A mathematical model of optimized radioiodine-131 therapy of Graves' hyperthyroidism

Optimized therapy is evaluated both in terms of the greatest separation of cure rate from hypothyroidism rate (non-ablative therapy) or in terms of early hypothyroidism (ablative therapy) by mathematical modeling of outcome after radioiodine and critically discussing the three common methods of RaI dosing for Graves' disease.Cure follows a logarithmic relationship to activity administered or absorbed dose, while hypothyroidism follows a linear relationship. The effect of including or omitting factors in the calculation of the administered I–131 activity such as the measured thyroid uptake and effective half-life of RaI or giving extra compensation for gland size is discussed.Very little benefit can be gained by employing complicated methods of RaI dose selection for non-ablative therapy since the standard activity model shows the best potential for cure and prolonged euthyroidism. For ablative therapy, a standard MBq/g dosing provides the best outcome in terms of cure and early hypothyroidism.Radioiodine-131 (RaI) therapy has been increasingly used for the treatment of hyperthyroid Graves' disease. Many factors contribute to the current popularity of this treatment modality as a primary and secondary management option, especially the recurrence of Graves' disease after drug therapy. Initially, the dosage (radioactivity) administered was worked out by a trial-and-error method but with increasing experience over the last century, RaI treatment methods evolved [1]. Initially, using a standard radioactivity of about 6 MBq (160 μCi) 131–I per gram of estimated thyroid weight, it was apparent that RaI therapy caused iatrogenic hypothyroidism. The incidence was about 20 – 40% in the first year after therapy, increasing by about 2.5% per year to 50 – 80% at 10 years [2]. In an effort to reduce this incidence of late hypothyroidism, Hagen and colleagues reduced the administered quantity of RaI to 3 MBq (80 μCi) per gram of estimated gland weight [2] resulting in a substantia