The influence of non-radioactive iodine (127I) on the outcome of radioiodine (131I) 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 (131)I by use of iodide ((127)I) two days after (131)I 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 (131)I therapy. Only group A patients received 600 μg of iodide a day for 3 days, two days after (131)I therapy. Radioiodine uptake (RAIU) after 24 and 48 hours, thyroid scintiscan and ultrasonography were done before and after 12 months of (131)I 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 therapy 50% 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 (131)I.

CONCLUSIONS

Administration of (127)I after (131)I 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 (131)I. This may minimize whole-body exposure to radiation and reduces the cost of treatment.