Effect of Tritiated Water on Female Germ Cells: Mouse Oocyte Killing and RBE

Summary

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 §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.