The influence of non-radioactive iodine (I-127) on the outcome of radioiodine (I-131) therapy in patients with Graves' disease and toxic nodular goitre

BACKGROUND: The aim of the study was to achieve an effective target dose in the thyroid by increasing the effective half-life (Teff) of I-131 by use of iodide (I-127) two days after I-131 therapy in patients with hyperthyroidism with low Teff. MATERIAL AND METHODS: The study was carried out in two groups. Group A - 41 patients, and Group B - 14 patients, all the patients were with hyperthyroidism with Teff less than 3 days qualified for I-131 therapy. Only group A patients received 600 mu g of iodide a day for 3 days, two days after I-131 therapy. Radioiodine uptake (RAIU) after 24 and 48 hours, thyroid scintiscan and ultrasonography were done before and after 12 months of I-131 therapy. RESULTS: In group A a significant increase was seen in the Teff (5 days on average) resulting in an increase in the energy target dose by 28% and 37%, in patients with Graves' disease (GD) and toxic nodular goitre (TNG), respectively. After one year of therapy50% of GD and 93% of TNG patients achieved euthyroidism; 28% of GD and 3% of TNG patients were in hypothyroidism. In Group B, all the patients had radioiodine treatment failure and received a second therapeutic dose of I-131. CONCLUSIONS: Administration of I-127 after I-131 treatment can lead to an increase in its effective half-life. This will also increase the absorbed energy dose in thyroid tissue, thereby improving therapeutic outcome without administration of a higher or second dose of I-131. This may minimize whole-body exposure to radiation and reduces the cost of treatment.