基于蒙特卡罗剂量计算模型的Leksell4C伽马刀单源高分辨率高精度剂量学特性

目的 建立蒙特卡罗剂量计算模型,模拟计算Leksell 4C伽马刀单源高分辨率剂量分布。 方法 搭建基于MPI环境的蒙特卡罗程序MCNPX并行计算平台,使用环形探测器和经过事先验证的2种降方差技术(源出射方向偏倚采样和部分结构内终止电子跟踪)模拟计算Leksell 4C伽马刀单源高分辨率高精度剂量场分布数据。比较不同光子和电子截止能量设置对模拟计算结果准确性的影响。 结果 模拟计算得到的Leksell 4C伽马刀单源剂量场分布数据空间分辨率更高,径向分辨率为0.1 mm,统计误差<1%,模拟计算用时约24 h。对于直径为4、8、14、18 mm的准直器,其焦平面Profile半影宽度和单侧半高宽分别为1.0、1.1、1.2、1.3 mm和2.2、4.3、7.3、9.3 mm。光子的截止能量分别为1 keV和10 keV时模拟计算结果与既往研究符合的较好,但电子的截止能量分别为1 keV和521 keV时模拟计算结果与既往研究符合的较差。 结论 基于MPI环境的蒙特卡罗程序MCNPX并行计算平台能在可接受的计算时间内获得高分辨率高精度的剂量场分布数据。在模拟时需谨慎设定光子和电子的截止能量。

Monte Carlo simulation of accurate dose distribution with high resolution for the single source channel of Leksell 4C gamma knife

Objective To obtain the high-resolution dose distribution for the single source channel of Leksell 4C gamma knife. Methods A parallel computing platform based on the Message Passing Interface (MPI) and Monte Carlo Code MCNPX was established. The ring-shaped detector and two pre-validated variance reduction techniques (emission direction-biased sampling of source and termination of electron tracking in partial structures) were adopted to derive the high-resolution dose distribution for the single source channel of Leksell 4C gamma knife. The effect of cut-off energy for both photon and electron on the accuracy of simulation outcomes was evaluated and statistically compared. Results Compared with previous findings,the spatial resolution of the dose distribution for the single source channel obtained in this study was higher (radial resolution=0.1 mm) with less statistical error (<1%).The calculation time was acceptable (approximately 24 h).For the 4-,8-,14-and 18-mm variable collimators,the penumbra and full width at the half maximum (FWHM) for single side were 1.0,1.1,1.2,1.3 mm and 2.2,4.3,7.3,9.3 mm,respectively,which were consistent with previous studies. The difference of the simulation results was extremely small between different cut-off energy for photon (1 keV vs.10 keV).However,the simulation results significantly differ between 1 and 521 keV electronic cut-off energy. Conclusions The MCNPX parallel computing platform based on the MPI environment can be utilized to derive highly accurate dose distribution with high resolution in acceptable calculation time. The cut-off energy of the photon and electron should be cautiously set up during simulation.