4 R's of radiobiology and Flash radiotherapy

In general, success or failure of standard clinical radiation treatment is determined by the 4 R's of radiobiology: repair of DNA damage, redistribution of cells in the cell cycle, repopulation, and reoxygenation of hypoxic tumor areas. In a FLASH radiotherapy presentation it was mentioned that the reoxygenation step might not have enough time for O2 diffusion to replenish target cells and tissues. Despite this, no substantial loss of antitumor efficiency was observed using FLASH. The author suggested that the doses used in the experiments were too low to cause depletion of O2 in the target tisues or tumors to a level that would elicit hypoxia induced radioresistance Source material Faraudon V, et al. Ultrahigh dose-rate FLASH SCI Transl Med (2014)