Can 18F-fluorodeoxyglucose positron emission tomography predict the response to radioactive iodine therapy in metastatic differentiated thyroid carcinoma?

Background: 131I radioactive iodine therapy (RAI) has been commonly applied for metastatic differentiated thyroid cancer (DTC) and played an adjunctive role to total thyroidectomy. However, there is no reliable method to predict therapeutic response to RAI in metastatic DTC. Several studies showed potential use of 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) in lesion detection or therapeutic response prediction of DTC. Thus we aimed to evaluate the feasibility of 18F-FDG PET for the prediction of therapeutic response to RAI in patients with metastatic DTC. Methods: We retrospectively evaluated 29 adult patients with metastatic DTC who underwent RAI after total thyroidectomy. 18F-FDG PET/CT was performed within three months before RAI, and the maximum, average and sum of each maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV) and total lesion glycolysis (TLG) were assessed. Therapeutic response to RAI was categorized into the progressive disease (PD) or non-progressive disease (Non-PD), based on the Response Evaluation Criteria in Solid Tumor (RECIST) 1.1 using pre- and post-therapeutic computed tomography (CT) or magnetic resonance imaging (MRI) images. The area under curve (ROC) analyses were performed to evaluate their predictive potentials of therapeutic response to RAI. Results: Among 29 patients (12 men; median age, 62.4 y.o.; range, 26–81), eight patients were classified into PD and 21 were into Non-PD. PD patients showed a significantly higher maximum, average and sum SUVmax, MTV and TLG before RAI, compared to the Non-PD group (p < 0.05). Among all the 18F-FDG PET/CT parameters, maximum SUVmax showed the highest sensitivity and positive predictive value (PPV) in predicting treatment response to RAI. With a cutoff value of 9.12, the highest area under curve (AUC) of 0.98 was obtained to differentiate between PD and Non-PD patients. Conclusions: 18F-FDG PET/CT before RAI was a useful predictor of therapeutic response to RAI, and maximum SUVmax was the most sensitive parameter. [ABSTRACT FROM AUTHOR]