PET/CT in Neuroendocrine Tumors.

The past three decades have witnessed a radical change in the diagnostic approach to neuroendocrine tumours (NEN). In the early 1990s, Krenning et al. [ 1 ] docu- mented the higher diagnostic accuracy of somatostatin receptor scintigraphy (SRS) over conventional morphological procedures (US, CT) for both the detection of the primary tumour and distant metastasis (overall detection rate ranging between 80 and 100 %). In fact the variable presentation of NEN, in terms of both size and primary tumour site, mainly accounts for the lower performance of conventional imaging modalities. The availability of radiotracers specifi cally binding to soma- tostatin receptors (SSTR) overexpressed on NEN cells has represented a major advance in the diagnosis of these tumour forms. Of course, with the advent of PET/CT, several new beta-emitting tracers have been employed in the clinic with good results, and the role of scintigraphy will become more and more marginal. PET/CT offers several advantages over SRS including a higher spatial resolution and higher accuracy in lesion detection [ 2 ], the possibility to semi-quantify the tracer uptake in the region of interest (SUV max ), lower costs [ 3 ] and shorter image acquisition protocol (2 h vs acquisitions at 4–24 h). A recent paper comparing PET/CT with 68Ga-DOTA-TATE (characterised by a high-binding affi nity for SSTR-2) with SRS, reported that in patients with negative or weakly positive fi ndings on SRS, PET/CT documented 168 vs 28 lesions [ 2 ]. At present, both receptor-based (68Ga-DOTA-peptides) and metabolic (18F- FDG and 18F-DOPA) beta-emitting tracers are available for imaging NEN with PET/CT (Fig. 7.1 ).