Scientists have shown, for the first time, that delivering a single picosecond‑scale electron pulse can reduce killing of both normal and cancer human cells compared with conventional X‑ray exposure. The study used a laser‑driven source that produced pulses about 1 ps long at mean dose rates above 10^10 Gy/s. Researchers tested normal retinal pigment epithelial cells (RPE‑1, AG01522‑D) and cancer cell lines (DU145, MCF7) by measuring surviving fractions in clonogenic assays and counting 53BP1 DNA‑damage foci. The experiments delivered up to 8 Gy per pulse. At doses up to ~3 Gy, the surviving fractions matched those obtained with a 2.4 Gy/min X‑ray beam. When the dose exceeded 3 Gy, all cell lines showed higher surviving fractions under the picosecond beam, corresponding to an average relative biological effectiveness (RBE) of 0.84 ± 0.05 at 10 % survival. The sparing effect is linked to a significant reduction in the β parameter of the linear‑quadratic model, indicating less cell killing from accumulated sub‑lethal damage. The same study reported a marked drop in early 53BP1 foci but no difference in residual foci after 24 h. A potential confounder comes from the ultra‑high dose‑rate over‑response of Gafchromic EBT3 film, which can bias dose measurements. The authors corrected for this effect using a dose‑dependent correction and found that the main conclusions – the dose‑dependent sparing and lower β values – remained unchanged. These findings suggest that the timing of energy deposition can influence biological damage. However, the observations were made in vitro under controlled laboratory conditions; further studies are needed to confirm whether the sparing effect translates to complex tissues or clinical settings. Visual: The figure shows clonogenic surviving fractions for the four cell lines under picosecond electron and conventional X‑ray irradiation, with fitted linear‑quadratic curves and calculated RBE values.