S2212
Physics - Intra-fraction motion management and real-time adaptive radiotherapy
ESTRO 2026
Margins for geometric uncertainty around organs at risk in radiotherapy. Radiother Oncol. 2002 Mar;62(3):299-307. Keywords: PRV margins, Small bowel, MRgRT
Proffered Paper 985
Deformable dose-guided MLC tracking enabled by motion-model-derived volumetric imaging in lung and liver cancer patients Laura Esther Büttgen 1,2 , Chandrima Sengupta 3 , Jonathan Sykes 4,5 , Danielle Chrystall 6 , Owen Dillon 3 , Jeremy Todd Booth 5,7 , Maegan Stewart 6,8 , Jonathan Hindmarsh 3 , Rene Werner 1,9 , Paul Keall 3 , Emily A Hewson 3 1 Institute for Applied Medical Informatics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany. 2 Department of Radiotherapy and Radio- Oncology, University Medical Center Hamburg- Eppendorf, Hamburg, Germany. 3 Image X Institute, Faculty of Medicine and Health, University of Sydney, Sydney, Australia. 4 Department of Radiation Oncology, Sydney West Radiation Oncology Network, Sydney, Australia. 5 Institute of Medical Physics, School of Physics, University of Sydney, Sydney, Australia. 6 Northern Sydney Cancer Centre, Royal North Shore Hospital, St Leonards, Sydney, Australia. 7 Radiation Oncology, Royal North Shore Hospital, St Leonards, Sydney, Australia. 8 School of Health Sciences, Faculty of Medicine and Health, University of Sydney, Sydney, Australia. 9 Institute of Computational Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany Purpose/Objective: Respiratory-induced anatomical deformation remains a major obstacle to accurate dose delivery in thoracic and abdominal radiotherapy. Real-time dose-guided radiotherapy seeks to overcome these limitations by integrating continuous volumetric imaging, dose calculation, and treatment adaption throughout treatment delivery. This study evaluates the feasibility and dosimetric benefit of using a motion model to generate intrafraction volumetric images for guiding deformable dose-guided multileaf collimator (MLC) tracking in lung and liver cancer patients. Material/Methods: Deformable dose-guided MLC tracking was simulated for ten cancer patients (4 lung, 6 liver). A patient- specific linear regression-based motion model was trained on planning 4DCT data to relate external respiratory signals to internal deformation vector fields (DVF). Respiratory traces recorded during patient treatments were input into the motion model to generate time-resolved volumetric images during simulated treatment. The MLC apertures were
Conclusion: This study presents an automated framework to derive PRV margins for the bowel. Across the cohort, 4.5 mm margin proved sufficient, which is considerably smaller than the previously found margins for inter-fraction motion2. The precision analysis showed a brief 2.5-minute scan can accurately predict patient-specific margins, potentially reducing them as low as 2.5 mm. These margins enable a balance between motion coverage and treatment planning flexibility. Automated small bowel segmentation solutions could help further practical implementation into clinic. References: 1. Stereotactic Ablative Body Radiation Therapy (SABR): A Resource, version 6.1 (2019). UK SABR Consortium. 2. Hysing LB, Kvinnsland Y, Lord H, Muren LP. Planning organ at risk volume margins for organ motion of the intestine. Radiother Oncol. 2006 Sep;80(3):349-54.3. Damen SLC, van Lier ALHMW, Zachiu C, Raaymakers BW. Bowel tracking for MR- guided radiotherapy: simultaneous optimization of small bowel imaging and tracking. Phys Med Biol. 2025 Mar 18;70(7).4. McKenzie A, van Herk M, Mijnheer B.
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