Cobalt-60






Co-60

Co-60 afterloader Co-60 eye plaques



Relevant historical data: Cobalt was discovered in 1735 by Swedish chemist Georg Brandt. He was attempting to prove that the blue color of glass was due to an unknown element rather than bismuth. Dr. William Myers of Ohio State University suggested replacing radium with cobalt-60 in 1946, calling it the "poor man's radium." Along with Dr. Joseph L. Morton, he conducted studies on the use of cobalt-60 needles in cancer treatment.
Chemical/Radioactive Composition: Chemical symbol: Co
Atomic number: 27
Mass number: 60
Energy Characteristics: Decays via beta decay to Ni-60. Emits photons of 1.17 and 1.33 MeV.
Exposure Rate Constant: 13.07 Rcm^2 / mg h
Half-life Properties: Half-life of 5.26 years
Forms available for use: eye plaques, used in afterloading devices as capsules or pellets, needles
HVL in lead: 11.0 mm
Measurement/Calibrations/QA: A working standard of Co-60 is calibrated in air at distances of 1 m or less using six spherical graphite cavity ionization chambers with volumes ranging from 1-50 cm^3. This is corrected to a distance of 1 m and also corrected for air attenuation, build up and room scatter. The source to be calibrated is compared to the working standard by calibrating in a concrete calibration range at distances between 0.5 and 1 m using a 2.8 L spherical aluminum ionization chamber. (Nag 93)
Used in formula/calculation:
Uses in Radiation Oncology: Cobalt-60 was used in eye plaques for the treatment of choroidal melanoma, but due to the high energy, surrounding tissue could not be adequately shielded. It can also be used for the treatment of gynecological cancers by either LDR or HDR brachytherapy.
Treatment Planning:
One other interesting fact:


Links:
www.ead.anl.gov/pub/doc/Cobalt.pdf
www.doh.wa.gov/ehp/rp/factsheets/factsheets-pdf/fs26co60.pdf
radmed.osu.edu/myers-about-wgm.html



References:
Khan, Faiz M. The Physics of Radiation Therapy. 3rd ed. Philadelphia: Lippincott Williams & Wilkins, 2003.
Nag, Subir. Principles and Practice of Brachytherapy. Armonk, NY: Futura Pulbishing Company, Inc., 1997.




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