[131]I percentage neck uptake as a determining factor for post-operative [131]I ablative dose quantification: validity and efficacy

ABSTRACT

This prospective study was executed to validate and evaluate the efficacy of the [131]I% neck uptake as a determining factor for postoperative [131]I ablative dose quantification for local thyroid remnant. 144 patients with well-differentiated thyroid carcinoma were the subject of this work. All of them were submitted to near-total or subtotal thyroidectomy, neck iiltrasonography, 48 hours[131]I whole body scan and%neck uptake prior to [131]I therapy dose. They were grouped into two groups according to the method of [131]I ablative dose quantification. Group 1 Included 65 patients receiving empirical [subjective] [131]I ablative dose. Group 2 included 79 patients receiving [131]I ablative dose according to the following protocol based on the 48 hours% neck uptake. Patients with% neck uptake <2%, 2-4%and >4% received 1.07 GBq 1.85 GBq and 3.7 GBq respectively. Follow-up [131]I scan and% neck uptake were done at least 3 months after [131]I therapy. Successful ablation was defined as the absence of visible uptake in the neck background. There were statistically significant correlations between% neck uptake and both thyroid residual volume and surface area[r=0.7 and 0.5 respectively, p <0.05]. The overall ablation rate in group 2 cases treated according to the proposed protocol was significantly higher than that of the empiric group [79.7%and 35.4% respectively, p<0.0001]. Also ablation rates per given dose of [131]I were significantly higher in group 2 than those of group I [p< 0.006]. Thirty [37.97%] out of 79 group 2 patients received 1.07 GBq as outpatients saving about 90 hospitalization days with 86.7% ablation rate. We concluded that [131]I% neck uptake is a simple, accurate, objective and effective method for [131]I dose quantification required for postoperative ablation of local thyroid remnant, allowing for a significant proportion of these cases to be treated on an outpatient basis while maintaining a high ablation rate