250 Radiation-Associated Thyroid Carcinoma © may go through more cell divisions before succumbing to radiation effects, whereas with higher doses the cells may die at their first mitosis. EFFECT OF THYROXINE TREATMENT In 1965 a panel of thyroid specialists, after reviewing the findings, recommended that the heavily ex- posed Rongelap group be placed on replacement thyroxine for life in order to block TSH secretion by the pituitary. Synthetic L-thyroxine (Synthroid) has been used. Two years ago the Ailingnae and in utero exposed groups were also placed on this treatment. Those of the Utirik people who developed thyroid tumors are also being given thyroxine. It was hoped that this suppresSive therapy would inhibit development of neoplasia, and that growth and development in the hormone-deficient children would be enhanced. It has been difficult to maintain a strictly regular treatment regimen, but the treatment has been of benefit in enhancing growth aud development in the growth retarded children and in Maintaining a normal metabolic state in the operated cases. Fig. 4 shows the improvement in growth and development in one of the stunted boys, shown standing beside his younger brother. It is uncertain whether or not the treatment has had any effect in preventing the development of nodules in the exposed Rongelap people. Some tumors developed before therapy was instituted. Since then, however, 14 people in this group who were not always consistent in taking their medication, but some of them were thought to be conscientious about it. In two cases nodules appeared to diminish on therapy. THYROID FUNCTION Tests of thyroid function were carried out in the earlier years by PBI analyses, later by an improved method involving ion exchange and more recently, by radioimmunoassays for Tg, triiodothyronine (T3), TSH, thyroxine binding globulin (TBG) and thyroglobulin (TG). Since 1974 function has also been tested by Ta incre-