* Name the most important and widely recognized measure for radiation protection.
* Discuss how radiation exposure affects bodily tissues.
* Differentiate between acute and chronic effects.
* Differentiate among 3 key types of radiation dose.
* Explain recent changes in the treatment of pregnant patients.
* Explain the importance of beam collimation and filtration in patient protection.
* Understand the role of shielding in patient protection.
* Understand how pregnancy affects employment and work duties in radiology.
* Identify and discuss the advantages and disadvantages of 4 common types of personnel dosimeters.
* Identify and discuss 3 commonly used area monitors.
Since its discovery at the end of the 19th century, ionizing radiation has handed clinicians and patients the gift of a double-edged sword. Radiation's benefits to diagnostic and therapeutic medicine are undisputed, yet always must be weighed against the potential dangers that overexposure to ionizing radiation presents. Early accounts of radiation's dangers were largely anecdotal and often dismissed. Shortly after discovery of the x-ray, some turn-of-the-century practitioners claimed that skin burns, hair loss and other symptoms were due to the electrical current being used or were simply the result of a patient's oversensitive nature. (1)
The practice of radiation protection in medical radiography, which is defined as safeguarding patients, personnel and the general public from unnecessary exposure that will not enhance the diagnostic information obtained, (2) began with the observations of some physicists, dentists and physicians who made early use of ionizing radiation and recorded its potentially disastrous effects.
Boston dentist William Herbert Rollins, who had observed the deleterious effects of x-rays on guinea pigs in his laboratory, published his notes in 1904 in the Boston Medical and Surgical Journal. His report was largely ignored at the time, yet many of the protective measures taken today had their beginnings in the early warnings and suggestions of Rollins and some of his more cautious colleagues.
In a detailed list of suggestions to practitioners, Rollins urged the use of lead-lined boxes to enclose x-ray tubes and admonished x-ray technicians, as they were then known, to wear a special film badge he had designed to warn them of excessive exposure. He also articulated the earliest admonitions that radiation exposure be kept to the minimum amount needed for the task at hand. (1) This principle, known today as ALARA (as low as reasonably achievable), remains radiologic technology's most important protective measure.
The deleterious effects of radiation exposure that Rollins and his colleagues sought to minimize originate at the cellular level when the ionizing radiation of x-rays passes through bodily tissue and deposits energy that causes molecular change. Affected molecules may in time begin to function improperly or cease to function at all, resulting in damaged tissue and possible organ damage. This process is sometimes reversible. Cells and tissues can recover from radiation injury. (3) The organs of the body exhibit a wide range of sensitivity to radiation. This radiosensitivity is determined by the function of a given organ in the body, the rate at which its cells mature and the inherent sensitivity of its cell type to radiation. (3)
Early radiobiologists--scientists who studied the radiosensitivity of various tissues and organs in detail--observed certain predictors of radiosensitivity that have stood the test of time. Stem cells are more radiosensitive than mature cells, which grow more resistant to radiation as they age. Younger tissues and organs, such as those of fetuses, infants and children, are more radiosensitive. A high metabolic activity level in cells leads to increased radiosensitivity. As the growth rate of cells and tissues increases, their sensitivity to radiation increases as well. A number of these long-recognized predictors of radiosensitivity provide the foundation for radiologic technology's practice of conscientiously protecting fetuses, infants and children from radiation exposure that would be far better tolerated by adults. (4)
Table 1 lists the degree of radiosensitivity of various cell types found throughout the human body. Note that reproductive and blood cells are among the most radiosensitive, while muscle and nerve cells are among the least sensitive. Organs with less need for cell renewal, such as the heart, skeletal muscle and nerves, are more resistant to the toxic effects of radiation. On the other hand, organs that undergo more self-renewal as part of their normal homeostasis, such as the blood-manufacturing bone marrow and the mucosal lining of the intestinal tract, are far more sensitive. (5) However, a precise knowledge of organ, tissue and cell sensitivity is not as important as a general understanding of the principles of radiosensitivity, which is helpful in comprehending and anticipating the effects of radiation exposure and the importance of radiation protection. (3)
Acute and Chronic Effects
Radiation effects can appear in either acute or chronic form. Acute effects generally result from accidental exposure or therapeutic treatment conducted at relatively high dose levels. Acute effects caused by therapeutic radiation typically manifest during treatment and resolve a few weeks after completion of therapy. (5) The severity of acute effects is determined by the amount of radiation exposure received, and any effects will be concentrated in the organs receiving the highest doses. Acute effects include some of those observed by the earliest practitioners of radiologic technology: peeling and ulcerated skin; damaged connective tissues, blood vessels or glands; alveolar damage; and fibrosis in the lungs. Acute effects also are known as nonstochastic or deterministic effects.
Chronic effects of excessive radiation result from longer-term exposure at relatively lower dose levels and take years to appear. They appear randomly and their severity is unrelated to the dose level received; thus, they also are known as stochastic (meaning random or arising from chance) or nondeterministic effects. They begin as slight cellular changes at the time of exposure, but eventually lead to an increased probability of radiation-induced cancer or leukemia. Chronic effects develop independently of acute effects and may occur despite recovery from acute effects. (5) There is no known threshold for the radiation dose required to cause chronic effects, and although the probability of induced cancer is related to the magnitude of the radiation dose received, the severity of that induced cancer is not. (6) At least 5 to 10 years, and as many as 12 to 25 years, pass before a radiation-induced tumor or leukemia appears.
This time lag places younger subjects of excessive radiation exposure at greater risk than older subjects. (7) These serious and potentially lethal effects necessitate protective measures, such as minimizing exposure, shielding patients and monitoring technologists, that are now commonplace in diagnostic imaging and therapeutic radiation facilities. Although all of these protective measures must be scrupulously observed, the effort to minimize patient dose is central to reducing unnecessary exposure. Minimizing patient dose during screening and diagnostic imaging procedures protects the well-being of the patient and also reduces the amount of radiation to which the radiologic technologist is occupationally exposed.
The amount of radiation absorbed by the patient-not the amount generated by the x-ray machine--determines patient dose. Measuring radiation dose begins by placing detectors at the patient's body surface or by irradiating phantoms that resemble the human form and substance. (5) An understanding of radiation dose begins by differentiating among the terms exposure, absorbed dose and effective dose or effective dose equivalent.
Exposure refers to the ability of x-rays to ionize air, and it measures the concentration of ionizing radiation in a given volume of air. It is not a direct measure of radiation dose to an organ or the patient as a whole, and it does not reveal how much energy is absorbed by tissues being irradiated. It is, however, easily measured and can be used in calculating radiation dose. Exposure is measured in roentgen (R). (6)
An absorbed dose measures the amount of energy deposited in tissue as ionizing radiation passes through it. Although absorbed dose describes the amount of energy absorbed in a 3-D volume, it does not take into account which organs or tissues absorbed the dose, their relative radiosensitivity or the risk of detrimental effects to those organs. (6) The principal unit for measuring absorbed dose is the gray (Gy). The gray replaces an earlier unit, the rad (radiation absorbed dose), which still may appear in some texts and is 100 times smaller than the gray; that is, 100 rad = 1 Gy.
Effective dose, sometimes referred to as effective dose equivalent, takes into account which tissues and organs have absorbed the radiation dose. The effective dose is expressed as a weighted average of organ doses, with the weighting factors estimated for each radiosensitive organ by the International Council on Radiation Protection. Effective dose is measured in sievert (Sv), and also is expressed in units of rem (100 rem = 1 Sv). (6)
The effective dose also attempts to reflect the equivalent whole-body dose, which results from actual absorbed dose to tissues that are irradiated during radiography or a computed tomography (CT) scan. Determining an equivalent whole-body dose may give some indication of the stochastic risk acquired during radiographic procedures. Understanding dose is the beginning of protecting patients during radiologic procedures.
Radiation Protection in Common Radiologic Procedures
For all diagnostic radiology procedures, there are common concerns and certain practices regarding radiation safety that must be followed. These concerns and practices are discussed in guidelines issued by the American College of Radiology. The guidelines stress the responsibility of all radiologists, radiologic technologists and supervising physicians to minimize radiation dose to individual patients, staff and the public while maintaining necessary diagnostic image quality. Facilities where radiologic professionals practice should develop and maintain policies and procedures that appropriately shield patients and adjust examination protocols to take into account individual patient characteristics, such as weight, height, body mass index and lateral width. Dose reduction devices available on imaging equipment should be activated, or manual techniques should be used, to moderate exposure while maintaining necessary image quality. Policies and procedures should be in place to immobilize or assist in positioning patients who are unable to cooperate or who cannot be positioned in the customary manner due to age or physical limitation, while also minimizing any concurrent irradiation of the facility's staff. Patient doses should be periodically measured by a medical physicist in accordance with appropriate standards. (8)
Computed tomography (CT) is responsible for a significant portion of the effective radiation dose from medical procedures. (6) CT uses a narrow beam of ionizing radiation from multiple angles to obtain cross-sectional images (nonhelical CT) or volumetric data sets (helical CT). (9) It typically uses multiple exposures along the length of the patient's body to cover a volume of anatomy.
The 2 main concerns related to patient dose during CT scanning are skin dose (the absorbed dose to the most superficial layers of the skin) and dose distribution during the acquisition of the adjacent tomographic slices that make up a CT scan. The skin dose received by patients during a CT scan is comparable to that received during an extensive series of ordinary radiographic studies and is considerably less than the skin dose typically received during a routine fluoroscopic procedure. (10)
Dose distribution during CT differs from distribution during ordinary radiography. On the positive side, the amount of scatter radiation generated by the tightly collimated CT x-ray beam is generally lower than scatter during ordinary radiography. In addition, less tissue outside the plane of concern is exposed to radiation during the acquisition of any given scan. The tightly collimated beam can be very accurately placed relative to the anatomy to be studied, sometimes sparing nearby radiosensitive organs. (10)
Concerns regarding dose distribution during CT arise from the fact that some overlap of the margins of the x-ray beams occurs when each single tomographic section in a series is imaged. In addition, some interslice scatter--that is, scatter to adjacent slices from the slice being imaged--also occurs during CT. Both tendencies contribute to a higher absorbed dose.
As the number of CT scans performed increases, ways to address concerns regarding patient dose are being explored. Direct shielding of radiosensitive organs typically has not been used during CT because of the rotational nature of the procedure. A recent study by Italian physicians, however, revealed the effectiveness of bismuth shields used to protect the lenses of the eyes during CT scans of the brain and to shield the breasts of female patients undergoing CT scans of the chest. These researchers found they could reduce patient dose to the eye by 34% and dose to the breast by approximately 47% without compromising the diagnostic usefulness of the images obtained. (11)
Techniques used in CT screening procedures usually use a lower radiation dose, as opposed to doses used in diagnostic or interventional tomography scans. Whether the decrease in radiation dose interferes with an accurate screening result depends on the screening task at hand. (6) The increased noise in images obtained at lower doses suggests that screening examinations that inherently have a high contrast between the disease sign and the background tissue are the best candidates for CT screening. Such exams include screening for calcium in coronary arteries, soft-tissue lung nodules and soft-tissue lesions in the colon. (6) This inherent high contrast means that a reduction in mAs used during these procedures--one of several techniques to decrease patient dose--will not have an unacceptably negative effect on image quality.
Together with fluoroscopy, mobile radiography accounts for 95% of a diagnostic radiologic technologist's occupational exposure to radiation. (12) Even in the absence of permanent structural barriers, several routine shielding and protective practices can help reduce this exposure. Every mobile radiography unit should have a protective apron assigned to it, and the radiologic technologist should wear it during all mobile studies. He or she also should maintain the maximum distance possible from the source of ionizing radiation. The exposure cord on any portable x-ray unit should be at least 2 m long. Regardless of whether the primary beam is activated or not, it should never be pointed at the technologist or other medical personnel. (12)
The 3 cardinal principles of radiation protection--time, distance and shielding--can help minimize both patient and occupational exposure during fluoroscopy. The radiologist should minimize x-ray beam on-time by using careful technique, including intermittent rather than continuous activation of the fluoroscopic beam. One common radiation protection practice is to maintain a log of fluoroscopy time by recording the x-ray beam on-time using a 5-minute reset timer. (12) The radiologic technologist should step back from the fluoroscopy table whenever his or her immediate presence or assistance is not required. Technologists also should routinely take advantage of all protective shielding, including any lead acrylic panels, aprons, curtains and Bucky slot covers. (12) If patient dose is estimated during fluoroscopy, it is typically done using a dosimeter to measure radiation exposure rate at the tabletop. (10)
Radiation safety is especially important in relation to screening mammography because this widely used procedure involves exposing the breast tissue of large numbers of healthy women to ionizing radiation. Breast tissue, particularly glandular tissue as opposed to adipose (fatty) tissue, is among the most radiosensitive tissues in the body. This increased sensitivity places younger women, whose breasts contain larger proportions of glandular tissue, at greater risk per unit of dose. (7,13)
For women of all ages, the benefits of screening mammography must be weighed against the slight possibility of radiation-induced cancer. Ample evidence suggests that the benefits of screening mammography substantially exceed these potential risks, but radiologic science assumes a linear relationship between radiation dose and the resulting risk of carcinogenesis; this requires dose to be minimized during screening mammography, even while maintaining the image quality necessary to achieve the procedure's screening benefits. (14)
Of greatest interest in calculating dose to the breast is the mean glandular dose, which most appropriately characterizes radiation risk from mammography. A kind of equivalent whole-body dose for the breast, it characterizes the effective dose absorbed by the breast's glandular tissues (ie, the acinar and ductal epithelium and associated stroma), which are assumed to have equal radiosensitivity throughout the breast. Variables affecting the mean glandular dose are the type of image receptor used, the x-ray beam energy (half-value layer, or HVL, and kVp), the degree of breast compression, the breast's size and its adiposity.
The optimum beam HVL for film-screen mammography is 0.3 to 0.4 mm Al. Breast dose is determined by the required optical density. Optimum settings for digital equipment are individually determined for each type of system, and breast dose is determined by the required signal-to-noise ratio.
Breast dose is reduced when x-ray beam energy (HVL) is increased, but this can result in reduced image contrast. The use of rhodium filters or targets also can reduce breast dose for thicker or more glandular breasts, but this may come at the cost of reduced image contrast. Dose associated with digital mammography is not governed by the need for proper image density or brightness, as these can be obtained for almost any dose by manipulating the window and level controls.
Compression of breast tissue during mammography improves image quality greatly and reduces breast dose by as much as 50%. Compression spreads the breast tissue laterally, thereby reducing the x-ray's path. A breast containing greater amounts of adipose tissue is more readily penetrated by x-rays and thus might receive a lower dose per image from the same technique. Dose values for a given technique also might vary greatly depending on the size of the breast. (14)
When mammography screening programs are established, the primary concern is the potential for carcinogenic risk to a large group of women, rather than to specific individuals. Consequently, the average value of the mean glandular dose for the group is most important, and the average breast thickness and composition are most relevant. When an individual woman expresses concern regarding the dose received from a mammogram, dose calculation should be modified to account for her actual breast tissue composition, if possible. (14)
The population of primary interest in screening mammography is women 40 years and older. Younger women are likely only to have diagnostic mammographic examinations resulting from physical findings or to receive a single baseline screening study. Therefore, it may be reasonably assumed that calculations of mean glandular dose apply primarily to breasts containing a larger fraction of adipose tissue, such as those found primarily in older women. (14) Various national organizations, as well as state regulatory agencies, recommend that mean glandular dose for a single projection of a compressed breast of average composition (50% water to 50% adipose) should not exceed 3 mGy. (14)
One of several advances in breast imaging technology to reduce dose while improving image quality is the automatic exposure control (AEC). Essentially a phototimer for mammography, it measures both x-ray intensity and quality. Use of this device can help ensure quality images at a low radiation dose, even as voltages vary from 23 to 32 kVp and breast thickness varies from 2 to 8 cm, regardless of breast composition. Positioned after the image receptor to minimize object-to-image distance, the AEC's detector (either an ionization chamber or a solid-state diode) estimates the beam quality after it passes through the breast, thereby allowing an assessment of breast tissue composition and selection of the correct target/filter combination. Thick, dense breasts are better imaged with rhodium/rhodium, and thin, fatty breasts with molybdenum/molybdenum. (15)
Devices such as the AEC can reduce the need for repeat exposures, which is an important factor in screening mammography efficacy and safety. Adhering to quality assurance measures and optimizing the 3 major components of image quality--contrast resolution, sharpness and signal-to-noise ratio--are important considerations for producing mammograms that contain sufficient information for interpretation. (13)
Special Concerns in Radiologic Imaging
The Pregnant Patient and Fetal Irradiation
Evidence has long suggested that the developing embryo or fetus is especially radiosensitive. Special care is taken routinely to avoid exposing the abdominal area of pregnant women to unnecessary radiation. Until recently, the embryo was believed to be most sensitive to radiation during its very earliest stages of development. In 1970 the International Commission on Radiation Protection proposed what came to be known as the "10-day rule," which suggested that whenever possible radiologic technologists and physicians should perform abdominal x-ray examinations on women of child-bearing age within 10 days of the last onset of menstruation because conception was unlikely to have occurred in this timeframe. The difficulty and impracticality of scheduling necessary radiographic examinations only in this timeframe, and the resultant unnecessary postponement of examinations for many women, led to reconsideration of the 10-day rule.
The rule also was revisited in the wake of research suggesting that the fetus is relatively insensitive to radiation in the earliest stages of pregnancy but, according to one source, is most sensitive between 8 and 15 weeks' gestation, when the rate of DNA proliferation in the brain is highest. (7) Potential effects of exposure at this stage include an increased incidence of Down syndrome and a substantial reduction in IQ. The risk of such a deleterious effect has been calculated at 30 IQ points reduction for every sievert; the risk of induced fatal childhood malignancy from exposure at this stage of gestation has been calculated at 28 cases per 1000 per Sv (or 28 "excess" cases of childhood cancer in a population of 1 million exposed to a fetal dose of 1 mSv). (7)
If any possibility of pregnancy exists, the general advice currently given to clinicians and radiologic technologists is to limit any abdominal or pelvic radiologic examination to within 28 days of the patient's last menstrual period, whenever possible. (7) Specific radiologic examinations that may give doses to the uterus in the tens of mGy (for example, barium enemas and pelvic or abdominal CT) have recently been returned, at least for a limited time, to the "10-day" rule; that is, these specific examinations should be conducted only within 10 days of the onset of the patient's last menstrual period. (7) Clinicians and technologists also are advised to schedule elective radiologic procedures within a few days of the patient's last onset of menstruation to minimize the possibility of irradiation to an embryo. (10)
The American College of Radiology practice guideline for the performance of abdominal radiography states that all imaging facilities should have policies and procedures in place to allow them to reasonably attempt to identify pregnant patients prior to performing any diagnostic examination involving ionizing radiation. (16) Such procedures might include the use of a questionnaire completed by the patient before the examination, which would include 2 or 3 simple questions regarding the date of onset of last menstrual cycle, possibility of pregnancy and history of hysterectomy. (17) If a facility does not wish to use such a questionnaire, posted signs reading, "Are you pregnant or could you be? If so, inform the radiologic technologist," could provide a suitable alternative. In addition to these measures, experts in radiologic science continue to believe that the ethical and professional responsibilities of the radiologic technologist include verbally screening female patients for pregnancy. (17) If pregnancy is determined, the possibility of using other imaging modalities, which are appropriate in many clinical situations, should be considered. (16)
Although there is no absolute contraindication to abdominal radiography, pregnancy remains a relative contraindication because the uterus is within the primary beam for almost all examinations. (16) Among the frequently performed radiographic examinations that cause greatest fetal dose is an anteroposterior (AP) projection of the lumbosacral spine (fetal dose = 40 mrad). Procedures resulting in a fetal dose equaling approximately 30 mrad are AP projections of the abdomen, kidneys, ureters and bladder. Images of the hip, for which gonadal shields should be used if possible, also result in a fetal dose equaling 30 mrad. (17)
Referring clinicians are advised always to consider the possibility that a woman of child-bearing age who is undergoing any radiologic examination involving the abdomen could be pregnant. Thus, the referring clinician should weigh the potential benefits of the diagnostic information against the risk of any possible deleterious effects and indicate on the order given to the radiologic technologist whether the procedure should be carried out if the woman is pregnant. (7)
In the event a pregnant woman does undergo a radiologic examination, special efforts should be made to minimize the dose received by the patient's lower abdomen and pelvic region. The technologist should select technical exposure factors that will produce a diagnostically useful radiograph by means of the smallest exposure possible. Use of a high-kVp technique is appropriate. (17) The beam should be collimated precisely to include only the anatomic area of interest. If the patient's lower abdomen and pelvic area are not of diagnostic interest, they should be covered with a lead apron or other suitable protective apparel. (10)
The Pregnant Technologist
Pregnancy does not prevent radiologic technologists working in diagnostic imaging from performing their work duties, but observing established radiation safety practices, which protect all radiologic technologists, is essential. (18) When a radiologic technologist becomes pregnant, she should notify her supervisor. After this notification, the pregnancy is considered "declared" and is recognized officially by the facility. At that point, regardless of the nature of the facility or the technologist's work experience, the supervisor should review acceptable practices of radiation protection with the pregnant technologist, emphasizing the cardinal rules of minimizing time, maximizing distance and using shielding. (17) The supervisor then should review the technologist's previous radiation-exposure history to determine whether adjustments are necessary.
The monthly equivalent dose to the embryo or fetus should not exceed 0.5 mSv per month or 50 mrem per month. This equivalent dose limit excludes medical and natural background radiation exposure and is designed to significantly restrict the total lifetime risk of leukemia and other malignancies in individuals exposed to radiation in utero. (18) Over the course of a pregnancy, embryonic and fetal dose should be limited to 5 mSv or 500 mrem. (17)
Many facilities provide pregnant radiographers with a second radiation monitor to be worn under the protective apron at waist level. Records of the exposure reported on this monitor should be identified as exposure to the fetus and maintained separately from records of the exposure reported on the monitor worn at collar level. Care should be taken to ensure that the monitors are never switched or the records confused.
Protective aprons worn by radiologic technologists should be at least 0.5-mm lead equivalent. These provide approximately 90% attenuation at 75 kVp. This level of protection is sufficient enough that heavier, thicker aprons (eg, 1-mm lead equivalent) are unnecessary, especially in light of potential back problems associated with later pregnancy. (17) Wraparound aprons generally are preferred during pregnancy. These should be properly fitted and need not extend below the knee.
Pregnant radiologic technologists working in radiation oncology and nuclear medicine observe additional precautions. In radiation oncology, pregnant technologists are advised to avoid participating in brachytherapy applications. Those working in nuclear medicine should handle only small quantities of radioactive material and should not elute radioisotope generators or inject millicurie quantities of radioactive material. (17)
The Pediatric Patient
The potential for biologic damage from exposure to ionizing radiation is more pronounced in children and infants, particularly in regard to chronic effects and genetic effects. The longer life expectancy of pediatric patients means they could easily survive long enough to develop a radiation-induced leukemia or a cancer of the lung or thyroid gland. (10) With these facts in mind, radiologic technologists should make every attempt to minimize exposure of pediatric patients to ionizing radiation.
Radiologic technologists are aided in this effort by the fact that smaller doses of ionizing radiation generally are sufficient to produce diagnostically useful images of pediatric subjects. For example, an AP projection of an infant's chest results in an entrance exposure of less than 5 mR. A PA or AP projection of an adult chest delivers an entrance exposure ranging from 12 to 26 mR. (10)
Conversely, patient motion that results in motion artifact on the image is of greater concern with pediatric patients than adults. To solve or minimize this problem, the radiologic technologist should shorten exposure times by selecting a high mA setting and using effective immobilization techniques. Special pediatric immobilization devices to hold the patient securely and safely in the required position are available for chest radiography and other radiographic procedures. Using these devices when available can help reduce the need for repeat exposures, thereby minimizing patient dose.
Facilities with sufficient resources may consider the possibility of setting aside special rooms for pediatric radiography and assigning personnel who are comfortable and experienced working with children. Cartoon posters, puppets and other potentially distracting entertainment can increase pediatric patient cooperation by helping children feel less intimidated.
Radiologic technologists working with children should be familiar with gonadal shielding. If gonadal tissue is more than 2 cm from the edge of the field of view, the use of a gonadal shield will not affect the gonadal dose significantly, assuming good collimation. For girls who require shielding, individual variation in the location of the ovaries necessitates shielding the iliac wings, as well as the sacral area. Effective gonadal shielding of either sex might not be possible during some radiographic studies in which shielding would obscure the area of interest. (10)
Projection orientation is also important in pediatric radiography. In female patients for whom either PA or AP projections are possible, technologists should note that a PA projection subjects the radiosensitive tissue of the breast to significantly lower doses. (10)
Collimation is an especially important consideration during pediatric radiography. Although an automatic collimation system reduces the radiation field size to the dimensions of the image receptor, many pediatric patients are significantly smaller than the image receptor, resulting in the need for additional manual adjustment of collimation. As in any other radiographic study, reduction of the field size to the anatomy of interest not only reduces patient exposure, but also improves image quality by reducing scatter.
Acquisition of CT scans in pediatric patients also requires adjustment of technical exposure factors because some factors normally used for adults undergoing CT are not appropriate for children. The scan kVp, as well as the mAs per slice, can be lowered for young children. CT imaging facilities that routinely use the same technical factors for pediatric patients as for adults are urged to develop new scanning protocols. (10)
Design for Radiation Protection
More than 100 radiation-protection devices and accessories are associated with modern x-ray equipment. Some are confined to fluoroscopic assemblies, others to radiographic ones. Among these are devices and accessories mandated by federal law to be available on all diagnostic x-ray equipment. (19)
Protective X-ray Tube Housing
Every x-ray tube used must be contained in a housing that reduces radiation leakage to less than 100 mR/hr, as measured at a distance of 1 meter. (19)
The operator's control panel must indicate whenever the x-ray tube is energized. Indicators for kVp and mA usually satisfy this requirement, but some control panels have either visual or audible signals indicating when the tube is energized.
It should be impossible to expose the image receptor while the radiologic technologist is standing outside the fixed protective barrier of the operating console booth. The exposure control should be fixed to the operating console and not to a long cord. (19)
A source-to-image-receptor distance (SID) indicator must be provided and, regardless of type, must be accurate to within 2% of the indicated SID. The operating console can be considered a secondary barrier to ionizing radiation exposure because of its capacity to intercept leakage and scatter. (19)
Proper beam collimation reduces scatter, thereby improving image contrast and effectively reducing patient dose by minimizing unnecessary irradiation of nearby organs outside the area of interest. (19) Attenuation of the useful beam by the collimator shutters must be equivalent to attenuation achieved by the protective housing. Cones and diaphragms may replace the collimator during special examinations.
Positive Beam Limitation and Beam Alignment
Most new radiographic systems continue to include a long-established and previously required feature--automatic light-localized variable-aperture collimators, also known as positive beam limitation (PBL) devices. These devices are adjusted so that the collimator shutters automatically provide an x-ray beam equal to the image receptor with any film size and at all standard SIDs. The PBL must be accurate to within 2% of the SID. In addition to proper collimation and positive beam limitation, each radiographic tube should be provided with a mechanism that ensures proper alignment of the x-ray beam with the image receptor. (19)
Filtration is an example of a design feature specifically added to the x-ray beam to reduce patient dose. (19) Perhaps the most important patient-protection characteristic of a radiographic unit, (20) beam filtration reduces exposure to the patient's skin and superficial tissue by absorbing most of the lower-energy photons, or "soft" x-rays, that contribute nothing to the imaging process. This filtering increases the mean energy or "quality" of the beam and also is referred to as "hardening" the beam. The remaining photons are more penetrating and less likely to be absorbed in body tissue. Consequently, absorbed dose to the patient decreases when proper filtration is placed in the beam's path.
Filtration begins with the inherent filtration available in the glass envelope that encases the x-ray tube--the insulating oil surrounding the tube and the glass window in the tube housing. This provides filtration approximately equal to 0.5 mm Al. Sheets of aluminum are placed outside the glass window of the tube housing above the collimator shutters. This added filtration is readily accessible to service personnel and can be changed as the x-ray tube ages. Combined inherent and added filtration should equal the amount required to filter the useful beam adequately. (10)
All general-purpose diagnostic x-ray beams must have a total filtration (inherent plus added) of at least 2.5 mm Al when operated above 70 kVp. Radiographic tubes that operate between 50 and 70 kVp must have at least 1.5 mm Al filtration. Operation below 50 kVp requires a total minimum of 0.5 mm Al filtration. Usually, it is not possible to measure filtration directly, so a measurement of the half-value layer of the x-ray beam is used. Filtration should be determined annually or after a change in the x-ray tube or tube housing. (20)
For any given radiographic technique, the output radiation intensity should be constant from one exposure to another. This is checked by making repeated exposures at the same technique and observing the average variation in radiation intensity. Reproducibility of x-ray exposure should not exceed 5% intensity change. (19)
Many of the design features mandated or highly recommended for modern radiographic units, including protective tube housings, filtration, automatic exposure controls and positive beam limitation devices for collimators, are deployed automatically during diagnostic imaging. The protection they offer to the patient, such as reducing the need for repeat exposures, improving image quality and effectively reducing dose, also help protect the radiologic technologist from unnecessary exposure. As diagnostic imaging begins, the radiologic technologist also must actively undertake protective practices, such as immobilization and shielding, that offer complementary protection to patient and technologist alike.
Patient Immobilization and Shielding
Shielding begins with effective communication between technologist and patient. Alleviating patient anxiety is the most important concern, as this increases the likelihood of cooperation and helps bring the procedure to a successful conclusion. (10) The technologist should take adequate time to explain the procedure in terms the patient can understand and give the patient an opportunity to ask questions. Listening attentively to these questions, and answering them truthfully and appropriately, helps create a sense of trust between patient and technologist, which is especially important before lengthier procedures. If pain, discomfort or unusual sensations are anticipated, the patient should be informed before the procedure begins to minimize the risk of sudden movement and the need to repeat exposures.
Patient motion during radiography creates artifacts on the image that can decrease image quality and interfere with diagnosis. Gaining the patient's cooperation will help decrease voluntary movement, as will immobilizing the patient when appropriate. A variety of devices to help immobilize either the entire body or the part to be radiographed are available.
Shortening exposure time to the minimum needed helps decrease the likelihood of involuntary motion, such as that associated with digestion or circulation. Exposure time can be shortened with an appropriate increase in mA and with the use of high-speed imaging receptors. (10)
Specific Area Shielding
Specific area shielding is indicated when a particularly sensitive organ or tissue is located in or near the useful beam. The lenses of the eyes, the breasts and the gonads frequently are shielded from the primary x-ray beam by either a contact shield or a shadow shield. These are made of lead strips, lead-impregnated materials or radiopaque material. Contact shields may be either flat or shaped and are placed directly on the patient's body. Shadow shields are suspended over the area of interest and cast a shadow over the organs they are intended to protect. (12) Patient protection during radiation treatment includes the use of lead shielding to shape the treatment field and limit the radiation exposure of normal tissue. (5)
Protection of the reproductive organs during diagnostic imaging is of particular concern because genetic effects can result from exposure to ionizing radiation. (10) The American College of Radiology recommends that gonadal shielding be used during abdominal radiography for all male pediatric patients and, where appropriate, for adults. (16) When it does not interfere with obtaining the required diagnostic information, shielding should be considered for all patients, especially children and adults who are potentially reproductive. Use of gonadal shields does not negate the need for proper patient positioning and beam collimation. (12)
During some radiologic procedures, the gonadal dose received by female patients is greater because the ovaries are located within the pelvic cavity, unlike the testes, which are located outside and below the pelvic cavity. For example, a female patient undergoing a radiographic examination of the lumbar spine would receive a gonadal dose of 400 mrad based on typical protocols, while a male patient undergoing the same procedure would receive a gonadal dose of 175 mrad. Male patients undergoing a radiographic examination of the pelvic area, however, typically would receive a gonadal dose of 300 mrad, while women typically would receive 150 mrad. Distribution of the tissue overlying the ovaries also can affect the gonadal dose received by female patients. (2)
Occupational Radiation Exposure
Radiologic technologists can do a lot to minimize occupational radiation exposure. Most control measures require neither sophisticated equipment nor rigorous training, but rather a conscientious attitude when performing assigned tasks. The key principles of radiation protection--time, distance and shielding--together with the practice of ALARA, remain the most important considerations in controlling occupational radiation exposure. (12) As noted earlier, recently developed equipment characteristics intended to enhance image quality also reduce patient dose, consequently reducing the radiologic technologist's occupational exposure as well.
Some occupational exposure to ionizing radiation is routine for radiologists and radiologic technologists. Levels of exposure depend on the nature and frequency of the diagnostic and therapeutic activities in which these personnel engage. An established radiation monitoring program uses strict procedures and specially designed devices to determine the quantity of radiation received by those working in a radiation environment. Scheduling secretaries, file clerks and darkroom technicians who work in a radiology or diagnostic imaging practice usually do not require monitoring for occupational radiation exposure. Some operating room personnel, such as those who routinely assist in cystoscopy or C-arm fluoroscopy, might require monitoring. (12) Wearing or using a radiation monitor does not itself afford any protection against ionizing radiation.
A personnel dosimeter is a monitoring device worn by radiologists, radiologic technologists and others to detect and measure the quantity of ionizing radiation the wearer has been exposed to over a period of time. Recommended for those who are exposed occupationally on a regular basis to ionizing radiation, personnel dosimeters are required for anyone at risk of receiving 10% or more of the annual occupational effective dose limit of 50 mSv (5 rem) in any single year. (21)
A variety of personnel dosimeters are available. Regardless of the type of personnel dosimeter worn, several considerations should be kept in mind:
* The instrument should be lightweight and durable enough to withstand normal daily use.
* It must detect and record both small and large exposures consistently and reliably.
* Outside factors such as very warm weather, ordinary mechanical shock or humidity should not affect its performance.
* It should be reasonably inexpensive to allow health care facilities to monitor as many radiation workers as possible in a cost-effective manner. (21)
Regardless of type, the dosimeter must be worn in the same location on the body each working day. All diagnostic imaging personnel should wear the primary dosimeter at collar level on the anterior surface of the body to approximate the maximum radiation dose to the thyroid gland, head and neck. During fluoroscopy and other radiographic procedures that produce high occupational exposure, some facilities require wearing a second dosimeter at waist level under a wrap-around style lead apron. Pregnant diagnostic imaging personnel should wear a second dosimeter to record the radiation dose to the abdomen during gestation. Such a monitor provides an estimate of the dose equivalent to the embryo or fetus. An extremity dosimeter is recommended as a second monitor when personnel perform radiographic procedures that require their hands to be near the primary x-ray beam. (See Fig. 1.) Nuclear medicine technologists should wear an extremity dosimeter when handling radioactive material. (12) Regardless of the type of dosimeter worn, a record of exposure becomes part of the employment record of all personnel working in a radiation environment. (21)
[FIGURE 1 OMITTED]
Four types of personnel dosimeters currently are used to measure individual exposure of the body to ionizing radiation. The oldest and best-established personnel dosimeter is the film badge; others include the optically stimulated luminescent (OSL) dosimeter, the pocket ionization chamber and the thermoluminescent dosimeter (TLD). A fifth type of dosimeter, the TLD ring badge, is intended to measure radiation exposure to the extremities and is normally worn on the hands.
Film badges are especially economical personnel monitoring devices that generally are used to record whole-body radiation exposure accumulated at a low rate over a long period of time. Film badges are composed of 3 parts: a plastic film holder, assorted metal filters and a radiographic film packet similar to dental film. Penetrating radiation casts a faint shadow of the metal filters on the processed dosimetry film, while softer radiation casts a more pronounced image of the filters. The density of the image permits an estimate of the energy of the radiation. Film badges also reveal the direction from which the radiation reached the film, such as from front to back or from back to front, and for this reason always must be worn with the proper side facing forward. Filter images also can be used to determine whether the exposure resulted from excessive amounts of scattered radiation or from a single exposure from a primary beam.
The film in badges is sensitive to doses ranging from 0.1 mSv (10 mrem) to 5000 mSv (500 rem). At the end of the monitoring period, perhaps a month, a densitometer is used to measure the optical density of the filter images on the film badge and determine the amount of radiation to which the film was exposed. An important advantage of the film badge is that it allows for maintenance of a permanent, legal record of personnel exposure. The badge is also inexpensive to buy and reuse, enabling facilities to regularly monitor as many employees as possible on a cost-effective basis. One disadvantage of the film badge is that it must be shipped to a monitoring company for processing, thus preventing determination of a radiation worker's exposure on the day it occurs. The film used as the badge's sensing device is susceptible to fogging caused by temperature extremes and humidity, and remains most accurate if worn no longer than a month. Other types of personnel dosimeters are more sensitive to lower levels of radiation (eg, less than 0.1 mSv or 10 rem) and, therefore, might be more appropriate in some situations. The film badge is most sensitive to photons having an energy level of 50 kiloelectron volts (keV); its sensitivity decreases for values above and below this energy range. (21)
Optically Stimulated Luminescent Dosimeters
The newer optically stimulated luminescent dosimeter resembles and handles similarly to traditional film and thermoluminescent dosimeters and combines the best features of both while eliminating some of the disadvantages. (21) (See Fig. 2.) The OSL uses an aluminum oxide radiation detector that is "read out" using selected frequencies of laser light. When laser light hits the sensing material of the detector, the material becomes luminescent in proportion to the amount of radiation exposure received.
[FIGURE 2 OMITTED]
The OSL dosimeter can give an accurate recording of exposure as low as 1 mrem for x-ray and gamma ray photons, with energies ranging from 5 keV to more than 40 million electron volts (MeV). For beta particles with energies from 150 KeV to more than 10 MeV, dose measurement by the OSL ranges from 10 mrem to 1000 rem. Neutron radiation, with energies ranging from 40 keV to more than 35 MeV, can be measured from 20 mrem to 25 rem with the OSL. The OSL's increased sensitivity makes it ideal for monitoring diagnostic imaging employees who are pregnant, as well as all those who work in low-radiation environments. (21)
Pocket Ionization Chambers
Pocket ionization chambers, also known as pocket dosimeters, are the most sensitive of all personnel dosimeters. (21) However, they are used infrequently in diagnostic imaging. The pocket dosimeter, which resembles an ordinary fountain pen, contains a thimble-sized ionization chamber to measure radiation exposure. The dosimeter can be clipped conveniently to the wearer's apparel, similar to a pen in a lab coat pocket.
This type of personnel dosimeter works by detecting the presence and sign of an electric charge. The pocket ionization chamber of the device contains 1 positively charged and 1 negatively charged electrode. When the charged electrodes are exposed to gamma radiation or x-radiation, the air surrounding the charged electrode becomes ionized and discharges the mechanism in direct proportion to the amount of radiation exposure. An indicator shows the net radiation exposure in milliroentgens. Pocket ionization chambers generally are sensitive to exposures ranging from 0 to 200 mR. (21)
The primary advantage of a pocket ionization chamber is its ability to provide an immediate readout of exposure for workers in high-radiation exposure areas, such as cardiac catheterization laboratories. The dosimeter can be read on site to determine the dose received during a given assignment. If necessary, workers then can alter their habits immediately. The pocket ionization chamber also can be used to provide one-time monitoring of nonradiologic personnel, such as nurses. (12) The accuracy and sensitivity of pocket dosimeters make them ideal monitoring devices for procedures that are of relatively short duration. (21) They are also compact, easy to carry and convenient to use, all considerations that are important in encouraging consistent daily use.
The disadvantages of pocket dosimeters begin with their cost--generally around $150 per unit. Readings should be obtained at least daily, as the electric charge tends to escape the chamber over time, resulting in an inaccurate reading. Pocket dosimeters also can discharge if dropped or subjected to other mechanical shock during the normal working day, again resulting in an inaccurate reading. The ionization chamber must be charged to a pre-determined voltage before use so that the indicator reads zero. Unlike film badges, pocket dosimeters provide no permanent, legal record of exposure. Therefore, readings must be recorded diligently by radiation safety personnel. (21)
A thermoluminescent dosimeter might look very similar to a film badge personnel dosimeter, but it operates completely differently. The device's sensing material is a crystalline form of lithium fluoride (LiF). Ionizing radiation causes some of the electrons in the molecules of the LiF crystals to absorb energy and rise to higher energy levels or bands. When the LiF crystals are heated, subsequent changes cause them to emit this energy in the form of visible light. The intensity of the light is measured with a photomultiplier tube and is proportional to the amount of radiation that interacted with the crystals.
Although a TLD badge can cost twice as much as a film badge, it has several advantages. The LiF crystals interact with ionizing radiation in a manner similar to the interaction of ionizing radiation with human soft tissue, thereby enabling dose to be determined more accurately. In addition to their use as personnel dosimeters, TLDs often are used to measure patient skin dose during fluoroscopy and other procedures. (11) These devices precisely measure exposures as low as 5 mR. Humidity and temperature extremes do not affect their accuracy, and TLD badges can be worn for up to 3 months at a time. After a reading has been obtained, the LiF crystals in the device can be reused, increasing the badge's cost effectiveness over time. (21)
However, the TLD does have some disadvantages in addition to its higher initial cost. Although the TLD badge and the crystals it contains can be reused, a TLD reading can be obtained only once; the process of obtaining the readout destroys the previous history of exposure. (21) As with pocket dosimeters, readings must be recorded diligently by radiation safety personnel.
Occupational Radiation Monitoring Report
Radiation safety personnel must comply with federal and state laws by recording results of occupational radiation monitoring in a precise and timely fashion. Records are maintained for weekly, monthly, quarterly or annual review. Each record for an individual worker must contain identifying information, such as a Social Security number, date of birth and gender. It also must specify the type of personnel dosimeter used. Records of exposure must include exposure for the week, month, quarter or year currently under review, as well as cumulative annual and lifetime exposures. Records of exposure from extremity and fetal monitors must be maintained or identified separately.
When a radiologic technologist changes employment, these records of exposure must follow, and the technologist should receive a copy of his or her total radiation exposure history at the facility before leaving. (12)
While personnel dosimeters like the ones described previously only measure cumulative radiation intensity, radiation survey instruments indicate the presence or absence of radiation and give a reasonably accurate measurement of the exposure when properly calibrated. The 3 most commonly used area monitoring devices are the ionization chamber-type survey meter (also known as a "cutie pie"), the proportional counter and the Geiger-Muller detector.
Regardless of the type of area monitor used, several considerations should be kept in mind:
* Area monitors should be easy to carry so that one person can operate them efficiently for a significant period of time.
* They should be durable enough to withstand normal transport and use and reliable enough that the amount and rate of exposure in a given area can be accurately assessed.
* Ideally, area monitors should interact with ionizing radiation in a manner similar to the way human tissue reacts, allowing dose to be determined more accurately.
* An area monitor should be able to detect all common types of ionizing radiation, with initial cost and subsequent maintenance charges as low as possible.
* To ensure consistency among individual users, neither the energy of the radiation nor its direction should significantly affect the unit's response. (21)
Ionization Chamber-type Survey Meter
This type of monitor measures both exposure rate and cumulative exposure. It measures x-radiation, gamma radiation and, when equipped with a suitable window, beta radiation. In its rate mode, it can measure intensities ranging from 1 mR per hour to several thousand R per hour, and in its integrate mode can keep track of exposures from 0.1 mR to 1 R. The "cutie pie" can monitor diagnostic x-ray installations when exposure times of at least 1 second are used. It also measures fluoroscopic scatter radiation exposure rates, exposure rates from patients receiving therapeutic doses of radioactive materials, exposure rates in radioisotope storage facilities and cumulative exposures received outside protective barriers. (21)
Commonly used to measure the exposure rates at various distances from a patient who has received radioactive materials for diagnostic or therapeutic purposes, the "cutie pie" cannot be used to measure exposures produced by typical diagnostic procedures because exposure times are generally too short for the meter to respond. The unit's other disadvantages include its relatively large size and the relative delicacy of its detector. (21)
Proportional counters are not used in diagnostic imaging. Rather, they are used in laboratories to detect alpha and beta radiation, between which they can discriminate, and to detect small amounts of other types of low-level radioactive contamination. The counter must be held close to the surface of the object being surveyed or it will not obtain an accurate reading of alpha radiation, which can travel only a short distance in air. (21)
This detector is the primary area monitor used in nuclear medicine facilities. With the exception of alpha particle emission, the unit easily can detect any area contaminated by radioactive material. Its capacity for rapid monitoring allows it to help locate a lost radioactive source or low-level radioactive contamination. Its audible sound system alerts the operator to the presence of ionizing radiation. It also can detect very-low-energy x-radiation and beta and gamma radiation, with readings in milliroentgen per hour. The major disadvantage of this detector is that, unlike the cutie pie meter, the energy of the radiation detected significantly affects the response of the unit, which can saturate or jam if placed in a very high-intensity radiation area, such as one with a linear accelerator used in radiation therapy. (21)
Barriers and Protective Apparel
Shielding used to absorb x-rays falls into 3 categories: fixed, mobile and personal. Fixed barriers include the wails, doors and protective cubicles of x-ray rooms. Such barriers typically have a lead equivalence of 1 to 3 mm, depending on the anticipated workload in the room, maximum kilovoltage likely to be used within and whether these permanent fixtures will need to absorb the primary beam. A protective cubicle should be large enough to accommodate students, nursing staff and visitors to the facility, as well as the radiology staff anticipated to use the room. Views into the x-ray room, and particularly of the patient, should be free of obstacles so that staff do not have to peek around the end of the screen to see the patient clearly. (7)
Mobile shields are particularly useful during fluoroscopic procedures that require a staff member to remain near a patient. A lead-acrylic panel suspended from the ceiling can considerably reduce doses to the upper body and head not otherwise blocked by a conventional lead-plastic apron. During procedures in which a staff member might be required to stand near the patient's head, such as gastroscopy, considerable protection can be provided by a lead-rubber sheet draped over an attachment to the side slots of the table and positioned on the operator's side of the irradiated area.
Protective aprons with a lead equivalence of at least 0.5 mm should be worn by everyone in the room, except the patient. Aprons thicker than this might prove uncomfortable or impractical to wear in some circumstances because of their increased weight. (7) In addition to aprons, personal protection extends to gloves used during fluoroscopy procedures or in operating wards.
Personnel Protection During Nuclear Medicine Procedures
Staff working in nuclear medicine imaging use good, efficient handling techniques to reduce external radiation exposure. They also keep close contact with radioactive patients to an absolute minimum. As is customary, disposable gloves should be worn when preparing and administering radionuclide injections. Accepted practice includes the use of tungsten, lead or bismuth alloy syringe shields, and doses should be drawn behind a lead-glass barrier to reduce exposure to the torso. Protective clothing worn during nuclear medicine procedures is intended to protect the sterility of the radiopharmaceutical being used and prevent radionuclide contamination from reaching the skin. (7)
Radiation protection begins with avoiding unnecessary radiographs and ends with strictly adhering to specific guidelines and limits established through years of research and observation. Discovering the dangers associated with ionizing radiation did not prevent us from making use of its many benefits. As radiation's use in medicine continues to be refined, medical physicists and others remain intrigued by its possibilities and continue to explore what radiation's judicious and respectful use might yet allow.
Directed Reading Continuing Education Quiz
To receive Category A continuing education credit for this Directed Reading, read the preceding article and circle the correct response to each statement. Choose the answer that is most correct based on the text. Transfer your responses to the answer sheet on Page 444 and then follow the directions for submitting the answer sheet to the American Society of Radiologic Technologists. You also may take Directed Reading quizzes online at www.asrt.org. Effective October 1, 2002, new and reinstated members are ineligible to take DRs from journals published prior to their most recent join date unless they have purchased a back issue from ASRT.
*Your answer sheet for this Directed Reading must be received in the ASRT office on or before this date.
1. Radiologic technology's most important protective measure is to:
a. keep exposure levels to the minimum required for the task at hand.
b. use audible signals to warn that the x-ray tube is energized.
c. have a medical physicist periodically measure patient doses.
d. ensure all technologists wear an apron that is at least 0.5-mm lead equivalent.
2. As ionizing radiation passes through the body's organs and tissues, it:
a. deposits energy.
b. leaves artifacts that show up on the radiograph.
c. must be completely absorbed.
d. can scar tissue permanently.
3. Radiologic technologists protect children and infants from unnecessary exposure because:
a. radiographs of children are harder to interpret.
b. children may become frightened during radiography.
c. parents request it.
d. younger tissues and organs are more radiosensitive.
4. The most radiosensitive cells in the body are:
a. connective tissue cells.
b. reproductive and blood cells.
c. nerve and muscle cells.
d. skin cells.
5. Acute aftereffects of radiation exposure can take the form of:
a. peeling and ulcerated skin.
b. weakened bones.
c. a low-grade fever.
d. insomnia and anxiety.
6. Chronic effects of radiation exposure can include:
a. weight gain and obesity.
b. leukemia and cancer.
c. lowered IQ.
d. secondary infections.
7. Radiation exposure measures:
a. the concentration of ionizing radiation in a given volume of air.
b. the amount of radiation escaping the x-ray tube.
c. radiation dose to the patient's body as a whole.
d. radiation doses received over the course of a technologist's career.
8. Absorbed radiation dose measures:
a. the amount of radiation needed to produce a high-quality radiograph.
b. dose absorbed by the most radiosensitive organs.
c. the amount of energy deposited in tissue as ionizing radiation passes through it.
d. the amount of radiation filtered out by the glass in the x-ray tube.
9. Effective dose or effective dose equivalent takes into account:
a. the relative radiosensitivity of tissues and organs that absorb the dose.
b. the patient's age.
c. how the patient was positioned for the examination.
d. how many x-ray examinations the patient has had that year.
10. According to the American College of Radiology, radiologic imaging facilities should be able to adjust examination protocols to take into account:
a. physician preferences.
b. a patient's weight, height, body mass index or lateral width.
c. the disease for which a patient is being screened.
d. the age and capability of the imaging equipment.
11. Which 2 types of examinations account for 95% of a diagnostic radiologic technologist's occupational exposure to radiation?
a. mobile radiography and mammography
b. mammography and pediatric examinations
c. mobile radiography and fluoroscopy
d. computed tomography (CT) and mammography
12. All of the following affect mean glandular dose to the breast during mammography except:
a. the degree of breast compression.
b. choice of image receptor.
c. how many mammograms the patient has had.
d. the breast's size and adiposity.
13. Various national organizations and state regulatory agencies have recommended that the mean glandular dose for mammography not exceed-- mGy for a single projection of a compressed breast.
14. The developing embryo or fetus is most sensitive to the harmful effects of ionizing radiation between -- and -- weeks' gestation.
c. 6, 13
d. 8, 15
15. Among the most frequently performed radiographic examinations, the one that results in greatest fetal dose is the:
a. AP of the lumbosacral spine.
b. PA of the chest.
c. AP of the thoracic spine.
d. axiolateral projection of the hip.
16. Over the course of a radiologic technologist's pregnancy, equivalent dose to the embryo and fetus should not exceed -- mSv or-- mrem.
a. 1, 100
b. 3, 300
c. 5, 500
d. 7, 700
17. How should kVp and mAs be adjusted for a CT scan of a pediatric patient compared with levels used for adult patients?
a. Both can be lowered from adult levels.
b. Both should be increased.
c. They must remain the same.
d. Increase kVp and decrease mAs.
18. What are the benefits of proper beam collimation?
1. reduces scatter
2. improves contrast
3. eliminates the need for beam filtration
a. 1 and 2
b. 1 and 3
c. 2 and 3
d. 1, 2 and 3
19. Radiographic tubes that operate between 50 and 70 kVp must have at least -- mm Al filtration.
20. When it does not interfere with obtaining required diagnostic information, gonadal shielding should be considered for which types of patients?
a. all patients, especially children and adults of reproductive age
b. postmenopausal women
c. male pediatric patients only
d. pregnant patients only
21. An individual radiologic technologist's occupational exposure is tracked chiefly by:
a. maintaining a log of fluoroscopy x-ray beam on-time.
b. using the Geiger-Muller detector, the "cutie pie" monitor or the proportional counter.
c. maintaining a written record of exposure to patients who have received therapeutic doses of radioactive materials.
d. using a film badge, optically stimulated luminescent (OSL) dosimeter, thermoluminescent dosimeter or pocket ionization chamber.
22. Which of the following is the most sensitive type of personnel dosimeter?
a. film badges
b. OSL dosimeters
c. pocket ionization chambers
d. thermoluminescent dosimeters
23. All of the following are advantages of thermoluminescent dosimeters compared with film badges except:
a. more accurate determination of dose.
b. not affected by temperature or humidity.
c. can be worn for up to 3 months at a time.
d. lower cost.
24. Records of occupational radiation exposure should include cumulative exposure for the current year and for the employee's lifetime.
25. Which type of detector is used in nuclear medicine departments to detect contamination with radioactive materials?
a. "cutie pie" monitor
b. ionization chamber-type survey meter
c. proportional counter
26. Fixed barriers, such as walls and doors, typically have a lead equivalence of: a. less than 1 mm.
b. 1 to 3 mm.
c. 4 to 6 mm.
d. more than 6 mm.
Expiration Date: June 30, 2009 * Approved for 1.5 Cat. A CE credits
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(2.) Sherer MAS, Visconti PJ, Ritenour ER. Introduction to radiation protection. In: Radiation Protection in Medical Radiography. 4th ed. St. Louis, Mo: Mosby; 2002:1-22.
(3.) Bushong SC. Human biology. In: Radiologic Science for Technologists: Physics, Biology and Protection. St. Louis, Mo: Mosby; 2001:450-461.
(4.) Bushong SC. Fundamental principles of radiobiology. In: Radiologic Science for Technologists: Physics, Biology and Protection. St. Louis, Mo: Mosby; 2001:462-468.
(5.) Hahn SM, Glatstein EG. Principles of radiation therapy. In: Kasper DL, Braunwald E, Fauci AS, et al, eds. Harrison's Principles of Internal Medicine. 16th ed. Columbus, Ohio: The McGraw-Hill Companies; 2006:chap 71.
(6.) McNitt-Gray MF. Radiation issues in computed tomography screening. Radiol Clin of N Am. 2004;42:711-723.
(7.) Robinson A. Radiation protection and patient doses in diagnostic imaging. In: Grainger RG, Allison D, Andreas A, et al, eds. Grainger and Allison's Diagnostic Radiology: A Textbook of Medical Imaging. 4th ed. London, England: Churchill Livingston Inc, 2001:chap 11.
(8.) American College of Radiology. ACR Guidelines and Standards. ACR practice guideline for general radiography. 2006:17-20. Available at: www.acr.org/s_acr/sec .asp?CID=1848&DID=16053. Accessed December 15, 2006.
(9.) American College of Radiology. ACR Guidelines and Standards. ACR practice guideline for the performance of computed tomography (CT) of the abdomen and computed tomography (CT) of the pelvis. 2006:351-354. Available at: www.acr.org/s_acr/sec.asp?CID =1848&DID = 16053. Accessed December 15, 2006.
(10.) Sherer MAS, Visconti PJ, Ritenour ER. Protection of the patient during diagnostic radiologic procedures. In: Radiation Protection in Medical Radiography. 4th ed. St. Louis, Mo: Mosby; 2002:155-200.
(11.) Colombo P, Pedroli G, Nicoloso M. Evaluation of the efficacy of a bismuth shield during CT examinations. La Radiologia Medica. 2004;108:560-568.
(12.) Bushong SC. Radiation protection procedures. In: Radiologic Science for Technologists: Physics, Biology and Protection. St. Louis, Mo: Mosby; 2001:546-564.
(13.) National Council on Radiation Protection and Measurements. Benefits and risks of mammography. In: A Guide to Mammography and Other Breast Imaging Procedures. Bethesda, Md: National Council on Radiation Protection and Measurements; 2004:235-266.
(14.) National Council on Radiation Protection and Measurements. Dose evaluation. In: A Guide to Mammography and Other Breast Imaging Procedures. Bethesda, Md: National Council on Radiation Protection and Measurements; 2004:168-201.
(15.) Bushong SC. Mammography. In: Radiologic Science for Technologists: Physics, Biology and Protection. St. Louis, Mo: Mosby; 2001:306-318.
(16.) American College of Radiology. ACR Guidelines and Standards. ACR practice guideline for the performance of abdominal radiography. 2006:301-305. Available at: www .acr.org/s_acr/sec.asp?CID =1848&DID =16053. Accessed December 15, 2006.
(17.) Bushong SC. Health physics. In: Radiologic Science for Technologists: Physics, Biology and Protection. St. Louis, Mo: Mosby; 2001:516-530.
(18.) Sherer MAS, Visconti PJ, Ritenour ER. Protecting occupationally exposed radiologic personnel. In: Radiation Protection in Medical Radiography. 4th ed. St. Louis, Mo: Mosby; 2002:201-224.
(19.) Bushong SC. Designing for radiation protection. In: Radiologic Science for Technologists: Physics, Biology and Protection. St. Louis, Mo: Mosby; 2001:531-545.
(20.) Bushong SC. Quality control. In: Radiologic Science for Technologists: Physics, Biology and Protection. St. Louis, Mo: Mosby; 2001:427-439.
(21.) Sherer MAS, Visconti PJ, Ritenour ER. Radiation monitoring. In: Radiation Protection in Medical Radiography. 4th ed. St. Louis, Mo: Mosby; 2002:225-244.
Joyce Helena Brusin, M.F.A., is a member of the American Medical Writers Association and works as an essayist and freelance medical writer and editor in Missoula, Mont. Her Directed Reading article on recent developments in digital mammography appeared in the January/February 2006 issue of Radiologic Technology.
Reprint requests may be sent to the American Society of Radiologic Technologists, Communications Department, 15000 Central Ave. SE, Albuquerque, NM 87123-3909.
Table 1 Response of Various Cell Types to Radiation Cell Type Radiosensitivity Lymphocytes High Spermatogonia High Erythroblasts High Intestinal crypt cells High Endothelial cells Intermediate Osteoblasts Intermediate Spermatids Intermediate Fibroblasts Intermediate Muscle cells Low Nerve cells Low Reprinted with permission from Bushong SC. Radiologic Science for Technologists: Physics, Biology and Protection. St. Louis, Mo: Mosby; 2001:459.
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|Title Annotation:||CE: DIRECTED READING|
|Author:||Brusin, Joyce Helena|
|Date:||May 1, 2007|
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