基于DPM的调强放疗计划剂量验证工具的实现

目的 基于简单快速蒙特卡罗程序DPM（dose planning method），通过植入照射源模型并改进程序，解决DPM中无法实现任意角度入射和非规则非均匀野模拟的问题，使其成为调强放疗计划系统的实用蒙特卡罗剂量验证工具。方法 通过加速器反演出的能谱结合优化给出的强度图模拟加速器的粒子输运过程。使用虚拟点源结合反演出加速器能谱模拟了加速器的照射源部分，基于DPM的粒子输运物理模型，结合调强放疗计划中的照射野强度分布，以及出射粒子的权重与强度图中的强度相结合，实现了算法。结果 通过将DPM模拟计算的规则野结果与三维水箱测量数据对比了百分深度剂量（PDD）和百分离轴剂量（OAR），误差在野内<2%，半影2~3mm。以及DPM模拟计算非规则野的结果与有限笔形束剂量计算方法FSPB计算结果的对比，趋势符合，γ分析通过率为95.1%，误差都在允许范围内。校验了改进的DPM的功能和计算精度。结论 植入简便照射源模型的DPM程序相较于经典蒙特卡罗程序，速度较快，计算精度和时间可以满足临床需求，可以作为调强放疗计划系统中剂量验证工具。

Realization of dose verification tool for IMRT plan based on DPM

Objective To build a Monte Carlo dose verification tool for IMRT Plan by implanting an irradiation source model into DPM code and to extend the ability of DPM to calculate any incident angles and irregular-inhomogeneous fields.Methods The virtual source and the energy spectrum unfolded from the accelerator measurement data were used, in combination with optimized intensity maps, to calculate the dose distribution of the irradiation irregular-inhomogeneous field.The irradiation source model of accelerator was substituted by a grid-based surface source.The contour and the intensity distribution of the surface source were optimized by IMRT.The dose calculation was realized by combining the position of the emitter with the fluence map from the IMRT plan.The weight of the emitter was decided by the grid intensity.The direction of the emitter was decided by the combination of the virtual source and the emitting position.The weighted fraction of the emitter was also combined with the flux grid intensity based on the particle transport model of DPM code.Results The accuracy of calculation was verified by comparing with the measured data.It was illustrated that the differences were acceptable (<2% inside the field, 2-3 mm in the penumbra).The dose calculation of irregular field by DPM simulation was also compared with that of FSPB (Finite Size Pencil Beam).The passing rate of gamma analysis was 95.1% for peripheral lung cancer.The regular field and the irregular rotational field were all within permissible range of error.The calculation time of regular fields were less than 2 h, and that of the test of peripheral lung cancer was 160 min.Conclusions The adapted DPM code with its simple irradiation source model is faster than that with classical Monte Carlo procedure.Its computational accuracy and speed satisfy the clinical requirement, and it can be useful as a Monte Carlo dose verification tool for IMRT Plan.