Radiation is a special kind of energy carried by waves or a stream of particles.
It can come from special machines or from radioactive substances. Many years ago doctors learned how to use this energy to see inside the body and find disease. Special equipment is used to aim the radiation at tumors or areas of the body where there is disease. The use of high energy rays or particles to treat disease is called radiation therapy. Sometimes it's called radiotherapy , x-ray therapy, cobalt therapy, electron beam therapy, or irradiation.