Dental radiology is one of the largest single groups of clinical radiographic examinations performed with somewhere in the region of 20 million dental x-ray examinations undertaken annually in both public and private dental practices in the UK and around 10% of examinations now involve panoramic or cone beam CT (CBCT) investigations. According to international surveys (UNSCEAR and IAEA) approximately 20% of all x-ray examinations worldwide are dental with some 520 million undertaken each year. Effective ( whole body equivalent ) doses employed in dental radiology are:
- Intra oral examination 1 – 8µSv
- Panoramic examination 4 – 30µSv
- Cephalometric examination 2 – 3µSv
- Cone beam CT (CBCT) 30 – 650µSv (for small dento-alveolar volumes) and 30 – 1079µSv (for large cranio-facial volumes)
These may be compared with an annual background level of radiation of approximately 2,000µSv (2 mSv) per annum.
Although the effective doses per image are generally small and the corresponding risks low there is still a need to ensure that cost-risks and benefits associated with this important clinical practice are maintained at acceptable levels. Radiation protection and its underlying elements quality assurance and control is very much concerned with the scientific basis of optimization of practices to ensure that costs-risks and benefits can be consistently maintained, especially as new imaging techniques and methods continue to be implemented in dental practice.
Over the past 20 years appropriate radiation protection advice and guidance has been provided to support dental radiology. A working party of the National Radiological Protection Board (subsequently rebranded as the Health Protection Agency) and Royal college of Radiologists published a report in 1994, which made recommendations covering all relevant aspects of dental radiology. This initiative was followed in 2001 by the publication of Guidance Notes for Dental Practitioners on the Safe use of X-ray Equipment by the Department of Health (D of H). This was followed in 2004 by European guidelines on radiation protection in dental radiology and further guidance and information can be found on the website of the IAEA (International Atomic Energy Authority) and Health Canada. Teaching packages in dental radiation protection are also readily available and numerous live and e-learning training courses are to be found.
Radiation protection support
Dental radiology is now a well established and extremely important aspect of dental healthcare. The amount spent annually on dental radiology in the UK is probably now over £50 million and continuing to rise as it becomes more widely employed and new technology is made available. Digital imaging is increasingly replacing film as its availability declines. The wider use of panoramic imaging systems, as well as the growth of CBCT, provide enhanced imaging facilities and associated improvements in patient care.
Dental radiology is regulated through the Ionizing Radiations Regulations (IRR) (Protection of the worker and general public) of 1999. Supporting the regulations are an Approved Code of Practice and a set of Medical and Dental Guidance Notes. Also of relevance is Guidance Note PM77 on the fitness of equipment used for medical exposure to ionizing radiation (third edition) published in 2006 by the Health and Safety Executive (HSE). Dental radiology is also covered by the Ionizing Radiation (Medical Exposure) Regulations (IRMER) of 2000 concerned with the protection of the patient.
Implementing and maintaining all the necessary legal requirements associated with the use of ionizing radiations will obviously carry a cost overhead. However, an important aim of any effective radiation protection support should be to ensure that the necessary legal requirements can be met cost-effectively by every dental practitioner, since ultimately it is the general public/customer that carries this cost burden.
There are a number of possible areas for cost-effective intervention. For example advice on the design and layout of dental surgeries where x-ray examinations are performed or in dedicated x-ray rooms where panoramic or CBCT examinations are performed can provide significant cost savings. Very often the specification of lead protected walls is automatically recommended (at high cost) at the design stage or even when an upgrade of an existing facility is proposed. Do walls automatically need to be lead protected?
A legal dose limit to a member of the general public is set at 1 mSv/year. A dose constraint of 1/3rd of this limit or 0.3 mSv/year, which is well below the legal limit for a member of the general public can be applied to all high occupancy areas adjacent to a dental surgery where x-rays are undertaken. High occupancy areas would include offices or reception areas or adjacent dental surgeries where staff are located throughout the working day. All staff not directly involved in the performance of an x-ray exposure within a surgery would be classed as members of the general public. This would also include a dentist in the adjacent surgery, dental nurses, receptionists and secretaries etc. Low occupancy areas would include corridors, decontamination areas, store rooms etc and a dose limit to these areas would be inversely proportional to the occupancy factor. Thus a 10% occupancy factor could theoretically raise the allowed design dose constraint 10X to 3 mSv/year for these areas.
If we assume 20 million dental x-ray examinations are undertaken in the UK each year on roughly 20,000 x-ray sets, then the average number of exposures for each unit per year is approximately 1000. This is equivalent to an average of 20 exposures per week. For this workload a patients head could be less than 1 meter from a studded (plasterboard wall) with 10mm thick plasterboards when undergoing an intra oral x-ray examinations and the 0.3 mSv/year limit in an adjacent area would not be breached. A studded wall of double thickness of plasterboard has approximately a 25% transmission for a 70 kV x-ray beam produced by most dental x-ray sets ie it reduces the intensity by 75%. Thus
- distance from a patient’s head,
- workload (exposures per week)
- occupancy in adjacent areas
should be considered before specifying any added protection. In fact workloads of up to 50 exposures per week can very often be accommodated. In fact any recommendations concerning the levels of added protection required should include an assessment of the associated risk reduction.
Similarly the dose that would be received by an operator who undertook all exposures in a surgery in any year and the associated risks expressed relative to an equivalent level of background radiation should underpin any decision to include added protection in doors. An operator located at an entrance or outside in a corridor is usually sufficient distance from the patient to ensure an acceptable annual level of dose. Such an operator would also have a clear view of the patient and x-ray exposure warning lights, as well as having control of the access to the room without the need for warning lights or signs.
Other aspects of legally radiation protection services that can be provided cost-effectively include:
- Compliance audits employing web based services
- Virtual RPA visits employing web cam or digital images/plans
- Quality assurance checks on equipment employing mailed test facility
- Patient dose audits and associated dose reference level verification
Modern IT based technology applied affectively can help to keep down the costs of meeting legal requirements in dental radiological practice.
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