Evaluation of differentiated thyroid cancer (DTC) patients with negative I-131 whole body scans (WBS) and raised serum thyroglobulin (Tg) by F18-FDG PET/CT scans

2092 Objectives To determine the role of FDG PET/CT in the follow up assessment of thyroid cancer with normal I-131 WBS and raised serum Tg. Methods 105 follow up patients (F:65; M:40) of DTC with negative I-131 WBSs and raised serum Tg were subjected to FDG PET/CT scans. The results were grouped into three categories: 1. Negative scans with no evidence of FDG avid disease; 2. Positive scans with FDG avid disease and 3. Equivocal scans. Results of the FDG PET/CT scans were correlated with clinical, radiological, cytological and/or histopathological findings. Results No FDG avid abnormalities were noted in 16 patients (Category-1). Two had borderline neck nodes on CT, which were biopsied, and confirmed to be metastatic. The rest 14 patients were followed up over a minimum period of 12 months. None demonstrated clinical or scintigraphic evidence of cancer. The serum thyroglobulin levels remained stable or declined. Eleven patients demonstrated equivocal findings (Category-3) on PET, mostly in the form of minimally increased FDG avidity in cervical nodes. Only in one out of these 11 patient the follow up scan revealed further increase in FDG avidity with increase in size of the node, subsequent biopsy revealed metastasis. FDG avid lesions suggestive of metastases were noted in 78 patients; most commonly in cervical nodes, followed by other nodes, mediastinum, lungs, bones and adrenal. Twenty patients were subjected to surgery. Histopathology confirmed metastases in 18/20 (90%) cases. Two had benign features (inflammation, Fibrous tissue). All patients with limited nodal or lung disease benefited from surgery. All patients with extensive metastatic disease continued to be treated with thyroid hormone suppression. Conclusions FDG PET scans helped in evaluating the extent of non-I-131 concentrating metastasis and identifying patients for surgical intervention. Patients with limited disease benefited from surgery like cervical nodal clearance or lung nodule resection