Comprehensive Analysis of Single Institution, Patient-Specific IMPT QA Data across 18 Disease Sites
Abstract
Purpose
To evaluate patient-specific quality assurance (PSQA) measurements across 18 disease sites treated with intensity modulated proton therapy (IMPT) from January 2024 through August 2025.
Methods
Retrospective analysis of 4,949 patient PSQA measurements across 18 disease sites was performed. High-volume sites (>60 measurements) included prostate+lymph nodes(P+LN) (including prostate-only(P), prostate bed(PBed), PBed+LN and PET positive nodes (PET+)] (1,049), head & neck(H&N) (886), breast (604), brain (599), craniospinal irradiation(CSI) (530), lung (334), pelvis (292), mediastinum(MDSTN) (166), esophagus(ESO) (120), abdomen(ABD) (92), liver (62), and anal (61)—representing 4,795 PSQA measurements across 12 disease sites. Disease sites with fewer than 60 measurements during the collection period included Spine (54), Base of Skull(BOS) (34), Extremity (32), Gynecological(GYN) (14), Grid therapy(Grid) (11) and Accelerated Partial Breast Irradiation(APBI) (9). Gamma index analysis (3%/3mm criterion) was collected for all PSQA measurements. Minimum gamma, mean gamma with 95% confidence intervals, and distribution statistics were computed for each treatment site and compared between 2024 and 2025.
Results
Mean gamma indices across all 18 sites ranged from 97.6% to 99.7%, with overall institutional mean of 99.0%. The mean gamma pass rate is 99.6% for CSI, 99.3% for P+LN, 99.3% for pelvis, and 99.3% for ABD. Low-volume sites (≤60 measurements; 6 sites, 154 PSQAs) showed comparable gamma performance (mean range: 97.6%–99.7%). Minimum gamma values exceeded 90% for all measurements analyzed. Year-over-year comparison revealed stable gamma distributions with no statistically significant degradation in dose verification accuracy (W=25.5, p=0.3013 : p > 0.05, Wilcoxon test).
Conclusion
This large-scale analysis demonstrates consistent and reliable PSQA performance across 18 distinct proton therapy treatment sites, supporting high-confidence dose delivery verification. Stability of gamma index metrics across the study period validates institutional PSQA protocols and treatment planning practices. These findings provide benchmarking data for multi-site proton therapy programs and support continued clinical expansion with maintained quality standards.