Comparison between ablation efficacy of 1.1 GBq and 3.7 GBq 131I for low- and intermediate-risk differentiated thyroid carcinoma

Abstract

Objective 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). Methods 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 99Tcm-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. Results 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 99Tcm-pertechnetate uptake for prediction of the successful ablation rate in 1.1 GBq group was 0.061 5. Conclusion The low- and intermediate-risk DTC patients with stage Ⅲ disease, 5 μg/L<ps-Tg≤10 μg/L or higher 99Tcm-pertechnetate uptake of remnant thyroid should be given 3.7 GBq other than 1.1 GBq 131I to obtain a better ablation efficacy. Key words: Thyroid neoplasms; Radiotherapy; Iodine radioisotopes; Radiotherapy dosage; Treatment outcome