Varian锥形束CT不同版本扫描协议的辐射剂量对比

Comparison of the radiation dose for different software versions of Varian cone-beam CT scanning protocols

放射治疗中,多次锥形束CT(Cone-beam CT,CBCT)扫描的累积辐射剂量不容忽视,对CBCT不同版本扫描协议(V1.4、V1.5、V1.6)的辐射剂量分析,可为临床应用中合理使用CBCT提供数据支持。按照美国医学物理学会(AAPM)111工作组建议的辐射剂量测量方法(TG111)使用加长型模体(长度为45 cm)和0.6 cm3指形电离室对Varian CBCT系统不同版本扫描协议的辐射剂量进行测量,根据TG111推荐的规范,计算得到CBCT的加权辐射剂量TG111W和归一化辐射剂量nTG111W。结果显示:V1.5版本(两种设备)扫描协议的加权辐射剂量整体高于另两个版本(盆腔协议除外),最大值为V1.5版本的高质量头协议(30.06mGy),最小值为V1.4版本的低剂量头协议(2.83 mGy);归一化辐射剂量差异均较小,最大差异在标准剂量头协议中(V1.4和V1.5(TrueBeam)的差异为1.33 mGy),最小差异在低剂量胸和盆腔协议中(V1.5(TrueBeam)和V1.6的差异均为0.01 mGy)。结果提示,各软件版本扫描协议的辐射剂量与管电压和曝光量等参数密切相关(曝光量影响最大),为了保证患者的安全,临床使用中需要根据使用扫描协议的不同,合理规划CBCT扫描的频次。

The cumulative radiation dose of multiple cone-beam computed tomography(CBCT)scanning cannot be ignored in radiotherapy.It can provide supporting data for the rational use of Varian cone-beam computed tomography in clinical practice by analyzing the radiation dose of different versions of CBCT scanning protocols(V1.4,V1.5 and V1.6).In accordance with the radiation dosimetry method(TG111)recommended by the American Association of Physicists in Medicine(AAPM)111 working group,an extended phantom(45 cm in length)and a 0.6 cm3 finger ionization chamber were used to perform the radiation dose measurement for different versions of the Varian CBCT system scanning protocols.According to the specifications recommended by TG111,the weighted radiation dose(TG111W)and the normalized radiation dose(nTG111W)of CBCT were calculated.The results showed that the weighted radiation dose of the V1.5 scanning protocol(in both equipment)was higher than that of the other two versions(except the pelvic protocol).The high-quality head protocol of the V1.5 version had the maximum dose(30.06 mGy),and the low-dose head protocol of the V1.4 version had the minimum dose(2.83 mGy).Minor differences were found among the protocols for the results of the normalized radiation dose;the standard-dose head protocol had the maximum difference(1.33 mGy;V1.4 vs.V1.5(TB)),and the low-dose thorax and pelvic protocols had the minimum difference(0.01 mGy;V1.5(TB)vs.V1.6).The results suggest that the radiation dose of each version of the scanning protocol is closely related to the parameters such as tube voltage and exposure(the maximum factor)and that frequency of the CBCT scanning needs to be planned reasonably according to the different scanning protocols used in clinical practice.