Measurements of Hydrogen Peroxide Yields in Ultra-High-Dose-Rate vs. Conventional Radiation

Area of Science:

• Radiation Chemistry
• Radiolysis
• Water Radiolysis

Background:

• Hydrogen peroxide (H2O2) is a key product of water radiolysis, crucial for understanding radiation-induced oxidation.
• Differences in H2O2 yields between ultra-high dose rate (UHDR) and conventional dose rate (CDR) irradiation are hypothesized to contribute to FLASH radiotherapy's healthy tissue sparing effect.

Purpose of the Study:

• To quantify radiolytic H2O2 yields under UHDR and CDR proton irradiation in deaerated and oxygen-saturated systems.
• To investigate the temporal dependence of H2O2 production using OH radical scavengers (methanol and DMSO).
• To compare H2O2 yields between different dose rates and scavenging conditions.

Main Methods:

• Experimental determination of H2O2 yields under UHDR (∼120 Gy/s) and CDR (1-5 Gy/s) proton irradiation.
• Use of methanol and DMSO as OH radical scavengers at various concentrations.
• Comparison of results with simulations using the TOPAS-nBio framework.
• Validation using gamma (γ) rays.

Main Results:

• H2O2 escape yield was ∼0.7 molecules/100 eV in deaerated solutions and increased to ∼1.0 molecules/100 eV in oxygen-saturated systems.
• In oxygenated solutions, moderate scavenging initially increased H2O2 yields, while high scavenging decreased them.
• Methanol yielded higher H2O2 than DMSO under oxygenated conditions (up to 40% greater).
• No statistically significant difference in H2O2 production was observed between UHDR and CDR irradiation.

Conclusions:

• H2O2 yields are highly sensitive to scavenger concentrations and oxygen presence.
• OH radical combination reactions are critical for H2O2 formation, especially in deaerated systems.
• UHDR irradiation does not significantly alter H2O2 yields compared to CDR, challenging its direct role in FLASH sparing via this mechanism.
• Further development of complex models is needed for accurate radiation chemistry studies in biological systems.