S2768
RTT - RTT contouring, target definition, and treatment planning
ESTRO 2026
1048 Does Intraprostatic Dose Painting Make a Difference in Pelvic and Prostatic SABR: Results from a Multicenter Phase II Prospective Clinical Trial Yasir Alayed 1 , Darin Gopaul 2 , Lucas Mendez 3 , Winkle Kwan 4 , Stanley Liu 5 , William Chu 6 , Chia-Lin Tseng 7 , Patrick Cheung 7 , Danny Vesprini 7 , Hans Chung 7 , Gerard Morton 7 , Rohann Correa 7 , Bindu Musunuru 8 , Melanie Davidson 9 , Ananth Ravi 10 , Renee Korol 9 , Andrea Deabreu 11 , Alexander Mamedov 11 , Zeeba Sadiq 11 , Nicole Mittmann 12 , Alice Dragomir 13 , Liying Zhang 14 , Andrew Loblaw 7,15 1 Radiation Oncology, King Saud University, Riyadh, Saudi Arabia. 2 Radiation Oncology, Grand River Regional Cancer Centre, Kingston, Canada. 3 Radiation Oncology, London Health Sciences Centre, London, Canada. 4 Radiation Oncology, British Columbia Cancer Centre, Surrey, Canada. 5 Radiaition Oncology, Sunnybrook Health Sciences Centre, Toronto, Canada. 6 Radiation Oncology, Durham Regional Cancer Centre, Oshawa, Canada. 7 Radiation Oncology, Sunnybrook Health Sciences Centre, Toronto, Canada. 8 Radiation Oncology, UPMC Hillman Cancer Center, Pittsburgh, USA. 9 Medical Physics, Sunnybrook Health Sciences Centre, Toronto, Canada. 10 Physics, Toronto Metropolitan University, Toronto, Canada. 11 Clinical Trials, Sunnybrook Health Sciences Centre, Toronto, Canada. 12 Scientific Evidence, Canada Drug Agency, Toronto, Canada. 13 Surgery, McGill University, Montreal, Canada. 14 Biostatistics, Sunnybrook Health Sciences Centre, Toronto, Canada. 15 Radiation Oncology, University of Toronto, Toronto, Canada Purpose/Objective: Given the added complexity of delivering SABR to the pelvis and prostate in unfavourable-risk prostate cancer (PCa), it was important to establish the safety and feasibility in a multicentric setting. Here we report the outcomes of a multicenter, phase II study of 5- fraction SABR with elective nodal irradiation (ENI) and an optional prostate microboost. Material/Methods: Patients had unfavorable-intermediate or high-risk non-metastatic PCa. All patients received 5 fractions of SABR weekly delivering 25Gy ENI. Three centers gave 40Gy to prostate simultaneously; one center gave 35Gy to the prostate and up to 50Gy to an MRI defined microboost. All patients had risk adapted duration of ADT (6 – 18 mo).The primary endpoint was acute GI and GU CTCAE toxicities. Secondary endpoints included late toxicities, quality of life, and biochemical failure (BF). Results: 76 patients were accrued at 4 Canadian hospitals with a median follow-up of 62.8 months. 37% and 63% of
patients had unfavorable intermediate or high-risk PCa. 41% of patients had an intraprostatic boost. Acute grade ≥ 2 GI and GU adverse events (AE) was 4.1% and 18%. At the last follow-up, 2.6% and 3.9% of patients had grade 2 GI and GU AE (no grade 3 GI/GU AE). 6 patients (8%) had BF for a 5-year cumulative BF of 10.5%. Among the patients who received a microboost, only 1 had BF compared to 5 failures in the no boost cohort (p = 0.08). The median PSA nadir was 0.2 ng/ml, with a median time to nadir of 19.6 months. 84% of patients recovered their testosterone level, with a median time to testosterone recovery (TTR) of 14.3 months. 20.6%, 23.5% and 33.9% of patients had a small change in QOL (SD*0.5) in the EPIC urinary, bowel domain, and sexual domains. Conclusion: 5-fraction SABR to prostate and pelvis for unfavourable-risk PCa was safe and feasible in a multicentric setting with or without a microboost. There were very few significant AEs, encouraging PSA kinetics and biochemical control. The results are currently being validated in randomized trials. Keywords: Prostate, SBRT, MRI-boost Digital Poster Highlight 1115 Using Diagnostic CT in Place of CT Simulation for Palliative Radiotherapy: A Retrospective Dosimetric Analysis Rebecca Hui-Qi Chia Division of Radiation Oncology, National Cancer Center Singapore, Singapore, Singapore Purpose/Objective: Palliative radiotherapy (RT) aims to relieve symptoms and improve quality of life in patients with metastatic disease. Conventionally, RT planning relies on CT- simulation (sCT) based workflow, but has limitations in CT-simulator availability and high patient load. sCT performed under standardized conditions ensures proper patient immobilization and patient set-up reproducibility for treatment. Many palliative patients already have recent diagnostic CT (dCT) scans acquired for disease assessment, which are often of adequate image quality and anatomical coverage hence the necessity of an additional sCT can be brought into question. This study evaluates whether dCT scans can replace sCT scans in the generation of clinically acceptable palliative RT treatment plans without dosimetric compromise. Material/Methods: Patients who underwent palliative RT to the thoracic, abdominal, spinal (thoracic/lumbar), or pelvic regions and had both dCT and sCT scans available were retrospectively reviewed. dCT scans must be done
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