A type of radiation therapy used to treat liver cancer or cancer that has spread to the liver. A thin, flexible tube is used to inject tiny beads that hold the radioactive substance yttrium Y 90 into the main blood vessel that carries blood to the liver. The beads collect in the tumor and in blood vessels near the tumor, and the yttrium Y 90 gives off radiation. This destroys the blood vessels that the tumor needs to grow and kills the cancer cells. Radioembolization is a type of internal radiation therapy. Also called intra-arterial brachytherapy.