Extract
The topic of radiation exposure for patients, physicians, and staff has become prominent in the lay press. It seems that every week another story about radiation safety makes the evening news. For physicians and surgeons, the largest radiation exposures involve fluoroscopy use with either fixed or mobile units. For patients, fluoroscopy (c-arm), computed tomography (CT), and nuclear medicine studies constitute the vast majority of exposures. The use of each of these modalities has grown dramatically with changes in the practice of medicine.
The topic of radiation exposure for patients, physicians, and staff has become prominent in the lay press. It seems that every week another story about radiation safety makes the evening news. For physicians and surgeons, the largest radiation exposures involve fluoroscopy use with either fixed or mobile units. For patients, fluoroscopy (c-arm), computed tomography (CT), and nuclear medicine studies constitute the vast majority of exposures. The use of each of these modalities has grown dramatically with changes in the practice of medicine.
C-arm use in orthopaedic surgery is increasing rapidly as surgery transitions to minimal-access surgery. With less direct visualization, surgery is being conducted with fluoroscopic guidance. When fluoroscopy is combined with a computer for navigation systems, radiation exposure sustained by surgeons can be reduced dramatically. This transition does not decrease the patient's radiation dose, and in some instances it can increase it substantially1.
CT scans have become accepted as commonplace. The rate of CT use is thirty times greater than it was twenty years ago, and the radiation exposure sustained by a patient can be dramatic2,3. Less than one-sixth of physicians receive any training in radiation safety4. One questionnaire study of physicians showed that 4% did not know that ultrasound did not involve ionizing radiation and 27% did not know that magnetic resonance imaging (MRI) did not involve radiation at all5. Approximately 90% of physicians underestimated the radiation exposure and risks from pediatric radiographs and CT scans4. A single pediatric abdominal CT scan exposes the patient to more radiation than the seventy-year exposure from living in the vicinity of the Chernobyl accident2. For a five-year-old patient who weighs 19 kg, a chest CT is the equivalent of 600 chest radiographs and a CT of the abdomen and pelvis is the same as 1400 chest radiographs4.
Even everyday events carry the risk of radiation exposure; however, compared with the exposures associated with imaging studies, the numbers should give clinicians reason for pause (Table I).
As educators, it is imperative that we are knowledgeable about radiation and its effects. If we are not, we cannot teach our residents and students. Very few if any orthopaedic training programs include any formal training in radiation physics or safety, leaving residents at higher risk from c-arm exposures. Compounding this problem, mentoring orthopaedists themselves often lack basic knowledge about radiation safety and physics. This ignorance is propagated and bad habits recapitulated over subsequent generations. Trainees are also not as adept at surgical techniques, so surgery usually lasts longer, requiring more radiographic images to check progress. This impacts the surgeon, the staff, and the patient.
Many institutions require prospective c-arm operators to obtain board-approved certification in order to operate the fluoroscope. Candidates must first undergo occupational training, which incorporates didactic sessions on radiation physics as well as radiation safety guidelines and protocols. The educational curricula should be frequently updated to ensure conformity to national standards and strictly adhered to by those who work with c-arm fluoroscopy in their daily practice. For example, changing how the arm is set up can result in a fiftyfold decrease in a patient's radiation exposure6-9. Since surgeon and staff exposure is related to patient exposure, there is a potential to reduce occupational exposure by 98%. By educating our trainees about the importance of the problem and potential solutions, we can help to protect current and future patients from the negative effects of radiation exposure.
Radiation safety overlaps the tort-reform and medicolegal arenas. There is a nearly linear relationship between patient radiation exposures and reports of medical malpractice litigation. The areas with the highest medicolegal liability had the highest radiation exposures per person, with a 50% difference from the highest to the lowest10,11. Physician orders are required for these procedures because the risk-to-benefit ratio has to be assessed. Unfortunately, the vast majority of physicians do not understand the risks to the patient, surgeon, and staff. While there is no arbitrary limit to the radiation a patient should get, the concept of ALARA (as low as reasonably achievable) must be followed. We have become complacent when it concerns radiation exposures.
When caring for a patient, we must provide the best care that we can. Any medically necessary test or procedure should be done regardless of the radiation exposure. Patients should not be denied appropriate evaluation and treatment for fear of radiation exposure. However, it is incumbent on us to ensure the concept of ALARA is followed.
Modern adaptations that allowed for the practical use of fluoroscopy were not developed until the 1950s. By the 1980s, fluoroscopy had gained a prominent foothold in the orthopaedic trauma community, where it was championed as a valuable tool during femoral nailing and hip pinning12,13. As indications for the use of mobile c-arm fluoroscopy expanded, its popularity grew commensurately. Now, through its relevance to numerous applications and overall convenience, the use of fluoroscopy has become commonplace and, in some cases, indispensible in the daily clinical practice of orthopaedics.
In 2006, an estimated 324 million radiographic procedures were performed in the U.S. These included 129 million chest radiographs, sixty-two million CT scans, fifty-six million extremity radiographs, twenty million spine radiographs, and nineteen million radiographs of the pelvis and hip14. It is estimated that half or more of the collective radiation dose received by the U.S. population from all medical procedures comes from CT scans. A recent study of >950,000 adults in five health-care markets across the U.S. found that >655,000 (69%) underwent at least one imaging procedure associated with radiation exposure during a two-year period15. They looked at radiographic exposures using annual effective doses with limits similar to those for occupational exposure. Radiation dose is reported as direct dose and effective dose. The milligray (mGy = 1/1000 J/kg) is used to describe the amount of radiation absorbed by the individual organs or tissues directly exposed to the radiation source. Effective dose is used to compare the risk of cancer from this nonuniform exposure and is reported in millisieverts (mSv). Less than 20 mSv was considered low or moderate. Between 20 and 50 mSv was high, with >50 mSv considered very high. In this population of almost 1 million people, 2% received high to very high exposures15. This study estimated that 75% of the collective radiation dose came from CT scans and nuclear imaging studies.
Between 1980 and 2006, the number of radiographic procedures increased by 47%. The cumulative estimated dose had increased by 727%. This was fueled by the explosion of CT volume, which grew 12% per year16. In Japan, there are three times as many CT scanners per person as in the U.S. This translates to an estimated 3% of cancers attributable to medical imaging17.
In one hospital system, orthopaedic surgeons had a fivefold increase in lifetime cancer rates over other employees who used radiographs18. A front-page article in USA Today stated that the "overuse of diagnostic CT scans may cause as many as 3 million excess cancers in the USA over the next two to three decades."19 The radiation risk for the American public is from CT scans, fluoroscopy, nuclear medicine, and radiographs. All of these are involved in the care of the musculoskeletal patient.
When the c-arm fluoroscope is set to the so-called normal mode, technique factors are adjusted automatically to produce an image of optimal clarity. Radiation production increases precipitously when imaging a larger body area with a greater cross-sectional area. Therefore, depending on the body area to be imaged, the amount of direct and scattered exposure may vary considerably. Imaging a larger body area causes a considerable amplification in direct exposure to the patient, as well as indirect scatter exposure to the surgical team6-9. This idea is especially pertinent to orthopaedists who practice spine surgery. Illustrating this point, Jones et al. found that dose rates encountered during spine procedures are ten to twelve times greater than those during non-spine procedures20. Giordano et al. further demonstrated that during a fluoroscopic examination using a large c-arm, radiation exposure to the patient increased nearly ten times when imaging a cervical spine specimen compared with a foot and ankle. Exposure to the surgical team increased two to three times6-9,20. With use of a mini c-arm for the same scenario, patient exposure increased three to four times and exposure sustained by the surgical team doubled.
Acute effects of diagnostic radiographs are occasionally reported and are almost always associated with high doses of fluoroscopy used in cardiac catheterization or interventional radiographic procedures. However, a recent incident involving stroke patients at a hospital in Los Angeles points to the potential hazards of CT scanners21. More than 250 patients undergoing CT angiograms were given more than eight times the intended radiation dose as the result of an error in programming the scan parameters. The error was not discovered until a number of patients complained of erythema and alopecia.
Probably the most substantial risk of low-level exposure to radiation is the induction of cancer. No large-scale epidemiologic study of cancer induction by diagnostic levels of radiation has been reported, to our knowledge. Several groups have attempted to evaluate the risk of cancer using known risk estimates, collective population doses, and number of CT scans performed per year in the U.S. Brenner et al. suggested that eventually 1.5% to 2% of all cancers in the U.S. could be attributed to radiation from CT scans2. de González and Darby estimated that 29,000 future cancers could be attributed to seventy-two million CT scans performed in 2007 in the U.S.17.
Effective dose is determined by calculating a weighted exposure to involved organs and tissues. The weighting factors reflect the radiation sensitivity of each involved organ or tissue. For example, a typical, single posteroanterior chest radiograph delivers a skin dose of 0.14 mGy to the posterior part of the chest. The effective dose, calculated from the radiation absorbed by the lungs, breasts, esophagus, and stomach, multiplied by the appropriate weighting factor, is 0.03 mSv22. A typical CT scan of the chest delivers an effective dose of 7 mSv, which is equal to approximately 233 posteroanterior chest radiographs (Table II).
Once the effective dose is known, the risk of fatal cancer can be estimated. A nominal probability of 5% per sievert is usually assumed for an adult population23. The situation is more complex for children; the probability increases with decreasing age3. Table II lists the effective dose and fatal cancer risk ratio for typical diagnostic radiographic studies. For the purposes of this example, the radiation risk to children is calculated for ten-year-old children with an equal proportion of boys and girls. In this case, the risk is estimated at 9.1% per sievert24.
In the last decade, many orthopaedists have embraced the concept of minimally invasive surgery. Technology supporting minimally invasive surgery has evolved, with some advocates reporting decreased morbidity, cost savings, and improved outcomes25-27. Unfortunately, many procedures that are touted as minimally invasive require the use of mobile c-arm fluoroscopy to indirectly visualize pertinent anatomy to achieve an optimal result on radiographs. This has caused many orthopaedists to rely heavily on the use of ionizing radiation for such procedures. Recently, Bindal et al. reported on surgeon and patient radiation exposure in minimally invasive transforaminal lumbar interbody fusion28. Surgeon exposure doses, which were recorded under a lead apron, peaked at 62 mrem (0.62 mSv), while patient skin entrance dose reached almost 270 mGy over an average fluoroscopy period of 1.69 minutes. While these levels clearly represent subthreshold values for deterministic effects (2 Gy), and low overall effective dose, they are nonetheless disconcerting.
Surgeons and their staff may perform hundreds of similar procedures in a given year, making them vulnerable to the effects of long-term subthreshold exposure. For patients who are subjected to multiple diagnostic imaging procedures over their lifetime, there is a substantial risk of lifetime overexposure, especially in younger patients. This is an especially common occurrence in orthopaedic trauma, osseous reconstruction, or extremity malalignment correction. As surgeons continue to study the purported clinical benefits of minimally invasive procedures, they must carefully weigh the potential for harm created by a growing dependence on fluoroscopy to complete such procedures.
As indications for the use of fluoroscopy continue to expand, many have become justifiably concerned that frequent exposure to low-dose ionizing radiation may negatively affect practitioners and patients. Mastrangelo et al. found that at a small community hospital where radiation safety practice was poor, orthopaedic surgeons who used fluoroscopy were five times more likely to develop cancer than other hospital employees who used radiographs18. Members of the mainstream media have also begun to echo the alarm voiced by the medical community. Although there are currently no exposure limits for patients, action is currently being undertaken to impose stricter guidelines for patients undergoing diagnostic imaging. The United States Food and Drug Administration (FDA) recently announced an initiative to reduce unnecessary exposure from CT, fluoroscopy, and nuclear medicine examinations. The FDA intends to impose regulations that require CT and fluoroscopic device manufacturers to develop safer technologies and provide appropriate training to practitioners. In turn, the industrial sector has responded by developing innovative technology that allows fluoroscopy scanners to display, record, and electronically report equipment settings and radiation dose to a patient's electronic medical record and national dose registries.
Representatives from federal agencies, such as the National Commission on Radiation Protection and the Standards of Practice Committee, are currently involved in federal hearings to address the FDA's growing concerns over medical radiation dose. This evolution stems from mounting public concern over rising exposure to medical radiation, as well as a recent series of high-profile errors involving both diagnostic and therapeutic uses of radiation. Given this recent attention, patients will undoubtedly begin to question the safety and necessity of their diagnostic tests. Medical providers, orthopaedists in particular, must be prepared to answer them, and offer supporting evidence that is practical and relevant.
There remains widespread disagreement on what constitutes an acceptable degree of risk associated with the use of mobile c-arm fluoroscopy. Nonetheless, most would agree that all practitioners who work with ionizing radiation should observe appropriate radiation safety principles. Moreover, dose reduction techniques should be learned, taught, and consistently utilized to minimize exposure to patients and staff.
As the lay press covers these stories, the American public is becoming more aware of the potential risks from our routine diagnostic studies. To reduce exposure, remember these four factors: distance, exposure, barriers, and technique, or DEBT.
Distance and Positioning
Increase the distance from the radiation source to the patient, physician, and staff. Radiation emanates from a point source and travels in straight but divergent directions when it exits the x-ray tube. Divergence increases with distance according to the inverse square law; thus, doubling the distance from the radiation source reduces exposure to a fourth. Observation of inverse square law principles can yield substantial reductions in exposure for the surgical team. Historically, surgeons have been led to believe that as long as they stand at least six feet from the fluoroscopy source, they are at essentially zero risk of being exposed to radiation29. This notion has recently been challenged in studies that have demonstrated exposure levels of more than forty times baseline at a distance of twenty feet from the fluoroscopy source7.
Orientation of the x-ray beam relative to the position of the patient and surgeon has been shown to impact exposure. Jones et al. established that placing the radiation source under the operating table might provide an effective beam stop20. Rampersaud et al. noted a dramatic reduction in exposure dose when the surgeon stood on the same side of the patient as the image intensifier30. This strategy is most useful when imaging body areas that completely fill the radiograph beam. However, when imaging smaller body areas, a portion of the x-ray beam passes by the specimen unimpeded, resulting in a higher dose on the side opposite to the radiation source. This adjustment should be taken into account when positioning operating staff safely.
The position of the imaged body area within the arc of the c-arm can also drastically impact radiation output from the fluoroscopy unit. Decreasing the distance between the patient's surface and the image intensifier reduces the relative air gap between the two, and subsequently reduces exposure. Giordano et al. found that positioning the cadaveric specimen as far as possible from the radiation source within the arc of the C-arm reduced patient exposure tenfold and surgeon exposure by half in comparison with imaging the specimen adjacent to the radiation source6,7.
Where personnel stand during the imaging can impact exposure. Stepping back a few inches can effect dramatic decreases in exposure. Despite the one study mentioned earlier, six feet away is still used as a safe distance. But, one must remember that while the radiation dose may not be significant at that distance, it is not zero.
Time of Exposure
Limit the time of exposure by doing fewer studies, fewer images, and shorter fluoroscopy exposures. It is intuitive that reduction of fluoroscopy time correlates with reduced exposure levels. However, tactics to reduce fluoroscopy time may be underutilized. Every effort should be made to eliminate the use of so-called live fluoroscopy. Instead, multiple so-called spot images should be obtained to achieve the same desired result. The audible warning indicating the fluoroscope must be restarted after five minutes should always be used and observed. Finally, it is critical that the patient not be exposed to fluoroscopic imaging while the operator is not viewing the screen image.
Use of Barriers
Effectively use barriers such as aprons. The use of lead shielding is recommended to attenuate exposure from scattered radiation. Depending on the thickness of the garment, protection afforded by lead shielding can vary considerably. In general, one can expect a reduction of >90% in scatter exposure from a lead gown of 1-mm Pb thickness. However, lead aprons do not provide total protection from radiation exposure. The protective benefit afforded by lead can be compromised by poor storage and maintenance. A recent report by the American Academy of Orthopaedic Surgeons showed exposures under lead to be only 30% to 60% less than those over the lead19.
The c-arm operator plays a vital role in managing radiation output from the fluoroscope. One way in which the c-arm operator can modulate radiation exposure is by reducing the field size of the x-ray beam through the use of barriers such as lead shutters or collimators. Collimation blocks out areas that are not of interest, improving resolution of the remaining structures. Also, because less tissue is exposed, patient dose and scatter production are reduced.
Technique
Modify the technique with collimation, avoid magnification, alter CT protocols, and image only the regions of concern during follow-up (L3-S1 for CT instead of T10-S1 if the patient has a known pathological condition such as a fracture). Operating the c-arm under the magnification function also greatly amplifies radiation exposure. Magnification is achieved by manipulating a smaller radiation input area over the same output area. This, in turn, lowers image brightness, which is automatically corrected by boosting radiation production and subsequent direct and scatter exposure.
Diagnostic testing in orthopaedics relies heavily on imaging studies. Many of these imaging modalities can be used interchangeably, with variable sensitivity for soft tissue or osseous anatomy. Meanwhile, procedures that rely on imaging for localization, indirect visualization, or instrument guidance often depend specifically on ionizing radiation as an imaging tool. For some minimally invasive orthopaedic procedures, c-arm fluoroscopy has supplanted direct visualization, and is requisite to successful completion of that procedure. To help to reduce intraoperative radiation exposure, some authors have begun to use alternate imaging modalities to perform procedures that formerly relied more heavily on fluoroscopy31-33. Although the use of such modalities is relatively untested, they offer promising new alternatives to imaging tools that use ionizing radiation.
Mini Compared with Large C-Arm Fluoroscopy
Over the past several decades, mini-c-arm fluoroscopy has emerged as a convenient imaging tool that has the potential to reduce radiation dose. However, recent data suggest that although the mini c-arm is capable of limiting exposure dose to the patient and surgeon, it must still be used prudently to optimize its dose-reducing properties8. Injudicious use of the mini c-arm can even exceed doses encountered when the large c-arm is used under equivalent imaging conditions (Figs. 1 and 2, Tables III and IV). Therefore, strict radiation protection measures, including the routine use of protective lead garments, should be observed when both mini and large c-arm fluoroscopes are used.
Computed Tomography Issues
The past two decades of medical advancement have seen remarkable improvements in high resolution, rapid acquisition technologies for CT imaging. The ease and clinical utility of these scans for defining the three-dimensional anatomy is unparalleled by other imaging techniques. For these reasons, CT has become the standard for imaging in many settings. In this country alone, more than sixty-two million CT scans are made every year3—a twentyfold increase in the utilization of CT since 1980. Consequently, there has been a concomitant increase in radiation exposure sustained by the population. Over the past twenty to thirty years, the average radiation dose to which we are exposed has doubled3; yet exposure from natural sources is unchanged. It is estimated that while CT accounts for only 5% to 10% of all diagnostic radiographic imaging, it is responsible for up to two-thirds of the effective dose of radiation to which the general public is exposed from medical sources34,35.
Given the high dose of radiation exposure from CT imaging, it is essential to ask if these imaging studies are being ordered appropriately. Studies have consistently demonstrated that the use of CT imaging is excessive but can be reduced while maintaining excellent clinical outcomes for many disorders, including pediatric appendicitis and head injuries36,37 as well as traumatic injury38,39, and for the diagnosis of pulmonary embolism40. One study has suggested that, by following selective imaging guidelines in the trauma setting, imaging costs could be reduced by 39% and radiation exposure reduced by 44%38.
Radiation Exposure from Musculoskeletal Computed Tomography
CT is one of the standard imaging studies for orthopaedic care. The three-dimensional information is particularly useful for defining osseous anatomy and fracture patterns such as when characterizing tibial plateau fractures41 and planning total joint arthroplasty42-44.
A recent study by our group described the radiation exposure from all types of orthopaedic CT scans and quantified how the dose changed on the basis of the anatomic location45. The goal was to quantify the effective dose of radiation delivered by CT scans of the spine and extremities.
The results of the study noted above are summarized in Figures 3-A and 3-B. The study found that imaging the hip and lumbar spine provided an effective dose of 3.09 mSv and 19.15 mSv, respectively. This is approximately equivalent to the same effective dose as 103 and 638 chest radiographs, respectively (one posteroanterior chest radiograph = 0.03 mSv). Not surprisingly, it was demonstrated that imaging the spine and pelvis had a much higher effective dose exposure than imaging the extremities. Additionally, the further from the torso, the lower the effective dose delivered to the patient. Thus, an ankle CT scan (0.07 mSv) delivered less exposure than a knee CT scan (0.15 mSv), which was much less than a hip CT scan (3.09 mSv).
This makes intuitive sense when considering the physical properties of the CT. Any anatomic region that passes within the aperture of the scanner will be exposed to the emitted radiation. Additionally, because of the side scatter of the radiation, even the anatomic regions that are not of clinical interest must be considered when evaluating exposure. For example, a CT scan of the hip irradiates the soft tissue at the same level, which may include portions of the gonads and pelvic organs, while imaging the thoracic spine may include irradiation of the breasts, lung, and thyroid. For more distal anatomic sites such as the wrist or ankle, the surrounding tissues are generally much less radiosensitive.
The study also highlighted how conscientious positioning of the patient can dramatically reduce the radiation exposure45. For elbow CT scans, the patient can be positioned with the elbow at the side or with the elbow lying on the table above the head. In the first example, the abdominal contents in the same plane as the elbow are exposed; however, if the elbow is above the head, then a substantially less effective dose is transmitted to the patient as no radiosensitive organs are within the path of the beam. The effective dose with the elbow tucked against the torso of the patient was 8.35 mSv (the equivalent of approximately 278 chest radiographs), while the dose when the elbow was raised over the head was only 0.14 mSv (4.67 chest radiographs), demonstrating how, with a simple change in the positioning of the patient, the radiation exposure was decreased by nearly sixtyfold.
Not surprisingly, CT scans of the spine are also associated with some of the most substantial exposures that were calculated (Fig. 3-B). Thoracic and lumbar CT scans were by far the most, with 18 and 19 mSv, respectively. Interestingly, this was considerably higher than the exposures reported for CT of the abdomen and pelvis, which tends to range between 5 and 8 mSv45,46. Although these CT scans are imaging the same anatomic regions, the difference lies in the increased radiation output and finer slices to achieve the fine osseous resolution required to adequately image spinal abnormalities. Both of the factors increase the radiation exposure above what is delivered with conventional abdominal and pelvic CT.
These high doses are particularly important when patients who require serial CT examinations for diagnosis and postoperative follow-up are considered. The cumulative dose exposure of nearly 20 mSv (667 chest radiographs) from each examination quickly raises the overall dose and increases the risk of carcinogenesis in these patients. Considering that some reports have indicated that exposure as low as 34 mSv may lead to increased risk of developing solid tumors, the radiation exposure to spine patients may be concerning47.
Conclusions Regarding CT
Computed tomography is a remarkably useful clinical tool for physicians and orthopaedists in particular. Its use is only expected to increase. We as orthopaedists must take care to ensure that we are not overutilizing these imaging tests. As discussed, CT scans impart considerable radiation exposure to patients that likely approaches dangerous levels in some of them.
Overutilization is common across many medical specialties, and the use of selective imaging guidelines could dramatically reduce the number of CT scans currently being ordered. This concept likely applies to all fields of medicine including orthopaedics, although no study has evaluated such guidelines, as far as we know. Regardless of how it is accomplished, it is essential for our patients that we carefully consider why a test is needed and not order it simply out of reflex. CT is useful in so many circumstances that there may be a tendency to order it without thought to the possible harm caused to the patient. Although the harm from the CT may not be as readily apparent as that from an invasive test such as a lumbar puncture or joint aspiration, as with all tests, it is present and potentially very serious. The harm from these tests includes not only the risk from the radiation exposure but also other risks including the psychological and physical stress associated with further work-up of incidental findings from an unnecessary examination.
Reducing the number of unnecessary CT scans is an extremely difficult task. There are many reasons why physicians feel obligated to order these tests including medicolegal concerns, economic incentives, and patients’ desires. Education about risks and better imaging guidelines may help to reduce the number of tests. However, to be effective, the physician must first consider these issues and critically examine whether the test is truly required to treat the patient.
As physicians and medical practitioners, we must be diligent to provide our patients with the best possible medical care. While patients must not be denied appropriate evaluation and treatment for fear of radiation exposure, it is incumbent on us to ensure the concept of ALARA is followed. When exposing a patient and medical staff to ionizing radiation cannot be avoided, specific measures can be taken to minimize that exposure, especially with regard to the use of fluoroscopy and CT. DEBT (distance, exposure, barriers, and time) is the genesis of practical guidelines for imagery. Exposure to ionizing radiation when computed tomography is used is more difficult to control. Necessary reductions in exposure are likely to be better realized through elimination of the overuse of CT or, indeed, any radiographic diagnostic tool, except in cases when the results will have a direct and immediate impact on treatment.
Note: The authors thank Kimberly A. Napoli for her assistance in the preparation of this manuscript.
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