(in-TER-nul RAY-dee-AY-shun THAYR-uh-pee) 
A type of radiation therapy in which a radioactive substance is sealed inside materials that can be implanted, such as pellets, seeds, ribbons, wires, needles, or capsules, and placed inside the body, directly into or near a tumor or within a body cavity. The implant may be placed through a small flexible tube called a catheter or through an applicator device. It may be kept in place for a few minutes, for many days, or for the rest of a person’s life. Internal radiation therapy is often used to treat cancers of the head and neck, breast, cervix, prostate, and eye. Also called brachytherapy, implant radiation therapy, and radiation brachytherapy.