Abstract:

Objective To analyse and compare the imaging data of ¹³¹I-SPECT/CT of different metastatic sites of differentiated thyroid carcinoma (DTC) 48 h after ¹³¹I therapy, and provide evidences for the dosimetry of ¹³¹I therapy for DTC. Methods Forty-eight hours after ¹³¹I intake, SPECT/CT imaging was performed on 20 patients with 53 metastatic sites. The data of size of metastatic lesions, tumor/non-tumor ratio, iodine uptake rate, radioactivity per unit volume and lesion density (CT value) were calculated with software. The features of data of different metastatic sites were analysed, and correlation analysis was conducted between these data and treatment efficiency of metastatic lesions. Results ①¹³¹I uptake per unit volume of bone metastases was significantly lower than the other metastatic sites [(1.01±1.23) MBq/cm3; P=0.029, 0.463, 0.003, respectively], and the efficacy was the worst. ②The most important factor influencing treatment efficacy was size of lesions. The smaller the soft tissue, lung and lymph node lesions were, the better the treatment efficacy was （r=-0.932,P=0.021; r=-0.897, P=0.000; r=-0.966,P=0.000）. While the correlation between size of bone metastatic lesions and treatment efficacy was not significant (r=-0.469, P=0.078). ③When no local damage or nodule in lesion sites was found with CT scan, the treatment was most efficient, and the lesions could be totally removed after one therapy. Conclusion Different sites of metastatic lesions of DTC have different iodine uptake capacity, which leads to significant differences in treatment efficiency. Imaging data analysis of each metastatic site should be conducted before treatment to design individualized regimens.

Key words: differentiated thyroid cancer, SPECT/CT, metastasis, dosimetry