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CBCT: lower radiation dosage AND get better images

7 March 2014

CBCT: lower radiation dosage AND get better images

It’s easy to become complacent when something you do every day in the course of your work doesn’t appear to generate any visible consequences. However, it’s safe to assume that by working in dentistry you are more likely to be exposed to greater levels of radiation than many other professions, which in turn could potentially expose you to greater risk of a number of cancers in the long term.

At Dentists’ Provident, cancer is responsible for the second highest number of female claims after musculoskeletal disorders, though only six per cent of male claims. In 2012 the company paid out over £500,000 for a variety of cancers in dentists including almost £60,000 for brain tumours, £50,000 for leukaemia, £30,000 for stomach tumours and varying amounts for almost 230 cases of breast cancer. While the evidence linking occupational radiation exposure to cancers remains unclear, the impact on health of excessive doses has been well documented so it’s clear that keeping exposure to a minimum is to be strongly recommended.

The maximum permissible dose for occupational exposure according to The International Commission on Radiological Protection should be 20mSv per year¹, averaged over five years, with a maximum of 50mSv in any one year. Most dental professionals are made aware of the risks early on in their careers and reminders of good practice are generally experienced at least once in a five-year cycle in accordance with the GDC’s core CPD requirements. But with new Cone Beam Computed Technology (CBCT) finding its way into more and more dental practices, updating health and safety regulations for the protection of both staff and patients has been essential.

CBCT systems
“The advent of CBCT is a great advancement within the dental field. It affords clinicians much greater ease of access to acquire 3D images which aids in accurate diagnosis and treatment planning,” says dentist Maria Hardman. “The 3D images generated are high quality, available within minutes and greatly assist communication with patients and ultimately increased patient acceptance.”
The beauty of these systems is that they are incredibly flexible in terms of producing the appropriate degree of precision required for the job in hand. For instance, to diagnose and treat a patient presenting an un-erupted lower third molar, a dentist will most likely select a small field of view, taking only one image, whereas positioning implants across the arch in multiple segments can be achieved with far greater accuracy using 3D images from several fields of view.

With conventional CT scanning, each scan produces a single slice image so several images are usually required, exposing the patient and the dental professional or operator, to several doses of radiation. With CBCT, a complete volume image can be created in a single rotation, or a localised area captured and examined from every angle, significantly reducing both exposure time and area. It is still likely to be a higher dose than a standard x-ray, however.

Because CBCT offers such accurate and informative images, there may be a temptation to use it more frequently and on patients with a wider variety of oral health conditions than would have been the case when only x-ray images were available. Being selective about its use is therefore important not just for the protection of each patient, but also for the staff operating the device.

“The focused field of view allows for the highest resolution at the lowest practical dose, ensuring quality images without compromising on safety,” explains Rob Charteris, Senior Imaging and Application Specialist at Carestream Dental.

Protection guidelines
Every dental practice using radiography is already obliged to appoint a Radiation Protection Adviser² (RPA) and follow the GDC’s guidance on the safe use of x-ray equipment. With the increasing use of CBCT, in 2012 the European Commission published ‘Radiation Protection: Cone Beam CT for Dental and Maxillofacial Radiology. Evidence based guidelines³, following up on a provisional set of guidelines introduced in 2009. As well as justification and referral criteria to protect patients, the document includes measures to protect staff through adequate training, equipment testing and restricting exposure.


In its ‘Guidance on the Safe Use of Cone Beam CT (Computed Tomography) Equipment 2010’ the Health Protection Agency (HPA) advises that recommendations previously given on adequate shielding is not adequate for dental CBCT and the appointed RPA needs to consider all aspects of the installation of equipment, room layout and the use and occupancy of rooms above and below the proposed location. Further guidance is expected shortly from Public Health England (PHE), which took over the functions of the HPA in April this year. Because of the higher levels of scattered doses during exposures, there are extra recommendations to restrict entry including fitting warning lights outside the radiography room, ensuring the operator does not need to enter the room in order to disconnect the equipment in the event of an incident and providing safeguards such as secure passwords to prevent use of the equipment by unauthorised personnel.


With conventional radiography, standing 1.5m away from and behind the x-ray tubehead is regarded as sufficient to avoid annual doses exceeding 1mSv; with CBCT, the doses over the same period could amount to 20mSv so it is suggested that the operator and all other staff should be positioned outside the room or behind a shielded area where possible. If the patient needs support during the procedure, the member of staff should wear a lead apron for protection which needs to be stored carefully after each use to avoid creasing or cracking.


Because CBCT equipment needs to perform self-calibration procedures each time it is switched on, it’s usual to leave the mains power on throughout the working day so the ‘controlled area’ cannot be temporary as it can with x-ray equipment so this may be a consideration if space is an issue in the practice.


Training
With the introduction of CBCT to a practice, additional staff training is vital and this is usually provided by the suppliers. Rob Charteris adds: “The training from Carestream Dental is completed over two days. The first covers all the basics areas straight after installation and then a further training day is provided when the customer is more comfortable with the equipment and has a better idea of what they don’t know – usually about a month later.”


While CBCT may have launched dentistry into a whole new era of technological precision, it isn’t without its risks. To be adequate for the safety of the practitioner, practice staff and patient, practice safeguards need to be even more rigorous than for x-ray equipment.


“It’s exciting to be able to embrace new advances in dental equipment, but it’s also essential for dentists to learn as much as possible about the technology and be fully aware of any potential risks,” says Bryan Gross, Head of Claims and Underwriting at Dentists’ Provident. “We see many unfortunate cases of dentists being struck down by long-term illnesses and unable to work in practice any longer. The more informed you are, the better you can protect yourself and your team against future health issues or long-term illnesses and diseases.”

Fig1      Fig 2      Fig3


References
¹ICRP, 2007. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann. ICRP 37 (2-4).

²Ionising Radiations Regulations 1999 (IRR99); HSE statement on radiation protection advisers, March 2007.

³’Cone Beam CT for Dental and Maxillofacial Radiology, Evidence Based Guidelines’, European Commission: Radiation Protection No 172

⁴’Guidance on the Safe Use of Cone Beam CT (Computed Tomography) Equipment 2010’, Health Protection Agency (HPA) Health Protection Agency (HPA) 2010. Guidance on the Safe Use of Dental Cone Beam CT (Computed Tomography) Equipment. Chilton, Oxford: HPA. Available from: https://www.hpa-radiationservices.org.uk/dxps/resources/.


Author Information:

David Claridge

David Claridge is currently the UK CAD/CAM Specialist at Carestream Dental. He began his career as a dental technician at The Briars Dental Centre, Newbury, before starting Claridge Dental Laboratory, and then Claridge Mouthguards. David has been closely involved in the digital impressioning/CAD/CAM world, through his role in the digital dentistry team at 3M ESPE, before joining Carestream Dental.

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