光子束不规则射野的等效方野计算方法

Calculation of an equivalent square field for irregular photon beam fields

目的探讨一种快捷、准确求光子束不规则射野等效方野的方法。方法不规则射野按对称射束中心与不对称射束中心分为两类,每类再以不规则野的周长与原开野周长的比值R分为:R>1,R=1,R<1三种情况。选择6种不规则射野,实测吸收剂量;分别用A,B,C3种方法计算其等效方野,用等效后方野剂量参数计算处方剂量,与实测剂量比较。结果R>1,B方法准确;R=1,A和C方法较准确,B方法亦符合精度要求;R<1,A,B,C方法一致准确。结论笔者推荐临床使用B方法,便于标准化操作。

Objective To explore a rapid method of calculating an equivalent square field for irregular photon beam fields. Methods Irregular photon fields can be divided into two types： the fields symmetric to the beam central axis and the fields dissymmetric to the beam central axis. Each type contains three conditions （i. e. R 〉 1, R = 1, R 〈 1 ） according to the perimeter ratios of the irregular fields to the original fields. To choose 6 irregular fields and measure the absorption doses. Then work out the equivalent square field of each of the 6 irregular fields by means of A, B and C. Finally compare the prescription doses and those measured. Results In the condition R 〉 1, method B worked precisely. In the condition R = 1, method A and method C worked rather precisely, while method B meet the accuracy demand. In the condition R 〉 1, method A, B and C worked precisely and consistently. Conclusion Method B can be recommended for clinical use, for it is convenient for standardized operations and meets the accuracy demand.