Influence of iodine application during radioiodine therapy in rase of impending therapy failure

Aim: We investigated whether additional application of "cold" iodine after therapy with radioiodine could result in a prolongation of the effective ha lf life of iodine-1 31 and would thus lead to on increase of the effective thyroid radiation dose. Methods: Time-activity-curves after therapy with ra dioiodine were analysed in 25 patients (16 women, 9 men). Nine patients suf fered from autonomously functioning thyroid nodules, 5 from autonomous mult inodular goiter and 11 from Graves' disease. These patients had an effectiv e half life shorter than 4 days resulting in an undertreatment of > 20% wit h respect to the desired effective thyroid radiation dose. 2-4 days after t herapy with radioiodine all patients received "cold" iodine for three days in a dose of 3 x 200 mu g per day. Results: In 14 of the 25 patients an inc rease of the effective half life was observed. patients with on autonomousl y functioning thyroid nodule showed a mean increase of the effective thyroi d radiation dose of 40 +/- 44 Fy, patients with toxic multinodular goiter o f 29 +/- 30 Gy and patients with Graves' disease of 37 +/- 37 Gy. Conclusio n: Additional application of "cold" iodine after therapy with radioiodine c on prolong the effective half life in selected patients. We suspect a corre lation with the thyroid iodine pool. This will be the basis for further inv estigations hopefully resulting in a better patient preselection to determi ne who might respond to this therapy.