Optimizing QACT Frequency in Proton Therapy: Analysis of Standard Guidelines Across Treatment Sites

Anatomical changes during proton therapy are typically monitored using quality assurance computed tomography (QACT) scans. However, excessive QACTs can increase patient burden, resource use, and health care costs. This study evaluates the impact of implementing standardized minimum QACT frequencies across treatment sites.

Adult patients treated with proton therapy before October 2024 at the Johns Hopkins Proton Therapy Center were reviewed. Head and neck (HN), thorax, and pelvis prostate patients were newly analyzed; cranium and breast guidelines were drawn from prior published work. Based on this, guidelines for minimum QACT frequency were established. The implementation impact was evaluated by comparing QACT usage and adaptive planning rates before (October 2019-April 2023) and after (August 2023-October 2024) guideline deployment. A 1-sided Student t-test was used to determine if the QACT rate was lowered after guideline implementation. A Wilcoxon signed rank test was used to determine if the adaptive planning rate was different before and after guideline implementation.

A total of 681 patients were analyzed prior to guideline implementation and 381 patients afterward. Guidelines were developed for breast, cranium, HN, thorax, and pelvis prostate sites. Following guideline implementation, QACT frequency significantly decreased overall (median reduced from 3 to 2 per patient, P < .0001), and specifically for cranium (P = .008), HN (P = .0009), and pelvis prostate (P < .0001) patients. Adaptive therapy rates were not significantly different between cohorts (P = .22), supporting that reduced QACT use did not compromise identifying needed treatment adaptations. CBCT was effective in identifying anatomical changes that prompted adaptive replanning in pelvis prostate patients.

Establishing standard minimum QACT frequencies led to a significant reduction in the number of QACTs performed across several treatment sites. These findings support the utility of structured QACT guidelines to enhance resource efficiency and reduce patient burden in proton therapy.