Author: Curtiland Deville, Rachel B. Ger, Heng Li, Todd R. McNutt 👨🔬
Affiliation: Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Johns Hopkins University 🌍
Purpose: Proton therapy patients receive quality assurance CT scans (QACTs) during treatment to verify dosimetric accuracy and determine adaptive therapy needs as proton treatments are highly sensitive to changes in patient setup or anatomy. However, excessive QACTs can lead to unnecessary radiation exposure and overburden CT simulators. This study aimed to investigate the QACT frequency in a clinical setting where daily CBCTs are acquired.
Methods: Patients treated between 2019-2023 were categorized into the following treatment sites: breast, cranium, head and neck, thorax, pelvis, and other. All patients were reviewed determining adaptive planning rates and timing of adaptive plans to develop guidelines for standard minimum QACT frequencies for each site that ensured needed adaptive plans were captured while not excessively acquiring QACTs. Prior to the guidelines, QACTs were per physician discretion or weekly. Patients treated after guideline implementation (up to 2024) were compared to before guidelines. QACT frequency was analyzed for each site, and one-sided t-tests were performed to assess significant reductions in QACTs following guideline implementation. Adaptive plan rates were also examined to ensure reduced QACTs did not compromise the detection of significant patient changes.
Results: A total of 679 patients were analyzed prior to guideline implementation and 381 patients afterward. Adaptive therapy rates did not significantly differ between the two groups (p=0.22). Significant reductions in QACT frequency were observed for breast (p=0.008), cranium (p=0.0009), and pelvis treatment sites (p<0.0001). No differences were found for thorax where the guideline recommended to maintain the QACT frequency. Overall, the median QACT frequency decreased by one scan, with a significant reduction in the overall distribution of QACTs (p<0.0001).
Conclusion: Optimized QACT frequency guidelines were implemented successfully across different treatment sites, reducing unnecessary radiation exposure without affecting adaptive therapy rates. These findings support improved patient safety and streamlined clinical workflow in proton therapy.