Varian Edge均整和非均整模式下6 MV和10 MV光子线能谱研究  

Energy spectra of 6 and 10 MV flattened and flattening filter-free photon beams from Varian Edge

作　　者：韩俊杰 陈立新[2] 朱金汉 潘燚[1] 梁瑜[1] 王学涛[3] 张白霖 邹文长[1] HAN Junjie;CHEN Lixin;ZHU Jinhan;PAN Yi;LIANG Yu;WANG Xuetao;ZHANG Bailin;ZOU Wenchang(Department of Radiation Oncology,Guangdong General Hospital,Guangzhou 510080,China;State Key Laboratory of Oncology in South China/Department of Radiation Oncology,Sun Yat-sen University Cancer Center,Guangzhou 510060,China;Department of Radiation Oncology,Guangdong Traditional Chinese Medicine Hospital,Guangzhou 510120,China)

机构地区：[1]广东省人民医院放疗科,广东广州510080 [2]中山大学附属肿瘤医院放疗科/华南肿瘤学国家重点实验室,广东广州510060 [3]广东省中医院放疗科,广东广州510120

出　　处：《中国医学物理学杂志》2018年第9期997-1004,共8页Chinese Journal of Medical Physics

基　　金：广东省自然科学基金(2016A030313276;2014A030310188);广州市科技计划项目(20160701168)

摘　　要：目的:研究Varian Edge均整(FF)和非均整(FFF)模式下6 MV和10 MV光子线能谱并对比其差异。方法:利用蒙特卡洛程序软件包EGSnrc/Beamnrc建立Varian Edge 6 MV FF和FFF、10 MV FF和FFF的加速器模型,模拟所对应的相空间文件,而后以相空间作为输入源,利用DOSXYZnrc计算其在水体模中的剂量分布,并与三维水箱的测量数据比对,当模拟值与测量值之间的差异在1%之内时,利用Beamdp分析此时的相空间文件,得到对应的光子线能谱,并比较相互之间的差异。结果:模拟的百分深度剂量曲线和离轴比曲线与测量值之间的差异在1%之内。相对于FF模式,FFF模式的能谱"软化",其中6 MV FFF的平均能量从1.587 MeV下降至1.172 MeV,低能(能量≤1 MeV)光子所占的份额由41.06%上升至60.04%;而10 MV FFF的平均能量从2.796 MeV下降至1.956 MeV,低能光子所占的份额由21.22%上升至44.63%。同一射野内FFF模式的能谱随离轴距离的改变较小,同时每初始粒子所引起的能量注量是FF模式的2～4倍,射野内的能量注量分布变得不均匀,非平坦度F上升;分析不同射野下的能谱发现FFF模式的机头散射较少。结论:本研究结果对理解FFF模式下光子线的物理特性提供了非常好的参考价值。Objective To study the energy spectra of 6 and 10MV flattening filter(FF)and flattening-filter-free(FFF)photon beams from Varian Edge and compare their differences.Methods Monte Carlo program package,EGSnrc/Beamnrc,was used to establish Varian Edge models,including 6 MV FF and FFF,10 MV FF and FFF,and the corresponding phase space files were simulated.Then with the phase space as input source,DOSXYZnrc was applied to measure the dose distributions in water phantom which were compared the simulated results obtained with three-dimensional water tank.If the differences between measurement and simulation were within 1%,the phase space files were analyzed with Beamdp in order to obtain the energy spectra.The differences among those obtained energy spectra were also compared.Results The differences of percentage depth dose and off axis ratio between simulation and measurement were within 1%.Compared with that of FF model,the energy spectra of FFF model became softer.The mean energy of 6 MV FFF decreased from 1.587 MeV to 1.172 MeV,and the percentage of low-energy photon(≤1 MeV)increased from 41.06%to 60.04%.The mean energy of 10 MV FFF decreases from 2.796 MeV to 1.956 MeV,and the percentage of low-energy photon increased from 21.22%to 44.63%.In the same field,the energy spectra of FFF model had slight changes with the increase of off axis distance,but the energy fluence caused by per initial particle was 2 to 4 times of FF model.Meanwhile,compared with that of FF model,the energy fluence distribution of FFF model became uneven,with a raising unflatness F.The analysis on the energy spectra in different fields revealed that the scattering from FFF accelerator head was less.Conclusion This study provides valuable references for the comprehension about the physical characteristic of FFF photon beams.

关 键 词：光子线 能谱 均整模式 非均整模式 VARIAN EDGE EGSNRC 

分 类 号：R811.1[医药卫生—放射医学]