TheraSphere is a medical device containing yttrium-90 (Y-90), a radioactive material that has been used to treat liver tumors. When Y-90 is put into microscopic glass beads, called microspheres, it can be injected directly into the liver by artery. This allows a large dose of radiation to be delivered directly to the tumor, which lowers the risk of experiencing toxic radiation side effects from the radiation to in other parts of the body, or to healthy liver tissue. The radiation from TheraSphere treatment stays in the body and begins to lose its effect within 12 days, due to physical decay (please refer to the package insert for more information for more information regarding this). The glass microspheres will stay in the body from that point on, but should not cause any health problems.