Effect of tritiated water on female germ cells: mouse oocyte killing and RBE

The relative biological effectiveness (RBE) of tritiated water (HTO) was investigated using mouse immature oocytes. Juvenile mice, having immature oocytes that are highly sensitive to radiation killing, were exposed to HTO, 137Cs gamma rays, 60Co gamma rays, or 252Cf fission neutrons. The 137Cs gamma rays were used to simulate the changing dose rate (but not the radiation quality) received from HTO (see section 2). On the 14th day after birth, female ICR strain mice were injected once in the abdominal cavity with HTO at levels of 1.70, 3.40, 6.81, or 10.21 MBq/10g body weight, and their ovaries were removed 2 weeks after the injection. (The cumulative doses are equivalent to 0.039, 0.077, 0.159 and 0.246 Gy, respectively.) The survival rate of oocytes was determined by light microscopy inspection of serial sections, and the results of the different exposures were compared. The number of surviving oocytes decreased exponentially with increasing dose of HTO or 137Cs, and RBEs of HTO compared to 137Cs gamma rays ranged from 1.1 to 3.5. The relative effectiveness of the different types of radiations was compared, and the results of the comparison, in order of increasing effectiveness, was 137Cs, 60Co, HTO, and 252Cf. The RBE of 252Cf compared to 60Co gamma rays ranged from 1.6 to 3.5.