Post-prostatectomy magnetic resonance-guided adaptive salvage radiotherapy: early toxicity and biochemical outcomes from a prospective single center cohort.

Abstract

PurposeMagnetic resonance-guided adaptive radiotherapy (MRgART) may support daily anatomical adaptation in salvage post-prostatectomy radiotherapy (sPPRT). This prospective single-center cohort reports early clinician-assessed toxicities and biochemical outcomes following post-prostatectomy MRgART.MethodsPatients ≥6-months post-radical prostatectomy with positive margins, biochemical recurrence, and/or PSMA-PET/MRI-detected local or nodal recurrence were prospectively recruited to undergo MRgART to the prostate bed +/- pelvic lymph node irradiation. Patients were treated using a daily Adapt-to-Shape (ATS) workflow. PSA levels and clinician-reported gastrointestinal (GI) and genitourinary (GU) toxicities were recorded at baseline, 3, 6, and 12 months post-treatment and at most recent clinical follow-up.ResultsFifty-one patients underwent salvage post-prostatectomy MRgART. Prescriptions included 52.5 Gy/20 fractions, 55 Gy/20 fractions, 64 Gy/32 fractions, 66 Gy/33 fractions, 68 Gy/34 fractions, or 70 Gy/35 fractions. A simultaneous integrated boost (SIB - additional 4.0-12.5 Gy) was delivered in 24 patients based on PSMA-PET and/or MRI findings. Median follow-up was 20.8 months (95% CI 17.8-34.1 months). At 3 months, 47% developed acute GU toxicity (39% grade 1; 8% grade ≥2). At 12 months, 25 patients reported GU toxicity (40% grade 1; 10% grade ≥2). GI toxicities were 12% acutely and 12% at 12 months. In exploratory subgroup analysis, no statistically significant toxicity difference was observed between patients receiving SIB and those not receiving SIB. Excluding 20 patients receiving ADT, PSA measurements demonstrated a median 95.2% reduction at 3 months post-treatment.ConclusionsPost-prostatectomy MRgART, with or without PSMA-PET/MRI-guided SIB, was feasible in this prospective single-center cohort and was associated with favourable early clinician-reported toxicity. SIB was not associated with a significant increase in early or late toxicity in exploratory analysis. Longer follow-up, reporting, patient-reported outcomes, and larger comparative studies are required to confirm durability of toxicity outcomes and define longer-term biochemical control.