基于GAMOS的蒙特卡罗方法模拟放疗电子线照射的剂量学研究

目的:探讨基于GAMOS的蒙特卡罗（MC）方法模拟电子线放疗的剂量精确性。方法:运用GAMOS MC程序，建立Varian Rapidarc加速器3档能量（6、9和12 MeV）及3种限光筒［（6×6）、（10×10）和（15×15） cm2］的束流模型，模拟束流在水模体中的剂量分布，并与测量得到的百分深度剂量和等平面剂量分布比较，评估GAMOS软件模拟电子线照射的精确性和运算效率。结果:模拟的粒子数越多，模拟与测量结果的误差越小；当模拟粒子的数量达到5×108时，各个能量的电子线射程（Rp）和50%剂量深度（R50）的模拟结果与测量结果一致；除建成区外，百分深度剂量模拟和测量的结果误差在2%以内；等平面剂量分布模拟和测量的结果误差也在2%以内，模拟的照射野大小与测量结果一致。运算效率中，能量越大，限光筒尺寸越大，并行同步模拟所用的时间越多，模拟时间的变化越大。结论:基于GAMOS的MC方法可准确地模拟放疗电子线照射剂量的分布，粒子数的增加可提高模拟的精确性，并行同步计算可提高模拟的效率。

GAMOS-based Monte Carlo simulation for dose calculation in electron radiotherapy: a dosimetric analysis

Abstract: Objective To discuss the accuracy of Monte Carlo simulation based on GAMOS for dose calculation in electron radiotherapy. Methods The physical model of electron beams for Varian Rapidarc linear accelerator was constructed by GAMOS-based Monte Carlo simulation. The model consisted of 3 levels of energy (6, 9, 12 MeV) and 3 applicators ［(6×6), (10×10), (15×15) cm2］. The dose distribution of electron beams in water phantom was simulated, and the obtained results were then compared with the measured results of percentage depth dose (PDD) and cross plane beam profile for evaluating the accuracy and efficiency of Monte Carlo simulation based on GAMOS for dose calculation in electron radiotherapy. Results With more simulated particles, the error between the simulation results and measurement results was smaller. When the number of simulated particles reached 5×108, the simulation results of electron beam range (Rp) and depth of 50% maximum dose (R50) were consistent with the measurement results. The error was within 2% between the PDD results of simulation and measurement excluding the building-up range. The error in cross plane beam profile was also within 2% between simulation results and measurement results among all range, and the simulated radiation field size was consistent with the measured results. With higher level of energy, the applicator size was larger, and the time used in parallel and synchronous simulation is longer, and the variation of simulation time was greater. Conclusion Monte Carlo simulation based on GAMOS can accurately simulate the dose distribution in electron radiotherapy. The increase number of particles can improve the accuracy of simulation, and the parallel and synchronous calculation can improve the efficiency of simulation.