Ultra-high dose-rate (FLASH) radiotherapy: Generation of early, transient, strongly acidic spikes in the irradiated tumor environment

Monte Carlo simulations of gamma/fast electron-radiolysis of water show that the in situ formation of H3O+ temporarily renders each native isolated spur/track region very acidic. For pulsed (FLASH) irradiation with high dose rate, this early time, transient acid-spike response is shown to extend evenly across the entire irradiated volume. Since pH controls many cellular processes, this study highlights the need to consider these spikes of acidity in understanding the fundamental mechanisms underlying FLASH radiotherapy. (C) 2020 Societe francaise de radiotherapie oncologique (SFRO). Published by Elsevier Masson SAS. All rights reserved.