统计过程控制方法在后装^(192)Ir放射源空气比释动能强度验证中的应用

Application of statistical process control method in verification of air-kerma strength of^(192)Ir brachytherapy source

目的:运用统计过程控制(SPC)方法分析研究后装^(192)Ir放射源空气比释动能强度(Sk)验证的精准性及稳定性。方法:首先使用PTW SOURCECHECK 4π井型电离室按照国标WS 262-2017的要求对^(192)Ir放射源Sk进行质控验证。再通过Minitab软件对测量值和计划系统计算值之间的偏差绘制均值-极差图,计算相应的上下控制线UCL、LCL及其过程能力指数Cp、Cpk,并判断该方法的精准稳定性。结果:25组偏差值的分布为-1.584%~0.915%,达到了WS 262-2017中小于±5%、AAPM-TG43中小于±3%的限值要求。各分组的均值都处于-1.518%~0.973%的上下控制线范围内,Cp、Cpk取值分别为1.66、1.51,整个测量过程处于较稳定的控制水平内。结论:SPC方法能够对^(192)Ir放射源Sk的质控验证结果即偏差值进行较好的监测与评估,发现其中的异常点,确保了后装治疗中剂量传递的准确性。

Objective To analyze the accuracy and stability of statistical process control(SPC)method in the verification of the air-kerma strength(Sk)of^(192)Ir brachytherapy source.Methods After completing the quality control verification of^(192)Ir radioactive source Sk with PTW SOURCECHECK 4πwell-type ionization chamber according to the requirements of national standard WS 262-2017,Minitab software was used to draw the mean value-range chart for the deviation between the measured value and the calculated value of the planning system.The corresponding upper and lower control lines and process capability indexes(Cp,Cpk)were calculated for evaluating and the accuracy and stability of SPC method.Results The distribution of the deviation values in the 25 groups ranged from-1.584%to 0.915%,reaching the limit requirements of less than±5%in WS 262-2017 and less than±3%in AAPM-TG43.The mean values of each group were within the range of upper and lower control lines(from-1.518%to 0.973%).Cp and Cpk were 1.66 and 1.51,respectively.The whole measurement process was at a relatively stable control level.Conclusion SPC method can better monitor and evaluate the quality control verification results(deviation values)of^(192)Ir brachytherapy source Sk,and find out the abnormal points,thereby ensuring the accuracy of dose delivery in brachytherapy.