Let the truth about CBCT be known

We are fond of Dr Peter Greco’s column on ethics, which appears every month in the AJO-DO .

In his December 2013 column, “Let the truth be known,” Dr Greco implied that he does not use cone-beam computed tomography (CBCT) as a standard imaging technique on all of his patients, and the tone of the column appeared critical of orthodontists who do. It seems Dr Greco assumed that they are using CBCT to derive 2-dimensional (2D) information, which they could just as well retrieve from panoramic, cephalometric, and periapical radiographs; in fact, many are not. We agree that if orthodontists are “just aligning crooked teeth,” then CBCT is overkill, as are most x-rays. But if, for example, orthodontists are using CBCT to screen and treat patients at risk for obstructive sleep apnea, then CBCT offers unique diagnostic information not available through traditional radiographs.

Many orthodontists routinely use low-dose CBCT to serve their patient’s best interest. The ethical and prudent recommendation should be this simple: use the imaging modality that best answers the clinical questions through ALARA (as low a reasonably available) principles. It is outrageous and irresponsible that Dr Greco presumes to dictate what those questions should be and what diagnostic information an orthodontist should or should not look for when treating a patient.

With regard to CBCT technology, when should its use for accurate assessment of the following entities NOT be routine: temporomandibular status, airway and sinus health, obstructive sleep apnea risk, palatal anatomy, asymmetries, transverse relationships, ectopic eruption patterns, true root positioning, root health, periodontal osseous housing, skeletal growth, incidental pathology, and possibly other conditions that can benefit from advanced 3D imaging using similar or even less radiation than a 2D series. With improvements in CBCT hardware and software, the question should not be whether to scan but, rather, under what settings (field of view, exposure time, voxel size) should the scan be performed when imaging is warranted.

Radiation risk is at the heart of his commentary. He failed to point out key information. The dosimetry level of 1 CBCT scan compared with that of a series of 2D images (panoramic, cephalometric, bitewing and periapical radiographs, or an FMX and so on) could be less at best, if not similar. When Dr Broadbent introduced cephalometrics to the United States in 1931, he likely didn’t anticipate that it would take nearly 30 years for it to gain common acceptance. Now, it is hard to imagine the profession without it. I’m sure many orthodontists then felt the same way about cephalometrics as Dr Greco feels about CBCT.

What was the exposure of a “reduced radiation” cephalometric film in 1958? Approximately 40 μSv. Now consider the exposure of a “full” orthodontic survey at that time. Approximately 2000 μSv. What was the International Commission on Radiological Protection’s dose limit in 1950? 3000 μSv per week. The data Dr Greco used on dosage are not up to date, and he failed to mention that the higher reported values were on older CBCT units with variable settings. The Hitachi MercuRay was a combined CBCT and medical fluoroscopy unit that could be operated with as little as 5 μSv.

The American Association of Physicists in Medicine issued the following position statement in December 2011: “Risks of medical imaging at effective doses below 50,000 μSv for single procedures or 100,000 μSv for multiple procedures over short time periods are too low to be detectable and may be nonexistent.” The International Commission on Radiological Protection recommends we keep nonoccupational exposure levels less than 1000 μSv per patient per year. Additionally, the United Nations Scientific Committee on the Effects of Atomic Radiation report states that no discernible effects of exposures below 0.1 Sv (100,000 μSv) appear to exist; this is compatible with known cellular-repair mechanisms.

In 1959, Dr Steiner published the transcript of his lecture to the Angle Society in which he said, “To those of you who are not fully employing cephalometric principles in your orthodontic practice, I ask these questions: Do you really want to know what you are doing to your patients or are you afraid to find out? Do you suspect that if you did know, you might sometimes be unhappy? If you did not like what you found, would you do something about it? If the answer to these questions is no, then you do not need a cephalometer.” Needless to say, this statement could easily be applied to CBCT today.

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Apr 6, 2017 | Posted by in Orthodontics | Comments Off on Let the truth about CBCT be known
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