ESTRO 2025 - Abstract Book

S1981

Clinical - Urology

ESTRO 2025

2067

Digital Poster Stereotactic Ablative Radiation (SAR-PROST) for localized prostate cancer, 32 Gy in four fractions: First clinical trial results.

Ines Ollinger, Julia García, Oscar Muñoz, Blas David Delgado, Patricia Cabrera Radiation Oncology, Hospital Universitario Virgen del Rocio, Seville, Spain

Purpose/Objective: Stereotactic body radiation therapy (SBRT) with 32 Gy in 4 fractions in patients with low-risk or favorable intermediate-risk prostate cancer provides an effective therapeutic response, comparable to conventional radiation therapy, with an acceptable and potentially lower toxicity profile. To evaluate the safety, complication rates, and tumor response (via prostate-specific antigen levels) of SBRT in low to intermediate-risk localized prostate cancer patients, demonstrating the feasibility of this ablative approach Material/Methods: A Phase I/II study of high dose SBRT for low-intermediate risk prostate cancer using 32 Gy in 4 fractions, 2 fraction/week. Corresponding to a DBE of 202.7 Gy (α/β = 1.5 Gy) for prostate, and a DBE of 117 Gy, for OAR’s (α/β = 3Gy). Genitourinary (GU) and Gastrointestinal (GI) toxicity by CTAE v4/EORTC-RTOG of side effects were recorded at each follow-up evaluation after treatment. In addition, PSA evaluation was requested 90 days after completion of radiotherapy and every 6 months at every follow-up. Results: This study included 32 patients treated at a tertiary hospital (Hospital Universitario Virgen del Rocío, Seville, Spain) between 2022 and 2024. The mean age was 71.78 years (range 53-83). Of the participants, 87.5% had an ECOG performance status of 0, and 12.5% had a status of 1. Most patients were diagnosed with Gleason 3+3 (84.4%), and staged as T1c (81.3%) and T2a (18.7%). The mean prostate volume was 35 cc, and 12.5% received semestral androgen deprivation therapy. Acute toxicity was minimal, with grade 1 GU toxicity in 21.9% and GI toxicity in 9.4%. Grade 2 GU toxicity was observed in 6.3%, and no grade 3 or higher toxicity occurred. The mean PSA at diagnosis was 6.33 ng/ml. Follow-up PSA levels were 1.43 ng/ml at 3 months (30/32), 1.08 ng/ml at 6 months (23/32), 0.62 ng/ml at 12 months (18/32), 0.27 ng/ml at 18 months (7/32), and 0.36 ng/ml at 24 months (2/32), (p < 0.001). The median International Prostate Symptom Score (IPSS) improved from 2.5 at diagnosis to 1 post-treatment (p < 0.001). Conclusion: SBRT for localized prostate cancer was well-tolerated, with minimal acute and late toxicity, demonstrating feasibility and efficacy. Further studies are required to confirm these findings and evaluate their broader clinical applicability.

Keywords: Prostate Cancer, SBRT, Toxicity