Published online Apr 24, 2026. doi: 10.5306/wjco.v17.i4.115851
Revised: December 10, 2025
Accepted: February 6, 2026
Published online: April 24, 2026
Processing time: 176 Days and 15.3 Hours
Patient-specific quality assurance (QA) is an essential component in the safe and precise delivery of radiotherapy, particularly in head and neck cancer cases where anatomical complexity and proximity to critical structures increase the risk of delivery deviations. As treatment techniques become more conformal and modu
To assess patient-specific QA performance, dosimetric accuracy, and long-term consistency using gamma analysis with statistical process control methods.
A retrospective analysis of intensity-modulated radiation therapy and volumetric modulated arc therapy head and neck treatment plans was performed using electronic portal imaging device-based gamma pass rates under global criteria. Individual and Moving Range charts were generated to assess QA stability and detect trends. Initial control limits were derived from 20 QA plans and validated on 350 QA plans. Tolerance limits (TL) and action limits (AL) were calculated. The resulting charts offered a robust framework for monitoring QA performance and identifying deviations.
The central line values decreased progressively with stricter gamma criteria, from 98.835% (3%/3 mm) to 94.4% (2%/2 mm). TL and AL narrowed correspondingly, with TL dropping from 97.869% to 93.672%. Exponentially Weighted Moving Average charts provided smoother detection of persistent small deviations compared to Individual and Moving Range charts, enhancing sensitivity. Across all criteria, QA processes remained statistically stable, although tighter thresholds reduced pass rates.
Gamma analysis is a reliable method for patient-specific QA in head and neck radiotherapy. The incorporation of statistical process control adds a valuable layer of continuous monitoring, supports site-specific tolerance/AL, and strengthens treatment accuracy.
Core Tip: This study shows that using gamma index-based patient-specific quality assurance, along with statistical process control, works well for head and neck radiotherapy. Long-term trends in dose delivery accuracy were tracked using Individual-Moving Range and Exponentially Weighted Moving Average charts, based on several global gamma index criteria. Even though stricter thresholds made it harder to pass, the quality assurance process stayed statistically stable, and statistical process control made it easier to find small differences sooner. This method helps make tolerance and action limits more reliable and makes treatment delivery more consistent overall.