To investigate the correlation between ¹³¹I uptake and therapeutic efficacy in metastatic differentiated thyroid carcinoma (DTC).

The clinical data of 138 patients with metastatic DTC (42 males, 96 females, age range: 8-74 years) treated with ¹³¹I in nuclear medicine departments of 31 centers all over China were retrospectively analyzed. The lesional ¹³¹I uptake was quantitatively analyzed with target-to-nontarget (T/NT) ratio through the regions of interest in metastatic lesions confirmed by either planar or tomographic ¹³¹I SPECT/CT imaging. The efficacies of ¹³¹I treatment on the metastatic DTC were divided into complete remission (CR), partial remission (PR), stable disease (SD) and progress disease (PD) based on the change of the lesion diameter before and after the treatment. Factors which may affect therapeutic efficacy were assessed by the univariate (Kruskal-Wallis rank sum test, χ² test and one-way analysis of variance) and binary logistic regression analyses. The receiver operating characteristic (ROC) curve of lesional T/NT ratio to predict the ineffectiveness of ¹³¹I therapy was performed.

A total of 1 165 efficacies were evaluated. The planar imaging results (n=653) showed that there was no statistically significant difference of T/NT ratio among CR, PR, SD and PD groups (χ²=4.15, P>0.05). The tomographic imaging results (n=512) suggested CR, PR, SD and PD in 7.6%(39/512), 65.8%(337/512), 22.9%(117/512), and 3.7%(19/512) of individuals, respectively, and the T/NT ratio among the four groups was significantly different (χ²=30.46, P<0.01). The univariate analysis also showed that age, stimulated thyroglobulin(sTg),¹³¹I dose were the factors affecting therapeutic efficacy (F or χ² values: 2.561, 7.095 and 8.799, all P<0.05). Furthermore, binary logistic regression analysis revealed that older patients (odds ratio (OR)=1.034, P=0.022) or patients with lower lesional T/NT (OR=1.086, P=0.006) had a higher probability of ineffectiveness. The area under ROC curve for T/NT ratio to predict ineffectiveness was 0.726, and the cut-off value was 6.2, with a sensitivity of 78.7%(107/136) and a specificity of 73.1%(275/376).

¹³¹I therapy is an effective treatment for metastatic DTC. The age at the time of metastatic diagnosis and the lesional T/NT ratio are independent influential factors for ineffectiveness of ¹³¹I therapy. When the leisonal T/NT ratio is lower than 6.2, the inefficiency of ¹³¹I is higher.

Thyroid neoplasms; Neoplasm metastasis; Radiotherapy; Iodine radioisotopes; Treatment outcome