What is an octreotide scan?
An octreotide scan is a form of somatostatin receptor imaging used to detect neuroendocrine tumours. These tumours, which arise from neuroendocrine hormone secreting cells, are characterised by an overexpression of somatostatin receptors.
The scan uses an isotope of indium, Indium-111, which is bound to pentetreotide to form 111In-pentetreotide, a radiopharmaceutical with a somatostatin analogue that binds to somatostatin receptors. The radiopharmaceutical is actively taken up by the overexpressed somatostatin receptors on neuroendocrine tumours (predominantly type 2 and 5).
What are the generally accepted indications for an octreotide scan?
Identifying a primary neuroendocrine tumour in the appropriate clinical setting, preoperative staging, restaging and assessment of treatment response.
Examples of tumours that have high overexpression of somatostatin receptors include, but are not limited to:
Paraganglioma, including phaeochromocytoma.
Gastroenteropancreatic neuroendocrine neoplasms, such as carcinoid, gastrinoma and glucagonoma. Imaging can be carried out on both functioning and non-functioning neoplasms.
Merkel cell carcinoma.
Small cell carcinoma.
Others tumours may have variable or low somatostatin receptor overexpression, such as insulinoma, medullary thyroid carcinoma, differentiated thyroid carcinoma, non-small cell lung cancer, lymphoma and, rarely, breast carcinoma.
What are the prerequisites for having an octreotide scan done?
Octreotide therapy should be temporarily discontinued before the 111In-pentetreotide scan in consultation with the referring clinician. The length of withdrawal depends on the type of therapeutic agent. Recommended duration ranges from 1–3 days for short-acting agents, and 4–6 weeks for long-acting agents.
Referrals should be accompanied by a history of the type of suspected or known primary tumour, its hormonal activity, the results of other imaging studies (CT, MRI), laboratory results (tumour markers), and a history of recent surgery, chemotherapy, radiation therapy and octreotide therapy should be available on the referral. A history of cholecystectomy should also be noted.
For patients suspected of having an insulinoma, an intravenous infusion of glucose should be available because of the potential for inducing severe hypoglycaemia.
Indium-111 octreotide should not be injected into existing I.V. lines used to administer other fluids or together with solutions for total parenteral nutrition. A complex glycosyl octreotide conjugate may form and reduce the sensitivity of the scan.
Patients should be well hydrated before and up to 1 day after the procedure. This ensures that the radiopharmaceutical passes quickly out of the body in the urine.
What are the absolute contraindications for an octreotide scan?
This study may not be suitable for pregnant women due to the low radiation risk to the both developing foetus and the mother. The benefit versus risk should be discussed with the nuclear medicine specialist.
Given that there is a small amount of radioactivity released for a while after the test, women who are breast-feeding may need to make special preparations after the test to stop breast-feeding for a short time. Similarly, close contact with young children should be avoided for a short time (see below).
What are the relative contraindications for an octreotide scan?
The doctor should contact the hospital or radiology practice and check the scanner bed limits if their patient is morbidly obese.
What are the adverse effects of an octreotide scan?
There are no adverse affects from an octreotide scan. The amount of radiation exposure is quite safe and should not result in any short- or long-term hazardous effects.
Is there any specific post procedural care required following a octreotide scan?
In-pentetreotide scan is eliminated from the body predominantly via the kidneys. Patients should be well hydrated before and after the scan. The biological half-life is approximately 6 hours.
If the scan was deemed medically necessary in pregnant and/or breast-feeding patients, hydration is crucial. The patient can express breast milk before the scan to use on the days of the scan. After the scan, milk should be discarded for the next 48 hours. The patient should minimise close contact with the baby and children under the age of 5 years for the next 24 hours. Patients should discuss this with their referring doctor or the nuclear medicine practice where they will have the test. See Nuclear Medicine for further information about the precautions to take with nuclear medicine studies for breast-feeding patients and those in close contact with children.
Are there alternative imaging tests, interventions or surgical procedures to an octreotide scan?
Other functional imaging includes 68Ga DOTA-Octreotate PET-CT scan and 123I/124I MIBG scan. PET imaging can be particularly useful in aggressive, rapidly-growing tumours that may not be seen on octreotide scanning.
CT and MRI can better delineate the anatomical relationships of any identifiable tumour.
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