S2603
Radiobiology - Radiobiological modelling
ESTRO 2026
Figure 2: Simulated oxygen depletion G-values for different initial oxygenation levels at 1 µs post-irradiation. Conclusion: In this work, simulations of the chemical stage were performed at different levels of water oxygenation, with electrostatic interactions taken into account. These interactions exert a significant influence on the radiolytic yields and on oxygen consumption. References: [1] Erdmann, R. et al. “Chemistry simulations following radiolysis with consideration of interaction potentials”, Digital Poster, ESTRO 2025; doi:10.1016/S0167-8140(25)01834-1.[2] Chappuis, F. et al. “Modeling of scavenging systems in water radiolysis with Geant4- DNA”, Physica Medica. 2023; 108:102549. Keywords: radiation chemistry, radiolysis, Monte Carlo
chemical stage at different oxygenation levels, in which the electrostatic interactions between radiolytic species are explicitly incorporated. The impact of this refinement on the temporal evolution of radiochemical yields and oxygen depletion is evaluated. Material/Methods: The set of species produced in water radiolysis can be divided into two groups: neutral and electrically charged ones. The latter interact with each other through electrostatic forces, which can be described by the Coulomb potential. To transport the species, the interaction potentials are included in the stochastic equations of motion. These interactions also influence the reaction probability of charged reactants within a time step, which is obtained numerically by sampling the reaction paths in the force field. A C++ code, PATHMC [1], implementing the proposed concept has been developed, and the radiochemical yields in a water-filled volume were compared with those obtained from the established Monte Carlo toolkit Geant4-DNA [2]. For 1 MeV electron irradiation at 4% oxygenation, the time evolution of G-values (number of molecules / 100 eV of deposited energy) of various radiolytic species was investigated. Additionally, oxygen depletion was evaluated for different water oxygenation levels. Results: If electrostatic interactions are neglected in PATHMC, the results agree with Geant4-DNA. When electrostatic interactions are included, G(H•) increases by about 15%, which in turn leads to an enhanced formation of the HO2• radical with a relative change of about 26% (Fig. 1). The oxygen consumption arising from the additional HO2• is reflected in a mean deviation of 8% in the oxygen depletion at 1 µs post-irradiation (Fig. 2).
Digital Poster 3284
Impact of instantaneous radical density on DNA strand breaks Yating Zhang 1,2 , David Weishaar 2 , Robin Erdmann 2 , Fabian Meister 3 , Natalie Hornik 2,4 , Kilian-Simon Baumann 2,5 1 Marburg University Hospital, Marburg University, Marburg, Germany. 2 Institute of Medical Physics and Radiation Protection, University of Applied Sciences, Gießen, Germany. 3 Department of Physics, Marburg University, Marburg, Germany. 4 LOEWE Research Cluster for Advanced Medical Physics in Imaging Therapy (ADMIT), University of Applied Sciences, Gießen, Germany. 5 Marburg Ion- Beam Therapy Center (MIT), University Hospital Marburg, Marburg, Germany Purpose/Objective: To investigate how radical accumulation during the chemical stage influences DNA damage under ultra high dose rate conditions, Geant4-DNA (molecularDNA [1]) was used to compare two simulation scenarios. In the standard scenario, each irradiation event generates radicals that react independently, so radicals from different primary particles never coexist and no inter-track interactions occur. In the cumulative scenario, radicals generated in multiple irradiation events are carried over to subsequent events, allowing species originating from different tracks to coexist within the same chemical stage and mimic an instantaneous high radical density. The objective was to determine whether radical accumulation promotes radical–radical recombination, reducing the number of radicals available to interact with DNA, or whether it enhances radical–DNA reactions and increases DNA damage. Material/Methods: The molecularDNA example was implemented to simulate electron irradiation of a DNA segment in liquid water. Electrons of 1 keV were emitted isotropically using the general particle source and ten irradiation events were simulated. In the standard condition A, radicals from each event evolved independently through the physical, physico-chemical and chemical stages. In the cumulative condition B, radicals generated during the first nine events were collected at the end of their pre-chemical stages and then injected together at the beginning of the chemical stage of the tenth event, resulting in a much higher instantaneous radical concentration. This setup enables investigation of how radical accumulation affects the yield of indirect DNA damage. Results: Figure 1 shows that, compared with the standard condition, the cumulative condition exhibits a higher initial radical density and a markedly stronger decrease within the first nanosecond. Table 1 shows that cumulative accumulation substantially increases radical- radical reaction frequencies. DNA damage analysis reveals that under standard condition, all DNA single-strand breaks originate
Figure 1: Time evolution of G-values for 1 MeV electrons, depositing a total energy of 10 keV in the water phantom with 4% oxygenation, as simulated by Geant4-DNA and PATHMC.
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