Guaranteed performance of individual control chart used in gamma passing rate-based patient-specific quality assurance

Guangjun Li; Qing Xiao; Guyu Dai; Qiang Wang; Long Bai; Xiangbin Zhang; Xiangyu Zhang; Lian Duan; Renming Zhong; Sen Bai

doi:10.1016/j.ejmp.2023.102581

Guaranteed performance of individual control chart used in gamma passing rate-based patient-specific quality assurance

Phys Med. 2023 May:109:102581. doi: 10.1016/j.ejmp.2023.102581. Epub 2023 Apr 19.

Authors

Guangjun Li¹, Qing Xiao¹, Guyu Dai¹, Qiang Wang¹, Long Bai¹, Xiangbin Zhang¹, Xiangyu Zhang¹, Lian Duan², Renming Zhong¹, Sen Bai³

Affiliations

¹ Radiotherapy Physics & Technology Center, Cancer Center, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China.
² Department of Radiation Oncology, Perelman School of Medicine, University of Pennsylvania, Philadelphia 19104, United States.
³ Radiotherapy Physics & Technology Center, Cancer Center, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China; Department of Radiation Oncology, Cancer Center, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China. Electronic address: baisen@scu.edu.cn.

PMID: 37084678
DOI: 10.1016/j.ejmp.2023.102581

Abstract

Purpose: To assess the effect of sampling variability on the performance of individual charts (I-charts) for PSQA and provide a robust and reliable method for unknown PSQA processes.

Materials and methods: A total of 1327 pretreatment PSQAs were analyzed. Different datasets with samples in the range of 20-1000 were used to estimate the lower control limit (LCL). Based on the iterative "Identify-Eliminate-Recalculate" and direct calculation without any outlier filtering procedures, five I-charts methods, namely the Shewhart, quantile, scaled weighted variance (SWV), weighted standard deviation (WSD), and skewness correction (SC) method, were used to compute the LCL. The average run length (ARL₀) and false alarm rate (FAR₀) were calculated to evaluate the performance of LCL.

Results: The ground truth of the values of LCL, FAR₀, and ARL₀ obtained via in-control PSQAs were 92.31%, 0.135%, and 740.7, respectively. Further, for in-control PSQAs, the width of the 95% confidence interval of LCL values for all methods tended to decrease with the increase in sample size. In all sample ranges of in-control PSQAs, only the median LCL and ARL₀ values obtained via WSD and SWV methods were close to the ground truth. For the actual unknown PSQAs, based on the "Identify-Eliminate-Recalculate" procedure, only the median LCL values obtained by the WSD method were closest to the ground truth.

Conclusions: Sampling variability seriously affected the I-chart performance in PSQA processes, particularly for small samples. For unknown PSQAs, the WSD method based on the implementation of the iterative "Identify-Eliminate-Recalculate" procedure exhibited sufficient robustness and reliability.

Keywords: Gamma passing rate; Individual control chart; Patient-specific quality assurance; Sample size; Sampling variability; Statistical process control.

MeSH terms

Humans
Quality Assurance, Health Care*
Reproducibility of Results