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 sci ntigraphy (WBS). The aim of this study was to assess the feasibility of emp loying fluorine-18 fluorodeoxyglucose and a dual-head positron emission tom ography (PET) camera to detect recurrent thyroid cancer in patients with el evated Tg levels and negative I-131 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 I-131 WBS and FDG using a dual-head PE T camera. The suspicion that these patients had recurrent thyroid cancer wa s based on elevated Tg levels. Thyroid stimulating hormone (TSH) and Tg lev els 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 t he PET images but who had no signs of recurrent thyroid cancer on WBS, ultr asonography and/or computed tomography or magnetic resonance imaging was pe rformed followed by fine-needle aspiration cytology. The mean Tg and TSH le vels 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 a ntibodies to thyroglobulin, In seven out of ten patients with negative I-13 1 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 corresponde d with the site of increased I-131 uptake. Malignancies with a diameter les s than 1 cm (n=3) were not depicted by either CT or US. It is concluded tha t detection of recurrent thyroid cancer by means of FDG dual-head PET is fe asible in patients with elevated Tg concentrations and negative I-131 WBS. The results justify a prolongation of the study.