S1683
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
Digital Poster Highlight 4305
pulse-width behaviour(Fig.1). Among passive detectors, alanine and FLASHDiamond agreed within 5%, indicating good overall consistency, while EBT4 films matched within 2% up to ≈8 Gy. Roos chamber readings were stable in CONV9. Charge and ADR increased linearly with PRF, demonstrating stable beam output across varying pulse frequencies(Fig.2).
Multi-detector characterisation of a 9 MeV FLASH electron beam for clinical dosimetry development Iris Apale 1,2 , Racell Nabha 1,2 , Sevérine Rossome 3 , Marlies Boussaer 1,2 , Milan Compernolle 4 , Brigitte Reniers 4 , Mark De Ridder 1,2 , Thierry Gevaert 1,2 1 Department of Radiotherapy, UZ Brussel, Vrije Universiteit Brussel, Brussels, Belgium. 2 Research Centre for Digital Medicine, Vrije Universiteit Brussel, Brussels, Belgium. 3 Dosimetry department, IBA, Louvain-la-Neuve, Belgium. 4 NuTeC, Uhasselt, Hasselt, Belgium Purpose/Objective: Accurate dosimetry is essential for the safe development and implementation of FLASH radiotherapy. This study benchmarks and compares the response of multiple detector system, including ionisation chambers, solid-state detectors, scintillators, and passive dosimeters which were exposed to 9 MeV ultra-high-dose-rate (UHDR) & conventional(CONV) electron beam . The study aimed to assess detector linearity, stability range, and agreement with alanine and EBT4 references under clinically relevant FLASH conditions. Material/Methods: Irradiations were performed using the THERYQ FLASHKNiFE (9 MeV, 10 × 10 cm² circular field) in FLASH9 (>300 Gy s ⁻ ¹) and CONV9 (10 Gy s ⁻ ¹) modes. Four exposure conditions were tested: (1) 300 Hz, 3 µs, 2 pulses; (2) 100 Hz, 1 µs, 6 pulses; (3) 300 Hz, 1 µs, 6 pulses; and (4) 10 Hz, 1 µs, 358 MU (CONV). Each delivered approximately 4 Gy.Detectors: FLASHDiamond, Exradin W1 scintillator, Razor Nano Diode, Razor Nano IC, two SiC prototypes (W1/W2), two PPC05 chambers (standard/reduced volume), Roos chamber, EBT4 film, and alanine pellets. Data were acquired using Dose1, DoseX, and Romeo electrometers, and analysed for dose-per-pulse (DPP), average dose rate (ADR), and repeatability across varying pulse width (0.5-4 µs), repetition frequency (10–300 Hz), and pulse number (1–30). Results: Dose-calibrated detectors (flashDiamond, Exradin W1, Roos, EBT4 films, and alanine) provided consistent absolute dose data; others were assessed through charge response. The Exradin W1 was stable at 0.5 µs (DPP ≈ 0.33 Gy pulse ⁻ ¹, ADR 40–70 Gy s ⁻ ¹); signal loss above 1 µs resulted from SuperMax electrometer saturation. FlashDiamond and Razor Nano Diode maintained ≤ 1 % variation across pulse width and PRF. SiC prototypes showed excellent charge linearity with minimal PRF dependence (< 2 %). PPC05 chambers were polarity-independent with < 1.5 % variation; the reduced-volume model collected ≈ 50 % less charge. Razor Nano IC exhibited linear charge-
Conclusion: Active and passive detectors showed consistent, linear, and reproducible performance under 9 MeV UHDR and conventional irradiation. Dose-calibrated systems confirmed absolute dose, while charge-based detectors remained stable and rate-independent, supporting their use in cross-calibration and real-time FLASH dosimetry. The close agreement between alanine, film, and active detectors establishes a foundation for UHDR dosimetry standardisation and represents a comprehensive clinical FLASH comparison. Keywords: FLASH, Detector Characterisation, UHDR Electrons Digital Poster Highlight 4379 Evaluation of the new RUBY adaptive MR phantom for MRgART QA Simon Woodings 1 , Daniela Eulenstein 2 , Wilfred de Vries 2 , Sima Sajadi 1 , Thomas Foppen 1 , Madelon van den Dobbelsteen 1 1 Radiotherapy, UMC Utrecht, Utrecht, Netherlands. 2 PTW Dosimetry, PTW, Freiburg, Germany Purpose/Objective: PTW (Freiburg, Germany) have developed the RUBY phantom for quality assurance of high-precision and stereotactic radiotherapy, including image-guided treatments1-3. New prototype organ-set inserts, equivalent to the original CT organ-sets but suitable for magnetic resonance imaging, have been developed
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