S1633
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
function of linear energy transfer (LET), responsible for quenching mechanism at CDRs and UHDRs, respectively. The new formulation quantitatively links the degree of track bunching and exciton population to reductions in scintillation efficiency Conclusion: This study provides a quantitative foundation for improved interpretation and calibration of PSD signals in FLASH proton therapy. The results may inform future standardization efforts for ultra-high dose-rate beam quality assurance and support the safe clinical implementation of FLASH proton therapy References: Favaudon V et al. Sci Transl Med. 2014. doi:10.1126/scitranslmed.3008973Vozenin MC et al. Clin Cancer Res. 2019. doi:10.1158/1078-0432.CCR- 17-3375Diffenderfer ES et al. Med Phys. 2022. doi:10.1002/mp.15276Petersson K et al. Med Phys. 2017. doi:10.1002/mp.12111Poirier Y et al. Med Phys. 2022. doi:10.1002/mp.15671Ravera E et al. Radiat Meas. 2024. doi:10.1016/j.radmeas.2024.107254Christensen JB, Andersen CE. Phys Med Biol. 2018. doi:10.1088/1361- 6560/aadf2dBirks JB. Proc Phys Soc A. 1951. doi:10.1088/0370-1298/64/10/303Blanc D et al. Compt rend. 1962. https://www.osti.gov/biblio/4812017Fenwick JD et al. Front Oncol. 2024. doi:10.3389/fonc.2024.1420337 Keywords: FLASH, Scintillation, Quenching Monte Carlo validation of the Cherenkov model using GAMOS/GEANT4 toolkit for applications in radiotherapy Andrea Vargas-Castillo 1 , Jose A. Díaz Merchan 2 , Tereza Hanušová 1,3 , Vladimír Linhart 1 1 Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Prague, Czech Republic. 2 Instituto de Cancerología Las Américas, AUNA, Medellin, Colombia. 3 Department of Medical Physics, Thomayer University Hospital, Prague, Czech Republic Purpose/Objective: Scintillator-based detectors are often used for relative dosimetry in radiotherapy (RT). However, Cherenkov light emission also contributes to the detected signal. The Cherenkov radiation has growing interest in RT dosimetry, given its correlation with the absorbed dose [1]. Moreover, Cherenkov imaging enables real- time dose verification and surface dose mapping in external beam RT [2, 3]. To understand this phenomenon, Monte Carlo (MC) simulations are essential for accurately modelling Cherenkov light production and transport.MC toolkits such as GAMOS Digital Poster Highlight 951
(Geant4-based Architecture for Medicine-Oriented Simulations), based on the Geant4 platform, have been extensively validated for RT applications. Since the treatment of ionizing and optical photon processes differs fundamentally, validating an MC framework that includes both is crucial. This study validates the GAMOS 6.2.0 toolkit for Cherenkov light generation and optical photon transport by comparing simulation results with published experimental and computational data to evaluate its suitability for dosimetric modelling. These results represent the first step toward implementing the Cherenkov effect to assess its contribution to a scintillator screen–based detector for RT quality assurance [4]. Material/Methods: Simulations were performed by initializing 105 primary particles for each electron energy from 6 to 18 MeV. A simple geometry was implemented, consisting of a monoenergetic, unidirectional electron beam (red line) incident on a spherical water phantom, as shown in Figure 1. The number of Cherenkov photons (green lines) generated within the phantom was recorded along with the deposited dose for 6, 9, 12, 15, and 18 MeV electrons. Water was selected due to the availability of reliable optical property data, namely refractive index and absorption coefficient.
Results: The simulation results agreed within 15% of the reference simulations [5] and showed a linear increase in Cherenkov photon yield with electron energy, consistent with previous experimental findings [6]. Figure 2 presents a comparison of our results with the reference data. Parameters influencing the modelling of optical photon generation and transport, as well as the number of simulated particles and computation time, are also discussed.
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