Daily quality control data analysis and process evaluation of linear accelerator

Abstract

Objective To analyze the quality control data of linear accelerator detected by Daily QA3 and to evaluate this quality control process using statistical process control. Methods After the calibrations of the accelerator and Daily QA3, Daily QA3 device was used to perform daily quality control by technicians and physicists and 100 groups and 30 groups of daily quality control data were collected. After the accelerator and Daily QA3 were re-calibrated, Daily QA3 device was utilized to perform daily quality control by technicians and 100 groups of the daily quality control data were repeatedly collected. The variations of normalized signal-to-noise ratio of quality control data collected after two calibrations were analyzed. The first 30 groups of daily quality control data measured by technicians and physicists were adopted to calculate the I-MR control chartsand compare the location of CL and the range of UCL and LCL. The process capability indices were calculated for three different quality control processes bytechnicians and physicists, respectively. Results For twice calibrations, normalized signal-to-noise ratio of quality control data significantly changed before 6 weeks, became stable between 6 and 8 weeks, and the changes became smaller after 8 weeks. For dose output measured by physicists, the rang of UCL and LCL was more narrow. In terms of flatness and symmetry, the location of CL was closer to zero. Regarding dose output and flatness, the process capability indices of three different quality control process were all satisfied ≥1, whereas unsatisfied for transverse symmetry. Conclusions The first 30-40 data points should be adopted to delineate I-MR control chart of the linear accelerator in daily quality control process. The quality control process should be completed by a fixed and small group of personnel and an optimal tolerance level should be customized. Key words: Linear accelerator; Quality control; Statistical process control; Control chart; Process capability index