Relative biological effectiveness of 125 I seeds for low-dose-rate irradiation of PANC-1

Objective To investigate the relative biological effectiveness(RBE) of National Model 6711 125I seeds and the response patterns of PANC-1 exposed to 125I seeds irradiation.Methods PANC-1 cells inexponential growth were irradiated at initial dose rate of 2.59 cGy/h in vitro and exposed to l,2,4,6,8 and 10 Gy.Meanwhile,the other part of cells were exposed to the same doses by 60Co at dose rate of 2.21 Gy/min. After irradiation,the cells were stained by trypan blue to measure the cellular mortality rate and to compare the changes along with plating times of 12,24,48 and 72 h after 4 Gy.The colonies were counted to obtain the plating efficiencies by colony-forming assay and the cell surviving fraction was calculated tO plot cell survival curves,and RBE of 125I seeds relative to 60Co was determined.Results The cell death rate for continuous low- dose-rate(LDR)irradiation by 125I seeds was greater than 60Co at the same doses above or equal to 4 Gy.After 4 Gy irradiation,the cellular mortality rates were increased with times.The difference was significant between125 I seeds and 60Co.The survival fractions of 125I were lower than those of 60Co.and the RBE of 125I relative to 60Co was determined to be 1.45.Conclusion The cell-killing effects for continuous low-dose-rate(LDR)irradiation by 125I seeds are greater than acute high-dose.rate of 60Co. Key words: Low-dose-rate;  125I seeds;  Relative biological effectiveness; Pancreatic cancer;  Cell slain