S1656
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
in photon beam dosimetry. Journal of Applied Clinical Medical Physics, 25(1), e14209. Keywords: scintillator, MRI-Linac, dosimetry
Digital Poster 2898
Fano Test for Therapeutic Carbon and Helium Beams in Magnetic Fields Using Geant4/GATE Jing Syuen Wong 1 , Kilian-Simon Baumann 2,3 , Armin Lühr 4 , Hugo Palmans 5,6 , Björn Poppe 1 , Hermann Fuchs 7 , Hui Khee Looe 1 1 University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany. 2 Department for Radiotherapy, University Hospital Giessen-Marburg, Marburg, Germany. 3 Institute of Medical Physics and Radiation Protection, University of Applied Sciences, Giessen, Germany. 4 Department of Physics, TU Dortmund University, Dortmund, Germany. 5 Department of Medical Physics, MedAustron Iontherapy Centre, Weiner Neustadt, Austria. 6 Institute of Physics, National Physical Laboratory, Teddington, United Kingdom. 7 Division of Medical Physics, Department of Radiation Oncology, Medical University of Vienna, Vienna, Austria
For small-fields, BP-PSD provides suitable FOFs’ values without requiring a correction factor, with differences of 0.2-0.85% versus Microdiamond. For standard fields, differences between BP-PSD and Semiflex range from 0.2 to 0.6%. The overall agreement with TPS values is between 0.01% and 1.8% (for smaller fields).
Purpose/Objective: Particle therapy offers highly conformal dose
distributions due to its Bragg-peak characteristics, but remains sensitive to anatomical changes along the beam path. MR-guided therapy can mitigate this issue, yet magnetic fields (MFs) alter dosimeter behavior, necessitating correction factors derived from experiments or Monte Carlo (MC) simulations. In this study, the Fano test was implemented for the first time for clinical carbon and helium ion beams in a uniform MF to assess the transport accuracy of MC simulations. Material/Methods: The Fano test was conducted in GATE(v9.4)/Geant4(v11.2.2) using a three-layer cylindrical geometry, where a low-density (air- equivalent) cavity was sandwiched between two water layers. Isotropic and uniform carbon and helium line sources with energies of 120 MeV/u, 250 MeV/u, and 400 MeV/u were simulated. MFs of 0.5 T and 1 T were applied perpendicular to the geometry’s central axis. Baseline transport parameters were adapted from Kretschmer et al., with a 1 µm production cut for electrons [1]. The maximum step size, dRoverRange, and final range were varied systematically based on Blum et al [2]. For each configuration, the Q value, defined as the ratio of the simulated energy to the theoretical value, was calculated. Results: As shown in Figure 1, for carbon ions, most
Conclusion: This study demonstrates that the BP-PSD is suitable for standard and small-field dosimetry with MRI-Linac. With this system, FOFs are the preferred calibration method. On the one side, larger differences in FOFs for small fields (0.83x0.83 cm2, 1.66x1.66 cm2) are mainly related to the difficult setup of the 1D water- phantom, on the other side discrepancies for larger fields (20.75x20.75 cm2, 24×24 cm2) can be explained by the collateral direct irradiation of a portion of the light fiber, due to the small size of the water-tank. Overall BP-PSD’s behavior shows an optimal agreement with the other tested detectors and the values obtained from the TPS. In conclusion, this suggest that it could be a useful tool for both the characterization and the commissioning of a hybrid machine. References: Khan, A. U., Das, I. J., & Yadav, P. (2024). Computational and experimental small field dosimetry using a commercial plastic scintillator detector for the 0.35 T MR-linac. Physica Medica, 123, 103403.Das, I. J., Sohn, J. J., Lim, S. N., Sengupta, B., Feijoo, M., & Yadav, P. (2024). Characteristics of a plastic scintillation detector
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