The Changing Role of Accelerators in Radiation Therapy

Conventional low energy x-rays have been used in radiation therapy since the turn of the century. Van de Graaff and Betatron accelerators changed the complexion of radiation therapy in the mid 1940´s by providing significantly deeper penetrating photon beams and also providing therapeutic quality electron beams. The development of Cobalt-60 teletherapy in the mid 1950´s suppressed the role of accelerators in radiation therapy for nearly 20 years. However, with the development of reliable isocentric rotating linear accelerators, accelerators are rapidly becoming the most popular conventional therapy devices. Following unfavorable clinical results with fast neutron therapy in the late 1930´s and early 1940´s, the role of cyclotron produced fast neutrons is presently experiencing a renewal in radiation therapy. Several facilities are also experimenting with heavy charged particle beams for therapy. This changing role of accelerators in radiation therapy will be observed in detail along with a look to the future. I will concentrate on developments in North America. However developments in Europe closely parallel them.