Clinical utility of ¹⁸F fluoro-deoxy-glucose positron emission tomography/computed tomography concurrent with ¹³¹I therapy in intermediate or high-risk differentiated thyroid cancer

Early detection of iodine-negative differentiated thyroid cancer (DTC) lesions is important because it triggers an adjustment in the treatment strategies. The uptake of fluoro-2-deoxyglucose (FDG) has been considered as a surrogate marker of potential iodine refraction and more aggressive behaviors of DTC. This study was aimed at establishing whether performing an FDG positron emission tomography-computed tomography (PET CT) scan as a routine in patients with intermediate- or high-risk DTC helps identify a subset of patients who would not respond to radioiodine therapy. The study aims to determine incremental value of ¹⁸F-FDG PET CT in postoperative risk stratification of patients with intermediate- to high-risk DTC over pathological staging, postoperative whole-body scan (WBS), and postoperative serum thyroglobulin and to determine whether the patients with FDG avid residual or metastatic disease had a different clinical course compared to those who had non-FDG avid disease. Of the 50 DTC patients, the residual or metastatic disease was detected in the low-dose ¹³¹-I WBS in 41/50 patients and ¹⁸F-FDG scan could detect it in 22/40 patients. Concordance between the two scans was found in 13/50 patients. Of these 22 ¹⁸F-FDG-positive patients, nine did not show iodine uptake. In three of these nine patients, there was evidence of residual gross disease and patients underwent resurgery, followed by radioiodine (RAI) therapy based on their initial risk stratification. At 6-month follow-up, all the three patients with FDG avid disease who underwent resection were found to be disease free. In the other six patients, who were given empiric RAI therapy despite negative diagnostic scan, 4/6 showed evidence of progressive disease. The other two patients demonstrated persistent stable residual disease