Fluorine-18 fluorodeoxyglucose dual-head positron emission tomography in the detection of recurrent differentiated thyroid cancer : Preliminary results

In the follow-up of patients with thyroid cancer, it may be very difficult to identify the site of recurrence in the presence of persistently elevated or rising thyroglobulin (Tg) levels and negative iodine-131 whole-body scintigraphy (WBS). The aim of this study was to assess the feasibility of employing fluorine-18 fluorodeoxyglucose and a dual-head positron emission tomography (PET) camera to detect recurrent thyroid cancer in patients with elevated Tg levels and negative 131I WBS. Eleven patients suspect of having recurrent thyroid cancer (five males, six females; mean age 47 years; range 26-73 years) were studied with both 131I WBS and FDG using a dual-head PET camera. The suspicion that these patients had recurrent thyroid cancer was based on elevated Tg levels. Thyroid stimulating hormone (TSH) and Tg levels as well as antibodies to Tg were measured 3 weeks after the withdrawal of tri-iodothyronine. In patients in whom pathological uptake was seen on the PET images but who had no signs of recurrent thyroid cancer on WBS, ultrasonography and/or computed tomography or magnetic resonance imaging was performed followed by fine-needle aspiration cytology. The mean Tg and TSH levels after discontinuation of L-thyroxine were 156 ng/ml (range 4-815 ng/ml) and 84 mU/l (range 43-159 mU/l), respectively. None of the patients had antibodies to thyroglobulin. In seven out of ten patients with negative 131I WBS, FDG PET showed focally increased uptake in the head and neck region. In one patient, the site of increased uptake on the PET images corresponded with the site of increased 131I uptake. Malignancies with a diameter less than 1 cm (n = 3) were not depicted by either CT or US. It is concluded that detection of recurrent thyroid cancer by means of FDG dual-head PET is feasible in patients with elevated Tg concentrations and negative 131I WBS. The results justify a prolongation of the study.