Cobalt therapy

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. 

The number of protons identifies an element. Some elements may have atoms that contain different numbers of neutrons. The different atoms of the same element are then called isotopes. Because of the different number of neutrons in one isotope of an element, it can be quite radioactive that is, the nucleus is progressively breaking apart and giving off radiation. The type and amount of radiation determines the degree of risk. The radiation from isotopes is used in controlled situations - for example, cobalt therapy, for treating cancer. Cobalt 60 therapy uses a cobalt isotope with 33 neutrons. Normal cobalt in vitamin B12 or soil fertihzer almost alw s contains only 32 neutrons. Your home smoke detector may contain a 37kBq source of americium 241. Some natural elements, e.g. chlorine, are a mixture of two long-lived isotopes of the element. 

Cobalt in nature consists of one single isotope, Co. By irradiation with neutrons in a nuclear reactor the radioactive isotope Co is obtained. It is a strong y-radiator with a half-life of 5.27 years. This radiation is of the same type as X-rays, and for this reason "°Co is used against cancer in cobalt therapy , a special form of radiotherapy. The radiation is also used for sterilizing medical equipment. 

In radiotherapy the radiation energy destroys tumor cells that are later replaced by fresh tissue. Two different methods of treatment are available cobalt therapy and treatment with X-rays, generated in linear accelerators. The latter equipment is technically very sophisticated and complicated. It can be used only in large hospitals with advanced expertise, both medical and technical. In contrast, cobalt therapy is simple and suitable for small hospitals and medical services in developing countries. For... 

Apparently the Eldoiado Ns first patient s disease was r achanoed, and she died within a few months of treatment. The Saskatoon patient was cured, aixl she was still alive thirty years later (Houston and Fadotuk, Saskatchewans Roles ). Johns would be the first to publish a formal paper on cobalt therapy. The December 15, 1951, issue of Nature included an aidde written by Johns and the NRC s Adair Moirison which described both the Eldorado and the Saskatchewan cobalt-60 units. 

This market acceptance would later gain offidal reinforcement when a special issue of the Journal of the Canadian Association ifRadiido sts ptesented the medical world with the first five-year report on the clinical applications of cobalt therapy units in June 1957. C. Smart Houston and Sylvia O. Fedoruk, Saskatchewan s role... 

Octasodium salt of octa-4,5-dicarboxyphthalocyanin cobalt(II) combined with ascorbic acid (teraphthal) as a new drug for binary catalytic therapy of malignant tumors 98MI57. 

Cobalt-60 cancer therapy. Gamma rays from the rotating radiation source are concentrated at the location of the diseased tissue. 

In a different way, metallic-core nanoparticles [346-349] (prepared cf. Section 3.10) equipped with biocompatible coats such as L-cysteine or dextrane may be exploited for highly efficient and cell-specific cancer cell targeting, i.e., for improving diagnosis and therapy of human cancer. In a recent proof-of-principle experiment an unexpectedly low toxicity of the L-cysteine-covered cobalt nanoparticles was demonstrated [433] For diagnostic purposes, it is expected to use the advantageous magnetic properties of the metallic-core nanoparticles to obtain a contrast medium for MRI with considerably increased sensitivity, capable to detect micro-metastases in the environment of healthy tissues [434 37]. 

Common radioactive material in use today includes the alpha emitters Americium-241 and Plutonim-238 the beta emitters Phosporus-32 and Strontium-90 and the gamma emitters Cesium-137, Cobalt-60, and Iridium-192 [44], These materials are commonly used in smoke detectors, oil exploration, industrial gauges, food and mail irradiation, cancer therapy, industrial radiography, and in research laboratories. 

Particles emitted from radioactive isotopes are generally too low in energy to provide the penetration required for conventional treatments of tumors with external radiation beams. Most external beam radiation therapies are performed with high-energy x-rays or electrons produced with compact linear accelerators with accelerating potentials between about 4 and 20 MeV. One notable exception is certain devices designed for stereotactical radiosurgery or radiation therapy of superficial tumors that use cobalt-60 y-rays. The... 

Improvements in the physical selectivity, from orthovoltage x-ray to cobalt-60 and high-energy linear accelerators, combined with more powerful diagnostic tools and radiation delivery methods have continuously improved the results of photon therapy (3-D or inverse planning, conformal- and intensity-modulated radiation therapy, and stereotactic methods). The safety and the reliability of photon therapy are well established. 

Historically, the progress in radiation therapy has been linked mainly to technological developments. The physical selectivity of the irradiations was significantly increased when 200-kV x-rays were progressively replaced by cobalt-60, betatrons, and linear accelerators. As a consequence, the clinical results were dramatically improved. 

Figure 28 Schematic presentation of the relative situation of the different types of radiations used in therapy. Two criteria are considered the physical selectivity and the LET (or radiobiological properties). For the low-LET radiations, the physical selectivity was improved from the historical 200-kV x-rays to cobalt-60 gamma rays and the modern linacs. Even with the linacs today, significant improvement is continuously achieved (IMRT, etc.). Among the low-LET radiation, the proton beams have the best physical characteristics, but one of the issues is the proportion of patients who will benefit from proton irradiation. A similar scale can be drawn for high-LET radiation the heavy-ion beams have a physical selectivity similar to protons. Selection between low- and high-LET radiation is a biological/medical problem it depends on the tumor characteristics, and reliable criteria still need to be established (see text). (From Ref 54.)...

Radioisotopes are also used in radiation therapy to treat cancer. The goal in radiation therapy is to kill malignant cells, while protecting healthy tissue from radiation effects. Radioisotopes such as yttrium-90, a beta emitter, may be placed directly in the tumor. Alternatively, the diseased tissue may be subjected to beams of gamma radiation. Cobalt-60 used in radiation therapy is prepared by a series of transmutations ... 

A cobalt-60 source purchased for the radiation therapy of cancer patients has an activity of 1.20 Ci. What will the activity of the source be after 5.0 y ... 

Cobalt must be supplied in the diet in its physiologically active form, vitamin B12. GI absorption of cobalt is about 25%, with wide individual variation excretion occurs mainly via the urine. The major part is excreted within days and the rest has a biological half-life of about two years. Originally, the therapy for pernicious anemia was to have patients eat large amounts of liver. The most reliable treatment now is monthly injections of cobalamin. 

Still other nuclear transmutations are carried out using neutrons, protons, or other particles for bombardment. The cobalt-60 used in radiation therapy for cancer patients can be prepared by neutron bombardment of iron-58. Iron-58 first absorbs a neutron to yield iron-59, the iron-59 undergoes j8 decay to yield cobalt-59, and the cobalt-59 then absorbs a second neutron to yield cobalt-60 ... 

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. 

Based on the avidity of cobalt for cyanide ions, intravenous injection of the cobalt EDT A complex has been recommended as being the best antidote in cyanide poisoning73). Earlier therapy was based on sodium nitrite and sodium thiosulphate, with partial conversion of haemoglobin to methaemoglobin. 

The medical applications of nuclear technology range from in vitro and in vivo injections for diagnostic tests to cobalt radiation for cancer therapy. A new medical specialty was created, a family of compact cyclotrons was developed to provide short-lived nuclides, and a sizable industry evolved to produce technetium. Until the nuclear industry was created, technetium had been missing from the chart of chemical elements because the half-life of the most stable member was too short, 21,000 years. Technetium and several other nuclides of importance here are discussed elsewhere in the chapter in connection with their production (see Table 21.19).60,61... 

Cobalt 60 5 years Beta and gamma Cancer therapy treatment... 

In addition to its many uses in medical and physiological research, radioisotopes are used in therapy, and in agricultural and industrial research. Radioactive cobalt, for example, became available for the treatment of deep-seated cancer. This isotope of atomic weight 60 loses half its radioactivity in about five days and is more than 300 times as powerful as radium. It is taking the place of radium and X-ray therapy in many hospitals. 

Patients who are critical and do not satisfactorily respond to supportive therapy should be administered specific cyanide antidotes as outlined in Table 19.5. Cyanide antidotes have been classified into three main groups based on their mechanism of action (1) methemoglobin inducers, (2) sulfur donors, and (3) cobalt compounds. The definitive treatment of cyanide poisoning differs in various countries due to different medical practices and guidelines. The safety... 

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. 

Henretig F, Joffe M, Baffa G, etal. (1998) Elemental cobalt toxicity and effects of chelation therapy. Veterinary and Human Toxicology 30 372-378. 

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