Plus-Hex CLINICAL
Methods of minimising exposure
Limit time spent near the radiation source
In the case of cats hospitalised for RAIT , no member of the veterinary team should spend more than 15 minutes in the treatment room per day .
At the dedicated Melbourne RAIT clinic , one staff member attends to the cats for 15 minutes in the morning and another person attends to them for 15 minutes in the afternoon / evening .
Once cats are discharged home , although the risk at this time to humans and other animals is minimal , ongoing caution with regard to handling should be maintained in the 2 weeks following discharge .
Maximise distance from the radiation source
Radiation risk reduces with distance in accordance with the inverse square law ( 1 / D ²), whereby radiation intensity is proportional to the inverse of the square of the distance between the source and the receiver , if there are no physical obstructions blocking the pathway .
In other words , standing 2 metres from the source will expose you to one-quarter of the radiation you would receive if standing 1 metre from the source .
An example of employing this principle is to place each cat in a carrier away from staff while they are cleaning its cage . However , ‘ the patient does not represent a pointsource of activity , so that the inverse-square law often does not apply until at least 3 metres from the patient ’ [ 10 ] .
Use appropriate barriers
This includes considerations such as clinic construction ( design and materials ), the cats ' housing in the treatment room , the storage and disposal of waste , and personal protective equipment ( PPE ).
In some clinics , lead-lined cages are required . Because the dedicated RAIT clinic in Melbourne is not staffed throughout the day , lead-lined cages are not needed under its licensing requirements .
Urine spray from treated cats is classified as a radiation spill and , as such , it is a potential source of exposure to clinic staff ; therefore , cages are fronted with clear Perspex to reduce this risk .
Radioactive waste is stored in lead-lined bins . The building ' s external walls are concrete , reducing the exposure of the external environment . PPE includes safety goggles , gowns and gloves when handling cats and I-131 capsules .
Management of radioactive waste
The main principles employed when working with radioactive waste are as follows [ 6 , 7 ] .
Delay and decay
Radioactive elements are in a continuous state of decay . Melbourne ' s dedicated RAIT clinic dates and stores double-bagged waste in lead-lined bins in a free-standing garage on the premises for 7 weeks . At this point , the waste is checked with a radiation monitor to ensure that enough decay has occurred for the waste to be disposed of with normal ( uncontaminated ) waste .
Dilute and disperse
By diluting radioactive liquid waste with running water , radiation levels become low enough to be safely released into the environment . Food / water bowls and litter trays are washed in cold to warm water . Hot water is avoided because it causes radiation to vaporise and potentially be inhaled . Running water prevents pooling of radiation , as would occur in a sink of water , although care must be taken to minimise splashing . Contaminated clothing , bedding and towels can safely be washed in a washing machine , as the addition of water dilutes the radiation to a safe level .
Concentrate and contain
This principle is rarely relevant in a veterinary hospital setting , but containment of waste as described above is one example of its use .
Conclusions
Veterinary personnel are at increased risk of radiation exposure compared with the general public . This is particularly so for veterinary nurses , who are often responsible for the daily care of cats hospitalised for RAIT . Prolonged and repeated exposure to radiation sources in a clinical setting occurs in addition to the background radiation to which we are exposed throughout our lives .
Radiation can cause serious health problems , or even death , if exposure to a single dose ( or multiple absorbed doses over time ) exceeds a safe threshold . Despite this , it is possible to work safely with radiation if the basic principles described in this article are followed , resulting in dosimeter readings that are well within the prescribed range for employees in a veterinary setting .
Acknowledgements
Many thanks to Dr Amanda Gross at The Hyperthyroid Cat Clinic for her time and assistance with these articles .
Volume 38 ( 5 ) • October 2023
39