Indium (111In) Pentetate

Indium (111In) Pentetreotide (OctreoScan). Pente-treotide is a modified peptide hormone that consists of a bi-functional chelating agent, DTPA, linked to octreotide, a long-acting analog of the endogenous hormone somato-statin. Somatostatin is a 14-amino acid peptide hormone that binds to the somatostatin receptor. These receptors have been found on many cells of neuroendocrine origin and are expressed in large numbers on nearly all tumors of such origin. The drug is indicated in the imaging of primary and metastatic neuroendocrine tumors bearing somatostatin receptors.

The kit utilized to prepare this radiotracer contains pen-tetreotide, a solution of indium (mIn) chloride/ferric chloride, and a transfer needle. The addition of ferric chloride and the use of the transfer needle are necessary to increase the labeling yield. The radiolabeled solution is added to the pentetreotide vial and incubated at room temperature for 30 minutes. The tagged product must be used within 6 hours of preparation. The structure of labeled radiopharmaceutical, indium (mIn) pentetreotide, is shown.13

The patient receives an intravenous injection of 3 to 6 mCi (111-222 MBq) of indium (111In) pentetreotide depending on the type of imaging camera that will be used to obtain images. Whole-body images are obtained 4 to 48 hours after injection to localize the primary tumor and sites of metastases.

Chapter 11 # Agents for Diagnostic Imaging 421 O

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