SIEMENS MD7745加速器射野大小对电子束输出因子的影响

The influence of different radiated fields from SIEMENS MD7745 accelerator on output factors of electrons beam

目的研究射野大小对高能电子束输出因子的影响。方法用Capintec292剂量测量系统测量SIMENS MD7745直线加速器9Mev和12 Mev电子辐射源各种射野成形情况下的输出因子,并进行数学分析,为临床准确使用该因子提供依据。结果得到了各种照射情况下的电子束输出因子,可知该因子对准直铅门大小、限光筒大小、铅档野开口大小和能量有很强的依赖性。结论为了保证剂量计算精度达到WHO规定的范围,临床实际工作中,限光筒大小应尽量接近实际所需射野,当射野边长大于电子束射程时,可直接使用标准限光筒输出因子,而对边长小于电子束射程的射野,必须有针对性地实际测量所用射野的输出因子。

Objective To study the influence of different radiated fields from accelerator on output factors of high-energy electron beam. Methods The influence of radiated fields from accelerator SIEMENS MD7745 of 12 Mev and 9Mev on output factors of high energy electron beam was measured by using 292 dosimetry systern. The data was analyzed to deduce the proper rules for clinical practice. Results The output factors gotten under different conditions were found to be strongly related to the collimator jaws,standard applicator sizes,lead block fields and electron energies. Conclusion In order to attain the rules required from WHO for quality assurance in radiotherapy, the applicator size must be close to the lead block field, on this basis the output factors can be used for standard applicators to replace the lead block field when the field size is larger than Rp, but the output factors must be measured for those fields which its sizea are less than Rp.