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

Abstract

Coincidence imaging with a dual-head gamma camera may offer a cost-effective alternative to dedicated PET. The aim of this study was to compare the diagnostic accuracy of coincidence imaging and PET in patients with differentiated thyroid cancer. Thirty-one patients were studied after thyroidectomy and radioiodine ablation. They were injected with a single dose of 300 MBq 18F-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 concurred in 69% of 118 lesions. Based on lesion size, concurrence was 96% in lesions larger than 1.5 cm, and 62% in those between 1 and 1.5 cm. Lesions smaller than 1 cm could not be identified with coincidence imaging. Identical staging was obtained with coincidence imaging and PET in 26/31 patients (84%). In four patients FDG accumulating lesions were shown by both the coincidence camera and the dedicated scanner, but not detectable with any other imaging means and were confirmed histologically on surgery. Although a coincidence camera is technically inferior to a dedicated PET scanner, 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.

Is [18F]-2-fluoro-2-deoxy-d-glucose (FDG) scintigraphy with non-dedicated positron emission tomography useful in the diagnostic management of suspected metastatic thyroid carcinoma in patients with no detectable radioiodine uptake?

“…Most of the above data have been obtained with dedicated cameras (dPET). An alternative method for FDG detection is the use of a gamma camera with coincidence detection capability, called non-dedicated PET (nPET) (19,20). The sensitivity and clinical impact of this easily available and less expensive method have not yet been precisely evaluated in thyroid cancer.…”

Controversies in the follow-up and management of well-differentiated thyroid cancer.

“…PET scanning is useful in identifying metastatic lesions in thyroid cancer, particularly for the more rapidly progressive and therefore metabolically active variants. These PET-positive tumors frequently lose the ability to transport and/or organify iodide and are not detected by I-131 scanning (Tiepolt et al 2000, Robbins et al 2001a, Schluter et al 2001, Larson & Robbins 2002, Lind et al 2003. Because PET scanning using FDG is not tumor specific, cervical recurrence of thyroid cancer may be difficult to distinguish from reactive cervical adenopathy.…”