ESTRO 2025 - Abstract Book

S3277

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

ESTRO 2025

Conclusion: This analysis demonstrates that prostate intra-fraction motion can be effectively managed with baseline-shift correction during UHFX-MRgRT. Without correction, considerable displacement was observed across all directions, particularly in the AP- and SI-axes. However, when applying a baseline-shift correction, displacement was significantly reduced, demonstrating that margins may be reduced to values less than 2 mm to account for residual prostate motion during online adaptive MRgRT.

Keywords: 2D-cine-MRI, prostate tracking, MRgRT

2716

Poster Discussion PET guided radiotherapy on the MR-linac: a technical feasibility study of a motion mitigated PET-MRL workflow Albert J Everard, Rodrigo Jose Santo, Prescilla Uijtewaal, Martin Fast, Bas W Raaymakers, Cornelis A.T van den Berg, Pim T.S Borman, Casper Beijst Radiotherapy, UMC utrecht, Utrecht, Netherlands Purpose/Objective: PET-guided radiotherapy on the MR-linac combines best of both worlds: PET imaging enables precise biological targeting of cancer cells, while the MR-linac facilitates accurate MR-guided stereotatic radiotherapy delivery. However, motion introduces uncertainty in radiotherapy, both during the pretreatment imaging for target definition and during treatment delivery. Therefore, motion correction strategies are essential in both phases.