1. Radiolabled Somatostatin Analog
Octreoscan
Radiolabled Somatostatin Analog

2. What Is Somatostatin?
Somatostatin is a naturally occurring neuropeptide found in the hypothalamus that possesses a wide range of pharmacological properties, including inhibition of growth hormone release and the suppression of insulin and glucagon secretion. In its relationship to these hormones it is similar to the feedback loop associated with thyroids and adrenals.

3. Peptide Biodistribution
They are not monoclonal antibodies
However, they behave in the same manner
The peptide forms a lock and key relationship with receptors on a tumor cell
The ability to detect tumors depends on the specificity of the peptide to the receptors on the tumor

4. Somatostatin Receptors
Somatostatin receptors have been demonstrated in endocrine cells throughout the body, as well as in numerous endocrine tumors.
Majority of neuroendocrine tumors, including carcinoids, islet cell carcinomas, and growth hormone producing pituitary adenomas have cell membrane receptors with a high affinity for somatostatin
Somatostatin has also shown to inhibit excessive production of hormones caused by a variety of neuroendocrine tumors, including carcinoids, vipomas (pancreatic tumor), gastrinomas, and insulinomas.

5. Somatostatin Receptors (Cont.)
Indications are for neuroendocrine tumors
Localizes in tumors with somatostatin receptors and are:
Meningioma Insulinoma
Pheochromocytoma Gastrinoma
Neuroblastoma Paraganglioma
Islet cell carcinoma Pituitary adenoma
Glucagonoma VIPoma
Small cell lung carcinoma Carcinoid
Medullary thyroid carcinoma

6. Peptides - Octreotide Other tumors also possess similar binding sites:
Meningiomas
Breast carcinoma
Astrocytomas
Small cell carcinoma of the lung

7. Ability to Detect Disease
Scintigraphy
In vitro
Medullary thyroid carcinoma
20/ %
10/ %
Pheochromocytoma
12/ %
38/ %
Carcinoid
69/ %
54/ %
Small cell lung cancer
34/ %
4/ %
Non-small cell lung cancer
36/ %
0/ %
Meningiomas
14/ %
54/ %
Breast cancer
37/ %
33/ %
Non-Hodgkin's Lymphoma
59/ %
Hodgkin's disease
23/ %
2/ %

8. Peptides In 1994 the FDA approved the first
radiolabeled peptide for diagnostic imaging:
111In Pentetreotide or (OctreoScanâ)
111In DTPA-d-Phe-octreotide

9. Peptide Biodistribution
They are not monoclonal antibodies
However, they behave in the same manner
The peptide forms a lock and key relationship with receptors on a tumor cell
The ability to detect tumors depends on the specificity of the peptide to the receptors on the tumor

10. Human – Synthetic
Octreotide is a synthetic peptide developed from Somatostatin
The human form of stomatostatin is composed of 14 amino acids
Octreotide only has 8 amino acids, however, it behaves just like
its human counter part
Being smaller, it clears faster and has improved target to
background

11. Labeled Octreotide Octreotide is labeled via DTPA to In111
Indium 111 pentreotide (Octreoscan) is a radiolabeled analog of somatostatin indicated for the scintigraphic localization of neuroendocrine tumors bearing somatostatin receptors.

12. Indications Primary and metastatic neuroendocrine tumors
GH & TSH producing pituitary tumors
Paragangliomas
Medullary thyroid CA
Small cell lung CA
As the first peptide imaging agents, Octreoscan goes beyond imaging tumor anatomy, providing valuable clinical information about tumor biochemistry.

13. Method of Localization
Following intravenous injection, In111 pentreotide binds to somatostatin receptors present in tissues throughout the body, concentrating in tumors that contain a high density of somatostatin receptors

14. Precautions and Patient Preparation
Insulinoma patients should be treated with IV glucose prior/during injection
Causes severe hypoglycemic reaction
Patients should be well hydrated
Octreoscan is excreted primarily through the kidneys, hydration will enhance renal clearance thus reducing radiation exposure
Bowel prep is warranted pre/post injection
Octreotide acetate therapy should be suspended prior to Octreoscan administration

15. Precautions (Cont.) Special Consideration - Insulinoma Patients
Theoretically pentetreotide may decrease glucagon levels to the degree that insulin from the tumor could significantly reduce blood glucose levels
Mallinckrodt recommends IV glucose solution be administered prior to and during OctreoScanâ administration

16. Scan to Injection Time
Imaging is performed either planar or SPECT 4 to 24 hours after injection.
Imaging can be done at 48 hours as a follow up to differentiate between neuroendocrince tumor and normal bowel uptake.

17. Radiopharmaceutical and Dose
In111 Chloride Pentreotide (Octreoscan)
Kit contains lypholized pentetreotide and 1.1 ml of 3 mCi of In111 Chloride solution
Should be stored in refrigerator and used within 6 hours of preparation
Dose is 3-6 mCi

18. Peptides - Octreotide Imaging Procedure has two considerations Planar
SPECT

19. Views and Camera Set Up Large field of view gamma camera
SPECT, WB and Static Imaging can be performed
Energy peaks at 20% window
173 keV and 247 keV
Medium energy collimator
Anterior and Posterior
Head, Chest, Abdomen, and Pelvis

20. Normal Distribution Interpretation Normal biodistribution
Pituitary gland
Spleen
Liver (especially in patients with ¯ renal clearance)
Kidneys
Urinary bladder
Normal thyroid gland (minimally)
Colon (depending on laxative effectiveness)

21. Normal Distribution the kidneys and bladder (the route of excretion)
the liver (diffuse low uptake)
the spleen (marked uptake)
the pituitary gland (modest)
thyroid gland (modest)
occasionally the large bowel at 24 hours.

22. Normal Biodistribution
4 Hr delayed images show vascular, renal excretion, and
liver/spleen uptake
24 Hr delayed images show some bone uptake with
significant liver/spleen uptake

23. Octreoscan Case 1
69 year old male presented, history of a 5 cm left hilar lung mass found to be small cell lung carcinoma.
Scan demonstrates two foci of increased uptake in the left hilum.
The patient was started on a course of radiotherapy to the left hilum.

24. Octreoscan Case 2
Intense increased tracer localization in the pancreatic mass (arrow head) and multiple abnormal foci of uptake throughout the liver (arrow) consistent with diffuse liver metastases.

25. VIPoma – Endocrine Tumor
Exam of abnormal distribution caused by neuroendocrine tumor
red arrows indicate disease
R image is the initial scan with a follow-up still showing
significant disease

26. Peptides - Octreotide Patient preparation
Well hydrated - Caution in patients with impaired renal function
Bowel preparation - Caution in patients with insulinoma
If patient is taking somatostatin therapeutically, discontinue if possible

27. Peptides - Octreotide Interpretation
Focal areas of increased activity outside these regions may indicate presence of tumor
Pitfalls
Bleomycin or external radiation of the lung may cause local pulmonary accumulation of the radiopharmaceutical, particularly along the pleura
Sites of a recent operation

28. Peptides - Octreotide Pitfalls (continued)
Patients with viral infections of the upper respiratory tract may have transient accumulation in the nasal region and the lung hili

29. Peptides - Octreotide Radiation Dosimetry Critical organ
Spleen
7.39 rads/3 mCi
14.77 rads/6 mCi
Effective dose equivalent
1.3 rem/3 mCi
2.61 rem/6 mCi

30. Additional Case Studies