Comparison of thyroid uptake and effective half-life between tracer and therapeutic 131I dose

Objective: To compare tracer and therapeutic activity kinetics of 131I. Method: Thyroid Uptake Ratio (TUR) and Effective Half-Life (EHL) measurements of tracer and therapeutic 131I dose were performed on 138 patients. Results: The average values of tracer dose (0.074 MBq) TUR and EHL were higher than those of therapeutic dose (44.4 - 1110.0 MBq) (t = 2.75, P < 0.01; t = 2.14, P < 0.05). The patients were followed-up for more than 6 months after treatment, and the clinic outcomes were classified into 3 groups (A. euthyroidism, B. persistent or recurrent hyperthyroidism, C. early hypothyroidism). Discrepancy of TUR between tracer and therapeutic dose in group B was larger than in group C (t = 2.07, P < 0.05), the discrepancy of EHL was not significant in 3 groups. Another 6 patients' TURs of therapeutic dose were much lower than that of tracer dose [(41.8 +- 10.7)% vs (76.7 +- 14.8)%], and after a supplementary dose of 131I (73.4 +- 31.0) MBq (calculated the dose again by absorbed TUR) they were cured and no early hypothyroidism occurred. Conclusions: The TUR and EHL measurements after 131I treatment can be helpful to study the actual absorbed dose in thyroid, and to predict the result of 131I therapy; if the absorbed dose is low, a supplementary 131I dose is needed to cure; and the attention should be paid to (early) hypothyroidism occurring