99m Tc-N 4 -[Tyr 3 ]Octreotate Versus 99m Tc-EDDA/HYNIC-[Tyr 3 ]Octreotide: An Intrapatient Comparison of Two Novel Technetium-99m Labeled Tracers for Somatostatin Receptor Scintigraphy

Tetraamine-[Tyr³]octreotate (Demotate) is a somatostatin (SST) analogue that can be easily labeled with ^99mTc at high specific activities and showed promising preclinical properties for SST receptor scintigraphy. This study reports on the first intra-patient comparison of ^99mTc-Demotate and another ^99mTc-labeled SST analogue, ^99mTc-EDDA/HYNIC-TOC (HYNIC-TOC). Five patients with carcinoid tumors (n = 2) and endocrine pancreatic tumors (n = 3) were investigated with both radiopharmaceuticals. ^99mTc-Demotate rapidly visualized somatostatin receptor positive tumors as early as 15 minutes post-injection (p.i.) with maximum tumor uptake and tumor/organ ratios already 1 hour p.i. Organs of predominant physiological uptake were the spleen and the kidneys with no intestinal excretion detectable up to 24 hours. ^99mTc-Demotate exhibited faster pharmacokinetic properties compared to HYNIC-TOC. Tumor/organ ratios at equivalent time points were higher or comparable for ^99mTc-Demotate in three patients with a matching scan result. Equivocal findings were observed in two patients, i.e. comparable uptake behavior in larger lesions with differences in smaller ones. ^99mTc-Demotate is a promising agent for somatostatin receptor scintigraphy providing images of excellent quality as early as 1 hour after injection.