Gifford Kent A, Price Michael J, Horton John L, Wareing Todd A, Mourtada Firas
Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030 , USA.
Med Phys. 2008 Jun;35(6):2279-85. doi: 10.1118/1.2919074.
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.
这项工作的目标是使用多群离散纵标代码计算高剂量率192Ir近距离治疗源周围的剂量分布，然后将结果与蒙特卡罗计算的剂量分布进行比较。使用非结构化四面体网格离散纵标代码Attila版本6.1.1来计算Nucletron microSelectron mHDRv2源周围水中的光子比释动能率分布。使用MCNPX 2.5.c来计算蒙特卡罗水中光子比释动能率分布。模拟了两亿个历史事件，总体上平均标准误差小于3%。除了解析射线追踪方法外，还改变了能量组数、S(n)（角阶）、P(n)（散射阶）和网格单元，以评估它们对确定性解的影响。将两个代码中的水光子比释动能率矩阵导出到内部数据分析软件中。该软件量化了剂量百分比差异分布、±3%和±5%范围内的点数以及两个代码之间的平均百分比差异。数据表明，5能组截面集的计算结果在15能组截面集的0.5%以内。S12足以在角度上解析解。散射截面的P2展开对于计算准确的分布是必要的。在直径30 cm的模体中，具有55064个四面体单元的计算网格在空间上解析了解。与蒙特卡罗方法相比，在上述参数下实现了110的效率因子。Attila代码为mHDRv2源的玻尔兹曼输运方程提供了准确而高效的解。
