Unraveling the Redox Mechanisms Underlying FLASH Radiotherapy: Critical Dose Thresholds and NRF2-Driven Sparing of...

FLASH radiation therapy (FLASH-RT) can achieve tumor control comparable to conventional dose-rate irradiation (CONV-RT) while reducing radiation damage to normal tissues. However, the physical conditions triggering the FLASH sparing effect remain unclear, and mechanisms related to oxidative stress and redox regulation are poorly understood. This study aimed to investigate the physical parameters and redox-related molecular mechanisms responsible for the FLASH effect.

This study uses a murine acute intestinal toxicity model to investigate how beam parameters influence the FLASH sparing effect and tumor control using innovative FLASH-RT and CONV-RT combined irradiation. We integrated kinetic simulations, experimental measurements of oxidative stress and lipid peroxidation, antioxidant interventions, RNA sequencing, nuclear factor E2-related factor 2 (NRF2) knockout mice and molecular analyses to elucidate the involved pathways.

The results demonstrate that a substantially reduced FLASH dose can still elicit the sparing effect, provided a total dose threshold is met. Kinetic simulation and experimental validation demonstrate that FLASH-RT enhances peroxyl radical recombination, reducing oxidative stress and lipid peroxidation. Antioxidant interventions further confirm the essential role of free radicals. Molecular profiling revealed that FLASH-RT activates the NRF2 antioxidant pathway while suppressing ERK signaling, thereby enhancing cellular redox defenses, reducing apoptosis, and mitigating radiation-induced tissue injury.

These findings highlight the feasibility of optimizing the FLASH-RT therapeutic window through redox modulation and provide a foundation for developing free radical-targeted strategies to improve its therapeutic efficacy.