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Optimization of deterministic transport parameters for the calculation of the dose distribution around a high dose‐rate I 192 r brachytherapy source
Author(s) -
Gifford Kent A.,
Price Michael J.,
Horton John L.,
Wareing Todd A.,
Mourtada Firas
Publication year - 2008
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2919074
Subject(s) - kerma , monte carlo method , brachytherapy , imaging phantom , computational physics , photon , ray tracing (physics) , dosimetry , physics , percentage depth dose curve , mathematics , nuclear medicine , optics , statistics , ionization chamber , ionization , medicine , ion , quantum mechanics , radiation therapy
The goal of this work was to calculate the dose distribution around a high dose‐rateI192 r 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.S 12was sufficient to resolve the solution in angle.P 2expansion 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.