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Selective Internal Radiation Therapy (SIRT)Intra-arterial radiation therapy is an innovative means of treating liver tumors. In cases where it is not possible to surgically remove the liver tumors, radioactive microspheres can be used to deliver targeted, internal radiation therapy directly to the tumor. This new therapy is called Selective Internal Radiation Therapy also known as SIRT.
How Does SIRT Work?
When tumors arise in the liver, their blood supply is derived from the hepatic artery; in contrast, normal liver tissue receives about 80% of its blood supply from the portal vein. SIRT takes advantage of this knowledge by using the portal vein as a direct route to deliver yttrium-90 radiation microspheres directly into the liver tumors. By selectively infusing radioactive material into the left, right or common hepatic artery, a concentrated dosage can be delivered directly into the tumor, while conserving normal liver tissue that surrounds the tumor.
These microspheres are very small, approximately 32 microns in size, and are about one-third the diameter of a strand of hair. SIRT is administered as an outpatient procedure by a specially trained physician known as an interventional radiologist. A small catheter is guided into the liver and the microspheres are infused through the catheter. The microspheres with the radioactive yttrium-90 are carried by the bloodstream directly to the tumors in the liver where they preferentially lodge in the small vessels feeding the tumor and deliver their dose of radiation. Unlike conventional external beam radiation, which can only be applied to limited areas of the body, SIRT microspheres selectively irradiate the tumors and therefore have the ability to deliver more potent doses of radiation directly to the cancer cells over a longer period of time.
There are currently two types of SIRT yttrium-90 microspheres that have been FDA approved for treatment of liver tumors. Therasphere® uses glass beads to deliver yttrium-90 radiation and Sir Spheres® uses resin beads. At Norton Healthcare, we offer both of these innovative procedures. Our liver cancer specialists work with the interventional radiologists, the radiation oncologists and the nuclear physicists to customize therapies and determine which treatment option offers the most benefit to the patient.
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