The utility of 18F-fluorodeoxyglucose positron emission tomography/computed tomography in differentiated thyroid cancer patients with biochemical recurrence and negative whole-body radioiodine scintigraphy and evaluation of the possible role of a limited regional scan

Purpose of the Study: 18F-Fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) is used in the management of recurrent differentiated thyroid cancer (DTC) patients presented with rising thyroglobulin (Tg) or anti-Tg antibody (Atg) levels and negative whole-body I-131 scan (WBS). We aimed to evaluate the utility of regional or limited PET/CT in a large population preset with variable Tg/(ATg) levels. Materials and Methods: In a retrospective study, we analyzed 137 PET/CT done on DTC patients presented with raised Tg/Atg and negative WBS. Retrospective evaluation of other available clinical information was done. Results: One hundred and thirty-seven patients aged 8-72 years (41 +/- 17.7 years) were included in the study. Eighty-nine (64.9%) patients had positive findings on 18F-FDG PET-CT. It included thyroid bed recurrence, cervical, mediastinal lymphadenopathy, lung, and bone lesions. In addition, 36 patients had metabolically inactive lung nodules detected on CT. Serum Tg and female sex were the only predictors for a positive PET scan. In most (97.1%) of the patients, the disease was limited to the neck and thoracic region. Conclusions: PET/CT is an excellent imaging modality for evaluating DTC patients presented with biochemical recurrence. It not only finds the disease in more than 80% of the patients but also detects distant metastatic disease, which precludes regional therapies. Lesions were noted mostly in the neck and thoracic region with very few distant skeletal metastases (4/137 patients). In most of the patients, routine vertex to mid-thigh imaging could be avoided.