ESTRO 2023 - Abstract Book

S1544

Digital Posters

ESTRO 2023

Conclusion It is feasible to estimate the absorbed dose distribution received from a CBCT chest scan by MC simulations in GATE. It has been shown that performing CBCT simulations on planning CT previous to the treatment, may account for additional absorbed doses to the patient and for a possible reassessment of the treatment, especially for young patients. Acknowledgement This Project has received funding from the Euratom research and training programme: 2019-2020 under grant agreement No. 945196 References [1] T Marchant, K Joshi. "Comprehensive Monte Carlo study of patient doses from cone-beam CT imaging in radiotherapy." Journal of Radiological Protection, 37 p13-30 (2017) (DOI: 10.1088/1361- 6498/37/1/13).

PO-1816 Dosimetric verification of a Monte Carlo treatment planning system for MR-guided proton therapy

H. Fuchs 1 , F. Padilla-Cabal 1 , B. Oborn 2,3,4 , E. Traneus 5 , D. Georg 1

1 Medical University of Vienna, Department of Radiation Oncology, Vienna, Austria; 2 OncoRay – National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany; 3 University of Wollongong, Centre for Medical Radiation Physics (CMRP), Wollongong, Australia; 4 Illawarra Cancer Care Centre, (ICCC), Wollongong, Australia; 5 RaySearch Laboratories AB, Research, Stockholm, Sweden Purpose or Objective The combination of on-bed MR-imaging with proton therapy (MRgPT) may allow the next step in treatment fidelity. In such a conceptual design the magnetic field does not only influence the spatial dose deposition; in addition the path of the primary treatment beam requires special modelling during dose calculation for treatment planning. We report the first results of a dosimetric verification of a Monte Carlo based treatment (MC) planning system (TPS) for MRgPT, i.e. a research version of RayStation (RaySearch Laboratories AB). Materials and Methods An electromagnet was positioned in front of a horizontal pencil beam scanning (PBS) research beam line to simulate the conditions during MRgPT. The electromagnet having a bore opening of 13.5 cm allows for magnetic field strengths of up to 1 T within a 20 cm diameter and fringe field ramp of 65 cm length. The magnetic field of the magnet was carefully modelled using COMSOL and input into the TPS as a 3D vector field. The MC transport in the TPS (RayStation 9A-IonPG) was modified to take 3D magnetic field maps into account during dose calculation. All basic data for beam modelling were determined without magnetic field.