S1770
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
4 Department of Radiotherapy and Radiation Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, TUD Dresden University of Technology, Dresden, Germany. 5 Shared senior authorship, OncoRay - National Center for Radiation Research in Oncology, Dresden, Germany Purpose/Objective: The planned clinical implementation of MR-integrated proton therapy (MRiPT) using a mobile in-beam MR scanner positioned in front of a proton pencil beam scanning (PBS) beamline requires a comprehensive and efficient quality assurance (QA) framework. To this end, a daily workflow for machine and patient specific QA (PSQA) was developed and implemented. The aim of this study was to validate the workflow through repeated QA testing and an end-to-end (E2E) evaluation. Material/Methods: For daily QA, first standard beam machine QA tests are performed (absolute dosimetry and 2D dose measurements of PBS spot patterns) without the MR scanner. Subsequently, the scanner is positioned in front of the beamline and MRI QA tests (i.e., stability of MR isocenter and geometric distortion) are performed. Finally, an MRI-beam co-linearity test is conducted using an in-house developed phantom before authorizing clinical use on the respective day.For the E2E test, the whole workflow was executed with a dedicated CT- and MR-compatible E2E phantom containing inserts for dose detectors (radiochromic film, ionization chamber): CT and MR image acquisition for target volume delineation and treatment planning, dose calculation accounting for magnetic-field-induced beam deflection, MR-guided phantom positioning at the beamline, and irradiation (Fig.1). Additionally, PSQA dose measurements inside the magnetic field of the MR scanner were performed.
Conclusion: Experimental results suggest that transmitted beams could potentially be used for position verification, complementing the solution prospected in [2]. Additionally, PT TB plans showed enhanced robustness under conventional or severe uncertainty conditions compared with gantry-based PT plans. References: (1) Vai et al., Transmission beam planning for improved robustness and efficiency in proton therapy for head and neck cancer, PHIRO, 2025(2) Engwall et al., Shoot-through layers in upright proton arcs unlock advantages in plan quality and range verification. Medical Physics, 2025 Keywords: proton, shoot-through, online QA Mini-Oral 4181 Implementation of a daily workflow for MR- integrated proton therapy using a mobile in-beam MR scanner: quality assurance program and end- to-end test Felix Horst 1,2 , Sergej Schneider 1,2 , Krishna Godino Padre 1,3 , Stefan Menkel 1,4 , Julia Hytry 1,4 , Daniela Kunath 1,4 , Marisa Cobanaj 1,2 , Franciska Lebbink 1,3 , Julia Thiele 4 , Michael Schürer 1,3 , Esther C G Troost 2,4 , Jörg Pawelke 1,2 , Christian Richter 5,2 , Aswin Hoffmann 5,2 1 Medical Radiation Physics, 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.
Fig.1: Setup used for E2E testing together with the treatment plan, positioning MR image, and film measurement. Results: The daily QA tests, performed multiple times over four months, consistently passed (Fig.2). The absolute dose output was stable within ±1% and the PBS characteristics were all within clinical tolerances. The MR isocenter was stable within ±0.5mm and the image distortion within a 20cm diameter spherical volume
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