Safety and Protection in Oral Radiology PDF

CHAPTER Safety and Protection...

CHAPTER Safety and Protection 3 m OUTLINE o Sources of Radiation Exposure Patient Exposure Continuing Education t.c Background Radiation Estimating Risk Talking with your Patient Medical Exposure Reducing Dental Exposure Consumer Products Patient Selection Criteria Other Sources Conducting the Examination po Dose Limits Exposures and Risk Protecting Personnel Dose Limits Quality Assurance D gs entists must be prepared to discuss intelligently with interactions of primary space radiation with the earth’s atmo- patients the benefits and possible hazards involved with sphere. Exposure from space radiation is primarily a function of lo the use of x rays and to describe the steps taken to reduce altitude, almost doubling with each 2000-m increase in elevation these hazards. This chapter considers sources of exposure, estimates because less atmosphere is present to attenuate the radiation. At of risks from dental radiography, and means to minimize exposure sea level, the exposure from space radiation is about 0.33 mSv/y; y.b from dental examinations. at an elevation of 1600 m (approximately 1 mile, the elevation of Denver, Colorado), it is about 0.50 mSv/y. Space radiation con- SOURCES OF RADIATION EXPOSURE tributes about 11% of background exposure. The general population is exposed to radiation primarily from Internal Radionuclides r natural background and medical sources (Table 3-1). Understand- Another source of background radiation is radionuclides that are ing these exposure sources provides a useful framework for consid- ingested. The greatest internal exposure comes from foods contain- ra ering dental exposure. ing uranium and thorium and their decay products, primarily potassium 40 but also rubidium 87, carbon 14, tritium, and others. BACKGROUND RADIATION The total exposure from ingestion contributes about 9% of back- llib All life on earth has evolved in a continuous exposure to natural ground exposure. background radiation (Fig. 3-1; see Table 3-1). Background radia- tion from space and various terrestrial sources yields an average Terrestrial Radiation annual effective dose of about 3.1 mSv in the United States. The final source of background radiation comes from exposure from radioactive nuclides in the soil, primarily potassium 40 and a Radon and Its Progeny the radioactive decay products of uranium 238 and thorium 232. Radon is a gas (radon 222) released from the ground that enters Most of the γ radiation from these sources comes from the top nt homes and buildings. By itself, radon does little harm, but it 20 cm of soil. Indoor exposure from radionuclides is close to the decays, releasing α particles, to polonium 218 and lead 214. These exposure occurring outdoors because the shielding provided by isotopes decay further, emitting more α particles. Radon and its structural materials balances the exposure from radioactive nuclides decay products may become attached to dust particles that can contained within these shielding materials. Terrestrial exposure de be inhaled and deposited on the bronchial epithelium in the contributes approximately 7% of background exposure. respiratory tract. Radon is estimated to be responsible for approxi- mately 73% of the background exposure of the world’s population. MEDICAL EXPOSURE Exposure to this quantity of radiation may cause 10,000 to 20,000 Humans have contributed many additional sources of radiation to lung cancer deaths per year in the United States, mostly in the environment (Fig. 3-2). The largest of these sources is medical smokers. imaging, with much smaller contributions from consumer pro­ ducts and other minor sources. Space Radiation Approximately 400 million x-ray examinations are performed Radiation from space comes from the sun or from cosmic rays. annually in the United States; about one quarter of these are It is composed primarily of protons, helium nuclei, and nuclei dental. More recent estimates suggest that medical exposure of heavier elements as well as other particles generated by the in developed countries has grown rapidly in recent decades, 29 30 PART I Foundations Consumer products TABLE 3-1 Average Annual Effective Dose and other Dental of Ionizing Radiation 4% 0.26% Conventional radiography and fluoroscopy Source Dose (mSv) 10% Natural background Interventional Radon 2.3 CT 47% radiography Space 0.3 and fluoroscopy Internal radionuclides 0.3 Nuclear 14% m Terrestrial 0.2 medicine 25% Subtotal background 3.1 Medical o CT 1.5 Nuclear medicine 0.8 t.c Medical, consumer products and other Interventional fluoroscopy 0.4 3.1 mSv/yr Conventional radiography and fluoroscopy 0.3 Dental 0.007 FIGURE 3-2 Sources of radiation in the United States from medical examinations and Subtotal medical 3.0 consumer products. The average person in the United States receives about as much radiation po from medical and consumer products sources (3.0 mSv/y) as from natural background expo- Consumer products and other 0.1 sure. Most medical x-ray exposures come from CT, nuclear medicine (primarily cardiac imaging), Grand total 6.2 fluoroscopy, and conventional radiography. Exposures from dental examinations and from occupational, fallout, and nuclear power sources are small. Although individuals with exposures Data from National Council on Radiation Protection and Measurements: Ionizing radiation exposure of from natural background are fairly evenly distributed in the population, most medically exposed gs the population of the United States, NCRP Report 160, Bethesda, MD, 2009, National Council on individuals are relatively old and sick. Radiation Protection and Measurements. Terrestrial Internal exposure from cigarette smoking, building materials, air travel, 7% radionuclides 9% lo mining and agriculture, and combustion of fossil fuels. As more people travel frequently above the protection of the earth’s atmo- sphere, cosmic radiation becomes a more significant contributor y.b Space to exposure. An airline flight of 5 hours in the middle latitudes at 11% an altitude of 12 km may result in an exposure of about 25 µSv. Radon Other minor sources of exposure from consumer products include 73% dental porcelain, television receivers, and smoke alarms. In total, consumer products contribute only about 1.6% of the total average r annual exposure. ra OTHER SOURCES Background Other sources of exposure affect caregivers or others in contact 3.1 mSv/yr with patients receiving nuclear medicine treatments; people who llib FIGURE 3-1 Natural background radiation contributes 3.1 mSv on average per year. Most work in nuclear power generation; individuals involved in areas of exposure comes from radon, but there are significant contributions from space, ingested radio- industrial, medical, educational, or research activities; workers in nuclides, and terrestrial sources including external radionuclides in the soil and building materials. medical and dental x-ray facilities; workers in airport inspection (Data from National Council on Radiation Protection and Measurements: Ionizing radiation systems; and commercial pilots. All these sources of radiation exposure of the population of the United States, NCRP Report 160, Bethesda, MD, 2009, combined contribute only about 0.1% of the total average annual a National Council on Radiation Protection and Measurements.) exposure. nt particularly computed tomography (CT) of the chest and abdomen DOSE LIMITS, EXPOSURES, AND RISK and increased use of cardiac nuclear medicine studies. The average This section considers governmental dose limits for individuals doses from medical exposures are comparable to natural back- who are occupationally exposed to radiation and for members of de ground exposure. CT (see Chapter 14) contributes more than the general population. It also covers the amounts of radiation half of medical exposure. In contrast to background radiation received by patients in dental and medical radiography and the exposures, which affect everyone relatively uniformly, the distri- estimated risks from these exposures. bution of medical exposures is highly skewed with older and sicker individuals receiving most medical exposures. Dental x-ray DOSE LIMITS examinations, although made relatively frequently, are responsible Recognition of the harmful effects of radiation and the risks for only 0.26% of the total exposure from medical imaging. involved with its use led the International Commission on Radio- logical Protection (ICRP) to establish guidelines for limitations on CONSUMER PRODUCTS the amount of radiation received by both occupationally exposed Consumer products contain some of the most interesting and individuals and the public (Table 3-2). These limits pertain to unsuspected sources. This group includes, in order of importance, planned exposure situations, not to background radiation and not  C H A P T E R 3 Safety and Protection 31 radiography. These standards require that most users of D-speed TABLE 3-2 International Commission film convert to E/F-speed film or a digital system. Multiple on Radiological Protection means to minimize unnecessary patient and operator exposure Recommended Dose Limits are described next. for Human Exposure to PATIENT EXPOSURE Ionizing Radiation Patient dose from dental radiography is usually reported as effec- tive dose, a measure of the amount of radiation received by various Type of Limit Occupational Public radiosensitive organs during the radiographic examination. Table m Effective dose 20 mSv per year, averaged over 1 mSv in a year 3-3 shows typical effective doses from common dental intraoral, defined periods of 5 years with a extraoral, and medical examinations. The equivalent exposure in maximum of 50 mSv in any one year terms of days of natural background radiation is shown. Dental exposures are a small fraction of the annual average background o Annual equivalent dose to exposure. Lens of eye 20 mSv, averaged over defined periods 15 mSv t.c of 5 years with a maximum of ESTIMATING RISK 50 mSv in any one year The primary risk from dental radiography is the unlikely chance Skin 500 mSv 50 mSv of radiation-induced cancer. Cancer is a common disease, affecting Hands and feet 500 mSv — about 40% of people at some time during their lives and account- po Data from the 2007 recommendations of the International Commission on Radiological Protection. ing for about 20% of all deaths. There is an extensive body of IRCP Publication 103, Ann ICRP 37:1-332, 2007; and ICRP Statement on Tissue Reactions, ICRP literature linking relatively large exposures of radiation to cancer ref 4825-3093-1464, 2011: http://www.icrp.org/docs/icrp%20statement%20on%20tissue%20 formation (both solid tumors and leukemias) in humans and reactions.pdf. research animals. Human epidemiologic studies include individu- gs als exposed as survivors of the atomic bombings in Hiroshima and Nagasaki, in the course of diagnostic radiology, through multiple fluoroscopies or radiation therapy, occupationally or environmen- to emergency situations. Since their establishment in the 1930s, tally. However, there is great uncertainty regarding the risk from these dose limits have been revised downward several times reflect- lo low-dose diagnostic procedures. Analysis of this literature has led ing increased knowledge concerning the harmful effects of radia- to the development of the linear nonthreshold (LNT) hypothesis tion and the increased ability to use radiation more efficiently. (Fig. 3-3). This hypothesis holds that there is a linear relationship y.b Occupationally exposed individuals include dentists and their between dose and the risk of inducing a new cancer, even at very staffs. Individuals in the reception area or who are walking in a low doses. In this hypothesis, there is no threshold or “safe dose” corridor outside a dental office are members of the public. Dose below which there is no added risk. limits for members of the public—individuals not exposed The LNT is a hypothesis that has been accepted widely for occupationally—are generally set at 10% of occupationally exposed setting policy in radiation safety and protection. It is not a dem- r individuals. The current occupational exposure limits have been onstrated scientific fact. There is a solid body of work demonstrat- established to ensure that no individuals will have deterministic ing increased risk of tumors in individuals exposed to more than ra effects and that the probability for stochastic effects is as low as about 100 mGy. However, there are relatively few studies showing reasonably and economically feasible. a risk in the diagnostic range. In this low-dose range, the LNT has Dentists and their staff are occupationally exposed workers and been consistently neither verified nor falsified. A major difficulty llib are allowed to receive an average of 20 mSv of whole-body radia- in such studies is that at doses less than 100 mGy, epidemiologic tion exposure per year. Although this level of exposure is consid- studies require such large sample sizes as to be impractical. Thus ered to present only a minimal risk, every effort should be made the validity of the model is uncertain. This situation is not expected to keep the radiation dose to all individuals as low as practical. to change in the near future. The dental profession does well in this area. The average dose for Despite its uncertainties in the low-dose range, there are several a individuals occupationally exposed in the operation of dental x-ray reasons for using the LNT. First, there needs to be a policy to set equipment is 0.2 mSv—1% of the allowable exposure. exposure limits for individuals exposed in the low-dose range, nt There are no limits on the exposure a patient can receive including from diagnostic radiology, in nuclear power plants, on from diagnostic examinations, interventional procedures, or radia- long airline flights, and from other exposures. Second, several lines tion therapy; this is because these exposures are made intentionally of evidence indicate that the LNT is scientifically plausible. The and for the direct benefit of the recipient. Individual circum- dose-response at doses greater than 100 mGy is linear. Complex de stances make the setting of limits inappropriate. However, increas- damage to DNA, the basis of cancer formation, may occur with ing concern for minimizing patient exposure has led multiple even one x-ray photon (see Fig. 2-2). Although sophisticated DNA institutions, including the National Council on Radiation Protec- repair mechanisms exist, some types of complex damage to DNA tion and Measurement (NCRP) to issue diagnostic reference levels may be beyond the enzymatic repair. Finally, much epidemiologic (DRL) for medical and dental diagnostic imaging. DRL exposure data are consistent with, and do not exclude, a risk at very low values represent the acceptable upper limits for patient exposure doses. Most radiation protection organizations believe that it is (75th percentile of general practice), whereas achievable doses prudent to assume that risk is proportional to dose, even for diag- represent the median dose (50th percentile) in general practice. nostic exposures, and that there is no safe threshold. It is fairly The NCRP recommends a DRL of 1.6 mGy entrance skin dose common to see in the literature estimates of numbers of fatalities for intraoral periapical and bitewing radiography. The NCRP that may be caused by various radiographic examinations. Such further recommends an achievable dose of 1.2 mGy for intraoral estimates are based on the LNT and are highly speculative and at 32 PART I Foundations TABLE 3-3 Effective Dose from Radiographic Examinations and Equivalent Background Exposure Examination Effective Dose (µSν) Equivalent Background Exposure (days) IN T R A O R A L 1 Rectangular collimation Posterior bitewings: PSP or F-speed film 5 0.6 Full-mouth: PSP or F-speed film 35 4 Full-mouth: CCD sensor (estimated) 17 2 m Round collimation Full-mouth: D-speed film 388 46 Full-mouth: PSP or F-speed film 171 20 o Full-mouth: CCD sensor (estimated) 85 10 t.c EX T R A O R A L Panoramic1–3 9–24 1–3 1,2,4 Cephalometric 2–6 0.3–0.7 po 5,6 Cone-beam CT Large field of view 68–1073 8–126 Medium field of view 45–860 5–101 Small field of view 19–652 2–77 gs Multislice CT Head: Conventional protocol6–9 860–1500 101–177 Head: Low-dose protocol6,8 180–534 21–63 Abdomen7 5300 624 Chest7 lo 5800 682 Plain films10 Skull 70 8 y.b Chest 20 2 Barium enema 7200 847 CCD, Charge-coupled device; PSP, photostimulable phosphor. 1. Data from 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 r regarding dose calculation, J Am Dent Assoc 139:1237-1243, 2008. 2. Data from Lecomber AR, Yoneyama Y, Lovelock DJ et al: Comparison of patient dose from imaging protocols for dental implant planning using conventional radiography and computed tomography, Dentomaxillofac ra Radiol 30:255-259, 2001. 3. Data from Ludlow JB, Davies-Ludlow LE, Brooks SL: Dosimetry of two extraoral direct digital imaging devices: NewTom cone beam CT and Orthophos Plus DS panoramic unit, Dentomaxillofac Radiol 32:229-234, 2003. 4. Data from Gijbels F, Sanderink G, Wyatt J et al: Radiation doses of indirect and direct digital cephalometric radiography, Br Dent J 197:149-152, 2004. 5. Data from Pauwels R, Beinsberger J, Collaert B et al: Effective dose range for dental cone beam computed tomography scanners, Eur J Radiol 81:267-271, 2012. llib 6. Data from Ludlow JB, Ivanovic M: Comparative dosimetry of dental CBCT devices and 64-slice CT for oral and maxillofacial radiology, Oral Surg Oral Med Oral Pathol Oral Radiol Endod 106:106-114, 2008. 7. Data from Shrimpton PC, Hillier MC, Lewis MA et al: National survey of doses from CT in the UK: 2003, Br J Radiol 79:968-980, 2006. 8. Data from Loubele M, Jacobs R, Maes F et al: Radiation dose vs. image quality for low-dose CT protocols of the head for maxillofacial surgery and oral implant planning, Radiat Prot Dosimetry 117:211-216, 2005. 9. Data from Loubele M, Bogaerts R, Van Dijck E et al: Comparison between effective radiation dose of CBCT and MSCT scanners for dentomaxillofacial applications, Eur J Radiol 71:461-468, 2009. a 10. Data from European Commission: Referral guidelines for imaging, Radiation Protection 118, 2007. http://www.sergas.es/Docs/Profesional/BoaPraticaClinica/RP118.pdf nt best represent the probable upper limits. The actual numbers may REDUCING DENTAL EXPOSURE de be substantially lower or even zero. Although the LNT is the consensus opinion of most radiation safety groups around the There are three guiding principles in radiation protection: world, there is controversy about whether there really is a risk. 1. Justification Some experts argue that there is no demonstrated risk at doses less 2. Optimization than 100 mGy, and on balance patients may not reap the full 3. Dose limitation diagnostic benefits by avoiding diagnostic imaging because of inap- The principle of justification means the dentist should identify propriate fear. If the actual risk is significantly less than predicted situations where the benefit to a patient from the diagnostic expo- by the LNT, there is a risk of harm to patients from making too sure likely exceeds the risk of harm. In practice, this principle few exposures. It is most reasonable to make radiographs only influences what patients are selected for radiographic examinations when there is a diagnostic need and to use all reasonable means and what examinations are chosen. These matters are considered to reduce patient exposure during the examination. in Chapter 16.  C H A P T E R 3 Safety and Protection 33 The dentist in each facility is responsible for the design and conduct of the radiation protection program. In this section, methods of exposure and dose reduction are described that can Probability be used in dental radiography. Each subsection begins with a of cancer recommendation of the American Dental Association (ADA) Council on Scientific Affairs. This recommendation is followed by a discussion of ways in which the recommendation can be Linear nonthreshold satisfied. All methods that reduce exposure to patients also reduce Background exposure to the dental staff and usually improve the quality of m incidence the radiographs made. PATIENT SELECTION CRITERIA Radiographic screening for the purpose of detecting o Dose Background dose disease before clinical examination should not be per- formed. A thorough clinical examination, consideration t.c FIGURE 3-3 Linear nonthreshold hypothesis. There is a certain natural prevalence of cancer of the patient history, review of any prior radiographs, and a certain natural background radiation exposure (gray-blue dot). Doses of radiation greater caries risk assessment and consideration of both the than about 100 mSv (green dots) result in a dose-dependent increase in the cancer rate. The dental and the general health needs of the patient should linear nonthreshold hypothesis posits that at doses less than 100 mSv down to the background precede radiographic examination (ADA 2012). po level, there is a linear relationship between dose and risk (orange dashed line) and that there The most effective means to reduce unnecessary exposure is to is no threshold dose below which there is no additional risk. reduce unnecessary radiographic examinations. Radiographs should be made only when there is a specific indication for a specific patient. The ADA has published radiographic selection gs criteria—clinical or historical findings that identify patients for BOX 3-1 Means for Reducing X-Ray Exposure whom a high probability exists that a radiographic examination would provide information affecting their treatment or prognosis. Use selection criteria to assist in determining type and frequency of radiographic These criteria satisfy the principle of justification and are consid- examinations lo ered in Chapter 16. Use E/F-speed film or digital sensors When a decision is made to obtain a radiograph, the dentist Use holders to support film or digital sensors intraorally should obtain the lowest dose image that would satisfy the task. y.b Make exposures with 60 to 70 kVp Table 3-3 shows that there is a wide range of patient exposures Replace short pointed aiming tubes with open-ended aiming cylinders from various common dental examinations. Use rectangular collimation for periapical and bitewing images Use thyroid collars CONDUCTING THE EXAMINATION Stand at least 6 feet (2 m) away from patient and away from the x-ray machine When a decision has been made that a radiographic examination r (preferably out of x-ray room) when making exposure is justified (using patient selection criteria), the way in which the examination is conducted, or the principle of optimization, greatly ra With film, use time-temperature film processing rather than “sight” processing, or use an automatic processor influences patient exposure to radiation. The conduct of the exami- Use rare-earth screens for panoramic and cephalometric film imaging or use digital nation may be divided into choice of equipment, choice of tech- systems nique, operation of equipment, and processing and interpreting llib Reduce cone-beam CT beam field of view to region of interest the radiographic image. Film and Digital Imaging Good radiologic practice includes use of the fastest image receptor compatible with the diagnostic task a The principle of optimization holds that dentists should use (F-speed film or digital) (ADA 2012). every reasonable means to reduce unnecessary exposure to their Intraoral dental x-ray film is available in two speed groups: D and nt patients, their staffs, and themselves. This philosophy of radiation E/F (see Chapter 5). Clinically, film of speed group E/F is approxi- protection is often referred to as the principle of ALARA (As Low mately twice as fast (sensitive) as film of group D and thus requires As Reasonably Achievable). ALARA holds that exposures to ion- only half the exposure (see Fig. 5-30). Fast films are desirable from izing radiation should be kept as low as reasonably achievable, the standpoint of exposure reduction. Multiple studies have found de economic and social factors being taken into account. The means that E/F-speed film is preferred because it has the same useful to accomplish this end are considered by dentists every day in their density range, latitude, contrast, and image quality as D-speed practices and are discussed later in this chapter (Box 3-1). films and can be used in routine intraoral radiographic examina- The principle of dose limitation provides dose limits for occu- tions without sacrifice of diagnostic information. Current digital pational and public exposures to ensure that no individuals are sensors (see Chapter 4) offer equal or greater dose savings than exposed to unacceptably high doses. This principle applies to E/F-speed film and comparable diagnostic utility. dentists and their staff who are exposed occupationally but not to patients because there are no dose limits for individuals exposed Intensifying Screens and Film for diagnostic purposes. Many of the steps described in the follow- Rare-earth intensifying screens are recommended … com- ing sections that optimize exposures of the patient also reduce bined with high-speed film of 400 or greater (ADA exposure to dentists and their staff. 2006). 34 PART I Foundations Contemporary intensifying screens used in extraoral radiography use the rare earth elements gadolinium and lanthanum (see Rectangular Collimation Chapter 5). These rare earth phosphors emit green light on interac- Since a rectangular collimator decreases the radiation tion with x rays. Compared with the older calcium tungstate dose by up to fivefold as compared with a circular one, screens, rare earth screens decrease patient exposure by 55% in radiographic equipment should provide rectangular col- panoramic and cephalometric radiography. limation for exposure of periapical and bitewing radio- In contrast to intraoral digital imaging, there is no significant graphs (ADA 2012). dose reduction to be gained by replacing fast extraoral screen-film Most state regulations require that the x-ray beam used in intraoral systems with digital imaging. Image resolution with digital systems radiography be collimated so that the field of radiation at the m is comparable to that obtained with rare earth screens matched patient’s skin surface is no more than 7 cm (2.75 inches) in diam- with appropriate film. eter. In view of the dimensions of No. 2 intraoral film (3.2 cm × 4.1 cm) or digital sensor, the area of such a field size is almost three Source-to-Skin Distance times larger than necessary to expose the image. Consequently, o Use of long source-to-skin distances of 40 cm, rather than limiting the size of the x-ray beam to the size of the image receptor short distances of 20 cm, decreases exposure by 10 to 25 significantly reduces unnecessary patient exposure. If the tissue t.c percent. Distances between 20 cm and 40 cm are appro- volume exposed is decreased, the amount of scattered radiation is priate, but the longer distances are optimal (ADA 2006). decreased, image fogging is decreased, and the resultant image has Two standard focal source-to-skin distances have evolved over the improved diagnostic quality. years for use in intraoral radiography, one 20 cm (8 inches) and There are several means to limit the size of the x-ray beam. First, po the other 41 cm (16 inches). Use of the distance results in a reduc- a rectangular position-indicating device (PID) may be attached to tion in exposed tissue volume because the x-ray beam is less the radiographic tube housing (Fig. 3-5). Use of a rectangular PID divergent (Fig. 3-4). The use of a longer source-to-object distance having an exit opening of 3.5 cm × 4.4 cm (1.38 inches × 1.34 also results in a smaller apparent focal spot size increasing the reso- inches) reduces the area of the patient’s skin surface exposed by gs lution of the radiograph (see Chapter 6). 60% over that of a round (7 cm) PID (see Fig. 3-4, C). However, this reduction in beam size may make aiming the beam difficult. To avoid the possibility of unsatisfactory radiographs (cone cutting), a film-holding instrument that centers the beam over the lo film or sensor is recommended (Fig. 3-6). Alternatively, film- positioning and sensor-positioning devices with rectangular colli- mators may be used with round aiming cylinders (Figs. 3-7 and y.b 3-8). These holders reduce patient exposure to the same degree as A rectangular PIDs. r ra llib B A a nt de C B FIGURE 3-5 A, A rectangular PID mounted on an x-ray machine provides a means to limit the shape of the x-ray beam to just larger than the film or digital sensor, thus minimizing FIGURE 3-4 Effect of source-to-skin distance and collimation on the volume of tissue irradi- the volume of tissue exposed. It may rotate to accommodate to the patient. B, An external ated. A larger volume of irradiated tissue results with use of a short source-to-skin distance (A) guide attaches to the end of the rectangular PID. The red, blue and yellow connectors on the compared with use of a longer source-to-skin distance (B), which produces a less divergent guide allow the user to attach a bite block with a film or sensor to the external guide using beam. Using a rectangular collimator between the round PID and the patient (C) results in a a Rinn XCP-ORA arm to obtain positive alignment to the x-ray machine and thereby prevent smaller, less divergent beam and a smaller volume of tissue irradiated than in A or B. cone cuts. (Courtesy Margraf Dental Manufacturing, Inc., www.margrafdental.com.)  C H A P T E R 3 Safety and Protection 35 o m t.c po FIGURE 3-8 Rectangular collimation. Another means to collimate a round beam to a rectangle is to place a metallic shield in the path of the beam, limiting the size of the exposure FIGURE 3-6 XCP film-holding instrument. The aiming ring aligns a circular aiming cylinder field to an area just larger than the film or sensor. The JADRAD Dental X-Ray Shield is shown. from an x-ray machine with the sensor to ensure that the image plane is perpendicular to the (Courtesy Dr. Jennifer Diederich, Farmington, CT.) central ray and in the middle of the beam. Note notches to align rectangularly collimated aiming gs devices, such as shown in Figures 3-5 or 3-7. The digital sensor and cord is in a plastic bag to prevent contamination from saliva. (Courtesy Dentsply Rinn: http://rinncorp.com.) minimum half-value layer, required for dental x-ray machines oper- ating at various kilovoltages. Practically, these requirements can be lo met by having 1.5 mm of aluminum total filtration when operat- ing from 50 to 70 kVp and 2.5 mm of aluminum total filtration when operating above 70 kVp. y.b Leaded Aprons and Thyroid Collars The thyroid gland is more susceptible to radiation expo- sure during dental radiographic exams given its anatomic position, particularly in children. Protective thyroid collars r and collimation substantially reduce radiation exposure to the thyroid during dental radiographic procedures. ra Because every precaution should be taken to minimize radiation exposure, protective thyroid collars should be used whenever possible (ADA 2012). llib The function of leaded aprons and thyroid collars (Fig. 3-9) is to reduce radiation exposure of the gonads and thyroid gland. The NCRP 2003 recommendations referred to by the ADA are FIGURE 3-7 Rectangular collimation. An alternative means of limiting the size of an x-ray principally those already described—use of patient selection crite- beam to a rectangle is to attach a device shown here into the end of a circular aiming cylinder ria, fast (E/F-speed film or digital sensors), and rectangular collima- a that restricts the beam field to a rectangle and provides guidance in aligning the film holder. tors. The NCRP and ADA concluded that leaded aprons are (Courtesy Interactive Diagnostic Imaging: http://www.idixray.com.) unnecessary because it is far more important in patient protection nt to place emphasis on reducing exposure of the primary beam to facial structures than to reduce the already very slight gonadal exposure. More recent research has shown that the risk of heritable Filtration effects from dental exposure is essentially insignificant (see Chapter de The x-ray beam emitted from the radiographic tube consists of a 2). However, most states currently require the use of leaded aprons. spectrum of x-ray photons. Low-energy photons, which have little In recent years, lead-free aprons have been offered for sale. The penetrating power, are absorbed mainly by the patient and con- virtues of these aprons are their lighter weight and avoiding the tribute nothing to the information on the image. The purpose of use of lead. These aprons include materials with high atomic filtration is to remove these low-energy x-ray photons preferentially numbers and low densities, such as antimony, tin, tungsten, or from the x-ray beam. Filtration results in decreased patient expo- bismuth, to provide beam attenuation. These aprons typically sure with no loss of radiographic information. attenuate about 98% as much as conventional aprons but weigh When an x-ray beam is filtered with 3 mm of aluminum, the only about 60% as much. surface exposure is reduced to about 20% of the exposure with no There is reason to be concerned about radiation exposure to filtration. In light of this and other information, the federal govern- the thyroid gland. Multiple studies, including studies performed ment has designated the specific amount of filtration, expressed as after the explosion of the Chernobyl reactor, have shown that the 36 PART I Foundations the image receptor (a “cone-cut”) and reduces image distortion (see Chapter 6). As discussed earlier, many film holders also collimate the beam to the size of the image receptor. Kilovoltage The optimal operating potential of dental x-ray units is between 60 and 70 kVp (ADA 2012). Although image diagnosis may be improved slightly with increased image contrast (low kVp) images, the patient dose is reduced with m higher kVp exposures. Most intraoral machines use 60 to 70 kVp. The availability of constant-potential (fully rectified), high- frequency or direct current (DC) dental x-ray units has made possible the production of radiographs with lower kilovoltage and o at reduced levels of radiation. The surface exposure required to produce a comparable radiographic density using a constant- t.c potential unit is approximately 25% less than that of a conven- tional self-rectified unit operating at the same kilovoltage. At the present time, several manufacturers produce DC units. po Milliampere-Seconds The operator should set the amperage and time settings for exposure of dental radiographs of optimal quality (ADA 2006). gs Of the three settings on an x-ray machine (tube voltage, filtration, and exposure time), exposure time is the most crucial factor in influencing diagnostic quality. In terms of exposure, optimal image quality means that the radiograph is of diagnostic density, neither lo overexposed (too dark) nor underexposed (too light). Both over- exposed and underexposed radiographs result in repeat exposures, leading to needless additional patient exposure. Image density is y.b controlled by the quantity of x rays produced, which is best controlled by the combination of milliamperage and exposure FIGURE 3-9 Leaded apron with a thyroid collar. Children are more sensitive to radiation time, termed milliampere-seconds (mAs) (see Chapter 1). Typi- than adults, and so the use of leaded aprons with thyroid collars is especially important for this cally, a radiograph of correct density demonstrates very faint soft population. (Courtesy Dentsply Rinn: http://rinncorp.com/.) tissue outlines. Dentin has an optical density of about 1.0. If r your x-ray machine has a variable milliampere control, it should be set at the highest choice. Proper exposure times should be ra thyroid gland in children is especially sensitive to radiation. It is determined empirically when using optimal film processing condi- entirely appropriate to protect the thyroid glands of children tions (see Chapter 5) or manufacturer’s recommendations for during radiographic examinations. The best ways to accomplish digital sensors. A chart showing optimal exposure times for each llib this aim are to use fast receptors, rectangular collimation, and region of the arch in children and adults should be mounted by thyroid collars. each x-ray machine. Because film-processing conditions are stan- dardized and the mA and kVp settings are fixed, the only decision Film and Sensor Holders the dentist or the assistant needs to make is to select the proper Film holders that align the film precisely with the colli- exposure time for the age of the patient (less for young patients) a mated beam are recommended for periapical and bite- and the region of the mouth being imaged (less in the anterior wing radiographs (ADA 2006). region). nt Film or digital sensor holders should be used when intraoral radio- graphs are made because they improve the alignment of the film, Film Processing or digital sensor, with teeth and x-ray machine. Their use results All film should be processed following the film and pro- in a significant reduction in unacceptable images and thus avoid- cesser manufacturer recommendations. Poor processing de able retakes. The use of film and sensor holders allows the operator technique, including sight-developing, most often results to control the position and alignment of the film or sensor with in underdeveloped films, forcing the x-ray operator to respect to the teeth and jaws. This is especially important when increase the dose to compensate, resulting in patient and digital imaging (see Chapter 4) is used with the paralleling tech- personnel being exposed to unnecessary radiation (ADA nique (see Chapter 6). In these cases, it is often desirable to 2012). position the receptor away from the teeth so as to get the best A major cause of unnecessary patient exposure is the practice of image and reduce patient discomfort. This requires the use of a overexposing films and compensating by underdevelopment. This film or sensor holder. Most such devices have an external guide procedure results in both needless exposure of the patient and in that shows the operator where to align the aiming cylinder (PID). films that are of inferior diagnostic quality because of incomplete As a result, the x-ray beam is properly directed toward the recep- development. Time-temperature processing is the best way to tors; this greatly reduces the chance of the beam partially missing ensure optimal film quality (see Chapter 5). To help ensure optimal  C H A P T E R 3 Safety and Protection 37 image quality, the dental assistant should follow the film manu- the exposure to nonoccupationally exposed individuals (e.g., facturer’s recommendation for processing solutions. someone occupying an adjacent office) is no greater than 100 µGy The use of automatic film processing machines has become per week. In most instances, it is not necessary to line the walls widespread with more than 90% of dentists using such processors. with lead to meet this requirement. Walls constructed of gypsum They should be used in a darkroom. Although some units have wallboard (drywall or sheet rock) are adequate for the average daylight loaders, allowing film to be placed in the machine in room dental office. light, such loaders are difficult to keep clean and free of contamina- Every effort should be made so that the operator can leave the tion. However, film processors can increase patient exposure if not room or take a position behind a suitable barrier or wall during an correctly maintained. Approximately 30% of all films retaken exposure. A leaded glass window or a mirror would be required so m because of incorrect film density are related to processor variability. that the operator can monitor the patient during the exposure. If Using a comprehensive maintenance program can reduce this leaving the room or making use of some other barrier is impossible, retake rate significantly, resulting in a substantial savings in both strict adherence to what has been termed the position-and- patient exposure and operating costs. distance rule is required: the operator should stand at least 6 feet o (2 m) from the patient, at an angle of 90 to 135 degrees to the Interpreting the Images central ray of the x-ray beam (Fig. 3-10). When applied, this rule t.c The dentist should view radiographs under appropriate not only takes advantage of the inverse square law to reduce x-ray conditions for analysis and diagnosis (ADA 2006). exposure to the operator but also takes advantage of the fact that Radiographs are best viewed in a semidarkened room with light in this position the patient’s head absorbs most scatter radiation. transmitted through the films; all extraneous light should be elimi- All practitioners should check their state’s regulations for use po nated. In addition, radiographs should be studied with the aid of of ionizing radiation regarding operator position during x-ray a magnifying glass to detect even the smallest change in image exposures. density. Similarly, digital images are best interpreted on a computer Second, the operator should never hold films or sensors in screen in a darkened environment. It is often useful to magnify place. Film or sensor-holding instruments should be used (see gs them electronically. earlier section on rectangular collimation). If correct film place- ment and retention are still not possible, a parent or other indi- PROTECTING PERSONNEL vidual responsible for the patient should be asked to hold the The methods of dose reduction discussed so far have emphasized sensor in place and be afforded adequate protection with a leaded lo the effect on patient exposure. However, any procedure or tech- apron. Under no circumstances should this person be one of the nique that reduces radiation exposure to the patient also reduces office staff. the possibility of operator or office personnel exposure from scat- Third, neither the operator nor the patient should hold the y.b tered radiation. In addition to those mentioned, several other steps radiographic tube housing during the exposure. Suspension arms can be taken to reduce the chance of occupational exposure. should be adequately maintained to prevent housing movement Operators of radiographic equipment should use barrier and drift. protection when possible, and barriers should contain a The best way to ensure that personnel are following office safety leaded glass window to enable the operator to view the rules such as those described previously is with personnel- r patient during exposure. When shielding is not possible, monitoring devices. These devices provide a means to measure if the operator should stand at least two meters from the the operator is accumulating any occupational exposure. The ADA ra tube head and out of the path of the primary beam (ADA recommends that workers who may receive an annual dose greater 2006). than 1 mSv should wear personal dosimeters to monitor their Dental operatories should be designed and constructed to meet exposure levels. Pregnant dental personnel operating x-ray equip- llib the minimal shielding requirement of the state regulations; this ment should use personal dosimeters, regardless of anticipated requires consultation with a qualified expert. This recommenda- exposure levels (ADA 2012). Use of personal dosimeters is not only tion states that walls must be of sufficient density or thickness that recommended but also required by law in certain states. Several a 90° nt 135° FIGURE 3-10 Position-and-distance rule. The operator may be exposed from leakage 6 fe de radiation from the x-ray tube head, scattered et radiation from the patient, and primary photons passing through the patient. If no barrier is avail- able, the operator should stand at least 6 feet 90° from the patient, at an angle of 90 to 135 6 fe degrees to the central ray of the x-ray beam et x when the exposure is made because this region receives the least overall exposure. 135° x 38 PART I Foundations companies in the United States offer dosimetry-monitoring ser- radiographs was significantly reduced. Two studies by a dental vices. These services provide badges that contain a radiosensitive insurance carrier demonstrated that after claims were rejected for crystal (Al2O3) that luminesces in proportion to the amount of unsatisfactory radiographs and the dentist was made aware of the radiation exposure (Fig. 3-11). These devices are sensitive to 10 µSv. errors and ways in which they could be corrected, the number of A printed report of accumulated exposure may be obtained at satisfactory radiographs submitted doubled. This study suggests regular intervals (Fig. 3-12). These reports indicate any undesirable that when the dentist is presented with guidelines for quality assur- change in work habits and help remove any apprehension office ance, along with proper motivation, patient exposure can be dra- staff members may have about the possibility of exposure to x rays. matically reduced. Commercial mail-in devices are available to dentists and radiation protection agencies to measure dental image QUALITY ASSURANCE m quality and dose of their radiographs. Quality assurance protocols for the x-ray machine, Some states require dental offices to establish written guidelines imaging receptor, film processing, dark room, and patient for quality assurance and to maintain written records of quality shielding should be developed and implemented for each assurance tests. Regardless of requirements, each dental office o dental health care setting (ADA 2012). should establish maintenance and monitoring procedures as out- Quality assurance may be defined as a program for periodic assess- lined in Chapter 15. t.c ment of the performance of all parts of the radiologic procedure. It is intended to ensure that a dental office consistently produces CONTINUING EDUCATION high-quality images with minimum exposure to patients and per- Practitioners should remain informed about safety updates sonnel (see Chapter 15). Studies have indicated that dentists may and the availability of new equipment, supplies and tech- po be needlessly exposing their patients to compensate for improper niques that could farther improve the diagnostic quality exposure techniques, film processing practices, and darkroom pro- of radiographs and decrease radiation exposure (ADA cedures. One study reported that only 33% of panoramic radio- 2006). graphs that accompanied biopsy specimens were of acceptable Individuals who administer ionizing radiation must become famil- gs diagnostic quality. However, when demands were placed on den- iar with the magnitude of exposure encountered in medicine, tists to improve their techniques, the number of unsatisfactory dentistry, and everyday life; the possible risks associated with such lo y.b Al2O3 r B ra A FIGURE 3-11 A personal optically stimu- llib lated luminescence dosimeter may contain a strip of Al2O3, which is sensitive to radiation. This strip Filter pack is enclosed in a filter pack containing an open window and plastic, aluminum, and copper filters. These are packaged into a blister pack and a worn by an operator. The amount and ratio of light output during the stimulation process from nt the regions of the Al2O3 under the filters allows determination of the energy and dose of radia- tion to which the badge was exposed. (Courtesy Landauer, Inc., Glenwood, IL.) de C D  C H A P T E R 3 Safety and Protection 39 o m t.c po gs lo y.b FIGURE 3-12 Sample radiation dosimetry report showing exposure received by various individuals during the month reported as well as type of dosimeter, its location, and the dose distribution. The report also shows totals for the year to date and lifetime exposure. (Courtesy Landauer, Inc., Glenwood, IL.) r exposure; and the methods used to affect exposure and dose reduc- will make only the exposures you specifically need for the patient’s tion. Although this chapter presents some of this information, benefit, most patients will appreciate your attention to their con- ra acquiring knowledge and developing and maintaining skills is a cerns and accept radiographs. lifelong process. In addition, assure new patients that you will contact their pre- vious dentist to obtain previous radiographs that may assist you in llib TALKING WITH YOUR PATIENT their diagnosis. The approach described in the preceding paragraph Although most patients readily accept dental radiographs as part is also appropriate for patients who are pregnant if you believe of their diagnosis, some have anxiety about radiation exposure for there may be a need for immediate treatment. Patients who have themselves or members of their families—usually their children. It had radiation therapy for head and neck cancers should be told is important to speak clearly and confidently with your patients if about the risk of caries and other problems that make it all the a they bring up these concerns. The first step is to allow the patient more important that they have regular follow-up examinations. to express his or her thoughts fully. Do not interrupt the patient’s nt comments or belittle the patient’s concerns. With all the discussion of radiation risks in the general media, it is completely reasonable BIBLIOGRAPHY that an individual may be concerned. After hearing your patient’s American Dental Association Council on Scientific Affairs: The use of remarks, you should first acknowledge them and show that you de dental radiographs: update and recommendations, J Am Dent Assoc understand their apprehension. Next, you should tell the patient 137:1304–1312, 2006. why you need radiographs as part of the patient’s personal American Dental Association Council on Scientific Affairs: Dental diagnosis—such as the detection of interproximal caries, the extent radiographic examinations: recommendations for patient selection of bone loss from periodontal disease suggested by probing, peri- and limiting radiation exposure. Revised 2012: http://www.ada.org/ apical infections suggested by pain, or whatever radiologic inves- sections/professionalResources/pdfs/Dental_Radiographic_ Examinations_2012.pdf. tigation that is specific to the patient’s condition. You should also Code of Federal Regulations 21, Subchapter J: Radiological health, part describe the many measures you take to reduce patient exposure, 1000, Washington, DC, 1994, Office of the Federal Register, General such as using fast film or digital sensors, rectangular collimation, Services Administration. and thyroid collars. Finally, it may be helpful to point out that Committee to Assess Health Risks from Exposure to Low Levels of with these protective steps the exposure is small in terms of natural Ionizing Radiations: Health risks from exposure to low levels of ionizing background radiation. With these assurances, including that you radiation: BEIR VII, Washington, DC, 2006, National Academy Press. 40 PART I Foundations Dental radiographs: Benefits and safety, J Am Dent Assoc 142:1101, 160, Bethesda, MD, 2009, National Council on Radiation Protection 2011. and Measurements. Environmental Protection Agency: Calculate your radiation dose: National Council on Radiation Protection and Measurements: Reference http://www.epa.gov/radiation/understand/calculate.html. levels and achievable doses in medical and dental imaging: recommendations Hall EJ, Giaccia AJ: Radiobiology for the radiologist, ed 6, Baltimore, 2006, for the United States, NCRP Report 172, Bethesda, MD, 2012, Lippincott Williams & Wilkins. National Council on Radiation Protection and Measurements. Horner K, Rushton VE, Walker A, et al: European guidelines on Nationwide Evaluation of X-Ray Trends (NEXT): tabulation and graphical radiation protection in dental radiology: the safe use of radiographs summary of the 1999 dental radiography survey, CRCPD Publication in dental practice, Radiat Protect 136:1–115, 2004. 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Sources and effects of ionizing radiation, UNSCEAR 2008 report: volumes I National Council on Radiation Protection and Measurements: and II, New York, 2008, UNSCEAR (United Nations Publications t.c Limitation of exposure to ionizing radiation, NCRP Report 116, vol I released in 2010 and vol II released in 2011). https://unp.un Bethesda, MD, 1993, National Council on Radiation Protection.org/details.aspx?pid=20417 and https://unp.un.org/Details.aspx? and Measurements. pid=21556. National Council on Radiation Protection and Measurements: Dental The 2007 recommendations of the International Commission on x-ray protection, NCRP Report 145, Bethesda, MD, 2003, National Radiological Protection. IRCP Publication 103, Ann ICRP 37:1–332, po Council on Radiation Protection and Measurements. 2007. National Council on Radiation Protection and Measurements: Ionizing Wall BF, Kendall GM, Edwards AA, et al: What are the risks from medical radiation exposure of the population of the United States, NCRP Report x-rays and other low dose radiation? Br J Radiol 79:285–294, 2006. gs lo r y.b ra a llib nt de