S1634
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
Conclusion: The optical Monte Carlo modelling performed using GAMOS demonstrates consistency and good agreement with reference data. GAMOS provides an efficient and user-friendly simulation environment suitable for modelling Cherenkov radiation and related optical processes. These results confirm that Cherenkov-induced optical photon production can be accurately simulated within GAMOS, supporting its use in dosimetry and radiotherapy research. Future work will involve generating primary particles from phase- space data to model a realistic external x-ray photon beam. References: [1] Glaser AK et al. Phys Med Biol. 2014;59:3789–3811. doi:10.1088/0031-9155/59/14/3789[2] Alexander DA et al. Pract Radiat Oncol. 2023;13(1):71–81. doi: 10.1016/j.prro.2022.06.009.[3] Robinson A et al. Pract Radiat Oncol. 2025. https://doi.org/10.1016/j.prro.2025.09.004[4] Hanušová T et al. Radiat Prot Dosimetry. 2022;198(9– 11):566–572. doi:10.1093/rpd/ncac100[5] Shrock Z et al. Med Phys. 2018;45:3315– 3320. https://doi.org/10.1002/mp.12927[6] Axelsson J et al. Med Phys. 2011;38(7):4127–4132. DOI: 10.1118/1.3592646 Keywords: Cherenkov effect, dosimetry, MC simulations
Because the prototype's performance depends on the chemical makeup of the active solution, optimizing the system requires a systematic study of the solution formulation. This work evaluates the effects of the chemical components of this water-based dosimeter on its response and identifies the optimal composition. Material/Methods: The approach is to test multiple solutions with different chemical compositions using the hydrated- electron dosimeter. Five aqueous solutions were prepared as follows: (1) NaOH (pH 12.2), (2) 50.5mM sodium ascorbate in NaOH (pH 12.2), (3) deionized water, (4) 2 mM ethanol in NaOH (pH 12.2), and (5) NaOH (pH 12.2). All solutions were prepared using Milli-Q deionized water and purged with gas to reduce dissolved oxygen levels–argon for solutions (1)–(4) and hydrogen for solution (5). Each solution sample in the prototype was irradiated with photon beams (6 MV, 6 MV FFF, 10 MV, 10 MV FFF, 15 MV) and an electron beam (6 MeV) from a Varian TrueBeam™ linac. The absorbed dose measured by the prototype was compared with EBT4 film measurements under identical conditions. The absorbance profiles were examined to assess the influence of each formulation and identify the preferred solution. Results: Among all samples, sample (3) produced the most accurate and stable dose response across beam energies, with most percentage differences between the doses measured by the hydrated-electron dosimeter and those measured by the EBT4 film remaining within 6%, indicating strong performance. Sample (1) showed the highest hydrated-electron concentration (0.367 nM), the longest half-life (23.416 μs), and better sensitivity at low dose-per-pulse due to the enhanced hydrated-electron yield at high pH, which allows reliable signal detection at lower dose ranges. In contrast, at higher dose-per-pulse conditions, where sensitivity becomes less critical, sample (3) may be preferable because of its greater chemical stability and higher dose accuracy.
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Evaluation of the chemical components in the active material of a hydrated-electron dosimeter Jingyi Bian 1 , Fernanda R Machado 2 , Robert Hopewell 3 , Hamed Bekerat 4 , Tanner Connell 5 , Jack C Sankey 2 , Shirin A Enger 1,6 1 Medical Physics Unit, Department of Oncology, McGill University, Montreal, Canada. 2 Department of Physics, McGill University, Montreal, Canada. 3 McConnell Brain Imaging Centre, Montreal Neurological Institute, Montreal, Canada. 4 Radiation Oncology Department, Jewish General Hospital, Montreal, Canada. 5 Medical Physics Unit, McGill University Health Centre, Montreal, Canada. 6 Lady Davis Institute for Medical Research, Jewish General Hospital, Montreal, Canada Purpose/Objective: Hydrated electrons produced by water radiolysis increase water's optical absorption, with these changes reflecting the absorbed dose. Our group previously developed a prototype hydrated-electron dosimeter to measure absorbed dose by tracking hydrated-electron concentration using absorption spectroscopy. Its feasibility has been demonstrated through EBT3 film comparison, showing potential for tissue-equivalent dosimetry in clinical radiotherapy.
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