基于双源光子模型的准直器散射因子新算法  

A simple and accurate algorithm based on a dual source photon beam model for calculation of collimator scatter factor

作　　者：杨勇[1] 张红志[1] 胡逸民[1] 

机构地区：[1]中国医学科学院中国协和医科大学肿瘤医院放射治疗科,北京100021

出　　处：《中华放射肿瘤学杂志》1999年第4期236-239,共4页Chinese Journal of Radiation Oncology

摘　　要：目的　建立一种简单准确适合于临床应用的准直器散射因子(Sc)的计算模型。方法　建立双源光子束模型,将到达计算点的射线分成原射线和机头散射线两部分,原射线由位于靶点的点源产生,散射线由位于焦点外具有轴对称性的面源产生。并用一个反向散射修正因子对次级准直器的反向散射进行修正。结果　(1) 对于4 cm ×4cm ～40cm ×40 cm 的方野、长短轴比最大为10 的矩形野以及挡铅形成的不规则野,Sc 的计算结果与测量结果的最大偏差<0 .6 % 。(2) 等中心处射野设为10cm ×10cm ,源—电离室距(SCD)从75.5cm 到140 .0cm 变化时,Sc 的计算结果与测量结果的最大偏差< 0.4 % 。结论　该算法可用于准确计算不同SCD处的方野、对称和不对称矩形野、挡铅或多叶光栏(MLC) 形成的不规则野的Sc,是一种适合于临床应用的简单准确的计算ScObjective To design up a simple and accurate calculation method for collimator scatter factor (Sc), which can be easily implemented in clinical works. Methods A dual source photon beam model is described, which presumed that linac output has two components. One component is direct radiation from the target and the remaining component is head scatter radiation from an extra focal cylindrically symmetric source. And a monitor backscatter factor is used to correct the effect of backscatter from secondary collimators. Results (1) This method gives value for Sc that differs from measured values by no more than 0.6% for square fields 4?cm to 40?cm wide,symmetric rectangular fields with long to short axis ratio as great as 10, and irregular fields formed by blocks. (2) The calculated Sc values differ from measured values by no more than 0.4% for source chamber distance from 75.5?cm to 140.0?cm while collimators are set up as 10?cm×10?cm at isocenter. Conclusions The collimator scatter factors for square fields , rectangular fields, symmetric and asymmetric, and irregular fields formed by blocks or multiple leaf collimator can be simply and accurately calculated with this method. It is suitable for clinical daily practice.

关 键 词：准直器散射因子 输出因子 双源光子束模型 

分 类 号：R815[医药卫生—放射医学]