影像引导放疗中千伏特锥形束CT患者剂量的测量

Patient dose evaluation for kilovoltage cone beam CT in image-guided radiotherapy

目的测量医用直线加速器机载千伏特锥形束CT扫描过程中患者的剂量。方法用PTW TM30009电离室分别在空气中、T40017头部和T40016躯干模体中，改变XⅥ锥形束CT的管电压、管电流、准直器以及机架旋转范围等参数测量空气CT剂量指数和加权CT剂量指数，计算相应的剂量长度乘积，并与ACQSim模拟定位CT的结果进行比较。结果千伏特锥形束CT在空气中和模体中的剂量指数随管电压二次方变化，随管电流线性变化。加权剂量指数和剂量长度乘积与准直器以及机架旋转范围有关。临床常用条件下千伏特锥形束CT归一化的剂量指数比模拟定位CT小。结论CT剂量指数能反映成像过程中患者接受的剂量，测量方法简单、重复性好，应定期进行测量。锥形束CT扫描时应该合理选择成像参数，尽量减小扫描范围，最大限度减少患者接受剂量。

Objective To evaluate patient dose from linac-integrated kilovolt cone beam CT （CBCT） imaging in image-guided radiotherapy. Methods Air CT dose index （CTDIair） and weighted CT dose index （CTDIw ） were measured with PTW TM30009 CT ion chamber in the air, in T40017 head phantom and T40016 body phantom, respectively. During the measurement, different combinations of tube voltage, current, exposure time per frame, collimator, and gantry rotation range of XⅥ CBCT were used. Dose length products （DLP） were subsequently calculated. Normalized CTDI was then compared to ACQSim simulator CT. Results Both CTDIair and CTDIw depended quadratically on the voltage, while linearly on mAs. CTDIw and DLP had close relation with the collimator and the gantry rotation range. Normalized CTDIw for X VI CBCT under routine clinical condition was lower than that of ACQSim simulator CT . Conclusions CTDIw, being convenient and reliable for measurement, can be used to assess the patient dose during CBCT imaging. Regular measurement should be performed in QA ＆ QC program. Optimal image parameters should be chosen to reduce the scanning range and patient dose.