Octreotide Scintigraphy

Updated: Jun 09, 2016
  • Author: Bishnu Prasad Devkota, MD, MHI, FRCS(Edin), FRCS(Glasg), FACP; Chief Editor: Gowthaman Gunabushanam, MD, FRCR  more...
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Overview

Background

Octreotide is a synthetic analogue of somatostatin, which is a cyclic neuropeptide that is normally found in neuronal and endocrine cells (brain, peripheral nerves, pancreatic endocrine cells). The plasma half-life of natural somatostatin is 1-3 minutes. Indium-111 (111In)–labelled pentetreotide specifically binds to somatostatin receptors (specially to subtypes 2 and 5). [1] Other somatostatin analogs (eg, technetium 99m depreotide [99mTc depreotide], DTPA) are used in the imaging of pituitary tumors. The presence of somatostatin receptors in numerous pituitary and parasellar tumors allows visualization with radionucleotide-labelled somatostatin analogs in vivo. In the pituitary gland, prolactin– and adrenocorticotrophic hormone–secreting adenomas cannot be localized, but clinically nonfunctioning pituitary adenomas are visualized in 75% of cases with 111In-DTPA-octreotide. [2, 3, 4]

A positive scan result in patients with growth hormone– and thyroid-stimulating-hormone–secreting pituitary tumors indicates a good suppressive effect of octreotide on hormone release by these tumors. [2] Octreotide is used for scintigraphic localization of primary and metastatic neuroendocrine tumors that bear somatostatin receptors. [1] Somatostatin receptors have been found in many neuroendocrine and several nonneuroendocrine cells. Capitalizing on this concept of somatostatin receptor positivity, somatostatin receptor scintigraphy has been developed to image tumors that arise from these cells. [5, 6] The study of diagnostic approaches that address these biological characteristics of various tumors could open a whole new therapeutic vista. [7]

Tumors with high expression of somatostatin receptors, which are normally detected with somatostatin receptor scintigraphy, include the following: [8]

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Indications

Common indications for octreotide scintigraphy include the following:

  • Detection and localization of various suspected neuroendocrine and some nonneuroendocrine tumors and their metastases (vide supra)
  • Staging neuroendocrine tumors
  • Follow-up in patients with known disease to evaluate potential recurrence
  • Determination of somatostatin-receptor status (patients with somatostatin receptor–positive tumors may be more likely to respond to octreotide therapy)
  • Selection of patients with metastatic tumors for peptide receptor radionuclide therapy (PRRT) and prediction of the effect of PRRT, where available
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Complication Prevention

In patients with suspected insulinoma, an intravenous infusion of glucose should be available, since 111In pentetreotide can cause severe hypoglycemia. [8]

It should not be injected into intravenous lines for total parenteral nutrition.

Manufacturer’s instructions should be followed for the administration of In-111 pentetreotide. If radiochemical purity is less than 90% or if the solution has any particulate matter or color, it should not be used. It should be used within 6 hours of preparation. [8, 1]

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Outcomes

Although the sensitivity of octreotide scanning is low for adrenal pheochromocytomas and juxtarenal paragangliomas (25%) owing to high renal uptake and excretion of 111In octreotide, its sensitivity is high for metastatic pheochromocytoma (87%) and paragangliomas of the head and neck (chemodectomas). [9]

In the management of inoperable or metastasized endocrine tumors, therapy with radiolabeled somatostatin analogs is a promising tool. It has been found promising in the diagnosis of primary lung cancer and its remote metastases, although it is less sensitive than positron emission tomography in detection of metastatic lung cancer in hilar and mediastinal lymph nodes. [10] Results obtained with [90Y-DOTA degrees ,Tyr(3)]octreotide and [177Lu-DOTA degrees ,Tyr(3)] octreotate are encouraging in tumor regression, although significant symptomatic improvement may be seen with all 111In–, 90Y–, or 177Lu–labeled somatostatin analogs that have been used for peptide receptor radionuclide therapy. [11, 12]

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Limitations

False-positive results can occur in the following settings:

  • Upper and lower respiratory tract infections or other infections [9]
  • Diffuse pulmonary or pleural accumulation after radiotherapy
  • Recent surgical and colostomy sites [9]
  • Accumulation of the tracer in normal structures (pituitary, thyroid, liver, spleen, kidneys, bowel, gallbladder, ureters, bladder, stimulated adrenal glands)

False-negative results can occur in the following settings:

  • Presence of unlabeled somatostatin due to either octreotide therapy or production of somatostatin by the tumor
  • Different somatostatin receptor subtypes have different affinities for the radioligand particularly in insulinomas and medullary thyroid carcinomas
  • Hepatic metastases of neuroendocrine tumors may appear isointense (normal liver may concentrate the radioligand at the same degree); correlation with subtraction scintigraphy with sulfur colloid or anatomic imaging (CT/MRI) should be considered [8, 4]

Dose adjustment may be necessary in patients with renal insufficiency; further research is needed.

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