Cell culture and irradiation

HEK‐293 T, A549, H1299, HCC827, and BEAS‐2B cell lines were procured from the American Type Culture Collection and cultured in Dulbecco's modified Eagle's medium. A549 and H1299 cell lines were irradiated for radiation‐resistance analysis. When cell confluence reached 50%, A549 and H1299 cells were subjected to X‐ray irradiation (2 Gy), cultured, digested with trypsin at a 90% convergence rate, and then reirradiated at a 50% convergence rate, with a 2 Gy daily fraction size being administered 30 times for a total dose of 60 Gy. Parental cells were cultured without radiation under the same conditions. In addition, there was an interval of four or five months between the last two partial exposures. Cells were replated for colony formation after recovering for 2–3 weeks after the last irradiation. After 2–3 weeks, the progenies of the clonogenic survivors were obtained.