Radiation-therapy equipment in the megavoltage or million-volt range was introduced in the 1930's; however, it was not applied widely due to cost and the necessity for more investigation. Beginning in the late 1940's with the installation of teletherapy60Co units and various generators including Van de Graaf, resonance transformers, linear accelerators, and betatrons, the past two decades can be termed the "supervoltage era." This search for a unique quality or energy of irradiation specific for cancer cells is all but limited to neutron-beam therapy. The establishment of 1 to 6 mev as the optimum therapeutic range related to physical characteristics and not to biologic specificity.
The advantages of supervoltage radiation therapy are its better tolerance by normal tissues, skin-sparing effects, better penetration so that greater depth doses can be achieved, no differential bone absorption, and less side scatter. Translated directly into the prostatic-cancer problem, the unsatisfactory side effects of