Radioembolization

Selective internal radiation therapy (SIRT) is a form of radiation therapy used in interventional radiology to treat cancer. It is generally for selected patients with unresectable cancers, those that cannot be treated surgically, especially or metastasis to the liver. The treatment involves injecting tiny microspheres of radioactive material into the arteries that supply the tumor. Because this treatment combines radiotherapy with embolization, it is also called radioembolization. The chemotherapeutic analogue (combining chemotherapy with embolization) is called chemoembolization, of which transcatheter arterial chemoembolization is the usual form.

Radiation therapy is used to kill cancer cells; however, normal cells are also damaged in the process. Currently, therapeutic doses of radiation can be targeted to tumors with great accuracy using linear accelerators (see radiation oncology); however, the normal liver tissue is very sensitive to external beam radiotherapy. Fortunately, malignancies (including primary and metastatic liver cancers) are often hypervascular; tumor blood supplies are often increased compared to those of normal tissue. Furthermore, the liver has a dual blood supply, receiving blood from both the hepatic artery and the portal vein. Hepatic malignancies derive most of their blood supply from the hepatic artery; whereas the normal liver derives most of its blood supply from the portal vein. Therefore, delivery of radioembolic particles through the branch of the hepatic artery supplying a tumor will preferentially lead to deposition of the particles in the tumor, while sparing normal liver from harmful side effects.

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