Radiation is an effective way to destroy tumour tissues and is used widely in cancer treatment.
However, the organs and tissues in the body are sensitive to radiation and may also be damaged by radiation treatment. Thus, conventional radiotherapy (external beam radiation delivered from outside the body) can only be given to limited areas of the body.
The liver can only tolerate small doses of external radiotherapy. Because Selective Internal Radiation Therapy (SIRT) with SIR-Spheres® Y-90 resin microspheres targets the tumour(s) internally, it can deliver a larger dose of radiation directly over a longer time than is possible with external beam radiation. This allows therapeutic radiation to be targeted within the liver tumour(s).
Although normal liver tissue will be radiated to some extent, the radiation dose is well below the limit the tissue can tolerate without serious damage.
Tumours get most of their blood supply from the hepatic artery, the main blood vessel that supplies blood to the liver. Normal liver tissue gets most of its blood supply from a blood vessel called the portal vein. Microspheres are injected into the hepatic artery so they are mainly delivered to the tumour.
The microspheres become trapped in the very small blood vessels of the tumour where they deliver their radiation dose to an area of about 2-3mm around where they are trapped. Most of the radiation is delivered within 2 weeks. In this way, radiation is delivered mostly to the tumour but causes very little damage to the surrounding healthy liver tissue.
Because the hepatic artery also supplies about 10-20% of the blood that goes to normal liver tissue, there is some radiation of this tissue. Your doctor will use a dose that will deliver radiation that is effective against the tumour but causes minimal or no damage to normal liver.
The microspheres only stay radioactive for a limited time. After 2 weeks only 3% of the initial radiation remains and after 1 month it all has decayed. The decayed resin microspheres stay in the liver permanently. They are harmless.
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