January 2014, Volume 10, Issue 1
Published by AEGIS Communications
Question: Does Radiation Dose Matter?
The answer to this question is absolutely yes!
The FDA has designated x-radiation as a proven carcinogen. The currently accepted model for radiation effects is probabilistic (“stochastic”), with any increased dose assumed to increase the risks of untoward effects. This is the model we need to follow until we get better information dividing risk more precisely, perhaps according to details of the specific human genome of individuals.
We should be always looking to balance the risk of using x-radiation with the risks to the patient from not making a diagnostic image. As professionals, we should follow the principle of risk within reason. If there is no added diagnostic or treatment guidance advantage for the patient from using x-radiation, professional judgment should be that the risks, however small, outweigh the benefits. Radiographs should not be taken as a routine indiscriminately on all patients, and should not be made merely for the convenience of the practitioner when there are safer suitable alternatives. The National Council on Radiation Protection (Report No. 106)1 found that the proportion of ionizing radiation affecting the US population from medical and dental sources rose from 15% in the early 1980s to 48% in 2006, mainly due to increased use of computed tomography (CT) and nuclear medicine procedures.
The best way to minimize dose to ionizing radiation is to be selective of the images made after a thorough history and clinical inspection of the individual patient by the dentist. Secondly, there is a need to use the lowest acceptable exposure that still provides a diagnostic image for the tasks at hand. This can be achieved by proper collimation of the beam to only the regions of interest, and using optimally low exposure parameters. Digital imaging is not always lower in terms of dose than modern analog film imaging. CMOS and photostimulable phosphor plates have wide recording latitude, and without appropriate professional care, it is possible to still get a nice looking diagnostic image when exposing the patient to up to 20 times the optimally lowest dose needed to achieve diagnostic quality. The achievement of the optimally lowest dose is mainly an issue of professional training and judgment, though some manufacturers do provide feedback mechanisms that are useful for intraoral radiography employing solid-state detectors. Having stated this need to keep dose “as low as reasonably achievable” (ALARA), when an image is needed, it should be exposed adequately so that the required diagnostic information is not depleted.
There are some individuals for whom radiation dose considerations are considered especially important. This includes young children and teenagers, who have a higher cell turnover during which radiation damage can happen and also have a longer life expectancy during which ill effects can occur. For this reason, the Society of Pediatric Radiology initiated the Image Gently Alliance.2 Dental members of this Alliance include the American Dental Association (ADA), the American Academy of Oral and Maxillofacial Radiology (AAOMR), the American Association of Oral and Maxillofacial Surgery, the American Association of Pediatric Dentistry, the American Association of Endodontists, the American Association of Periodontists, and the European Academy of Dental and Maxillofacial Radiology.
The importance of minimizing radiation dose during dental procedures is further indicated by the recent decision of the National Council on Radiation Protection to completely revisit Report No. 145 on Radiation Protection in Dentistry. The Committee for this is being jointly chaired by Drs. Alan Lurie and Mel Kantor, and has representation from the FDA, the American Association of Physicists in Medicine, and the AAOMR. The new report can be expected in 2 to 3 years and will add greatly to recommendations concerning digital imaging, including cone-beam computed tomography (CBCT).
In 1946, Hermann Joseph Muller was awarded the Nobel Prize for his discovery that mutations can be induced by x-rays.3 Our more contemporary colleague, S. Jullian Gibbs, professor emeritus at Vanderbilt University, believed very much that radiation dose matters. He dedicated much of his career to the study of the biologic effects of radiation.4 Dentistry lost a valued member of the profession when Dr. Gibbs passed away last year. Research in this area must continue as our patients put their welfare in our hands when we prescribe, acquire, and utilize radiographs on their behalf.
The principle of ALARA guides all of us in dentistry.5 To properly diagnose oral conditions, it is prudent that we weigh risk to the patient as well as benefit to be derived from x-rays. There are many ways that dentists can minimize dose to patients in their practices.
Thoughtful prescription of radiographic procedures can reduce dose to patients. It is not appropriate to prescribe a full-mouth series to every new patient entering a practice. A diligent effort should be made to obtain prior imaging.5 Disease progression and healing can be evaluated by comparing previous x-rays to current ones. Often patients cannot recall exactly what or when treatment transpired in the past, and radiographs can tell a story when the patient falters.
Offices using film can reduce radiation to their patients by using F-speed film. This film uses about 75% the exposure of E-speed film and only about 40% of that of D-speed.5 The use of digital sensors further reduces exposure to patients by 40% to 60%.6 It is important to use a sensor of good quality. Many practitioners attempt to improve digital image quality by increasing exposure time, which results in increased dose to the patient.
Proper use of a thyroid collar protects the thyroid and parathyroid glands. It should fit snugly against the neck if it is to be effective. It is especially important when treating children, whose dose should be limited to 10% of that of adults.5 Leaded aprons should be used routinely for all patients whenever possible.
Rectangular collimation is a powerful yet vastly underused method of reducing exposure to patients. Dose can be reduced up to five-fold as compared with a circular collimator.5 There is a bit of a learning curve involved with its use, but when you use rectangular collimation effectively, you can look your patients in the eye and can tell them that you are doing everything in your power to reduce radiation on their behalf, and they will appreciate it. Furthermore, image quality is enhanced by reducing scatter and fogging.
Positioning devices are not only for novice practitioners. Using them minimizes retakes and improves image quality.
A very helpful document produced by the ADA last year guides the Radiology Department here at University of the Pacific. It is called “Dental Radiographic Examinations: Recommendations for Patient Selection and Limiting Radiation Exposure.” This publication can be accessed online at no cost. Reviewing these guidelines may be more convincing to you than my words in finding ways of reducing radiation to your patients in your practices.
There has been considerable and steadily increasing public and professional interest in controlling the radiation doses in diagnostic imaging during the past 5 years. This is due in large part to the reports of substantial increases in population radiation doses from diagnostic radiology exposures, especially those associated with CT and nuclear medicine studies.7-9 Diagnostic radiology now accounts for more than half of the annual population radiation dose, and dental radiation exposures, for the first time, are separated from medical and occupy their own identified component to the population exposure.
In the recently published SEDENTEXCT Project,10 the increased radiation risk, almost entirely cancer induction, was cited at three times greater than adults for children younger than 10 years and two times greater than adults for children aged 10 to 20 years. This is due to the increased proliferative activity of cells in children, the greater number of less differentiated cells in children, and the longer projected lifespan of children. Tissues at particular risk in dental imaging are the thyroid gland, parotid gland, and bone marrow, which comprise 58% of the effective dose in CBCT examinations.11 This increased sensitivity to radiation induction of cancer becomes especially important when large field-of-view CBCT examinations are used on children without a clearly demonstrated clinical need and benefit to the outcome. The ALARA Principle should always be applied to imaging of any individual, but especially children.6,12
The Image Gently Alliance strongly promotes safe, effective and patient-centered imaging for children.2 As mentioned above, the ADA, AAOMR and four other specialties of dentistry have formally joined the Image Gently Alliance and are preparing materials for the dental section of the website directed to parents, radiologists, referring doctors and staff. As clearly stated on the Image Gently website, one size does not fit all; the techniques we use to image adults and the risk associated with that imaging are not at all the same for children. We need to “child-size” our radiation exposures, we need to maintain professional competency in performing and interpreting imaging studies, and we need to image appropriately according to the clinical condition we are treating.
1. Ionizing radiation exposure of the population of the United States. National Council on Radiation Protection. www.ncrponline.org/PDFs/2012/DAS_DDM2_Athens_4-2012.pdf. Accessed September 15, 2013.
2. Image Gently website. www.pedrad.org/associations/5364/ig. Accessed September 15, 2013.
3. Hermann J. Muller – biographical. Nobelprize.org website. www.nobelprize.org/nobel_prizes/medicine/laureates/1946/muller-bio.html. Accessed September 15, 2013.
4. Vanderbilt mourns loss of imaging pioneer Gibbs. Vanderbilt University Medical Center Reporter website. http://news.vanderbilt.edu/2012/11/vanderbilt-mourns-loss-of-imaging-pioneer-gibbs. Accessed October 1, 2013.
5. White SC, Pharoah MJ . Oral Radiology: Principles and Interpretation. 6th ed. St. Louis, MO: Mosby; 2008:36-39, 225-243.
6. American Dental Association and U.S. Department of Health and Human Services. The selection of patients for dental radiographic examinations. U.S. Food and Drug Administration website. www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/MedicalX-Rays/ucm116504.htm. November 28, 2012. Accessed November 11, 2013.
7. Mettler FA, Bhargavan M, Faulkner K, et al. Radiologic and nuclear medicine studies in the United States and worldwide: frequency, radiation dose, and comparison with other radiation sources – 1950-2007 . Radiology. 2009;253(2):520-531.
8. United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and effects of ionizing radiation . Medical radiation exposures, annex A. 2008 Report to the General Assembly with annexes. New York, NY: United Nations; 2010.
9. U.S. Food and Drug Administration. Nationwide Evaluation of X-Ray Trends (NEXT). Rockville, MD: Center for Devices and Radiological Health, U.S. Food and Drug Administration; 2003.
10. SEDENTEXCT Project, European Commission. Radiation Protection No 172. Cone Beam CT for dental and maxillofacial radiology (evidence-based guidelines). Luxembourg, 2012.
11. Pauwels R, Beinsberger J, Collaert B, et al. Effective dose range for dental cone beam computed tomography scanners . Eur J Radiol. 2012;81(2):267-271.
12. American Academy of Oral and Maxillofacial Radiology. Clinical recommendations regarding use of cone beam computed tomography in orthodontics. Position statement by the American Academy of Oral and Maxillofacial Radiology . Oral Surg Oral Med Oral Pathol Oral Radiol. 2013;116(2):238-257.
About the Authors
Allan G. Farman, BDS, PhD, DSc, is professor of radiology and imaging science in the department of surgical and hospital dentistry at the University of Louisville in Louisville, Kentucky.
Lola Giusti, DDS, is associate professor of dental practice and coordinator of radiology clinical services at the University of the Pacific’s Arthur A. Dugoni School of Dentistry in San Francisco, California.
Alan G. Lurie, DDS, PhD, is professor in the department of oral health and diagnostic sciences, chair of the division of oral and maxillofacial diagnostic sciences and chair of the section of oral and maxillofacial radiology at the University of Connecticut School of Dental Medicine in Farmington, Connecticut. He is also immediate past president of the American Academy of Oral and Maxillofacial Radiology.