S2985
Invited Speaker
ESTRO 2026
of proton therapy. Combining the highly conformal dose delivery of proton therapy with the superior soft- tissue contrast and real-time imaging capabilities of MRI may contribute to the full exploitation of the predicted physical and biological benefits for proton therapy. Whereas near-room MRI-guidance using an intra- hospital shuttle-based approach has shown promise to account for inter-fractional anatomical changes in daily adaptive carbon therapy, the full integration of in-beam MRI guidance offers the additional capability of adapting for intra-fractional changes due to tumour and organ motion. The latter would enable motion tracking and real-time gated treatment, thereby further increasing the targeting precision of proton therapy for moving tumours. In the past few years, several studies have investigated the physics challenges and technical feasibility of integrating MRI scanners with proton therapy delivery systems. In proof-of-concept experiments, in-beam MRI was shown to be feasible during dose delivery, without relevant dosimetric changes due to the presence of the MR magnetic fields. However, challenges still need to be overcome to ensure artifact- free imaging during dose delivery, since dynamic magnetic fringe fields generated by the proton pencil beam scanning steering magnets interfere with the magnetic fields of the in-beam MR scanner. For accurate dose calculation, the treatment planning system needs to incorporate the measured 3D magnetic vector field of the in-beam MR scanner and comprehensive experimental dose validation with adequate dose detectors in the presence of the MR magnetic field. Furthermore, methods need to be implemented and validated to compensate for magnetic field induced dose deformations. This contribution provides an overview of the current experimental progress and status of in-beam MR- integrated proton therapy. A roadmap for clinical introduction and implementation is presented. The tumour sites that would benefit from an integrated MRI-guided proton system are also discussed. Finally, recent developments in upright particle therapy have paved the way for research into the use of upright MRI scanners to investigate the impact of anatomical changes and tumour movement between supine and upright postures. Hence the concept of upright, in- beam MR-guided proton therapy is a promising area of research and development. 5268 Bridging modalities: Joint photon and proton strategies Nathan Torelli Department of Radiation Oncology, University Hospital Zurich and University of Zurich, Zurich, Switzerland
opportunities and challenges of integrating multi- parametric imaging into treatment planning. Adaptive radiotherapy builds upon this foundation by incorporating longitudinal imaging acquired during the treatment course to monitor tumour response and anatomical changes. While most current adaptive strategies focus primarily on geometric variations, the true potential of adaptation lies in accounting for dynamic biological processes, enabling dose escalation or de-escalation based on treatment response. This shifts the paradigm from static planning towards a time-dependent, patient-specific optimisation problem, where both spatial and temporal aspects of tumour control are considered. The “see, adapt, treat” paradigm encapsulates this evolution into a closed-loop framework, where imaging continuously informs decision-making. Functional imaging data can be used to guide dose painting strategies, identify resistant subregions, and update treatment plans in response to evolving tumour biology. This iterative process aims to maximise tumour control while limiting normal tissue toxicity, ultimately moving towards truly personalised radiotherapy. However, translating this paradigm into routine clinical practice requires addressing several key challenges. These include the validation and standardisation of imaging biomarkers, ensuring reproducibility across imaging platforms and institutions, and integrating complex imaging and planning workflows into time- constrained clinical environments. Robust quantitative models linking imaging signals to radiobiological parameters are also essential to support reliable decision-making. In this talk, the “see, adapt, treat” loop will be illustrated through examples for lung and head and neck cancers, demonstrating how functional imaging can be incorporated into adaptive radiotherapy workflows to improve treatment individualisation and clinical outcomes. 5267 Stand up for precision: The proton-MR advantage Aswin L. Hoffmann Medical Radiation Physics, OncoRay - National Center for Radiation Research in Oncology, Dresden, Germany The lack of high soft-tissue contrast image-guidance in proton therapy is considered a major hindrance for exploiting its full potential to outperform conventional X-ray guided proton therapy and MR-guided photon therapy with MR-linacs for soft-tissue tumours, especially for moving tumours. Due to the greater sensitivity of protons to anatomical variations, advanced image guidance is essential for the success
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