Technically, radiation therapy in general is not considered a subset of nuclear medicine. In fact, most radiation therapy has nothing to do with the nucleus of an atom (e.g. external beam therapy involves accelerated electrons and bremmstrahlung x-rays). The specific field of nuclear medicine is a well-defined specialty considered a part of medical physics and having to do with the use of radionuclides for diagnostic and therapeutic purposes. See nuclear medicine. 64.131.242.198 20:32, 8 April 2007 (UTC)