius, Petrus Christiaan

    2015-12-01

    Stable operation of submerged-arc furnaces producing high-carbon ferromanganese (HCFeMn) and silicomanganese (SiMn) requires tapping of consistent amounts of liquid slag and metal. Minimal effort to initiate and sustain tapping at reasonable rates is desired, accommodating fluctuations in especially slag chemical composition and temperature. An analytical model is presented that estimates the tapping rate of the liquid slag-metal mixture as a function of taphole dimensions, coke bed particulate properties, and slag and metal physicochemical properties with dependencies on chemical composition and temperature. This model may be used to evaluate the sensitivity to fluctuations in these parameters, and to determine the influence of converting between HCFeMn and SiMn production. The model was applied to typical HCFeMn and SiMn process conditions, using modeled slag viscosities and densities. Tapping flow rates estimated were comparable to operational data and found to be dependent mostly on slag viscosity. Slag viscosities were generally lower for typical SiMn slags due to the higher temperature used for calculating viscosity. It was predicted that flow through the taphole would mostly develop into laminar flow, with the pressure drop predominantly over the coke bed. Flow rates were found to be more dependent on the taphole diameter than on the taphole length.

  10. Improvements in Critical Dosimetric Endpoints Using the Contura Multilumen Balloon Breast Brachytherapy Catheter to Deliver Accelerated Partial Breast Irradiation: Preliminary Dosimetric Findings of a Phase IV Trial

    SciTech Connect

    Arthur, Douglas W.; Vicini, Frank A.; Todor, Dorin A.; Julian, Thomas B.; Lyden, Maureen R.

    2011-01-01

    Purpose: Dosimetric findings in patients treated with the Contura multilumen balloon (MLB) breast brachytherapy catheter to deliver accelerated partial breast irradiation (APBI) on a multi-institutional Phase IV registry trial are presented. Methods and Materials: Computed tomography-based three-dimensional planning with dose optimization was performed. For the trial, new ideal dosimetric goals included (1) {>=}95% of the prescribed dose (PD) covering {>=}90% of the target volume, (2) a maximum skin dose {<=}125% of the PD, (3) maximum rib dose {<=}145% of the PD, and (4) the V150 {<=}50 cc and V200 {<=}10 cc. The ability to concurrently achieve these dosimetric goals using the Contura MLB was analyzed. Results: 144 cases were available for review. Using the MLB, all dosimetric criteria were met in 76% of cases. Evaluating dosimetric criteria individually, 92% and 89% of cases met skin and rib dose criteria, respectively. In 93% of cases, ideal target volume coverage goals were met, and in 99%, dose homogeneity criteria (V150 and V200) were satisfied. When skin thickness was {>=}5 mm to <7 mm, the median skin dose was limited to 120.1% of the PD, and when skin thickness was <5 mm, the median skin dose was 124.2%. When rib distance was <5 mm, median rib dose was reduced to 136.5% of the PD. When skin thickness was <7 mm and distance to rib was <5 mm, median skin and rib doses were jointly limited to 120.6% and 142.1% of the PD, respectively. Conclusion: The Contura MLB catheter provided the means of achieving the imposed higher standard of dosimetric goals in the majority of clinical scenarios encountered.

  11. Reliable Estimation of Prediction Uncertainty for Physicochemical Property Models.

    PubMed

    Proppe, Jonny; Reiher, Markus

    2017-07-11

    One of the major challenges in computational science is to determine the uncertainty of a virtual measurement, that is the prediction of an observable based on calculations. As highly accurate first-principles calculations are in general unfeasible for most physical systems, one usually resorts to parameteric property models of observables, which require calibration by incorporating reference data. The resulting predictions and their uncertainties are sensitive to systematic errors such as inconsistent reference data, parametric model assumptions, or inadequate computational methods. Here, we discuss the calibration of property models in the light of bootstrapping, a sampling method that can be employed for identifying systematic errors and for reliable estimation of the prediction uncertainty. We apply bootstrapping to assess a linear property model linking the (57)Fe Mössbauer isomer shift to the contact electron density at the iron nucleus for a diverse set of 44 molecular iron compounds. The contact electron density is calculated with 12 density functionals across Jacob's ladder (PWLDA, BP86, BLYP, PW91, PBE, M06-L, TPSS, B3LYP, B3PW91, PBE0, M06, TPSSh). We provide systematic-error diagnostics and reliable, locally resolved uncertainties for isomer-shift predictions. Pure and hybrid density functionals yield average prediction uncertainties of 0.06-0.08 mm s(-1) and 0.04-0.05 mm s(-1), respectively, the latter being close to the average experimental uncertainty of 0.02 mm s(-1). Furthermore, we show that both model parameters and prediction uncertainty depend significantly on the composition and number of reference data points. Accordingly, we suggest that rankings of density functionals based on performance measures (e.g., the squared coefficient of correlation, r(2), or the root-mean-square error, RMSE) should not be inferred from a single data set. This study presents the first statistically rigorous calibration analysis for theoretical M

  12. Modeling adsorbate-induced property changes of carbon nanotubes.

    PubMed

    Groß, Lynn; Bahlke, Marc Philipp; Steenbock, Torben; Klinke, Christian; Herrmann, Carmen

    2017-05-05

    Because of their potential for chemical functionalization, carbon nanotubes (CNTs) are promising candidates for the development of devices such as nanoscale sensors or transistors with novel gating mechanisms. However, the mechanisms underlying the property changes due to functionalization of CNTs still remain subject to debate. Our goal is to reliably model one possible mechanism for such chemical gating: adsorption directly on the nanotubes. Within a Kohn-Sham density functional theory framework, such systems would ideally be described using periodic boundary conditions. Truncating the tube and saturating the edges in practice often offers a broader selection of approximate exchange-correlation functionals and analysis methods. By comparing the two approaches systematically for NH3 and NO2 adsorbates on semiconducting and metallic CNTs, we find that while structural properties are less sensitive to the details of the model, local properties of the adsorbate may be as sensitive to truncation as they are to the choice of exchange-correlation functional, and are similarly challenging to compute as adsorption energies. This suggests that these adsorbate effects are nonlocal. © 2017 Wiley Periodicals, Inc.

  13. The investigation of prostatic calcifications using μ-PIXE analysis and their dosimetric effect in low dose rate brachytherapy treatments using Geant4.

    PubMed

    Pope, D J; Cutajar, D L; George, S P; Guatelli, S; Bucci, J A; Enari, K E; Miller, S; Siegele, R; Rosenfeld, A B

    2015-06-07

    Low dose rate brachytherapy is a widely used modality for the treatment of prostate cancer. Most clinical treatment planning systems currently in use approximate all tissue to water, neglecting the existence of inhomogeneities, such as calcifications. The presence of prostatic calcifications may perturb the dose due to the higher photoelectric effect cross section in comparison to water. This study quantitatively evaluates the effect of prostatic calcifications on the dosimetric outcome of brachytherapy treatments by means of Monte Carlo simulations and its potential clinical consequences.Four pathological calcification samples were characterised with micro-particle induced x-ray emission (μ-PIXE) to determine their heavy elemental composition. Calcium, phosphorus and zinc were found to be the predominant heavy elements in the calcification composition. Four clinical patient brachytherapy treatments were modelled using Geant4 based Monte Carlo simulations, in terms of the distribution of brachytherapy seeds and calcifications in the prostate. Dose reductions were observed to be up to 30% locally to the calcification boundary, calcification size dependent. Single large calcifications and closely placed calculi caused local dose reductions of between 30-60%. Individual calculi smaller than 0.5 mm in diameter showed minimal dosimetric impact, however, the effects of small or diffuse calcifications within the prostatic tissue could not be determined using the methods employed in the study. The simulation study showed a varying reduction on common dosimetric parameters. D90 showed a reduction of 2-5%, regardless of calcification surface area and volume. The parameters V100, V150 and V200 were also reduced by as much as 3% and on average by 1%. These reductions were also found to relate to the surface area and volume of calcifications, which may have a significant dosimetric impact on brachytherapy treatment, however, such impacts depend strongly on specific factors

  14. Dosimetric Impact of Intrafraction Motion During RapidArc Stereotactic Vertebral Radiation Therapy Using Flattened and Flattening Filter-Free Beams

    SciTech Connect

    Ong, Chin Loon; Dahele, Max; Cuijpers, Johan P.; Senan, Suresh; Slotman, Ben J.; Verbakel, Wilko F.A.R.

    2013-07-01

    Purpose: To study the dosimetric impact of relatively short-duration intrafraction shifts during a single fraction of RapidArc delivery for vertebral stereotactic body radiation therapy (SBRT) using flattened (FF) and flattening filter-free (FFF) beams. Methods and Materials: The RapidArc plans, each with 2 to 3 arcs, were generated for 9 patients using 6-MV FF and 10-MV FFF beams with maximum dose rates of 1000 and 2400 MU/min, respectively. A total of 1272 plans were created to estimate the dosimetric consequences in target and spinal cord volumes caused by intrafraction shifts during one of the arcs. Shifts of 1, 2, and 3 mm for periods of 5, 10, and 30 seconds, and 5 mm for 5 and 10 seconds, were modelled during a part of the arc associated with high doses and steep dose gradients. Results: For FFF plans, shifts of 2 mm over 10 seconds and 30 seconds could increase spinal cord D{sub max} by up to 6.5% and 13%, respectively. Dosimetric deviations in FFF plans were approximately 2-fold greater than in FF plans. Reduction in target coverage was <1% for 83% and 96% of the FFF and FF plans, respectively. Conclusion: Even short-duration intrafraction shifts can cause significant dosimetric deviations during vertebral SBRT delivery, especially when using very high dose rate FFF beams and when the shift occurs in that part of the arc delivering high doses and steep gradients. The impact is greatest on the spinal cord and its planning-at-risk volume. Accurate and stable patient positioning is therefore required for vertebral SBRT.

  15. Helium ions at the heidelberg ion beam therapy center: comparisons between FLUKA Monte Carlo code predictions and dosimetric measurements

    NASA Astrophysics Data System (ADS)

    Tessonnier, T.; Mairani, A.; Brons, S.; Sala, P.; Cerutti, F.; Ferrari, A.; Haberer, T.; Debus, J.; Parodi, K.

    2017-08-01

    In the field of particle therapy helium ion beams could offer an alternative for radiotherapy treatments, owing to their interesting physical and biological properties intermediate between protons and carbon ions. We present in this work the comparisons and validations of the Monte Carlo FLUKA code against in-depth dosimetric measurements acquired at the Heidelberg Ion Beam Therapy Center (HIT). Depth dose distributions in water with and without ripple filter, lateral profiles at different depths in water and a spread-out Bragg peak were investigated. After experimentally-driven tuning of the less known initial beam characteristics in vacuum (beam lateral size and momentum spread) and simulation parameters (water ionization potential), comparisons of depth dose distributions were performed between simulations and measurements, which showed overall good agreement with range differences below 0.1 mm and dose-weighted average dose-differences below 2.3% throughout the entire energy range. Comparisons of lateral dose profiles showed differences in full-width-half-maximum lower than 0.7 mm. Measurements of the spread-out Bragg peak indicated differences with simulations below 1% in the high dose regions and 3% in all other regions, with a range difference less than 0.5 mm. Despite the promising results, some discrepancies between simulations and measurements were observed, particularly at high energies. These differences were attributed to an underestimation of dose contributions from secondary particles at large angles, as seen in a triple Gaussian parametrization of the lateral profiles along the depth. However, the results allowed us to validate FLUKA simulations against measurements, confirming its suitability for 4He ion beam modeling in preparation of clinical establishment at HIT. Future activities building on this work will include treatment plan comparisons using validated biological models between proton and helium ions, either within a Monte Carlo

  16. Helium ions at the heidelberg ion beam therapy center: comparisons between FLUKA Monte Carlo code predictions and dosimetric measurements.

    PubMed

    Tessonnier, T; Mairani, A; Brons, S; Sala, P; Cerutti, F; Ferrari, A; Haberer, T; Debus, J; Parodi, K

    2017-08-01

    In the field of particle therapy helium ion beams could offer an alternative for radiotherapy treatments, owing to their interesting physical and biological properties intermediate between protons and carbon ions. We present in this work the comparisons and validations of the Monte Carlo FLUKA code against in-depth dosimetric measurements acquired at the Heidelberg Ion Beam Therapy Center (HIT). Depth dose distributions in water with and without ripple filter, lateral profiles at different depths in water and a spread-out Bragg peak were investigated. After experimentally-driven tuning of the less known initial beam characteristics in vacuum (beam lateral size and momentum spread) and simulation parameters (water ionization potential), comparisons of depth dose distributions were performed between simulations and measurements, which showed overall good agreement with range differences below 0.1 mm and dose-weighted average dose-differences below 2.3% throughout the entire energy range. Comparisons of lateral dose profiles showed differences in full-width-half-maximum lower than 0.7 mm. Measurements of the spread-out Bragg peak indicated differences with simulations below 1% in the high dose regions and 3% in all other regions, with a range difference less than 0.5 mm. Despite the promising results, some discrepancies between simulations and measurements were observed, particularly at high energies. These differences were attributed to an underestimation of dose contributions from secondary particles at large angles, as seen in a triple Gaussian parametrization of the lateral profiles along the depth. However, the results allowed us to validate FLUKA simulations against measurements, confirming its suitability for (4)He ion beam modeling in preparation of clinical establishment at HIT. Future activities building on this work will include treatment plan comparisons using validated biological models between proton and helium ions, either within a Monte Carlo

  17. Dosimetric consequences of manual pullback procedure for coronary artery radiotherapy with 90Sr/90Y beta-source.

    PubMed

    Iftimia, Ileana; Devlin, Phillip M; Martin, Andre-Guy; Shakur, Rameen; Almonacid, Alexandra; Kazakin, Julia; Chin, Lee M; Cormack, Robert A

    2004-01-01

    This work presents a quantitative dosimetric analysis of the Novoste (90)Sr/(90)Y beta-source cardiovascular brachytherapy treatments using a manual pullback technique for patients with in-stent restenosis. Based on our previous measurements, a model was developed to estimate the dose in the middle of the junction region for tandem irradiation expressed as fraction of prescription dose (FPD) and dosimetric overlap length (DOL) receiving more/less than a threshold dose. The overlap/gap size was measured using the digital cine images recorded during treatment and then FPD and DOL were quantified. Statistical analysis of 55 patients showed that the overlap size and the FPD at 2 mm radial distance were in range of 0 to 23 mm and 13-200% of prescription dose (Rx), respectively. Four gaps out of 76 pullback cases were found, but their size was at most 5 mm. Use of a 5 mm overlap avoided underdosed regions in the vast majority of the cases. These results are the first step towards an analysis of the clinical outcome of these patients.

  18. Verification of dosimetric accuracy on the TrueBeam STx: Rounded leaf effect of the high definition MLC

    SciTech Connect

    Kielar, Kayla N.; Mok, Ed; Hsu, Annie; Wang Lei; Luxton, Gary

    2012-10-15

    Purpose: The dosimetric leaf gap (DLG) in the Varian Eclipse treatment planning system is determined during commissioning and is used to model the effect of the rounded leaf-end of the multileaf collimator (MLC). This parameter attempts to model the physical difference between the radiation and light field and account for inherent leakage between leaf tips. With the increased use of single fraction high dose treatments requiring larger monitor units comes an enhanced concern in the accuracy of leakage calculations, as it accounts for much of the patient dose. This study serves to verify the dosimetric accuracy of the algorithm used to model the rounded leaf effect for the TrueBeam STx, and describes a methodology for determining best-practice parameter values, given the novel capabilities of the linear accelerator such as flattening filter free (FFF) treatments and a high definition MLC (HDMLC). Methods: During commissioning, the nominal MLC position was verified and the DLG parameter was determined using MLC-defined field sizes and moving gap tests, as is common in clinical testing. Treatment plans were created, and the DLG was optimized to achieve less than 1% difference between measured and calculated dose. The DLG value found was tested on treatment plans for all energies (6 MV, 10 MV, 15 MV, 6 MV FFF, 10 MV FFF) and modalities (3D conventional, IMRT, conformal arc, VMAT) available on the TrueBeam STx. Results: The DLG parameter found during the initial MLC testing did not match the leaf gap modeling parameter that provided the most accurate dose delivery in clinical treatment plans. Using the physical leaf gap size as the DLG for the HDMLC can lead to 5% differences in measured and calculated doses. Conclusions: Separate optimization of the DLG parameter using end-to-end tests must be performed to ensure dosimetric accuracy in the modeling of the rounded leaf ends for the Eclipse treatment planning system. The difference in leaf gap modeling versus physical

  19. Dosimetric characterization of a microDiamond detector in clinical scanned carbon ion beams.

    PubMed

    Marinelli, Marco; Prestopino, G; Verona, C; Verona-Rinati, G; Ciocca, M; Mirandola, A; Mairani, A; Raffaele, L; Magro, G

    2015-04-01

    To investigate for the first time the dosimetric properties of a new commercial synthetic diamond detector (PTW microDiamond) in high-energy scanned clinical carbon ion beams generated by a synchrotron at the CNAO facility. The detector response was evaluated in a water phantom with actively scanned carbon ion beams ranging from 115 to 380 MeV/u (30-250 mm Bragg peak depth in water). Homogeneous square fields of 3 × 3 and 6 × 6 cm(2) were used. Short- and medium-term (2 months) detector response stability, dependence on beam energy as well as ion type (carbon ions and protons), linearity with dose, and directional and dose-rate dependence were investigated. The depth dose curve of a 280 MeV/u carbon ion beam, scanned over a 3 × 3 cm(2) area, was measured with the microDiamond detector and compared to that measured using a PTW Advanced Markus ionization chamber, and also simulated using fluka Monte Carlo code. The detector response in two spread-out-Bragg-peaks (SOBPs), respectively, centered at 9 and 21 cm depths in water and calculated using the treatment planning system (TPS) used at CNAO, was measured. A negligible drift of detector sensitivity within the experimental session was seen, indicating that no detector preirradiation was needed. Short-term response reproducibility around 1% (1 standard deviation) was found. Only 2% maximum variation of microDiamond sensitivity was observed among all the evaluated proton and carbon ion beam energies. The detector response showed a good linear behavior. Detector sensitivity was found to be dose-rate independent, with a variation below 1.3% in the evaluated dose-rate range. A very good agreement between measured and simulated Bragg curves with both microDiamond and Advanced Markus chamber was found, showing a negligible LET dependence of the tested detector. A depth dose curve was also measured by positioning the microDiamond with its main axis oriented orthogonally to the beam direction. A strong distortion in Bragg

  20. Dosimetric robustness against setup errors in charged particle radiotherapy of skull base tumors.

    PubMed

    Ammazzalorso, Filippo; Jelen, Urszula; Engenhart-Cabillic, Rita; Schlegel, Wolfgang

    2014-12-05

    It is expected that physical dose deposition properties render charged particle dose distributions sensitive to targeting uncertainties. Purpose of this work was to investigate the robustness of scanned-beam particle therapy plans against setup errors for different optimization modalities, beam setups and ion species. For 15 patients with skull base tumors, localized in regions of severe tissue density heterogeneity, scanned lateral-opposed-beam treatment plans were prepared with the treatment planning system TRiP98, employing different optimization settings (single- and multiple-field modulation) and ion species (carbon ions and protons). For 10 of the patients, additional plans were prepared with individually selected beam setups, aiming at avoiding severe tissue heterogeneities. Subsequently, multiple rigid positioning errors of magnitude 1-2 mm (i.e. within planning target expansion) were simulated by introducing a shift of the irradiation fields with respect to the computed tomography (CT) data and recomputing the plans. In presence of shifts, in carbon ion plans using a lateral-opposed beam setup and fulfilling clinical healthy tissue dose constraints, the median reduction in CTV V95% was up to 0.7 percentage points (pp) and 3.5 pp, for shifts of magnitude 1 mm and 2 mm respectively, however, in individual cases, the reduction reached 5.1 pp and 9.7 pp. In the corresponding proton plans similar median CTV V95% reductions of up to 0.9 pp (1 mm error) and 3.4 pp (2 mm error) were observed, with respective individual-case reductions of at most 3.2 pp and 11.7 pp. Unconstrained plans offered slightly higher coverage values, while no relevant differences were observed between different field modulation methods. Individually selected beam setups had a visible dosimetric advantage over lateral-opposed beams, for both particle species. While carbons provided more conformal plans and generally more advantageous absolute dose values, in presence of setup errors

  1. Dosimetric characterization of a microDiamond detector in clinical scanned carbon ion beams

    SciTech Connect

    Marinelli, Marco; Prestopino, G. Verona, C.; Verona-Rinati, G.; Ciocca, M.; Mirandola, A.; Mairani, A.; Raffaele, L.; Magro, G.

    2015-04-15

    Purpose: To investigate for the first time the dosimetric properties of a new commercial synthetic diamond detector (PTW microDiamond) in high-energy scanned clinical carbon ion beams generated by a synchrotron at the CNAO facility. Methods: The detector response was evaluated in a water phantom with actively scanned carbon ion beams ranging from 115 to 380 MeV/u (30–250 mm Bragg peak depth in water). Homogeneous square fields of 3 × 3 and 6 × 6 cm{sup 2} were used. Short- and medium-term (2 months) detector response stability, dependence on beam energy as well as ion type (carbon ions and protons), linearity with dose, and directional and dose-rate dependence were investigated. The depth dose curve of a 280 MeV/u carbon ion beam, scanned over a 3 × 3 cm{sup 2} area, was measured with the microDiamond detector and compared to that measured using a PTW Advanced Markus ionization chamber, and also simulated using FLUKA Monte Carlo code. The detector response in two spread-out-Bragg-peaks (SOBPs), respectively, centered at 9 and 21 cm depths in water and calculated using the treatment planning system (TPS) used at CNAO, was measured. Results: A negligible drift of detector sensitivity within the experimental session was seen, indicating that no detector preirradiation was needed. Short-term response reproducibility around 1% (1 standard deviation) was found. Only 2% maximum variation of microDiamond sensitivity was observed among all the evaluated proton and carbon ion beam energies. The detector response showed a good linear behavior. Detector sensitivity was found to be dose-rate independent, with a variation below 1.3% in the evaluated dose-rate range. A very good agreement between measured and simulated Bragg curves with both microDiamond and Advanced Markus chamber was found, showing a negligible LET dependence of the tested detector. A depth dose curve was also measured by positioning the microDiamond with its main axis oriented orthogonally to the beam

  2. Electromagnetic sinc Schell-model beams and their statistical properties.

    PubMed

    Mei, Zhangrong; Mao, Yonghua

    2014-09-22

    A class of electromagnetic sources with sinc Schell-model correlations is introduced. The conditions on source parameters guaranteeing that the source generates a physical beam are derived. The evolution behaviors of statistical properties for the electromagnetic stochastic beams generated by this new source on propagating in free space and in atmosphere turbulence are investigated with the help of the weighted superposition method and by numerical simulations. It is demonstrated that the intensity distributions of such beams exhibit unique features on propagating in free space and produce a double-layer flat-top profile of being shape-invariant in the far field. This feature makes this new beam particularly suitable for some special laser processing applications. The influences of the atmosphere turbulence with a non-Kolmogorov power spectrum on statistical properties of the new beams are analyzed in detail.

  3. Reginal Frequency Analysis Based on Scaling Properties and Bayesian Models

    NASA Astrophysics Data System (ADS)

    Kwon, Hyun-Han; Lee, Jeong-Ju; Moon, Young-Il

    2010-05-01

    A regional frequency analysis based on Hierarchical Bayesian Network (HBN) and scaling theory was developmed. Many recording rain gauges over South Korea were used for the analysis. First, a scaling approach combined with extreme distribution was employed to derive regional formula for frequency analysis. Second, HBN model was used to represent additional information about the regional structure of the scaling parameters, especially the location parameter and shape parameter. The location and shape parameters of the extreme distribution were estimated by utilizing scaling properties in a regression framework, and the scaling parameters linking the parameters (location and shape) to various duration times were simultaneously estimated. It was found that the regional frequency analysis combined with HBN and scaling properties show promising results in terms of establishing regional IDF curves.

  4. Geometrical properties of the Potts model during the coarsening regime.

    PubMed

    Loureiro, Marcos P O; Arenzon, Jeferson J; Cugliandolo, Leticia F

    2012-02-01

    We study the dynamic evolution of geometric structures in a polydegenerate system represented by a q-state Potts model with nonconserved order parameter that is quenched from its disordered into its ordered phase. The numerical results obtained with Monte Carlo simulations show a strong relation between the statistical properties of hull perimeters in the initial state and during coarsening: The statistics and morphology of the structures that are larger than the averaged ones are those of the initial state, while the ones of small structures are determined by the curvature-driven dynamic process. We link the hull properties to the ones of the areas they enclose. We analyze the linear von Neumann-Mullins law, both for individual domains and on the average, concluding that its validity, for the later case, is limited to domains with number of sides around 6, while presenting stronger violations in the former case. © 2012 American Physical Society

  5. SPECIES - EVALUATING THERMODYNAMIC PROPERTIES, TRANSPORT PROPERTIES & EQUILIBRIUM CONSTANTS OF AN 11-SPECIES AIR MODEL

    NASA Technical Reports Server (NTRS)

    Thompson, R. A.

    1994-01-01

    Accurate numerical prediction of high-temperature, chemically reacting flowfields requires a knowledge of the physical properties and reaction kinetics for the species involved in the reacting gas mixture. Assuming an 11-species air model at temperatures below 30,000 degrees Kelvin, SPECIES (Computer Codes for the Evaluation of Thermodynamic Properties, Transport Properties, and Equilibrium Constants of an 11-Species Air Model) computes values for the species thermodynamic and transport properties, diffusion coefficients and collision cross sections for any combination of the eleven species, and reaction rates for the twenty reactions normally occurring. The species represented in the model are diatomic nitrogen, diatomic oxygen, atomic nitrogen, atomic oxygen, nitric oxide, ionized nitric oxide, the free electron, ionized atomic nitrogen, ionized atomic oxygen, ionized diatomic nitrogen, and ionized diatomic oxygen. Sixteen subroutines compute the following properties for both a single species, interaction pair, or reaction, and an array of all species, pairs, or reactions: species specific heat and static enthalpy, species viscosity, species frozen thermal conductivity, diffusion coefficient, collision cross section (OMEGA 1,1), collision cross section (OMEGA 2,2), collision cross section ratio, and equilibrium constant. The program uses least squares polynomial curve-fits of the most accurate data believed available to provide the requested values more quickly than is possible with table look-up methods. The subroutines for computing transport coefficients and collision cross sections use additional code to correct for any electron pressure when working with ionic species. SPECIES was developed on a SUN 3/280 computer running the SunOS 3.5 operating system. It is written in standard FORTRAN 77 for use on any machine, and requires roughly 92K memory. The standard distribution medium for SPECIES is a 5.25 inch 360K MS-DOS format diskette. The contents of the

  6. SPECIES - EVALUATING THERMODYNAMIC PROPERTIES, TRANSPORT PROPERTIES & EQUILIBRIUM CONSTANTS OF AN 11-SPECIES AIR MODEL

    NASA Technical Reports Server (NTRS)

    Thompson, R. A.

    1994-01-01

    Accurate numerical prediction of high-temperature, chemically reacting flowfields requires a knowledge of the physical properties and reaction kinetics for the species involved in the reacting gas mixture. Assuming an 11-species air model at temperatures below 30,000 degrees Kelvin, SPECIES (Computer Codes for the Evaluation of Thermodynamic Properties, Transport Properties, and Equilibrium Constants of an 11-Species Air Model) computes values for the species thermodynamic and transport properties, diffusion coefficients and collision cross sections for any combination of the eleven species, and reaction rates for the twenty reactions normally occurring. The species represented in the model are diatomic nitrogen, diatomic oxygen, atomic nitrogen, atomic oxygen, nitric oxide, ionized nitric oxide, the free electron, ionized atomic nitrogen, ionized atomic oxygen, ionized diatomic nitrogen, and ionized diatomic oxygen. Sixteen subroutines compute the following properties for both a single species, interaction pair, or reaction, and an array of all species, pairs, or reactions: species specific heat and static enthalpy, species viscosity, species frozen thermal conductivity, diffusion coefficient, collision cross section (OMEGA 1,1), collision cross section (OMEGA 2,2), collision cross section ratio, and equilibrium constant. The program uses least squares polynomial curve-fits of the most accurate data believed available to provide the requested values more quickly than is possible with table look-up methods. The subroutines for computing transport coefficients and collision cross sections use additional code to correct for any electron pressure when working with ionic species. SPECIES was developed on a SUN 3/280 computer running the SunOS 3.5 operating system. It is written in standard FORTRAN 77 for use on any machine, and requires roughly 92K memory. The standard distribution medium for SPECIES is a 5.25 inch 360K MS-DOS format diskette. The contents of the

  7. Study of the dosimetric characteristics of cosmic radiation at civil aviation altitudes.

    PubMed

    Ferrari, A; Pellicioni, M; Rancati, T

    2002-01-01

    The dependence of the doses on solar activity for intermediate levels of the solar modulation parameter has been studied by means of simulations carried out by the Monte Carlo transport code FLUKA. The vertical cut-off rigidities investigated lie between 0.4 and 6.1 GV. The calculated results show that the linear dependence proposed in a previous work, for the effective dose rate as a function of the solar modulation parameter, can be considered as an acceptable approximation. In addition, some dosimetric characteristics of cosmic radiation and some properties of the dosemeters in use for monitoring in the cosmic ray environment have been analysed with a view to simplifying measurements. The depth-dose curves in the ICRU sphere and the response of a tissue-equivalent ionisation chamber have been determined by the FLUKA code for a number of cosmic ray spectra On the basis of the calculated results, it is concluded that a value of the depth. d, which would make the ambient dose equivalent a conservative predictor of the effective dose, cannot be specified for cosmic radiation. However, the operational quantity can be useful in order to verify the predictions of Monte Carlo calculations. It is demonstrated that a crude approximation of the ambient dose equivalent could be obtained by multiplying by 2 the absorbed dose measured by a tissue-equivalent ionisation chamber with wall thickness of 10 mm.

  8. Dosimetric and bremsstrahlung performance of a single convergent beam for teletherapy device.

    PubMed

    Figueroa, R G; Santibáñez, M; Valente, M

    2016-12-01

    The present work investigates preliminary feasibility and characteristics of a new type of radiation therapy modality based on a single convergent beam of photons. The proposal consists of the design of a device capable of generating convergent X-ray beams useful for radiotherapy. The main goal is to achieve high concentrated dose delivery. The first step is an analytical approach in order to characterize the dosimetric performance of the hypothetical convergent photon beam. Then, the validated FLUKA Monte Carlo main code is used to perform complete radiation transport to account also for scattering effects. The proposed method for producing convergent X-rays is mainly based on the bremsstrahlung effect. Hence the operating principle of the proposed device is described in terms of bremsstrahlung production. The work is mainly devoted characterizing the effect on the bremsstrahlung yield due to accessories present in the device, like anode material and geometry, filtration and collimation systems among others. The results obtained for in-depth dose distributions, by means of analytical and stochastic approaches, confirm the presence of a high dose concentration around the irradiated target, as expected. Moreover, it is shown how this spot of high dose concentration depends upon the relevant physical properties of the produced convergent photon beam. In summary, the proposed design for producing single convergent X-rays attained satisfactory performance for achieving high dose concentration around small targets depending on beam spot size that may be used for some applications in radiotherapy, like radiosurgery.

  9. Analytical calculation of central-axis dosimetric data for a dedicated 6-MV radiosurgery linear accelerator.

    PubMed

    Yang, James N; Pino, Ramiro

    2008-10-01

    Narrow beams are extensively used in stereotactic radiosurgery. The accuracy of treatment planning dose calculation depends largely on how well the dosimetric data are measured during the machine commissioning. Narrow beams are characterized by the lack of lateral electronic equilibrium. The lateral electronic disequilibrium in the radiation field and detector's finite size are likely to compromise the accuracy in dose measurements in these beams. This may have a profound impact on outcome in patients who undergo stereotactic radiosurgery. To confirm the measured commissioning data for a dedicated 6-MV linear accelerator-based radiosurgery system, we developed an analytical model to calculate the narrow photon beam central-axis dose. This model is an extension of a previously reported method of Nizin and Mooij for the calculation of the absorbed dose under lateral electronic disequilibrium conditions at depth of dmax or greater. The scatter factor and tissue-maximum ratio were calculated for narrow beams using the parametrized model and compared to carefully measured results for the same beams. For narrow beam radii ranging from 0.2 to 1.5 cm, the differences between the analytical and measured scatter factors were no greater than 1.4%. In addition, the differences between the analytical and measured tissue-maximum ratios were within 3.3% for regions greater than the maximum dose depth. The estimated error of this analytical calculation was less than 2%, which is sufficient to validate measurement results.

  10. Analytical calculation of central-axis dosimetric data for a dedicated 6-MV radiosurgery linear accelerator

    SciTech Connect

    Yang, James N.; Pino, Ramiro

    2008-10-15

    Narrow beams are extensively used in stereotactic radiosurgery. The accuracy of treatment planning dose calculation depends largely on how well the dosimetric data are measured during the machine commissioning. Narrow beams are characterized by the lack of lateral electronic equilibrium. The lateral electronic disequilibrium in the radiation field and detector's finite size are likely to compromise the accuracy in dose measurements in these beams. This may have a profound impact on outcome in patients who undergo stereotactic radiosurgery. To confirm the measured commissioning data for a dedicated 6-MV linear accelerator-based radiosurgery system, we developed an analytical model to calculate the narrow photon beam central-axis dose. This model is an extension of a previously reported method of Nizin and Mooij for the calculation of the absorbed dose under lateral electronic disequilibrium conditions at depth of d{sub max} or greater. The scatter factor and tissue-maximum ratio were calculated for narrow beams using the parametrized model and compared to carefully measured results for the same beams. For narrow beam radii ranging from 0.2 to 1.5 cm, the differences between the analytical and measured scatter factors were no greater than 1.4%. In addition, the differences between the analytical and measured tissue-maximum ratios were within 3.3% for regions greater than the maximum dose depth. The estimated error of this analytical calculation was less than 2%, which is sufficient to validate measurement results.

  11. Electromechanical properties of smart aggregate: theoretical modeling and experimental validation

    NASA Astrophysics Data System (ADS)

    Wang, Jianjun; Kong, Qingzhao; Shi, Zhifei; Song, Gangbing

    2016-09-01

    Smart aggregate (SA), as a piezoceramic-based multi-functional device, is formed by sandwiching two lead zirconate titanate (PZT) patches with copper shielding between a pair of solid-machined cylindrical marble blocks with epoxy. Previous researches have successfully demonstrated the capability and reliability of versatile SAs to monitor the structural health of concrete structures. However, the previous works concentrated mainly on the applications of SAs in structural health monitoring; no reasonable theoretical model of SAs was proposed. In this paper, electromechanical properties of SAs were investigated using a proposed theoretical model. Based on one dimensional linear theory of piezo-elasticity, the dynamic solutions of a SA subjected to an external harmonic voltage were solved. Further, the electric impedance of the SA was computed, and the resonance and anti-resonance frequencies were calculated based on derived equations. Numerical analysis was conducted to discuss the effects of the thickness of epoxy layer and the dimension of PZT patch on the fundamental resonance and anti-resonance frequencies as well as the corresponding electromechanical coupling factor. The dynamic solutions based on the proposed theoretical model were further experimentally verified with two SA samples. The fundamental resonance and anti-resonance frequencies of SAs show good agreements in both theoretical and experimental results. The presented analysis and results contribute to the overall understanding of SA properties and help to optimize the working frequencies of SAs in structural health monitoring of civil structures.

  12. Stability properties of elementary dynamic models of membrane transport.

    PubMed

    Hernández, Julio A

    2003-01-01

    Living cells are characterized by their capacity to maintain a stable steady state. For instance, cells are able to conserve their volume, internal ionic composition and electrical potential difference across the plasma membrane within values compatible with the overall cell functions. The dynamics of these cellular variables is described by complex integrated models of membrane transport. Some clues for the understanding of the processes involved in global cellular homeostasis may be obtained by the study of the local stability properties of some partial cellular processes. As an example of this approach, I perform, in this study, the neighborhood stability analysis of some elementary integrated models of membrane transport. In essence, the models describe the rate of change of the intracellular concentration of a ligand subject to active and passive transport across the plasma membrane of an ideal cell. The ligand can be ionic or nonionic, and it can affect the cell volume or the plasma membrane potential. The fundamental finding of this study is that, within the physiological range, the steady states are asymptotically stable. This basic property is a necessary consequence of the general forms of the expressions employed to describe the active and passive fluxes of the transported ligand.

  13. MECHANICAL PROPERTY CHARACTERIZATIONS AND PERFORMANCE MODELING OF SOFC SEALS

    SciTech Connect

    Koeppel, Brian J.; Vetrano, John S.; Nguyen, Ba Nghiep; Sun, Xin; Khaleel, Mohammad A.

    2008-03-26

    This study provides modeling tools for the design of reliable seals for SOFC stacks. The work consists of 1) experimental testing to determine fundamental properties of SOFC sealing materials, and 2) numerical modeling of stacks and sealing systems. The material tests capture relevant temperature-dependent physical and mechanical data needed by the analytical models such as thermal expansion, strength, fracture toughness, and relaxation behavior for glass-ceramic seals and other materials. Testing has been performed on both homogenous specimens and multiple material assemblies to investigate the effect of interfacial reactions. A viscoelastic continuum damage model for a glass-ceramic seal was developed to capture the nonlinear behavior of this material at high temperatures. This model was implemented in the MSC MARC finite element code and was used for a detailed analysis of a planar SOFC stack under thermal cycling conditions. Realistic thermal loads for the stack were obtained using PNNL’s in-house multiphysics solver. The accumulated seal damage and component stresses were evaluated for multiple thermal loading cycles, and regions of high seal damage susceptible to cracking were identified. Selected test results, numerical model development, and analysis results will be presented.

  14. Dynamic modeling, property investigation, and adaptive controller design of serial robotic manipulators modeled with structural compliance

    NASA Technical Reports Server (NTRS)

    Tesar, Delbert; Tosunoglu, Sabri; Lin, Shyng-Her

    1990-01-01

    Research results on general serial robotic manipulators modeled with structural compliances are presented. Two compliant manipulator modeling approaches, distributed and lumped parameter models, are used in this study. System dynamic equations for both compliant models are derived by using the first and second order influence coefficients. Also, the properties of compliant manipulator system dynamics are investigated. One of the properties, which is defined as inaccessibility of vibratory modes, is shown to display a distinct character associated with compliant manipulators. This property indicates the impact of robot geometry on the control of structural oscillations. Example studies are provided to illustrate the physical interpretation of inaccessibility of vibratory modes. Two types of controllers are designed for compliant manipulators modeled by either lumped or distributed parameter techniques. In order to maintain the generality of the results, neither linearization is introduced. Example simulations are given to demonstrate the controller performance. The second type controller is also built for general serial robot arms and is adaptive in nature which can estimate uncertain payload parameters on-line and simultaneously maintain trajectory tracking properties. The relation between manipulator motion tracking capability and convergence of parameter estimation properties is discussed through example case studies. The effect of control input update delays on adaptive controller performance is also studied.

  15. Quality assessment of modeled protein structure using physicochemical properties.

    PubMed

    Rana, Prashant Singh; Sharma, Harish; Bhattacharya, Mahua; Shukla, Anupam

    2015-04-01

    Physicochemical properties of proteins always guide to determine the quality of the protein structure, therefore it has been rigorously used to distinguish native or native-like structure from other predicted structures. In this work, we explore nine machine learning methods with six physicochemical properties to predict the Root Mean Square Deviation (RMSD), Template Modeling (TM-score), and Global Distance Test (GDT_TS-score) of modeled protein structure in the absence of its true native state. Physicochemical properties namely total surface area, euclidean distance (ED), total empirical energy, secondary structure penalty (SS), sequence length (SL), and pair number (PN) are used. There are a total of 95,091 modeled structures of 4896 native targets. A real coded Self-adaptive Differential Evolution algorithm (SaDE) is used to determine the feature importance. The K-fold cross validation is used to measure the robustness of the best predictive method. Through the intensive experiments, it is found that Random Forest method outperforms over other machine learning methods. This work makes the prediction faster and inexpensive. The performance result shows the prediction of RMSD, TM-score, and GDT_TS-score on Root Mean Square Error (RMSE) as 1.20, 0.06, and 0.06 respectively; correlation scores are 0.96, 0.92, and 0.91 respectively; R(2) are 0.92, 0.85, and 0.84 respectively; and accuracy are 78.82% (with ± 0.1 err), 86.56% (with ± 0.1 err), and 87.37% (with ± 0.1 err) respectively on the testing data set. The data set used in the study is available as supplement at http://bit.ly/RF-PCP-DataSets.

  16. Soil hydraulic properties near saturation, an improved conductivity model

    NASA Astrophysics Data System (ADS)

    Børgesen, Christen D.; Jacobsen, Ole H.; Hansen, Søren; Schaap, Marcel G.

    2006-06-01

    The hydraulic properties near saturation can change dramatically due to the presence of macropores that are usually difficult to handle in traditional pore size models. The purpose of this study is to establish a data set on hydraulic conductivity near saturation, test the predictive capability of commonly used hydraulic conductivity models and give suggestions for improved models. Water retention and near saturated and saturated hydraulic conductivity were measured for a variety of 81 top and subsoils. The hydraulic conductivity models by van Genuchten [ van Genuchten, 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J. 44, 892-898.] (vGM) and Brooks and Corey, modified by Jarvis [ Jarvis, 1991. MACRO—A Model of Water Movement and Solute Transport in Macroporous Soils. Swedish University of Agricultural Sciences. Department of Soil Sciences. Reports and Dissertations 9.] were optimised to describe the unsaturated hydraulic conductivity in the range measured. Different optimisation procedures were tested. Using the measured saturated hydraulic conductivity in the vGM model tends to overestimate the unsaturated hydraulic conductivity. Optimising a matching factor ( k0) improved the fit considerably whereas optimising the l-parameter in the vGM model improved the fit only slightly. The vGM was improved with an empirical scaling function to account for the rapid increase in conductivity near saturation. Using the improved models, it was possible to describe both the saturated and the unsaturated hydraulic conductivity better than a previously published model by Jarvis. The pore size boundary of the macropores was found at a capillary pressure of -4 hPa corresponding to a circular pore diameter of 750 μm.

  17. Quantitative property-structural relation modeling on polymeric dielectric materials

    NASA Astrophysics Data System (ADS)

    Wu, Ke

    Nowadays, polymeric materials have attracted more and more attention in dielectric applications. But searching for a material with desired properties is still largely based on trial and error. To facilitate the development of new polymeric materials, heuristic models built using the Quantitative Structure Property Relationships (QSPR) techniques can provide reliable "working solutions". In this thesis, the application of QSPR on polymeric materials is studied from two angles: descriptors and algorithms. A novel set of descriptors, called infinite chain descriptors (ICD), are developed to encode the chemical features of pure polymers. ICD is designed to eliminate the uncertainty of polymer conformations and inconsistency of molecular representation of polymers. Models for the dielectric constant, band gap, dielectric loss tangent and glass transition temperatures of organic polymers are built with high prediction accuracy. Two new algorithms, the physics-enlightened learning method (PELM) and multi-mechanism detection, are designed to deal with two typical challenges in material QSPR. PELM is a meta-algorithm that utilizes the classic physical theory as guidance to construct the candidate learning function. It shows better out-of-domain prediction accuracy compared to the classic machine learning algorithm (support vector machine). Multi-mechanism detection is built based on a cluster-weighted mixing model similar to a Gaussian mixture model. The idea is to separate the data into subsets where each subset can be modeled by a much simpler model. The case study on glass transition temperature shows that this method can provide better overall prediction accuracy even though less data is available for each subset model. In addition, the techniques developed in this work are also applied to polymer nanocomposites (PNC). PNC are new materials with outstanding dielectric properties. As a key factor in determining the dispersion state of nanoparticles in the polymer matrix

  18. Quantum Electrostatic Model for Optical Properties of Nanoscale Gold Films

    NASA Astrophysics Data System (ADS)

    Qian, Haoliang; Xiao, Yuzhe; Lepage, Dominic; Chen, Li; Liu, Zhaowei

    2015-11-01

    The optical properties of thin gold films with thickness varying from 2.5 nm to 30 nm are investigated. Due to the quantum size effect, the optical constants of the thin gold film deviate from the Drude model for bulk material as film thickness decreases, especially around 2.5 nm, where the electron energy level becomes discrete. A theory based on the self-consistent solution of the Schrödinger equation and the Poisson equation is proposed and its predictions agree well with experimental results.

  19. Modeling of Euclidean braided fiber architectures to optimize composite properties

    NASA Technical Reports Server (NTRS)

    Armstrong-Carroll, E.; Pastore, C.; Ko, F. K.

    1992-01-01

    Three-dimensional braided fiber reinforcements are a very effective toughening mechanism for composite materials. The integral yarn path inherent to this fiber architecture allows for effective multidirectional dispersion of strain energy and negates delamination problems. In this paper a geometric model of Euclidean braid fiber architectures is presented. This information is used to determine the degree of geometric isotropy in the braids. This information, when combined with candidate material properties, can be used to quickly generate an estimate of the available load-carrying capacity of Euclidean braids at any arbitrary angle.

  20. Infrared radiometer for measuring thermophysical properties of wind tunnel models

    NASA Technical Reports Server (NTRS)

    Corwin, R. R.; Moorman, S. L.; Becker, E. C.

    1978-01-01

    An infrared radiometer is described which was developed to measure temperature rises of wind tunnel models undergoing transient heating over a temperature range of -17.8 C to 260 C. This radiometer interfaces directly with a system which measures the effective thermophysical property square root of rho ck. It has an output temperature fluctuation of 0.26 C at low temperatures and 0.07 C at high temperatures, and the output frequency response of the radiometer is from dc to 400 hertz.

  1. Thermodynamical properties of Strunz’s quantum dissipative models

    SciTech Connect

    Zen, Freddy P.; Sulaiman, A.

    2015-09-30

    The existence of the negative of specific heat from quantum dissipative theory is investigated. Strunz’s quantum dissipative model will be used in this studies. The thermodynamical properties will be studied starts out from the thermo-dynamic partition function of the dissipative system. The path integral technique is used to calculate the partition function under consideration. The results shows that the specific heat can be negative if the damping parameter more than a half the oscillator frequency and also occur at low temperatures. For damping factor greater than the frequency of harmonic oscillator then specific heat will oscillate at low temperatures and approaching normal conditions at a high temperature.

  2. Dosimetric Comparison in Breast Radiotherapy of 4 MV and 6 MV on Physical Chest Simulator

    SciTech Connect

    Donato da Silva, Sabrina; Passos Ribeiro Campos, Tarcisio; Batista Nogueira, Luciana; Lima Souza Castro, Andre; Alves de oliveira, Marcio; Galvao Dias, Humberto

    2015-07-01

    According to the World Health Organization (2014) breast cancer is the main cause of death by cancer in women worldwide. The biggest challenge of radiotherapy in the treatment of cancer is to deposit the entire prescribed dose homogeneously in the breast, sparing the surrounding tissue. In this context, this paper aimed at evaluating and comparing internal dose distribution in the mammary gland based on experimental procedures submitted to two distinct energy spectra produced in breast cancer radiotherapy. The methodology consisted of reproducing opposite parallel fields used in the treatment of breast tumors in a chest phantom. This simulator with synthetic breast, composed of equivalent tissue material (TE), was previously developed by the NRI Research Group (UFMG). The computer tomography (CT) scan of the simulator was obtained antecedently. The radiotherapy planning systems (TPS) in the chest phantom were performed in the ECLIPSE system from Varian Medical Systems and CAT 3D system from MEVIS. The irradiations were reproduced in the Varian linear accelerator, model SL- 20 Precise, 6 MV energy and Varian linear accelerator, 4 MV Clinac 6x SN11 model. Calibrations of the absorbed dose versus optical density from radiochromic films were generated in order to obtain experimental dosimetric distribution at the films positioned within the glandular and skin equivalent tissues of the chest phantom. The spatial dose distribution showed equivalence with the TPS on measurement data performed in the 6 MV spectrum. The average dose found in radiochromic films placed on the skin ranged from 49 to 79%, and from 39 to 49% in the mammary areola, for the prescribed dose. Dosimetric comparisons between the spectra of 4 and 6 MV, keeping the constant geometry of the fields applied in the same phantom, will be presented showing their equivalence in breast radiotherapy, as well as the variations will be discussed. To sum up, the dose distribution has reached the value expected in

  3. Laser Treatment of Benign Prostatic Hyperplasia: Dosimetric and Thermodynamic Considerations

    NASA Astrophysics Data System (ADS)

    Anvari, Bahman

    1993-01-01

    Benign prostatic hyperplasia (BPH) is the most commonly occurring neoplastic disease in the aging human male. Currently, surgical treatment of BPH is the primary therapeutic method. However, due to surgical complications, less invasive methods of treatment are desirable. In recent years, thermal coagulation of the hyperplastic prostate by a laser has received a considerable amount of attention. Nevertheless, the optimum laser irradiation parameters that lead to a successful and safe treatment of BPH have not been determined. This dissertation studies the physics of laser coagulation of prostate from both basic science and practical perspectives. Optical properties of prostatic tissue are determined over a spectrum of wavelengths. Knowledge of these properties allows for selection of appropriate laser wavelengths and provides a basis for performing dose equivalency studies among various types of lasers. Furthermore, knowledge of optical properties are needed for development of computer simulation models that predict the extent of thermal injury during laser irradiation of prostate. A computer model of transurethral heating of prostate that can be used to guide the clinical studies in determining an optimum dosimetry is then presented. Studies of the effects of non-laser heating devices, optical properties, blood perfusion, surface irrigation, and beam geometry are performed to examine the extent of heat propagation within the prostate. An in vitro model for transurethral laser irradiation of prostate is also presented to examine the effects of an 810 nm diode laser, thermal boundary conditions, and energy deposition rate during Nd:YAG laser irradiation. Results of these studies suggest that in the presence of laminar irrigation, the convective boundary condition is dominated by thermal diffusion as opposed to the bulk motion of the irrigation fluid. Distinct phases of thermal events are also identified during the laser irradiation. The in vivo studies of

  4. Error Analysis of non-TLD HDR Brachytherapy Dosimetric Techniques

    NASA Astrophysics Data System (ADS)

    Amoush, Ahmad

    The American Association of Physicists in Medicine Task Group Report43 (AAPM-TG43) and its updated version TG-43U1 rely on the LiF TLD detector to determine the experimental absolute dose rate for brachytherapy. The recommended uncertainty estimates associated with TLD experimental dosimetry include 5% for statistical errors (Type A) and 7% for systematic errors (Type B). TG-43U1 protocol does not include recommendation for other experimental dosimetric techniques to calculate the absolute dose for brachytherapy. This research used two independent experimental methods and Monte Carlo simulations to investigate and analyze uncertainties and errors associated with absolute dosimetry of HDR brachytherapy for a Tandem applicator. An A16 MicroChamber* and one dose MOSFET detectors† were selected to meet the TG-43U1 recommendations for experimental dosimetry. Statistical and systematic uncertainty analyses associated with each experimental technique were analyzed quantitatively using MCNPX 2.6‡ to evaluate source positional error, Tandem positional error, the source spectrum, phantom size effect, reproducibility, temperature and pressure effects, volume averaging, stem and wall effects, and Tandem effect. Absolute dose calculations for clinical use are based on Treatment Planning System (TPS) with no corrections for the above uncertainties. Absolute dose and uncertainties along the transverse plane were predicted for the A16 microchamber. The generated overall uncertainties are 22%, 17%, 15%, 15%, 16%, 17%, and 19% at 1cm, 2cm, 3cm, 4cm, and 5cm, respectively. Predicting the dose beyond 5cm is complicated due to low signal-to-noise ratio, cable effect, and stem effect for the A16 microchamber. Since dose beyond 5cm adds no clinical information, it has been ignored in this study. The absolute dose was predicted for the MOSFET detector from 1cm to 7cm along the transverse plane. The generated overall uncertainties are 23%, 11%, 8%, 7%, 7%, 9%, and 8% at 1cm, 2cm, 3cm

  5. Modified fractal model and rheological properties of colloidal networks.

    PubMed

    Tang, Dongming; Marangoni, Alejandro G

    2008-02-15

    The scaling relationship between the storage modulus (G(')) and the volume fraction of solids (Phi) in fat crystal networks has been explained by the fractal model developed by our group. However, many experimental results and simulation studies suggest that the stress distribution within a colloidal network is dramatically heterogeneous, which means that a small part of the network carries most of the stress, while the other part of the network does not contribute much to the elastic properties of the system. This concept was introduced into a modified fractal model. The volume fraction of solids term (Phi) in the original fractal model was replaced by Phi(e), the effective volume fraction of solids, in the modified fractal model, which represents the volume fraction of stress-carrying solids. A proposed expression for Phi(e) is given and a modified expression for the scaling relationship between G(') and Phi is obtained. The modified fractal model fits the experiment data well and successfully explains the sometimes observed nonlinear log-log behavior between the storage modulus of colloidal networks and their volume fraction of solids.

  6. An evacuation model accounting for elementary students' individual properties

    NASA Astrophysics Data System (ADS)

    Tang, Tie-Qiao; Chen, Liang; Guo, Ren-Yong; Shang, Hua-Yan

    2015-12-01

    In this paper, we propose a cellular automata model for pedestrian flow to investigate the effects of elementary students' individual properties on the evacuation process in a classroom with two exits. In this model, each student's route choice behavior is determined by the capacity of his current route to each exit, the distance between his current position and the corresponding exit, the repulsive interactions between his adjacent students and him, and the congestion degree near each exit; the elementary students are sorted into rational and irrational students. The simulation results show that the irrational students' proportion has significant impacts on the evacuation process and efficiency, and that all students simultaneously evacuating may be inefficient.

  7. Quantitative properties of clustering within modern microscopic nuclear models

    SciTech Connect

    Volya, A.; Tchuvil’sky, Yu. M.

    2016-09-15

    A method for studying cluster spectroscopic properties of nuclear fragmentation, such as spectroscopic amplitudes, cluster form factors, and spectroscopic factors, is developed on the basis of modern precision nuclear models that take into account the mixing of large-scale shell-model configurations. Alpha-cluster channels are considered as an example. A mathematical proof of the need for taking into account the channel-wave-function renormalization generated by exchange terms of the antisymmetrization operator (Fliessbach effect) is given. Examples where this effect is confirmed by a high quality of the description of experimental data are presented. By and large, the method in question extends substantially the possibilities for studying clustering phenomena in nuclei and for improving the quality of their description.

  8. Electronic properties of ZnO varistors: a new model

    SciTech Connect

    Pike, G.E.

    1981-01-01

    Much of the research on ZnO varistors has concentrated on the explanation of their dc current-voltage characteristics. However, varistors also have unusual ac properties which can be technologically important, and must be described by any comprehensive model. In an ideal varistor with identical grain boundaries throughout, there should be no dispersive capacitance at zero bias. In real varistors this capacitance varies considerably with frequency. This dispersion has two causes, charge trapping in the depletion regions and differing grain boundary barriers. Calculations for each process are given. As the voltage across the varistor is increased, the low frequency capacitance is observed to increase well below the breakdown voltage. At even higher voltages the capacitance turns over and becomes negative. All of these effects can be described with a double depletion layer/thermionic emission model.

  9. Dynamical properties of random-field Ising model.

    PubMed

    Sinha, Suman; Mandal, Pradipta Kumar

    2013-02-01

    Extensive Monte Carlo simulations are performed on a two-dimensional random field Ising model. The purpose of the present work is to study the disorder-induced changes in the properties of disordered spin systems. The time evolution of the domain growth, the order parameter, and the spin-spin correlation functions are studied in the nonequilibrium regime. The dynamical evolution of the order parameter and the domain growth shows a power law scaling with disorder-dependent exponents. It is observed that for weak random fields, the two-dimensional random field Ising model possesses long-range order. Except for weak disorder, exchange interaction never wins over pinning interaction to establish long-range order in the system.

  10. Thermodynamic properties derived from the free volume model of liquids

    NASA Technical Reports Server (NTRS)

    Miller, R. I.

    1974-01-01

    An equation of state and expressions for the isothermal compressibility, thermal expansion coefficient, heat capacity, and entropy of liquids have been derived from the free volume model partition function suggested by Turnbull. The simple definition of the free volume is used, and it is assumed that the specific volume is directly related to the cube of the intermolecular separation by a proportionality factor which is found to be a function of temperature and pressure as well as specific volume. When values of the proportionality factor are calculated from experimental data for real liquids, it is found to be approximately constant over ranges of temperature and pressure which correspond to the dense liquid phase. This result provides a single-parameter method for calculating dense liquid thermodynamic properties and is consistent with the fact that the free volume model is designed to describe liquids near the solidification point.

  11. Modelling the optical properties of composite and porous interstellar grains

    NASA Astrophysics Data System (ADS)

    Voshchinnikov, N. V.; Il'in, V. B.; Henning, Th.

    2005-01-01

    There are indications that interstellar and interplanetary dust grains have an inhomogeneous and fluffy structure. We investigate different methods to describe light scattering by such composite particles. Both a model of layered particles and discrete dipole calculations for particles with Rayleigh and non-Rayleigh inclusions are used. The calculations demonstrate that porosity is a key parameter for determining light scattering. We find that the optical properties of the layered particles depend on the number and position of layers if the number of layers is small (⪉ 15). For a larger number of layers the scattering characteristics become independent of the layer sequence. The optical properties of particles with inclusions depend on the size of inclusions provided the porosity is large. The scattering characteristics of very porous particles with inclusions of different sizes are found to be close to those of multi-layered spheres. We compare the results of these calculations with the predictions of the effective medium theories (EMT) which are often used in astronomy as a tool to calculate the optical properties of composite particles. The results of our analysis show that the internal structure of grains (layers versus inclusions) only slightly affects the optics of particles provided the porosity does not exceed 50%. It is also demonstrated that in this case the optical properties of composite grains calculated with EMT agree with the results of the exact method for layered particles. For larger porosity, the standard EMT rules (i.e., Garnett and Bruggeman rules) give reliable results for particles with Rayleigh inclusions only.

  12. Dosimetric predictors of esophageal toxicity after stereotactic body radiotherapy for central lung tumors.

    PubMed

    Wu, Abraham J; Williams, Eric; Modh, Ankit; Foster, Amanda; Yorke, Ellen; Rimner, Andreas; Jackson, Andrew

    2014-08-01

    Stereotactic body radiotherapy (SBRT) to central lung tumors can cause esophageal toxicity, but little is known about the incidence or risk factors. We reviewed central lung SBRT patients to identify dosimetric factors predictive of esophageal toxicity. We assessed esophageal toxicity in 125 SBRT patients. Using biological equivalent doses with α/β=10 Gy (BED₁₀), dose-volume histogram variables for the esophagus (Dv and Vd) were assessed for correlation with grade ⩾2 acute toxicity. Incidence of grade ⩾2 acute toxicity was 12% (n=15). Highly significant logistic models were generated for D₅cc and Dmax (p<0.001). To keep the complication rate <20%, the model requires that D₅cc⩽26.3 BED₁₀. At 2 years, the probability of complication with BED₁₀D₅cc>14.4 Gy was 24%, compared to 1.6% if ⩽14.4 Gy. This novel analysis provides guidelines to predict acute esophageal toxicity in lung SBRT. Dose to the hottest 5cc and Dmax of the esophagus were the best predictors of toxicity. Converting the BED₁₀ limits to physical doses, D₅cc to the esophagus should be kept less than 16.8, 18.1 and 19.0 Gy for 3, 4, and 5 fractions, respectively, to keep the acute toxicity rate <20%. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

  13. Topological properties of the mean-field ϕ4 model

    NASA Astrophysics Data System (ADS)

    Andronico, A.; Angelani, L.; Ruocco, G.; Zamponi, F.

    2004-10-01

    We study the thermodynamics and the properties of the stationary points (saddles and minima) of the potential energy for a ϕ4 mean-field model. We compare the critical energy vc [i.e., the potential energy v(T) evaluated at the phase transition temperature Tc ] with the energy vθ at which the saddle energy distribution show a discontinuity in its derivative. We find that, in this model, vc≫vθ , at variance to what has been found in different mean-field and short ranged systems, where the thermodynamic phase transitions take place at vc=vθ [Casetti, Pettini and Cohen, Phys. Rep. 337, 237 (2000)]. By direct calculation of the energy vs(T) of the “inherent saddles,” i.e., the saddles visited by the equilibrated system at temperature T , we find that vs(Tc)˜vθ . Thus, we argue that the thermodynamic phase transition is related to a change in the properties of the inherent saddles rather than to a change of the topology of the potential energy surface at T=Tc . Finally, we discuss the approximation involved in our analysis and the generality of our method.

  14. Pharmacokinetic properties and in silico ADME modeling in drug discovery.

    PubMed

    Honório, Kathia M; Moda, Tiago L; Andricopulo, Adriano D

    2013-03-01

    The discovery and development of a new drug are time-consuming, difficult and expensive. This complex process has evolved from classical methods into an integration of modern technologies and innovative strategies addressed to the design of new chemical entities to treat a variety of diseases. The development of new drug candidates is often limited by initial compounds lacking reasonable chemical and biological properties for further lead optimization. Huge libraries of compounds are frequently selected for biological screening using a variety of techniques and standard models to assess potency, affinity and selectivity. In this context, it is very important to study the pharmacokinetic profile of the compounds under investigation. Recent advances have been made in the collection of data and the development of models to assess and predict pharmacokinetic properties (ADME--absorption, distribution, metabolism and excretion) of bioactive compounds in the early stages of drug discovery projects. This paper provides a brief perspective on the evolution of in silico ADME tools, addressing challenges, limitations, and opportunities in medicinal chemistry.

  15. Dark matter properties implied by gamma ray interstellar emission models

    NASA Astrophysics Data System (ADS)

    Balázs, Csaba; Li, Tong

    2017-02-01

    We infer dark matter properties from gamma ray residuals extracted using eight different interstellar emission scenarios proposed by the Fermi-LAT Collaboration to explain the Galactic Center gamma ray excess. Adopting the most plausible simplified ansatz, we assume that the dark matter particle is a Majorana fermion interacting with standard fermions via a scalar mediator. To trivially respect flavor constraints, we only couple the mediator to third generation fermions. Using this theoretical hypothesis, and the Fermi residuals, we calculate Bayesian evidences, including Fermi-LAT exclusion limits from 15 dwarf spheroidal galaxies as well. Our evidence ratios single out one of the Fermi scenarios as most compatible with the simplified dark matter model. In this scenario the dark matter (mediator) mass is in the 25-200 (1-1000) GeV range and its annihilation is dominated by bottom quark final state. Our conclusion is that the properties of dark matter extracted from gamma ray data are highly sensitive to the modeling of the interstellar emission.

  16. A semi-analytical variable property droplet combustion model

    NASA Astrophysics Data System (ADS)

    Sisti, John

    A multizone droplet burn model is developed to account for changes in the thermal and transport properties as a function of droplet radius. The formulation is semi-analytical---allowing for accurate and computationally efficient estimates of flame structure and burn rates. Zonal thermal and transport properties are computed using the Cantera software and pre-tabulated for rapid evaluation during run-time. Model predictions are compared to experimental measurements of burning n-heptane, ethanol and methanol droplets. An adaptive zone refinement algorithm is developed that minimizes the number of zones required to provide accurate estimates of burn time without excess zones. A sensitivity study of burn rate and flame stand-off with far-field oxygen concentration is conducted with comparisons to experimental data. Overall agreement to data is encouraging with errors typically less than 20% for predictions of burn rates, stand-off ratio and flame temperature for the fuels considered. The quiescent quasi-steady solution is extended to a convective transient solution without the need to solve an eigenvalue solution in time. The time history of the burning droplets show good comparison with experimental data. To further decrease computational cost, the source terms for the transient solution are linearized for an explicit time marching solution. An error convergence study was performed to show a time-step independent solution exists at a reasonable Delta t.

  17. Fast radio burst source properties and curvature radiation model

    NASA Astrophysics Data System (ADS)

    Kumar, Pawan; Lu, Wenbin; Bhattacharya, Mukul

    2017-07-01

    We use the observed properties of fast radio bursts (FRBs) and a number of general physical considerations to provide a broad-brush model for the physical properties of FRB sources and the radiation mechanism. We show that the magnetic field in the source region should be at least 1014 G. This strong field is required to ensure that the electrons have sufficiently high ground state Landau energy so that particle collisions, instabilities and strong electromagnetic fields associated with the FRB radiation do not perturb electrons' motion in the direction transverse to the magnetic field and destroy their coherent motion; coherence is required by the high observed brightness temperature of FRB radiation. The electric field in the source region required to sustain particle motion for a wave period is estimated to be of the order of 1011 esu. These requirements suggest that FRBs are produced near the surface of magnetars perhaps via forced reconnection of magnetic fields to produce episodic, repeated, outbursts. The beaming-corrected energy release in these bursts is estimated to be about 1036 erg, whereas the total energy in the magnetic field is at least ˜1045 erg. We provide a number of predictions for this model which can be tested by future observations. One of which is that short duration FRB-like bursts should exist at much higher frequencies, possibly up to optical.

  18. 2D microscopic model of graphene fracture properties

    NASA Astrophysics Data System (ADS)

    Hess, Peter

    2015-05-01

    An analytical two-dimensional (2D) microscopic fracture model based on Morse-type interaction is derived containing no adjustable parameter. From the 2D Young’s moduli and 2D intrinsic strengths of graphene measured by nanoindentation based on biaxial tension and calculated by density functional theory for uniaxial tension the widely unknown breaking force, line or edge energy, surface energy, fracture toughness, and strain energy release rate were determined. The simulated line energy agrees well with ab initio calculations and the fracture toughness of perfect graphene sheets is in good agreement with molecular dynamics simulations and the fracture toughness evaluated for defective graphene using the Griffith relation. Similarly, the estimated critical strain energy release rate agrees well with result of various theoretical approaches based on the J-integral and surface energy. The 2D microscopic model, connecting 2D and three-dimensional mechanical properties in a consistent way, provides a versatile relationship to easily access all relevant fracture properties of pristine 2D solids.

  19. Computational Models and Emergent Properties of Respiratory Neural Networks

    PubMed Central

    Lindsey, Bruce G.; Rybak, Ilya A.; Smith, Jeffrey C.

    2012-01-01

    Computational models of the neural control system for breathing in mammals provide a theoretical and computational framework bringing together experimental data obtained from different animal preparations under various experimental conditions. Many of these models were developed in parallel and iteratively with experimental studies and provided predictions guiding new experiments. This data-driven modeling approach has advanced our understanding of respiratory network architecture and neural mechanisms underlying generation of the respiratory rhythm and pattern, including their functional reorganization under different physiological conditions. Models reviewed here vary in neurobiological details and computational complexity and span multiple spatiotemporal scales of respiratory control mechanisms. Recent models describe interacting populations of respiratory neurons spatially distributed within the Bötzinger and pre-Bötzinger complexes and rostral ventrolateral medulla that contain core circuits of the respiratory central pattern generator (CPG). Network interactions within these circuits along with intrinsic rhythmogenic properties of neurons form a hierarchy of multiple rhythm generation mechanisms. The functional expression of these mechanisms is controlled by input drives from other brainstem components, including the retrotrapezoid nucleus and pons, which regulate the dynamic behavior of the core circuitry. The emerging view is that the brainstem respiratory network has rhythmogenic capabilities at multiple levels of circuit organization. This allows flexible, state-dependent expression of different neural pattern-generation mechanisms under various physiological conditions, enabling a wide repertoire of respiratory behaviors. Some models consider control of the respiratory CPG by pulmonary feedback and network reconfiguration during defensive behaviors such as cough. Future directions in modeling of the respiratory CPG are considered. PMID:23687564

  20. Sensitivity of postplanning target and OAR coverage estimates to dosimetric margin distribution sampling parameters.

    PubMed

    Xu, Huijun; Gordon, J James; Siebers, Jeffrey V

    2011-02-01

    A dosimetric margin (DM) is the margin in a specified direction between a structure and a specified isodose surface, corresponding to a prescription or tolerance dose. The dosimetric margin distribution (DMD) is the distribution of DMs over all directions. Given a geometric uncertainty model, representing inter- or intrafraction setup uncertainties or internal organ motion, the DMD can be used to calculate coverage Q, which is the probability that a realized target or organ-at-risk (OAR) dose metric D, exceeds the corresponding prescription or tolerance dose. Postplanning coverage evaluation quantifies the percentage of uncertainties for which target and OAR structures meet their intended dose constraints. The goal of the present work is to evaluate coverage probabilities for 28 prostate treatment plans to determine DMD sampling parameters that ensure adequate accuracy for postplanning coverage estimates. Normally distributed interfraction setup uncertainties were applied to 28 plans for localized prostate cancer, with prescribed dose of 79.2 Gy and 10 mm clinical target volume to planning target volume (CTV-to-PTV) margins. Using angular or isotropic sampling techniques, dosimetric margins were determined for the CTV, bladder and rectum, assuming shift invariance of the dose distribution. For angular sampling, DMDs were sampled at fixed angular intervals w (e.g., w = 1 degree, 2 degrees, 5 degrees, 10 degrees, 20 degrees). Isotropic samples were uniformly distributed on the unit sphere resulting in variable angular increments, but were calculated for the same number of sampling directions as angular DMDs, and accordingly characterized by the effective angular increment omega eff. In each direction, the DM was calculated by moving the structure in radial steps of size delta (=0.1, 0.2, 0.5, 1 mm) until the specified isodose was crossed. Coverage estimation accuracy deltaQ was quantified as a function of the sampling parameters omega or omega eff and delta. The

  1. Sensitivity of postplanning target and OAR coverage estimates to dosimetric margin distribution sampling parameters

    SciTech Connect

    Xu Huijun; Gordon, J. James; Siebers, Jeffrey V.

    2011-02-15

    Purpose: A dosimetric margin (DM) is the margin in a specified direction between a structure and a specified isodose surface, corresponding to a prescription or tolerance dose. The dosimetric margin distribution (DMD) is the distribution of DMs over all directions. Given a geometric uncertainty model, representing inter- or intrafraction setup uncertainties or internal organ motion, the DMD can be used to calculate coverage Q, which is the probability that a realized target or organ-at-risk (OAR) dose metric D{sub v} exceeds the corresponding prescription or tolerance dose. Postplanning coverage evaluation quantifies the percentage of uncertainties for which target and OAR structures meet their intended dose constraints. The goal of the present work is to evaluate coverage probabilities for 28 prostate treatment plans to determine DMD sampling parameters that ensure adequate accuracy for postplanning coverage estimates. Methods: Normally distributed interfraction setup uncertainties were applied to 28 plans for localized prostate cancer, with prescribed dose of 79.2 Gy and 10 mm clinical target volume to planning target volume (CTV-to-PTV) margins. Using angular or isotropic sampling techniques, dosimetric margins were determined for the CTV, bladder and rectum, assuming shift invariance of the dose distribution. For angular sampling, DMDs were sampled at fixed angular intervals {omega} (e.g., {omega}=1 deg., 2 deg., 5 deg., 10 deg., 20 deg.). Isotropic samples were uniformly distributed on the unit sphere resulting in variable angular increments, but were calculated for the same number of sampling directions as angular DMDs, and accordingly characterized by the effective angular increment {omega}{sub eff}. In each direction, the DM was calculated by moving the structure in radial steps of size {delta}(=0.1,0.2,0.5,1 mm) until the specified isodose was crossed. Coverage estimation accuracy {Delta}Q was quantified as a function of the sampling parameters {omega} or

  2. SU-E-T-613: Dosimetric Consequences of Systematic MLC Leaf Positioning Errors

    SciTech Connect

    Kathuria, K; Siebers, J

    2014-06-01

    Purpose: The purpose of this study is to determine the dosimetric consequences of systematic MLC leaf positioning errors for clinical IMRT patient plans so as to establish detection tolerances for quality assurance programs. Materials and Methods: Dosimetric consequences were simulated by extracting mlc delivery instructions from the TPS, altering the file by the specified error, reloading the delivery instructions into the TPS, recomputing dose, and extracting dose-volume metrics for one head-andneck and one prostate patient. Machine error was simulated by offsetting MLC leaves in Pinnacle in a systematic way. Three different algorithms were followed for these systematic offsets, and are as follows: a systematic sequential one-leaf offset (one leaf offset in one segment per beam), a systematic uniform one-leaf offset (same one leaf offset per segment per beam) and a systematic offset of a given number of leaves picked uniformly at random from a given number of segments (5 out of 10 total). Dose to the PTV and normal tissue was simulated. Results: A systematic 5 mm offset of 1 leaf for all delivery segments of all beams resulted in a maximum PTV D98 deviation of 1%. Results showed very low dose error in all reasonably possible machine configurations, rare or otherwise, which could be simulated. Very low error in dose to PTV and OARs was shown in all possible cases of one leaf per beam per segment being offset (<1%), or that of only one leaf per beam being offset (<.2%). The errors resulting from a high number of adjacent leaves (maximum of 5 out of 60 total leaf-pairs) being simultaneously offset in many (5) of the control points (total 10–18 in all beams) per beam, in both the PTV and the OARs analyzed, were similarly low (<2–3%). Conclusions: The above results show that patient shifts and anatomical changes are the main source of errors in dose delivered, not machine delivery. These two sources of error are “visually complementary” and uncorrelated

  3. Effect of endorectal balloon positioning errors on target deformation and dosimetric quality during prostate SBRT.

    PubMed

    Jones, Bernard L; Gan, Gregory; Kavanagh, Brian; Miften, Moyed

    2013-11-21

    An inflatable endorectal balloon (ERB) is often used during stereotactic body radiation therapy (SBRT) for treatment of prostate cancer in order to reduce both intrafraction motion of the target and risk of rectal toxicity. However, the ERB can exert significant force on the prostate, and this work assessed the impact of ERB position errors on deformation of the prostate and treatment dose metrics. Seventy-one cone-beam computed tomography (CBCT) image datasets of nine patients with clinical stage T1cN0M0 prostate cancer were studied. An ERB (Flexi-Cuff, EZ-EM, Westbury, NY) inflated with 60 cm(3) of air was used during simulation and treatment, and daily kilovoltage (kV) CBCT imaging was performed to localize the prostate. The shape of the ERB in each CBCT was analyzed to determine errors in position, size, and shape. A deformable registration algorithm was used to track the dose received by (and deformation of) the prostate, and dosimetric values such as D95, PTV coverage, and Dice coefficient for the prostate were calculated. The average balloon position error was 0.5 cm in the inferior direction, with errors ranging from 2 cm inferiorly to 1 cm superiorly. The prostate was deformed primarily in the AP direction, and tilted primarily in the anterior-posterior/superior-inferior plane. A significant correlation was seen between errors in depth of ERB insertion (DOI) and mean voxel-wise deformation, prostate tilt, Dice coefficient, and planning-to-treatment prostate inter-surface distance (p < 0.001). Dosimetrically, DOI is negatively correlated with prostate D95 and PTV coverage (p < 0.001). For the model of ERB studied, error in ERB position can cause deformations in the prostate that negatively affect treatment, and this additional aspect of setup error should be considered when ERBs are used for prostate SBRT. Before treatment, the ERB position should be verified, and the ERB should be adjusted if the error is observed to exceed tolerable values.

  4. Instability properties under a model mode-1 internal tide

    NASA Astrophysics Data System (ADS)

    John, S.; Peter, D.

    2016-11-01

    The instability properties of the bottom boundary layer (BBL) under a model mode-1 internal tide in linearly stratified finite-depth water are studied, using 2-D direct numerical simulations (DNS) based on a spectral multidomain penalty method model. This model internal tide is a proxy for its lower-mode oceanic counterpart which is generated when stratified water is forced over topography by barotropic tidal currents. Such low-mode internal tidal waves tend to propagate long distances from the point of generation, carrying with them large amounts of energy. One mechanism through which this energy is dissipated is through wave-BBL interactions, where strong shear layers develop along the bed, leading to focused instabilities which are precursors for localized turbulent events. Such events in the BBL can cause sediment resuspension and drive benthic nutrient fluxes, playing a crucial role in ecosystem balances. In the model problem, the stability response of the time-dependent BBL is examined by introducing low-amplitude perturbations near the bed. The corresponding time-evolving BBL-integrated perturbation energy growth rates are then computed, by comparing both the perturbed and unperturbed cases. When an instability actually occurs, its vorticity structure and preferred location is identified. Ultimately, a stability boundary is constructed as a function of perturbation amplitude and internal wave steepness, aspect ration and Reynolds number.

  5. Connectivity properties of the random-cluster model

    NASA Astrophysics Data System (ADS)

    Weigel, Martin; Metin Elci, Eren; Fytas, Nikolaos G.

    2016-02-01

    We investigate the connectivity properties of the random-cluster model mediated by bridge bonds that, if removed, lead to the generation of new connected components. We study numerically the density of bridges and the fragmentation kernel, i.e., the relative sizes of the generated fragments, and find that these quantities follow a scaling description. The corresponding scaling exponents are related to well known equilibrium critical exponents of the model. Using the Russo-Margulis formalism, we derive an exact relation between the expected density of bridges and the number of active edges. The same approach allows us to study the fluctuations in the numbers of bridges, thereby uncovering a new singularity in the random- cluster model as q < 4 cos2 (π/√3) in two dimensions. For numerical simulations of the model directly in the language of individual bonds, known as Sweeny's algorithm, the prevalence of bridges and the scaling of the sizes of clusters connected by bridges and candidate-bridges play a pivotal role. We discuss several different implementations of the necessary connectivity algorithms and assess their relative performance.

  6. Local electric conductive property of Si nanowire models

    NASA Astrophysics Data System (ADS)

    Ikeda, Yuji; Senami, Masato; Tachibana, Akitomo

    2012-12-01

    Local electric conductive properties of Si nanowire models are investigated by using two local electric conductivity tensors, {{σ }limits^{leftrArr }}_{ext}(r) and {{σ }limits^{leftrArr }}_{int}(r), defined in Rigged QED. It is emphasized that {{σ }limits^{leftrArr }}_{int}(r) is defined as the response of electric current to the actual electric field at a specific point and does not have corresponding macroscopic physical quantity. For the Si nanowire models, there are regions which show complicated response of electric current density to electric field, in particular, opposite and rotational ones. Local conductivities are considered to be available for the study of a negative differential resistance (NDR), which may be related to this opposite response. It is found that {{σ }limits^{leftrArr }}_{int}(r) shows quite different pattern from {{σ }limits^{leftrArr }}_{ext}(r), local electric conductivity defined for the external electric field. The effects of impurities are also studied by using the model including a Ge atom, in terms of the local response to electric field. It is found that the difference from the pristine model is found mainly around the Ge atom.

  7. Mechanical properties and modeling of seal-forming lithologies

    SciTech Connect

    Kronenberg, A.K.; Russell, J.E.; Carter, N.L.; Mazariegos, R.; Ibanez, W.

    1993-01-01

    Specific goals and accomplishments of this research include: (1) The evaluation of models of salt diaper ascent that involve either power law, dislocation creep as determined experimentally by Horseman et al. (1993) or linear, fluid-assisted creep as reported by Spiers et al. (1988, 1990, 1992). We have compared models assuming these two, experimentally evaluated flow laws and examined the predictions they make regarding diaper incubation periods, ascent velocities, deviatoric stresses and strain rates. (2) The evaluation of the effects of differential loading on the initiation an of salt structures. (3) Examination of the role of basement faults on the initiation and morphologic evolution of salt structures. (4) Evaluation of the mechanical properties of shale as a function of pressure and determination of the nature of its brittle-ductile transition. (5) Evaluation of the mechanical anisotropies of shales with varying concentrations, distributions and preferred orientations of clay. (6) The determination of temperature and ratedependencies of strength for a shale constitutive model that can be used in numerical models that depend on viscous formulations. (7) Determination of the mechanisms of deformation for argillaceous rocks over awide range of conditions. (8) Evaluation of the effects of H[sub 2]O within clay interlayers, as adsorbed surface layers.

  8. Fading memory and kernel properties of generic cortical microcircuit models.

    PubMed

    Maass, Wolfgang; Natschläger, Thomas; Markram, Henry

    2004-01-01

    It is quite difficult to construct circuits of spiking neurons that can carry out complex computational tasks. On the other hand even randomly connected circuits of spiking neurons can in principle be used for complex computational tasks such as time-warp invariant speech recognition. This is possible because such circuits have an inherent tendency to integrate incoming information in such a way that simple linear readouts can be trained to transform the current circuit activity into the target output for a very large number of computational tasks. Consequently we propose to analyze circuits of spiking neurons in terms of their roles as analog fading memory and non-linear kernels, rather than as implementations of specific computational operations and algorithms. This article is a sequel to [W. Maass, T. Natschläger, H. Markram, Real-time computing without stable states: a new framework for neural computation based on perturbations, Neural Comput. 14 (11) (2002) 2531-2560, Online available as #130 from: ], and contains new results about the performance of generic neural microcircuit models for the recognition of speech that is subject to linear and non-linear time-warps, as well as for computations on time-varying firing rates. These computations rely, apart from general properties of generic neural microcircuit models, just on capabilities of simple linear readouts trained by linear regression. This article also provides detailed data on the fading memory property of generic neural microcircuit models, and a quick review of other new results on the computational power of such circuits of spiking neurons.

  9. Dosimetric Study of a Low-Dose-Rate Brachytherapy Source

    NASA Astrophysics Data System (ADS)

    Rodríguez-Villafuerte, M.; Arzamendi, S.; Díaz-Perches, R.

    Carcinoma of the cervix is the most common malignancy - in terms of both incidence and mortality - in Mexican women. Low dose rate (LDR) intracavitary brachytherapy is normally prescribed for the treatment of this disease to the vast majority of patients attending public hospitals in our country. However, most treatment planning systems being used in these hospitals still rely on Sievert integral dose calculations. Moreover, experimental verification of dose distributions are hardly ever done. In this work we present a dosimetric characterisation of the Amersham CDCS-J 137Cs source, an LDR brachytherapy source commonly used in Mexican hospitals. To this end a Monte Carlo simulation was developed, that includes a realistic description of the internal structure of the source embedded in a scattering medium. The Monte Carlo results were compared to experimental measurements of dose distributions. A lucite phantom with the same geometric characteristics as the one used in the simulation was built. Dose measurements were performed using thermoluminescent dosimeters together with commercial RadioChromic dye film. A comparison between our Monte Carlo simulation, the experimental data, and results reported in the literature is presented.

  10. Dosimetric, mechanical, and geometric verification of conformal dynamic arc treatment.

    PubMed

    Malatesta, T; Landoni, V; delle Canne, S; Bufacchi, A; Marmiroli, L; Caspiani, O; Bonanni, A; Tortoreto, F; Leone, M V; Capparella, R; Fragomeni, R; Begnozzi, L

    2003-01-01

    A conformal dynamic arc (CD-arc) technique has been implemented at the S. Giovanni Calibita-Fatebenefratelli Hospital Radiotherapy Center. This technique is performed by rotational beams and a dynamic multileaf collimator (DMLC): during the treatment delivery the gantry rotates and the field shape, formed by the DMLC changes continuously. The aim of this study was to perform dosimetric, mechanical, and geometric verification to ensure that the dose calculated by a commercial treatment planning system and administered to the patient was correct, before and during the clinical use of this technique. Absolute dose values, at the isocenter and at other points placed in dose heterogeneity zone, have been verified with an ionization chamber in a solid homogeneous phantom. In uniform dose regions measured dose values resulted in agreements with the calculated doses within 2%. Isodose distributions have also been determined by radiographic films and compared with those predicted by the planning system. Distance to agreement between calculated and measured isodoses in dose gradient zone was within 2 mm. In conclusion, our results demonstrated the feasibility and the accuracy of the CD-arc technique for achieving highly conformal dose distributions. Up till now 20 patients have been treated with CD-arc therapy.

  11. Dosimetric implications of new compounds for neutron capture therapy (NCT)

    SciTech Connect

    Fairchild, R.G.

    1982-01-01

    Systemic application of radiolabeled or cytotoxic agents should allow targeting of primary and metastatic neoplasms on a cellular level. In fact, drug uptake in non-target cell pools often exceeds toxic levels before sufficient amounts are delivered to tumor. In addition, at the large concentration of molecules necessary for therapy, effects of saturation are often found. Application of NCT can circumvent problems associated with high uptake in competing non-target cell pools, as the /sup 10/B(n,..cap alpha..)/sup 7/Li reaction is activated only within the radiation field. A comparison with other modes of particle therapy indicated that NCT provides significant advantages. It is however, difficult to obtain vehicles for boron transport which demonstrate both the tumor specificity and concentration requisite for NCT. A number of biomolecules have been investigated which show both the necessary concentration and specificity. These include chlorpromazine, thiouracil, porphyrins, amino acids, and nucleosides. However, these analogs have yet to be made available for NCT. Dosimetric implications of binding sites are considered, as well as alternate neutron sources. (ERB)

  12. Dosimetric implications of age related glandular changes in screening mammography

    NASA Astrophysics Data System (ADS)

    Beckett, J. R.; Kotre, C. J.

    2000-03-01

    The UK National Health Service Breast Screening Programme is currently organized to routinely screen women between the ages of 50 and 64, with screening for older women available on request. The lower end of this age range closely matches the median age for the menopause (51 years), during which significant changes in the composition of the breast are known to occur. In order to quantify the dosimetric effect of these changes, radiographic factors and compressed breast thickness data for a cohort of 1258 women aged between 35 and 79 undergoing breast screening mammography have been used to derive estimates of breast glandularity and mean glandular dose (MGD), and examine their variation with age. The variation of mean radiographic exposure factors with age is also investigated. The presence of a significant number of age trial women within the cohort allowed an extended age range to be studied. Estimates of MGD including corrections for breast glandularity based on compressed breast thickness only, compressed breast thickness and age and for each individual woman are compared with the MGD based on the conventional assumption of a 50:50 adipose/glandular composition. It has been found that the use of the conventional 50:50 assumption leads to overestimates of MGD of up to 13% over the age range considered. By using compressed breast thickness to estimate breast glandularity, this error range can be reduced to 8%, whilst age and compressed breast thickness based glandularity estimates result in an error range of 1%.

  13. Monte Carlo simulations and dosimetric studies of an irradiation facility

    NASA Astrophysics Data System (ADS)

    Belchior, A.; Botelho, M. L.; Vaz, P.

    2007-09-01

    There is an increasing utilization of ionizing radiation for industrial applications. Additionally, the radiation technology offers a variety of advantages in areas, such as sterilization and food preservation. For these applications, dosimetric tests are of crucial importance in order to assess the dose distribution throughout the sample being irradiated. The use of Monte Carlo methods and computational tools in support of the assessment of the dose distributions in irradiation facilities can prove to be economically effective, representing savings in the utilization of dosemeters, among other benefits. One of the purposes of this study is the development of a Monte Carlo simulation, using a state-of-the-art computational tool—MCNPX—in order to determine the dose distribution inside an irradiation facility of Cobalt 60. This irradiation facility is currently in operation at the ITN campus and will feature an automation and robotics component, which will allow its remote utilization by an external user, under REEQ/996/BIO/2005 project. The detailed geometrical description of the irradiation facility has been implemented in MCNPX, which features an accurate and full simulation of the electron-photon processes involved. The validation of the simulation results obtained was performed by chemical dosimetry methods, namely a Fricke solution. The Fricke dosimeter is a standard dosimeter and is widely used in radiation processing for calibration purposes.

  14. Dosimetric predictors of diarrhea during radiotherapy for prostate cancer.

    PubMed

    Sanguineti, Giuseppe; Endres, Eugene J; Sormani, Maria Pia; Parker, Brent C

    2009-06-01

    To investigate dosimetric predictors of diarrhea during radiotherapy (RT) for prostate cancer. All patients who underwent external-beam radiotherapy as part of treatment for localized prostate cancer at the University of Texas Medical Branch, Galveston, TX, USA, from May 2002 to November 2006 were extracted from the own database. From the cumulative dose-volume histogram (DVH), the absolute volumes (V-value) of intestinal cavity (IC) receiving 15, 30, and 45 Gy were extracted for each patient. Acute gastrointestinal toxicity was prospectively scored at each weekly treatment visit according to CTC (Common Toxicity Criteria) v2.0. The endpoint was the development of peak grade >or= 2 diarrhea during RT. Various patient, tumor, and treatment characteristics were evaluated using logistic regression. 149 patients were included in the analysis, 112 (75.2%) treated with whole-pelvis intensity-modulated radiotherapy (WP-IMRT) and 37 (24.8%) with prostate-only RT, including or not including, the seminal vesicles (PORT +/- SV). 45 patients (30.2%) developed peak grade >or= 2 diarrhea during treatment. At univariate analysis, IC-V(15) and IC-V(30), but not IC-V(45), were correlated to the endpoint; at multivariate analysis, only IC-V(15) (p = 0.047) along with peak acute proctitis (p = 0.041) was independently correlated with the endpoint. These data provide a novel and prostate treatment-specific "upper limit" DVH for IC.

  15. Active pixel as dosimetric device for interventional radiology

    NASA Astrophysics Data System (ADS)

    Servoli, L.; Baldaccini, F.; Biasini, M.; Checcucci, B.; Chiocchini, S.; Cicioni, R.; Conti, E.; Di Lorenzo, R.; Dipilato, A. C.; Esposito, A.; Fanó, L.; Paolucci, M.; Passeri, D.; Pentiricci, A.; Placidi, P.

    2013-08-01

    Interventional Radiology (IR) is a subspecialty of radiology comprehensive of all minimally invasive diagnostic and therapeutic procedures performed using radiological devices to obtain image guidance. The interventional procedures are potentially harmful for interventional radiologists and medical staff due to the X-ray diffusion by the patient's body. The characteristic energy range of the diffused photons spans few tens of keV. In this work we will present a proposal for a new X-ray sensing element in the energy range of interest for IR procedures. The sensing element will then be assembled in a dosimeter prototype, capable of real-time measurement, packaged in a small form-factor, with wireless communication and no external power supply to be used for individual operators dosimetry for IR procedures. For the sensor, which is the heart of the system, we considered three different Active Pixel Sensors (APS). They have shown a good capability as single X-ray photon detectors, up to several tens keV photon energy. Two dosimetric quantities have been considered, the number of detected photons and the measured energy deposition. Both observables have a linear dependence with the dose, as measured by commercial dosimeters. The uncertainties in the measurement are dominated by statistic and can be pushed at ˜5% for all the sensors under test.

  16. Dosimetrical evaluation of Leksell Gamma Knife 4C radiosurgery unit

    NASA Astrophysics Data System (ADS)

    Sajeev, Thomas; Mustafa, Mohamed M.; Supe, Sanjay S.

    2011-01-01

    A number of experiments was performed using standard protocols, in order to evaluate the dosimetric accuracy of Leksell Gamma Knife 4C unit. Verification of the beam alignment has been performed for all collimators using solid plastic head phantom and Gafchromic™ type MD-55 films. The study showed a good agreement of Leksell Gammaplan calculated dose profiles with experimentally determined profiles in all three axes. Isocentric accuracy is verified using a specially machined cylindrical aluminium film holder tool made with very narrow geometric tolerances aligned between trunnions of 4 mm collimator. Considering all uncertainties in all three dimensions, the estimated accuracy of the unit was 0.1 mm. Dose rate at the centre point of the unit has been determined according to the IAEA, TRS-398 protocol, using Unidose-E (PTW-Freiburg, Germany) with a 0.125 cc ion chamber, over a period of 6 years. The study showed that the Leksell Gamma Knife 4C unit is excellent radiosurgical equipment with high accuracy and precision, which makes it possible to deliver larger doses of radiation, within the limits defined by national and international guidelines, applicable for stereotactic radiosurgery procedures.

  17. Physical Property Modeling of Concentrated Cesium Eluate Solutions, Part I - Derivation of Models

    SciTech Connect

    Choi, A.S.; Pierce, R. A.; Edwards, T. B.; Calloway, T. B.

    2005-09-15

    Major analytes projected to be present in the Hanford Waste Treatment Plant cesium ion-exchange eluate solutions were identified from the available analytical data collected during radioactive bench-scale runs, and a test matrix of cesium eluate solutions was designed within the bounding concentrations of those analytes. A computer model simulating the semi-batch evaporation of cesium eluate solutions was run in conjunction with a multi-electrolyte aqueous system database to calculate the physical properties of each test matrix solution concentrated to the target endpoints of 80% and 100% saturation. The calculated physical properties were analyzed statistically and fitted into mathematical expressions for the bulk solubility, density, viscosity, heat capacity and volume reduction factor as a function of temperature and concentration of each major analyte in the eluate feed. The R{sup 2} of the resulting physical property models ranged from 0.89 to 0.99.

  18. Development and Dosimetric Characterization of a Tissue Substitute (Bolus) For Use in Linear Accelerator Electron Radiotherapy

    NASA Astrophysics Data System (ADS)

    Estrada Trujillo, Jorge; Villaseñor Navarro, Luis Felipe; Mitsoura, Eleni

    2003-09-01

    We propose the design of a new custom made material, to be used as a tissue substitute in external beam electron radiotherapy, based on cotton fabric and beeswax. Due to its inexpensive, easy preparation, constant thickness, flexibility, uniform density and physical properties similar to those of soft tissue, this bolus will insure personalized optimal dose build up and dose distribution in irregular treatment regions. Materials and Methods: We used commercial Campeche beeswax and 100% cotton fabric to prepare the bolus. Beeswax's physical characteristics were determined by thermal and density analysis. Its chemical properties are to be determined by electronic microcopy. We performed quality control tests and calibration of the Varian 2100C linear accelerator. The tissue equivalence of the material is established for a range of electron energies (6, 9, 12, 16, 20 MeV) using a water equivalent solid phantom (PTW; Freiburg, Germany) and a plane parallel ionization chamber (PTW) associated to a PTW electrometer. Results: Beeswax's absolute density was found to be 0.9181g/ml at 21°C, with a melting point of 45°C. For the bolus elaboration, the cotton fabric was soaked in liquid beeswax and thin sheets of approximately 1 mm were obtained. These presented high flexibility, physical stability (color, texture, thickness) and homogeneity. Determination of this dosimetric characteristics and equivalent thickness are still in process. Discussion and conclusions: Our preliminary results suggest that the tissue substitute is easily made, inexpensive to produce, molds well to the treatment area and its positioning is easy and reproducible over the course of the treatment. So we consider that it's a good alternative to the commercial bolus.

  19. Modelling the optical properties of aerosols in a chemical transport model

    NASA Astrophysics Data System (ADS)

    Andersson, E.; Kahnert, M.

    2015-12-01

    According to the IPCC fifth assessment report (2013), clouds and aerosols still contribute to the largest uncertainty when estimating and interpreting changes to the Earth's energy budget. Therefore, understanding the interaction between radiation and aerosols is both crucial for remote sensing observations and modelling the climate forcing arising from aerosols. Carbon particles are the largest contributor to the aerosol absorption of solar radiation, thereby enhancing the warming of the planet. Modelling the radiative properties of carbon particles is a hard task and involves many uncertainties arising from the difficulties of accounting for the morphologies and heterogeneous chemical composition of the particles. This study aims to compare two ways of modelling the optical properties of aerosols simulated by a chemical transport model. The first method models particle optical properties as homogeneous spheres and are externally mixed. This is a simple model that is particularly easy to use in data assimilation methods, since the optics model is linear. The second method involves a core-shell internal mixture of soot, where sulphate, nitrate, ammonia, organic carbon, sea salt, and water are contained in the shell. However, by contrast to previously used core-shell models, only part of the carbon is concentrated in the core, while the remaining part is homogeneously mixed with the shell. The chemical transport model (CTM) simulations are done regionally over Europe with the Multiple-scale Atmospheric Transport and CHemistry (MATCH) model, developed by the Swedish Meteorological and Hydrological Institute (SMHI). The MATCH model was run with both an aerosol dynamics module, called SALSA, and with a regular "bulk" approach, i.e., a mass transport model without aerosol dynamics. Two events from 2007 are used in the analysis, one with high (22/12-2007) and one with low (22/6-2007) levels of elemental carbon (EC) over Europe. The results of the study help to assess the

  20. 3D-Digital soil property mapping by geoadditive models

    NASA Astrophysics Data System (ADS)

    Papritz, Andreas

    2016-04-01

    In many digital soil mapping (DSM) applications, soil properties must be predicted not only for a single but for multiple soil depth intervals. In the GlobalSoilMap project, as an example, predictions are computed for the 0-5 cm, 5-15 cm, 15-30 cm, 30-60 cm, 60-100 cm, 100-200 cm depth intervals (Arrouays et al., 2014). Legacy soil data are often used for DSM. It is common for such datasets that soil properties were measured for soil horizons or for layers at varying soil depth and with non-constant thickness (support). This poses problems for DSM: One strategy is to harmonize the soil data to common depth prior to the analyses (e.g. Bishop et al., 1999) and conduct the statistical analyses for each depth interval independently. The disadvantage of this approach is that the predictions for different depths are computed independently from each other so that the predicted depth profiles may be unrealistic. Furthermore, the error induced by the harmonization to common depth is ignored in this approach (Orton et al. 2016). A better strategy is therefore to process all soil data jointly without prior harmonization by a 3D-analysis that takes soil depth and geographical position explicitly into account. Usually, the non-constant support of the data is then ignored, but Orton et al. (2016) presented recently a geostatistical approach that accounts for non-constant support of soil data and relies on restricted maximum likelihood estimation (REML) of a linear geostatistical model with a separable, heteroscedastic, zonal anisotropic auto-covariance function and area-to-point kriging (Kyriakidis, 2004.) Although this model is theoretically coherent and elegant, estimating its many parameters by REML and selecting covariates for the spatial mean function is a formidable task. A simpler approach might be to use geoadditive models (Kammann and Wand, 2003; Wand, 2003) for 3D-analyses of soil data. geoAM extend the scope of the linear model with spatially correlated errors to

  1. Dosimetric effects of patient rotational setup errors on prostate IMRT treatments

    NASA Astrophysics Data System (ADS)

    Fu, Weihua; Yang, Yong; Li, Xiang; Heron, Dwight E.; Saiful Huq, M.; Yue, Ning J.

    2006-10-01

    The purpose of this work is to determine dose delivery errors that could result from systematic rotational setup errors (ΔΦ) for prostate cancer patients treated with three-phase sequential boost IMRT. In order to implement this, different rotational setup errors around three Cartesian axes were simulated for five prostate patients and dosimetric indices, such as dose-volume histogram (DVH), tumour control probability (TCP), normal tissue complication probability (NTCP) and equivalent uniform dose (EUD), were employed to evaluate the corresponding dosimetric influences. Rotational setup errors were simulated by adjusting the gantry, collimator and horizontal couch angles of treatment beams and the dosimetric effects were evaluated by recomputing the dose distributions in the treatment planning system. Our results indicated that, for prostate cancer treatment with the three-phase sequential boost IMRT technique, the rotational setup errors do not have significant dosimetric impacts on the cumulative plan. Even in the worst-case scenario with ΔΦ = 3°, the prostate EUD varied within 1.5% and TCP decreased about 1%. For seminal vesicle, slightly larger influences were observed. However, EUD and TCP changes were still within 2%. The influence on sensitive structures, such as rectum and bladder, is also negligible. This study demonstrates that the rotational setup error degrades the dosimetric coverage of target volume in prostate cancer treatment to a certain degree. However, the degradation was not significant for the three-phase sequential boost prostate IMRT technique and for the margin sizes used in our institution.

  2. Comparing the dosimetric characteristics of the electron beam from dedicated intraoperative and conventional radiotherapy accelerators.

    PubMed

    Baghani, Hamid Reza; Aghamiri, Seyed Mahmoud Reza; Mahdavi, Seyed Rabi; Akbari, Mohammad Esmail; Mirzaei, Hamid Reza

    2015-03-08

    The specific design of the mobile dedicated intraoperative radiotherapy (IORT) accelerators and different electron beam collimation system can change the dosimetric characteristics of electron beam with respect to the conventional accelerators. The aim of this study is to measure and compare the dosimetric characteristics of electron beam produced by intraoperative and conventional radiotherapy accelerators. To this end, percentage depth dose along clinical axis (PDD), transverse dose profile (TDP), and output factor of LIAC IORT and Varian 2100C/D conventional radiotherapy accelerators were measured and compared. TDPs were recorded at depth of maximum dose. The results of this work showed that depths of maximum dose, R90, R50, and RP for LIAC beam are lower than those of Varian beam. Furthermore, for all energies, surface doses related to the LIAC beam are substantially higher than those of Varian beam. The symmetry and flatness of LIAC beam profiles are more desirable compared to the Varian ones. Contrary to Varian accelerator, output factor of LIAC beam substantially increases with a decrease in the size of the applicator. Dosimetric characteristics of beveled IORT applicators along clinical axis were different from those of the flat ones. From these results, it can be concluded that dosimetric characteristics of intraoperative electron beam are substantially different from those of conventional clinical electron beam. The dosimetric characteristics of the LIAC electron beam make it a useful tool for intraoperative radiotherapy purposes.

  3. Permanent Planar Iodine-125 Implants: The Dosimetric Effect of Geometric Parameters for Idealized Source Configurations

    SciTech Connect

    Cormack, Robert A.

    2007-11-15

    Purpose: To provide dosimetric information about permanent planar {sup 125}I implants in a manner that is useful to the brachytherapist in the operative setting. Methods and Materials: Reference planar permanent implants were simulated for a variety of areas with sources placed uniformly on a 1-cm grid. Implants having variable source spacing and curvature were simulated and compared with the reference implants. Dosimetric measures were calculated at 0.5 and 1.0 cm from the implant plane. Results: A method for calculating dosimetric statistics for permanent implants ranging from 5 x 5 cm to 13 x 13 cm is presented. A formula to predict the reference source strength needed to achieve a desired dosimetric quantity is also presented. The effect of adjusting strand spacing to compensate for source activity is presented and is shown to be an effective means to adjust implants to use source strengths other than the reference strength. The effect of implant curvature compared with flat implants on dosimetric statistics is presented as a function of radius of curvature. Conclusions: The results presented in this work may be used to provide information about dose delivered from planar permanent implants.

  4. Modeling Classroom Discourse: Do Models That Predict Dialogic Instruction Properties Generalize across Populations?

    ERIC Educational Resources Information Center

    Samei, Borhan; Olney, Andrew M.; Kelly, Sean; Nystrand, Martin; D'Mello, Sidney; Blanchard, Nathan; Graesser, Art

    2015-01-01

    It has previously been shown that the effective use of dialogic instruction has a positive impact on student achievement. In this study, we investigate whether linguistic features used to classify properties of classroom discourse generalize across different subpopulations. Results showed that the machine learned models perform equally well when…

  5. Cellular uptake of {sup 212}BiOCl by Ehrlich ascites cells: A dosimetric analysis

    SciTech Connect

    Roeske, J.C.; Whitlock, J.L.; Harper, P.V.; Rotmensch, J.; Stinchcomb, T.G.; Schwartz, J.L.; Hines, J.J.

    1999-01-01

    Bi-212 is an alpha-emitting radionuclide being investigated as a therapeutic agent in the intraperitoneal treatment of micrometastatic ovarian carcinoma. In evaluating a new therapeutic modality, cell-survival studies are often used as a means of quantifying the biological effects of radiation. In this analysis, Ehrlich ascites cells were irradiated under conditions similar to therapy in various concentrations of Bi-212. Immediately following irradiation, a cell survival assay was performed in which cells were plated and colonies were counted after 10--14 days. Both a macrodosimetric and a microdosimetric approach were used in analyzing these data. These models used as input the fraction of activity within the cell and in solution, the distribution of cell sizes, and the variation of LET along individual alpha-particle tracks. The results indicate that the energy deposited within the nucleus varies significantly among individual cells. There is a small fraction of cell nuclei which receive no hits, while the remaining cells receive energy depositions which can differ significantly from the mean value. These dosimetric parameters are correlated with measured cell survival and will be a useful predictor of outcome for therapeutic doses.

  6. Dosimetric evaluation of a Monte Carlo IMRT treatment planning system incorporating the MIMiC

    NASA Astrophysics Data System (ADS)

    Rassiah-Szegedi, P.; Fuss, M.; Sheikh-Bagheri, D.; Szegedi, M.; Stathakis, S.; Lancaster, J.; Papanikolaou, N.; Salter, B.

    2007-12-01

    The high dose per fraction delivered to lung lesions in stereotactic body radiation therapy (SBRT) demands high dose calculation and delivery accuracy. The inhomogeneous density in the thoracic region along with the small fields used typically in intensity-modulated radiation therapy (IMRT) treatments poses a challenge in the accuracy of dose calculation. In this study we dosimetrically evaluated a pre-release version of a Monte Carlo planning system (PEREGRINE 1.6b, NOMOS Corp., Cranberry Township, PA), which incorporates the modeling of serial tomotherapy IMRT treatments with the binary multileaf intensity modulating collimator (MIMiC). The aim of this study is to show the validation process of PEREGRINE 1.6b since it was used as a benchmark to investigate the accuracy of doses calculated by a finite size pencil beam (FSPB) algorithm for lung lesions treated on the SBRT dose regime via serial tomotherapy in our previous study. Doses calculated by PEREGRINE were compared against measurements in homogeneous and inhomogeneous materials carried out on a Varian 600C with a 6 MV photon beam. Phantom studies simulating various sized lesions were also carried out to explain some of the large dose discrepancies seen in the dose calculations with small lesions. Doses calculated by PEREGRINE agreed to within 2% in water and up to 3% for measurements in an inhomogeneous phantom containing lung, bone and unit density tissue.

  7. Effects of Gamma Radiation on Tertiary Butylhydroquinone and its Dosimetric Features

    NASA Astrophysics Data System (ADS)

    Tuner, Hasan; Korkmaz, Mustafa

    2008-04-01

    The effects of gamma radiation on tertiary butylhydroquinone (TBHQ) are reported using electron spin resonance (ESR) spectroscopy. While unirradiated (control) TBHQ exhibited no ESR signal, irradiated one presented an ESR spectrum with five characteristic resonance peaks extended over a magnetic field region of 1.5 mT. Variations of the heights of the resonance peaks and the spectrum area as function of the microwave power, applied dose, storage time, and temperature were studied. The kinetic features and spectroscopic parameters of the species responsible for the experimental ESR spectrum were investigated by annealing studies performed at four different temperatures and simulation calculations, respectively. A model based on the presence of two species having different kinetic and spectroscopic features was found to describe best the experimental results. The dosimetric potential of TBHQ was also investigated, and it was concluded that the discrimination of irradiated TBHQ from unirradiated one was possible even long after the radiation treatment, and that radiation doses above 5 kGy could be measured with an accuracy better than 3% by using TBHQ. Two tentative radical species were proposed.

  8. Monte Carlo calculations and experimental measurements of dosimetric parameters of the IRA-103Pd brachytherapy source.

    PubMed

    Sadeghi, Mahdi; Raisali, Gholamreza; Hosseini, S Hamed; Shavar, Arzhang

    2008-04-01

    This article presents a brachytherapy source having 103Pd adsorbed onto a cylindrical silver rod that has been developed by the Agricultural, Medical, and Industrial Research School for permanent implant applications. Dosimetric characteristics (radial dose function, anisotropy function, and anisotropy factor) of this source were experimentally and theoretically determined in terms of the updated AAPM Task group 43 (TG-43U1) recommendations. Monte Carlo simulations were used to calculate the dose rate constant. Measurements were performed using TLD-GR200A circular chip dosimeters using standard methods employing thermoluminescent dosimeters in a Perspex phantom. Precision machined bores in the phantom located the dosimeters and the source in a reproducible fixed geometry, providing for transverse-axis and angular dose profiles over a range of distances from 0.5 to 5 cm. The Monte Carlo N-particle (MCNP) code, version 4C simulation techniques have been used to evaluate the dose-rate distributions around this model 103Pd source in water and Perspex phantoms. The Monte Carlo calculated dose rate constant of the IRA-103Pd source in water was found to be 0.678 cGy h(-1) U(-1) with an approximate uncertainty of +/-0.1%. The anisotropy function, F(r, theta), and the radial dose function, g(r), of the IRA- 103Pd source were also measured in a Perspex phantom and calculated in both Perspex and liquid water phantoms.

  9. High spatial resolution dosimetric response maps for radiotherapy ionization chambers measured using kilovoltage synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Butler, D. J.; Stevenson, A. W.; Wright, T. E.; Harty, P. D.; Lehmann, J.; Livingstone, J.; Crosbie, J. C.

    2015-11-01

    Small circular beams of synchrotron radiation (0.1 mm and 0.4 mm in diameter) were used to irradiate ionization chambers of the types commonly used in radiotherapy. By scanning the chamber through the beam and measuring the ionization current, a spatial map of the dosimetric response of the chamber was recorded. The technique is able to distinguish contributions to the large-field ionization current from the chamber walls, central electrode and chamber stem. Scans were recorded for the NE 2571 Farmer chamber, the PTW 30013, IBA FC65-G Farmer-type chambers, the NE 2611A and IBA CC13 thimble chambers, the PTW 31006 and 31014 pinpoint chambers, the PTW Roos and Advanced Markus plane-parallel chambers, and the PTW 23342 thin-window soft x-ray chamber. In all cases, large contributions to the response arise from areas where the incident beam grazes the cavity surfaces. Quantitative as well as qualitative information about the relative chamber response was extracted from the maps, including the relative contribution of the central electrode. Line scans using monochromatic beams show the effect of the photon energy on the chamber response. For Farmer-type chambers, a simple Monte Carlo model was in good agreement with the measured response.

  10. Dosimetric study of photobiomodulation therapy in 5-FU-induced oral mucositis in hamsters

    NASA Astrophysics Data System (ADS)

    Cotomacio, Claudia Carrara; Campos, Luana; Nesadal de Souza, Douglas; Arana-Chavez, Victor Elias; Simões, Alyne

    2017-01-01

    Oral mucositis (OM) is a debilitating consequence of cancer treatment that could be treated with photobiomodulation therapy (PBMT); however, there is no consensus about its dosimetric parameters for OM healing. The aim of this study was to compare different PBMT protocols on OM treatment, through clinical and histological analysis. Thirty hamsters were used, in an induced model of OM by 5-fluorouracil (5-FU) and superficial scratching, in seven days of follow-up. The animals were divided into five groups: control (C), which received only anesthesia and chemotherapeutic vehicle; chemotherapy (Ch), which received anesthesia, 5-FU, and scratches; laser 1 (L1), the same as Ch group, PBMT 6 J/cm2 and 0.24 J (one point); laser 2 (L2), the same as Ch group, PBMT 25 J/cm2 and 1 J (one point); and laser 3 (L3), the same as Ch group, PBMT 4 points of 0.24 J and 6 J/cm2 each. The laser used has λ=660 nm, 0.04 cm2 of spot area, and 40 mW. The best PBMT protocol to maintain lowest OM levels compared to Ch group was L1, followed by L2 and L3. Our results suggest that the application mode of PBMT and the energy delivered per area could interfere with the OM healing.

  11. Model Checking Linear-Time Properties of Probabilistic Systems

    NASA Astrophysics Data System (ADS)

    Baier, Christel; Größer, Marcus; Ciesinski, Frank

    This chapter is about the verification of Markov decision processes (MDPs) which incorporate one of the fundamental models for reasoning about probabilistic and nondeterministic phenomena in reactive systems. MDPs have their roots in the field of operations research and are nowadays used in a wide variety of areas including verification, robotics, planning, controlling, reinforcement learning, economics and semantics of randomized systems. Furthermore, MDPs served as the basis for the introduction of probabilistic automata which are related to weighted automata. We describe the use of MDPs as an operational model for randomized systems, e.g., systems that employ randomized algorithms, multi-agent systems or systems with unreliable components or surroundings. In this context we outline the theory of verifying ω-regular properties of such operational models. As an integral part of this theory we use ω-automata, i.e., finite-state automata over finite alphabets that accept languages of infinite words. Additionally, basic concepts of important reduction techniques are sketched, namely partial order reduction of MDPs and quotient system reduction of the numerical problem that arises in the verification of MDPs. Furthermore we present several undecidability and decidability results for the controller synthesis problem for partially observable MDPs.

  12. Thermodynamic properties of model CdTe/CdSe mixtures

    DOE PAGES

    van Swol, Frank; Zhou, Xiaowang W.; Challa, Sivakumar R.; ...

    2015-02-20

    We report on the thermodynamic properties of binary compound mixtures of model groups II–VI semiconductors. We use the recently introduced Stillinger–Weber Hamiltonian to model binary mixtures of CdTe and CdSe. We use molecular dynamics simulations to calculate the volume and enthalpy of mixing as a function of mole fraction. The lattice parameter of the mixture closely follows Vegard's law: a linear relation. This implies that the excess volume is a cubic function of mole fraction. A connection is made with hard sphere models of mixed fcc and zincblende structures. We found that the potential energy exhibits a positive deviation frommore » ideal soluton behaviour; the excess enthalpy is nearly independent of temperatures studied (300 and 533 K) and is well described by a simple cubic function of the mole fraction. Using a regular solution approach (combining non-ideal behaviour for the enthalpy with ideal solution behaviour for the entropy of mixing), we arrive at the Gibbs free energy of the mixture. The Gibbs free energy results indicate that the CdTe and CdSe mixtures exhibit phase separation. The upper consolute temperature is found to be 335 K. Finally, we provide the surface energy as a function of composition. Moreover, it roughly follows ideal solution theory, but with a negative deviation (negative excess surface energy). This indicates that alloying increases the stability, even for nano-particles.« less

  13. Thermodynamic properties of model CdTe/CdSe mixtures

    SciTech Connect

    van Swol, Frank; Zhou, Xiaowang W.; Challa, Sivakumar R.; Martin, James E.

    2015-02-20

    We report on the thermodynamic properties of binary compound mixtures of model groups II–VI semiconductors. We use the recently introduced Stillinger–Weber Hamiltonian to model binary mixtures of CdTe and CdSe. We use molecular dynamics simulations to calculate the volume and enthalpy of mixing as a function of mole fraction. The lattice parameter of the mixture closely follows Vegard's law: a linear relation. This implies that the excess volume is a cubic function of mole fraction. A connection is made with hard sphere models of mixed fcc and zincblende structures. We found that the potential energy exhibits a positive deviation from ideal soluton behaviour; the excess enthalpy is nearly independent of temperatures studied (300 and 533 K) and is well described by a simple cubic function of the mole fraction. Using a regular solution approach (combining non-ideal behaviour for the enthalpy with ideal solution behaviour for the entropy of mixing), we arrive at the Gibbs free energy of the mixture. The Gibbs free energy results indicate that the CdTe and CdSe mixtures exhibit phase separation. The upper consolute temperature is found to be 335 K. Finally, we provide the surface energy as a function of composition. Moreover, it roughly follows ideal solution theory, but with a negative deviation (negative excess surface energy). This indicates that alloying increases the stability, even for nano-particles.

  14. Phase behaviors and membrane properties of model liposomes: temperature effect.

    PubMed

    Wu, Hsing-Lun; Sheng, Yu-Jane; Tsao, Heng-Kwong

    2014-09-28

    The phase behaviors and membrane properties of small unilamellar vesicles have been explored at different temperatures by dissipative particle dynamics simulations. The vesicles spontaneously formed by model lipids exhibit pre-transition from gel to ripple phase and main transition from ripple to liquid phase. The vesicle shape exhibits the faceted feature at low temperature, becomes more sphere-like with increasing temperature, but loses its sphericity at high temperature. As the temperature rises, the vesicle size grows but the membrane thickness declines. The main transition (Tm) can be identified by the inflection point. The membrane structural characteristics are analyzed. The inner and outer leaflets are asymmetric. The length of the lipid tail and area density of the lipid head in both leaflets decrease with increasing temperature. However, the mean lipid volume grows at low temperature but declines at high temperature. The membrane mechanical properties are also investigated. The water permeability grows exponentially with increasing T but the membrane tension peaks at Tm. Both the bending and stretching moduli have their minima near Tm. Those results are consistent with the experimental observations, indicating that the main signatures associated with phase transition are clearly observed in small unilamellar vesicles.

  15. Modelization of the optical and colorimetric properties of lustred ceramics

    NASA Astrophysics Data System (ADS)

    Reillon, V.; Berthier, S.

    2006-05-01

    The lustre decoration is one of the most famous decorations of glazed ceramics in the Mediterranean basin. Unfortunately, the recipes and fabrication techniques used during medieval times have been lost and that is why these objects have been widely studied. But until now, little was known on their optical properties. In this work it is shown that, despite the common belief, the chemical composition of the decoration (copper and/or silver nanoparticles) is not the only relevant parameter in order to explain the optical properties of lustres. By the use of optical characterization and the elaboration of a model - based on the Maxwell Garnett theory and the Abeles matrices theory for interferences -, simulated reflection spectra have been obtained in good agreement with the measured reflection spectra, confirming that the concentration of metal, the size of the metallic nanoparticles as well as the optical index of the glaze play a key-role in order to explain the coloured metallic shine exhibited by the lustres.

  16. Phase behaviors and membrane properties of model liposomes: Temperature effect

    NASA Astrophysics Data System (ADS)

    Wu, Hsing-Lun; Sheng, Yu-Jane; Tsao, Heng-Kwong

    2014-09-01

    The phase behaviors and membrane properties of small unilamellar vesicles have been explored at different temperatures by dissipative particle dynamics simulations. The vesicles spontaneously formed by model lipids exhibit pre-transition from gel to ripple phase and main transition from ripple to liquid phase. The vesicle shape exhibits the faceted feature at low temperature, becomes more sphere-like with increasing temperature, but loses its sphericity at high temperature. As the temperature rises, the vesicle size grows but the membrane thickness declines. The main transition (Tm) can be identified by the inflection point. The membrane structural characteristics are analyzed. The inner and outer leaflets are asymmetric. The length of the lipid tail and area density of the lipid head in both leaflets decrease with increasing temperature. However, the mean lipid volume grows at low temperature but declines at high temperature. The membrane mechanical properties are also investigated. The water permeability grows exponentially with increasing T but the membrane tension peaks at Tm. Both the bending and stretching moduli have their minima near Tm. Those results are consistent with the experimental observations, indicating that the main signatures associated with phase transition are clearly observed in small unilamellar vesicles.

  17. Atomistic modeling of thermomechanical properties of SWNT/Epoxy nanocomposites

    NASA Astrophysics Data System (ADS)

    Fasanella, Nicholas; Sundararaghavan, Veera

    2015-09-01

    Molecular dynamics simulations are performed to compute thermomechanical properties of cured epoxy resins reinforced with pristine and covalently functionalized carbon nanotubes. A DGEBA-DDS epoxy network was built using the ‘dendrimer’ growth approach where 75% of available epoxy sites were cross-linked. The epoxy model is verified through comparisons to experiments, and simulations are performed on nanotube reinforced cross-linked epoxy matrix using the CVFF force field in LAMMPS. Full stiffness matrices and linear coefficient of thermal expansion vectors are obtained for the nanocomposite. Large increases in stiffness and large decreases in thermal expansion were seen along the direction of the nanotube for both nanocomposite systems when compared to neat epoxy. The direction transverse to nanotube saw a 40% increase in stiffness due to covalent functionalization over neat epoxy at 1 K whereas the pristine nanotube system only saw a 7% increase due to van der Waals effects. The functionalized SWNT/epoxy nanocomposite showed an additional 42% decrease in thermal expansion along the nanotube direction when compared to the pristine SWNT/epoxy nanocomposite. The stiffness matrices are rotated over every possible orientation to simulate the effects of an isotropic system of randomly oriented nanotubes in the epoxy. The randomly oriented covalently functionalized SWNT/Epoxy nanocomposites showed substantial improvements over the plain epoxy in terms of higher stiffness (200% increase) and lower thermal expansion (32% reduction). Through MD simulations, we develop means to build simulation cells, perform annealing to reach correct densities, compute thermomechanical properties and compare with experiments.

  18. Validation and Application of Concentrated Cesium Eluate Physical Property Models

    SciTech Connect

    Choi, A.S.

    2004-03-18

    This work contained two objectives. To verify the mathematical equations developed for the physical properties of concentrated cesium eluate solutions against experimental test results obtained with simulated feeds. To estimate the physical properties of the radioactive AW-101 cesium eluate at saturation using the validated models. The Hanford River Protection Project (RPP) Hanford Waste Treatment and Immobilization Plant (WTP) is currently being built to extract radioisotopes from the vast inventory of Hanford tank wastes and immobilize them in a silicate glass matrix for eventual disposal at a geological repository. The baseline flowsheet for the pretreatment of supernatant liquid wastes includes removal of cesium using regenerative ion-exchange resins. The loaded cesium ion-exchange columns will be eluted with nitric acid nominally at 0.5 molar, and the resulting eluate solution will be concentrated in a forced-convection evaporator to reduce the storage volume and to recover the acid for reuse. The reboiler pot is initially charged with a concentrated nitric acid solution and kept under a controlled vacuum during feeding so the pot contents would boil at 50 degrees Celsius. The liquid level in the pot is maintained constant by controlling both the feed and boilup rates. The feeding will continue with no bottom removal until the solution in the pot reaches the target endpoint of 80 per cent saturation with respect to any one of the major salt species present.

  19. Mechanical properties of metallic nanowires using tight-binding model

    NASA Astrophysics Data System (ADS)

    Aish, Mohammed; Starostenkov, Mikhail

    2016-01-01

    The mechanical properties of Nickel nanowires have been studied at different temperatures using molecular dynamics simulations. Molecular Dynamics (MD) simulations have been carried out on pure Nickel (Ni) crystal with face-centered cubic (FCC) lattice upon application of uniaxial tension at nanolevel with a speed of 20 m/s. The deformation corresponds to the direction <001>. To the calculated block of crystal, free boundary conditions are applied in the directions <100>, <010>. A many body interatomic potential for Ni within the second moment approximation of the tight binding model (the Cleri-Rosato potentials) was employed to carry out three dimensional molecular dynamics simulations. MD simulation used to investigate the effect of temperature of Ni nanowire on the nature of deformation and fracture. Temperature effect on the extension property of metal nanowire is discussed in detail. The mechanical strengths and the mechanical strain of the nanowires decrease linearly with the increasing temperature. The feature of deformation energy can be divided into four regions: quasi-elastic, plastic, flow and failure. Experiments have shown that when the temperature increases the yielding stress decreases, the first stage of deformation was narrowed, and the second stage was widened. The results showed that breaking position depended on temperature.

  20. Predictive Computer Models for Biofilm Detachment Properties in Pseudomonas aeruginosa

    PubMed Central

    Cogan, Nick G.; Harro, Janette M.; Stoodley, Paul

    2016-01-01

    ABSTRACT Microbial biofilm communities are protected against environmental extremes or clearance by antimicrobial agents or the host immune response. They also serve as a site from which microbial populations search for new niches by dispersion via single planktonic cells or by detachment by protected biofilm aggregates that, until recently, were thought to become single cells ready for attachment. Mathematically modeling these events has provided investigators with testable hypotheses for further study. Such was the case in the recent article by Kragh et al. (K. N. Kragh, J. B. Hutchison, G. Melaugh, C. Rodesney, A. E. Roberts, Y. Irie, P. Ø. Jensen, S. P. Diggle, R. J. Allen, V. Gordon, and T. Bjarnsholt, mBio 7:e00237-16, 2016, http://dx.doi.org/10.1128/mBio.00237-16), in which investigators were able to identify the differential competitive advantage of biofilm aggregates to directly attach to surfaces compared to the single-celled planktonic populations. Therefore, as we delve deeper into the properties of the biofilm mode of growth, not only do we need to understand the complexity of biofilms, but we must also account for the properties of the dispersed and detached populations and their effect on reseeding. PMID:27302761

  1. Properties of Coupled Oscillator Model for Bidirectional Associative Memory

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Satoshi

    2016-08-01

    In this study, we consider the stationary state and dynamical properties of a coupled oscillator model for bidirectional associative memory. For the stationary state, we apply the replica method to obtain self-consistent order parameter equations. The theoretical results for the storage capacity and overlap agree well with the numerical simulation. For the retrieval process, we apply statistical neurodynamics to include temporal noise correlations. For the successful retrieval process, the theoretical result obtained with the fourth-order approximation qualitatively agrees with the numerical simulation. However, for the unsuccessful retrieval process, higher-order noise correlations suppress severely; therefore, the maximum value of the overlap and the relaxation time are smaller than those of the numerical simulation. The reasons for the discrepancies between the theoretical result and numerical simulation, and the validity of our analysis are discussed.

  2. Coarse grained modeling of transport properties in monoclonal antibody solution

    NASA Astrophysics Data System (ADS)

    Swan, James; Wang, Gang

    Monoclonal antibodies and their derivatives represent the fastest growing segment of the bio pharmaceutical industry. For many applications such as novel cancer therapies, high concentration, sub-cutaneous injections of these protein solutions are desired. However, depending on the peptide sequence within the antibody, such high concentration formulations can be too viscous to inject via human derived force alone. Understanding how heterogenous charge distribution and hydrophobicity within the antibodies leads to high viscosities is crucial to their future application. In this talk, we explore a coarse grained computational model of therapeutically relevant monoclonal antibodies that accounts for electrostatic, dispersion and hydrodynamic interactions between suspended antibodies to predict assembly and transport properties in concentrated antibody solutions. We explain the high viscosities observed in many experimental studies of the same biologics.

  3. Solar Corona Simulation Model With Positivity-preserving Property

    NASA Astrophysics Data System (ADS)

    Feng, X. S.

    2015-12-01

    Positivity-preserving is one of crucial problems in solar corona simulation. In such numerical simulation of low plasma β region, keeping density and pressure is a first of all matter to obtain physical sound solution. In the present paper, we utilize the maximum-principle-preserving flux limiting technique to develop a class of second order positivity-preserving Godunov finite volume HLL methods for the solar wind plasma MHD equations. Based on the underlying first order building block of positivity preserving Lax-Friedrichs, our schemes, under the constrained transport (CT) and generalized Lagrange multiplier (GLM) framework, can achieve high order accuracy, a discrete divergence-free condition and positivity of the numerical solution simultaneously without extra CFL constraints. Numerical results in four Carrington rotation during the declining, rising, minimum and maximum solar activity phases are provided to demonstrate the performance of modeling small plasma beta with positivity-preserving property of the proposed method.

  4. Elastic properties of compressed cryocrystals in a deformed atom model

    NASA Astrophysics Data System (ADS)

    Gorbenko, Ie. Ie.; Zhikharev, I. V.; Troitskaya, E. P.; Chabanenko, Val. V.; Pilipenko, E. A.

    2013-06-01

    A model with deformed atom shells was built to investigate the elastic properties of rare-gas Ne and Kr crystals under high pressure. It is shown that the observed deviation from the Cauchy relation δ cannot be adequately reproduced when taking into account only the many-body interaction. The individual pressure dependence of δ is the result of competition of the many-body interaction and the quadrupole interaction associated with the quadrupole-type deformation of electron shells of the atoms during the displacement of the nuclei. Each kind of interaction makes a strongly pressure dependent contribution to δ. In the case of Ne and Kr, contributions of these interactions are compensated to a good precision, providing δ being almost constant against pressure.

  5. New method to perform dosimetric quality control of treatment planning system using PENELOPE Monte Carlo and anatomical digital test objects

    NASA Astrophysics Data System (ADS)

    Benhdech, Yassine; Beaumont, Stéphane; Guédon, Jean-Pierre; Torfeh, Tarraf

    2010-04-01

    In this paper, we deepen the R&D program named DTO-DC (Digital Object Test and Dosimetric Console), which goal is to develop an efficient, accurate and full method to achieve dosimetric quality control (QC) of radiotherapy treatment planning system (TPS). This method is mainly based on Digital Test Objects (DTOs) and on Monte Carlo (MC) simulation using the PENELOPE code [1]. These benchmark simulations can advantageously replace experimental measures typically used as reference for comparison with TPS calculated dose. Indeed, the MC simulations rather than dosimetric measurements allow contemplating QC without tying treatment devices and offer in many situations (i.p. heterogeneous medium, lack of scattering volume...) better accuracy compared to dose measurements with classical dosimetry equipment of a radiation therapy department. Furthermore using MC simulations and DTOs, i.e. a totally numerical QC tools, will also simplify QC implementation, and enable process automation; this allows radiotherapy centers to have a more complete and thorough QC. The program DTO-DC was established primarily on ELEKTA accelerator (photons mode) using non-anatomical DTOs [2]. Today our aim is to complete and apply this program on VARIAN accelerator (photons and electrons mode) using anatomical DTOs. First, we developed, modeled and created three anatomical DTOs in DICOM format: 'Head and Neck', Thorax and Pelvis. We parallelized the PENELOPE code using MPI libraries to accelerate their calculation, we have modeled in PENELOPE geometry Clinac head of Varian Clinac 2100CD (photons mode). Then, to implement this method, we calculated the dose distributions in Pelvis DTO using PENELOPE and ECLIPSE TPS. Finally we compared simulated and calculated dose distributions employing the relative difference proposed by Venselaar [3]. The results of this work demonstrate the feasibility of this method that provides a more accurate and easily achievable QC. Nonetheless, this method, implemented

  6. Modeling the interaction of electric current and tissue: importance of accounting for time varying electric properties.

    PubMed

    Evans, Daniel J; Manwaring, Mark L

    2007-01-01

    Time varying computer models of the interaction of electric current and tissue are very valuable in helping to understand the complexity of the human body and biological tissue. The electrical properties of tissue, permittivity and conductivity, are vital to accurately modeling the interaction of the human tissue with electric current. Past models have represented the electric properties of the tissue as constant or temperature dependent. This paper presents time dependent electric properties that change as a result of tissue damage, temperature, blood flow, blood vessels, and tissue property. Six models are compared to emphasize the importance of accounting for these different tissue properties in the computer model. In particular, incorporating the time varying nature of the electric properties of human tissue into the model leads to a significant increase in tissue damage. An important feature of the model is the feedback loop created between the electric properties, tissue damage, and temperature.

  7. Modeling the thermal properties and processing of composite materials

    SciTech Connect

    Pitchumani, R.

    1992-01-01

    The manufacture of partially cured, thermoset matrix composite systems is modeled. A generalized analysis, applicable to almost all the fiber-resin systems encountered in practice, is carried out in terms of four key dimensionless groups formed of the process and the product parameters - (1) the Damkohler number (K(sub o)) which is a relative measure of the conduction and the reaction time scales, (2) the dimensionless activation energy (E(sub o)), (3) the adiabatic reaction temperature (B(sub o)) which represents the temperature rise potential in the composite due to the heat of the cure reaction, and (4) the Biot number (B(sub i)) which characterizes the post-cure convective cooling of the composite product. Optimal cure cycles which yield a homogeneous cure in the composite, are obtained as a function of the dimensionless parameters. Design plots for the optimal cure temperature and duration are presented. Their use in practical situations is illustrated in the context of a commercially available graphite-epoxy prepreg from Hercules, which is widely used in the aerospace industry. The thermal properties of the composite namely, the transient thermal diffusivity and the steady state thermal conductivity, are essential parameters in the process modeling studies, as well for the design of composite materials for several high temperature applications. Transient heat conduction in fibrous composites is investigated with the aim of devising a criterion for the validity of the analysis of composite materials as homogeneous media having the effective thermal properties. A homogeneity criterion based on the composite thickness is derived in terms of the fiber volume fraction and the fiber diameter. The criterion, which is the first of its kind for fibrous composites, is valid in the practical range of composite parameters. An analytical means for evaluating the effective thermal diffusivity is also presented.

  8. Electrophysiological properties of inferior olive neurons: A compartmental model.

    PubMed

    Schweighofer, N; Doya, K; Kawato, M

    1999-08-01

    As a step in exploring the functions of the inferior olive, we constructed a biophysical model of the olivary neurons to examine their unique electrophysiological properties. The model consists of two compartments to represent the known distribution of ionic currents across the cell membrane, as well as the dendritic location of the gap junctions and synaptic inputs. The somatic compartment includes a low-threshold calcium current (I(Ca_l)), an anomalous inward rectifier current (I(h)), a sodium current (I(Na)), and a delayed rectifier potassium current (I(K_dr)). The dendritic compartment contains a high-threshold calcium current (I(Ca_h)), a calcium-dependent potassium current (I(K_Ca)), and a current flowing into other cells through electrical coupling (I(c)). First, kinetic parameters for these currents were set according to previously reported experimental data. Next, the remaining free parameters were determined to account for both static and spiking properties of single olivary neurons in vitro. We then performed a series of simulated pharmacological experiments using bifurcation analysis and extensive two-parameter searches. Consistent with previous studies, we quantitatively demonstrated the major role of I(Ca_l) in spiking excitability. In addition, I(h) had an important modulatory role in the spike generation and period of oscillations, as previously suggested by Bal and McCormick. Finally, we investigated the role of electrical coupling in two coupled spiking cells. Depending on the coupling strength, the hyperpolarization level, and the I(Ca_l) and I(h) modulation, the coupled cells had four different synchronization modes: the cells could be in-phase, phase-shifted, or anti-phase or could exhibit a complex desynchronized spiking mode. Hence these simulation results support the counterintuitive hypothesis that electrical coupling can desynchronize coupled inferior olive cells.

  9. Design and dosimetric analysis of a 385 MHz TETRA head exposure system for use in human provocation studies.

    PubMed

    Schmid, Gernot; Bolz, Thomas; Uberbacher, Richard; Escorihuela-Navarro, Ana; Bahr, Achim; Dorn, Hans; Sauter, Cornelia; Eggert, Torsten; Danker-Hopfe, Heidi

    2012-10-01

    A new head exposure system for double-blind provocation studies investigating possible effects of terrestrial trunked radio (TETRA)-like exposure (385 MHz) on central nervous processes was developed and dosimetrically analyzed. The exposure system allows localized exposure in the temporal brain, similar to the case of operating a TETRA handset at the ear. The system and antenna concept enables exposure during wake and sleep states while an electroencephalogram (EEG) is recorded. The dosimetric assessment and uncertainty analysis yield high efficiency of 14 W/kg per Watt of accepted antenna input power due to an optimized antenna directly worn on the subject's head. Beside sham exposure, high and low exposure at 6 and 1.5 W/kg (in terms of maxSAR10g in the head) were implemented. Double-blind control and monitoring of exposure is enabled by easy-to-use control software. Exposure uncertainty was rigorously evaluated using finite-difference time-domain (FDTD)-based computations, taking into account anatomical differences of the head, the physiological range of the dielectric tissue properties including effects of sweating on the antenna, possible influences of the EEG electrodes and cables, variations in antenna input reflection coefficients, and effects on the specific absorption rate (SAR) distribution due to unavoidable small variations in the antenna position. This analysis yielded a reasonable uncertainty of <±45% (max to min ratio of 4.2 dB) in terms of maxSAR10g in the head and a variability of <±60% (max to min ratio of 6 dB) in terms of mass-averaged SAR in different brain regions, as demonstrated by a brain region-specific absorption analysis.

  10. Dosimetric impact assessment using a general algorithm in geant4 simulations for a complex-shaped multileaf collimator.

    PubMed

    Perales, Á; Cortés-Giraldo, M A; Miras, H; Arráns, R; Gallardo, M I

    2017-09-01

    We have developed an inhouse algorithm for the multileaf collimator (MLC) geometry model construction with an appropriate accuracy for dosimetric tests. Our purpose is to build a complex type of MLC and analyze the influence of the modeling parameters on the dose calculation. Using radiochromic films as detector the following tests were done: (I) Density test field: to compare measured and calculated dose distributions in order to determine the tungsten alloy physical density value. (II) Leaf ends test field: to verify the penumbra shape sensitivity against the discretization level set to simulate the curved leaf ends. (III) MLC-closed field: to obtain the value of the air gap between opposite leaves for a closed configuration which completes the modeling of the MLC leakage radiation. (IV) Picket-fence field: to fit the leaf tilt angle with respect of the divergent ray emerging from the source. For a 18.5g/cm(3) density value we have obtained a maximum, minimum and mean leakage values of 0.43%, 0.36% and 0.38%, similar to the experimental ones. The best discretization level in the leaf ends field shows a 5.51mm FWHM, very close to the measured value (5.49mm). An air gap of 370μm has been used in the simulation for the separation between opposite leaves. Using a 0.44° tilt angle, we found the same pattern as the experimental values. Our code can reproduce complex MLC designs with a submilimetric dosimetric accuracy which implies the necessary background for dose calculation of high clinical interest small fields. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

  11. Chemically Aware Model Builder (camb): an R package for property and bioactivity modelling of small molecules.

    PubMed

    Murrell, Daniel S; Cortes-Ciriano, Isidro; van Westen, Gerard J P; Stott, Ian P; Bender, Andreas; Malliavin, Thérèse E; Glen, Robert C

    2015-01-01

    In silico predictive models have proved to be valuable for the optimisation of compound potency, selectivity and safety profiles in the drug discovery process. camb is an R package that provides an environment for the rapid generation of quantitative Structure-Property and Structure-Activity models for small molecules (including QSAR, QSPR, QSAM, PCM) and is aimed at both advanced and beginner R users. camb's capabilities include the standardisation of chemical structure representation, computation of 905 one-dimensional and 14 fingerprint type descriptors for small molecules, 8 types of amino acid descriptors, 13 whole protein sequence descriptors, filtering methods for feature selection, generation of predictive models (using an interface to the R package caret), as well as techniques to create model ensembles using techniques from the R package caretEnsemble). Results can be visualised through high-quality, customisable plots (R package ggplot2). Overall, camb constitutes an open-source framework to perform the following steps: (1) compound standardisation, (2) molecular and protein descriptor calculation, (3) descriptor pre-processing and model training, visualisation and validation, and (4) bioactivity/property prediction for new molecules. camb aims to speed model generation, in order to provide reproducibility and tests of robustness. QSPR and proteochemometric case studies are included which demonstrate camb's application.Graphical abstractFrom compounds and data to models: a complete model building workflow in one package.

  12. A linear programming model for optimizing HDR brachytherapy dose distributions with respect to mean dose in the DVH-tail

    SciTech Connect

    Holm, Åsa; Larsson, Torbjörn; Tedgren, Åsa Carlsson

    2013-08-15

    Purpose: Recent research has shown that the optimization model hitherto used in high-dose-rate (HDR) brachytherapy corresponds weakly to the dosimetric indices used to evaluate the quality of a dose distribution. Although alternative models that explicitly include such dosimetric indices have been presented, the inclusion of the dosimetric indices explicitly yields intractable models. The purpose of this paper is to develop a model for optimizing dosimetric indices that is easier to solve than those proposed earlier.Methods: In this paper, the authors present an alternative approach for optimizing dose distributions for HDR brachytherapy where dosimetric indices are taken into account through surrogates based on the conditional value-at-risk concept. This yields a linear optimization model that is easy to solve, and has the advantage that the constraints are easy to interpret and modify to obtain satisfactory dose distributions.Results: The authors show by experimental comparisons, carried out retrospectively for a set of prostate cancer patients, that their proposed model corresponds well with constraining dosimetric indices. All modifications of the parameters in the authors' model yield the expected result. The dose distributions generated are also comparable to those generated by the standard model with respect to the dosimetric indices that are used for evaluating quality.Conclusions: The authors' new model is a viable surrogate to optimizing dosimetric indices and quickly and easily yields high quality dose distributions.

  13. A linear programming model for optimizing HDR brachytherapy dose distributions with respect to mean dose in the DVH-tail.

    PubMed

    Holm, Åsa; Larsson, Torbjörn; Tedgren, Åsa Carlsson

    2013-08-01

    Recent research has shown that the optimization model hitherto used in high-dose-rate (HDR) brachytherapy corresponds weakly to the dosimetric indices used to evaluate the quality of a dose distribution. Although alternative models that explicitly include such dosimetric indices have been presented, the inclusion of the dosimetric indices explicitly yields intractable models. The purpose of this paper is to develop a model for optimizing dosimetric indices that is easier to solve than those proposed earlier. In this paper, the authors present an alternative approach for optimizing dose distributions for HDR brachytherapy where dosimetric indices are taken into account through surrogates based on the conditional value-at-risk concept. This yields a linear optimization model that is easy to solve, and has the advantage that the constraints are easy to interpret and modify to obtain satisfactory dose distributions. The authors show by experimental comparisons, carried out retrospectively for a set of prostate cancer patients, that their proposed model corresponds well with constraining dosimetric indices. All modifications of the parameters in the authors' model yield the expected result. The dose distributions generated are also comparable to those generated by the standard model with respect to the dosimetric indices that are used for evaluating quality. The authors' new model is a viable surrogate to optimizing dosimetric indices and quickly and easily yields high quality dose distributions.

  14. Impacts of gantry angle dependent scanning beam properties on proton PBS treatment.

    PubMed

    Lin, Yuting; Clasie, Benjamin; Lu, Hsiao-Ming; Flanz, Jacob; Shen, Tim; Jee, Kyung-Wook

    2017-01-21

    While proton beam models in treatment planning systems are generally assumed invariant with respect to the beam deliveries at different gantry angles. Physical properties of scanning pencil beams can change. The gantry angle dependent properties include the delivered charge to the monitor unit chamber, the spot position and the spot shape. The aim of this study is to investigate the extent of the changes and their dosimetric impacts using historical pencil beam scanning (PBS) treatment data. Online beam delivery records at the time of the patient-specific qualify assurance were retrospectively collected for a total of 34 PBS fields from 28 patients treated at our institution. For each field, proton beam properties at two different gantry angles (the planned and zero gantry angles) were extracted by a newly-developed machine log analysis method and used to reconstruct the delivered dose distributions in the cubic water phantom geometry. The reconstructed doses at the two different angles and a planar dose measurement by a 2D ion-chamber array were compared and the dosimetric impacts of the gantry angle dependency were accessed by a 3D γ-index analysis. In addition, the pencil beam spot size was independently characterized as a function of the gantry angle and the beam energy. The dosimetric effects of the perturbed beam shape were also investigated. Comparisons of spot-by-spot beam positions between both gantry angles show a mean deviation of 0.4 and 0.7 mm and a standard deviation of 0.3 and 0.6 mm for x and y directions, respectively. The delivered giga-protons per spot show a percent mean difference and a standard deviation of 0.01% and 0.3%, respectively, from each planned spot weight. These small deviations lead to an excellent agreement in dose comparisons with an average γ passing rate of 99.1%. When each calculation for both planned and zero gantry angles was compared to the measurement, a high correlation in γ values was also observed, also

  15. Impacts of gantry angle dependent scanning beam properties on proton PBS treatment

    NASA Astrophysics Data System (ADS)

    Lin, Yuting; Clasie, Benjamin; Lu, Hsiao-Ming; Flanz, Jacob; Shen, Tim; Jee, Kyung-Wook

    2017-01-01

    While proton beam models in treatment planning systems are generally assumed invariant with respect to the beam deliveries at different gantry angles. Physical properties of scanning pencil beams can change. The gantry angle dependent properties include the delivered charge to the monitor unit chamber, the spot position and the spot shape. The aim of this study is to investigate the extent of the changes and their dosimetric impacts using historical pencil beam scanning (PBS) treatment data. Online beam delivery records at the time of the patient-specific qualify assurance were retrospectively collected for a total of 34 PBS fields from 28 patients treated at our institution. For each field, proton beam properties at two different gantry angles (the planned and zero gantry angles) were extracted by a newly-developed machine log analysis method and used to reconstruct the delivered dose distributions in the cubic water phantom geometry. The reconstructed doses at the two different angles and a planar dose measurement by a 2D ion-chamber array were compared and the dosimetric impacts of the gantry angle dependency were accessed by a 3D γ-index analysis. In addition, the pencil beam spot size was independently characterized as a function of the gantry angle and the beam energy. The dosimetric effects of the perturbed beam shape were also investigated. Comparisons of spot-by-spot beam positions between both gantry angles show a mean deviation of 0.4 and 0.7 mm and a standard deviation of 0.3 and 0.6 mm for x and y directions, respectively. The delivered giga-protons per spot show a percent mean difference and a standard deviation of 0.01% and 0.3%, respectively, from each planned spot weight. These small deviations lead to an excellent agreement in dose comparisons with an average γ passing rate of 99.1%. When each calculation for both planned and zero gantry angles was compared to the measurement, a high correlation in γ values was also observed, also

  16. NOTE: Monte Carlo dosimetric study of the BEBIG Co-60 HDR source

    NASA Astrophysics Data System (ADS)

    Ballester, F.; Granero, D.; Pérez-Calatayud, J.; Casal, E.; Agramunt, S.; Cases, R.

    2005-11-01

    Although not as widespread as Ir-192, Co-60 is also available on afterloading equipment devoted to high dose rate brachytherapy, mainly addressed to the treatment of gynaecological lesions. The purpose of this study is to obtain the dosimetric parameters of the Co-60 source used by the BEBIG MultiSource remote afterloader (BEBIG GmbH, Germany) for which there are no dosimetric data available in the literature. The Monte Carlo code GEANT4 has been used to obtain the TG43 parameters and the 2D dose rate table in Cartesian coordinates of the BEBIG Co-60 HDR source. The dose rate constant, radial dose function and anisotropy function have been calculated and are presented in a tabular form as well as a detailed 2D dose rate table in Cartesian coordinates. These dosimetric datasets can be used as input data and to validate the treatment planning system calculations.

  17. Transport and dosimetric solutions for the ELIMED laser-driven beam line

    NASA Astrophysics Data System (ADS)

    Cirrone, G. A. P.; Romano, F.; Scuderi, V.; Amato, A.; Candiano, G.; Cuttone, G.; Giove, D.; Korn, G.; Krasa, J.; Leanza, R.; Manna, R.; Maggiore, M.; Marchese, V.; Margarone, D.; Milluzzo, G.; Petringa, G.; Sabini, M. G.; Schillaci, F.; Tramontana, A.; Valastro, L.; Velyhan, A.

    2015-10-01

    Within 2017, the ELIMED (ELI-Beamlines MEDical applications) transport beam-line and dosimetric systems for laser-generated beams will be installed at the ELI-Beamlines facility in Prague (CZ), inside the ELIMAIA (ELI Multidisciplinary Applications of laser-Ion Acceleration) interaction room. The beam-line will be composed of two sections: one in vacuum, devoted to the collecting, focusing and energy selection of the primary beam and the second in air, where the ELIMED beam-line dosimetric devices will be located. This paper briefly describes the transport solutions that will be adopted together with the main dosimetric approaches. In particular, the description of an innovative Faraday Cup detector with its preliminary experimental tests will be reported.

  18. Dosimetric characterization of the (60)Co BEBIG Co0.A86 high dose rate brachytherapy source using PENELOPE.

    PubMed

    Guerrero, Rafael; Almansa, Julio F; Torres, Javier; Lallena, Antonio M

    2014-12-01

    (60)Co sources are being used as an alternative to (192)Ir sources in high dose rate brachytherapy treatments. In a recent document from AAPM and ESTRO, a consensus dataset for the (60)Co BEBIG (model Co0.A86) high dose rate source was prepared by using results taken from different publications due to discrepancies observed among them. The aim of the present work is to provide a new calculation of the dosimetric characteristics of that (60)Co source according to the recommendations of the AAPM and ESTRO report. Radial dose function, anisotropy function, air-kerma strength, dose rate constant and absorbed dose rate in water have been calculated and compared to the results of previous works. Simulations using the two different geometries considered by other authors have been carried out and the effect of the cable density and length has been studied.

  19. Titan’s South Polar cloud optical properties modelization

    NASA Astrophysics Data System (ADS)

    Toledo, Daniel; Rannou, Pascal; West, Robert A.; Lavvas, Panayotis

    2014-11-01

    Cassini/ISS cameras detected, in june 2012, a newly formed large cloud in the south polar region of Titan. Images of this cloud in filters at 889 nm (MT3) and 935 nm (CB3) clearly reveal different important characteristics. The cloud patch is observed beyond the latitude -77 degrees and with values of the SZA higher than 90 degrees. In this work, we analyze the radiance factor I/F in the methane 890-nm (MT3) filter by using radiative transfer simulations in order to retrieve constraints on the cloud properties, as its opacity, the size of the droplets and the refractive index. The cloud simulation requires the use of a three-dimensional Monte-Carlo radiative transfer model in spherical geometry since the plane-parallel approximation breaks down for high solar zenith angle (SZA). To model the outgoing intensity and because the cloud is not spherically symmetric but has a finite size and is located near the pole, we first use the source function computed in the atmosphere including the effect of haze and methane, but without cloud. Then, we add the cloud as a lower boundary condition, with a specific term of scattered intensity. We then re-integrate the radiative transfer equation from the cloud level to the top of the atmosphere to obtain outgoing intensity in the presence of the cloud. Doing that, the cloud is treated as an additive term. The haze optical properties are taken from Tomasko et al. (2008), and the methane absorption is taken from the band model of Karkoschka and Tomasko (2012). The phase Function and single scattering albedo of the cloud are calculated by the Mie theory. The effective size of particles is allowed to vary between 3 µm and 5 µm, whereas the effective variance is fixed at 0.2. We use as optical constants for the cloud particles, the real refractive index of 1.4 , while the imaginary part k, is left as a free parameter between 10-5 and 10-3.We then find, with our analysis, that the optical depth of the cloud can only take values between

  20. Thermophysical properties and modeling of a hydrogenic pellet production system

    NASA Astrophysics Data System (ADS)

    Leachman, Jacob William

    applicable to the Herschel-Bulkley visco-plastic model and correlations are developed based on this observation. Reductions of the shear stress with parameters of the Lennard-Jones 6-12 potential indicate a favorable prediction of tritium properties using the quantum law of corresponding states.

  1. Modelling soil properties in a crop field located in Croatia

    NASA Astrophysics Data System (ADS)

    Bogunovic, Igor; Pereira, Paulo; Millan, Mesic; Percin, Aleksandra; Zgorelec, Zeljka

    2016-04-01

    Development of tillage activities had negative effects on soil quality as destruction of soil horizons, compacting and aggregates destruction, increasing soil erosion and loss of organic matter. For a better management in order to mitigate the effects of intensive soil management in land degradation it is fundamental to map the spatial distribution of soil properties (Brevik et al., 2016). The understanding the distribution of the variables in space is very important for a sustainable management, in order to identify areas that need a potential intervention and decrease the economic losses (Galiati et al., 2016). The objective of this work is study the spatial distribution of some topsoil properties as clay, fine silt, coarse silt, fine sand, coarse sand, penetration resistance, moisture and organic matter in a crop field located in Croatia. A grid with 275x25 (625 m2) was designed and a total of 48 samples were collected. Previous to data modelling, data normality was checked using the Shapiro wilk-test. As in previous cases (Pereira et al., 2015), data did not followed the normal distribution, even after a logarithmic (Log), square-root, and box cox transformation. Thus, for modeling proposes, we used the log transformed data, since was the closest to the normality. In order to identify groups among the variables we applied a principal component analysis (PCA), based on the correlation matrix. On average clay content was 15.47% (±3.23), fine silt 24.24% (±4.08), coarse silt 35.34% (±3.12), fine sand 20.93% (±4.68), coarse sand 4.02% (±1.69), penetration resistance 0.66 MPa (±0.28), organic matter 1.51% (±0.25) and soil moisture 32.04% (±3.27). The results showed that the PCA identified three factors explained at least one of the variables. The first factor had high positive loadings in soil clay, fine silt and organic matter and a high negative loading in fine sand. The second factor had high positive loadings in coarse sand and moisture and a high

  2. Theoretical dosimetric evaluation of carbon and oxygen minibeam radiation therapy.

    PubMed

    González, Wilfredo; Peucelle, Cécile; Prezado, Yolanda

    2017-05-01

    Charged particles have several advantages over x-ray radiations, both in terms of physics and radiobiology. The combination of these advantages with those of minibeam radiation therapy (MBRT) could help enhancing the therapeutic index for some cancers with poor prognosis. Among the different ions explored for therapy, carbon ions are considered to provide the optimum physical and biological characteristics. Oxygen could be advantageous due to a reduced oxygen enhancement ratio along with a still moderate biological entrance dose. The aforementioned reasons justified an in-depth evaluation of the dosimetric features of carbon and oxygen minibeam radiation therapy to establish the interest of further explorations of this avenue. The GATE/Geant4 6.2 Monte Carlo simulation platform was employed to simulate arrays of rectangular carbon and oxygen minibeams (600 μm × 2 cm) at a water phantom entrance. Th