S1673
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
1. Fonseca GP, Johansen JG, Smith RL, Beaulieu L, Beddar S, Kertzscher G, Verhaegen F, Tanderup K. In vivo dosimetry in brachytherapy: Requirements and future directions for research, development, and clinical practice. Phys Imaging Radiat Oncol. 2020 Sep 28;16:1-11.2. B. Sobiech, J. Winiecki, S. Witkiewicz- Łukaszek, Y. Zorenko, R. Makarewicz, and P. Wróbel, “In vivo measurement of radiation dose during brachytherapy treatment using scintillation detectors,” Polish Journal of Medical Physics and Engineering, vol. 30, Art. no. 4, 2024, doi: 10.2478/pjmpe-2024-0036. Keywords: in vivo, scintillation, Proffered Paper 3873 Leveraging plastic scintillation detectors for independent characterization of gating performance at a 1.5T MR-Linac Moritz Schneider 1 , Elisa Schwaak 1 , David Mönnich 1 , Daniela Thorwarth 1,2 1 Section for Biomedical Physics, Department of Radiation Oncology, University Hospital Tübingen, Tübingen, Germany. 2 German Cancer Consortium (DKTK) partner site Tübingen;, and German Cancer Research Center (DKFZ), Heidelberg, Germany Purpose/Objective: Realtime MRI enables MR-Linac beam gating for the treatment of moving targets. Quality assurance (QA) of such systems remains challenging, as current methods typically rely on time information provided by the MR- Linac and 4D phantoms. These approaches do not capture all workflow latencies and are not applicable to every phantom model.This study introduces a measurement-based method to directly quantify the gating performance of a 1.5T MR-Linac by exploiting the ultra-short integration time of a plastic scintillation detector and a dose-related position encoding. Material/Methods: Gating performance was evaluated using the ZEUS MRgRT motion phantom (CIRS, Norfolk, VA, USA). The target performed either a cos⁶ or sinusoidal motion (10 mm amplitude, 4 s period) in the inferior–superior direction to represent exhale- and mid-position gating strategies. The gating threshold was set to ± 3 mm from the respective target position. A Hyperscint RP200 detector (Medscint, Quebec, Canada) was placed inside the moving target, set to an integration time of 0.07 s.First, a reference acquisition without gating was recorded using a single irradiation field ensuring a dose gradient along the motion axis for spatial position encoding within the detector signal. Comparison of each gated detector signal with the reference allowed for a reconstruction of the detector position during beam-on (fig.1). For 50 gating cycles per motion type, the mean and maximum errors in
Figure 2. In vivo dose measurement for EBRT purposes: a, b - detector for measurement in teleradiotherapy with a 3D-printed build-up overlay c- angular characteristic of the detector in 6MV EBRT , d- dose distribution calculated in the TPS treatment planning system. Results: The very first measurements were first performed in the clinical environment of the Oncology Center in Bydgoszcz. We verified the suitability of our system for in vivo dose measurement in the case of conventional 6MV, 6MeV, 7MV (Linac-MR) beams and brachytherapy using an Ir-192 source. The experimental measurement was performed using the Alderson anthropomorphic phantom. In all three test cases, the measured dose did not differ from the expected dose (Eclipse and Oncentra) by more than 3%. Conclusion: The experimental setup seams to be wery promissing for clinical applications but needs further investication. The presented FOD detector is a very universal sensor that allows for measurements in both EBRT and brachytherapy. As shown, the response of the intensonialy grown crystal is very stable, which makes it suitable for various clinical applications. References:
Made with FlippingBook - Share PDF online