Experimental and Simulated H2O2 Radiolytic Yields In Ultra-Pure Water Under Proton Irradiation at High Dose Rate.
Abstract
Purpose
High-dose-rate (HDR, >40 Gy/s) irradiation can enhance the tolerance of healthy tissue. To investigate water radiolysis in proton irradiations (IBA Cyclone 70 XP, Nantes, France) for dose rates ranging from 0.2 Gy/s to 115 Gy/s, we compared H2O2 yields measured in ultra-pure water samples with Monte Carlo simulation.
Methods
A proton beamline reproducing ultra-pure water irradiation experiments was simulated using GATE (version 10). Beam alignment, homogeneity, and entrance dose were verified using Orthochromic film dosimetry compared with 2D dose maps from simulations. Using Geant4-DNA (version 11.4.0-beta), water radiolysis simulations were performed accounting for pH, oxygen, and dissolved CO2 level. The linearity of H2O2 production was first evaluated at 100 Gy/s. Subsequently, experimental and simulated H2O2 yields were compared for dose rates between 0.2 and 150 Gy/s under aerated and deaerated conditions using a fixed pulse duration of 50 ms.
Results
The gamma index evaluation demonstrated a high level of agreement between the measured and simulated dose distributions, with 97.42% of pixels passing the 2%/2 mm criteria. The linearity of H2O2 production was then confirmed at 100 Gy/s, showing excellent agreement between experimental and simulated data (R² = 0.9994 and 0.9997, respectively). Under aerated conditions, at the highest simulated dose rate (114 Gy/s), simulated G(H2O2) (1.69 ±0.01) molecules/100 eV was within the experimental range of 1.64±0.09 molecules/100 eV measured at 115 Gy/s. Under deaerated conditions, simulated G(H2O2) decreased from 1.56 to 1.22 molecules/100 eV as the dose rate increased, with relative differences of 1.9% and 14% compared to experiments.
Conclusion
We succeeded in reproducing H2O2 production under different dose rates and O2 levels. Both experiments and simulations show that G(H2O2) decreases under HDR, and simulations also show an effect of CO2 at physiological levels.