MatriXX电离室矩阵角度修正因子验证及分析

摘要

Objective: To analyze the effects of beam directions and treatment couch to angle correction factors of MatriXX.Methods: The Matrixx putted in the middle of the MultiCube Phantom was scanned and the images were sent to the plan system. The measurement point was set at the centre of Matrixx central plane,and it was also the central point of planning. All data calculated from TPS and actually measured with and without treatment couch had gained as following conditions: 8 MV, 200 MU, 20 cm×20 cm field, the directions of beam were from 0°to 180°with interval of 5°. The angle correction factors of MatriXX with and without treatment couch were calculated and compared to the data given by manufacturer. All data was analyzed with SPSS 13.0. Results: T test of MatriXX angle correction factors between with and without treatment couch was P＜0.005. The result of t test between actually calculated factors of 8 MV and factors of 6 MV given by manufacturer was also P＜0.005. The results indicated that the difference was obvious. Conclusions: There is a error of MatriXX correction factors between actually measured and given by manufacturer, and the error is obvious if the treatment couch is considered. So we suggest that the angle correction factors of MatriXX should be measured actually before usage.%目的:分析射野入射方向及加速器治疗床对MatriXX电离室矩阵角度修正因子的影响.方法:获取MatriXX和MultiCube模体所组成的测量装置的CT影像,并将其导入计划系统,以MatriXX有效测量平面中心为计划中心,设置一能量为8MV X射线、机器跳数为200MU、20 cm×20 cm的对称方野.在机架角度为0°～180°范围内以5°为间隔定义射野入射方向,分别计算各入射方向的射野在计划中心点的剂量,并与在相同条件下存在加速器治疗床和无加速器治疗床两种情况下的实际剂量测量结果做比值,得出有无加速器治疗床两种情况的MatriXX电离室矩阵的角度修正因子.应用SPSS13.0软件对这两组现场测量计算得到的MatriXX电离室矩阵角度修正因子值及厂家的给定值之间进行t检验比较.结果:实测得到的有无加速器治疗床的两组MatriXX电离室矩阵角度修正因子值比较的t检结果为P<0.005,治疗床的存在对修正因子有显著的影响;实测的8MV无治疗床的修正因子与厂家给定的6MV的修正因子进行比较的t检验结果为P<0.005,实测修正因子与厂家给定值之间存在差异.结论:现场测量MatriXX电离室矩阵的角度修正因子与厂家给定值之间存在一定的误差,当把加速器治疗床对射线吸收影响考虑在内时,误差更大;建议使用单位对角度修正因子进行实际测量.