Modeling water radiolysis with Geant4-DNA: Impact of the temporal structure of the irradiation pulse under oxygen conditions

TL;DR

This study introduces a new Geant4-DNA chemistry model that simulates water radiolysis considering the temporal structure of irradiation pulses, revealing how pulse timing affects reactive oxygen species production under various oxygen conditions.

Contribution

The paper presents a novel Geant4-DNA model that incorporates pulse temporal structure in water radiolysis simulations, enabling detailed analysis of dose rate and oxygen effects.

Findings

Pulse temporal structure influences ROS production.

Higher dose rates reduce ROS levels.

Model covers a wide dose rate range from 0.01 to 10^5 Gy/s.

Abstract

The differences in H2O2 production between conventional (CONV) and ultra-high dose rate (UHDR) irradiations in water radiolysis are still not fully understood. The lower levels of this radiolytic species, as a critical end product of water radiolysis, are particularly relevant for investigating the connection between the high-density energy deposition during short-duration physical events (ionizations or excitations) and biological responses of the FLASH effect. In this study, we developed a new Geant4-DNA chemistry model to simulate radiolysis considering the time structure of the irradiation pulse at different absorbed doses to liquid water of 0.01, 0.1, 1, and 2 Gy under 1 MeV electron irradiation. The model allows the description of the beam's temporal structure, including the pulse duration, the pulse repetition frequency, and the pulse amplitude for the different beam irradiation conditions through a wide dose rate range, from 0.01 Gy/s up to about 105 Gy/s, at various oxygen concentrations. The preliminary results indicate a correlation between the temporal structure of the pulses and a significant reduction in the production of reactive oxygen species (ROS) at different dose rates.