Postoperative or Salvage Proton Radiotherapy for Prostate Cancer After Radical Prostatectomy

Purpose: Postprostatectomy radiation improves disease control, but limited data exist regarding outcomes, toxicities, and patient-reported quality of life with proton therapy. Method and Materials: The first 102 patients who were enrolled on an outcome tracking protocol between 2006 and 2017 and treated with double-scattered proton therapy after prostatectomy were retrospectively reviewed. Eleven (11%) received adjuvant radiation, while 91 (89%) received salvage radiation. Seventy-four received double-scattered proton therapy to the prostate bed only. Twenty-eight received a double-scattered proton therapy prostate-bed boost after prostate-bed and pelvic-node treatment. Eleven adjuvant patients received a median dose of 66.6 GyRBE (range, 66.0–70.2). Ninety-one salvage patients received a median dose of 70.2 GyRBE (range, 66.0–78.0). Forty-five patients received androgen deprivation therapy for a median 9 months (range, 1–30). Toxicities were scored using Common Terminology Criteria for Adverse Events v4.0 criteria, and patient-reported quality-of-life data were reviewed. Results: The median follow-up was 5.5 years (range, 0.8–11.4 years). Five-year biochemical relapse-free and distant metastases-free survival rates were 72% and 91% for adjuvant patients, 57% and 97% for salvage patients, and 57% and 97% overall. Acute and late grade 3 or higher genitourinary toxicity rates were 1% and 7%. No patients had grade 3 or higher gastrointestinal toxicity. Acute and late grade 2 gastrointestinal toxicities were 5% and 2%. The mean values and SDs of the International Prostate Symptom Score, International Index of Erectile Function, and Expanded Prostate Cancer Index Composite bowel function and bother were 7.5 (SD = 5.9), 10.2 (SD = 8.3), 92.8 (SD = 11.1), and 91.2 (SD = 6.4), respectively, at baseline, and 12.1 (SD = 9.1), 10.1 (SD = 6.7), 87.3 (SD = 18), and 86.7 (SD = 13.8) at the 5-year follow-up. Conclusion: High-dose postprostatectomy proton therapy provides effective long-term biochemical control and freedom from metastasis, with low acute and long-term gastrointestinal and genitourinary toxicity.