锥形束计算机断层扫描的剂量学研究

The Study on Dose Measurement for CBCT of XVI System

目的:探讨影像引导下放射治疗(IGRT)的锥形束计算机断层扫描(CBCT)产生的额外剂量,寻找合适的临床扫描方案,减少CBCT额外剂量对病人重要器官的影响。方法:用Elekta Synergy直线加速器的XVI系统,对临床扫描方案("头颈方案"和"盆腔方案")进行剂量测量。采用密度均匀的圆柱形模体,该模体在中央和四周共有5个电离室测量孔,测得这5点的绝对剂量后,引入加权CT剂量指数CTDIw参数评价扫描产生平均剂量。结果:(1)测量参数mAs对剂量影响较大;(2)测量平均剂量在0.1 cGy^5.39 cGy之间,使用"盆腔"方案在模体上测得的剂量最高;(3)采用不同滤过器F0和F1,剂量学上有明显差异,使用F0滤过器,测得剂量较F1大25%~30%。结论:为减少病人接受的额外剂量,对于儿童病人及头颈部病人,建议尽量使用头颈部扫描方案及F1滤过器;对于胸部和盆腔部扫描,也建议使用F1过滤器。

Objective：To explore a dose measurement method for CBCT scanning of XVI system.Methods：In the study,we measured clinical used protocols in our department（＂head and neck protocol＂ and ＂pelvis protocol＂）,uniform-density cylindri-cal acrylic phantom was used for all measurements.The phantom included ion chamber placement holes in the center and at periphery,absolute dose of the total 5 points can be separately achieved,computed tomography dose index（CTDIw） was used to evaluate average dose from the scan.Results：（1）The average dose is closely related to mAs;（2）The average dose ranges from 0.1 cGy to 5.39 cGy with the highest dose measured using the ＂pelvis＂ protocol with the phantom;（3）For different kinds of fil-ter,F0 and F1,dose difference is obvious.Conclusions：To reduce extra dose to patients,for pediatric as well as head and neck patients,it＇s advised to adopt ＂head and neck＂ protocol and F1 filter.For chest and pelvis scan,it＇s also advised to use F1 filter.