Procedure
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). In-111 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 post injection). [10] It is eliminated principally by the kidneys (half of the injected dose appears in the urine by 6 hours, 85% within 1 day) and a small amount by the liver (2%). It is unclear whether 111In pentetreotide is removed by hemodialysis. [2, 10]
Images are obtained at 4 hours and 24 hours, or at 24 hours and 48 hours, post injection. Patients should empty their bladder before imaging. If significant bowel activity is 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, 4-hour images offer information prior to the start of 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, extremities can be acquired for 10-15 minutes per image, using a 512 × 512-word or a 256 × 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.
With a multidetector gamma camera, SPECT imaging of appropriate regions should be performed based on the clinical history. Early and delayed SPECT may differentiate bowel activity from pathologic lesions. If multiple SPECT images are not possible, single image acquisition at 24 hours is preferred because of a higher target-to-background ratio. [2, 10]
Raw SPECT data should be filtered by applying a low-pass filter, per software manufacturer recommendations. Data should be reconstructed via use of a ramp filter and attenuation correction. Newer models may allow iterative reconstruction algorithms.
Images should be fused or evaluated with relevant anatomic images (CT or MRI).
The optimal time interval for localizing lesions is 24 hours post injection or later. Images obtained at 4 hours with high background activity may be important for comparison and evaluation of abdominal activity at 24 hours. Activity is noted normally in the pituitary, thyroid, liver, spleen, kidneys, and bladder, and occasionally in the gallbladder. Intestinal activity is normally absent at 4 hours, but images at 24 hours normally show activity; however, images at 48 hours may be needed to clarify abdominal activity. [10]
Recommendations provided in the Society of Nuclear Medicine Guidelines on General Imaging should be followed in preparation of the report. Additionally, the report should highlight relevant history, laboratory evaluation, medications (eg, octreotide, chemotherapy), and description and limitations of the procedure, including false-positive results. [10]
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 mesenteral neuroendocrine tumor became clearly visible in 4/2005 (arrow). Image from Ectopic Cushing's 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.
Approach Considerations
In a case report, Wang and associates described the first known instance of successful treatment with octreotide long-acting release (LAR) in a patient with metastatic advanced adrenocortical carcinoma (ACC) who showed poor tolerance to mitotane following positive octreoscan scintigraphy. She showed major partial response to the somatostatin analog. Next-generation sequencing–based circulating tumor DNA analysis failed to identify any alterations. These findings suggest that octreotide LAR may be a good option for treatment of metastatic ACC in selected patients. [16]
Another case report showed effective use of SPECT and/or CT 111In octreotide scintigraphy for early diagnosis of pulmonary sarcoidosis, a granulomatous disease of unknown etiology. Octreoscan confirmed morphologic involvement of bilateral hilar lymph nodes, and a mediastinoscopy biopsy specimen confirmed diagnosis of pulmonary sarcoidosis stage 0. [17]
-
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 mesenteral neuroendocrine tumor became clearly visible in 4/2005 (arrow). Image from Ectopic Cushing's 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.
