二维空气电离室矩阵MatriXX系统的应用研究  

Research on the application of 2-D air vented ionization chamber array MatriXX system

作　　者：张书旭[1] 周凌宏[2] 陈光杰[2] 林生趣[1] 沈国辉[1] 王余峰[1] 

机构地区：[1]广州医学院附属肿瘤医院放疗中心,510095 [2]南方医科大学生物医学工程学院

出　　处：《中华放射医学与防护杂志》2009年第1期93-96,共4页Chinese Journal of Radiological Medicine and Protection

基　　金：广东省科技计划基金资助项目（20078031509009）

摘　　要：目的探讨二维空气电离室矩阵MatriXX系统应用于放疗质量控制中的特点。方法用MatriXX系统和自制的剂量测量体模，对临床放疗质量控制中的一些重要内容进行了初步的研究，主要包括MatriXX系统的刻度、X线虚拟楔形野的离轴比、半野和偏心野衔接、均整块的校准、放疗计划剂量分布的二维验证、散射屏对大面积电子线特殊野的影响、大野附加散射屏后铅挡块的遮挡效果和挡块的最佳位置和厚度的确定。结果任意角度的虚拟楔形野的离轴比均可用MatriXX来测量，测量时只需要1次照射；半野和偏心野衔接位置可精确到小于1mm；用MatriXX系统可对照射野内任一点的计算值与测量值，或整个射野内任意百分比的等剂量曲线分布以及任意方向离轴比进行对比分析；均整块校准后射野的平坦度和对称性分别为1．85％和0．98％；散射屏明显改变了电子线射野的剂量特性，大面积电子线特殊野照射时远距离遮挡难以达到遮挡目的，近距离或直接遮挡效果最佳。结论二维空气电离室矩阵MatriXX系统用于放疗质量控制时，比普通指形电离室和胶片剂量测量更简便、高效，是放疗质量控制的理想工具。Objective To investigate the features of 2-D air vented ionization chamber array MatriXX system to use the QA procedures of radiotherapy. Methods Some important QA procedure of clinical radiotherapy practice were investigated by using a MatriXX system and a phantom made in house, mainly including the calibration of MatriXX, the off-axis rate （OAR） of virtual wedge fields, the connection between two haft-fields or two asymmetry-fields, the skillful adjustment of the clinac flat filter, the 2-D dose distribution verification of radiotherapy planning, the influence of scatter screen to a large area electron beam field, the effect and best thickness and shielding position of block for a large area electron beam fields with scatter screen. Results The OAR of any virtual wedge field can be measured by a MatriXX system in a single irradiation. The conjunction accuracy of two half-fields or two asymmetry-fields may be less than 1 mm. The difference between the calculated and measured dose of any point or any isodose or any OAR of a field can be determined by using a MatriXX system. After the adjustment of the clinac flat filter with the help of MatriXX system, the flatness and symmetry of the field are 1.85 % and 0.98 %, respectively. The dose characteristic of a large area electron beam field may be distinctively influenced by a scatter screen, and under this condition, the block faraway from the shielded target can hardly protect the organ at risk, and directe block which is put on or near the organ at risk is perfect. Conclusion Compared with conventional ionization chamber （Farmer type） or fihn dose measuring, the MatriXX combined with the OmniPro I＇mRT software is much more convenient and effective in QA practice of clinical radiotherapy, and it＇s a perfect tool for the QA procedure of radiation therapy.

关 键 词：二维空气电离室矩阵 MatriXX系统 二维剂量验证 体模 

分 类 号：R730.55[医药卫生—肿瘤]