测量后装近距离放射治疗^192Ir源参考空气比释动能方法学研究  

Development of measurement methodology with reference air kerma of ^192Ir source afterloding in bracytherapy

作　　者：罗素明[1] 何志坚[1] 高磊[1] 

机构地区：[1]中国疾病预防控制中心辐射防护与核安全医学所,北京100088

出　　处：《中华放射医学与防护杂志》2008年第4期398-400,共3页Chinese Journal of Radiological Medicine and Protection

基　　金：科技部社会公益研究专项资助（2004DIBIJ035）

摘　　要：目的用NE2570剂量仪，2571指形电离室，测量^192Ir源空气比释动能支架，测量1m处^192Ir源参考空气比释动能。方法将测量支架放在离墙、地面1m处，指形电离室插入有机玻璃测量支架夹具中，源中心距电离室中心的最佳距离是16cm，源通过后装机的传输系统传输到施源器中，测量源参考空气比释动能。根据^60Co γ射线，250kVX射线空气照射量刻度因子换算为空气比释动能刻度因子，再由内插公式计算^192Ir源空气比释动能刻度因子。对墙、地、空气、测量支架的散射校准因子，通过阴影屏蔽实验得到；对初始光子减弱校准因子；电离室壁产生的电子非均匀校准因子，均由IAEA的1079号报告（近距离放射治疗源的刻度）中查表得到。结果在相同环境条件下，使用2种测量方法，指形电离室测量^192Ir源空气比释动能，经转换系数计算源外观活度为1．584×10^11 Bq；井型电离室测量^192Ir源空气比释动能强度，经转换系数计算源外观活度为1．561×10^11 Bq，2个结果的相对偏差为1．4％。结论指形电离室测量源空气比释动能，该物理量与源的结构、尺寸、壳材料、电离室形状、材质和尺寸无关，测量源空气比释动能与源的空气照射量比较，不确定度误差小。Objective To develop measurement of reference air kerma for ^192Ir sources with NE 2570 electrometer, 2571 ion-chamber and machining measured holder. Methods The measuring holder was placed at the distance of 1 m from the walls, the floor and ceiling, the ion-chamber was insert into the polymethyl methaerylate （PMMA） jig of the measuring holder, the optimum distance is 16 cm from the source centre to ionchamber centre. The source was transmitted by the afterloding system to the plastic pipe to measure reference air kerma of the source. According to calibration factors from ^60Coγ rays and 250 kV X rays with air exposure to calculated the air kerma calibration factor, the air kerma calibration factor of 192 Ir source was calculated by ^60Co T rays and the effective energy of the 250 kV X ray beam. The scatter correction factor was given by the shadow shield experiment for the walls, the floor, the air and the measuring holder, the correction factors were given for the attenuation of primary photons in air and the electrons entering the air cavity are mainly generated in the inner wall of the chamber by 1079 report in IAEA. Results Two measuring methods were used for ^192 Ir source under same environment condition, the ion-chamber and well-type chamber values are 1.584 × 10^11 Bq and 1.561 ×10^11 Bq respectively, and the relative deviation from them is within 1.4%. Conclusions The air kerma measurement of ^192Ir source the ion-chamber with is not depended on the source geometry （ point source, line source etc）, the size and the material of shell, the shape, the quality of materials and the size of the chamber. The uncertainty error of the air kerma is lessin comparison to the air exposure.

关 键 词：后装治疗机 指形电离室 ^192Ir源参考空气比释动能 

分 类 号：R144[医药卫生—公共卫生与预防医学]