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| Version | User | Scope of changes |
|---|---|---|
| Apr 13 2009, 1:12 AM EDT (current) | JeremiahDonner | 1 word added |
| Apr 12 2009, 4:42 PM EDT | cchambers | 12 words added, 3 words deleted |
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Key: Additions Deletions
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Links:
1. Centers for Disease Control and Prevention (CDC) - http://www.bt.cdc.gov/radiation/isotopes/cobalt.asp
2. Cobalt-60; Wikipedia - http://en.wikipedia.org/wiki/Cobalt-60
3. Cobalt-60 Fact Sheet - http://www.doh.wa.gov/EHP/RP/factsheets/factsheets-pdf/fs26co60.pdf
References:
1. Khan, Faiz M. The Physics of Radiation Therapy. 3rd Edition. Philadelphia: Lippincott Williams & Wilkins; 2003: p.367, 358, 361, 369-371.
2. Radioisotope Brief: Cobalt-60 (Co-60). Centers for Disease Control and Prevention (CDC). Available at: http://www.bt.cdc.gov/radiation/isotopes/cobalt.asp. 11 March 2009.
3. Bentel, Gunilla C. Radiation Therapy Planning. 2nd Edition. New York: The McGraw-Hill Companies; 1996: p. 61, 22, 536.
4. Wikipedia. Gamma knife. Available at: http://en.wikipedia.org/wiki/Gamma_knife. Accessed: 12 March 2009.
5. Cobalt. Answers.com. Available at: http://www.answers.com/topic/cobalt. Accessed: 12 March 2009.
6. "Session: 7.06 – Sources for Remote Afterloading Devices. Stanford Web-Based Dosimetry Training Tool. http://www.dosimetrytrainingtool.com. Accessed: 8 March 2009.
7. Cobalt. Radiation Protection. Available at http://www.epa.gov/radiation/radionuclides/cobalt.html#discovered. Accessed on April 4, 2009.
8. Cobalt -60. Fact Sheet. Available at http://www.doh.wa.gov/EHP/RP/factsheets/factsheets-pdf/fs26co60.pdf. Accessed on April 4, 2009.
9. Cobalt -60. Human Health Fact Sheet. Available at http://www.ead.anl.gov/pub/doc/Cobalt.pdf. Accessed on April 4, 2009.
10. Martinez, Orton, and Mould. Brachytherapy HDR and LDR. Colombia: Nucletron Corporation; 1990. p. 138-142.
11. Wikipedia. Co-60. Available at: http://en.wikipedia.org/wiki/File:Cobalt-60_Decay_Scheme.svg Accessed: 6 April 2009.
Group Colors:
Theresa. Brandie, Christy, Jeremiah
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| Relevant Historical Data: | Cobalt was discovered in 1735 by Georg Brandt, a Swedish chemist.(5) Non-Radioactive Cobalt: occurs naturally in various minerals and has long been used as a blue coloring agent for ceramic and glass. (2) People previously thought the blue color in the colored glass was bismuth, which occurs in nature with cobalt. (7) Radioactive Co-60: produced commercially through linear acceleration for use in medicine and industry. (2) Radioactive CO-60 was discovered by Glenn T. Seaborg and John Livingood at the University of California - Berkeley in the late 1930's. (7) Co-60: can also be a byproduct of nuclear reactor operations, when metal structures, such as steel rods, are exposed to neutron radiation.(2) Produced by bombarding stable Co-59 with neutrons in a nuclear reactor.(6) The first source of Co-60 for medical use was produced in 1951 in Canada and was used by Johns and Coworkders in the first Co-60 teletherapy machine for external beam therapy in 1952. (3) |
| Chemical/Radioactive Composition: | A radioactive isotope, Cobalt-60 (with gamma ray emission 25 times that of radium), is prepared by neutron bombardment.(5) Metallic solid that can become magnetically charged. (2) Solid under normal conditions and is generally similar to iron and nickel in its properties. (7) |
| Energy Characteristics: | Beta decay to Ni-60 Beta energy is 0.097 MeV (9) Gamma energy is 2.5 MeV. This comes from emitting a beta particle with two energetic gamma rays (one has and energy of 1.2 MeV and the other an energy of 1.3 MeV). (9) Decay Properties: Decay by Beta particles and gamma radiation; gamma radiation in the energy of 1.17 & 1.33 Mev.(1,2,6) The beta decay to Ni-60 is non radioactive. (7) Activity 1,100 Ci/g (9) |
| Exposure Rate Constant: | 13.07 c (Rcm2/mCi-h) (1,6) |
| Half-life Properties: | Half Life: 5.26 yr (1,6) Biological: 0.5 day (transfer compartment), 6 days (0.6 in all tissues), 60 days (0.2 in all tissues), 800 days (0.2 in all tissues) (8) This half life is short enough to make isolation a useful treatment strategy for contaminated areas. Waiting 10 to 20 years will allow for sufficient decay to make the site acceptable for use again. (7) |
| Forms available for use: | "Solid Material" -may appear as small metal disks or in a tube, enclosed at both ends, that holds the small disks.(2) "Powder" if the solid sources have been ground or damaged.(2) "Opthalmic Plaques"; used in recent years for treatment of ocular melanomas - these are stored and reused for years.(3) Remote Afterloading; usually in the shape of "capsules" or "pellets" with an outer diametr of 2.5mm.(6) Cobalt brachytherapy sources are usually fabricated in the form of a wire that is encapsulated in a sheath of platinum iridium or stainless steel.(1) Cobalt-60 is used in many common industrial applications, such as in leveling devices and thickness gauges, and in radiotherapy in hospitals. Large sources of cobalt-60 are increasingly used for sterilization of spices and certain foods. The powerful gamma rays kill bacteria and other pathogens, without damaging the product. After the radiation ceases, the product is not left radioactive. This process is sometimes called "cold pasteurization." (7) |
| HVL in lead: | 11 mm lead (1,6) |
| Measurement/Calibrations/QA: | The National Institute of Standards and Technology (NIST) established exposure rate calibration standards for some of the brachytherapy sources including Co-60. Its method consists of calibrating a working standard of each type using open air geometry and a series of spherical graphite cavity chambers. A given source is then calibrated by intercomparison with the working standard using a 2.5 liter spherical aluminum ionization chamber, positioned at a distance of about 1m. (1) The NRC requires that, for Afterloading HDR units, the reproducibility of the source positioning be checked each day of use with a precision of 1mm. To ensure this precision, you may use a television system along with a transparent jig to visually confirm the positioning. You may also use autoradiography to confirm position. (10) |
| Used in formula/calculation: | Time = prescribed dose dose rate (ref) x area factor (3) Dose rate at Dmax = time x dose rate (ref) x area factor (3) |
| Uses in Radiation Oncology: | Main uses for 60Co: (11)
Co-60 is used medically for radiation therapy as implants and as an external source of radiation exposure. (2) Co-60 is used at a medical tracer. A medical tracer is a material that is introduced into the body to make possible the observation of chemical, physical or biological processes in the body, (8) Total Body Irradiation: Gamma Knife Radiosurgery: gamma knife device contains 201 cobalt 60 sources of approximately 30 curies each, placed in a circular array in a heavily shielded assembly. The device aims gamma radiation through a target point in the patient's brain. The patient wears a specialized helmet that is surgically fixed to their skull so that the brain tumor remains stationary at target point of the gamma rays. An ablative dose of radiation is thereby sent through the tumor in one treatment session, while surrounding brain tissues are relatively spared.(4) Gamma knife radiosurgery has proven effective for patients with benign or malignant brain tumors, vascular malformations such as an arteriouvenous malformation (AVM), and pain.(4) Co-60 has been used in opthalmic plaques for the treatment of ocular melanomas, which are stored and reused over several years. (3) |
| Treatment Planning: | The exposure rate distribution can be calculated using the Sievert integral. This method consists of dividing the line source into small elementary sources and applying inverse square law and filtration corrections for each. Several other additional corrections are applied to compute the exposure rate accurately using the Sievert integral. A correction for self-absorption and wall thickness as well. An effective attenuation coefficient is needed and varies with filter thickness. Because the Sievert integral uses the energy absorption coefficient, the underlying assumption is that the emitted energy fluence is exponentially attenuated by the filter thickness traversed by the photons. However, the Monte Carlo simulations have shown that beyond the end of the active source region, the Sievert approach introduces significant errors and practically breaks down in the extreme oblique directions. (1) |
| One other interesting fact: | Co-60 is a hard, gray-blue metal. It resembles iron or nickel.(2) In the periodic table it occupies a position between iron and nickel in the third period.(5)* see photo Atomic number 27; atomic weight 58.9332; melting point 1,495°C; boiling point 2,900°C; specific gravity 8.9; valence 2, 3.(5) It is also used industrially in leveling gauges and to x-ray welding seams and other structural elements to detect flaws. Co-60 also is used for food irradiation, a sterilization process. (2) After entering a living mammal (such as a human), most of the 60Co gets excreted in feces. A small amount is absorbed by liver, kidneys, and bones, where the prolonged exposure to gamma radiation can cause cancer. (11) Gastrointestinal absorption from food or water is the principal source of internally deposited cobalt in the general population. (9) |
Links:
1. Centers for Disease Control and Prevention (CDC) - http://www.bt.cdc.gov/radiation/isotopes/cobalt.asp
2. Cobalt-60; Wikipedia - http://en.wikipedia.org/wiki/Cobalt-60
3. Cobalt-60 Fact Sheet - http://www.doh.wa.gov/EHP/RP/factsheets/factsheets-pdf/fs26co60.pdf
References:
1. Khan, Faiz M. The Physics of Radiation Therapy. 3rd Edition. Philadelphia: Lippincott Williams & Wilkins; 2003: p.367, 358, 361, 369-371.
2. Radioisotope Brief: Cobalt-60 (Co-60). Centers for Disease Control and Prevention (CDC). Available at: http://www.bt.cdc.gov/radiation/isotopes/cobalt.asp. 11 March 2009.
3. Bentel, Gunilla C. Radiation Therapy Planning. 2nd Edition. New York: The McGraw-Hill Companies; 1996: p. 61, 22, 536.
4. Wikipedia. Gamma knife. Available at: http://en.wikipedia.org/wiki/Gamma_knife. Accessed: 12 March 2009.
5. Cobalt. Answers.com. Available at: http://www.answers.com/topic/cobalt. Accessed: 12 March 2009.
6. "Session: 7.06 – Sources for Remote Afterloading Devices. Stanford Web-Based Dosimetry Training Tool. http://www.dosimetrytrainingtool.com. Accessed: 8 March 2009.
7. Cobalt. Radiation Protection. Available at http://www.epa.gov/radiation/radionuclides/cobalt.html#discovered. Accessed on April 4, 2009.
8. Cobalt -60. Fact Sheet. Available at http://www.doh.wa.gov/EHP/RP/factsheets/factsheets-pdf/fs26co60.pdf. Accessed on April 4, 2009.
9. Cobalt -60. Human Health Fact Sheet. Available at http://www.ead.anl.gov/pub/doc/Cobalt.pdf. Accessed on April 4, 2009.
10. Martinez, Orton, and Mould. Brachytherapy HDR and LDR. Colombia: Nucletron Corporation; 1990. p. 138-142.
11. Wikipedia. Co-60. Available at: http://en.wikipedia.org/wiki/File:Cobalt-60_Decay_Scheme.svg Accessed: 6 April 2009.
Group Colors:
Theresa. Brandie, Christy, Jeremiah
