Description
Laser-driven plasma accelerators generate ultra-short (picosecond-femtosecond) and extremely high dose-rate (10$^{10}$ -10$^{13}$ Gy/s) radiation sources that can induce unique cellular responses. These beams deliver multi-Gy doses on timescales overlapping with the earliest physico-chemical stages of radiation interaction. We present the in vitro cell response of biological samples to single-pulse, multi-Gy electron radiation, delivered over picosecond timescales.
Single-pulse doses of up to 8 Gy (dose-rates of 10$^{10}$ -10$^{12}$ Gy/s), were delivered to two healthy and two cancer human cell lines. Dosimetric characterisation from radiochromic film and Monte Carlo simulations confirmed high beam uniformity across samples, with transverse and longitudinal dose variations of <10 % and 1%, respectively. Biological outcomes were compared with conventional (CONV) 160 kVp X-ray irradiation (2.4 Gy/min).
At doses <3 Gy, responses were consistent with CONV irradiation (RBE$_{50}$ ~ 1 for all cell lines). At doses >3 Gy, a consistent departure was observed, with reduced radiosensitivity indicative of a FLASH-like sparing effect. This was reflected in decreased RBE$_{10}$ values (RBE$_{10}$ ~ 0.84 for all cell lines).
These results establish the potential of laser-driven plasma sources for investigating radiation responses at previously inaccessible timescales, providing a pathway to mechanistic insight into the earliest radiochemical processes involved in high dose-rate radiobiology.