二维电离室矩阵中射野边界位置对调强验证Gamma通过率的影响  

Effects of field edge position in a two-dimensional ion chamber array on Gamma passing rate

作　　者：包超恩[1] 卢军丽[1] 翟福山[1] 曹晓辉[1] 刘兵[1] 杨永锋[1] 刘明[1] 李枫[1] BAO Chaoen;LU Junli;ZHAI Fushan;CAO Xiaohui;LIU Bing;YANG Yongfeng;LIU Ming;LI Feng(Department of Oncology,the Third Hospital of Hebei Medical University,Shijiazhuang 050051,China)

机构地区：[1]河北医科大学第三医院肿瘤科

出　　处：《中国医学物理学杂志》2019年第8期898-902,共5页Chinese Journal of Medical Physics

基　　金：河北省卫生厅科研基金（ZD20140115）

摘　　要：目的:针对(10×10)cm^2射野,探讨改变射野边界在矩阵中的位置对测量射野大小及Gamma(γ)通过率的影响。方法:使用MatriXX二维电离室矩阵测量(10×10)cm^2射野剂量分布,保持射野大小不变,移动X方向准直器和在Y方向移动治疗床两种方式改变射野边界在矩阵中的位置,用OmniPro I'mRT(1.7)软件分析每次移动0.1 cm时射野边长的改变量,同时用实测剂量分布和XiO(4.40)治疗计划系统相应射野剂量分布对比,记录3%/3 mm评估标准下的γ通过率和γ为100%时的评估标准。结果:在矩阵电离室腔外间隙射野边长改变量低于0.1 cm,且在每两个电离室腔外间隙正中改变量最小接近0.05 cm;在电离室腔体内改变量高于0.1 cm,且在每一个电离室腔体中心接近最大值0.2 cm。3%/3 mm下的γ结果显示射野边界不通过点数随位置变化明显不同,在射野边长改变量最大和最小附近通过率高,全部通过的评估标准范围是2%/2 mm至6%/3 mm。结论:选取射野边界在矩阵电离室腔体中心或腔外间隙正中位置时,所测射野大小偏差最小。同时上述射野边界位置γ通过率最高,因此,在调强计划剂量分布验证中要充分考虑射野剂量梯度较大处在电离室矩阵的位置对γ通过率的影响,可调整剂量分布在矩阵中位置或改变不同评估标准详细分析γ通过率差异,从而提高γ通过率的有效性,对临床工作具有一定的指导作用。Objective To discuss the effects of the position of a(10×10)cm^2 field edge in ion chamber array on the measurement of field sizes and Gamma passing rates.Methods A two-dimensional ion chamber array detector(MatriXX)was used to measure the radiation dose distributions of a(10×10)cm^2 field.The position of the field edge was changed by either moving the collimator in X direction or the treatment couch in Y direction while keeping the field size constant.The length variation of the field edge after each 0.1 cm movement was recorded and analyzed with OmniPro I'mRT(1.7)software.The measured dose distribution and the corresponding radiation dose distribution in the treatment planning system of XiO(4.40)were compared.The Gamma passing rates(3%and 3mm)and the minimum acceptance criterion at 100%Gamma passing rate were recorded.Results The length variations of the field edge in the outer space of ion chamber cavity were less than 0.1 cm,and the minimum length variation of the field edge in the middle of two outer spaces was close to 0.05 cm.However,the length variations were larger than 0.1cm when the field edge was in the ion chamber cavity and the length variation at the center of each ion chamber cavity nearly reached the maximum value of 0.2 cm.The analysis on Gamma passing rates(3%and 3 mm)showed that the number of failure points was related to the position of field edge;and that the highest Gamma passing rates were found when the length variation of field edge was maximumor minimum;and that the range of evaluation criterion at 100%Gamma passing rate was 2%/2 mm-6%/3 mm.Conclusion The deviation in the measurement of field size is minimal when the field edge is in the center of the ion chamber and in the middle of two outer spaces,and the Gamma passing rate is the highest when the field edge is as above.Therefore,the effects of the position of high dose gradient area in the ion chamber array on Gamma passing rates during the dose verification of intensity-modulated radiotherapy should be comprehensively considered.

关 键 词：放射治疗 电离室矩阵 γ通过率 射野边界 

分 类 号：R318.6[医药卫生—生物医学工程] R811.1[医药卫生—基础医学]