FLASH irradiation results in reduced mortality compared to CONV dose-rate irradiation at high doses. Kaplan-Meier survival curves of mice. Control: 0 Gy (n = 5); FLASH: 10, 16, 20, 30 and 40 Gy (n = 5 each); CONV: 10, 16, 20, 30 and 40 Gy (n = 5 each). Control (0 Gy), FLASH (10, 16, 20 and 30 Gy) and CONV (10, 16, 20 Gy) irradiation groups all had a 100% survival and are shown as a single curve. Censored subjects are shown as ticks. There was significantly longer survival with 30 Gy FLASH compared to 30 Gy CONV irradiation, and also significantly longer survival with 40 Gy FLASH irradiation compared to 40 Gy CONV irradiation; *log-rank P < 0.05.