padtingmei eye in 3 TfFemme the vadioactivitey rOllowed a Teascnubiv sj : tie = ali - TALIA. decay, representing normal cyciing of iodine back to the chyro d, but sub- sequen wm tye te be (after = / to 14 days) followed an altered and more ragid decline, hypothryroidism was predictable at a reasonably early date. §S mul taneous with the change in the thyroidal disappearance curve, there wa a rise in radioactive iodide in the sermm and in the urine, showing that the trapping mechanism for iodide in the thyroid had been damaged. Loss of this mechan- ism appears to be the first physiological evidence of radiatio I damage. The free iodide which becomes available from the deiodination Df thyroxine (T,) is not returning to the gland. If the amount of free circulating radioactive iodide is ] ess than the amount of radioactive thyroxine 4 or 5 hours after a treatment dose has been given, the disappearance from the thyroid will be rapid, the a arculating . radioactive T, will be sustained high, the dose of radiation qo the thyroid will be less than anticipated and the treatment will not be fi lly This indicated effective. a very rapid synthesis and turnover and wa: associated with the more clinically toxic natient. Inadequate therapy was most unfortunate. If radioactive triiodothyronine (T,)was found to be high in the cir- culation a few hours after treatment, it will ravidly find it 5 way into the urine and thus not be available to recycle through the th roid. result has been less than the expected therapeutic effect. The If the desired dose is calculated in the usual way, three or four treatments will be required in high T. producing patients. The ideal treatment of hyperthyroidism with t 31 I should be tbh bring the patient to a euthyroid level and no lower. Throughout these studies over B0 vears, it is 1 apparent that almost all patients treated with 13 I will ultimate become hypothyroik Although some physicians give a "standard dose" of 13 1, and wait see if it has cor rected the disease, it is more desirable to strive for the euthyrdid state. As a res of these studies, it is clear that the dose required among individuals is quite varia