AIM: To determine whether ¹²⁵I seeds continuous low dose rate irradiation caused radiation-induced biological effect of pancreatic carcinoma cells in vitro and the mechanism by which this occurred.
METHODS: In vitro, SW1990 and Panc-1 cells in exponential growth were exposed to the dose of 0, 2, 4, 6, and 8Gy with ¹²⁵I seeds (initial dose rate of 12.13cGy/h), respectively. After irradiation, survival fraction (SF2) were calculated and compared between the two cell lines. The ratio of apoptosis and cell cycle were assessed with the tritiated thymidine (³H-TDR) incorporation experiments, and were compared between different groups of cell lines and radiation dosages.
RESULTS: No significant difference was found for the SF2 between SW1990 (0.766±0.063) and Panc-1 (0.729±0.045). The rate of apoptosis increased with radiation dosage. As the doses increased, the percentage of G2/M cell cycle arrest increased while the DNA incorporation rate decreased in both cell lines, with the peak and valley point at 6Gy.
CONCLUSION: For the continuous low dose rate irradiation in vitro with ¹²⁵I seed, there are no significant differences of cellular radiosensitivity between SW1990 and Panc-1 cell lines with the dosage ranging from 0Gy to 8Gy, and 6Gy is an efficient dosage. The major mechanisms of cell-killing effects for ¹²⁵I radioactive seeds are the apoptosis and the G2/M cell cycle arrest.