调强计划验证中MatriXX电离室的角度响应修正

目的 用MatriXX验证调强计划时其存在角度响应问题,本工作旨在对MatriXX电离室矩阵中的每个电离室分别进行角度响应修正。方法 在0°机架角且射野开野28 cm×28 cm条件下,用MatriXX测量平面剂量分布,并与计划系统的计算值对比,得到MatriXX中各单元电离室的剂量校准系数。在此基础上,测量不同机架角且开野条件时的平面剂量分布,通过相应计算值对各角度各电离室的测量值进行角度修正。用MatriXX测量实际调强计划中的剂量分布,比较角度响应修正后和未修正时的验证结论,评价该修正方法的作用。结果 0°机架角时,各电离室的剂量校准系数随X、Y坐标值增加略有增加,平均为1.00±0.01。各电离室的角度响应修正系数在机架角为60°~150°和210°~300°范围内时变化范围大且波动大,且分别在90°和270°附近达到最小。经过修正后的计划验证结论好于未修正的。结论 经角度响应修正后,MatriXX可以更好适用于多机架角IMRT计划的验证。

Correction of Angular Dependence of MatriXX Ion Chambers for IMRT Plan Verification

Objective Angular dependence of MatriXX is a problem when used in composite dose verification of IMRT,and this work aimed at correcting angular dependence of each unit ion chamber(UIC) in MatriXX array respectively.Methods At 0° gantry angle with open field 28cm×28cm,plane dose distribution was measured by MatriXX,and then compared to the calculated value from treatment planning system(TPS),so that dose calibration coefficients of each UIC were obtained.Based on this,dose distributions under different gantry angles and open field were also measured,and corrected by the corresponding calculated value for each UIC at each gantry angle.Then,dose distributions from actual IMRT plan fields were measured,and plan verification Results with angular dependence correction or not were both obtained and compared,in order to evaluate this correction method.Results At 0° gantry angle,the dose calibration coefficients of each UIC lightly increased with their X,Y values increasing,and were averaged to be 1.00 ±0.01. For 60°~150° and 210°~300° gantry angle ranges,the angular dependence coefficients had large range and fluctuation,and around 90° and 270°,the coefficients reached the smallest. Verification results after correction were better than those without.Conclusion After this angular dependence correction,MatriXX could be more suitably used for actual IMRT plan with different gantry angles.