3311 - Stereotactic Body Radiotherapy (SBRT) Re-Irradiation for Local Recurrence of Prostate Cancer: A Multi-Institutional Experience in Uruguay

Purpose/Objective(s): Local recurrence after definitive radiotherapy for prostate cancer (PCa) is a therapeutic challenge. In this scenario, re-irradiation with SBRT has emerged as a minimally invasive therapeutic alternative with curative intent in carefully selected patients. We evaluated the efficacy, survival outcomes, and toxicity of SBRT re-irradiation as a salvage strategy in a contemporary Uruguayan cohort.

Materials/Methods: We conducted a retrospective study of 71 patients previously irradiated with 77.4 Gy (40-80) at an age of 65 (51-86) years. Recurrence was confirmed by PET/TC_PSMA (98.6% of cases), MRI, or biopsy, and they were re-irradiated between 2018 and 2024. The median interval since previous radiation was 8.6 years (1.2-18.7). SBRT was administered using VMAT and daily CBCT-IGRT, with a standard dose of 35 Gy in 5 fractions on alternate days. Toxicity was classified using the CTCAE v5.0 and RTOG scales. Survival was calculated using Kaplan-Meier analysis.

Results: With a median follow-up of 3.3 years (9.3 months-6.4 years), the median age at the time of reirradiation was 73 years (57-89). Overall survival (OS) was 91.1% (95% CI: 84.6%-98.2%) at 2 years and 70.8% (95% CI: 58.6%-85.6%) at 5 years. Cancer-specific survival (CSS) was 96.8% (95% CI: 92.6%-100.0%) in 2 years and 85.0% (95% CI: 75.0%-96.4%) in 5 years. Local progression-free survival (LPFS) was 95.2% (95% CI: 89.9%-100.0%) in 2 years and 70.9% (95% CI: 55.1%-91.2%) in 5 years. Distant progression-free survival (DPFS) was 89.7% (95% CI: 82.7%-97.2%) in 2 years and 78.6% (95% CI: 68.0%-90.9%) in 5 years. PSA levels after SBRT showed a significant biochemical response (p < 0.001). Safety was a highlight: no patients (0%) experienced grade 3 acute or chronic toxicity in the gastrointestinal (GI) or genitourinary (GU) tract. Grade 2 acute dysuria and proctitis occurred in 5.0% of cases. Grade 2 chronic proctitis was observed in only 3.5% of patients. Sexual dysfunction (grade 3) occurred in 46.7% of patients, but these symptoms had already been documented at baseline prior to SBRT.

Conclusion: Salvage SBRT re-irradiation is an effective and safe option for local PCa recurrence, showing excellent long-term CSS and negligible high-grade toxicity. Our findings translate data into dialogue by proving that SBRT re-irradiation is not only clinically effective but a high-value, safe strategy that facilitates communication between specialists and patients in the management of local recurrence.