ESTRO 2025 - Abstract Book

S3083

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2025

694

Digital Poster Clinical Implementation and Dosimetric Analysis of Cone Beam CT Guided Online Adaptive Bladder Radiotherapy Julie Fox, Andrew Bromiley, Adam El-Qmache, Sara Talebikhanmiri, John McLellan, Rachel Adam, Megan Fraser-Bell, Catriona Burnett, Amy Hamilton, Gillian Mcintosh, Nicola Miller, Martin Rudge, Polly Darby, David Carnegie, Anne E Kiltie, Rhona McMenemin, Judith Grant, Jacqueline Ogg, Brandon Tan, Graham Macdonald Radiotherapy Department, Aberdeen Royal Infirmary, Aberdeen, United Kingdom Purpose/Objective: The purpose of this work was to establish and evaluate a sustainable radiographer led workflow delivering online adaptive radiotherapy (oART) on Ethos for bladder cancer patients. This study is a novel comparison of the oART dose delivered using this new technique to the dose that would have been delivered using the local image guided radiotherapy (IGRT) workflow. Material/Methods: Seven bladder patients were treated in 140 adaptive sessions on Ethos. During oART treatment artificial intelligence (AI) - driven bladder and rectum contours are generated on the pre-treatment CBCT and edited by the adaptor where necessary 1 . The adaptive clinical target volume (CTV), planning target volume (PTV) and a re-optimised treatment plan are automatically generated. A innovative technique was developed to generate the adaptive CTV directly from the bladder contour to minimise online contour editing and therefore treatment time and intra-fraction motion. RAIDAR 2 CTV to PTV margins were used for the IGRT plan and for the first five adaptive fractions. oART patient specific margins were then derived from the bladder contour in the pre and post treatment daily cone-beam CTs (CBCTs) and used for the remainder of treatment. Retrospectively, the delivered adaptive dose and the planned IGRT dose were calculated on the daily CBCTs. Across the whole treatment course, the adaptive CTV and organ at risk (OAR) doses in the IGRT and adaptive plans were compared using a paired t-test. Results: An oART radiographer led workflow was implemented, with a mean oART treatment time of 14.9 min (σ=2.1). Statistically significant (p<0.01) improved CTV coverage was achieved with the adaptive plan compared to IGRT. The CTV D100% mean dose increased from 93.0% (σ=5.4) for IRGT to 96.5% (σ=1.3) for oART. For all patients the treated PTV volume was reduced compared to IGRT with a mean reduction for all patients of 35.5%. Intestinal cavity sparing was observed for oART plans with the all-patient mean V30Gy reduced by 31.1% and rectum V40Gy reduced by 68.6%. Conclusion: oART in bladder on Ethos enables greater and more consistent treatment of the bladder CTV compared to IGRT, even with reduced CTV-PTV margins after fraction five. References: 1. Patrik Sibolt * , Lina M. Andersson, Lucie Calmels, David Sjostr ¨ om, ¨ Ulf Bjelkengren, Poul Geertsen, Claus F. Behrens Clinical implementation of artificial intelligence-driven cone-beam computed tomography-guided online adaptive radiotherapy in the pelvic region. Physics and Imaging in Radiation Oncology 17, 2021 2. Hafeez S, Lewis R, Hall E, Huddart R: Advancing Radiotherapy for Bladder Cancer: Randomised Phase II Trial of Adaptive Image-guided Standard or Dose-escalated Tumour Boost Radiotherapy (RAIDER). Clinical Oncology Volume 33, March 2021 Keywords: Bladder, Cone-beam CT, Artificial Intelligence