Comparison of thyroid function in mice after various injected activities of 123I, 125I and 131I

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 10(2) 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.