INTRODUCTION
In October, we published a report outlining the potential impact of the National Council on Radiation Protection’s new guidelines, as detailed in the NCRP’s Report #145 and published in Dentistry Today.1 In this article, we identify a simple, economical approach and product that will help dentists conform to some of these guidelines. Readers are invited to refer to the article cited above for even more details.
The NCRP “…is a nonprofit corporation chartered by Congress in 1964 to:
- Collect, analyze, develop, and disseminate in the public interest, information and recommendations about (a) protection against radiation and (b) radiation measurements, quantities, and units, particularly those concerned with radiation protection.
- Provide a means by which organizations concerned with the scientific and related aspects of radiation protection and of radiation quantities, units, and measurements may cooperate for effective utilization of their combined resources, and to stimulate the work of such organizations.
- Develop basic concepts about radiation quantities, units and measurements, about the application of these concepts, and about radiation protection.
- Cooperate with the International Commission on Radiological Protection Units and Measurements, and other national and international organizations, governmental and private, concerned with radiation quantities, units, and measurements and with radiation protection.”
This agency is charged with periodically assessing new technology and the practices of radiation safety to make recommendations about radiological practices based on available scientific data. These recommendations are usually adopted by educational institutions and government agencies first, and then by education into the end user’s clinical practice. This report, #145, and amends the initial report for dentistry, #35, published in 1970.
1. LEAD APRONS
Among the changes cited in this report, are new recommendations to dramatically change the use of leaded aprons and thyroid collars, mandate the use of rectangular collimation for X-ray generators, and mandate the use of “selection criteria”; that is, how a dentist must “prescribe” radiographs.
All dentists continue to strive to minimize X-ray doses to their patients. We protect our patients by using faster and faster image receptors and digital systems, and by collimating our X-ray beams to as small a skin surface area as possible (more on this later). To this end, we have been protecting our patients with lead aprons and thyroid collars.
Let’s discuss some of the changes regarding the use of leaded aprons. The report states:
“The use of leaded aprons on patients shall not be required if all other recommendations in this Report are rigorously followed.”
“Thyroid shielding shall be provided for children…” and for adults, the recommendation states: “… and should be provided for adults, when it will not interfere with the examination.”
It appears that this recommendation asserts that the thyroid collar should NOT be used for extraoral procedures on children or adults such as panoramic and cephalometric X-ray image acquisition. This is a major departure from the current standard, but will be welcomed by the profession.
2. X-RAY COLLIMATION CHANGES
Collimating the X-ray beam to the precise size of the image receptor eliminates scatter radiation. Most vendors produce large,DENTRIX round cones with large X-ray beam patterns so the operator “cannot miss” the film or receptor. This not only adds scatter radiation, reducing image quality, but also adds significantly to the patient’s X-ray dosage. Scatter radiation to any receptor—film, sensor, or phosphor plate dramatically reduces image quality. The new report mandates the use of a rectangular collimator. This is actually GOOD news for image quality, but may make assistants shudder because of the smaller area of the beam. They might think that they will produce more errors such as “cone cuts” and “missed apices.” And they might. However, help is on the way!
Dentists and their auxiliaries will have to use a rectangular collimator of the precise size of the image receptor. This will improve the images taken by reducing scatter radiation. This collimation also reduces the patient’s skin surface X-ray dosage by almost 60%, simply because the beam size is so much smaller—but “Where’s the help?”
The NCRP report #145 states: “Rectangular collimation of the beam shall be used routinely for periapical radiography. Each dimension of the beam, measured in the plane of the image receptor should not exceed the dimension of the image receptor by more than 2% of the source-to-image receptor distance. Similar collimation shall be used, when feasible, for interproximal (bitewing) radiography.”
3. NEW COLLIMATION DEVICES
“HELP IS HERE!” The newest of these simple, efficient improvement devices is a unique, retrofitable collimator called Tru-Image™ from a company called Interactive Diagnostic Imaging (IDI) that will improve your office procedures and your office productivity while reducing your patient’s radiation burden and improving image quality.
Tru-Image™ attaches to your existing X-ray machine to further collimate the beam size more precisely to the image receptor. The advantages of collimating the beam to the size of the receptor includes:
- Less patient dosage
- Reduced X-ray scatter
- Improved image quality
In addition to these direct benefits, the routine use of rectangular collimation, provided that the image receptor is directly fixed to the collimating device, is increased office productivity, since the number of “retakes” due to errors of angulation will be minimized or even eliminated in most offices. This leads to quicker image availability and faster decision-making and treatment with improved efficiency.
And, if devices such as Tru-Image™ are coupled with solid state detectors like CCDs or CMOS receptors, the time savings and office productivity will be greatly improved. This could have tremendous economic implications in the dental office.
How does rectangular collimation impact on my current intraoral X-ray equipment?
There is certainly no reason to consider buying a whole new X-ray machine(s). Here there are two factors to consider:
- The need to collimate the beam to about the size of the film or receptor/sensor.
- Some means must be available to aim and align the beam, as “point-and-shoot” techniques will most likely result in alignment errors and most certainly “cone cuts.”
Devices such as the Rinn XCP® position-indicating instruments are readily available for this purpose.
Are there additional methods to convert my existing intraoral X-ray machines?
To convert existing X-ray machines there are three basic methods in addition to TruImage™:
- The use of a position-indicating device with the round cone that collimates the beam at the skin surface. This device is made of metal and is called the Masel Positioning Instrument.
- A round cone can be converted to rectangular collimation by slipping a collimator on the end of the round cone. The collimator SAuItDumn 2005E itself will rotate at its base in order to properly align the now rectangular beam with the film/sensor. Such a device is available from the Rinn Company.
- The use of a rectangular cone or BID. This cone must also rotate at its base where it attaches to the tube head in order to align the rectangular beam with the film/sensor. Rectangular cones designed to adapt to most models of X-ray machines even those 25 and 30 years old are available from the Margraf Company. Margraf is also the manufacturer of TruImage™ for IDI.
How does this affect current intraoral X-ray exposure techniques?
Collimating the X-ray beam does not alter the exposure times for a given film or sensor type. It does however require the use of a film-holding and beam alignment device.
Are film holder-beam indicating devices needed?
Yes.
Is rectangular collimation the same for film-based and digital intraoral systems?
Yes. However practitioners will need to be certain the position indicating device bite block can accommodate the digital sensor. For example Photostimulable Phosphor Plates (PSPs) are extremely susceptible to scratching with routine placement into the bite block. Electronic sensors with a wire such as the Charge Coupled Device (CCD) or Complimentary Metal Oxide Sensor (CMOS) all have varying thicknesses and slight differences in size so the bite block must be designed to accommodate the specific sensor and the wire. Wireless sensors are a little bulkier thus a specific holder will be needed.
What sources are available for rectangular collimation conversion devices?
- Masel film holder & positioning device
- Rinn Rectangular collimator
- Margraf rectangular cone
- IDI TruImage™
What are the costs of conversion to rectangular collimation?
Approximately $100–$300
So, with all those options, this is the ultimate “win-win” situation for the dentist, staff, and patient; that is, reduced X-ray dosage, improved office efficiency, and the best image quality achievable. Why wouldn’t every practicing dentist adopt this remarkable technology?
4. IMAGE RECEPTORS AND COLLIMATION
Dentists will need to consider using the faster E- or F-speed films. Dentists will probably have to adopt F-speed film since the largest film manufacturer, Eastman Kodak, discontinued its manufacture of E-speed film after December 2001. Of course, other film manufacturers still make speed Group E-type film. The report states:
“Image receptors of speeds slower than ANSI speed Group E films shall not be used for intraoral radiography. Faster receptors should be evaluated and adopted if found acceptable.”
This is actually very good news. The faster image receptors are more sensitive to scatter radiation, so the use of a collimator to restrict the beam to precisely the size of the receptor will greatly improve image quality—something every dentist wants and needs! The adoption of the new rectangular collimators will be easy. They can be made to fit all existing X-ray machines, so that the purchase of a new X-ray will not be required in most cases. This change will be simple, useful, and economic.
5. EXTRAORAL X-RAY PROCEDURES
For panoramic and cephalometric imaging slow-speed blue fluorescing calcium tungstate screens will no longer be recommended. The report states:
“The fastest imaging system consistent with the imaging task shall be used for all extraoral dental radiographic projections. High speed (400 or greater) rare earth screen-film systems or digital imaging systems of equivalent or greater speed shall be used.”
Dentists can convert panoramic and cephalometric cassettes by simply removing the old screens and replacing them with the new screens. Also, the new screens will need to be matched to a compatible film such as green sensitive “T-Mat G” film. Although the above recommendation is not very specific about digital receptors, the mere mention of “digital image receptors” by the NCRP may prompt the practitioner to consider the purchase of a new factory-equipped digital panoramic or “pan-ceph” machine.
6. “SELECTION CRITERIA”
Dentists must examine their patient BEFORE ordering or prescribing X-ray images whether or not they are film, phosphor plate, or solid-state images. Actually, this is NOT new. Guidelines about this had been published several years earlier and adopted by the American Dental Association.
The report states also states, “Radiographic examination shall be performed only when indicated by patient history, physical examination by the dentist, or laboratory findings.”
The report goes on to define the difference between a symptomatic patient and an asymptomatic patient, “For symptomatic patients, radiographic examination shall be limited to hose images required for diagnosis and planned treatment (local or comprehensive) of current disease”… “For asymptomatic patients, the extent of radiographic examination of new patients, and the frequency and extent for return patients, shall adhere to published selection criteria.” Note: the published selection criteria are included in the report.
7. OTHER PERTINENT RECOMMENDATIONS
Additional recommendations relate to eliminating “pointed cones” and using only “open-ended cones” as well as restricting the source-to-image distance to a minimum of 20 cm (approximately 8 inches, 1 inch = 2.54 cm). Adopting a rectangular beam device will eliminate this potential problem.
8. YOUR OFFICE RADIATION PROTECTION PROGRAM, INCLUDING RADIATION SAFETY TRAINING OF STAFF
This section will have a significant impact on the way you perform radiographic procedures, including image processing. If you are using conventional X-ray film image processing, you may consider switching to digital imaging since switching largely eliminates all of the steps necessary to meet these new recommendations when using film.
The “shall” statements/recommendations include:
- Having a written quality assurance protocol (manual)
- Having your equipment inspected by a qualified expert
- Evaluating your chemistry daily
- Evaluating each type of film used monthly for fog or artifacts
- Inspecting screen-film cassettes after any accident for integrity and performance
- Repairing any defect(s) found
- Evaluating your darkroom monthly for leaks; or after any changes made to filters, lamps, etc.
- Visually inspecting leaded aprons monthly
- Providing training to all X-ray personnel in radiation protection that is sufficient to ensure they understand the recommendations made in the NCRP report.
CONCLUSIONS
This report will be received with mixed emotions in our profession. And, it is clear that the recommendations will make a considerable, positive impact on X-ray practices in dental offices. You must reexamine your X-ray procedures, equipment, and receptor selections to ensure that you are within these new national standards. You will need to examine each patient personally to determine their precise radiographic needs using “selection criteria.” You will need to purchase devices to permit rectangular collimation. Finally, you may need to reconsider adopting digital imaging systems and receptors to avoid some fairly dramatic changes related to a film-based radiation protection program. We all will be practicing better dentistry and reducing our patients’ X-ray dosage even further—AND THAT’S A GOOD THING! We hope this article helps make your decisions to adopt these changes easier.
References
1. Miles DA and Langlais RP: NCRP Report #145 New Dental X-Ray Guidelines: Their Potential Impact on Your Dental Practice, Dentistry Today 2004; 23(9):128, 2004.
2. National Council on Radiation Protection and Measurements. Dental X-ray Protection. Bethesda, MD: NCRP; 1970. NCRP Report No.35.
3. Joseph LP. The selection of patients for x-ray examinations. Rockville, MD. The Dental Radiographic selection Criteria Panel, Centers for Devices and Radiological Health; 1987. HHS Publication No. FDA 88-8273.
4. Matteson SR, Joseph LP, Bottomley W et al. The report to the panel to develop radiographic selection criteria for dental patients. Gen Dent, 1991; 264-270.