Address you patients' concerns... Are they necessary? Yes. Are they safe? They can be safer.
Well, it’s official - Dr. Oz has spoken! On September 28, 2010, this well-known physician suggested the use of thyroid collars and protective leaded aprons to reduce a patient's x-ray exposure to the thyroid gland. Actually, the statement was both appropriate and timely. It has caused tremendous discussion among both medical and dental professions and among consumers.
Rectangular collimation
Interestingly, as pointed out in the “Issues Alert” bulletin from the American Dental Association on April 6, 2011, the ADA already “strongly recommends” this strategy for “children, women of childbearing age and pregnant women who are especially susceptible to radiation effects”. This position is also endorsed by the AAOMR (American Academy of Oral and Maxillofacial Radiology). Not only has our radiology specialty been saying this for years, but we've been teaching this for over 30 years in all North American dental schools. Why then, is there such resistance to the adoption of “rectangular collimation”? Well, my colleagues, it’s like the comic strip character Pogo said:
“We have met the enemy and he is us”.
Most dentists are convinced (as well as some dental auxiliaries) that, because of their experience and dental schools, you cannot “hit” the x-ray receptor target - whether film phosphor plate or solid state detector - with anything less than a large round cone. This is not only false, but silly as well...because there is technology available today that allows the easy adoption of rectangular collimation for use on all existing dental x-ray tube heads.
By retrofitting an existing x-ray generator with one such device called Tru-Align, you can reduce excess surface radiation to the patient by as much as 98%. And, you can do this without much fuss, training or expense. The diagram below illustrates the use of a rectangular collimation device which is only 2% larger than the actual image receptor.
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| Figure 1a. The yellow area represents the area of exposure to the patient using a round cone. The green shaded area represents the area exposed using a rectangular collimating device like the Tru-Align, seen in Figure 1b. |
By fixing the receptor to the rectangular collimator, almost all “retakes” due to missing the image receptor are eliminated—easily and effectively. In addition, linking the receptor to the dental x-ray tube head forces perfect parallelism. This results in the elimination of any missionaries and distortion (which also reduce image quality and can lead to additional “retakes”).1
In the RSNA (Radiology Society of North America), teaching files -as posted by the State University of New York - collimation of the x-ray beam to the receptor is beneficial to the patient and the clinician because:
“X-ray beam collimation for radiography and fluoroscopy projection imaging is important for patient dose and image quality reasons. Actively collimating to the volume of interest reduces the overall integral dose to the patient and thus minimizes the radiation risk. Less volume irradiated will result in less x-ray scatter incident on the detector. This results in improved subject contrast and image quality.”2
To summarize then, rectangular collimation of any "flavor":
- reduces patient dose
- reduces or eliminates retakes
- cleans up scatter to the receptor, thus
- improving image quality
Does anyone see a downside to the adoption of rectangular collimation?
Are dental X-rays safe?
The short answer is “Yes”, but not absolutely. Any x-ray exposure carries with it some risk. All medical and dental professionals should weigh the benefits of an x-ray procedure, no matter what the modality, against the risk of x-ray exposure dose to the patient. This too, we’ve been teaching for decades. As low as our dental x-ray doses to the patient are, the risk of inducing a cancer in a patient is cited as "one in 1 million". The citation however, is for one FMX (full mouth x-ray) series or CMS (complete mouth series), most often 18 to 20 images, taken with conventional dental x-ray films.
Many in our profession have moved beyond film as their primary dental x-ray receptor. Unfortunately, not all professionals have moved to solid state detector imaging. Even those who have adopted phosphor plate technology, use exposure times which are less than film but still much greater than CCD or CMOS receptors. So, as a profession we have moved towards the fastest receptors possible eliminating much of the x-ray dose. However, most of our profession has not adopted the rectangular collimation for use with these faster receptors. This is like buying a Lamborghini with a two-stroke "Smart Car" engine. We haven’t gone far enough because we can’t go fast enough.
The dose from a digital intraoral receptor is about 0.005 mSv. This is very low. By comparison, a chest film is 0.1 mSv and a CT examination of the chest is 7.0 mSv. Mammography at 0.4 mSv is considered “very low”, the equivalent of 7 weeks of background radiation - estimated at 3.0mSv/year3. So our profession is doing very well!
However, we dentists perform multiple x-ray procedures at multiple times over a patient’s lifetime. And, although x-ray dose itself is not cumulative, any damaging effects suffered at the time of exposure are. We must do our best to reduce our x-ray exposure doses to our patients to as little as possible. This is the concept behind the “Selection Criteria”4 developed by both the FDA and members of our profession. These selection criteria give us recommendations for the number, type and frequency of our x-ray procedures for patients. They are based on a thorough examination and history of our patient PRIOR to ordering any diagnostic test referred to as an “x-ray”.
Are dental X-rays necessary?
No prudent dental clinician would consider performing a surgical procedure, something as simple as a cavity preparation, without x-ray information to help them characterize the disease process and make an informed clinical decision. In most cases, our profession does a good job of determining what dental, panoramic, and now even cone beam x-ray procedures are necessary for patients. Again, these selection criteria published by the FDA, the ADA and our radiology specialty in several journal publications are available to give the clinician guidelines for the safe use of x-ray radiation. The first publication of these selection criteria was actually in the Journal of the American Dental Association in 19885. However, like collimation, these guidelines have largely been ignored.
So yes, most dental x-rays performed by our profession are necessary. What we need to do better is use the publish selection criteria for ordering our images and use the most contemporary radiologic devices such as solid-state detectors and x-ray collimation to ensure that we move forward in step with the concept of ALARA - As Low As Reasonably Achievable. Rectangular collimation, although a seemingly small step will indeed result in a huge reduction of x-ray exposure dose to the patient. Now that it has been made simple, economical and widely available, there is simply no valid reason for not employing it in our dental practices. The ADA, the FDA and many specialty organizations in dentistry recommend it. Our patients will begin to demand it, especially in light of all the recent concerns raised in the journalistic media.
Why not jump on the bandwagon now, accept the inevitable, and "do the right thing" in your practice? You can even market your new "radiation hygiene" to your patients, on your website and in your marketing materials.
The Bottom Line
Now that I have made the argument based on reduction of patient x-ray dose by the use of selection criteria and the rectangular collimation, let’s make the argument based on ROI (return on investment). For the radiologist reading this article, yes I know, ROI in our paradigm means “region of interest”. But for clinical colleagues these two uses of the acronym ROI are not mutually exclusive - nor should it be.
Dentists delegate x-ray procedures for almost all patients that walk through the doors of their office. New patient examinations, re-care examinations, orthodontic examinations emergency examinations, growth and development examinations, pain evaluation, TMJ evaluation, paranasal sinus evaluation, airway analysis, and pre-surgical evaluation of third molars for possible extraction are just some of the ways that dentists and dental specialists must evaluate their patients. I’m a radiologist. I am not saying take these x-ray examinations to make money. IT JUST HAPPENS! The x-ray procedure has the biggest “margin” of any procedure performed in the dental office. You don’t do a crown every day or an implant, but you do order radiographs!
Even with the use of selection criteria to minimize the number of x-rays taken, the average clinician will generate substantial revenue from their x-ray procedures. If you don’t believe me just use your practice management software for producing a “productivity report”. Instead of generating a generic report, only query your software for productivity related to the procedures for radiographs - all the CDT codes in the “2” series. If you run this report for six months you will be shocked to see the income generated. Your shock will be translated into the absolute need to purchase and use the best equipment available, the fastest receptors available, and will justify your move to a total digital x-ray environment. Clinicians who I have directed to perform this procedure has been both rewarded and motivated to contemporize their x-ray procedures and devices. Those who have been resistant to leaving film behind have happily made the move and suffered no regret.
Summary
Compared to daily risks we take, x-rays are safe. After clinical and historical examination of the patient the majority of x-rays are necessary. The clinician must take all steps possible to reduce x-ray exposure dose to his or her patient. Selection criteria and contemporary devices such as the ones that incorporate rectangular collimation, simply an economically are the best way to improve your practice, allay your patients’ fears and doubts about x-ray exposures and increase the “bottom line” of your practice. Again, where's the downside? And, what are you waiting for?
References:
- Miles DA, Van Dis ML, Williamson G and Jensen C: Radiographic Imaging for Dental Auxiliaries. WB Saunders Co., Philadelphia, PA (Fourth Edition, October, 2008).
- Collimation Effects: http://www.upstate.edu/radiology/rsna/fluoro/collimation/
- Radiation Exposure in X-ray and CT Examinations. http://www.radiologyinfo.org/en/safety/index.cfm?pg=sfty_xray
- American Dental Association Council on Scientific Affairs The use of dental radiographs Update and recommendations. J Am Dent Assoc, Vol 137, No 9, 1304-1312.
- Council on Dental Materials, Instruments, and Equipment. Recommendations in radiographic practices: an update, 1988. J Am Dent Assoc. 1989;118:115-117.
Disclaimer: Dr. Miles is one of the founders of Interactive Diagnostic Imaging.