This may be achieved by using peptide vectors having a higher affinity for the SSTR or a broader affinity profile for the different receptor subtypes or by using compounds recognizing more binding sites, such as SSTR antagonists. On the other hand, new developments in SSTR PET ligands are strongly driven by the need for improved lesion targeting, especially for tumors with low SSTR expression. Therefore, possibilities of using other PET radionuclides are being explored. Furthermore, gallium-68 has a relatively long positron range, compromising spatial resolution on modern PET cameras. Centralized production and distribution is challenging due to the low production yield and relatively short half-life of gallium-68. However, implementation of 68Ga-DOTA-peptides in routine clinical practice is often limited by practical, economical and regulatory factors related to the use of the current generation of 68Ge/ 68Ga generators. 68Ga-DOTA-peptide PET has superseded 111In-DTPA-octreotide scintigraphy as the modality of choice for SSTR imaging. Tracers currently in clinical use are 68Ga-DOTA-Tyr 3-octreotide ( 68Ga-DOTATOC), 68Ga-DOTA-Tyr 3-octreotate ( 68Ga-DOTATATE) and 68Ga-DOTA-1-NaI 3-octreotide ( 68Ga-DOTANOC), collectively referred to as 68Ga-DOTA-peptides. A major leap forward was the introduction of gallium-68 labeled SSAs for positron emission tomography (PET) offering improved sensitivity. 111In-DTPA-octreotide has long been the standard in SSTR scintigraphy. Using radiolabeled somatostatin analogs (SSAs), the presence of SSTRs on tumor cells may be exploited for molecular imaging and for peptide receptor radionuclide therapy. Somatostatin receptors (SSTRs) are variably expressed by a variety of malignancies.
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