Inside Dental Radiology
Volume 9, Issue 4
Published by AEGIS Communications
The ALARA Principle in Practice
Techniques and technologies to minimize patients’ radiation exposure
In 2012, the American Dental Association (ADA), in collaboration with the Food and Drug Administration (FDA), released updated recommendations for the prescription of dental radiographic examinations. Dental Radiographic Examinations: Recommendations for Patient Selection and Limiting Radiation Exposure was developed to “serve in conjunction with dentists’ professional judgment on when it’s appropriate to use diagnostic imaging.”1
It is the dental healthcare provider’s responsibility to minimize patient exposure by following the ALARA Principle (as low as reasonably achievable). Examples of good radiologic practice include:
• use of the fastest image receptor compatible with the diagnostic task (digital using the lowest exposure parameters consistent with a diagnostic image, or F-speed film)
• collimation of the beam to no greater than the size of the receptor whenever feasible
• proper exposure and processing techniques
• use of appropriate radiation shielding (eg, thyroid shields and lead aprons), when appropriate
• limiting the number of images obtained to the minimum necessary to obtain essential diagnostic information2
These new guidelines detail steps that may be taken—from receptor selection to patient positioning to quality assurance—that can moderate some of the risks of radiation while maintaining the considerable diagnostic benefits. However, the final judgment—and responsibility—remains with the conscientious clinician, taking into consideration the short- and long-term health of the patient.
For a foundation on the many aspects of radiology, Jeffery Price, DDS, Associate Professor in Oral Diagnostic Sciences at University of Maryland, School of Dentistry, recommends that dentists review the NCRP Report No. 145, published by the National Council on Radiation Protection and Measurements.3 “Although it was published in 2004, Radiation Protection in Dentistry still holds true, and the recommendations from the ADA report draw on that heavily.”
The major recommendations of this report include: 1) that dentists should be collimating their beams for intraoral radiography; and 2) that they should use their professional training to assess selection of task- and patient-specific diagnostic imaging needs. “That was one of the main points of the 2012 ADA update: the updated selection criteria,” Price explains. In other words, the clinician identifies a diagnostic task or a diagnostic reason to take an radiograph, thereby decreasing patient exposure simply by individualizing when radiographs are required.
“We need to look at risk within reason by professional judgment,” says Allan Farman, BDS, Professor of Radiology and Imaging Science at the University of Louisville, School of Dentistry. “There should be no situation in which radiographs should be taken merely as routine, in which the same radiographs are taken on every patient that comes into a practice.”
The Impact of Medical Radiation
The average annual radiation exposure from natural sources in the United States is about 3.1 millisieverts (mSv)4 and no adverse health effects have been proven from these levels. Man-made sources of radiation from medical and dental sources contributed about 48% of the total annual radiation exposure, according to NCRP Report No. 160 (2006), up from only 18% at the beginning of the 1980s. Perhaps the largest of these sources of this rising exposure proportion is computed tomography (CT) scans and nuclear medicine.5
Where does dentistry fall on this scale? According to the ADA, dental radiographs on average account for approximately 2.5% of the effective dose received from medical radiographs and fluoroscopies.2
Farman breaks it down further. “For an individual periapical radiograph, you may be getting approximately 4 microsieverts (µSv) to 6 µSv; panoramic radiographs are approximately 15 µSv to 30 µSv. A CBCT is on the order of 30 µSv to 240 µSv, although it varies depending upon the machine and settings applied. Patients could maybe get as much as 150 µSv with a full-mouth intraoral survey as well.” It should be remembered that the doses for dental radiographs are received over a relatively short period of time, and concentrated in one area.6,7
Regarding dental healthcare workers, Kirt E. Simmons, DDS, Orthodontic Director at Arkansas Children’s Hospital, explains, “The staff limit in the United States is up to 50 mSv for the radiation worker. Most dental radiation workers average 2/10 of a mSv a year, which is 4/10 of the 50 mSv annual limit.”3 Of course, workers must follow strict guidelines for protection, such as standing behind protective barriers.
One of the reasons that the public, medical profession, and regulatory agencies became concerned about radiation was a 2006 National Council on Radiation Protection and Measurements (NCRP) report that showed that between the early 1980s and 2006, the amount of radiation from medical and dental sources increased on average in the population from 18% to approximately 48%.5 “So even though we’re moving over to these safer systems, people are getting a higher radiation dose, mainly because of greater use of computed tomography and nuclear medicine,” Farman says.
“If you look at the programs that have been put in place, the number of scans per population has been declining since 2006,” Simmons says. “Now, clearly that’s not because medical conditions have been declining, or the need to diagnose has decreased, but there’s been an awareness of the fact that this is ionizing radiation and it isn’t without some risks.
“The mission has been to inform the public, explain what patients need to be asking all their doctors—physician, dentist, podiatrist, chiropractor,” he adds. “Do I really need this? What kind of information is this going to provide to you?”
Maximizing Technology to Minimize Exposure
Radiographs that are taken for diagnostic purposes based upon justified professional judgment and patient selection criteria are, of course, worthwhile—and the quality of the images needs to be adequate for the purpose. “The radiation needs to be sufficient to provide radiographs; otherwise, the result could be a suboptimal diagnosis or an increase in the radiation dose by having to subsequently repeat the radiographic exposure,” Farman says.
“Because ionizing radiation is a known carcinogenic, we need to find a balance between the two situations—and we don’t always get a balance,” he explains. “The amount of radiation used in dentistry can be low with judicious use, modern techniques, the fastest speed film, or digital techniques—these can reduce the amount of radiation to a fraction of the dose amount that was necessary many years ago. In fact, I’m using a quarter of 1% of the radiation that was necessary for an individual intraoral radiograph taken 90 years ago. That’s because of changes and improvements in technology.”
In Farman’s opinion, the manufacturers have been effective at trying to bring radiation to a minimum. “It’s the practitioners’ education and use of that equipment that is sometimes faulty,” he explains. “I would suggest that practitioners should buy systems that incorporate exposure feedback, so that they get used to what is the appropriate amount of radiation to use on a patient.”
In some cases, especially in larger patients, image quality is not necessarily being taken into account or being evaluated in the quest to lower the radiation exposure. “There is a dearth of information in the scientific literature comparing dose to the diagnostic yield,” Farman says. “Unfortunately, it has come to my attention that whenever practitioners complain about image quality to various technical services, the response is often, ‘if you want to get a better image, you are going to have to increase the dose.’ Now, we have on one side the possibility of using a low dose. On the other side, practitioners need to have an image they can diagnose from. Remember, every time we increase the radiation dose by 5 kilovolts (kV), we are doubling the dose to the patient. If you move from 80kV to 90kV, you are quadrupling the dose.”
Simmons agrees that on the industry side, there’s a concerted effort to reduce the amount of radiation to patients by making more sensitive sensors and making the machines more efficient. “There are a lot of different ways of approaching this problem,” he says. “For instance, allowing the machine to expose a smaller area of the patient.”
Collimation is another recommended approach to limiting patient exposure. The new 2012 guidelines stipulate that the x-ray beam should not exceed the minimum coverage necessary, and that each dimension of the beam should be collimated so that the beam does not exceed the receptor dimensions by more than 2%.2
“Until you get used to collimation, you may have a few more retakes,” Price says. “But once you are experienced, you are reducing your patient’s exposure by almost 60%, decreasing the size of the tissue exposed to the beam.” For example, he states that using D-speed film with round collimation for a full-mouth series results in 388 µSv of radiation. “If you switch to a digital receptor, collimated to a rectangular-shaped beam, that can drop the dose to about 35 µSv. The combination of switching to a fast receptor and collimating your beams has the potential to reduce over 90% of the radiation.”
Price expects advances in technology will decrease exposure significantly. “There is new technology on the horizon that may increase the sensitivity of the receptors by 20 to 50 times more than today’s digital receptors. In 10 years, by the time it goes from laboratory research to commercial use, we may be able to decrease the radiation even more.” As an example, he mentions that most digital receptors today use an output measured in hundredths of seconds, “but in the future we may be measuring it in thousandths of seconds.”
Beyond reducing radiation, there are also advances in other diagnostic imaging options. “If you look at the CDT codes for 2013, you may notice that under Diagnostic Imaging, there are more non-ionizing radiation techniques being suggested,” Farman says. “There are now codes for ultrasounds and MRIs. As we move forward, we may find a progression of not just a reduction of dose of ionizing radiation, but also some substitution of other techniques that don’t use ionizing radiation whatsoever.”
Farman cites a number of examples. “In Germany there are studies going on with small MRI units with special sequences that are specific to dental caries and periodontal disease detection. Ultrasound is also being used, especially in conjunction with oral surgery, for looking at soft tissue changes and for guiding the taking of biopsies, especially in the United Kingdom and China. Sialoendoscopy is a technology through which one can look inside the salivary glands and at the same time do surgical procedures. There are new techniques being used that use electrical conductance or visible light for the detection of dental caries on the occlusal surface of teeth, which are difficult to evaluate using radiographs. So, yes, there is a whole host of new possibilities coming forward, and we may see an increase in use of these techniques. Of course, they don’t, at this point, replace all uses of radiation.”
Appropriate Risk-to-Benefit Ratio
According to Simmons, although there are certainly dentists who may be overusing ionizing radiation, “I think there are also dentists, from my experience, who may be underusing it because of safety concerns. Research use of radiation is very highly monitored. You have to absolutely justify the risks and the benefits to the patient and society in general. But in practice, the responsibility lies with the provider.”
While the radiation risk for any one patient may be low, as Simmons explains, the doctor is making the decision for the patient—weighing the current health benefit against future risk of cancer. “It’s important how you present this decision to the patient. What are the odds? We may not be able to completely eliminate this risk, but if we have to take the chance, how can we minimize the risk?
“My underlying concern is if taking an image is not going to change what I’m going to do for a patient, then why am I taking the image?” Simmons continues. “What am I suspicious of, and what’s the best way to access information that will confirm or deny a suspicion? That’s the clinician’s conundrum.”
The public and government entities, along with the entire medical profession, are concerned about the possibility of overradiating patients, particularly children. “There’s an age effect of radiation,” he says. “The younger you are, the more chances you take every time you are exposed. Everyone who’s involved in pediatrics right now is really pushing minimizing ionizing radiation to children, justifying every film. If you can put off some of this radiation until a later age, that’s a better option.
“Some of the children we’re treating right now are going to get cancer someday,” Simmons says. “And when that happens, if it’s one of these cancers that’s potentially linked to ionizing radiation, someone is going to look back at the number of x-rays they had as a child.”
Farman agrees. “Children have multiple times the vulnerability of adults for several reasons. First, they have a longer life ahead of them, therefore unhealthful changes can occur. And it can take decades before the effects of radiation become apparent. Second, they have a greater rate of turnover of their tissues while they are growing. As radiation damage occurs during the division of cells, they are more susceptible to it. Nevertheless, radiation-induced cancers do not differ from those arising from other causes, and proof of cause in an individual, as opposed to a large population, is not possible.”
In summary, “The ideal scenario is to take the right image, on the right patient, under the right conditions at the right time, with as low a dose as possible, to answer the question that led you to take a radiograph in the first place,” Simmons explains. “There should always be a reason why you’re taking a radiograph. What question are you trying to answer? Or are you just doing it because, well, that’s what we always do, that’s what we were taught in school. That’s not a sufficient answer.”
Informed Patients and Practitioners
As concerns about the effects of radiation permeate the consumer news and commentary, improved patient education and knowledge about lifetime dose reporting are needed to help balance the discussion. The ADA advises dentists to be prepared to discuss the benefits and risks of radiographs. To help answer patient questions about dental radiology safety, the American Academy of Oral and Maxillofacial Radiology and the Alliance for Radiation Safety in Pediatric Imaging have developed education materials targeted at parents and patients.
In addition, dental practitioners should develop and implement a radiation protection program in their offices. They should strive to remain informed on safety updates and the availability of new equipment, supplies, and techniques that could further improve the diagnostic ability of radiographs and decrease exposure.
Ultimately, the ADA notes that its guidelines are intended to serve as a resource for the practitioner and are not intended as standards of care, requirements, or regulations. Knowing the patient’s health history and vulnerability to disease, the dentist is in the best position to make a judgment in the interest of the patent.2
“The risk from radiation in dentistry is not a high risk, but if it’s an unnecessary risk, it shouldn’t be taken,” Farman notes. “And by unnecessary, I mean both extremes of the range. That is, if we need to take a radiograph, it also needs to be taken well—and that means sometimes minimizing the dose when this causes a radiograph to be suboptimal for diagnostic purposes is not the way to go. Whatever dose used must produce an image that is of value. It’s all about risk within reason.”
1. Soderlund K. ADA updates dental radiograph recommendations. ADA News. November 28, 2012. http://www.ada.org/news/7996.aspx. Accessed August 20, 2013.
2. American Dental Association Council on Scientific Affairs, U.S. Department of Health and Human Services Food and Drug Administration. Dental Radiographic Examinations: Recommendations for Patient Selection and Limiting Radiation Exposure. Revised 2012.
3. NCRP Report No. 145, Radiation Protection in Dentistry (2003). Bethesda, MD: National Council on Radiation Protection and Measurement; 2003.
4. United States Nuclear Regulatory Commission. Fact Sheet on Biological Effects of Radiation. http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/bio-effects-radiation.html. Accessed August 20, 2013.
5. NCRP Report No. 160, Ionizing Radiation Exposure of the Population of the United States. (2006). Bethesda, MD: National Council on Radiation Protection and Measurement; 2006.
6. Ludlow JB, Davies-Ludlow LE, White SC. Patient risk related to common dental radiographic examinations: The impact of 2007 International Commission on Radiological Protection recommendations regarding dose calculation. J Am Dent Assoc. 2008;139(9):1237-1243.
7. Roberts JA, Drage NA, Davies J, Thomas DW. Effective dose from cone beam CT examinations in dentistry. Br J Radiol. 2009;82(973):35-40.