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In the early days of teletherapy, X-rays and radium were used for the treatment of cancer. These methods were supplanted with the understanding and application of the Cobalt-60 gamma rays in nuclear medicine in the mid 1900s.

Cobalt-60 is a radionuclide , or radioactive isotope of Cobalt, of half-life 5.27 years and emits photons of energy 1.17MeV and 1.33MeV. This isotope is produced by irradiating pure cobalt-59 pellets with neutrons in a reactor.

Cobalt radionuclide is used because it can deliver doses of irradiation with deep penetration into the body tissue with minimal skin reaction. The half-life of cobalt radionuclide is also another favorable factor for use in medicine.

Radionuclides are used in cancer treatment in many forms. Most of which we have often heard of is irradiation from a distant source. Irradiation is delivered to the affected region , affecting both cancerous and normal cells at the targeted region. As cancer cells are more sensitive to radiation than normal cells, irradiation must be conducted in doses so that normal cells are given time to recover before the next treatment.

Diagnosis of certain disease can also be in the form of ingestion of controlled doses of radionuclides and tagging its progress in the body. Radionuclides can be used as a tracer in the body to study absorption and distribution of certain elements in the body. Vitamin B12 absorption difficulties can be investigated by ingesting vitamin B12 tagged with radioactive cobalt .

Cobalt radionuclides is also used for local treatment of certain cancers by the implantation method, or interstitial brachytherapy. Cobalt radionuclide "seed"or capsule of the correct dosage is introduced to the site of the tumor for near or local irradiation of diseased tissues. This form of treatment is especially successful on tumors in the region of the prostate, breast, and head, just to name a few. Multiple side effects, eg dry mouth, skin itch, thrush that occur are localized at point of treatment.

Cobalt-60 radionuclide is used for sterilizing medical instruments because it can penetrate deep into matter. The instruments can be sealed in plastic and then treated by cobalt gamma-60 ray, minimizing contact with microbes.It is also a very attractive alternative to sterilizing with other conventional methods especially when the equipment is to be used repeatedly.

Finally, cobalt-60 is the working principle behind the "gamma knife". The "gamma knife" uses precise, concentrated beams of radiation from Cobalt-60 to cut diseased tissue. 201 beams intersect at a point to form a surgical knife for the purpose of excising the tumor. Predominantly used in brain surgery, the gamma knife is the latest in Cobalt teletherapy to offer hope to patients suffering from brain cancer.

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