Varian RapidARC直线加速器6 MeV-X线虚拟源模型的建立

Establishment of a virtual source model of Varian Rapid ARC linear accelerator with 6 MeVX-ray

目的:减少直线加速器commission过程的工作量,对加速器出束信息进行建模,使用蒙特卡罗方法进行剂量计算,并验证模型的准确性。方法:将光子束区分为初始光子束和散射光子束,分别用数学公式描述其能量和方向,建立虚拟源模型,使用蒙特卡罗方法计算在水中的剂量分布,与水箱中的测量数据比较。使用源模型计算病例计划,与商用TPS计算结果比较。结果:计算得到的PDD误差基本在1.0%以内,OAR误差在2.0%以内。在1例前列腺病例计划中,本方法计算得到的DVH曲线与不同TPS计算得到的结果基本一致。结论:本虚拟源模型方法可以很好地模拟直线加速器的出束信息,计算单个病例时间在40 s量级,可以实现病人治疗前实时的剂量验证,且有用于直线加速器自动commission过程的潜力。

Objective To model the accelerator beam information for reducing the workload of linear accelerator commissioning process,and to verify the accuracy of established model based on the dose calculation of Monte Carlo method.Methods The energy and direction of the photon beam which was divided into primary photon beam and scattered photon beam were described with mathematical formula in order to establish the virtual source model.The dose distribution in water calculated with Monte Carlo method was compared with the measurement data in the water tank,and the actual plan calculated using source model was compared with the results of commercial treatment planning system（TPS）.Results The errors of percent depth dose and off-axis ratio curves were basically within 1.0% and within 2.0%,respectively.In a case of prostate plan,the dose-volume histogram curve calculated by the proposed method was basically the same as that calculated by different TPS.Conclusion The virtual source model method which can represent the beam information of linear accelerator and calculate the plan for a single case within 40 seconds realizes the real-time dose verification before treatment and has potential in the automatic commission process of linear accelerator.