Most gamma radiation is eliminated from the body as part of the normal decay process and is excreted from treated cats in their urine , saliva and faeces over a period of 3 – 5 days ; these excretions are handled as hazardous waste . The retention and excretion of radioisotopes is influenced by their uptake by the thyroid gland , the size of the thyroid gland and the biological half-life of the radioiodine [ 5 ] .
Measuring radiation
Radiation exposure is measured using the absorbed dose , the equivalent dose and the effective dose . The absorbed dose is the energy created by ionising radiation . Radiation activity is measured in becquerels ( Bq ) and is the amount of radioactive substance present ; 1 Bq represents the decay of one nucleus per second and is therefore a very low level of radioactivity . The radioactivity of I-131 is typically measured in megabecquerels ( MBq ); 1 MBq = 1,000,000 Bq ( Figure 1 ).
When working with radiation and animals undergoing diagnostic procedures and treatments such as X-rays and RAIT , veterinary professionals should minimise their effective dose exposure .
1,000,000 Bq = 1 MBq 1 Sv = 1,000 mSv = 1,000,000 μSv
Absorbed dose + radiation type ( e . g . α , β , γ ) + organ sensitivity = effective dose
Radiation safety
We are all constantly exposed to radiation , both from the external environment and from substances we inhale or ingest . The numerous changes to human lifestyle over time , such as living inside with reduced airflow , modern gadgets in our homes and workplaces , and travelling by air at high altitudes , have increased our radiation exposure . In addition to this background radiation , we are exposed to radiation from medical procedures such as X-rays .
Excessive exposure to radiation can result in health issues , which are divided into deterministic effects ( tissue / organ damage ) and stochastic effects ( cancer and heritable diseases ) [ 9 ] .
The International Commission on Radiological Protection ( ICRP ) has determined that the maximum acceptable effective dose for a single person ( separate from background radiation ) is 20 mSv per year , averaged over a 5-year period , with no single year greater than 50 mSv [ 7 ] . In the UK , ‘ the legal dose limit is the maximum permissible dose of ionising radiation … currently 1 mSv / year for members of the public ’ [ 5 ] . This 1 mSv limit for members of the public also applies in Australia , with a maximum annual dose of 20 mSv for people working with radiation in an occupational setting .
Figure 1 . The outer packaging of a single I-131 capsule The radioactivity of this capsule when it was calibrated was 152 MBq .
The equivalent dose is used to determine the dangers of different types of radiation ( e . g . alpha , beta or gamma ) interacting with different body tissues in varying biological environments .
The effective dose represents the overall effect on health . It is determined by factoring in the absorbed dose and the cumulative equivalent doses throughout the body . The effective dose is measured in sieverts ( Sv ); it measures the likelihood of risk to health from exposure to ionising radiation .
Veterinary personnel have always been included in previous ICRP radiation safety recommendations , but ‘ veterinary practice is now addressed explicitly , as the modern complexities associated with this practice warrant dedicated consideration … radiological protection should be applied in practice principally for the protection of humans , but with explicit attention to the protection of exposed animals ’ [ 9 ] .
When working around radioactive substances , there are three primary methods of minimising exposure . The specifics of individual radiation safety protocols ( e . g . timing ) might vary depending on the location of the veterinary clinic and the requirements of relevant governing bodies , but the principles are the same [ 6 , 9 ] .
38 Veterinary Nursing Journal