Treatment in which the source of the therapeutic radiation is at a distance from the body. Because teletherapy is often used to treat malignant tumors deep within the body by bombarding them with a high-energy beam of gamma rays (from a radioisotope such as cobalt-60) projected from outside the body, it is often called “external beam radiotherapy.” For related information, see the Backgrounder on Medical Use of Radioactive Materials.

Page Last Reviewed/Updated Tuesday, March 09, 2021