FLASH-induced DNA damage reduction measured in vitro correlates with effective oxygen depletion determined in silico: further support for oxygen depletion contributing to FLASH's reduced damage burden in vitro.

Objectives: FLASH irradiation demonstrates notable normal-tissue protective effects, including reduced damage in vitro. Radiochemical mechanisms proposed include radical-radical recombination and transient oxygen depletion (TOD), but the relative contributions remain unclear. This study compares FLASH-mediated DNA damage reduction in vitro with oxygen depletion for FLASH radiotherapy modelled in silico, to i) investigate the contribution of TOD towards the reduced damage burden in vitro, and ii) evaluate its contribution to the broader FLASH effect in vivo.

Methods: An in silico model was used to identify and compare the parameter space for FLASH-induced oxygen depletion in an in-vitro setup with experimental DNA damage reduction data, previously determined using the alkaline comet assay.

Results: Correlation analysis revealed a strong relationship between model-predicted oxygen depletion and experimentally-observed DNA damage reduction (Spearman's = 0.87, p = 2 x 10-6; Pearson's = 0.85, p = 4 x 10-6).

Conclusions: Findings support a significant role for TOD in the FLASH-induced reduction in damage in vitro at low oxygen tensions. However, parameter spaces identified, for both oxygen depletion in silico and DNA damage reduction in vitro, suggest that TOD may only partially contribute to the wider-ranging FLASH sparing effects in vivo. Further work is required to clarify this.

Advances in knowledge: Findings support TOD as a key mechanism for the reduced damage burden of FLASH in vitro. However, further work is required to demarcate the sparing effects of FLASH in vivo.