Patient receiving cobalt-60 therapy.
Because the cobalt machines were expensive and required specialist support they were often housed in cobalt units.
In 1961 cobalt therapy was expected to replace X-ray radiotherapy.
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 The role of the cobalt unit has partly been replaced by the linear accelerator, which can generate higher energy radiation.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.
The cobalt-60 has a half-life of 5.3 years so the cobalt-60 needs to be replaced occasionally.