Selective internal radiotherapy

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The selective internal radiation therapy (SIRT or Radioembolization) is an interdisciplinary therapy for the treatment of unresectable hepatic cancer, particularly in advanced forms of primary liver tumors ( hepatocellular carcinoma , Cholangiocellular carcinoma ) and hepatic metastasis as a result of tumors in other organs such as colon, lung, breast, Skin, pancreas and stomach. For the treatment, several million tiny spheres with the beta emitter yttrium-90 are inserted directly into the tumors.

Procedure and mode of action

The doctor places a catheter from the inguinal artery into the hepatic artery . From there, the spheres with the blood flow directly into the tumor and get stuck in the finely branching vessels. There they work in two ways: They destroy the tumor from the inside with radiation, which however only has a very short range of up to 11 mm, so that the rest of the liver tissue is spared. At the same time, the globules block the blood supply to the tumor and thus “starve” it. Because of this dual mode of action, the therapy is also known as "radioembolization".

The procedure takes advantage of the fact that liver tumors are usually supplied by arterial blood vessels, while healthy liver tissue, on the other hand, receives 80% of its blood from branches of the portal vein . The microspheres with a diameter of approx. 30 µm (approx. A third of a hair's width) therefore remain mainly in the capillary vessels of the tumor and irradiate it with a dose of approx. 200 Gy, while the rest of the liver is only exposed to approx.

Yttrium -90 is a beta emitter with a half-life of 64 hours . 94% of the radiation dose is released after eleven days. It decays to the stable isotope zirconium -90. The microspheres remain in the liver. Since they are biocompatible, they have no further effect on the liver tissue.

Possible uses

Scientific studies confirm the success of SIRT therapy especially for the following tumor types:

  • Hepatocellular carcinoma
  • Liver metastases in colorectal carcinoma
  • Liver metastases in breast cancer
  • Liver metastases in neuroendocrine tumors

In addition to these standard indications, promising results are also available for a number of other tumors (e.g. for bile duct carcinoma, pancreatic carcinoma or choroidal melanoma).

Patients must meet certain minimum requirements in order to be suitable for SIRT:

  • The cancer should be concentrated in the liver, as the therapy can only achieve effects there.
  • The liver still needs to function well.
  • The expected life expectancy of the patient should be more than three months

Therapy goals

Selective internal radiotherapy is used to extend the survival time of people with liver metastases or liver cancer and to improve the quality of life. The therapy is suitable for significantly reducing the size and number of liver tumors. Based on more recent data, doctors are starting to use SIRT in combination with chemotherapy in the earlier stages of liver cancer.

The procedure is also used to downgrade an inoperable liver tumor to an operable tumor, because the preferred form of therapy for liver tumors is surgery or radiofrequency ablation , in which the tumor is "boiled up". However, the prerequisite for an operation is that at least 25 percent of the functional liver epithelium is retained in the patient. If a tumor is too large or the number of tumors too high, an operation could impair the functioning of the liver too much and SIRT can then be considered as a therapy.

Formally, the SIRT is a brachytherapy with open radionuclides ( radionuclide therapy ), which is only carried out in the control area with the cooperation of nuclear medicine specialists . Similar methods are local chemoperfusion (injection of cytostatics into the hepatic artery) and chemoembolization (injection of particles or tissue glue to cut off the blood supply to the tumor).

Admission

Since then, the form of therapy has spread steadily. The products currently available are approved in Europe as medical devices with CE certification for the treatment of liver cancer.

The spheres available on the market are made of glass ( TheraSpheres, MDS Nordion) or resins ( SIR-Spheres, Sirtex Medical). Both products are approved for treatment in the US and the EU.

refund

The therapy is reimbursed by the health insurance companies if the tumor is inoperable and chemotherapy does not show any effect (as of 2011). The number of clinics that offer SIRT is steadily increasing.

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  • Ralf-Thorsten Hoffmann, Maximilian F. Reiser and others: Selective internal radiotherapy (SIRT) - basics and clinical application. UNI-MED, 2008, ISBN 978-3-8374-1033-4 .
  • Ralf-Thorsten Hoffmann among others: Selective internal radiotherapy for advanced liver tumors and metastases. In: Dtsch med Wochenschr . 2008; 133 (41), pp. 2099-2102, doi : 10.1055 / s-0028-1091244 .
  • D. D'Avola, M. Inarrairaegui, JI Bilbao et al .: A Retrospective Comparative Analysis of the Effect of y90-radioembolisation on the Survival of Patients with Unresectable Hepatocellular Carcinoma. In: Hepatogastroenterology. 2009 Nov-Dec; 56 (96), pp. 1683-1688. PMID 20214218 .

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