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Statistical process control and process capability analysis for non-normal volumetric modulated arc therapy
Qing Xiao1, Sen Bai1, Guangjun Li1
1Department of Radiation Oncology, Cancer Center and State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China.
Medical Physics
|July 18, 2020
Summary
Statistical process control (SPC) and process capability analysis (PCA) are crucial for quality assurance in volumetric modulated arc therapy (VMAT). This study found non-normal-based methods are more reliable for VMAT patient-specific quality assurance (PSQA) processes, unlike conventional methods that inflate false alarms.
Area of Science:
- Medical Physics
- Radiation Oncology
- Quality Assurance
Background:
- Statistical process control (SPC) and process capability analysis (PCA) are recommended for intensity-modulated radiotherapy (IMRT)/volumetric modulated arc therapy (VMAT) patient-specific quality assurance (PSQA).
- A comprehensive analysis of PSQA processes with non-normal distributions is currently lacking.
- This study addresses the need for robust statistical methods in VMAT PSQA.
Purpose of the Study:
- To investigate the application and effectiveness of SPC and PCA methods for non-normal IMRT/VMAT PSQA processes.
- To compare the performance of non-normal-based SPC/PCA methods against conventional methods in VMAT PSQA.
- To assess the reliability and accuracy of different statistical approaches for non-normal data in PSQA.
Main Methods:
- 1119 VMAT PSQAs were conducted on three beam-matched linear accelerators (linacs) using gamma analysis.
- Normality testing was performed using the Anderson-Darling statistic.
- Non-normal-based SPC and PCA methods were developed and compared with the conventional Shewhart method and conventional calculation of the capability index (Cpk).
Main Results:
- All three PSQA processes exhibited non-normal distributions (P < 0.005).
- Conventional methods showed significantly higher false alarm rates (0.83%–4.95%) and overestimated process capabilities compared to non-normal-based methods.
- The process capabilities of the three beam-matched linacs varied, highlighting the need for accurate assessment tools.
Conclusions:
- Conventional SPC and PCA methods are unreliable for non-normal VMAT PSQA, leading to increased false alarms and overestimated capabilities.
- Non-normal-based SPC and PCA methods provide more accurate and reliable assessments for non-normal PSQA processes.
- SPC and PCA are valuable tools for evaluating the performance of beam-matched linear accelerators in VMAT.
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