Comparison of Thyroid Function in Mice after Various Injected Activities of ¹²³I, ¹²⁵I and ¹³¹I

Summary

The radiotoxicity of ¹²³I, ¹²⁵I and ¹³¹I to the thyroid gland was compared in groups of mice subjected to activities of the three isotopes ranging from 10⁻² to 10² MBq. The thyroid function was determined fifteen months later on the basis of the 24-hour uptake of a tracer activity of ¹³¹I. A reduction in uptake to 20 per cent of the control value for untreated mice was found for mice injected with 35 MBq of ¹²³I, 13 MBq of ¹²⁵I and 2·2 MBq of ¹³¹I. On estimating the average absorbed dose in different parts of the thyroid by means of a refined method of dose calculation, that found in the cell layers surrounding the follicles seemed to be most indicative for impairment of thyroid function.