Cobalt therapy or cobalt-60 therapy is the medical use of gamma rays from the radioisotope cobalt-60 to treat conditions such as cancer. Beginning in the 1950s cobalt-60 was widely used in external beam radiotherapy (teletherapy) machines, which produced a beam of gamma rays which was directed into the patient's body to kill tumor tissue. Because these "cobalt machines" were expensive and required specialist support, they were often housed in cobalt units. Dr. V.S Jeyaraman., MD.,(RT).,DMRD.,Radiation Safety Officer(RSO) Mr. A. Jaya Kumar.,