Cobalt therapy

src: upload.wikimedia.org

cobalt therapy or cobalt-60 therapy is the medical use of gamma rays from cobalt-60 radioisotopes to treat conditions such as cancer. Beginning in the 1950s cobalt-60 is widely used in external beam radiotherapy (teleterapy), which produces gamma-ray rays directed to the patient's body to kill the tumor tissue. Because these "cobalt machines" are expensive and require special support, they are often placed in the cobalt unit. Cobalt therapy is a revolutionary advance in radiotherapy in the post-World War II period but is now being replaced by other technologies such as linear accelerators.

Video Cobalt therapy

History

Prior to the development of a medical linear accelerator in the 1970s, the only source of artificial radiation used for teletapy was the x-ray tube. Researchers found ordinary x-ray tubes, which use 50-150 keV voltages, can treat superficial tumors, but lack the energy to reach tumors deep within the body. To have the ability to penetrate to reach a deep tumor without burdening the healthy tissue into dangerous radiation doses requires an energy ray of approximately one million electron volts (MeV), called "megavoltage" radiation. To produce a significant amount of X-ray MeV required potential on a 3-5 million volt tube (3-5 megavolts), requires a large and expensive x-ray machine. By the end of the 1930s this was being built, but they were only available in some hospitals.

Radioisotopes produce gamma rays in the megavolt range, but before World War II virtually the only radioisotope available for radiotherapy was natural radium (producing a gamma ray 1-2Ãƒ, MeV), which is very expensive because of its low incidence in ores. In 1937 the total radium supply worldwide available for radiotherapy (teleterapy) was 50 grams, valued at $ 50 million in 2005 dollars.

The discovery of a nuclear reactor at the Manhattan Project during World War II enabled the creation of artificial radioisotopes for radiotherapy. Cobalt-60, produced by the neutron irradiation of ordinary cobalt metal in the reactor, is a high-energy gamma ray activity, emitting 1.17 and 1.33 gamv of MeV rays with an activity of 44 TB TBq/g (about 1,100 Ci/g). The main reason for its widespread use in radiotherapy is that it has a longer half-life, 5.27 years, than many other gamma transmitters. But half of this life still needs cobalt sources to be replaced every 5 years.

In 1949, Dr. Harold E. Johns of the University of Saskatchewan sent a request to the Canadian National Research Council (NRC) that asked him to produce the cobalt-60 isotope for use in the prototype cobalt therapy unit. Two cobalt-60 apparatuses were then built, one in Saskatoon at the Saskatchewan University cancer wing and the other in London, Ontario. Dr. Johns collected deep dose data at the University of Saskatchewan which would later become the world standard. The first patient treated with cobalt-60 radiation was admitted on October 27, 1951, at Victoria Hospital in London, Ontario. In 1961, cobalt therapy was expected to replace X-ray radiotherapy. In 1966, Walt Disney's lung cancer was treated with this procedure, but could not prevent his death.

Maps Cobalt therapy

Current use

The role of cobalt units has been partially replaced by linear accelerators, which can produce higher energy radiation, and does not generate radioactive waste radioisotopes do with the disposal problems of their officers. The cobalt treatment still has a useful role to play in certain applications and is still widely used worldwide, because the machine is relatively reliable and easy to maintain compared to modern linear accelerators.

Atomic Energy of Canada Ltd. Cobalt-60 Therapy Machine - Canada ...

src: ingeniumcanada.org

Isotope

As used in radiotherapy, the cobalt unit produces stable beams, varying from 1.17 and 1.33 MeV, producing an average light energy of 1.25 MeV. The cobalt-60 isotope has a half-life of 5.3 years so cobalt-60 needs to be replaced occasionally.