The race for megavoltage - X-rays versus telegamma

Roentgen's discovery was announced in January, 1896, and x-ray therapy trials followed in 1897, Becquerel rays and radioactive minerals were identified during 1896 through 1898, Radium was used for therapy by 1901, even though a pure standard was not achieved until 1910-1912, Quantities of radium finally became available after 1919, and for 20 years telegamma therapy machines underwent progressive development, Their megavoltage beam was much preferred over the standard 200-250 KV x-ray units of that time, Nuclear physicists during the Great Depression modified electron accelerators into giant 600-900 KV medical x-ray therapy machines and achieved one MV by 1937-1939, These were huge, complex, expensive, and unique to major academic and/or metropolitan centers, During World War II nuclear reactors superseded cyclotrons as efficient factories for new radioisotopes, including 'artificial radium'. Pew seemed interested in the latter for use in telegamma therapy until 1949-1951, when three competing teams from Canada and the USA designed telecobalt machines, From this competition, among then unknown innovators, emerged three future giants in radiation therapy: A.E.C.L., H. Johns, and G.H. Fletcher, The clinical application of telecobalt therapy was to revolutionize cancer care in community hospitals worldwide.