Kawrakow I
National Research Council, Ottawa, ON, Canada.
Med Phys. 2000 Mar;27(3):499-513. doi: 10.1118/1.598918.
In this report the condensed history Monte Carlo simulation of electron transport and its application to the calculation of ion chamber response is discussed. It is shown that the strong step-size dependencies and lack of convergence to the correct answer previously observed are the combined effect of the following artifacts caused by the EGS4/PRESTA implementation of the condensed history technique: dose underprediction due to PRESTA'S pathlength correction and lateral correlation algorithm; dose overprediction due to the boundary crossing algorithm; dose overprediction due to the breakdown of the fictitious cross section method for sampling distances between discrete interaction and the inaccurate evaluation of energy-dependent quantities. These artifacts are now understood quantitatively and analytical expressions for their effect are given.
本报告讨论了电子输运的凝聚历史蒙特卡罗模拟及其在电离室响应计算中的应用。结果表明，先前观察到的对步长的强烈依赖性以及缺乏收敛到正确答案的情况，是由凝聚历史技术的EGS4/PRESTA实现所引起的以下假象的综合效应：由于PRESTA的路径长度校正和横向关联算法导致剂量预测不足；由于边界穿越算法导致剂量预测过高；由于离散相互作用之间采样距离的虚拟截面方法失效以及能量相关量的评估不准确导致剂量预测过高。现在已经对这些假象进行了定量理解，并给出了其效应的解析表达式。
