When treating liver tumors, doctors need ways to attack the cancer while sparing healthy tissue. One advanced technique is Selective Internal Radiation Therapy, or SIRT. It’s a type of treatment that delivers radiation directly to tumors inside the liver.

This method is also known as radioembolization. It combines the blockage of blood vessels that feed a tumor (embolization) with highly localized radiation. The goal is to shrink or destroy liver tumors with minimal damage to the surrounding healthy parts of the liver.

SIRT uses microscopic spheres, called microspheres, that are loaded with a radioactive element: Yttrium-90 (Y90). These spheres are incredibly small, about a third of the width of a human hair. A doctor injects millions of these spheres into the hepatic artery, the main blood vessel that supplies the liver.

Liver tumors get most of their blood supply from this artery, while healthy liver tissue is mostly supplied by a different vessel, the portal vein. This difference in blood flow is key. It means the Y90 microspheres are carried directly to the tumor, where they get trapped in the tiny blood vessels feeding it. The healthy liver tissue is largely bypassed.

Once lodged in place, the Yttrium-90 begins to release radiation. Y90 is a radioisotope, an unstable element that emits energy to become stable. Specifically, it emits beta radiation, a type of energy that travels only a very short distance—just a few millimeters.

This short range is crucial. The radiation damages the DNA of the nearby tumor cells, causing them to die, but it doesn't reach far enough to harm healthy tissues elsewhere in the body. The microspheres deliver a high dose of radiation from the inside out, precisely where it's needed.

While the principle is the same, there are two main types of Y90 microspheres used in SIRT. They differ in the material they are made from, which affects some of their properties.

Both resin and glass microspheres are designed to safely carry Yttrium-90 and become lodged in the tumor's vasculature. The choice between them depends on various clinical factors. For now, just know that both serve the same fundamental purpose: to deliver targeted, internal radiation to liver tumors.