Radioactive iodine in thyroid medicine--how it started in Sweden and some of today's challenges.

In Sweden, radioactive iodine for thyroid diagnostics and therapy was introduced by Jan Waldenström (1906-1996) and Bengt Skanse (1918-1963). The paper describes the start of the clinical use of radioiodine, the various iodine isotopes available, measurement techniques and dosimetry. There are still problems to solve in relation to an optimal clinical use of radioiodine. One of the remaining challenges is to get consensus about the goal of the treatment of hyperthyreosis, as well as about a method for individual absorbed dose calculations. Careful dose estimates will prevent unnecessary radiation exposure and constitute a base for a future optimised radioiodine therapy. For the dose calculation, it is important to understand if there is any clinically significant temporary reduction in the ability of thyroid tissue to trap or retain 131I-iodide following prior administration of a diagnostic activity of 131I-iodide (stunning of the thyroid). This may be of special concern in connection with treatment of thyroid cancer and its metastases. Finally, the production capacity, availability and delivery of 123I have to be improved to increase clinical access to this radionuclide, which is optimal for diagnostic imaging and which gives lower absorbed dose and therefore also less risk for thyroid stunning than 131I.