W Bruce Howerton Jr addresses recent news related to radiation and computed tomography technology

Recently, articles and newscasts have emerged regarding high exposure of radiation from medical computed tomography (CT) scans that have generated misconceptions about dental CBCT (cone beam computed tomography).

1-3 These articles and news stories discuss possible links to cancer from medical computed tomography (CT) scans. It is important to note the differences between medical CTs and the cone beam computed tomography (CBCT) technology available for dental practices today. Traditionally, dentists and medical professionals follow the ALARA (As Low As Reasonably Achievable) protocol concerning radiation levels to expose their patients to the least amount of radiation possible while still gaining the most useful information for proper diagnosis.4 CBCT is being used in dentistry as a revolutionary method of gaining three-dimensional (3-D) information without high levels of radiation compared to medical CT scans.5 CBCT offers different fields of view that reduce radiation exposure to the patient6 to determine bone structure and tooth orientation, as well as view nerve canals, pathology, and in many cases, eliminate the need for exploratory surgery.

Cone beam technology opens up new possibilities for safer and less invasive dental treatments. The 3-D “surgical views” offer views or slices of the entire anatomy from anterior to posterior, lateral, and axial positions with non-distorted magnification provided by the software. Before beginning many treatments this information is imperative to determining anatomical variations that can affect the success or failure of procedures.

Orthodontic practices also benefit from CBCT scans. A full field of view, 17 cm, in the case of the i-CAT? (Imaging Sciences International, Inc.), captures all of the soft tissue and hard tissue landmarks required for cephalometric analysis as well as panoramic, frontal ceph, paranasal sinuses, temporomandibular joint, and airway views in a single scan. Because children are more susceptible to radiation, lower radiation doses compared to medical CT allow this technology to be beneficial to those patients requiring more detailed information.

Because CBCT offers unparalleled detailed information of the oral and maxillofacial complex, it is important to determine whether the patient absorbs more radiation from CBCT or medical CT. Here are some facts concerning radiation exposure from a panoramic image, CBCT scan, or a medical CT scan.

For more than 20 years, dentists have referred patients to hospitals for medical CT data, mainly to determine the amount of hard tissue available and document pertinent anatomy for dental implant placement. The average medical CT scan of the oral and maxillofacial area can reach levels of 1200-3300 millisieverts (mSv), a measurement of radiation absorbed by the body’s tissue.5,7 These significant levels are attributed to the method of exposing tissues to radiation. The anatomy is exposed in small, overlapping fan-shaped or flat slices, as the machine makes multiple revolutions around the patient’s head. In order for adequate information to be collected from the exposure, there is overlapping radiation.

In recent years, researchers have developed a different technology to achieve the same information gained from medical CTs. These scanners work much differently than medical CT scanners—they capture all the anatomy in one single cone-shaped beam rotation. This method exposes the patient to up to 10 times less radiation.8 For example, the radiation exposure of a standard scan (13 cm height ? 16 cm D, 0.4 voxel) from an i-CAT® CBCT machine (Imaging Sciences International) is 36 mSv.9 (A voxel is the 3D version of a pixel.) Keep in mind that the typical two-dimensional (2-D) full-mouth series runs 150 mSv while a 2-D digital panoramic image ranges between 4.7-14.9 mSv.9 Because CBCT imaging is becoming more available in most areas of the country, dentists now have the opportunity to acquire valuable diagnostic information without exposing the patient to higher radiation levels.

As an Oral Maxillofacial Radiologist and an educator in this field, I believe that the knowledge that is achieved through 3-D imaging is essential for dentists, but along with that knowledge comes increased responsibility to use imaging effectively and efficiently, and, most importantly, provide safe and effective patient care.

W Bruce Howerton, Jr, DDS, MS, is board-certified oral and maxillofacial radiologist who practices privately in Raleigh, North Carolina. www.carolinaomfimaging.com

References

1. Liz Szabo. Radiation from CT scans linked to cancers, deaths. USA Today online. http://www.usatoday.com/news/health/2009-12-15-radiation15_st_N.htm?loc=interstitialskip. Updated 12/14/2009. Accessed 1/12/10.

2. Jonathan LaPook. New Focus on Dangers of CT Scans. CBS News online. http://www.cbsnews.com/stories/2009/12/14/eveningnews/main5979332.shtml. Dec. 14, 2009. Accessed 1/12/10.

3. Shirley S. Wang. CT Scans Linked to Cancer. Wall Street Journal online. http://online.wsj.com/article/SB126082398582691047.html. December 15, 2009. Accessed 1/21/10.

4. American Dental Association. Peer Review and Quality Assessment--Radiation. http://www.ada.org/prof/prac/tools/peer_components.asp. Accessed 1/21/10.

5. Radiation Doses and Risks of CBCT. http://www.sedentexct.eu/content/radiation-doses-and-risks-cbct. Accessed 1/21/10.

6. CBCT Imaging: Discussing the Field of View Concept. Interview with W. Bruce Howerton, DDS, MS. OsseoNews: the world of implant dentistry online. http://www.osseonews.com/cbct-imaging-discussing-the-field-of-view-concept/. Accessed 1/21/10.

7. Dictionary of Radiological Terms. U.S. Department of Health and Human Services http://www.remm.nlm.gov/dictionary.htm. Accessed 1/21/10.

8. Patient benefits. http://www.conebeam.com/patient. Accessed 1/21/10.

9. Next Generation i-CAT—Specifications. Imaging Sciences International. http://www.imagingsciences.com/pro_icat_ng_specs.htm. Accessed 1/21/10.