2416 - Salvage Proton Therapy after Primary Cryosurgery or HIFU for Prostate Cancer

Purpose/Objective(s): 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/Methods: Outcomes were assessed for thirty-one patients who underwent salvage PT at our institution between 2007 and 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, 70.2–82.0) delivered at 1.8–2 CGE per fraction. Androgen deprivation therapy was administered to 12 patients (38.7%) for a median of 7 months (range, 6–24). Freedom from biochemical failure (FFBF) was defined per the Phoenix criteria. Freedom from regional failure (FFRF) and distant failure (FFDF) were 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 the Common Terminology Criteria for Adverse Events Version 5.0. 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: The median follow-up time was 8.0 years (range, 1.9–13.5). The 5- and 10-year FFBF rates were 72.4% and 64.7%, respectively. 5- and 10-year overall survival rates were 86.0% and 71.1%. At 5 and 10 years, FFRF was 83.3% and 73.7%. Two patients experienced distant failure. One late grade 3 hematuria occurred (3.2%) requiring transfusion, and two late grade 2 rectal hemorrhages occurred (6.4%) requiring formalin and anusol suppositories, respectively. Two patients experienced a new skin cancer outside the treatment field, one with melanoma on the chest and one with squamous cell carcinoma on the head and forearm. Median EPIC domain and IPSS scores remained stable from pre-PT through five years after treatment end. Urinary: 95.5 pre-PT to 95.2 five years post-PT, Bowel: 96.4 to 98.2, Sexual: 25.3 to 24.3, IPSS: 6.5 to 6.0.

Conclusion: These long-term results demonstrate that salvage PT following CS or HIFU provides acceptable biochemical control with low toxicity and minimal impact on reported quality of life. These profiles compare favorably to historical prostate ablation salvage outcomes. Future studies should investigate dose escalation and multi-center collaborations to optimize treatment strategies for recurrent prostate cancer.