Iodine isotope (I-131) therapy for toxic nodular goitre: treatment efficacy parameters

BACKGROUND: When planning radioactive iodine therapy, it frequently happens, both in Poland and world-wide, that inadequate attention is paid to such easily measurable parameters as: 1) the serum concentration of thyrotropin (TSH) before administering radioiodine, which is a key factor for extranodular (non-autonomous) iodine uptake of the thyroid gland, 2) thyroid gland iodine uptake, and 3) the effective half-life of I-131 (T-eff.). The aim of the study is to evaluate the impact of the above factors on the efficacy of I-131 treatment in hyperthyroid patients. METHODS: The material consisted of 4140 patients: 2190 with autonomous toxic nodules (ATN) and 1950 with toxic multinodular goitres (TMG). The patients were prepared for treatment in such a way that the concentration of TSH did not exceed 0.1 mU/l and T-eff. < 5 days. The therapeutic activity of I-131 was calculated using Marinelli's formula. The selection of absorbed dose value was determined by the degree of suppression of extranodular tissue. Monitoring was performed every eight weeks. RESULTS: At one year after I-131 administration showed that a euthyroid status was achieved in 94%, hypothyroidism was seen observed in 3%, while persistence or recurrence of hyperthyroidism in 3% of ATN patients and, respectively, 89%, 4% and 7% of TMG patients. CONCLUSIONS: Patients with toxic nodular goitre who are to be treated with radioiodine should have the lowest possible serum concentration of TSH. The suppression of extranodular determines the optimal value of absorbed dose for Marinelli's formula.