Physics of radiation therapy and medical imaging - an historical overview

When a beam of x rays or gamma rays strike an object such as the body of a patient the quanta or photons undergo various interactions which can be broadly classified as attenuation, absorption and scattering. Attenuation describes the decrease in intensity as the beam passes through the body. Absorption refers to the transfer of part of the incoming energy from photons to electrons in the medium by the photoelectric effect, the Compton effect and the creation of positron-electron pairs. Procedures for reducing the harmful effects of radiation have been given the name radiation protection