Radiation treatment, diagram. Radiation treatment, or radiotherapy, is used to treat certain types of cancer. It consists of a radiation source such as cobalt, used to deliver a finite, high-power dose to a localised area. The radioisotope used, cobalt-60, is a powerful gamma-ray emitter. The radiation is aimed at the target area with the aid of laser beams. If the patient's head is being treated, as seen here, it is immobilised in a fixed helmet.