Abstract
As we work towards a holistic approach to radiation protection, we begin to consider and integrate protection beyond humans to include, among other things, non-human biota. Non-human biota not only includes environmental flora and fauna, but also livestock, companion animals, working animals, etc. Although under consideration, there is currently little guidance in terms of protection strategies for types of non-human biota beyond wildlife. For example, in recent years, veterinary procedures that make use of ionising radiation have increased in number and have diversified considerably, which has made radiation protection in veterinary applications of ionising radiation more challenging, both for humans and the animal patients. In fact, the common belief that doses to professionals and members of the public from these applications will be very low to negligible, and doses to the animals will not be acutely harmful nor even affect their lifetime probability of developing cancer, needs to be revisited in the light of higher dose diagnostic and interventional techniques, and certainly in the case of therapeutic applications. This paper provides a brief overview of the initiatives of the International Commission on Radiological Protection concerning radiation protection aspects of veterinary practice, and poses a variety of perspectives for consideration and further discussion.
1. Introduction
After Roentgen’s discovery of x rays, veterinarians were among the first to perceive the potential benefits of radiology for animal health care (Schnelle, 1968; Kealy, 2002). Starting with the increase in small animal practice in the 1930s, plain film radiography was the only veterinary application of ionising radiation for many decades. Moreover, the number of procedures was limited and the doses to human bystanders were low to trivial, provided that some simple rules were followed. Consequently, veterinary use of ionising radiation was not a high priority for radiation protection, although there were some relevant publications (e.g. NCRP, 1970; NHMRC, 1982, 1984). Even 15 years ago, the prevalence of veterinary radiology was acknowledged to be low (NCRP, 2004). However, since then, veterinary procedures making use of ionising radiation have increased substantially, with available modalities now as diverse as in human health care. Veterinary diagnostic radiology has become more popular worldwide for various reasons, including digitalisation and the wider availability of higher dose applications such as computed tomography (CT) and cone beam computed tomography (CBCT) scanning. Interventional radiology procedures have entered the practice field, and so have nuclear medicine applications, both diagnostic and therapeutic. Lastly, external beam radiotherapy has become available in several centres around the world.
Radiation-related risks have also increased and diversified because of these important practice changes. For example, in addition to the external exposure associated with nuclear medicine procedures, relevant veterinary clinics also need to consider the risk of contamination by radioactive substances to staff, owners, handlers, and the environment. Lessons learned from human medicine inform us that radiation exposure of veterinary staff involved in interventional procedures needs to be monitored closely as doses could be far from negligible (e.g. Klein et al., 2009; Durán et al., 2013; Ko et al., 2018), as could the doses to the animal patients themselves (e.g. Wagner, 2007; Balter and Miller, 2014; Arkans et al., 2017). Moreover, unique issues associated with animal patients may result in higher occupational doses associated with certain procedures (Martinez et al., 2012).
Societal changes also play a role in the increasing number and diversity of procedures performed on animals. Many companion animals are considered by their owners to be ‘part of the family’, and therefore entitled to the best care available. The same may hold true for working animals, exotic animals, and sports animals, simply because of their monetary value. More and more animals have health insurance, which may not only imply radiological examinations as part of insurability checks, but also removes financial barriers that would otherwise restrict the use of these more expensive imaging or treatment options. The imaging of animals also has a prominent place in a wide variety of suitability checks, such as suitability for breeding or for a career in sports. These procedures, which are not primarily performed for the benefit of the animal exposed, may become a radiation protection challenge in terms of the high number of exposures, and the fact that a limited number of staff and laypersons may be involved in many procedures.
The impact of these changes in veterinary practice on radiation protection needs and challenges has not gone unnoticed, and some authorities and organisations have produced guidance accordingly. For example, the National Council on Radiation Protection and Measurements revised the relevant 1970 report in 2004, and succinctly summarised the goal of radiation protection in veterinary medicine (NCRP, 2004):
The International Commission on Radiological Protection (ICRP), now recognising that the complexities of veterinary practice warrant dedicated clarification within the system of radiological protection, has decided that there is a need to strengthen the application of its protection principles in this area. The objective of the associated work is to provide an initial set of relevant recommendations; its primary focus will be the protection of humans involved in or affected by the procedures, both professionals and members of the public. Protection of the animal patient and the environment from nuclear medicine applications are also considered.
2. Veterinary medicine within the system of radiological protection
The primary aim of the system of radiological protection is ‘to contribute to an appropriate level of protection for people and the environment against the detrimental effects of radiation exposure without unduly limiting the desirable human actions that may be associated with such exposure’ (ICRP, 2007a). For people, radiation exposures are managed with the goal of reducing stochastic effects to the extent reasonable, and preventing tissue reactions that are unnecessary (e.g. in radiotherapy, a tissue reaction may be unavoidable in order to obtain effective treatment). Different exposure situations and categories are defined within the system of radiological protection to take into consideration the specific circumstance under which an exposure occurs. The exposure situations include planned (situations in which protection can be planned ahead of time), emergency (unexpected situations that may necessitate urgent intervention), and existing (situations that already exist and may need a decision on management or control).
Exposure categories include public (exposure received apart from occupational, medical, and natural background), occupational (exposure received at work due to the nature of the work), and medical (exposure received as a patient or from a patient as a volunteer comforter/carer). As the recommendations are currently written (ICRP, 2007a,b), the medical exposure category appears to apply solely to human medicine. As veterinary medicine appears to fall somewhere in between, or at the intersection of, the above exposure categories, local governments and regulatory agencies manage veterinary exposures in different ways. Although not specified as such, environmental exposure (exposure to the living environment) is a fourth category. Thus far, ICRP has focused on the natural environment, with the goal of maintaining biological diversity, conserving species, and maintaining the health status of associated habitats, communities, and ecosystems. Task Groups 107 (Advice on Radiological Protection of the Patient in Veterinary Medicine) and 110 (Radiological Protection in Veterinary Practice) are the first initiatives within ICRP to consider non-human biota in the managed environment, namely, companion animals and livestock.
The core of the system of radiological protection consists of three fundamental principles: justification, optimisation, and application of dose limits. The principle of justification specifies that any activity or intervention that changes the exposure scenario should be overall beneficial to individuals and/or society. The principle of optimisation specifies that doses should be as low as reasonably achievable, considering economic and societal factors. The principle of limitation applies to planned exposure situations (other than medical and environmental), and indicates that doses should not exceed appropriately established limits. Limitation does not apply to medical exposures in order not to interfere with necessary, medically indicated diagnostic or therapeutic procedures. In these cases, justification and optimisation are strongly emphasised. Additionally, diagnostic procedures use diagnostic reference levels, which are not seen as limits but instead indicate if a dose received from an imaging procedure is unusually high or low, to guide the optimisation process and thus help manage patient exposures (ICRP, 2007b). Neither do limits apply to environmental radiation protection, but derived consideration reference levels are used to inform the appropriate level of management or control of an exposure. Derived consideration reference levels are bands of absorbed dose rates, usually an order of magnitude, likely to affect key biological parameters of a reference species (ICRP, 2014). Finally, emergency and existing exposure situations utilise reference levels rather than limits, because what defines a reasonable or tolerable exposure will be strongly dependent on the prevailing circumstances of the exposure in these situations. The current work on radiation protection in veterinary practice focuses on planned exposure situations, although there will potentially be veterinary concerns in the other exposure situations as well.
The three main ethical theories underpinning the system of radiological protection (utilitarianism, deontology, and virtue ethics) are also frequently taught in veterinary ethics (Fawcett et al., 2018). The core ethical values of the system are beneficence/non-maleficence, prudence, justice, and dignity (ICRP, 2018), which are consistent with, but not the only ethical values or principles important in, veterinary practice. For example, the ‘One Welfare’ framework (Garcia Pinillos et al., 2016; Fawcett et al., 2018) recognises and emphasises the inter-relationships between human health and well-being, animal welfare, socio-economic development, biodiversity, and environmental conservation, and highlights additional ethical principles consistent with a holistic approach to sustainable development, similar to, but broader than, those presented in
3. Current status of the use of ionising radiation in veterinary medicine
As many applications have come about without the active involvement of persons knowledgeable in radiation protection, and often also in the absence of an appropriate radiation protection framework, several issues have arisen. These need to be identified and rectified, preferably with close collaboration between the relevant stakeholders (e.g. the practising veterinarians and the radiation protection competent authorities). The issues listed should be seen as illustrative and by no means have the pretention of being exhaustive.
3.1. Unique aspects
Compared with human medicine applications, challenges for radiation protection could be greater in veterinary practice. Many radiological procedures on large animals are performed outside of a regulated environment, or new equipment may have been retrofitted in an existing building without due consideration of shielding requirements. Justification is not supported by a veterinary equivalent of the ‘referral guidance’ or ‘appropriateness criteria’ we know from human medicine, there are no diagnostic reference levels, there is little to no agreement on activities of radiopharmaceuticals to be administered for therapeutic purposes, there is no involvement of a medical physicist, and, last but not least, not all practitioners performing higher dose diagnostic or even radiotherapy procedures have undergone specific or specialist education and training.
Conventional radiology is available in many small veterinary practices. CT scanners, CBCT, C-arms, and O-arms can be found in an ever-growing number of veterinary clinics, where shielding strategies may require particular attention because of retrofitted devices. The use of mobile radiographic equipment is standard in dealing with large animals as it is performed on farms, in stables, at auctions, or in the open field. The delimitation of a safe working area and proper use of mobile equipment may require extra attention. Nuclear medicine diagnostics and treatments are not so common, but may have been introduced without sufficient consideration of contamination problems, such as in dealing with radioactive waste, particularly urine. Some therapeutic interventions may be performed outside of veterinary clinics, such as when radioactive substances are administered into a horse’s joints at a riding stable, resulting in potential contamination concerns. In nuclear medicine in general, the animal as an ambulatory radiation and possible contamination source deserves specific consideration, particularly when outside the clinic. Other radiotherapy treatments, either teletherapy or brachytherapy, are still fairly rare and restricted to veterinary clinics, but the potential radiological risks – both to the animals and to people involved in the procedures – should not be neglected.
Although more and more dedicated veterinary equipment is becoming available, second-hand equipment coming from human medicine is still very prevalent in veterinary practice. Safety and performance of the equipment should be verified before first use and then on a regular basis afterwards by means of a quality control programme. Mobile equipment may need more frequent checks than fixed installations. Quality checks need to include all pieces of equipment throughout the imaging or treatment chain, and should not be restricted to radiation-emitting equipment or sources. This means the inclusion of software, cameras in nuclear medicine, image monitors, etc. There is a growing influx of specialty veterinary equipment (e.g. FIDEX CT) that falls under industrial rather than medical standards. Additionally, mobile equipment is being marketed as ‘lighter’ because shielding has been reduced from, say, 6 kg to 4 kg. Although dedicated, fit-for-purpose equipment is certainly welcome in principle, it must still meet appropriate radiation safety standards. Similarly, clinics may not have given due consideration to shielding needs. For example, a room may have been designed to have adequate shielding for conventional x-ray applications on a fixed table with the primary beam directed from the ceiling to the floor, but that room may not be adequately shielded for interventional procedures using a C-arm.
For historic reasons, most veterinarians learn how to use standard radiologic equipment (fixed, mobile, or both) in their basic curriculum. This should comprise at least the basic notions of radiation protection. More risk-baring applications, such as the use of scanners, interventional radiology, nuclear medicine, and radiotherapy, certainly call for additional education and training, including the corresponding radiation protection. Such programmes are on offer, for instance, through the American College of Veterinary Radiology and European College of Veterinary Diagnostic Imaging, but they are not systematically formally required by the relevant authorities. One could ask whether practising these more complex and risk-baring techniques should not be restricted to veterinarians who have successfully completed such ‘specialist’ programmes. In general, there are striking differences in the basic and specific education and training requirements related to applying different imaging and therapy modalities in veterinary applications of ionising radiation.
These differences can also be observed for the connected radiation protection requirements, where some harmonisation of training requirements seems necessary (Gregorich et al., 2018). This includes continuous efforts to refresh, update, and, where needed, extend theoretical knowledge and practical skills, as well as adapt competences and attitudes. It should be obvious that if other professional groups, such as radiographers, radiotherapy technologists, and the like, actively intervene or even autonomously perform radiologic or radiotherapeutic procedures of any type, they should have had, and continue to have throughout their professional life, corresponding education and training. This should necessarily include radiation protection. It is up to the licensee, or otherwise authorised person or entity responsible for the installation, to clearly establish the roles and responsibilities of all those involved in the procedures, within the bounds of the appropriate regulatory framework, and ensure that they have, and continue to have, corresponding education and training.
3.2. Justification
Compared with human medical applications, the absence of an equivalent to ‘referral guidelines’ or ‘clinical imaging guidelines’ is striking. This may lead to the impression that ionising radiation is used intuitively rather than based on scientific evidence. This absence of formal consensus on what type of imaging is (most) indicated to diagnose or exclude a given health condition may be partly responsible for the impressive number of radiologic/nuclear medical examinations to which some racehorses and showjumpers are submitted (e.g. Judy, 2013); series are often repeated when another potential purchaser shows up.
In terms of balancing risk and benefit within justification, little concern has been demonstrated for the possible detrimental effects on the animals exposed, apart from radiotherapeutic applications. The scarcity of scientific data on the possible effects of low-dose radiation exposures on typical companion animals, horses, etc. is not helpful in this respect. Human exposure related to diagnostic procedures has also rarely been regarded as a risk worth considering, although this attitude certainly needs to be revisited in view of higher potential exposures in CT, nuclear medicine, interventional radiology, and radiotherapy. Anecdotally, there is also a common misconception that an animal with a short life span compared with a human will not experience radiogenic cancer. In fact, cancer patterns in mammals are similar and, in general, are relative to life span (e.g. Albert et al., 1994), and animal models are frequently used to extrapolate health risk, carcinogenic or otherwise, to humans (Fjeld et al., 2007). Although not specific to the practice of veterinary medicine, and predominantly high doses or dose rates, there is a good amount of data on the effects of animal exposure to a variety of radiation types (e.g. Haley et al., 2011; Tang et al., 2017).
The three levels of justification for a radiological practice in medicine, described in
Lately, there has been increasing concern about the overuse of radiological procedures in medicine, with a substantial proportion of medical imaging procedures deemed unjustified. While similar surveys have not been carried out in veterinary medicine, the problem of unjustified use of ionising radiation likely exists here as well, as many of the drivers of overuse are also present in veterinary medicine. These include, among others, lack of awareness of doses and associated risks, self-referral, ‘self’-presentation, defensive medicine, lack of access to previously performed examinations at other veterinary practices, and lack of confidence in the clinical diagnosis.
Self-referral is the norm rather than the exception in veterinary medicine. Radiographic equipment is widespread, both in general veterinary practice and in larger veterinary hospitals. Frequently, the veterinary practitioner ordering a radiological procedure will also be the person performing the procedure and interpreting its results. This person may also be the owner of the radiographic equipment or may be employed by a veterinary practice which explicitly or implicitly expects their staff to ensure return on their investment in radiographic equipment. Hence, strong financial incentives for the use of radiological equipment are often present in veterinary medicine. Of particular concern recently is the wide adoption of CT, and the corresponding use (i.e. repeated studies from a young age, generally employing a full-body CT) and impact of teleradiology. Additionally, there is a growing impact of commercial firms providing easy access to sophisticated equipment, and then pressuring the facility or veterinarian to generate a certain amount of financial gain from that equipment’s use.
‘Self’-presentation, in which the owner or handler of an animal requests a diagnostic imaging or therapeutic procedure without previous clinical examination of the animal and hence without a radiology referral from a veterinary practitioner, or where the owner/handler demands a diagnostic or therapeutic procedure not considered to be indicated by their veterinary practitioner, is also a pertinent issue in veterinary medicine. As the veterinary field is service-oriented and is comprised mainly of private practitioners, some veterinarians may feel compelled to comply with such consumer demands to avoid losing business to veterinary practices that oblige such requests.
Diagnostic techniques are also quite commonly used for economic purposes rather than the health of the examined animal, such as in the case of pre-sales examinations on racehorses or showjumpers, as mentioned previously. Screening programmes for canine hip and elbow dysplasia are also in place in many countries, and large numbers of animals are thus imaged as part of the breeding selection process. For such non-medical procedures on asymptomatic animals, there should be a scientific basis for the imaging procedures, a demonstrable relationship between the outcome and goal of the screening, and stricter requirements for evidence bases than for individual medical procedures.
3.3. Optimisation
Veterinarians face many occupational challenges and hazards, one of which is exposure to ionising radiation. Optimisation in veterinary care is a process to ensure that the likelihood and magnitude of exposures and the number of individuals exposed are as low as reasonably achievable, with consideration given to practical, animal welfare, economic, societal, and environmental factors.
From the point of view of procedure optimisation, considerable differences in approach can be observed. In some countries, the presence of non-professionals, such as the owners or handlers, during x-ray procedures on small animals is prohibited, whereas in many other countries, it is common practice for them to be present and restrain the animal.
The presence of members of the public is very common in radiographic procedures performed with mobile equipment outside of veterinary practices or clinics. Some persons, such as stable boys, may be repeatedly involved in assisting with these procedures, which might not be performed in an optimised fashion from a radiation protection point of view. The question then is whether some of these people should be considered as professionally exposed, whereas, in general, they are considered as members of the public. Data on the exposure of human bystanders, both professionally exposed persons and members of the general public, are scarce in veterinary practice settings. If data are available, they most often relate to actual practices, rather than what would result from best practice.
Activities of the same radioactive substance, administered to examine or even treat animals of the same species and characteristics in similar clinical settings (e.g. administration of 131I to cats weighing approximately 4 kg, presenting with hyperthyroidism) may differ considerably from one centre to another, indicating important room for evidence-based optimisation.
Data on doses to the animals themselves are even more rare. A practical difficulty with second-hand equipment such as CT scanners coming from human medicine is that their standard protocols have been designed to offer high-quality images for reasonably optimised exposure settings, but with the human patient as a reference. Dose estimates presented by these machines suffer the same restriction, and should not be applied as such on animals that have different anatomical features and dimensions. In veterinary medicine, the lack of supporting professionals such as medical physicists (Arkans et al., 2017) could potentially allow the continued use of non-optimised protocols. Animals may therefore be exposed to doses in excess of what is required, which consequently leads to excessive doses to humans as well.
4. Relevant icrp initiatives and scope of ongoing work
There is a real need to strengthen the radiation protection framework and its application in practice about where exposure of animals to ionising radiation takes place, in part because of the connected exposure of humans. As such, ICRP initiated work to clarify and elaborate upon its recommendations with respect to veterinary medicine, resulting in the establishment of two related task groups, as mentioned above.
The mandate of Task Group 107 was to advise the ICRP Main Commission on the possibility and desirability of it becoming involved in protection of the patient with respect to the application of ionising radiation in diagnostic, interventional, and therapeutic veterinary medicine. With the final report delivered to the Main Commission in October 2018, the work of this task group is complete, concluding that ICRP should consider the animal patient in its recommendations.
The current mandate of Task Group 110 is to advise the ICRP Main Commission on radiological protection aspects involved in the applications of ionising radiation in veterinary medicine. As such, this includes treatment of occupational and public exposure of humans as it relates to delivery of veterinary care, and radiological protection considerations for the animals receiving such care. In addition, Task Group 110 is to consider the risks resulting from contamination of the environment from the applications of nuclear medicine in veterinary medicine. Task Group 110 will include the ethical considerations underlying various types of veterinary practice, and the ethics applied to protection of animals and plants in the environment. This publication will provide initial guidance and set the stage for additional considerations that may be appropriate.
Footnotes
Acknowledgements
The authors wish to gratefully acknowledge the work of members of Task Groups 107 and 110, whose various contributions can be found within this paper.