医用电子直线加速器射野能谱特性研究

Research on the Characteristics of the Radiation Spectral of the Medical Linear Accelerator

目的 探究医用电子直线加速器射野变化对X射线能量注量、能谱及平均能量的影响,为加速器能谱测量作为射野运行精度的质控手段提供理论依据。方法 以基于蒙特卡罗算法的EGSnrc程序用于电离辐射传输模拟,使用BEAMnrc建立Varian TrueBeam系列加速器机头模型,并分别设置1 cm×1 cm~10 cm×10 cm射野。使用BEAMdp调用BEAMnrc计算生成的相空间文件进行能量注量、能谱及平均能量的结果分析。结果 射野大小对能量注量及能谱结构影响较大,射野越大,相同能量下的注量越高,普峰值越大。在选定射野中能量注量差异最大达98.9%,能谱差异最大达99.0%,有均整过滤器(Flattening Filter,FF)模式下高注量能量区间为0.5~1.2 MeV,峰位约0.33 MeV。与无均整过滤器(Flattening Filter Free,FFF)模式下高注量能量区间为0.3~1.0 MeV,峰位约0.26 MeV。同时射野大小对平均能量影响不明显,FF模式约为1.4MeV,FFF模式约为1.2 MeV。结论 医用电子直线加速器不同射野能量注量及能谱具有一定特异性,可通过对能量注量和能谱的分析作为判断加速器射野运行精度的辅助手段。

Objective To explore the impact of field size variation of medical electronic linear accelerator on X-ray energy dose,spectrum and mean energy,to provide theoretical basis for accelerator spectrum measurement as a quality control method for field operation accuracy.Methods The EGSnrc program based on Monte Carlo algorithm was used for ionizing radiation transfer simulation,and BEAMnrc was used to build the head model of the Varian TrueBeam series accelerator,and the square field was set from 1 cm×1 cm to 10 cm×10 cm.BEAMdp was used to call the phase space file generated by its calculation to analyze the results of energy fluence,energy spectrum and mean energy.Results The size of the field had a great influence on the energy fluence and spectrum structure.With the same energy,the larger the field,the higher the general peak value of the injection.In the selected field,the maximum energy difference was 98.9%,and the maximum energy spectrum difference was 99.0%.Under the flattening filter(FF)mode,the energy range of high injection volume was 0.5~1.2 MeV,and the peak was about 0.33 MeV.The energy range of the high injection volume was 0.3~1.0 MeV and the peak was about 0.26 MeV under the flattening filter free(FFF)mode.At the same time,the impact of field size on the average energy was not obvious,FF mode was about 1.4 MeV,FFF mode was about 1.2 MeV.Conclusion The energy fluence and energy spectrum of different fields of the medical electron linear accelerator have certain specificity,and the analysis of the energy fluence andenergy spectrum can be used as an auxiliary means to judge the accuracy of the accelerator field operation.