直线加速器低MU照射对高能X线剂量学的影响  

The dosimetry influence of high energy X-rays generated from linear accelerator with low monitor units

作　　者：张颖[1] 陶建民[1] 胡杰[1] 张莹[1] 

机构地区：[1]同济大学附属第十人民医院放射治疗科,上海200072

出　　处：《同济大学学报（医学版）》2010年第4期35-38,共4页Journal of Tongji University(Medical Science)

基　　金：上海市铁路局科技研究开发项目(2002Y04)

摘　　要：目的直线加速器机器跳数MU设置的减少可能导致射线束特性发生变化,探讨直线加速器低MU照射对高能X线剂量学的影响。方法对Siemens Mevatron MD7745直线加速器6 MV-X线辐射源,机器跳数设置1～100MU范围,先测量辐射质指数TPR_(10)^(20);然后在最大剂量深度1.5 cm处测量相应MU数时的吸收剂量D_(MU),并计算每MU对应的cGy;最后测量10cm×10cm射野百分深度剂量(percent depth dose,PDD)以及边长3～20 cm范围方野的总散射因子Sc,P,然后分析数据。结果不同大小MU设置,MU与cGy的对应关系有很大的差别,偏差最大达10.6%,低MU设置对辐射质指数TPR_(10)^(20)、百分深度剂量PDD和总散射因子Sc,P影响很小,<1%。结论为保证体模中剂量计算精度达到WHO规定的精度要求,当MU<8时,必须修正MU与cGy的对应关系,而低MU照射对辐射质指数、百分深度剂量和总散射因子的影响可忽略不计。Objective Low MU may change the beam characteristics. To study the influence on dosimetry of high energy X rays with low monitor units from linear accelerator. Methods The monitor units were set between 1 and 100 MU, TPR10^20 were first measured; then the dose at depth of 1.5 cm with 10 cm × 10 cm field and 100 cm source skin distance （SSD） were measured and cGy per monitor and the deviation with monitors were calculated; finally the percent depth dose（PDD） with 10 cm× 10 cm field and Collimator and Phantom Scattor Factor（Sc,p） for the field between 3 cm ×3 cm and 20 cm ×20 cm were measured. Results The influence on PDD and Sc, p were less than 1% at low monitor traits but the deviation to cGy per unit was increased, and the most deviation was as high as 10.6%. Conclusion In order to attain the rules of WHO for Quality Assurance in radiotherapy that the accuracy for dose in phantom must be better than 3%, cGy per MU must be corrected when the MU settings are less than 8, but the influence on TPR10^20 PDD and Sc, p from low monitor unit setting can be neglected.

关 键 词：直线加速器 低剂量监测计数 放射治疗 剂量 

分 类 号：R814[医药卫生—影像医学与核医学]