External beam radiation therapy for salvage after focal therapy as primary treatment in prostate adenocarcinoma.

e17153 Background: Focal therapy (FT) for prostate adenocarcinoma (PCa) aims to minimize adverse effects while achieving tumor control. While FT is becoming more prevalent, there is no consensus on treatment after FT failure. The goal of this study was to measure the toxicity and oncological outcomes of external beam radiation therapy (EBRT) after cryosurgery (CS) or high-intensity focused ultrasound (HIFU) to evaluate its role as a salvage treatment option for FT failure. Methods: Institutional databases were queried to identify patients diagnosed with PCa from 2002 to 2024 who were treated with CS or HIFU as the initial treatment. Patients who underwent intensity-modulated radiation therapy (IMRT) or proton therapy (PT) for recurrent localized PCa were included. Patients received concurrent androgen deprivation therapy (ADT) as recommended. Primary outcomes were acute and late genitourinary (GU) and gastrointestinal (GI) toxicity from EBRT using the modified Radiation Therapy Oncology Group (RTOG) scale. Acute and late toxicities were defined as events occurring during and up to 3 months after EBRT and after 3 months, respectively. Secondary outcomes were biochemical recurrence-free survival (bFS), metastasis-free survival (MFS), and overall survival (OS). Biochemical recurrence was defined as a PSA increase of ≥2 ng/mL above the nadir. Toxicity outcomes were reported using descriptive statistics, and survival outcomes were analyzed using Kaplan-Meier analysis. Results: 36 patients were included in this study (23 CS, 12 HIFU, and 1 both). 28 patients received IMRT and 8 patients proton therapy. 30 patients underwent confirmation biopsy before the radiation therapy with the following Gleason scores: 7 (3+4) in 15 patients, 7 (4+3) in 6 patients, 8 (4+4) in 10 patients, ≥9 in 3 patients. The median dose was 76 Gy (range 72-79.2 Gy) in 1.8 Gy (24 patients) or 2.0 Gy (12 patients) per fraction. 32 patients received ADT with radiation for a median duration of 6 months (range 4-24). Median follow-up period was 38 months (IQR 20.5–61.8). Acute genitourinary (GU) toxicities of grade 1 and grade 2 were observed in 11 patients (30.6%) and 7 patients (19.4%), respectively. Acute gastrointestinal (GI) toxicities of grade 1 and grade 2 were reported in 7 patients (19.4%) and 1 patient (2.8%), respectively. There were no grade 3 or higher acute GU or GI toxicities seen. Late GU toxicities included grade 1 and grade 2 in 2 patients each (8.3%), with grade 3 late GU toxicity (hematuria) occurring in 1 patient (4.2%). Grade 1 late GI toxicity was observed in 2 patients (8.3%). There was no grade 2 or higher late GI toxicity. bFS, MFS, and OS were 94.1%, 100%, and 100% at 5 years and 70.6%, 83.3%, and 75.8% at 10-years, respectively. Conclusions: Our data demonstrate that EBRT after FT failure is a safe and effective treatment. Studies with larger patient cohorts are required to further validate the use of EBRT as a salvage treatment.