加速器机载kV锥形束CT有效剂量的分析

目的 分析医用直线加速器机载kV锥形束CT扫描过程中患者的有效剂量随扫描条件的变化。方法 用PTW TM30009电离室分别在T40017头模和T40016躯干模体中,改变XVI锥形束CT的管电压、毫安秒、准直器以及机架旋转范围等参数测量加权CT剂量指数,计算相应的剂量长度乘积和有效剂量。结果 kV锥形束CT的加权剂量指数和有效剂量随管电压呈二次方变化,随毫安秒线性变化,与准直器以及机架旋转范围密切相关。临床常用条件下,kV锥形束CT单次扫描的剂量长度乘积和有效剂量低于参考剂量水平。结论 锥形束CT扫描过程中患者接受的有效剂量与扫描条件密切相关。锥形束CT扫描时,应该根据患者的解剖部位合理选择成像参数,最大限度减少患者接受剂量。

Effective dose evaluation for linac-integrated kV cone beam CT

Objective To evaluate the variations of effective doses with the preset scanning parameters from linac-integrated kV cone beam CT (CBCT).Methods Weighted CT dose index (CTDI_W) were measured with PTW TM30009 CT ion chamber in head phantom and body phantom, respectively, for different combinations of tube voltage, mAs, collimator and gantry rotation range. Dose length products (DLP) were derived from CTDI_W and effective doses (E) were calculated by the DLP and E_DLP.Results CTDI_W and effective dose had the quadratical relationship with tube voltage, depending linearly on product of tube current and exposure time. Effective dose had close relationship with the collimator and the gantry rotation range. Both the DLP and ED for CBCT were lower than the reference dose level recommended for conventional CT.Conclusions Effective dose from CBCT has a close relationship with the scanning parameters. Optimal imaging parameters should be chosen according to the patient's anatomy to reduce patient dose.