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Radiation doses in dental radiology

FAQs for health professionals

» What is meant by radiation “dose” of X rays?

Radiation dose is a measure of how much energy is absorbed when something or someone is exposed to X-rays. This is important because it is this absorption of energy that can cause damage to a person. Different quantities are used to express dose.

» Which quantity is used in practice to relate radiation dose to risk?

A commonly used quantity to express the dose to a person is effective dose, which takes into account the dose to different organs/tissues which are exposed (as different organs/tissues have varying sensitivity to radiation). Effective dose is related to the risk for stochastic effects (cancer and genetic effects). Effective dose and its associated risk should not be applied to individuals, but can be used to compare between modalities, techniques and other sources of exposure (e.g. natural background levels). Non-stochastic effects (tissue reactions / deterministic effects may also occur at organ dose levels above a specific threshold. 

» Which quantities are used to measure the dose from dental X ray equipment?

Since the effective dose cannot be measures, in practice, other dose quantities that are directly measurable are used for the purpose of optimization, dose monitoring, and quality assurance. They are specific to a certain imaging modality. 

The measurable quantity is the entrance surface air kerma/dose. The unit of entrance surface kerma is the gray (Gy), but in dental radiology the dose levels are usually a small fraction of one gray - milligray (mGy), or even microgray (µGy).

In cephalometric, panoramic radiography and in CBCT the measurable quantity is usually the product of kerma (dose) and the X ray field, called Kerma-area product, measured in mGy.cm2.

» What is a typical dose from a dental radiological procedure?

In the scope of quality assurance, measurable doses from radiological procedures are often expressed as diagnostic reference levels (DRL), based on local surveys of typical patient doses. DRL values for adult exposures from various national surveys are in the following ranges:

  • 0.65 to 3.7 mGy in terms of entrance surface kerma, and 26 to 87 mGy.cm2 in terms of kerma-area product for intraoral radiography; 
  • 3.3 to 4.2 mGy in terms of entrance surface dose, and 84 to 120 mGy.cm2 in terms of kerma-area product for panoramic radiography;
  • 41 to 146 mGy.cm2 (adults) and 25 to 121 mGy.cm2 (children) in terms of kerma-area product for lateral cephalometric radiography.

Typical effective doses are for:

  • intraoral dental X ray imaging procedure 1–8 μSv; 
  • panoramic examinations 4-30 μSv; 
  • cephalometric examinations 2-3 μSv, 
  • CBCT procedures (based on median values from literature): 50 μSv or below for small- or medium-sized scanning volumes, and 100 μSv for large volumes. 

Thus the doses from intraoral and cephalometric dental radiological procedures are lower, usually less than one day of natural background radiation. Doses for panoramic procedures are more variable, but even at the high end of the range are equivalent to a few days of natural background radiation which is similar to that of a chest radiograph. CBCT doses cover a wide range, but may be tens or even hundreds of µSv of effective dose higher than conventional radiographic techniques, depending upon the technique. Rapid technological improvements to CBCT equipment mean that typical dose ranges are likely to change.

» Who should I ask for detailed information regarding doses?

A qualified expert (e.g. medical physicist) can measure the abovementioned dose quantities, and is able to provide more detailed information regarding these subjects.