ABSTRACT
Clinical cobalt therapy units and MV linear accelerators were introduced nearly simultaneously in the early 1950s. e rst two clinical cobalt therapy units were installed in October 1951 in Saskatoon and London, Ontario (Litt 2000). e rst MV linear accelerator installed solely for clinical use was at Hammersmith Hospital, London in June 1952 (Bernier et al. 2004). In August 1953, the rst patient was treated with this machine. e deeply penetrating ionizing photon beams quickly became the mainstay of radiation therapy, allowing the widespread noninvasive treatment of deep-seated tumors. An additional advantage of these photon beams was based on the fact that photons deliver most of their dose through the interactions of highly energetic
scattered electrons. e dose delivery properties of the photon/ scattered electron system leave the patient’s skin surface with a considerably lower dose than inside the body. is allowed aggressive doses to be used internally while sparing the skin from severe radiation damage. Consequently, this feature was called skin sparing and played an important role in the clinical utility of linear-accelerator and cobalt-beam therapies.
