ESTRO 2025 - Abstract Book

S1974

Clinical - Urology

ESTRO 2025

1828

Digital Poster Acute Genitourinary and Gastrointestinal Toxicity and Quality of Life of a Novel SBRT Fraction Regimen for Organ Confined Prostate Cancer Chiara Chissotti 1,2 , Federica Ferrario 1,2 , Valeria Faccenda 3 , Riccardo Ray Colciago 2 , Denis Panizza 3,2 , Stefano Arcangeli 1,2 1 Department of Radiation Oncology, Fondazione IRCCS San Gerardo dei Tintori, Monza, Italy. 2 School of Medicine, Università degli Studi di Milano Bicocca, Milano, Italy. 3 Department of Medical Physics, Fondazione IRCCS San Gerardo dei Tintori, Monza, Italy Purpose/Objective: The aim of this prospective analysis is to assess treatment-related toxicity and patients' QoL of a novel fractionation regimen of prostate SBRT with radical intent. Material/Methods: Patients with organ confined prostate cancer (PCa), irrespective of the risk class and the prostate volume, received linac-based SBRT to the prostate ± seminal vesicles. The fractionation dose was 30 Gy in 3 fractions (EQD2 1.5 98.6 Gy, EQD2 3 78 Gy), administered every other day. All patients were positioned supine with an empty rectum and a filled bladder. A real-time 4D ultrasound monitoring of prostate movement during treatment delivery enabled 3 mm isotropic expansion from the CTV to the PTV. Alpha-blockers were administered to prevent side effects. Maximum acute toxicity was assessed using CTCAE v.5. Patient-reported outcomes and biochemical control were evaluated through IPSS, EPIC-CP, and IIEF questionnaires, as well as PSA serum levels at baseline and at 3-month of follow-up. Paired t-test was used to compare pre-treatment and post-treatment questionnaire scores, with MID established as a change in the questionnaire scores of > 0.5 pooled SD from the baseline. A logistic regression analysis was conducted to evaluate potential associations between patient, tumor, or treatment factors and adverse clinical outcomes. Results: From December 2023 to August 2024, 25 patients were treated. Intrafractional ultrasound tracking was successfully performed in all sessions. Median age was 78 (62-85) years. The median CTV and PTV were 60 (42-116) cc and 101 (69-169) cc, respectively. 12 and 8 patients were intermediate and high-risk, respectively; 15 pts received ADT. No G3 or higher toxicities were recorded. Maximum acute GU toxicity was G0 in 12 patients (48%), G1 in 6 patients (24%) and G2 in 7 patients (28%), respectively. The same features for the maximum acute GI toxicity were G0 in 20 patients (80%), G1 in 4 pts (16%) and G2 and 1 pts (4%), respectively. A statistically significant difference between baseline and 3-month follow-up was observed in the EPIC-CP scores for quality of life, sexual and hormone domains, as well as in the IIEF questionnaire, with a proportion of patients experiencing a MID equal to 8 (32%), 5 (20%), 9 (36%), 6 (24%), respectively. Conclusion: Our study shows that 3-fraction SBRT schedule, with effective intrafraction monitoring, is a safe treatment, irrespective of the risk group and the prostate volume, associated with a short-term mild decline in the QoL of patients with organ confined PCa. Long-term follow-up is necessary to confirm these findings and demonstrate efficacy.

Keywords: prostate cancer, sbrt, real-time tracking