Optimization of deterministic transport parameters for the calculation of the dose distribution around a high dose-rate 192Ir brachytherapy source.

The goal of this work was to calculate the dose distribution around a high dose-rate 192Ir brachytherapy source using a multi-group discrete ordinates code and then to compare the results with a Monte Carlo calculated dose distribution. The unstructured tetrahedral mesh discrete ordinates code Attila version 6.1.1 was used to calculate the photon kerma rate distribution in water around the Nucletron microSelectron mHDRv2 source. MCNPX 2.5.c was used to compute the Monte Carlo water photon kerma rate distribution. Two hundred million histories were simulated, resulting in standard errors of the mean of less than 3% overall. The number of energy groups, S(n) (angular order), P(n) (scattering order), and mesh elements were varied in addition to the method of analytic ray tracing to assess their effects on the deterministic solution. Water photon kerma rate matrices were exported from both codes into an in-house data analysis software. This software quantified the percent dose difference distribution, the number of points within +/- 3% and +/- 5%, and the mean percent difference between the two codes. The data demonstrated that a 5 energy-group cross-section set calculated results to within 0.5% of a 15 group cross-section set. S12 was sufficient to resolve the solution in angle. P2 expansion of the scattering cross-section was necessary to compute accurate distributions. A computational mesh with 55 064 tetrahedral elements in a 30 cm diameter phantom resolved the solution spatially. An efficiency factor of 110 with the above parameters was realized in comparison to MC methods. The Attila code provided an accurate and efficient solution of the Boltzmann transport equation for the mHDRv2 source.

[1]  R. Sloboda,et al.  Combined experimental and Monte Carlo verification of brachytherapy plans for vaginal applicators , 1998, Physics in medicine and biology.

[2]  J F Williamson,et al.  Dose calculations about shielded gynecological colpostats. , 1990, International journal of radiation oncology, biology, physics.

[3]  J F Williamson,et al.  Dosimetric modeling of the microselectron high-dose rate 192Ir source by the multigroup discrete ordinates method. , 2000, Medical physics.

[4]  F. Mourtada,et al.  Dosimetric evaluation of the Fletcher–Williamson ovoid for pulsed-dose-rate brachytherapy: a Monte Carlo study , 2005, Physics in medicine and biology.

[5]  Edward W. Larsen,et al.  Fast iterative methods for discrete-ordinates particle transport calculations , 2002 .

[6]  J. Williamson,et al.  Monte Carlo-aided dosimetry of a new high dose-rate brachytherapy source. , 1998, Medical physics.

[7]  George A Sandison,et al.  Reconstruction of electron spectra using singular component decomposition. , 2002, Medical physics.

[8]  G. Glasgow,et al.  Specific gamma-ray constant and exposure rate constant of 192Ir. , 1979, Medical physics.

[9]  Feyzi Inanc,et al.  Integral-transport-based deterministic brachytherapy dose calculations. , 2003, Physics in medicine and biology.

[10]  M. Lindstrom,et al.  The dose distribution surrounding 192Ir and 137Cs seed sources. , 1991, Physics in medicine and biology.

[11]  J F Williamson,et al.  Multigroup discrete ordinates modeling of 125I 6702 seed dose distributions using a broad energy-group cross section representation. , 2002, Medical physics.

[12]  J. Williamson,et al.  Template-guided interstitial implants: Cs-137 reusable sources as a substitute for Ir-192. , 1987, Radiology.

[13]  Firas Mourtada,et al.  Comparison of a finite-element multigroup discrete-ordinates code with Monte Carlo for radiotherapy calculations , 2006, Physics in medicine and biology.

[14]  Feyzi Inanc,et al.  Distortions induced by radioactive seeds into interstitial brachytherapy dose distributions. , 2004, Medical physics.