Radiation is an effective way to destroy tumour tissues and is used widely in cancer treatment. However, all types of organs and tissues in the body are sensitive to radiation and the healthy ones may also be damaged by radiation treatment. Thus, conventional radiotherapy (external beam radiation delivered from outside the body) can only be given to some areas of the body. The liver for instance can only tolerate low doses of external radiotherapy. Selective Internal Radiation Therapy (SIRT) with SIR-Spheres® Y-90 resin microspheres targets the tumour(s) internally, therefore a higher dose of radiation can be delivered directly to the tumour tissue over a longer time than is possible with external beam radiation. Although normal liver tissue will be radiated to some extent, the dose is well below the limit the tissue can tolerate without serious damage.

How do SIR-Spheres Y-90 resin microspheres get to the tumour?

The liver is unique in the way it is supplied with blood, it receives blood via two distinct circulatory routes: the hepatic artery and the portal vein. However, liver tumours get most of their blood supply from the hepatic artery, whereas normal liver tissue gets most of its blood from the portal vein. SIR-Spheres Y-90 resin microspheres are injected into the hepatic artery to be mainly delivered to the tumour(s).

The microspheres become trapped in the very small blood vessels of the tumour(s) where they emit radiation to tissue in a radius of about 2-3mm . Thus, the tumour(s) is/are damaged, but the surrounding healthy liver tissue is mostly spared.

Since the hepatic artery also supplies about 10-20% of the blood to normal liver tissue, some radiation will reach this tissue. Your doctor will calculate a dose that will be effective against the tumour(s) but will only cause minimal or no damage to normal liver tissue.

The microspheres stay radioactive for a limited time. After 2 weeks only 3% of the initial radiation remains and after 1 month it all has disapeared. The microspheres stay in the liver permanently, they are harmless.



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