Outcomes of Salvage Proton Therapy After Primary CS or HIFU for Recurrent Localized Prostate Cancer

Purpose To report long-term outcomes for patients treated with salvage proton therapy (PT) following primary cryosurgery (CS) or high-intensity focused ultrasound (HIFU) for recurrent localized prostate cancer. Materials and Methods We assessed 31 patients who underwent salvage PT at our institution between 2007-2017 for biopsy-confirmed, localized prostate cancer recurrence after CS (n=21) or HIFU (n=10). Patients had no evidence of nodal or distant metastases. Median PT dose was 74 CGE (range, 70.2–82) delivered at 1.8–2 CGE/fraction. Androgen deprivation therapy was administered to 12 patients for a median of seven months (range, 6–24). Freedom from biochemical failure (FFBF) was defined per the Phoenix criteria. Freedom from regional failure (FFRF) and distant failure (FFDF) defined as the absence of radiologic or clinical evidence of metastatic disease in pelvic lymph nodes and distant to pelvic lymph nodes, respectively. Toxicities were graded using CTCAEV5. Patient-reported outcomes were assessed using the International Prostate Symptom Score (IPSS) and Expanded Prostate Index Composite (EPIC). Kaplan-Meier estimates were used to calculate survival and oncologic outcomes. Results Median follow-up was 8.0 years (range, 1.9–13.5). The 5- and 10-year FFBF rates were 72.4% and 64.7%, respectively. Overall survival at 5- and 10-years was 86.0% and 71.1%, respectively. At 10-years, FFRF was 73.7% and FFDF was 96.8%. One late grade 3 hematuria occurred (3.2%), and two transient late grade 2 rectal hemorrhages occurred (6.4%). Median EPIC and IPSS scores remained stable from pre-PT through 5-years after treatment. Conclusion Our results demonstrate salvage PT as a safe and effective option following CS or HIFU with low toxicity and minimal impact on reported quality of life. PT outcomes are comparable with recent prostate cancer ablation salvage reports. Future studies should include multi-center collaborations to investigate elective pelvic nodal radiation to optimize treatment strategies for recurrent prostate cancer.