Octreotide scan
An octreotide scan is a type of SPECT scintigraphy used to find carcinoid, pancreatic [neuroendocrine tumor]s, and to localize sarcoidosis. It is also called somatostatin receptor scintigraphy. Octreotide, a drug similar to somatostatin, is radiolabeled with indium-111, and is injected into a vein and travels through the bloodstream. The radioactive octreotide attaches to tumor cells that have receptors for somatostatin. A gamma camera detects the radioactive octreotide, and makes pictures showing where the tumor cells are in the body, typically by a SPECT 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 or DOTATATE 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 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 which offers higher resolution and more rapid imaging.
Indications
An octreotide scan may be used to locate suspected primary neuroendocrine tumours 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. Pentetreotide is a DTPA conjugate of octreotide.Approximately 200 megabecquerels of indium-111 is injected intravenously. Imaging takes place 24 hours after injection, but may also be carried out at 4 and 48 hours.