Abstract Body

Animal models have demonstrated that FLASH-RT preserves healthy tissues while yielding similar tumor growth delay as conventional irradiation. Despite the promise of FLASH-RT, the physico-chemical and biological mechanisms underlying the FLASH effect are still under investigation. Recent studies have demonstrated that radiotherapy induces ferroptosis through intensive lipid peroxidation. Lipid peroxidation is a chemical reaction consuming oxygen, which might be involved in the FLASH effect. In this work, we used linoleic acid micelles and phosphatidylcholine (PC) liposomes as a proxy for cell membrane to investigate the lipid peroxidation yield after irradiation with electrons in FLASH and CONV modalities. With this system, we measured significant differences in concentrations of lipid peroxidation endproducts between both modalities of irradiation. The lipid micelles and PC liposomes exhibited enhanced and linear dose-dependent levels of lipid peroxidation with CONV, while FLASH did not induce lipid peroxidation. The lipid peroxidation yield dropped rapidly when the dose per pulse was increased from 0.008 Gy·pulse-1 to 10 Gy·pulse-1, with no lipid peroxidation occurring above 0.2 Gy·pulse-1. By measuring the oxygen consumption rate during irradiation, we confirmed that CONV irradiation leads to much higher lipid peroxidation yield compared to FLASH. In addition, we demonstrated also that not only the concentration but also the composition in PUFA of the liposomes bilayer has importance in propagating the peroxidation reaction. Our results are the first to identify the lack of lipid peroxidation after FLASH-RT, and point to lipids as potentially critical target in rationalizing possible mechanisms underlying the FLASH effect across multiple normal tissue sites.