Answer to Question #11138 Submitted to "Ask the Experts"

Category: Medical and Dental Patient Issues — Dental

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

Q

What is the radiation exposure from a digital cone-beam CT (computerized tomography) scan? I'm concerned because I just had a set of full-mouth x rays done recently and I've had two CT scans of my head for medical reasons several years ago.

A

I understand that you are concerned about the radiation exposure that you will receive from a cone-beam scan. I also understand that you have had two medical CT scans of your head several years ago as well as a set of full-mouth radiographs last March. I will equate the amount of radiation from a cone-beam CT to a panorex because you previously asked and received a response regarding radiation doses from panoramic radiographs.

A cone-beam CT is a low-dose scan that will allow your dentist to evaluate the anatomy of your jaws in all three planes and can be a useful tool for many dental problems. It is the recommended examination to determine anatomical relationships as stated by the American Academy of Oral and Maxillofacial Radiology if an implant is going to be placed (Tyndall et al. 2012). The amount of radiation received from a cone-beam CT of the jaws will vary from approximately 18–200 µSv depending on the size of the field of view, resolution of the images, size of the patient, location of the region of interest, as well as the manufacturer settings. Below is a table of various cone-beam CT units and their approximate radiation dosages.

Cone-Beam CT Scanner Effective Dose in µSvA Digital Panoramic Equivalent B Number of Days of Annual Per Capita Background RadiationC
Sirona Orthophos XG 3D 32–85 depending on setting*1 2.2–6 4–10.3
Galileos Comfort 70–128 depending on setting* 5–9.1 8.5–15.6
I-CAT Next Generation 45–83 depending on FOV/settings** 3.2–5.9 5.5–10.1
NewTom 3G 68* 4.9 8.3
Kodak CS 9300 18–200 depending on the FOV/settings*2 1.3–14.3 2.2–24.4
Comparison with Somatom Sensation 32-row/64-slice MultiDetector CT 860* 61.4 104.9

*Ludlow et al.
**Pauwels et al.
*¹ Courtesy of Ludlow JB, 50–75 percent increase in dose when HD mode is used.
*²Ludlow JB;Dosimetry of CS9300 Cone Beam CT Unit Study conducted 10 June 2011 on the CS 9300 serial number ZAAN009.
AEffective dose calculated with International Commission on Radiological Protection 2007 tissue weights.
BMedian of published effective dose for digital dental panoramic radiography = 14 µSv.
CAnnual per Capita = 3.0 mSv (3,000 µSv) per annum or approximately 8.2 µSv per day

We can assume that an average radiation dose for a cone-beam CT of the jaws taken for implant purposes is approximately 130 µSv. Compared to the effective dose for a panoramic radiograph (conservatively approximately 14 µSv) (Ludlow et al. 2008), a cone-beam CT is similar to having approximately nine panoramic radiographs depending on the factors stated above. We can also compare this to the amount of radiation that one received on the earth every day. The daily background radiation received from the natural environment is approximately 8.2 µSv per day in the United States (NCRP 2003). Therefore, the average cone-beam CT is similar to being alive on the earth for a little over two weeks (approximately 16 days). In comparison a medical CT of the head is approximately 860 µSv which equates to approximately 105 days of being alive on the earth. (Editor’s Note: The dose from head CT scans will vary depending on what one is looking for, e.g., brain, sinuses, jaw. A typical effective dose from a CT scan of an adult brain is around 2 mSv or 2,000 µSv.)

The amount of radiation received for a cone-beam CT is minimal in comparison to what we receive being alive on the earth. However, we always want to be careful with any amount of radiation and will use the principles of ALARA (As Low As Reasonably Achievable) as well as patient selection criteria when deciding what dental images should be taken. A cone-beam CT can be a very useful tool in planning your dental treatment and your dentist will only use this tool when the benefits of the examination outweigh any of the minimal risks.

Heidi Kohltfarber, DDS, MS, Dip. ABOMR
Dental Radiology Diagnostics Consultant

References

  • Tyndall DA, Price JB, Tetradis S, Ganz SC, Hildebolt C. Position statement of the American Academy of Oral and Maxillofacial Radiology on selection criteria for the use of radiology in dental implantology with emphasis on cone beam computed tomography. Oral Surg Oral Med Oral Pathol Oral Radiol 113:817–826; 2012.
  • Ludlow JB, Davies-Ludlow LE, White SC. Patient risk related to common dental radiographic examinations. J Am Dent Assoc 139 1237–1243; 2008.
  • National Council on Radiation Protection and Measurements. Radiation protection in dentistry: Recommendations of the National Council on Radiation Protection and Measurements. Bethesda, Md: NCRP; NCRP Report No. 145; 2003.
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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