ESTRO 2025 - Abstract Book

S3349

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

ESTRO 2025

Conclusion: We demonstrated that the Unity MR-linac together with the clinical CMM software facilitate dosimetrically accurate MLC-tracking for 2-fraction SBRT prostate translational target motion.

Keywords: MLC tracking, 2-fraction prostate SBRT, CMM

References: [1] Meijers, L., et al . (2023). Optimization and evaluation of T2 TSE cine images and comparison to the standard bTFE cine images used for a drift-compensated workflow of prostate cancer patients at the Unity MR-linac. MRinRT , Rome. [2] Uijtewaal, P., et al. (2021). Dosimetric evaluation of MRI ‐ guided multi ‐ leaf collimator tracking and trailing for lung stereotactic body radiation therapy. Medical Physics , 48 (4), 1520-1532. [3] Uijtewaal, P., et al. (2024). Performance characterization of a novel hybrid dosimetry insert for simultaneous spatial, temporal, and motion ‐ included dosimetry for MR ‐ linac. Medical Physics , 51 (4), 2983-2997.

4350

Digital Poster Intrafraction and intra-breath-hold uncertainties in the thorax assessed using fast 3D MRI Laura A Rechner 1 , Rasmus H Hansen 2 , Isak H Wahlstedt 2 , Peter Meidahl Petersen 2 , Stephen F Kry 3 1 Department of Oncology, Copenhagen University Hospital - Herlev and Gentofte, Herlev, Denmark. 2 Department of Oncology, Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark. 3 Department of Radiation Physics, University of Texas, MD Anderson Cancer Center, Houston, USA Purpose/Objective: Breath-hold techniques are widely used in radiotherapy to reduce organ at risk doses and motion uncertainties for targets affected by respiratory motion. However, data on positional uncertainties within and between breath-holds is limited. This study assessed the positional uncertainties of thoracic internal anatomy relative to an external marker during and between breath-hold scans.