S1131
Clinical - Urology
ESTRO 2026
Fossa 4,10 , Thomas Zilli 11,12 , Rupesh Kotecha 13,14 , Shankar Siva 15 , Matthias Guckenberger 16 , Ł ukasz Kuncman 7,8 1 Radiotherapy Department, Affidea Nu-med Center of Oncological Diagnostics and Therapy, Zamo ść , Poland. 2 Clinics of Radiotherapy, Medical University of Lublin, Lublin, Poland. 3 Department of Radiation Oncology, Mayo Clinic, Rochester, USA. 4 Department of Oncology and Hemato-Oncology, University of Milan, Milan, Italy. 5 Department of Radiotherapy, Saint John’s Cancer Center, Lublin, Poland. 6 Department of Medical Physics, Saint John's Cancer Center, Lublin, Poland. 7 Department of Radiotherapy, Medical University of Lodz, Ł ód ź , Poland. 8 Department of External Beam Radiotherapy, Copernicus Memorial Hospital in Lodz Comprehensive Cancer Center and Traumatology, Ł ód ź , Poland. 9 Radiotherapy Planning Department, Copernicus Memorial Hospital in Lodz Comprehensive Cancer Center and Traumatology, Ł ód ź , Poland. 10 Division of Radiation Oncology, European Institute of Oncology IRCCS, Milan, Italy. 11 Department of Radiation Oncology, Oncology Institute of Southern Switzerland,, Bellinzona, Switzerland. 12 Faculty of Biomedical Sciences, Università della Svizzera italiana, Lugano, Switzerland. 13 Department of Radiation Oncology, Miami Cancer Institute, Miami, USA. 14 Department of Oncological Science, Herbert Wertheim College of Medicine, Miami, USA. 15 Peter MacCallum Cancer Centre and Sir Peter MacCallum Department of Oncology of Radiation Oncology, University of Melbourne, Melbourne, Australia. 16 Department of Radiation Oncology, University Hospital Zurich, Zurich, Switzerland Purpose/Objective: The widespread use of prostate-specific membrane antigen (PSMA)-PET/CT has refined the detection of rib metastases in prostate cancer. However, the role of clinical target volume (CTV) margins beyond the gross tumor volume (GTV) in stereotactic body radiotherapy (SBRT) remains controversial. Concerns include unnecessary dose escalation to the ribs and chest wall, with potential for toxicity and fractures. We investigated local control (LC), toxicity, and rib fracture (RF) risk following SBRT for rib metastases, focusing on the relevance of CTV expansion in the PSMA-PET era. Material/Methods: This retrospective multicenter study included 102 prostate cancer patients treated with rib SBRT between 2021 and 2024, with ≥ 12 months follow-up. Patients were stratified by contouring strategy: GTV- only vs. GTV+CTV (3–10 mm). Imaging modality (PSMA- PET/CT vs. CT-only), systemic therapy, dose/fractionation, and dosimetric parameters were recorded. Outcomes were assessed using Kaplan– Meier, Cox regression, and competing risk analyses. Endpoints included LC, pain response, toxicity, and RF
risk. Results:
With a median follow-up of 20 months, 1- and 2-year LC rates were 97.9% and 96.3%, respectively. No LC difference was observed between GTV-only and GTV+CTV groups (p=NS). Notably, LC remained excellent when GTV-only contouring was used with PSMA-PET guidance, whereas 3–5 mm CTV margins were paradoxically associated with higher local progression (13.5%). Rib fractures occurred in 2.9% of patients (1 symptomatic), with baseline pain and extraosseous infiltration as independent predictors. Higher PTV D50% was the strongest dosimetric correlate of RF (p = 0.041). No acute or late ≥ G3 toxicities occurred. Acute and late toxicities were rare and limited to Grade 1–2 musculoskeletal pain. Conclusion: SBRT for rib metastases in prostate cancer yields excellent local control, reliable pain relief, and minimal toxicity. In the PSMA-PET era, GTV-only contouring appears sufficient, while routine CTV expansion may not confer added benefit and could increase irradiated volume. For centers limited to CT-only imaging, a cautious CTV margin may still be justified. These results support PSMA-PET–guided SBRT as a precise, safe, and effective strategy for rib metastases and suggest that routine CTV expansion may no longer be necessary in contemporary practice. Keywords: SBRT, rib metastases, prostate cancer, PSMA-PET CT-guided Online Adaptive Radiotherapy for Bladder Cancers: First Clinical Results and Dosimetric Benefits from Two European Centers Morgan Michalet 1 , Rémi Colin 2 , Maxime Bertrand- Chevrier 1 , Jeppe Friborg 3 , Ivan Richter Vogelius 3 , Peter Meidahl Petersen 3 , Malene Eppler Bak 3 , Olivier Riou 1 , Marie Charissoux 1 , Carmen Llacer-Moscardo 1 , Thomas Batt 1 , Dorian Trauchessec 1 , Jessica Prunaretty 1 , Norbert Aillères 1 , Azria David 1 , Pauline Hinault 1 1 Radiation oncology, Institut du Cancer de Montpellier, Montpellier, France. 2 Biostatistics, Institut du Cancer de Montpellier, Montpellier, France. 3 Oncology, Rigshospitalet, Copenhagen, Denmark Digital Poster 223 Purpose/Objective: Recent advances in online adaptive radiotherapy (oART) have enabled reduction of PTV margins across several tumor sites (1). Trimodal therapy (TMT) achieves favorable outcomes in selected patients with muscle-invasive bladder cancer (MIBC) (2). This study reports the first clinical results of cone-beam CT (CBCT)-guided oART for bladder cancer and evaluates its dosimetric benefits.
Made with FlippingBook - Share PDF online