Octreotide Scintigraphy 

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

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]

  • Adrenal medullary tumors (pheochromocytoma, neuroblastoma, ganglioneuroma, paraganglioma)

  • Gastroenteropancreatic neuroendocrine tumors (formerly classified into carcinoid, gastrinoma, glucagonoma, vasoactive intestinal polypeptide-secreting tumor, pancreatic polypeptide-secreting tumor, etc, or nonfunctioning gastroenteropancreatic tumors), more recently classified by the World Health Organization as low grade, intermediate grade, and high grade (G1, G2, G3, respectively)

  • Merkel cell tumor of the skin

  • Pituitary adenoma

  • Small-cell lung carcinoma

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

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]

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]

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.

 

Periprocedural Care

Pre-Procedure Planning

The patient’s pertinent history should be obtained, including the type of suspected primary or metastatic tumor, its endocrine status, results of other imaging modalities (eg, CT, MRI, tumor biomarkers), and history of chemotherapy, radiation therapy, recent surgery, and octreotide therapy. Cholecystectomy history should also be obtained.[1]

Patient Preparation

Patients should be well hydrated before and for at least one day after injection to decrease the radiation exposure. Octreotide therapy should be stopped for one day before 111In pentetreotide administration, while monitoring the patient for signs of withdrawal. When the abdomen is the area of interest, laxatives should be used to clean the bowels. A mild oral laxative should be used in the evening before and after the injection. The necessity for bowel preparation should be individualized, and, of course, laxatives should not be administered in patients with diarrhea.[1]

 

Technique

Octreotide Scintigraphy

The recommended administered activity of 111In pentetreotide is 5 MBq/kg (0.14 mCi/kg) in children and 222 MBq (6 mCi) in adults. The amount of pentetreotide injected is 10-20 mg (this dose is not expected to have a clinically significant pharmacologic effect). 111In pentetreotide is cleared rapidly from the blood (one third of the injected dose remains in the blood pool at 10 minutes and 1% at 20 hours postinjection).[8] It is eliminated principally by the kidneys (half of the injected dose appears in the urine by 6 hours, 85% within one day) and a small amount by the liver (2%). It is unclear whether 111In pentetreotide is removed by hemodialysis.[8, 1]

Images are obtained at 4 hours and 24 hours or 24 hours and 48 hours postinjection. Patients should empty their bladder before imaging. If there is significant bowel activity noted at 24 hours (which may potentially obscure lesions), 48-hour images will be necessary. As tumor-to-background ratio is lower at 4 hours than at 24 hours and 48 hours, some lesions may be missed at 4 hours; nevertheless, the 4-hour images offer information prior to activity in the gut.

Large-field-of-view gamma camera planar images should be obtained.

Planar localized images of the head, chest, abdomen, pelvis, and, if needed, the extremities can be acquired for 10-15 minutes per image, using a 512 x 512 word or 256 x 256 word matrix.

Metastases in the cervical lymph nodes may not be visible on whole-body images. Additional planar localized images of the head and neck (including lateral views) should be obtained.

Using a multidetector gamma camera, SPECT imaging of the appropriate regions based on the clinical history should be performed. Early and delayed SPECT may differentiate bowel activity from pathological lesions. If multiple SPECT images are not possible, a single image acquisition at 24 hours is preferred because of higher target-to-background ratio.[8, 1]

Raw SPECT data should be filtered by applying a low-pass filter, per software manufacturer recommendations. Data reconstruction should be performed by using a ramp filter and attenuation correction. Newer models may allow iterative reconstruction algorithms.

Images should be fused or evaluated with relevant anatomical images (CT or MRI).

The optimal time interval to localize lesions is at 24 hours postinjection or later. Images obtained at 4 hours with high background activity may be important to compare and evaluate abdominal activity at 24 hours. Activity is normally noted in the pituitary, thyroid, liver, spleen, kidneys, bladder, and occasionally the gallbladder. Intestinal activity is normally absent at 4 hours, but images at 24 hours normally show the activity; however, images at 48 hours may be needed to clarify abdominal activity.[8]

Recommendations of the Society of Nuclear Medicine Guideline on General Imaging should be followed in preparation of the report. Additionally, the report should also highlight the relevant history, laboratory evaluation, medications (eg, octreotide, chemotherapy), description, and limitations of the procedure, including false-positive results.[8]

Abnormal octreotide scan. 111In-pentetreotide scin Abnormal octreotide scan. 111In-pentetreotide scintigraphy of a 41-year-old man with ectopic Cushing's syndrome caused by a neuroendocrine carcinoma of the mesentery. Radiotracer accumulation in the left thyroid in 10/2003 (arrow). The mesenterial neuroendocrine tumor became clearly visible in 4/2005 (arrow). Image from Ectopic Cushing' syndrome caused by a neuroendocrine carcinoma of the mesentery, Fasshauer M et al, BMC Cancer 2006, 6:108; available at: http://www.biomedcentral.com/1471-2407/6/108.
Normal octreotide scan. Normal octreotide scan.