Determining thyroid 131I effective half‐life for the treatment planning of Graves’ disease

Purpose: Thyroid {sup 131}I effective half-life (T{sub eff}) is an essential parameter in patient therapy when accurate radiation dose is desirable for producing an intended therapeutic outcome. Multiple {sup 131}I uptake measurements and resources from patients themselves and from nuclear medicine facilities are requisites for determining T{sub eff}, these being limiting factors when implementing the treatment planning of Graves' disease (GD) in radionuclide therapy. With the aim of optimizing this process, this study presents a practical, propitious, and accurate method of determining T{sub eff} for dosimetric purposes. Methods: A total of 50 patients with GD were included in this prospective study. Thyroidal {sup 131}I uptake was measured at 2-h, 6-h, 24-h, 48-h, 96-h, and 220-h postradioiodine administration. T{sub eff} was calculated by considering sets of two measured points (24-48-h, 24-96-h, and 24-220-h), sets of three (24-48-96-h, 24-48-220-h, and 24-96-220-h), and sets of four (24-48-96-220-h). Results: When considering all the measured points, the representative T{sub eff} for all the patients was 6.95 ({+-}0.81) days, whereas when using such sets of points as (24-220-h), (24-96-220-h), and (24-48-220-h), this was 6.85 ({+-}0.81), 6.90 ({+-}0.81), and 6.95 ({+-}0.81) days, respectively. According to the mean deviations 2.2 ({+-}2.4)%, 2.1 ({+-}2.0)%, and 0.04 ({+-}0.09)% found inmore » T{sub eff}, calculated based on all the measured points in time, and with methods using the (24-220-h), (24-48-220-h), and (24-96-220-h) sets, respectively, no meaningful statistical difference was noted among the three methods (p > 0.500, t test). Conclusions: T{sub eff} obtained from only two thyroid {sup 131}I uptakes measured at 24-h and 220-h, besides proving to be sufficient, accurate enough, and easily applicable, attributes additional major cost-benefits for patients, and facilitates the application of the method for dosimetric purposes in the treatment planning of Graves' disease.« less