Somatostatin Receptor Scintigraphy

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Somatostatin Receptor Scintigraphy
Normal activity in the liver, bile, spleen, kidneys and bladder

The somatostatin receptor scintigraphy , also octreotide scan mentioned, is an imaging technique which is substantially in the diagnosis of neuroendocrine tumors is used (NET).

Implementation and principle of operation

Somatostatin receptor scintigraphy is performed with a special radiopharmaceutical . This consists of three chemically linked components:

Immediately before the injection, the complexing agent – ​​somatostatin analogue conjugate is loaded with the radioisotope, usually 111 indium . The free indium ions are completely chelated by the complexing agent . The radiopharmaceutical produced in this way is administered intravenously and is distributed in the patient's bloodstream. The radiopharmaceutical accumulates in cells that have the appropriate somatostatin receptors . These include the hypothalamus , the cerebral cortex and the brain stem , as well as a number of tumors and their metastases . An initial exposure is made approximately four hours after the administration of the radiopharmaceutical. The duration is about an hour. The enriched radiopharmaceutical breaks down. The gamma radiation emitted in the process penetrates the surrounding tissue and is detected by a gamma camera and combined to form an image using image processing . The number of decay events is particularly high in the areas of enrichment. A second scintigraphy is usually done the next day. (see also: Scintigraphy and Single Photon Emission Computed Tomography )

The only radiopharmaceutical approved in Europe and the USA for somatostatin receptor scintigraphy was 111 indium pentetreotide (= 111 indium-DTPA- [D-Phe 1 ] -octreotide, OctreoScan ® ). The administered activity is usually between 100 and 200 MBq . The radiation exposure ( equivalent dose ) is around 10 mSv when using 110 MBq 111 indium  .

Another radiopharmaceutical, 99m Tc - Tektrotyd, was approved in mid-2008 . Due to the more favorable physical properties of technetium-99m, higher activities can be used, which leads to better image quality and higher sensitivity compared to the examination with indium-octreotide. The manufacturer specifies 370 to 925 MBq as the activity to be administered.

application

Gastro-entero-pancreatic neuro-endocrine tumors ( GEP-NET ) are difficult to detect with the usual imaging methods ( sonography , endoscopy , computed tomography and magnetic resonance tomography ). By expressing somatostatin receptors, these tumors can be localized using somatostatin receptor scintigraphy. The use of somatostatin receptor scintigraphy has been tested on a large number of patients with a wide variety of tumors in various clinical studies. With the exception of insulinomas, the sensitivity of neuroendocrine tumors is very high.

Although other tumor cells, such as breast cancer , also express somatostatin receptors to a greater extent, the sensitivity in these cases is considerably lower and the results less clear.

An antiproliferative effect of octreotide has also been demonstrated in colorectal carcinomas (colon cancer). However, only about 40% of colorectal carcinomas express somatostatin receptors.

Development history

In 1981 the first results on the distribution of somatostatin receptors were published. The first somatostatin analogue octreotide was synthesized in 1985 by the same working group and tested in vivo . The first scintigraphic studies in animal models were carried out in 1990. For this purpose, the structure of the octreotide was changed so that the phenylalanine in position 3 was replaced by tyrosine . The hydroxyl group of the tyrosine was replaced by the radioactive isotope 123 iodine immediately before injection for labeling . In 1991 the first scintigraphy with 111 indium and octreotide was described in an animal model.

A new, but not yet approved , development is the use of 68 Gallium- DOTATOC as a radiopharmaceutical. The radioisotope 68 gallium is used instead of 111 indium . It is no longer a scintigraphic process, but a positron emission tomography .

Individual evidence

  1. ↑ TM Behr et al.: Nuclear medical diagnosis and therapy of neuroendocrine tumors of the gastrointestinal tract including the carcinoid. In: Nuklearmediziner 26/2003, pp. 121-33.
  2. ↑ M. Hofmann, T. Krause. Therapy with receptor-affine peptides. In: Torsten Kuwert, Frank Grünwald , Uwe Haberkorn , Thomas Krause (Eds.) Nuclear Medicine. Stuttgart 2008, ISBN 978-3-13-118504-4
  3. ↑ Austrian Federal Office for Safety in Health Care  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (PDF; 60 kB)@1@ 2Template: Toter Link / www.basg.at  
  4. ↑ M. Gabriel et al. An intrapatient comparison of 99mTc-EDDA / HYNIC-TOC with 111In-DTPA-octreotide for diagnosis of somatostatin receptor-expressing tumors. J Nucl Med. 2003 May; 44 (5): 708-16. PMID 12732671
  5. ↑ In-111-Octreoscan (PDF; 122 kB) German Society for Nuclear Medicine
  6. ↑ EP Krenning include: somatostatin receptor scintigraphy with [111 In-DTPA-D-Phe 1] - and [123 I-Tyr 3] -octreotide: the Rotterdam experience with more than 1,000 patients. In: Eur J Nucl Med 20/1993, pp. 716-31.
  7. ↑ K. Joseph et al.: Receptor Scintigraphy with 111In-Pentetreotide for Endocrine Gastroenteropancreatic Tumors. In: Horm Metab Res 27/1993, pp. 28-35.
  8. ↑ JK Seifert et al.: 111-indium-DTPA-octreotide scintigraphy in colorectal liver metastases. In: Langenbeck's Archives of Surgery 382/1997, pp. 332-36.
  9. ↑ JC Reubi et al. a .: High affinity binding sites for a somatostatin-28 analog in rat brain. In: Life sciences 28/1981, pp. 2191-8.
  10. ↑ JC Reubi et al .: Specific high affinity binding sites for somatostatin-28 on pancreatic beta-cells: differences with brain somatostatin receptors. In: Endocrinology 110/1982, pp. 1049-51.
  11. ↑ JC Reubi: A somatostatin analogue inhibits chondrosarcoma and insulinoma tumor growth. In: Act Endol 109/1985, pp. 108-14
  12. ^ WH Bakker et al: Receptor Scintigraphy with a Radioiodinated Somatostatin Analogue: Radiolabelling, Purification, Biologic Activity, and In Vivo Application in Animals. In: J Nucl Med 31/1990, pp. 1501-9.
  13. ^ WH Bakker et al: In Vivo Use of Radioiodinated Somatostatin Analogue: Dynamics, Metabolism, and Binding to Somatostatin Receptor-Positive Tumors in Man. In: J Nucl Med 32/1991, pp. 1184-9.

literature

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