加速器机载锥形束CT输出量及稳定性分析

Radiation Output Evaluation of Kilovoltage Cone Beam CT Unit

目的分析医用电子直线加速器机载kV级锥形束CT的输出剂量及其稳定性。方法用Unidos剂量仪和0.6cc电离室在空气中对Synergy机载的XVIkV级锥形束CT的空气比释动能、剂量输出稳定性、百分深度剂量进行测量。结果拍片模式下XVI空气比释动能随管电压呈二次方变化;空气比释动能随管电流和曝光时间线性变化;透视模式下,空气比释动能随图像桢数线性变化。输出剂量的重复性以及随机架角度的波动小于±1%。体模中百分深度剂量随管电压增加而变大。结论锥形束CT的剂量输出比较稳定,但随成像参数的设置变化范围大。临床应用时需要合理选择曝光条件,尽量减少患者接受的剂量。

Objective To evaluate the radiation output and stability of linac-integrated kV cone beam CT unit. Methods Air kermas in radiographic mode were measured with 0.6cc ion chamber and Unidos electrometer for Synergy-integrated XVI kV cone beam CT unit. Air kermas vs image frames were measured in fluoroscopic mode. Output stability and depth doses were measured. Results The air kerma increased quadratically with the increased tube voltage, while increasing linearly with the tube current, exposure time, and number of frames. The radiation output stability and its change with the gantry angle were within ± 1%. The percentage depth dose increased with higher tube voltage. Conclusion The radiation output of XVI is stable. The radiation outputs change considerably with the preset parameters. Parameters should be optimally chosen to reduce the patient dose.