Answer to Question #14412 Submitted to "Ask the Experts"

Category: Medical and Dental Patient Issues — Worker Issues

The following question was answered by an expert in the appropriate field:

Q

I am a trainer on dental cone-beam computed tomography systems (CBCT). I would like to know if I take a CBCT (includes upper and lower jaw) approximately how many full-mouth series would it take to result in an equivalent radiation dose to the patient?
 

A

This is actually a difficult question to answer because there is too much variation between CBCT scanners to provide a single number. In order to make a comparison between imaging techniques, the effective dose is usually used, expressed in microsieverts (µSv). To calculate the effective dose the absorbed dose is measured, typically with a humanoid phantom and thermoluminescent dosimeters (TLD), and then weighting factors applied, accounting for the various organs' risk of biological consequences from the radiation exposure such as cancer.

The range of effective doses for CBCT scanners is large: 19–1,073 µSv, although the machine with the highest doses is no longer on the market. Factors affecting the radiation dose include specific scanner, imaging parameters (kilovolt peak [kVp], milliampere seconds [mAs]), resolution (voxel size), type of imaging detector, and field of view (FOV). In general, the larger the imaging parameters, resolution, and FOV, the larger the dose.

The range of doses for a large field of view (FOV) scan (both jaws and including the neck and orbital region), excluding the discontinued scanner, is 68–498 µSv. For a medium FOV scan (both jaws but limited other structures) the range is 69–265 µSv. For a small FOV scan (typically a single quadrant or single arch) the range is 19–652 µSv. The reason for the increased dose in some of the small FOV scans is the increased resolution used.

For comparison, the effective dose from a dental panoramic radiograph is 4–28 µSv and for a full-mouth intraoral series is 170 µSv (round cone, F-speed film or storage phosphor plate digital) to 388 µSv (round cone, D-speed film).

All of these numbers come from an excellent 2013 review paper by Li, regarding patient radiation doses from cone-beam computed tomography. You may wish to consult this paper to find the information about the specific scanners you work with. Some of the scanner manufacturers can also provide up-to-date information about radiation dose with their scanner. Some of the machines have an ultra-low-dose protocol that is sometimes used in orthodontics when fine detail is not required.

In your training of dental professionals to use the CBCT equipment they have purchased, I recommend that you discuss the various factors that can affect patient dose and encourage them to use the scan protocols that will provide the lowest exposure while still answering the clinical question triggering the need for the scan.

Sharon L. Brooks, DDS, MS
Professor Emerita, University of Michigan School of Dentistry
Diplomate, American Board of Oral and Maxillofacial Radiology

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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