Radioiodine therapy of benign thyroid-disorders

In radioiodine therapy (RIT) of benign thyroid-disorders empirical half-lives (HL_emp) may be used to calculate therapeutic dose. In this study the effective half-life (HLf as well as potential influence factors were retrospectively determined in order to better estimate HL_emp.

Data from patients undergoing RIT from 01/09 to 04/14 were analysed (empirically estimated HL_eff stratified by metabolic state and diagnosis). Inclusion criteria were: Benign thyroid-disorders, singular capsule administration and ≥ 6 dosimetry time-points (i. e. > 72 h inpatient stay). The effects of metabolic state, previous thy- reostatic medication and sex on HL_eff were assessed by non-parametric ANOVA. The effects of target-volume and patient-age were assessed by regression analysis and nonparametric correlation (Spearman).

Data of 1,498 patients were analyzed: Graves' Disease (GD), n = 286; multinodular goiter/disseminated autonomy (AMG/DA), n = 751; autonomous thyroid nodules (ATN), n = 421; euthyroid goiter (EG), n = 40. Mean HL_eff (days ± SD) was 5.4 ± 1.5 in GD, 6.6 ± 1.2 in AMG/DA, 5.5 ± 1.6 in ATN and 6.9 ± 0.7 in EG. HL_eff differed by metabolic state in GD, AMG/DA, and ATN, whereas neither thyreos- tatic medication nor sex were relevant. Moreover, target-volume (all diagnoses) and age (ATN and GD only) were associated with HL_eft although the effect was small (R² < 3.8%).

When using standard HL_eff for RIT, diagnosis and metabolic state should be considered for dose-calculations in RIT. Despite partial significance, the effects of target-volume and patient-age are small and a correction of HL_eff, for these factors doesn't appear to be necessary in a routine setting.