2.3. Cell Irradiation and Culture of Irradiation-Resistant Cells

Siemens Primus Linear Accelerator (Siemens, Germany) was used to generate a 6 MV X-ray beam for radiotherapy at a radiation dose rate of 3 Gy per minute. The X-ray beam was delivered vertically at 0, 2, 4, 6, and 8 Gy, respectively. The radiation field was 10 cm × 10 cm, with a source-to-target distance of 3 cm. The survival fraction was estimated after irradiation. According to the literature [18], when the parental BxPC-3 cells (named BxPC-3-P) entered the logarithmic growth phase (70%-80%), X-ray beam was generated with a linear accelerator for the radiotherapy. The culture medium was replaced after 24 h of irradiation. When the cells continued to grow or new colonies were formed, the cells were digested and loaded into another flask. The cells which reached 70-80% confluency were reirradiated at 4 Gy for a total dose of 40 Gy. The cells obtained after the above procedures were screened out and identified as radioresistant pancreatic cancer cells BxPC-3-RR¹².