ESTRO 2025 - Abstract Book

S1975

Clinical - Urology

ESTRO 2025

1859

Proffered Paper Outcomes of SBRT for PSMA PET diagnosed hormone-sensitive oligorecurrent prostate cancer: results from a large international multi-center cohort Timo F.W. Soeterik 1 , Marcin Miszczyk 2,3 , Max Peters 4 , Mateusz Bilski 5,6,7 , Giulio Francolini 8 , Pietro Garlatti 8 , Māris Mežeckis 9 , Justyna Kociolek 10 , Carlo Greco 10 , Tomasz Techmanski 11 , Eline Huele 12 , Freek Teunissen 13 , Paulien Westhoff 13 , Petra Kroon 1 , Wessel Vis 4 , Dorien R.N. Haverkort 4 , Jochem Van der Voort van Zyp 1 , Martijn Intven 1 , Joanne M van der Velden 1 , Wietse S.C. Eppinga 1 1 Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, Netherlands. 2 Department of Urology, Medical University of Vienna, Vienna, Austria. 3 Collegium Medicum - Faculty of Medicine, WSB University, Dąbrowa Górnicza, Poland. 4 Department of Radiation Oncology, Radiotherapiegroep, Deventer, Netherlands. 5 Brachytherapy Department, Saint John’s Cancer Center, Lublin, Poland. 6 Radiotherapy, Medical University of Lublin, Lublin, Poland. 7 Radiotherapy, Saint John’s Cancer Center, Lublin, Poland. 8 Department of Radiation Oncology, Azienda Ospedaliero-Universitaria Careggi, Florence, Italy. 9 University of Latvia, Sigulda Hospital Centre of Stereotactic Radiosurgery, Sigulda, Latvia. 10 Department of Radiation Oncology, The Champalimaud Centre for the Unknown, Lisbon, Portugal. 11 3rd Department of Radiotherapy and Chemotherapy, Maria Skłodowska -Curie National Research Institute of Oncology, Gliwice, Poland. 12 Division of Imaging and Oncology, University Medical Center Utrecht, Utrecht, Netherlands. 13 Department of Radiation Oncology, Radboud University Medical Center, Nijmegen, Netherlands Purpose/Objective: Metastasis-directed therapy (MDT) has been shown to significantly delay the initiation of androgen deprivation therapy (ADT) in patients with oligorecurrent prostate cancer (PCa). However, existing evidence from prospective trials is primarily based on conventional imaging, with modest patient numbers from predominantly single-center studies. Therefore, in this study, we evaluated a large, multicenter cohort of oligorecurrent PCa patients staged using PSMA PET and treated with radiotherapy-based MDT to defer ADT. Material/Methods: This retrospective multicenter study included patients with oligorecurrent, hormone- sensitive prostate cancer (≤5 lesions), staged using PSMA PET, and treated with SBRT to all metastatic sites without concurrent or adjuvant systemic therapy. Conducted across nine tertiary centers in six European countries, the study evaluated ADT-free survival, radiographic progression-free survival, second-line systemic therapy-free survival, polymetastatic disease free survival, and overall survival using Kaplan- Meier analysis. Rates of CTCAE grade ≥2 toxicities were recorded. Results: The study included 561 patients, with 52.4% presenting pelvic nodal, 39.2% distant, and 8.4% mixed pelvic and distant metastasis. Of those with distant metastasis, 73% had bone involvement, 16.5% distant nodal, 3.3% visceral, and 7.1% multiple sites. Median number of lesions treated during first SBRT cycle was 1 (IQR 1-2). During median follow-up of 37 months (IQR 24 – 58), 31% underwent a second SBRT cycle, and 10% three or more cycles. Grade 2 toxicity after first SBRT was reported in 10 (1.8%) patients including urinary incontinence, transient diarrhea and pain. Grade 3 toxicity was reported in 2 (0.4%) patients; both vertebral insufficiency fractures. The rates of ADT-free survival at 1, 2, and 5 years were 85%, 69%, and 37%, respectively. Progression-free survival was 71% at 1 year, 46% at 2 years, and 19% at 5 years. Polymetastatic-free survival was 92% at 1 year, 82% at 2 years, and 61% at 5 years. Second-line systemic therapy-free survival was 97% at 1 year, 92% at 2 years, and 71% at 5 years. Finally, overall survival rates were 100%, 98%, and 90%, at 1, 2, and 5 years, respectively. Conclusion: To our best knowledge, this is the largest real-world cohort study on MDT for PSMA PET-staged hormone-sensitive oligorecurrent PCa. Our findings confirm that SBRT effectively delays ADT, with over two-thirds of patients remaining ADT-free at two years. However, we emphasize the need for improved patient selection criteria, as one in six patients required ADT within a year despite the use of PSMA PET for lesion targeting.