ESTRO 2023 - Abstract Book

S188

Saturday 13 May

ESTRO 2023

Conclusion We successfully developed and implemented robustly DLO automated IMPT planning for OPC. Our prospective study shows that DLO plans are preferred over manual plans in almost all cases (5/6). This result is in accordance with the findings of the retrospective study. PD-0252 2D dosimetric impact of an in-beam MR magnetic field on scanned proton pencil beam spot fields B. Gebauer 1,2 , J. Pawelke 1,2 , A. Hoffmann 1,3,4 , A. Lühr 5 1 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; 2 Institute of Radiooncology-OncoRay, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany; 3 Institute of Radiooncology- OncoRay, Helmholtz-Zentrum Dresden-Rossendorf , Dresden, Germany; 4 Department of Radiotherapy and Radiation Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany; 5 Department of Physics, TU Dortmund University, Dortmund, Germany Purpose or Objective Magnetic resonance imaging-integrated proton therapy (MRiPT) is considered a next step in advancing image guidance for proton therapy as it is expected to improve the targeting precision. However, the presence of the MR magnetic field poses a challenge to the dose delivery due to the Lorentz force affecting the proton beam path. This study aims to investigate the dosimetric impact of the static magnetic (B0) field of an in-beam MR scanner on the delivery of scanned proton pencil beams. Materials and Methods An MRiPT prototype comprising a horizontal pencil beam scanning beamline and an open 0.32 T in-beam MR scanner with a B0 field oriented perpendicular to the central beam axis was used to measure the 2D dosimetric impact of the B0 imaging and fringe field on proton beam transport. Beam transmission measurements in-air were conducted for three proton energies (100, 150, and 220 MeV) and two spot maps (15 × 15 cm ² and 30 × 20 cm ² ). 2D relative dose spot profiles were measured with EBT3 films placed vertically in the imaging field (position P_isoc) without and with the B0 field. P_isoc was located centrally in the imaging volume at 58.2 cm and 122.4 cm downstream of the beam isocenter and exit window, respectively. A 2D Gaussian fit was applied to each dose spot to determine its central position (X, Y), minimum and maximum lateral standard deviation ( σ _min and σ _max), orientation ( θ ), and eccentricity ( ε ). Results