F-18-FDG for the staging of patients with differentiated thyroid cancer: Comparison of a dual-head coincidence gamma camera with dedicated PET

Coincidence imaging with a dual-head gamma camera may offer a cost-effectiv e alternative to dedicated PET. The aim of this study was to compare the di agnostic accuracy of coincidence imaging and PET in patients with different iated thyroid cancer. Thirty-one patients were studied after thyroidectomy and radioiodine ablati on. They were injected with a single dose of 300 MBq F-18-FDG. Scanning was performed on a dedicated PET system after 1 hr, and on a coincidence gamma camera after 4 hrs. Based on a lesion-by-lesion comparison, coincidence imaging and PET concurr ed in 69% of 118 lesions. Based on lesion size, concurrence was 96% in lesi ons larger than 1.5 cm, and 62% in those between 1 and 1.5 cm. Lesions smal ler than 1 cm could not be identified with coincidence imaging. Identical staging was obtained with coincidence imaging and PET in 26/31 pa tients (84%). In four patients FDG accumulating lesions were shown by both the coincidence camera and the dedicated scanner, bur not detectable with a ny other imaging means and were confirmed histologically on surgery. Although a coincidence camera is technically inferior to a dedicated PET sc anner, it may provide clinically useful results in situations were a lesion of sufficient size and FDG uptake is to be expected, e.g. when evaluating a known lesion for malignancy.