The fluorod dosimeter system was used to measure the gamma exposure dose from mc levels of I131 to the neck, stomach, small intestine, kidney, bladder and gonads of euthyroid and thyroidectomized dogs. The retention kinetics of these levels of I131 were found to differ from that of tracer observations; as a result of I131 thyroid ablation, large amounts of the radionuclide rapidly left the body. The retention in extrathyroid regions, representing 76 per cent of the total effective retention, was not appreciably affected by the range in initial thyroid status represented. The measured gamma exposure doses were several times higher than predicted by the usual models. This was attributed to heterogeneity in I131 distribution within the extrathyroid regions.
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