Accuracy of two simple methods for estimation of thyroidal I 131 kinetics for dosimetry‐based treatment of Graves’ disease

One of the major challenges to the more widespread use of individualized, dosimetry‐based radioiodine treatment of Graves’ disease is the development of a reasonably fast, simple, and cost‐effective method to measure thyroidalI131kinetics in patients. Even though the fixed activity administration method does not optimize the therapy, giving often too high or too low a dose to the gland, it provides effective treatment for almost 80% of patients without consuming excessive time and resources. In this article two simple methods for the evaluation of the kinetics ofI131in the thyroid gland are presented and discussed. The first is based on two measurements 4 and 24 h after a diagnosticI131administration and the second on one measurement 4 h after such an administration and a linear correlation between this measurement and the maximum uptake in the thyroid. The thyroid absorbed dose calculated by each of the two methods is compared to that calculated by a more completeI131kinetics evaluation, based on seven thyroid uptake measurements for 35 patients at various times after the therapy administration. There are differences in the thyroid absorbed doses between those derived by each of the two simpler methods and the “reference” value (derived by more complete uptake measurements following the therapeuticI131administration), with 20% median and 40% 90‐percentile differences for the first method (i.e., based on two thyroid uptake measurements at 4 and 24 h afterI131administration) and 25% median and 45% 90‐percentile differences for the second method (i.e., based on one measurement at 4 h post‐administration). Predictably, although relatively fast and convenient, neither of these simpler methods appears to be as accurate as thyroid dose estimates based on more complete kinetic data.