Author: Xu Cao, Wesley S. Culberson, Aubrey Parks, Brian W Pogue, William Scott Thomas 👨🔬
Affiliation: Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin - Madison, University of Wisconsin-Madison, University of Wisconsin - Madison, UW-Madison 🌍
Purpose:
The hydrated electron is a critical reactive species generated during the radiolysis of water when ionizing radiation interacts with biological tissues. It plays a pivotal role in mediating radiation-induced chemical reactions, particularly those contributing to DNA damage and oxidative stress. Understanding the behavior of hydrated electrons under Ultra-High Dose Rate (UHDR) irradiation is essential to elucidate the mechanisms underlying the FLASH effect. This study aimed to quantify the transient production of hydrated electrons in vivo under UHDR electron irradiation using an optical absorption measurement approach.
Methods:
UHDR electron irradiation was delivered using a 9 MeV electron beam to the targeted tissue with a precisely defined 3 cm² circular radiation field. A 730 nm near-infrared laser (0.5 cm dot-point source) illuminated the tissue at the irradiation site. A silicon photodiode module with an active area of 0.8 mm² was use to detect the transmitted light signals. The transient absorbance was analyzed to estimate the concentration of hydrated electrons.
Results:
The concentration of hydrated electrons produced in vivo during UHDR irradiation was significantly lower than that observed in pure water under identical conditions. A linear relationship was observed between the total radiation dose and the production of hydrated electrons in both in vivo tissues and pure water. However, the slope of absorbance curve was steeper for pure water, indicating higher radical yields compared to the biological environment.
Conclusion:
This study successfully quantified the transient production of hydrated electrons in vivo under UHDR electron irradiation, providing critical insights into the radiochemical dynamics of FLASH radiotherapy. The significantly lower yield of hydrated electrons in vivo compared to pure water underscores the complexity of radiation-induced chemistry in biological systems. These results suggest that biological scavengers and tissue-specific factors play a crucial role in modulating radical production and may contribute to the observed FLASH effect.