title: Optimization of deterministic transport parameters for the calculation of the dose distribution around a high dose-rate 192Ir brachytherapy source.
abstract: 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.
authors.affiliation: Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030 , USA. kagifford@mdanderson.org
authors.forename: Kent A
authors.initials: KA
authors.lastname: Gifford
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Price
authors.forename: John L
authors.initials: JL
authors.lastname: Horton
authors.forename: Todd A
authors.initials: TA
authors.lastname: Wareing
authors.forename: Firas
authors.initials: F
authors.lastname: Mourtada
mesh_terms: D019985:Benchmarking; D001918:Brachytherapy / Q000379:methods*; D003198:Computer Simulation; D007496:Iridium Radioisotopes / Q000627:therapeutic use*; D009010:Monte Carlo Method; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D013997:Time Factors
chemical_list: D007496:Iridium Radioisotopes