Figure 1.
Induction of DNA damage in skin carcinoma cells irradiated at a very high dose rate by a single ultrashort bunch of high-energy electrons. (a) Image showing the overlap between the 2D dose deposition of a femtosecond quasi-monoenergetic electron bunch (100 fs pulse duration, mean energy of 95 MeV) and the pellet containing about 5 × 105 human skin carcinoma cells. The dose delivered in the pellet (semi-ellipse) by an ultrafast single shot (1.02±0.13 Gy, dose rate 1013 Gy s−1) is determined from Monte Carlo calculations. The exact number of electrons is deduced from scintillator measurements, which have been absolutely calibrated.9 (b, c) Time-dependent evaluation of DNA damage using the alkaline comet assay for sham-irradiated (0 Gy) and irradiated carcinoma cells (1 Gy) immediately after the femtosecond irradiation (b) and after 1 h of repair time at 37°C (c). The frequencies of cells as a function of their damage level expressed by the comet tail moments are shown (300 comets analyzed per sample using Komet 6 software, Kinetic Imaging Ltd., Bromborough, UK). Gray bars represent the % of cells above a tail moment of 4 (arbitrary unit). A significant difference between the distributions of 0 and 1 Gy samples was found for initial damage (χ2 test, P<0.002)