Clinical experience with an online adaptive radiotherapy for prostate cancer: successful treatment time optimization

BACKGROUND: Online adaptive radiotherapy (oART) can provide dosimetric advantages by accounting for daily anatomic changes, potentially improving target coverage and sparing of organs at risk. However, clinical adoption is sometimes limited by concerns over increased per-session treatment time. In this single-center study, we present 1.5 years of clinical experience focused on reducing the oART session time for prostate cancer patients. METHODS: We analyzed 1366 oART sessions from 69 prostate cancer patients treated on a Varian Ethos system between July 2023 and December 2024. We recorded (i) total session time - time between patient entry and exit from the treatment room, and (ii) adaptation time - time from start of the daily cone-beam-CT acquisition to completion of contour review/correction. We assessed the effects of two time-saving measures: automated contouring of the posterior rectal wall and installation of Varian HyperSight imaging. Statistical comparisons used the Mann-Whitney U test. RESULTS: Automated posterior rectal wall contouring decreased mean adaptation time from 16.0 to 10.5 min ([Formula: see text]). Installation of HyperSight reduced mean total session time from 25.8 to 23.3 min ([Formula: see text]); the adaptation component improved by 0.5 min but not statistically significant ([Formula: see text]). We achieved a total session time of [Formula: see text] min for 93% of sessions. CONCLUSIONS: Cone-beam-CT-guided oART is feasible in routine prostate cancer practice. Our findings indicate that a 30-minute time slot is sufficient for most adaptive prostate cancer treatments, and a median total session time of 23 minutes can be reached through workflow and imaging optimization. Clinics considering oART should note that treatment time decreases with operator experience, and targeted measures can further reduce session duration.