Predicting 131 I-avidity of metastases from differentiated thyroid cancer using 18 F-FDG PET/CT in postoperative patients with elevated thyroglobulin.

The quantitative relationship between iodine and glucose metabolism in metastases from differentiated thyroid cancer (DTC) remains unknown. Aim of the prospective study was to establish the value of 18 F-FDG PET/CT in predicting 131 I-avidity of metastases from DTC before the first radioiodine therapy. A total of 121 postoperative DTC patients with elevated stimulated serum thyroglobulin (ssTg) who underwent 131 I adjuvant therapy or therapy after 18 F-FDG PET/CT scan were enrolled. The Receiver operating characteristic curve was established to create an optimal cut-off point and evaluate the value of SUVmax for predicting 131 I-avidity. In our study, the median SUVmax in 131 I-nonavid metastatic target lesions was also significantly higher than that in 131 I-avid metastatic target lesions (5.37 vs. 3.30; P = 0.000). At a cut-off value of 4.0 in SUVmax, the area under curve was 0.62 with the sensitivity, specificity, positive predictive value and negative predictive value of 75.3%, 56.7%, 76.1%, and 54.8%, respectively. These results suggest that 18 F-FDG PET/CT may be of great value in identifying metastases in postoperative DTC patients with elevated ssTg before 131 I administration, leading to an improved management of disease. 18 F-FDG positive metastatic DTC with SUVmax of greater than 4.0 possesses higher probability of non-avidity to radioiodine.