Cobalt is a bioessential element due to its location at the centre of vitamin B12. Vitamin B12 plays a number of vital roles in the physiology of the human body. Cobalt is also important in treatments of radiotherapy in the form of the isotope 60Co.
Other medical uses of cobalt include the detection of tumours and metastases, sterilisation of surgical equipment and the imaging of damage to the brain.
Cobalt is also used in the prosthetic alloys sector, being utilised in hip, knee and dental replacements.
Detection of Tumours and Metastases
55Co and 57Co have been used in medicine for the past 30 years in detecting brain and lung Metastases. Both 55Co and 57Co labelled bleomycin are preferentially taken up by tumours. By measuring the radiation emitted from these cobalt isotopes the location of the tumour can be found.
Although relatively effective (the detection of lung cancers has a success rate of 92-96%) the long half-life of 57Co prevents routine clinical use.
Imaging damage to the brain
55Co has a half-life of 17.53 h, decaying 23% by electron capture and 77% by positron emission (B+). Due to 55Co’s long half-life and decay characteristics it can be used as a B+ emitter to study slow biological processes.
The most important application of 55Co came about in the late 1990s in the field of neuro-imaging neuronal damage from a stroke or traumatic injury.
A key hallmark of these injuries is calcium-mediated neuronal damage and inflammation; biomarkers that are unable to be visualised using Computed Tomography and Magnetic Resonance Imaging techniques. Positron Emission Tomography (PET) using 55Co as a calcium tracer can image affected tissues. PET 55Co can also distinguish between old and new localised necrosis caused by a lack of blood supply.
Measuring vitamin B12 absorption
Radio-labelled cobalamins are used in measuring the absorption of vitamin B12 in patients who have pernicious anaemia or another cobalamin deficient disease. Either 57Co or 58Co is used as the radioactive label. 57Co labelled cyanocobalamin for whole body measurement of vitamin B12 uptake in humans has an advantage over 58Co due to a lower cumulative radiation in the liver. It has a disadvantage however in terms of attenuation. The Schilling method is routinely used in evaluating the in vivo absorption of vitamin B12.
Equipment sterilisation and radiotherapy treatment
60Co is a gamma and beta ray emitter. The gamma rays emitted have energies of 1.173 and 1.333 MeV and the isotope has a half-life of 5.3 years. In medicine 60Co is used as a radiotracer isotope, sterilisation for surgical equipment and most commonly, as a radiation source for radiotherapy.
60Co had been used in treating malignancies for many decades. During this time many different devices have been created to meet the requirements of clinical treatments. Such devices range between irradiation of very small areas to whole body radiation. 60Co has been commonly used in the treatment of brain tumours and has also been used in cancer of the breast, anus, larynx, bladder, tongue, prostate and kidney. 60Co has also been used in the treatment of Hodgkin’s disease, retinoblastoma and Graves opthalmopathy.