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.
Radiation therapy is a local treatment as opposed to chemotherapy that is a systemic treatment.
That is, radiation treats only the area at which it is directed. High levels of radiation can kill cells or keep them from growing and dividing. Radiation therapy is a useful tool for treating cancer because cancer cells are growing and dividing more rapidly than many of the normal cells around them. In addition, most normal cells appear to recover more fully from radiation effects than cancer cells. Doctors carefully monitor the intensity of treatments and the amount of normal tissue being treated.