Diagnostic Accuracy of Gallium-68-DOTATATE PET/CT Compared to Indium-111-pentetreotide Scintigraphy (SPECT/CT) for Gastroenteropancreatic Neuroendocrine Tumors

Background

Neuroendocrine tumors Neuroendocrine tumors (NET) are heterogeneous slow-growing neoplasms, occurring in 1-4/100,000 people per year. They origin from endocrine cells that derive from entodermal stem cells and are characterized by an endocrine metabolism and a typical pathologic pattern.

Slow metabolic rates of NET, small lesion size and variable anatomical localization have represented the major limits for lesions diagnosis. The diagnostic workup for NET has relied on conventional morphological imaging procedures including computed tomography (CT), ultrasound (US) and magnetic resonance imaging (MRI) combined with gamma camera functional imaging, namely whole-body somatostatin receptor scintigraphy (SRS). SRS show a higher diagnostic accuracy than CT for NET diagnosis at both the primary and metastatic site, but there is still room for improvement. Novel PET tracers specifically developed for NET may increase diagnostic accuracy considerably as outlined below.

Somatostatin receptor scintigraphy (SRS) As NET have high affinity somatostatin receptors, scintigraphic methods have been developed in the early nineties to allow in vivo imaging. SRS using Indium-111-DTPA-octreotide (Indium-111-pentetreotide scintigraphy), is the most widely used diagnostic test. Although rather sensitive and helpful for whole body staging compared to traditional imaging methods, this technique has pitfalls, one of them being the poor spatial resolution, leading to the development of PET-based imaging.

Gallium-68-DOTA-peptide PET In the past decade, several positron emitting tracers have been developed for NET imaging. 68Ga-DOTA-peptides are a group of PET tracers that specifically bind to somatostatin receptors (SSTR) over-expressed on NET cells. Gallium-68-DOTA-peptides structure can be summarized in (1) the active part binding to SSTR (TOC, NOC, TATE), (2) the chelant (DOTA) and (3) the isotope (68Ga). Indications to perform 68Ga -DOTA-peptides studies in NET patients include: staging, re-staging after therapy, identification of the site of the unknown primary tumor in patients with proven NET secondary lesions and selection of cases eligible for therapy with somatostatin analogues.