Background: Due to no corresponding action limits for some new daily QA items , limits of the monthly or annual QA procedures have to be used for daily QA program at present. The general purpose of this paper is to discuss whether it is feasible to do so.
Methods: 3 groups daily quality control process during 2017-2019 performed with Daily QA3 were analyzed using SPC. In Calculation of capability indices for output, daily QA tolerance ±3% in the TG142 was used as specification limit, while for flatness and symmetry, annual QA tolerance ±1% was used. An appropriate number of data points were analyzed , capability indices (Cp, Cpk, Cpm and Cpmk) were calculated, and customized tolerance and action limits were established for each process. Meanwhile, the locations of the UCL、CL、LCL in I-MR charts of daily QA performed by 5 therapists in turns were compared with that of daily QA performed by only one physicist during the same period .
Results: Process capability indices of output were all ≥1, some were even up to 3-4. While, for symmetry, most of them failed to meet the requirements. For the same daily QA item, the calculated customized limit of different quality control processes were quite different. For the daily QA performed with only one physicist, the range of UCL and LCL was smaller or the central line was closer to the target value 0 in I-MR charts.
Conclusions: It is necessary to establish customized limits for daily QA program performed with Daily QA3, because customized limits and improved operation constancy both can improve the daily quality control level.