Irradiation

Irradiation was performed at room temperature with a linear accelerator using a dose rate of 4.8 Gy min⁻¹ and a dose of 2 Gy was applied. To measure the colony-forming ability after irradiation, 1 x 10³ cells were resuspended in 1 ml culture medium, plated into 3.5 cm Petri dishes with a 2.5 mm grid (Nunc, Langenselbold, Germany) and incubated for about 6 days in a CO₂ incubator at 37°C. Cell colonies with more than 50 cells were counted using a microscope (Olympus, Hamburg, Germany). The survival fraction was calculated as follows: plating efficiency treated/plating efficiency control. Radiation resistance was analyzed by two independent researchers (SKK, AvD).