6MV医用电子直线加速器的蒙特卡罗模拟  

Monte Carlo simulation of 6 MV medical electron linear accelerator

作　　者：时颖华[1] 周凌宏[1] 刘迎军[1] 甄鑫[1] 卢文婷[1] 张书旭[2] 

机构地区：[1]南方医科大学生物医学工程学院,广州510515 [2]广州医学院附属肿瘤医院

出　　处：《中华放射医学与防护杂志》2011年第2期220-224,共5页Chinese Journal of Radiological Medicine and Protection

基　　金：国家自然科学基金（30970866）;广东省重点科技计划（2008A030102011）

摘　　要：目的探讨入射电子束的能量和径向强度分布对百分深度剂量曲线和离轴比的影响，并寻找与百分深度剂量曲线和离轴比的测量值最接近的两者参数组合。方法利用OMEGA／EGSnrc系统，模拟Varian600C医用电子直线加速器，计算水模体百分深度剂量曲线和10cm深度处离轴比。若测量值和计算值的相对误差经过剂量最大点后在2％之内，则接受入射电子束值。结果电子束的能量在经过剂量最大点后对深度剂量曲线没有明显影响。离轴比对能量敏感，能量越高，离轴比尖角越小。径向强度分布对深度剂量曲线在误差允许的范围内没有影响，而离轴比曲线对电子束径向强度分布非常敏感，随着径向强度分布半高全宽增大而减小。深度剂量曲线的计算值与测量值一致。在射野范围内，离轴比曲线计算值和测量值一致；但在半影区和射野外，个别测量点的最大误差达到了18.5％。结论在射野内找到了电子束能量和径向强度分布的最优参数组合，而在半影区和射野外，未能找到合适的两者参数组合。Objective To analyze the influence of the mean energy and the full-width of half maximum （FWHM） of incident electron beam intensity distribution （assumed Gaussian distribution） on depth dose curves and off-axis ratios and to derive a most optimal combination of mean energy and FWHM of incident electron beam intensity distribution. Methods The study simulated 6 MV photon beam produced by Varian 600C medical linear accelerator with OMEGA/EGSnrc by matching the relative error of calculated and measured depth dose curves past depth of maximum dose and off-axis ratios at a depth of 10. 0 cm in water within 2%. Results The depth dose curves were relatively insensitive to the mean energy past depth of maximum dose and the FWHM of the incident electron beam intensity distribution. Dose profiles were sensitive to the mean energy and FWHM. The dose profiles horns decreased as the mean energy and the FWHM of the incident electron beam intensity distribution increased. The calculated value of the depth dose curves matched well with the measured value. The calculated value of the off-axis ratio was consistent with the measured value within the radiation field. However, the maximum errors of individual measurement points in the penumbra region and out of the field reached 18.5%. Conclusions In the field, the most optimal combination of mean energy and FWHM of incident electron beam intensity distribution can be derived, however, can not be derived out of the field and in the penumbra region.

关 键 词：加速器 模拟 蒙特卡罗 百分深度剂量曲线 离轴比 

分 类 号：R730.5[医药卫生—肿瘤]