Octreotide Scan Machine
Vikki Nagindas
An octreotide scan is a type of SPECT scintigraphy used to find carcinoid, pancreatic neuroendocrine tumors, and to localize sarcoidosis. It is also called somatostatin receptor scintigraphy (SRS). Octreotide, a drug similar to somatostatin, is radiolabeled with indium-111,[1] and is injected into a vein and travels through the bloodstream. The radioactive octreotide attaches to tumor cells that have receptors for somatostatin (i.e. gastrinoma, glucagonoma, etc.). 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.[2][3]
Instead of gamma-emitting 111In, certain octreotide derivatives such as edotreotide (DOTATOC) 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 (compared with SPECT) 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 (PET) which offers higher resolution and more rapid imaging.[5]
The 99mTc product is supplied as a kit with two vials, one containing the chelating agent ethylenediaminediacetic acid (EDDA) and the other the HYNIC-Tyr3-octreotide chelator and somatostatin analog.[13] Approximately 400-700 MBq may be administered, with imaging at 2, 4, and occasionally 24 hours post administration.[14] 99mTc based octreotide imaging shows slightly higher sensitivity than 111In.[2][15]
CT is an imaging technique that uses a highly specialized X-Ray machine and computers to create multiple cross-sectional images of the body. CT can generate images of different body tissues as well as help detect tumors. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly.
MRI uses radio waves, a powerful magnetic field, and a computer to generate detailed (2 or 3 dimensional) images of the body. These images are very useful in contrasting different types of tissue as well as detecting abnormal growths such as tumors within the body.
Patients who take somatostatin analogs should discuss with their doctor the best timing for their exam as treatment can interfere with the test. Talk to your doctor about how to adjust your somatostatin analog before testing.
A very small amount of radioactive octreotide is injected into a vein and travels through the bloodstream. Octreotide attaches to the tumor, and a special camera that detects radioactivity shows where the tumors are in the body.
In 2020, the U.S. Food and Drug Administration approved a copper Cu 64 dotatate injection for use in positron emission tomography (PET) scans for certain kinds of neuroendocrine tumors (NETs). Diagnostic tracers like Cu 64 dotatate are used with PET scans and other functional imaging scans to improve how NETs are detected and staged.
Available under the commercial name DetectnetTM, the copper Cu 64 dotatate agent is a radiopharmaceutical tracer agent used in the localization of somatostatin receptor positive NETs in adults. Developed by RadioMedix Inc. and its commercial partner Curium, Detectnet is the first commercially available Cu 64 diagnostic agent on the U.S market.
According to phase 3 trials, Detectnet demonstrated clinical sensitivity to allow clinicians to develop more precise treatment approaches for their patients who have NETs. In addition, less than 2% of study participants in clinical trials experienced adverse reactions to the agent, which typically included nausea, vomiting, and flushing.
FDG-PET can find fast-growing neuroendocrine cancer cells for aggressive tumors. A small amount of FDG, a type of radioactive glucose (sugar), is injected into a vein. The PET scanner rotates around the body and makes a picture of where the body is using glucose. Cancer cells show up brighter in the picture because they are more active and take up more glucose than normal cells do. FDG is most commonly used to detect tumors that are high grade and/or poorly differentiated.
An MIBG scan is used to find certain neuroendocrine tumors, such as pheochromocytoma and paraganglioma. A very small amount of a radioactive substance called MIBG is injected into a vein and travels through the bloodstream. The scan detects neuroendocrine tumor cells that take up MIBG. Scans may be taken over 1-3 days.
Endoscopy is a medical procedure that uses an endoscope to view the lining of multiple organs and tracts of the body. An endoscope is a flexible or rigid tube that has imaging capabilities and can enable small surgical procedures. Endoscopy can be used to visualize tumors in the lungs and gastrointestinal tract (stomach, small and large intestine and rectum). Sometimes an ultrasound probe is put on the end of the endoscope to perform what is called an endoscopic ultrasound (EUS), which can be particularly useful for looking at gut-adjacent organs like the pancreas.
Bronchoscopy is a procedure to look inside the trachea and large airways in the lung for abnormal areas. A bronchoscope is a thin, tube-like instrument with a light and a lens for viewing. It may also have a tool to remove tissue samples to be checked under a microscope for signs of cancer. A physician inserts a bronchoscope through the nose or mouth into the trachea and lungs.
Neuroendocrine tumors (NETs) look and act differently than a lot of other tumors, which can make them harder to spot. Your doctor may ask you to take several different tests that can help them make a diagnosis.
"Many of the NETs are what we call low-grade tumors, which means they're very slow growing," says Bassel El-Rayes, MD, director of the gastrointestinal oncology program at the Emory University Winship Cancer Institute. Because of that, you may not notice any symptoms at first.
Sometimes doctors discover NETs accidentally, while doing tests to look for other diseases. But if you do have any symptoms, like diarrhea, fatigue, or redness and heat in your face, let your doctor know right away. Lab and imaging tests can find the cause -- and the right treatment.
Your doctor can also test your urine for high levels of a substance called 5-HIAA, which comes from the breakdown of serotonin. For this test, you'll take a 24-hour urine sample, which means you collect all of your pee during one day and bring it to your doctor for testing.
For both of these tests, you lie down on a table that slides into the opening of a large, scanning machine. The technician will ask you to be still during the scan. You'll be able to talk to them through a speaker. During an MRI scan, you might hear loud noises that sound like tapping or banging. You can wear ear plugs or headphones if this bothers you.
Before either of these scans, your doctor may inject you with a special dye to see the inside of your body more clearly. You might not be allowed to have anything to eat or drink for a few hours beforehand.
While imaging tests show you where the tumor is and what it looks like, nuclear medicine tests go one step further. They give you an idea of how the tumor functions, El-Rayes says. Together these two types of tests give doctors "a complete picture."
"Most NET cells possess a very specific lock that allows you to put a key in it to detect," says Thomas O'Dorisio, MD, director of neuroendocrine tumor clinics at the University of Iowa. That lock is called a somatostatin receptor.
A lab technician injects a small amount of an octreotide with a radioactive substance called a tracer into a vein in your arm or hand. The tracer attaches to tumor cells that have the somatostatin receptor on their surface.
PET, or positron emission tomography. It also makes pictures inside your body. Just like with an octreotide scan, a technician puts a little bit of something that's radioactive into one of your veins. Cancer cells pick up this substance, which makes them easier to see.
A PET scan creates a clearer image than an octreoscan. Another advantage: It takes less time -- only 2 hours -- says Lowell Anthony, MD, chief of the division of medical oncology at the University of Kentucky. "It's a lot more convenient for patients."
For your biopsy, your doctor may also look inside your digestive tract with a thin, flexible, lighted tube with a camera on the end called an endoscope. One type has an ultrasound on the tip -- a device that makes an image with sound waves.
After the cells are removed, a specialist checks them under a microscope to see if they're cancer. The biopsy also let them look at their features and predict how your disease may act next, El-Rayes says.
If the results show you have a cancerous NET, your doctor will give your disease a grade and stage. These describe the size of your cancer, how it looks under a microscope, and whether it has grown and spread.
"Each of the tests is a piece of the puzzle. The pieces have to fit together nicely to make a complete picture," El-Rayes says. Your doctor will use all of the information gathered from your tests to find the best treatment for you.
Octreotide scintigraphy uses 111In-labeled octreotide, which is a somatostatin analog; it is also known as Octreoscan, a brand name for 111In-labeled pentetreotide. Pentetreotide is a DTPA-conjugated form of octreotide, originally manufactured by Mallinckrodt Nuclear Medicine LLC, which now forms part of Curium.
The radiotracer is characterized by a high affinity of bond with the somatostatin receptor 2 (SST2). It penetrates inside the cell by endocytosis, first held by lysosomes and then transferred to the nucleus 4,5.
An octreotide scan is used to detect and monitor treatment of neuroendocrine tumours, which arise from cells that produce hormones that are carried in the bloodstream. Many of these tumours are benign (non-cancerous), but some are malignant and can spread around the body. Sometimes the abnormal hormones produced by these tumours can produce a variety of unusual symptoms depending on where the tumours are located.
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