Post-prostatectomy Magnetic Resonance-guided Radiotherapy on a 1.5 Tesla Magnetic Resonance Integrated Linear Accelerator: Feasibility, Toxicity, and Preliminary Clinical Outcomes.

Introduction: This study aimed to prospectively investigate magnetic resonance (MR)-guided radiotherapy (MRgRT) for post-prostatectomy prostate cancer and report preliminary clinical outcomes.

Methods: All included patients underwent salvage or adjuvant adaptive MRgRT on a 1.5T MR integrated linear accelerator (MR-LINAC). Gastrointestinal and genitourinary toxicities were assessed. The primary endpoint was the progression-free survival (PFS) rate estimated by Kaplan-Meier (KM) survival analysis. A progression event was defined as the first occurrence of biochemical failure, radiological progression, or death. Secondary endpoints were biochemical failure-free survival (bFFS) rate, radiological PFS (rPFS) rate, and ≥G2 adverse events.

Results: Thirty post-prostatectomy patients were enrolled and followed (median follow-up: 32.0 months; 3.0-48.1 months). Three patients had biochemical failure during follow-up. One patient developed pelvic node metastases. All patients were alive. The estimated PFS rates were 96.4% (95% confidence interval [95%CI]: 89.8%-100.0%) at 2 years and 78.8% (95%CI: 61.3%-100%) at 3 years. The estimated bFFS rates were 96.4% (95%CI: 89.8%-100%) /86.6%(95%CI: 73.4%-100%) at 2/3 years, respectively. The corresponding rPFS rates were 100% at 2 years and 92.3% (95%CI: 78.9%-100%) at 3 years, respectively. There was only one acute G2 GI adverse event (1/30, 3.33%) of abdominal pain occurred. Two late G2 events (one rectal bleeding and one urinary frequency) were scored (2/30, 6.67%). No ≥G3 events were observed.

Conclusion: Our findings suggest the feasibility, excellent patient tolerance, and encouraging efficacy of post-prostatectomy MRgRT, extending our knowledge of the clinical outcomes of MRgRT and serving as a benchmark for future investigation.