DPM蒙卡方法在放疗剂量计算中的应用研究

目的:探讨最新推出基于蒙特卡罗方法的DPM(dose planning method)程序在放疗剂量计算中的应用,研究DPM程序计算放疗剂量的准确性及其临床应用的可行性。方法:对DPM源文件编译形成四个可执行文件,使其能在Windows系统下运行。(1)通过借助蒙卡BEAMnrc程序模拟我院Varian Clinac 21EX直线加速器治疗头,得到其相空间文件,并计算出SSD=100cm处的相空间(Phase Space)数据。(2)使用BEAMDP程序对该相空间文件进行能谱分析,获取到6MV-X线能谱分布。(3)修改DPM源程序,使之能调用该能谱。(4)DPM计算出水模体内百分深度剂量并用MATLAB软件显示PDD曲线分布,与实际测量进行拟合。(5)DPM计算非均匀组织内方野剂量,相同条件下与实测量、TPS计算值进行了比较。结果:蒙卡DPM程序调用直线加速器能谱计算水模体内的PDD曲线与实测曲线的拟合完全吻合,证明了DPM程序调用能谱方法可行而且计算准确。DPM蒙卡程序在非均匀组织中的计算也是准确的。结论:DPM蒙卡方法可应用实现组织中放疗剂量计算的研究。

Study of Dose Calculation Using Monte Carlo Method in Radiotherapy

Objective： Dose calculation using Monte Carlo＇s DPM （dose planning method）program in radiotherapy has been studied, and the accuracy of dose calculation and the clinical feasibility of DPM program were evaluated. Methods： The original file of DPM was compiled into 4 executable files in the Windows. （1） Monte Carlo＇s BEAMNRC was programmed to simulate the head of the Varian Clinac 21EX linear accelerator using the Phase Space file. The data of the Phase Space was gotten under the condition of SSD=100 cm. （2）The spectral analysis of the Phase Space file in the BEAMDP program was done for achieving the spectral distribution of accelerator 6 MV-X ray. （3）The original DPM program was modified in order to calculate this spectrum. （4）The percent depth dose （PDD） in the water phantom was calculated in the DPM program, and displayed using the MATLAB software, then fit the measured data in the 3D water phantom. （5）Dose calculation in the inhomogeneity tissue was done under the square fields, and compared with the actual results by Dosemeter＇s measurement and TPS calculation under the same conditions. Results： Using the linear accelerator spectrum, the calculated results of PDD curves in the water were well accorded with the measured curves. The reliability and accuracy of introducing spectrum in the DPM program were approving. The precision of the dose calculation for the inhomogeneity tissue in the Monte Carlo＇s DPM program compared with the measured value and the TPS calculation was also well-pleasing. Coneulsion： Monte Carlo＇s DPM program could be applied to the dose calculation of tissue in radiotherapy.