Cobalt-60, cancer treatment with

Teletherapy is radiation treatment where the radiation source is not in direct contact with the tumour to be treated. The radiation used for the treatment can be of different types and energies and originate from different sources. Gamma-emitting radioactive sources such as cobalt-60 are often used, because they are convenient, need virtually no maintenance, and are almost ideal gamma emitters. Many of these sources are in use for cancer treatment. 

Cobalt exists in valence states from 0 to 5, with the most stable (4-2 and - -3) being most common. While there is only one stable isotope of cobalt, there are a number of unstable isotopes. Two of these, cobalt-60 and cobalt-57, are in use commercially. Cobalt-60 is used for cancer treatment and for food irradiation. Cobalt-57 has research applications. 

Cobalt-60 is an isotope used in diagnostic medicine and cancer treatment. It decays with y ray emission. Calculate the wavelength of the radiation in nanometers if the energy of the y ray is 2.4 X 10 J/pho-ton. 

An instrument for cancer treatment containing a cobalt-60 source was manufactured in 1978. In 1995 it was removed from service and, in error, was buried in a landfill with the source still in place. What percentage of its inihal radioactivity will remain in the year 2010 (See Table 10.2 for the half-life of cobalt-60.)... 

The metal is oxidized by hot air and also reacts with carbon, phosphorus, sulphur, and dilute mineral acids. Cobalt salts, usual oxidation states II and III, are used to give a brilliant blue colour in glass, tiles, and pottery. Anhydrous cobalt(II) chloride paper is used as a qualitative test for water and as a heat-sensitive ink. Small amounts of cobalt salts are essential in a balanced diet for mammals (seeESSENTiAL element). Artificially produced cobalt-60 is an important radioactive tracer and cancer-treatment agent. The element was discovered by Georg Brandt (1694-1768) in 1737. 

Unlike Errington, Johns had his own cancer clinic where he could give his machine a tryout. Errington made arrangements with Ivan Smith in London to ensure that there would be a home for his machine. The Ontario Cancer Treatment and Research Foundation had formed a committee earlier in the year to consider installing super-voltage equipment in at least one of the eight provincial radiotherapy facilities. The committee recommended purchase of such equipment but modified its plans to allow for installation of a cobalt-60 BTU in Smith s clinic in London as well. 

With or without a therapy machine, cobalt-60 was CPDs best-selling product by frr. Indeed, management became concerned that CPD was too dependent on it. If a better cancer treatment came along, it could wipe out sales, and the firm would have no other significant business to foil back on. 

Therapeutic Procedures Therapeutic procedures—those in which radiation is used to kill diseased tissue—can involve either external or internal sources of radiation. External radiation therapy for the treatment of cancer is often carried out with y rays from a cobalt-60 source. The highly radioactive source is shielded by a thick lead container and has a small opening directed toward the site of the tumor. By focusing the radiation beam on the tumor and rotating the patient s body, the tumor receives the full exposure while the exposure of surrounding parts of the body is minimized. Nevertheless, sufficient exposure occurs so that most patients suffer some effects of radiation sickness. 

Radioactive substances also have life-saving uses. A radioactive form of cobalt is extensively used in radiation therapy for cancer patients. The treatment was first developed by Harold Johns (1915—) in Canada, where he pioneered cobalt therapy units at the University of Saskatchewan. One of the artificially made elements, Americium (atomic number 95, i.e., with 95 protons in its atomic nucleus), is another life-saving radioactive element. As it decays, it emits alpha particles, which strip electrons from surrounding gas molecules ionized air conducts electricity much better than air containing smoke particles, and the reduction in conductivity produced by smoke is what triggers the alarm in smoke detectors. 

Almost all elements found in nature can now be made radioactive. Radioactive potassium and phosphorus are used as tracers to measure how effectively plants take up fertilizer from soil. Radioactive iodine is applied in nuclear medicine to diagnose and treat thyroid problems. Radiation treatment for cancer therapy uses radioactive cobalt, which is made by irradiating ordinary cobalt with neutrons. 

Cobalt-60, with a half-life of 5 years, is used in cancer radiation treatments. If a hospital purchases a supply of 30.0 g, how much would be left after 15 years ... 

Cobalt-60 and iodine-131 are used in treatments for some types of cancer. Cobalt-60 decays with a half-life of 5.27 years, emitting beta particles with a maximum energy of 0.32 MeV. Iodine-131 decays with a half-life of 8.04 days, emitting beta particles with a maximum energy of 0.60 MeV. 

The cobalt treatments used in medicine to arrest certain types of cancer rely on the ability of gamma rays to destroy cancerous tissues. Cobalt-60 decays with the emission of beta particles and gamma rays, with a half-life of 5.27 years. 

FIGURE 13.3 Treatment for cancer with gamma radiation from cobalt-60. By adjusting the rotation of the radiation source, the radiation is concentrated where the beams cross at the location... 

Radiation therapy can also be used to treat disease. Probably the best-known example of radiation therapy is in the treatment of cancer. The strategy is to use radiation to selectively kill cancer cells. The radioactive isotope most commonly used is cobalt-60, which is a beta emitter with a half-life of 5.3 years. Radiation may be used to shrink a tumor prior to surgery, to kill any remaining cancer cells after surgery, or in combination with chemotherapy. A drawback of radiation therapy is that damage may also be done to the healthy tissue that surroimds a tumor. 

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