R. E. P. Taylor

Benchmarking brachydose : Voxel based egsnrc monte carlo calculations of TG-43 dosimetry parameters

In this study, BrachyDose, a recently developed EGSnrc Monte Carlo code for rapid brachytherapy dose calculations, has been benchmarked by reproducing previously published dosimetry parameters for three brachytherapy seeds with varied internal structure and encapsulation. Calculations are performed for two 125I seeds (Source Tech Medical Model STM1251 and Imagyn isoSTAR model 12501) and one l03Pd source (Theragenics Model 200). Voxel size effects were investigated with dose distribution calculations for three voxel sizes: 0.1 x 0.1 x 0.1 mm(3), 0.5 x 0.5 x 0.5 mm(3), and 1 X 1 X 1 mm(3). In order to minimize the impact of voxel size effects, tabulated dosimetry data for this study consist of a combination of the three calculations: 0.1 X 0.1 x 0.1 mm(3) voxels for distances in the range of 0<r< or = l cm, 0.5 x0.5 0.5 mm(3) voxels for 1 <r< or =5 cm and 1 x 1 X 1 mm(3) voxels for 5<r< or = 10 cm. Dosimetry parameters from this study are compared with values calculated by other authors using Williamsons PTRAN code and to measured values. Overall, calculations made with Brachydose show good agreement with calculations made with PTRAN although there are some exceptions.

An EGSnrc Monte Carlo-calculated database of TG-43 parameters

Monte Carlo methods are used to calculate a complete TG-43 dosimetry parameter data set for 27 low-energy photon emitting brachytherapy sources (18 I125 and 9 Pd103). All Monte Carlo calculations are performed using the EGSnrc user-code BrachyDose. TG-43 dosimetry parameters, including dose rate constants, radial dose functions (with functional fitting parameters), and anisotropy data, are calculated with finer spatial resolution, greater range of distances, and smaller uncertainties than data currently available in the literature for many of these sources. In particular, for most of the seeds, this is the first time that anisotropy data have been tabulated at distances less than 0.5cm from the source. These calculations employ the state-of-the-art XCOM photon cross sections, and detailed source geometries are modeled using Yegins multigeometry package. This data set serves as a completely independent verification of the currently available dosimetry parameters calculated using other Monte Carlo codes, including MCNP and PTRAN. This report also describes the Carleton Laboratory for Radiotherapy Physics TG-43 Parameter Database, a publicly accessible web site (at http://www.physics.carleton.ca/clrp/seed_database/) through which all of the data calculated for this study can be accessed. Also available on the web site are descriptions of the methods and Monte Carlo models used in this study and comparisons of data calculated in this study with data calculated by other authors.

EGSnrc Monte Carlo calculated dosimetry parameters for 192Ir and 169Yb brachytherapy sources

This study presents the results of EGSnrc Monte Carlo calculations of the dose distribution surrounding a high dose rate Yb169 brachytherapy source and 14 high dose rate and pulsed dose rate Ir192 brachytherapy sources. Energy-weighted spectra of emitted photons, a full set of TG-43 dosimetry parameters, along-away dose tables, and a description of the materials and geometry used for each source are provided. In addition to this, separate tallies are made of the dose contributed from primary, single-scattered, and multiply-scattered photons. Separation of dose in this manner allows one to use convolution/superposition methods to calculate the dose surrounding a brachytherapy source accounting for a non-homogeneous medium. The effect of phantom size on TG-43 dosimetry parameters and scattered dose is also investigated for the Ir192 microSelectron v2 HDR source. This paper describes the calculation methods and presents the dose rate constants calculated for each source with the full set of dosimetry data being available online at the Carleton Laboratory for Radiotherapy Physics brachytherapy database (http://www.physics.carleton.ca/clrp/seeḏdatabase/).

Monte Carlo dosimetry for and eye plaque brachytherapy

A Monte Carlo study of dosimetry for eye plaque brachytherapy is performed. BrachyDose, an EGSnrc user code which makes use of Yegins multi-geometry package, is used to fully model I125 (model 6711) and Pd103 (model 200) brachytherapy seeds and the standardized plaques of the Collaborative Ocular Melanoma Study (COMS). Three-dimensional dose distributions in the eye region are obtained. In general, dose to water is scored; however, the implications of replacing water with eye tissues are explored. The effect of the gold alloy (Modulay) backing is investigated and the dose is found to be sensitive to the elemental composition of the backing. The presence of the silicone polymer (Silastic) seed carrier results in substantial dose decreases relative to water, particularly for Pd103. For a 20mm plaque with a Modulay backing and Silastic insert, fully loaded with 24 seeds, the dose decrease relative to water is of the order of 14% for I125 and 20% for Pd103 at a distance of 1cm from the inner sclera along the plaques central axis. For the configurations of seeds used in COMS plaques, interseed attenuation is a small effect within the eye region. The introduction of an air interface results in a dose reduction in its vicinity which depends on the plaques position within the eye and the radionuclide. Introducing bone in the eyes vicinity also causes dose reductions. The dose distributions in the eye for the two different radionuclides are compared and, for the same prescription dose, Pd103 generally offers a lower dose to critical normal structures. BrachyDose is sufficiently fast to allow full Monte Carlo dose calculations for routine clinical treatment planning.

Monte Carlo dosimetry for 125I and 103Pd eye plaque brachytherapy.

A Monte Carlo study of dosimetry for eye plaque brachytherapy is performed. BrachyDose, an EGSnrc user code which makes use of Yegins multi-geometry package, is used to fully model I125 (model 6711) and Pd103 (model 200) brachytherapy seeds and the standardized plaques of the Collaborative Ocular Melanoma Study (COMS). Three-dimensional dose distributions in the eye region are obtained. In general, dose to water is scored; however, the implications of replacing water with eye tissues are explored. The effect of the gold alloy (Modulay) backing is investigated and the dose is found to be sensitive to the elemental composition of the backing. The presence of the silicone polymer (Silastic) seed carrier results in substantial dose decreases relative to water, particularly for Pd103. For a 20mm plaque with a Modulay backing and Silastic insert, fully loaded with 24 seeds, the dose decrease relative to water is of the order of 14% for I125 and 20% for Pd103 at a distance of 1cm from the inner sclera along the plaques central axis. For the configurations of seeds used in COMS plaques, interseed attenuation is a small effect within the eye region. The introduction of an air interface results in a dose reduction in its vicinity which depends on the plaques position within the eye and the radionuclide. Introducing bone in the eyes vicinity also causes dose reductions. The dose distributions in the eye for the two different radionuclides are compared and, for the same prescription dose, Pd103 generally offers a lower dose to critical normal structures. BrachyDose is sufficiently fast to allow full Monte Carlo dose calculations for routine clinical treatment planning.

Sci—Sat AM(2): Brachy — 05: Fast Monte Carlo Dose Calculations for Brachytherapy with BrachyDose

A fast dose calculation algorithm called BrachyDose has been developed for brachytherapy applications. BrachyDose is based on the EGSnrc code system for simulating radiation transport. Complex geometries are modelled through the superposition of basic geometric entities (spheres, cuboids, cylinders, and cones) using Yegins multi-geometry package; the phantom geometry may be defined using a CT dataset. A database of brachytherapy sources has been developed and benchmarked, as has a database of eye plaque applicators. BrachyDose scores collision kerma, which is equivalent to absorbed dose for most situations of interest, using a tracklength estimator. The phase space of particles emitted from brachytherapy sources may be generated with BrachyDose and used in subsequent simulations to avoid the repeated simulation of particle transport within sources. A particle recycling feature has been implemented for multisource configurations in which the first source acts as a particle generator; particles emitted from this source are reinitiated at each source location. Dose calculations for prostate permanent implants achieving 2% average uncertainty in the prostate region take less than 30 seconds in (2 mm)3 voxels on a single 3.0 GHz Woodcrest core; calculation times for eye plaque therapy are on the order of three minutes in (0.5 mm)3 voxels. These calculation times are sufficiently fast for routine clinical treatment planning. A graphical user interface (GUI) for BrachyDose has been developed. Working towards clinical implementation, efforts are underway to integrate data in the DICOM-RT format with BrachyDose.

SU‐FF‐T‐113: BrachyDose: A New Fast Monte Carlo Code for Brachytherapy Calculations

Purpose: To develop a fast Monte Carlo code based on EGSnrc for accurate dose calculation around brachytherapy sources. Method and Materials: Sources and phantom geometries are modeled by using the Multi‐geometry technique which allows various predefined geometry elements (eg, sources, applicators, catheters) a phantom geometry. Sources such as an HDR Ir‐192 source and LDR I‐125 or Pd‐103 seed sources were modeled. One or more sources from a database can be duplicated many times and placed in arbitrary locations. Besides the above sources, BrachyDose can calculate dose around a miniature x‐ray‐tube source since it is based on EGSnrc. It also can use CT data in the phantom geometry. Variance reduction techniques are applied to speed up computation time. Dose is calculated by scoring the collision kerma using a tracklength estimator. There is an option to reuse every photon which escapes from a seed as if it came from every seed in the implant with same direction relative to the seed itself. Results: The speed of the BrachyDose calculation is specified by the time required to attain an average of 2\% statistics in the central region of an implant of 125 seeds spaced at 5 mm separation in a 1000 cm∧3 cubic phantom. The time required scales roughly as the inverse of the volume of the voxels. On an 2.4 MHz CPU, the computation time is 510 s for 1 mm voxels. The DVHs for 1 mm voxels are significantly different from those in 2 mm voxels. Changing phantom material from water to prostate tissue causes the dose to vary by +/−5% vs dose to water, depending on distance from the seeds. Conclusions: The Monte Carlo code developed is fast enough for routine clinical applications. Calculated dose values include inter‐seed effects and other effects from tissue inhomogeneities.

Monte Carlo dosimetry for {sup 125}I and {sup 103}Pd eye plaque brachytherapy

A Monte Carlo study of dosimetry for eye plaque brachytherapy is performed. BrachyDose, an EGSnrc user code which makes use of Yegins multi-geometry package, is used to fully model I125 (model 6711) and Pd103 (model 200) brachytherapy seeds and the standardized plaques of the Collaborative Ocular Melanoma Study (COMS). Three-dimensional dose distributions in the eye region are obtained. In general, dose to water is scored; however, the implications of replacing water with eye tissues are explored. The effect of the gold alloy (Modulay) backing is investigated and the dose is found to be sensitive to the elemental composition of the backing. The presence of the silicone polymer (Silastic) seed carrier results in substantial dose decreases relative to water, particularly for Pd103. For a 20mm plaque with a Modulay backing and Silastic insert, fully loaded with 24 seeds, the dose decrease relative to water is of the order of 14% for I125 and 20% for Pd103 at a distance of 1cm from the inner sclera along the plaques central axis. For the configurations of seeds used in COMS plaques, interseed attenuation is a small effect within the eye region. The introduction of an air interface results in a dose reduction in its vicinity which depends on the plaques position within the eye and the radionuclide. Introducing bone in the eyes vicinity also causes dose reductions. The dose distributions in the eye for the two different radionuclides are compared and, for the same prescription dose, Pd103 generally offers a lower dose to critical normal structures. BrachyDose is sufficiently fast to allow full Monte Carlo dose calculations for routine clinical treatment planning.

Monte Carlo dosimetry for I125 and Pd103 eye plaque brachytherapy

A Monte Carlo study of dosimetry for eye plaque brachytherapy is performed. BrachyDose, an EGSnrc user code which makes use of Yegins multi-geometry package, is used to fully model I125 (model 6711) and Pd103 (model 200) brachytherapy seeds and the standardized plaques of the Collaborative Ocular Melanoma Study (COMS). Three-dimensional dose distributions in the eye region are obtained. In general, dose to water is scored; however, the implications of replacing water with eye tissues are explored. The effect of the gold alloy (Modulay) backing is investigated and the dose is found to be sensitive to the elemental composition of the backing. The presence of the silicone polymer (Silastic) seed carrier results in substantial dose decreases relative to water, particularly for Pd103. For a 20mm plaque with a Modulay backing and Silastic insert, fully loaded with 24 seeds, the dose decrease relative to water is of the order of 14% for I125 and 20% for Pd103 at a distance of 1cm from the inner sclera along the plaques central axis. For the configurations of seeds used in COMS plaques, interseed attenuation is a small effect within the eye region. The introduction of an air interface results in a dose reduction in its vicinity which depends on the plaques position within the eye and the radionuclide. Introducing bone in the eyes vicinity also causes dose reductions. The dose distributions in the eye for the two different radionuclides are compared and, for the same prescription dose, Pd103 generally offers a lower dose to critical normal structures. BrachyDose is sufficiently fast to allow full Monte Carlo dose calculations for routine clinical treatment planning.

TU-AB-BRC-08: Egs_brachy, a Fast and Versatile Monte Carlo Code for Brachytherapy Applications

PURPOSE To introduce egs_brachy, a new, fast, and versatile Monte Carlo code for brachytherapy applications. METHODS egs_brachy is an EGSnrc user-code based on the EGSnrc C++ class library (egs++). Complex phantom, applicator, and source model geometries are built using the egs++ geometry module. egs_brachy uses a tracklength estimator to score collision kerma in voxels. Interaction, spectrum, energy fluence, and phase space scoring are also implemented. Phase space sources and particle recycling may be used to improve simulation efficiency. HDR treatments (e.g. stepping source through dwell positions) can be simulated. Standard brachytherapy seeds, as well as electron and miniature x-ray tube sources are fully modelled. Variance reduction techniques for electron source simulations are implemented (Bremsstrahlung cross section enhancement, uniform Bremsstrahlung splitting, and Russian Roulette). TG-43 parameters of seeds are computed and compared to published values. Example simulations of various treatments are carried out on a single 2.5 GHz Intel Xeon E5-2680 v3 processor core. RESULTS TG-43 parameters calculated with egs_brachy show excellent agreement with published values. Using a phase space source, 2% average statistical uncertainty in the PTV ((2mm)3 voxels) can be achieved in 10 s for 100 125 I or 103 Pd seeds in a 36.2 cm3 prostate PTV, 31 s for 64 103 Pd seeds in a 64 cm3 breast PTV, and 56 s for a miniature x-ray tube in a 27 cm3 breast PTV. Comparable uncertainty is reached in 12 s in a (1 mm)3 water voxel 5 mm away from a COMS 16mm eye plaque with 13 103 Pd seeds. CONCLUSION The accuracy of egs_brachy has been demonstrated through benchmarking calculations. Calculation times are sufficiently fast to allow full MC simulations for routine treatment planning for diverse brachytherapy treatments (LDR, HDR, miniature x-ray tube). egs_brachy will be available as free and open-source software to the medical physics research community. This work is partially funded by the Canada Research Chairs program, the Natural Sciences and Engineering Research Council of Canada, and the Ontario Ministry of Research and Innovation (Ontario Early Researcher Award).