Association between Refractoriness to 131ITherapy for Differentiated Thyroid Carcinomaand 18F-FDG Accumulation in Lung Metastasis

Background: The purpose of this study was to retrospectively investigate the association between 2-[F-18]-fluoro-2-deoxy-D-glucose (18F-FDG) accumulation in lung metastasis (LM) before 131I therapy and refractoriness to 131I therapy for differentiated thyroid carcinoma (DTC) patients. Methods and Findings: Sixty-one DTC patients with LM who underwent Positron emission tomography/computed tomography using 18F-FDG (18F-FDG PET/ CT) before an initial 131I therapy were retrospectively evaluated. Maximum of standardized uptake value (SUVmax) in LM with the highest 18F-FDG accumulation was measured in each patient. The SUVmax was compared between patients with and without 131I-positive LM, and between patients with and without an increased level of thyroglobulin (tumor marker) 12 ± 2 months after 131I therapy using the Wilcoxon test. Discussion: Predictability for the patients with an increased thyroglobulin level was also analyzed by receiver-operating-characteristic (ROC) analysis. SUVmax of LM was significantly greater for patients without 131I-positive LM than for those with 131I-positive LM (5.9 ± 6.0 vs. 1.9 ± 2.0, p 3.8 showed an increased TG level after 131I therapy. Use of the optimal cutoff threshold for SUVmax of 1.6 differentiated patients with an increased level of TG from those without at a sensitivity of 74.2%, a specificity of 94.4%, an accuracy of 81.6% and an AUC of 0.91. Conclusion: 18F-FDG accumulation in LM from DTC can be one of predictors for refractoriness to 131I therapy.