Neuenschwander H, Mackie T R, Reckwerdt P J
Department of Medical Radiation Physics, University of Berne, Inselspital, Switzerland.
Phys Med Biol. 1995 Apr;40(4):543-74. doi: 10.1088/0031-9155/40/4/005.
The macro Monte Carlo (MMC) method has been developed to improve the speed of traditional Monte Carlo (MC) high-energy electron transport calculations without loss in accuracy. The MMC algorithm uses results derived from conventional MC simulations of electron transport through macroscopic spheres of various radii and consisting of a variety of media. Based on these results, electrons are transported in macroscopic steps through the absorber. The absorber geometry is represented by a three-dimensional (3D) density matrix, typically derived from computer tomographic (CT) data. Energy lost by the electrons along their paths through the absorber is scored in a 3D dose matrix. Transport of secondary electrons and bremsstrahlung photons is taken into account. Major modifications of the original implementation of the MMC algorithm have resulted in an improved version of the code, resolving earlier problems with electron transport across interfaces of different materials, and running at a substantially higher speed. Furthermore, the code has been integrated into a clinical 3D treatment planning system. MMC results are in good agreement with results from conventional MC codes and are obtained with a speed gain of about one order of magnitude for clinically relevant irradiation situations. Calculation times to obtain a relative statistical accuracy of 2% per dose grid voxel for small electron field sizes are short enough to be routinely useful in radiotherapy clinics on present day affordable workstation computers. Considering speed, accuracy and memory requirements, MMC is a promising alternative to currently available electron dose planning algorithms.
宏观蒙特卡罗（MMC）方法已被开发出来，用于提高传统蒙特卡罗（MC）高能电子输运计算的速度，同时不损失精度。MMC算法使用从电子通过各种半径且由多种介质组成的宏观球体的传统MC模拟得出的结果。基于这些结果，电子以宏观步长穿过吸收体。吸收体的几何形状由三维（3D）密度矩阵表示，通常从计算机断层扫描（CT）数据导出。电子在穿过吸收体的路径上损失的能量在3D剂量矩阵中计分。考虑了二次电子和轫致辐射光子的输运。MMC算法原始实现的主要改进产生了一个改进版本的代码，解决了早期电子在不同材料界面处输运的问题，并以显著更高的速度运行。此外，该代码已被集成到临床3D治疗计划系统中。MMC结果与传统MC代码的结果高度一致，并且在临床相关的照射情况下，速度提高了约一个数量级。对于小电子场大小，获得每个剂量网格体素相对统计精度为2%的计算时间足够短，在当今价格合理的工作站计算机上，可在放射治疗临床中常规使用。考虑到速度、精度和内存需求，MMC是当前可用电子剂量规划算法的一个有前途的替代方案。
