An octreotide scan is a type of

SPECT Single-photon emission computed tomography (SPECT, or less commonly, SPET) is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera (that is, ...

scintigraphy used to find carcinoid, pancreatic neuroendocrine tumors, and to localize sarcoidosis. It is also called somatostatin receptor scintigraphy (SRS). Octreotide, a drug similar to

somatostatin Somatostatin, also known as growth hormone-inhibiting hormone (GHIH) or by several other names, is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G protein-couple ...

, is radiolabeled with

indium-111 Indium-111 (111In) is a radioactive isotope of indium (In). It decays by electron capture to stable cadmium-111 with a half-life of 2.8 days. Indium-111 chloride (111InCl) solution is produced by proton irradiation of a cadmium target (112Cd(p,2n) ...

, and is injected into a vein and travels through the bloodstream. The radioactive octreotide attaches to tumor cells that have receptors for somatostatin (i.e. gastrinoma,

glucagonoma Glucagonoma is a very rare tumor of the pancreatic alpha cells that results in the overproduction of the hormone, glucagon. Typically associated with a rash called necrolytic migratory erythema, weight loss, and mild diabetes mellitus, most people ...

, etc.). A gamma camera detects the radioactive octreotide, and makes pictures showing where the tumor cells are in the body, typically by a

technique. A technetium-99m based radiopharmaceutical kit is also available. Octreotide scanning is reported to have a sensitivity between 75% and 100% for detecting pancreatic neuroendocrine tumors. Instead of gamma-emitting ¹¹¹In, certain octreotide derivatives such as edotreotide (DOTATOC) or

DOTATATE DOTA-TATE (DOTATATE, DOTA-octreotate, oxodotreotide, DOTA-(Tyr3)-octreotate, and DOTA-0-Tyr3-Octreotate) is an eight amino acid long peptide, with a covalently bonded DOTA bifunctional chelator. DOTA-TATE can be reacted with the radionuclides ...

are able to be linked by chelation to positron-emitting isotopes such as gallium-68 and copper-64 which in turn can be evaluated with more precise (compared with SPECT) scanning techniques such as PET-CT. Thus, the octreotide scan is now being replaced in most centers with gallium-68 DOTATATE and copper-64 DOTATATE scans. Somatostatin receptor imaging can now be performed with positron emission tomography (PET) which offers higher resolution and more rapid imaging.

Indications

An octreotide scan may be used to locate suspected primary neuroendocrine tumours (NET) or for follow-up or staging after treatment. Where indicated, octreotide scanning for NET tumors is being increasingly replaced by gallium-68 DOTA and copper-64 DOTATATE scans.

Procedure

Indium-111

The indium-111 pentetreotide radiopharmaceutical is prepared from a kit in a

radiopharmacy Nuclear pharmacy, also known as radiopharmacy, involves preparation of radioactive materials for patient administration that will be used to diagnose and treat specific diseases in nuclear medicine. It generally involves the practice of combining ...

. Pentetreotide is a DTPA conjugate of octreotide. Approximately 200

megabecquerel The becquerel (; symbol: Bq) is the unit of radioactivity in the International System of Units (SI). One becquerel is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. For applications relatin ...

s (MBq) of indium-111 is injected intravenously. Imaging takes place 24 hours after injection, but may also be carried out at 4 and 48 hours.

Technetium-99m

The ^99mTc product is supplied as a kit with two vials, one containing the

chelating agent Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These ligands are ...

ethylenediaminediacetic acid Ethylenediaminediacetic acid (EDDA) is the organic compound with the formula C2H4(NHCH2CO2H)2. It is a derivative of two molecules of glycine, wherein the amines are linked. It is a white solid. The conjugate base is a tetradentate ligand. A r ...

(EDDA) and the other the HYNIC-Tyr3-octreotide chelator and somatostatin analog. Approximately 400-700 MBq may be administered, with imaging at 2, 4, and occasionally 24 hours post administration. ^99mTc based octreotide imaging shows slightly higher sensitivity than ¹¹¹In.

References

External links

*
Octreotide scan
entry in the public domain NCI Dictionary of Cancer Terms {{DEFAULTSORT:Octreotide Scan 2d nuclear medical imaging Medical imaging