To compare the ablation efficacy and therapy response with 1.1 GBq and 3.7 GBq ¹³¹I in postoperative patients with low- and intermediate-risk differentiated thyroid carcinoma(DTC).

A total of 190 patients (43 males, 147 females, age: (45.8±11.1)years) were enrolled from July 2016 to July 2017. Among them, 96 patients received 1.1 GBq ¹³¹I and 94 were given 3.7 GBq ¹³¹I. Diagnostic whole-body scan was performed 6 months after ¹³¹I ablation for treatment response evaluation, and the successful rate of ¹³¹I ablation was calculated. χ² test or Fisher′s exact test was used for data analysis. The cut-off value of ⁹⁹Tc^m-pertechnetate uptake for predicting the successful rate of remnant thyroid ablation in 1.1 GBq group was determined by receiver operating characteristic (ROC) curve analysis.

The successful ablation rates in 1.1 GBq and 3.7 GBq groups were 79.2%(76/96) and 81.9%(77/94), respectively (χ²=0.229, P>0.05). There was no significant difference in the therapy response between the two groups (χ²=1.371, P>0.05). The successful ablation rate in 3.7 GBq group was higher than that in 1.1 GBq group for patients with stage Ⅲ (5/6 vs 1/7, P=0.029). Moreover, for patients with 5 μg/L<preablative-stimulated thyroglobulin (ps-Tg)≤10 μg/L, the ablation rate in 1.1 GBq group was lower than that in 3.7 GBq group (3/11 vs 10/13, P=0.038). ROC curve analysis showed the cut-off value of ⁹⁹Tc^m-pertechnetate uptake for prediction of the successful ablation rate in 1.1 GBq group was 0.061 5.

The low- and intermediate-risk DTC patients with stage Ⅲ disease, 5 μg/L<ps-Tg≤10 μg/L or higher ⁹⁹Tc^m-pertechnetate uptake of remnant thyroid should be given 3.7 GBq other than 1.1 GBq ¹³¹I to obtain a better ablation efficacy.

Thyroid neoplasms; Radiotherapy; Iodine radioisotopes; Radiotherapy dosage; Treatment outcome