Jeff D. Winter

We report early toxicity outcomes after institutional implementation of prostate SBRT using 42.7 Gy in seven fractions delivered with either MR-guided adaptive SBRT (MRgSBRT) or CT-guided non-adaptive SBRT (CTgSBRT). Between July 2019 and May 2023, 216 patients received this regimen. Genitourinary (GU) and gastrointestinal (GI) toxicities were retrospectively assessed using the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. Most patients had intermediate-risk disease (86%), and 14% had high-risk disease. Median prostate volume was 40 mL, and median baseline International Prostate Symptom Score (IPSS) was 8 among patients with available data. MRgSBRT and CTgSBRT were used in 100 (46%) and 116 (54%) patients, respectively. At a median follow-up of 19 months, 12- and 24-month grade ≥ 2 GU toxicity rates were 20.0% and 18.2%, while grade ≥ 2 GI toxicity rates were 3.5% and 3.6%, respectively. No statistically significant platform-related differences were detected; however, these comparisons were exploratory and potentially confounded by nonrandomized platform selection, treatment era, rectal-spacer use, adaptive workflow and differing PTV margins. On univariable analysis, baseline GU symptoms were associated with higher 12-month grade ≥ 2 GU toxicity (OR, 3.68; 95% CI, 1.52–10.37; p = 0.007), while prostate-volume category was not significantly associated with this endpoint.

MR-guided adaptive radiotherapy (ART) enables daily plan optimization for prostate cancer but is resource-intensive. This study evaluated dosimetric and clinical outcomes following transition from radiation oncologist (RO)-led to radiation therapist (RTT)-led MR-guided ART. All prostate cancer patients treated with MR-guided ART on a 1.5T MR-linac were retrospectively reviewed. Consecutive RO-led (September 2019–November 2021) and RTT-led (April 2022–October 2023) cohorts were compared, excluding the actual transition period. Toxicities (CTCAE v5.0), dose–volume metrics from daily adapted plans, target volume variation, and biochemical recurrence-free survival (BRFS) were analyzed. A total of 166 patients were included (78 RO-led, 88 RTT-led; median follow-up 40 and 35 months). Dosimetric differences between the cohorts were statistically small (n = 2 vs. n = 0), likely reflecting higher baseline urinary dysfunction; no post-treatment differences persisted. Early biochemical outcomes were comparable, with 36-month BRFS of 93.5% (RO-led) and 95.0% (RTT-led). RTT-led MR-guided ART achieved comparable dosimetric quality and early biochemical outcomes to RO-led workflows with adverse advents that resolved in the long term. With structured training and a mature practice setting, RTT-led ART represents a scalable model to support future adaptive radiotherapy practice.