统计过程控制方法在加速器日常输出剂量稳定性中的研究

目的:运用统计过程控制(SPC)方法研究医用直线加速器6 MV X射线输出剂量稳定性。方法:使用PTW QUICKCHECK webline晨检仪采集湘雅常德医院Varian Trilogy加速器2019年1月12月257个工作日的6 MVX射线的中心轴输出剂量,使用SPC方法绘制均值-极差控制图(X-R图),将样本大小设定为2,观察129个样本点分布情况并计算过程能力指数(CP和CPK)判断加速器6 MVX射线输出剂量稳定性情况。结果:129个样本点中存在3个超过上控制线的数据异常点(119号、121号以及122号),提示物理师在此时间段内需人为干预调整输出剂量,过程能力指数CP=1.48和CPK=1.35,表明加速器6 MVX射线中心轴输出剂量在整个测量过程中处于稳定可控水平。结论:SPC方法可以实现对医用加速器6 MV X射线输出剂量的日常运行监测评估,为加速器质量管理提供信息参考依据,保证加速器运行处于安全稳定状态。

Statistical process control method in evaluating the stability of daily output dose of linear accelerator

Objective To study the stability of the 6 MV X-ray output dose of linear accelerator using statistical process control(SPC) method.Methods PTW QUICKCHECK webline was used to collect the 6 MV X-ray central-axis dose of the Varian Trilogy accelerator in Xiangya Changde Hospital within 257 working days during January to December 2019.SPC method was used to draw the mean-range control chart(X-R chart).The distribution of 129 sample points was obtained with the sample size of 2,and the process capability indexes(Cp and CPK to determine the stability of output dose of the accelerator were calculated.Results Three out of 129 sample points exceeded the upper control line(points 119,121 and 122),which remaindered the physicists to adjust the output dose during these periods.The calculated Cp=1.48 and CPK=1.35 indicated that the 6 MV X-ray central-axis dose of the accelerator was stable and was at a controllable level during the measurement.Conclusion SPC method can be used to monitor and evaluate the stability of daily output dose of linear accelerator,thereby providing critical information for quality management and ensuring the safe and stable operation of linear accelerator.