Quantitive Study about Influence of ¹³¹I Diagnostic Dose on Uptake of ¹³¹I for Differentiated Thyroid Carcinoma

There are 52 patients with DTC who were referred to our department for radioiodine ablation for the first time were adopted. 30 patients (experimental group) were given a diagnostic scan (Dscan) 24 hours after the administration of 74 MBq ¹³¹I before radioiodine therapy, and a therapeutic scan (Tscan) was performed after radioiodine therapy. The fractional concentrations of ¹³¹I in remnants or functional metastases were quantified on Dscan and Tscan, and were expressed as D_x and T_x respectively. 22 patients (control group) received ¹³¹I therapy directly after thyroidectomy. And Tscan was performed after the radioiodine ablation. As a result the mean T_x(experimental group) was lower both than D_x(experimental group) and T_x(control group). According to the interval time between the diagnostic dose and therapy dose was 1.2, 3.7 and 832 days, the experimental group patients were divided into three subgroups A、B、C. The mean T_x/D_x of subgroup B was lower than T_x/D_x of subgroups A and C. There was no statistically significant difference of T_x/D_x between subgroup A and C. In conclusions that 74 MBq ¹³¹I for diagnostic scan can cause thyroid stunning. And the stunning effect is more significant when the radioiodine ablation was performed on 3 to 7 days after diagnostic dose.