ESTRO 2025 - Abstract Book

S3529

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTRO 2025

3390

Digital Poster Experimental validation of a commercial TPS for predicting the effect of the magnetic field of an in-beam MR scanner on proton dose distributions Felix Horst 1,2 , Louisa Schäfer 1 , Krishna Godino Padre 1,3 , Marisa Cobanaj 1,2 , Franciska Lebbink 1,3 , Michael Schürer 1,3 , Julia Hytry 1,4 , Daniela Kunath 1,4 , Christian Richter 1,2,4 , Erik Traneus 5 , Hoffmann Aswin 1,2,4 , Pawelke Jörg 1,2 1 Faculty of Medicine and University Hospital Carl Gustav Carus, Technical University Dresden and Helmholtz Zentrum Dresden-Rossendorf, OncoRay - National Center for Radiation Research in Oncology, Dresden, Germany. 2 Institute of Radiooncology - OncoRay, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany. 3 German Cancer Research Center (DKFZ), Heidelberg, Germany; Faculty of Medicine and University Hospital Carl Gustav Carus, TUD Dresden University of Technology, Dresden, Germany; Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany, National Center for Tumor Diseases Dresden (NCT/UCC), Dresden, Germany. 4 Department of Radiotherapy and Radiation Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, TUD Dresden University of Technology, Dresden, Germany. 5 RaySearch Laboratories, RaySearch Laboratories, Stockholm, Sweden Purpose/Objective: The integration of MRI-guidance in proton therapy is a challenging research topic. When treating patients inside an in-beam MR scanner, the magnetic field effects on proton beam trajectories via the Lorentz force need to be taken into account during dose calculation and treatment planning. This study presents results of the initial experimental validation of a commercial treatment planning system (TPS) capable of proton dose calculation in the presence of realistic MR magnetic fields. Material/Methods: Dosimetric experiments were conducted in the presence of the 0.32T magnetic field of an in-beam MR scanner prototype. Proton pencil beams and extended fields (squared shapes and complex patient plans) were irradiated at a pencil beam scanning nozzle. Absolute and relative dose distributions were measured in air using a 2D ionization chamber array at different positions A-E (Fig. 1a), in water-equivalent phantoms, and using different detectors (ionization chamber array, microDiamond detector, Advanced Markus chamber) in an in-house developed MR conditional motorized 3D water phantom (Fig. 2a). The comprehensive experimental dataset was then used to systematically evaluate the dosimetric performance and accuracy of the RayStation TPS. A research version that allowed to incorporate a measured 3D magnetic vector field map of the MR scanner during proton dose calculation was used.

(a) IC array at different positions (A-E) in the in-beam MR scanner. (b) Comparison of calculated and measured lateral beam deflection for different beam energies.