调强计划验证中MatriXX电离室的角度响应修正

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

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果,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果好于未修正的。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。

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 x 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 eorre- sponding calculated value for each UIC at each gantry angle. Then, dose distributions from actual IMRT plan fields were meas- ured, and plan verification results with. angular dependence correction or not were both obtained and compared, in order to e- valuate 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 cor- rection, MatriXX could be more suitably used for actual IMRT plan with different gantry angles.