Because the cobalt machines were expensive and required specialist support they were often housed in cobalt units.
In 1949, Dr. Harold E. Johns of the University of Saskatchewan sent a request to the National Research Council (NRC) asking them to produce Cobalt-60 isotopes for use in a cobalt therapy unit prototype. Two Cobalt-60 apparatuses were then built, one in Saskatoon in the cancer wing of the University of Saskatchewan and the other in London, Ontario. Dr. Johns collected depth-dose data at the University of Saskatchewan which would later become the world standard. The first patient to be treated with Cobalt-60 radiation was treated on October 27, 1951, at Victoria Hospital in London, Ontario. In 1961 cobalt therapy was expected to replace X-ray radiotherapy. The role of the cobalt unit has partly been replaced by the linear accelerator, which can generate higher energy radiation. Cobalt treatment still has a useful role to play in certain applications and is still in widespread use worldwide, since the machinery is relatively reliable and simple to maintain compared to the modern linear accelerator.
As used in radiotherapy, cobalt units produce stable, dichromatic beams of 1.17 and 1.33 MeV, resulting in an average beam energy of 1.25 MeV. The cobalt-60 isotope has a half-life of 5.3 years so the cobalt-60 needs to be replaced occasionally.