ESTRO 2025 - Abstract Book

S3281

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2025

Conclusion: Effectively reusing pre-existing plans has the potential to fast-track oART and reduce hospital resources in 1/4 of fractions, even when the most conservative acceptability criteria are applied. This success rate is at least 3 times higher (depending on acceptability criteria) than using the reference plan alone. These results are sufficiently promising to motivate further developments in the software tools needed to bring this concept to fruition to ultimately lower the barriers of clinical implementation of oART.

Keywords: MR-linac, online adaptive radiotherapy, prostate

References: [1] L. Nierer et al. , “Dosimetric benefit of MR-guided online adaptive radiotherapy in different tumor entities: liver, lung, abdominal lymph nodes, pancreas and prostate,” Radiation Oncology , vol. 17, no. 1, Dec. 2022. [2] J. de Leon, et al., “Optimising the MR-Linac as a standard treatment modality,” Dec. 01, 2023, John Wiley and Sons Ltd . [3] H. G. Nasief et al. , “Predicting necessity of daily online adaptive replanning based on wavelet image features for MRI guided adaptive radiation therapy,” Radiotherapy and Oncology , vol. 176, pp. 165–171, Nov. 2022.

2741

Digital Poster Intrafraction MR-based bowel motion statistics Saskia L.C. Damen, Astrid van Lier, Cornel Zachiu, Bas W. Raaymakers Radiotherapy Department, UMC Utrecht, Utrecht, Netherlands

Purpose/Objective: To evaluate the intrafraction motion statistics of the small bowel for a patient and volunteer cohort, in the context of MR-guided radiotherapy. Here we further build on a workflow for which we optimized and validated a combination of a dynamic MRI sequence and deformable image registration framework to accurately quantify