基于蒙特卡罗方法的6 MV Truebeam剂量计算

使用蒙特卡罗方法快速准确地模拟6 MV Varian Truebeam医用电子直线加速器射野剂量特性，探究厂家提供相位空间源的可用性及模拟方法的准确性。以Varian公司提供的出束窗口位置处相位空间文件作为Beamnrc/EGSnrc输入源，模拟射野形成结构并计算10 cm10 cm射野下的均匀水体模中的剂量分布，将计算结果与相同条件下的实验测量数据进行比较。同一计算机模拟时，传统完整机头模拟方法需4~5 h，文中所述方法模拟时间可缩减至48 min，剂量计算结果与相同条件下所得实际测量数据可较好地吻合，两者的百分深度剂量差异低于3%，且建成区吻合良好；不同深度处80%等剂量线所包含的射野区域内百分离轴剂量比差异均低于3%，且半影区效果好。使用厂家提供相位空间文件作为EGSnrc入射源，能快速模拟治疗头，得到剂量计算结果与实际测量值的差异满足剂量计算精度要求。

Dose calculation of 6 MV Truebeam using Monte Carlo method

The purpose of this work is to simulate 6 MV Varian Truebeam linac dosimeter characteristics using Monte Carlo method and to investigate the availability of phase space file and the accuracy of the simulation. With the phase space file at linac window supplied by Varian to be a source, the patient-dependent part was simulated. Dose distributions in a water phantom with a 10 cm×10 cm field were calculated and compared with measured data for validation. Evident time reduction was obtained from 4-5 h which a whole simulation cost on the same computer to around 48 minutes. Good agreement between simulations and measurements in water was observed. Dose differences are less than 3% for depth doses in build-up region and also for dose profiles inside the 80% field size, and the effect in penumbra is good. It demonstrate that the simulation using existing phase space file as the EGSnrc source is efficient. Dose differences between calculated data and measured data could meet the requirements for dose calculation.