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Octreoscan
Radiolabled Somatostatin Analog
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.
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
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.
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
Peptides - Octreotide
Other tumors also possess similar binding sites:
 Meningiomas
 Breast carcinoma
 Astrocytomas
 Small cell carcinoma of the lung
Ability to Detect Disease
Disease
Scintigraphy
In vitro
Medullary thyroid carcinoma
20/28 71%
10/26 38%
Pheochromocytoma
12/14 86%
38/52 73%
Carcinoid
69/72 96%
54/62 88%
Small cell lung cancer
34/34 100%
4/7 57%
Non-small cell lung cancer
36/36 100%
0/17 0%
Meningiomas
14/14 100%
54/55 98%
Breast cancer
37/50 74%
33/72 46%
Non-Hodgkin's Lymphoma
59/74 80%
0/17 0%
Hodgkin's disease
23/24 96%
2/2 100%
Peptides
In 1994 the FDA approved the first
radiolabeled peptide for diagnostic imaging:
111In
Pentetreotide
111In
or (OctreoScan)
DTPA-d-Phe-octreotide
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
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
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.
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.
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
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
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
OctreoScan administration
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.
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
Peptides - Octreotide
Imaging Procedure has two considerations
– Planar
– SPECT
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
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)
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.
http://www.med.harvard.edu/JPNM/TF94_95/Nov1/WriteUpNov1.html
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
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
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.
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
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
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
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
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
Additional Case Studies