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n Review Article Instructions 1. Review the stated learning objectives at the beginning of the CME article and determine if these objectives match your individual learning needs. 2. Read the article carefully. Do not neglect the tables and other illustrative materials, as they have been selected to enhance your knowledge and understanding. 3. The following quiz questions have been designed to provide a useful link between the CME article in the issue and your everyday practice. Read each question, choose the correct answer, and record your answer on the CME Registration Form at the end of the quiz. 4. Type or print your full name and address and your date of birth in the space provided on the CME Registration Form. 5. Indicate the total time spent on the activity (reading article and completing quiz). Forms and quizzes cannot be processed if this section is incomplete. All participants are required by the accreditation agency to attest to the time spent completing the activity. 6. Complete the Evaluation portion of the CME Registration Form. Forms and quizzes cannot be processed if the Evaluation portion is incomplete. The Evaluation portion of the CME Registration Form will be separated from the quiz upon receipt at Orthopedics. Your evaluation of this activity will in no way affect the scoring of your quiz. 7. Send the completed form, with your $15 payment (check or money order in US dollars drawn on a US bank, or credit card information) to: Orthopedics CME Quiz, PO Box 36, Thorofare, NJ 08086, OR take the quiz online. Visit www. Healio.com/EducationLab/Orthopedics for details. 8. Your answers will be graded, and you will be advised whether you have passed or failed. Unanswered questions will be considered incorrect. A score of at least 80% is required to pass. If a passing score is achieved, Vindico Medical Education will issue an AMA PRA Category 1™ certificate within 4-6 weeks. 9. Be sure to mail the CME Registration Form on or before the deadline listed. After that date, the quiz will close. CME Registration Forms received after the date listed will not be processed. CME ACCREDITATION This activity has been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education through the joint sponsorship of Vindico Medical Education and Orthopedics. Vindico Medical Education is accredited by the ACCME to provide continuing medical education for physicians. Vindico Medical Education designates this Journal-based CME activity for a maximum of 1 AMA PRA Category 1 Credit™. Physicians should claim only the credit commensurate with the extent of their participation in the activity. This CME activity is primarily targeted to orthopedic surgeons, hand surgeons, head and neck surgeons, trauma surgeons, physical medicine specialists, and rheumatologists. There is no specific background requirement for participants taking this activity. FULL DISCLOSURE POLICY In accordance with the Accreditation Council for Continuing Medical Education’s Standards for Commercial Support, all CME providers are required to disclose to the activity audience the relevant financial relationships of the planners, teachers, and authors involved in the development of CME content. An individual has a relevant financial relationship if he or she has a financial relationship in any amount occurring in the last 12 months with a commercial interest whose products or services are discussed in the CME activity content over which the individual has control. Drs Fabricant, Berkes, Dy, and Bogner have no relevant financial relationships to disclose. Dr Aboulafia, CME Editor, has no relevant financial relationships to disclose. Dr D’Ambrosia, Editor-in-Chief, has no relevant financial relationships to disclose. The staff of Orthopedics have no relevant financial relationships to disclose. UNLABELED AND INVESTIGATIONAL USAGE The audience is advised that this continuing medical education activity may contain references to unlabeled uses of FDA-approved products or to products not approved by the FDA for use in the United States. The faculty members have been made aware of their obligation to disclose such usage. MAY 2012 | Volume 35 • Number 5 cme ARTICLE Diagnostic Medical Imaging Radiation Exposure and Risk of Development of Solid and Hematologic Malignancy Peter D. Fabricant, MD; Marschall B. Berkes, MD; Christopher J. Dy, MD, MSPH; Eric A. Bogner, MD educational objectives As a result of reading this article, physicians should be able to: 1. Understand the research used to govern safe radiation exposure doses. 2. Understand recent initiatives in decreasing radiation exposure. 3. Review specific techniques that may help decrease radiation exposure in the daily practice of orthopedic surgery. 4. Gain perspective on spectrum of doses of ionizing radiation from common imaging modalities. Abstract Limiting patients’ exposure to ionizing radiation during diagnostic imaging is of concern to patients and clinicians. Large singledose exposures and cumulative exposures to ionizing radiation have been associated with solid tumors and hematologic malignancy. Although these associations have been a driving force in minimizing patients’ exposure, significant risks are found when diagnoses are missed and subsequent treatment is withheld. Therefore, based on epidemiologic data obtained after nuclear and occupational exposures, dose exposure limits have been estimated. A recent collaborative effort between the US Food and Drug Administration and the American College of Radiology has provided information and tools that patients and imaging professionals can use to avoid unnecessary Drs Fabricant, Berkes, and Dy are from the Department of Orthopaedic Surgery, and Dr Bogner is from the Department of Radiology, Hospital for Special Surgery, New York, New York. The material presented in any Vindico Medical Education continuing education activity does not necessarily reflect the views and opinions of Orthopedics or Vindico Medical Education. Neither Orthopedics nor Vindico Medical Education nor the authors endorse or recommend any techniques, commercial products, or manufacturers. The authors may discuss the use of materials and/or products that have not yet been approved by the US Food and Drug Administration. All readers and continuing education participants should verify all information before treating patients or using any product. Correspondence should be addressed to: Peter D. Fabricant, MD, Hospital for Special Surgery, Department of Orthopaedic Surgery, 535 E 70th St, New York, NY 10021 ([email protected]). doi: 10.3928/01477447-20120426-11 415 n Review Article cme ARTICLE ionizing radiation scans and ensure use of the lowest feasible radiation dose necessary for studies. Further collaboration, research, and development should focus on producing technological advances that minimize individual study exposures and duplicate studies. This article outlines the research used to govern safe radiation doses, defines recent initiatives in decreasing radiation exposure, and provides orthopedic surgeons with techniques that may help decrease radiation exposure in their daily practice. D iagnostic imaging technology has advanced significantly since the introduction of the radiograph by Wilhelm Röntgen in 1895.1 At that time, little was known about the harmful effects of radiograph beam radiation, and accidental exposures served as hard lessons in the consequences of exposure. Following Röntgen’s development of the radiograph, Thomas Edison attempted to use the radiograph tube to develop an illuminating lamp but soon discovered that his assistant developed alopecia and skin ulcerations and subsequently died of metastatic carcinoma in 1904.2 Large single-dose exposures and cumulative exposures have been associated with solid tumors and hematologic malignancy. Over the past 100 years, multiple cohorts of exposed populations have been examined for dose–response relationships between radiation exposure and malignancy, and these historical data have been used to determine harmful and lethal doses and have subsequently helped establish personal and occupational exposure limits. Since the discovery of radiographs, ionizing (eg, radiography, fluoroscopy, and computed tomography [CT] scan) and nonionizing (eg, ultrasound and magnetic resonance imaging) modalities have emerged. Patient safety remains a priority with these newer imaging modalities. Due to their frequent use and the higher dose of ionizing radiation, CT scans are of the highest concern. Exposure is common, 416 and therefore the at-risk population is large, owing to the fact that 72 million CT scans are performed in the United States each year, and the rate has increased 12% annually from 1993 to 2007.3 As of 2007, medicine represented the largest source of ionizing radiation exposure to the US population4 and has been reported to be the single largest manmade population exposure, affecting nearly everyone who seeks medical care.5 Appearance of this information in popular media created a scare among patients and brought the issue of CT scanning overuse and radiation exposure to the forefront of the medical lay press.6,7 Although associations between ionizing radiation and increasing frequency of CT scanning have been a driving force in minimizing patients’ exposure to ionizing radiation, significant risks occur when diagnoses are delayed or missed and subsequent treatment is withheld due to fears of radiation exposure. Overexposure to ionizing radiation and missed diagnoses have large economic and biopsychosocial consequences, affecting patients, families, and the medical system. Maximizing patients’ benefits and minimizing potential harm involves judicious use of radiological studies, use of nonionizing radiation modalities whenever possible, and properly dosing ionizing radiation when needed to maximize study resolution without delivering excessive radiation doses. This article outlines the research used to govern safe radiation doses, defines recent initiatives in decreasing radiation exposure, and provides orthopedic surgeons with specific techniques that may help decrease radiation exposure in their daily practice. Current Research Several obstacles exist when attempting to study the effects of ionizing radiation on humans. Ionizing radiation is carcinogenic in humans and teratogenic in fetuses. Because there is, by definition, no safe dose to administer for human testing, experimental human study designs are unethical, and information gleaned from animal studies is limited due to their dissimilar genome and physiology compared with those of humans. Therefore, limited pure biologic evidence exists, but animal studies support the view that low-dose radiation acts principally on the early stages of tumorigenesis, and a dose-dependent relationship exists between radiation dose and induction of DNA damage in cells.8 No large-scale epidemiologic study of cancer induction by diagnostic radiation is reported in the literature.9 Therefore, the greatest amount of information regarding human exposure to radiation is from studies of atomic-bomb survivors, which provide the ability to calculate dose-response. Many advantages are found in studying this population: a large number of participants (120,321 in the original Life Span Study [LSS] cohort), inclusion of both sexes, a varied array of dose ranges, and total body exposure, which allows for assessment of cancers at various body sites.8 Although medical radiation studies, occupational exposures, and environmental studies have also provided some insight, the LSS cohort is the most robust cohort of clinical participants. Samartzis et al10 reviewed the LSS cohort to determine threshold exposures for the development of radiation-induced bone sarcoma. They analyzed 80,181 participants and determined a threshold dose of 0.85 Gy using Poisson regression. The most common tumor was pelvic osteogenic sarcoma. Survival in these patients was low, with a 5-year mortality rate of 75%. The same cohort has also been analyzed for increased incidence and radiation threshold of nonmusculoskeletal tumors.11 Hematologic malignancy rates were higher than those seen in the general population, including leukemia and lymphoma. In total, 34% of leukemia deaths were attributable to radiation exposure in survivors exposed to .0.005 Gy.11 A meta-analysis by Daniels and Schubauer-Berigan12 evaluated 23 pri- Healio.com The new online home of ORTHOPEDICS | Healio.com/Orthopedics Medical Imaging Radiation Exposure | Fabricant et al cme ARTICLE mary research investigations that assessed occupational protracted exposures to lowdose ionizing radiation and calculated an excess relative risk of leukemia of 0.19 at 0.1 Gy. This is lower than that noted in the LSS cohort but can be explained by differences in exposure types: single-event vs chronic protracted exposure. Further epidemiological data suggest that acute exposures are 2 to 5 times more potent on increased cancer risk in humans than protracted exposures.13 Li et al14 evaluated the LSS cohort for solid and hematologic malignancies and noted an incidence of 17.2% for solid tumors, 0.35% for leukemias, and 0.52% for lymphomas and myelomas. All cancers studied (ie, gastric, lung, colon, liver, female breast, thyroid, bladder, lymphoma, and leukemia) noted a threshold value of 0.005 Gy, with varying increases in relative risk with levels above that threshold. Malignancies most sensitive to radiation dose were those with greater increases in relative risk for dose exposures .0.005 Gy, and included lung, colon, female breast, thyroid, bladder, and leukemia. These data were corroborated by Preston et al,15 who noted that 11% of solid tumors in participants exposed to .0.005 Gy could be attributed to radiation exposure, with increasing relative risk in a dose–response relationship. They also noted a decrease in excess relative risk of 17% per decade increase in age at exposure when controlling for age at diagnosis, and an increase in excess relative risk throughout the study period when controlling for age at exposure, indicating that radiationassociated increases in cancer rates persist throughout life regardless of age at exposure. When evaluating nonsex-specific cancers, no sex differences existed in rates of malignancy. Studies of the LSS cohort have produced robust evidence that exposure to ionizing radiation .0.005 Gy (5 mSv) confers an increased risk of solid and hematologic malignancy, with a dosedependent increase in relative risk. Bone MAY 2012 | Volume 35 • Number 5 tumors have a higher exposure threshold of 0.85 Gy (850 mSv) prior to excess relative risk. Estimates of excess relative risk from the LSS cohort are higher than those from studies examining participants with protracted low-dose exposure, and therefore may lead to an overestimate of the LSS studies on cancer risk. Radiation-associated increases in cancer rates persist throughout life regardless of age at exposure, and earlier exposure is associated with increased excess relative risk of developing radiation-induced malignancy during one’s lifetime. Given these data, risk of malignancy increases in a dose-dependent manner. Therefore, it is important to determine current patient exposures from diagnostic radiology studies and identify potential methods of decreasing patient exposure. Fazel et al16 analyzed utilization data from 952,420 participants aged between 18 and 64 years to determine average annual radiation exposure doses. Median effective dose was 0.1 mSv per participant per year. Cumulative effective doses increased with advancing age and were higher in women than in men. Interestingly, CT scans accounted for 75.4% of exposure, with 81.4% of those being administered in the outpatient setting. In total, 80% of men and 78% of women were exposed to no or low doses (0-3 mSv) of radiation annually. Although a significant minority of participants were exposed to higher doses of radiation, they were typically elderly patients.16 Table 1 shows the average dose of various imaging procedures that use ionizing radiation. Plain radiography creates less exposure than fluoroscopy (continuous radiograph) or CT scanning, with interventional procedures generating the greatest exposures. For comparison, Table 2 lists sources of background radiation and average effective dose.18 Extremity radiography exposes patients to 1/3000 of yearly background radiation and 1/1000 of the radiation exposure of a round-trip transcontinental flight. Fluoroscopic and CT examination exposures are greater Table 1 Common Musculoskeletal and Medical Imaging Procedures and Corresponding Average Effective Dosea Average Effective Exposure, mSv Study Myocardial perfusion imaging 15.6 Chest (noncoronary) CT angiography 15 Percutaneous coronary intervention 15 Abdomen CT 8 Chest CT 7 Nuclear bone imaging 6.3 Cervical spine CT 6 Lumbar spine CT 6 Pelvis CT 6 Neck CT 3 Head or brain CT 2 Thyroid uptake 1.9 Lumbar spine radiography 1.5 Abdomen radiography 0.7 Mammography 0.4 Chest radiography Extremity radiography 0.1-0.02 0.001 Abbreviation: CT, computed tomography. a Adapted from Mettler et al4 and the American College of Radiology and Radiological Society of North America.17 Table 2 Background Radiation Sources and Average Effective Dose18 Source Average Effective Exposure, mSv Cosmic radiation/ background 3 Radon gas 2 Living at plateau/ altitude 11.5 Coast-to-coast round-trip flight 10.03 417 n Review Article cme ARTICLE and, therefore, of higher clinical concern with repeated studies. Children’s exposure to ionizing radiation is an elevated concern given their developing physiology and increased risk of lifetime malignancy with early radiation exposure. The use of CT scans in children has increased rapidly and has been primarily driven by the speed with which a scan can be performed (within a matter of seconds), which essentially eliminates the need for anesthesia to limit motion during imaging.19 Adult and pediatric victims of blunt trauma routinely undergo intense imaging in the emergency room and trauma bay to facilitate rapid diagnosis. To determine pediatric exposure in a cohort of blunt trauma patients, Mueller et al20 prospectively studied all pediatric (aged 0-17 years) blunt trauma patients presenting at a major tertiary care urban medical center emergency department. Dosimeters were placed on reproducible anatomical landmarks of all children prior to initial CT evaluation. Mean wholebody effective dose was 17.43 mSv, which falls within the range of historical doses correlated with an increased risk of leukemia and solid tumors.14,15 Although an increased risk of future malignancy exists, the emergent nature of obtaining an accurate and rapid diagnosis for the presenting pediatric trauma patient outweighs such future risk because the consequences of misdiagnosis can be immediately fatal. Clearly, obstacles exist in conducting meaningful research in this field despite its ubiquitous importance. Again, because it is unfeasible and unethical to conduct directed human research by exposing participants to radiation, studies largely comprise epidemiologic data from atomic-bomb survivors (eg, the LSS cohort), occupational exposures, and observational studies. All methods have strengths and weaknesses. Although the LSS cohort includes patients of varying ages and both sexes, exposures are estimated and acute exposures may overestimate the effect that would be seen with protracted 418 low-dose exposures. Observational studies typically have fewer participants and smaller exposures, but dosimetry allows for more accurate and precise dose measurements. Experimental designs in animals are limited by the genetic and physiologic differences between humans and animals. Regardless of research methodology, it is accepted that ionizing radiation is carcinogenic and that a dose–response relationship exists between exposure and several types of malignancy. Future Direction It is in the best interest of physicians and patients to minimize exposure to ionizing radiation. However, studies requiring the use of ionizing radiation are clinically necessary and allow for rapid, accurate diagnosis of various disease entities and traumatic conditions. Therefore, future research should be directed toward reducing ionizing radiation as much as is clinically reasonable. As technology emerges, practice guidelines should be updated based on scientific study of new imaging modalities and scanner protocols. Joint efforts between the American College of Radiology and the US Food and Drug Administration, called Image Wisely (in adults) and Image Gently (in children), have initiated educational efforts of patients, families, radiologists, and radiology technicians in an attempt to eliminate unnecessary radiation exposure in patients and health care workers.21-23 Minimizing excessive radiation exposure involves using a dose as low as reasonably achievable to obtain proper resolution and therefore prevent the need for repeat imaging. Lead shielding of radiosensitive body parts, collimation (restricting beam area), patient positioning, exposure time during fluoroscopy, and appropriate safety training of all radiology technologists are also imperative.9 Research and development of new technology has the potential to achieve higher image resolution with minimal radiation dose. For example, diagnostic workup of certain bony hip abnormalities requires 3-dimensional rendering of bony structures.24 Previously, routine pelvic CT scans were used to obtain these images, and orthopedic surgeons analyzed bony structures while the increased radiation dose used to obtain soft tissue resolution was wasted. Early intrainstitutional collaboration between treating orthopedic surgeons and radiologists led to the development of lowdose CT scanning protocols that allow the surgeon to gain comprehensive diagnostic information while using minimal radiation exposure. According to personal communication with D. Gallagher, RT, in 2011, this has led to a pelvic CT scanning protocol that gains 3-dimensional imaging of a CT scan while using 2.5 mSv, or the equivalent dose of 4 to 6 pelvic radiographs. This underscores a vital need for an open dialogue between treating physicians, radiologists, and patients and their families regarding the goals of diagnosis and treatment. In addition, early private-sector research has developed CT scanning protocols that minimize radiation by 40% while maintaining a similar level of diagnostic resolution.25 This leads to more desirable software and equipment that can competitively enter the market, further driving industry research and innovation that benefits patients. Additional future areas of research should include practical and accessible methods of image portability. A universal imaging display language and accessible electronic medical records would eliminate the need for repeat imaging if patients do not possess their imaging studies. A complete log of cumulative year-to-date and lifetime radiation exposures would allow patients and physicians to make more informed decisions “on the margin” regarding the risk–benefit ratio of further imaging, given the patients’ cumulative dose from multiple studies across multiple practitioners. Minimizing Radiation Exposure: Practical Considerations Through the use of advanced diagnostic technology, improved operating room Healio.com The new online home of ORTHOPEDICS | Healio.com/Orthopedics Medical Imaging Radiation Exposure | Fabricant et al cme ARTICLE instrumentation, proper safety principles, and rational decision making, orthopedic surgeons can decrease the amount of radiation exposure to themselves, patients, and ancillary medical staff. The easiest and least expensive way to reduce radiation exposure in the operating room is to use standard radiation safety precautions. This involves using the low-dose or pulsed fluoroscopy (rather than extended exposures) to obtain an adequate quality image, which has been shown to dramatically reduce exposure to ionizing radiation.26 Similarly, a mini C-arm fluoroscopy unit can be used in lieu of a standard C-arm for intraoperative extremity fluoroscopy when feasible, which releases a lower dose of ionizing radiation.27 Also, the effective dose received by the operating room staff or patient can be dramatically reduced if they are located at least 36 inches away from the beam.28 Therefore, it is recommended that all nonessential staff remain at least 36 inches away from the radiation source during fluoroscopic exposure. Proper safety equipment, including radiation safety gowns, thyroid shields, gloves, and radiopaque glasses, should be used habitually.29 Advances in surgical instrumentation can also lead to less ionizing radiation in the operating room. For instance, a large number of fluoroscopic images are often required to appropriately place interlocking screws through an intramedullary device via the perfect circles technique. However, several readily available devices largely decrease the need for fluoroscopy for this surgical technique, including a mechanical aiming arm, which affixes to an intramedullary nail proximally and allows for accurate placement of distal interlocking screws.30,31 In addition, techniques using computer navigation and electromagnetic field guidance have been developed to eliminate the use of fluoroscopy for interlocking screw placement.32 Computer navigation has also been well described for several orthopedic procedures. This technology allows for MAY 2012 | Volume 35 • Number 5 increased surgical precision with less reliance on intraoperative fluoroscopy use and, therefore, decreased radiation exposure. Studies have shown that navigation can dramatically reduce fluoroscopy time during spine surgery when pedicle screw instrumentation is performed.33,34 In addition, navigation has also been described for retrograde drilling of osteochondral lesions, eliminating the need for fluoroscopic radiation.35 This reduction in intraoperative fluoroscopy use is particularly important when dealing with pediatric patients, and posterior spinal fusions with pedicle screw instrumentation and osteochondral lesion drilling are common procedures in the pediatric population that would benefit greatly from a reduction in ionizing radiation exposure. Finally, patients’ exposure to ionizing radiation can be reduced through rational clinical decision making. Surgeons must ask themselves, “Is this radiograph really necessary?” Some recent publications have suggested that radiography use can be limited without negative diagnostic or clinical consequences. For instance, the standard workup for nonaccidental trauma involves a skeletal survey of the entire body and a follow-up survey a few weeks after the initial encounter. Sonik et al36 reported that no new fractures of the skull, spine, or pelvis had been detected in the follow-up survey based on their series and data from the literature. From this, it can be inferred that routine repeat imaging of the skull, spine, and pelvis is unnecessary unless a high clinical suspicion of injury exists; this is especially important because these anatomic areas receive the highest amount dose exposure, compared with the extremities. Another example is the use of immediate postoperative pelvis radiographs following total hip arthroplasty. The standard practice in many institutions is to obtain an immediate radiograph of the pelvis in the operating room or recovery room to rule out dislocation or periprosthetic fracture. Ndu et al37 reported that, in a series of 632 re- covery room radiographs following total hip arthroplasty, 17% of radiographs were inadequately performed. In addition, only 1.9% (12 of 632) identified technical issues, of which only 0.3% (2 of 632) required intervention; 1 was a dislocation diagnosed by clinical examination prior to the radiograph being taken.37 Based on these data, immediate postoperative radiographs may be avoided given the unnecessary economic and health burden associated with their use. Conclusion It is important to balance the immediate, frequently substantial clinical need for radiological studies and procedures against the rare but significant risk of cancer that would not be evident for years, if at all.16 Current research and policies by radiological societies and governmental organizations have brought these concerns to the forefront. Future research should focus on developing technology that allows for improved diagnostic accuracy with less radiation, as well as developing systems-based approaches to image and medical record portability to eliminate duplicate imaging studies. For the time being, orthopedic surgeons should use the techniques outlined in this article to minimize radiation exposure to themselves, patients, and medical staff. References 1.Riesz PB. The life of Wilhelm Conrad Roentgen. AJR Am J Roentgenol. 1995; 165(6):1533-1537. 2. Upton AC. Cancer research 1964: thoughts on the contributions of radiation biology. Cancer Res. 1964; 24(11):1861-1868. 3. Berrington de González A, Mahesh M, Kim KP, et al. Projected cancer risks from computed tomographic scans performed in the United States in 2007. Arch Intern Med. 2009; 169(22):2071-2077. 4.Mettler FA Jr, Huda W, Yoshizumi TT, Mahesh M. Effective doses in radiology and diagnostic nuclear medicine: a catalog. Radiology. 2008; 248(1):254-263. 5. Moores BM, Regulla D. A review of the scientific basis for radiation protection of the patient [published online ahead of print 419 n Review Article cme ARTICLE August 16, 2011]. Radiat Prot Dosimetry. 2011; 147(1-2):22-29. 6. Rabin RC. With rise in radiation exposure, experts urge caution on tests. The New York Times. June 19, 2007; Health. 7. Sternberg S. Study: Unnecessary CT scans exposing patients to excessive radiation. USA Today. November 29, 2007; Health & Behavior. 8.National Research Council. Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2. Washington, DC: National Academies Press; 2006. 9. Giordano BD, Grauer JN, Miller CP, Morgan TL, Rechtine GR II. Radiation exposure issues in orthopaedics. J Bone Joint Surg Am. 2011; 93(12):e69(1-10). 10.Samartzis D, Nishi N, Hayashi M, et al. Exposure to ionizing radiation and development of bone sarcoma: new insights based on atomic-bomb survivors of Hiroshima and Nagasaki. J Bone Joint Surg Am. 2011; 93(11):1008-1015. 11. Richardson D, Sugiyama H, Nishi N, et al. Ionizing radiation and leukemia mortality among Japanese atomic bomb survivors, 19502000. Radiat Res. 2009; 172(3):368-382. 12. Daniels RD, Schubauer-Berigan MK. A metaanalysis of leukaemia risk from protracted exposure to low-dose gamma radiation [published online ahead of print October 8, 2010]. Occup Environ Med. 2011; 68(6):457-464. 13. Brenner DJ, Doll R, Goodhead DT, et al. Cancer risks attributable to low doses of ionizing radiation: assessing what we really know [published online ahead of print November 10, 2003]. Proc Natl Acad Sci U S A. 2003; 100(24):13761-13766. 14.Li CI, Nishi N, McDougall JA, et al. Relationship between radiation exposure and risk of second primary cancers among atomic bomb survivors. Cancer Res. 2010; 70(18):7187-7198. 15. Preston DL, Ron E, Tokuoka S, et al. Solid cancer incidence in atomic bomb survivors: 1958-1998. Radiat Res. 2007; 168(1):1-64. 16.Fazel R, Krumholz HM, Wang Y, et al. Exposure to low-dose ionizing radiation from medical imaging procedures. N Engl J Med. 2009; 361(9):849-857. 17.American College of Radiology and The Radiological Society of North America. Patient Safety: Radiation Exposure in X-ray 420 and CT Examinations. RadiologyInfo Web site. http://www.radiologyinfo.org/en/safety/ index.cfm?pg=sfty_xray. Updated 2011. Accessed November 15, 2011. 18.American College of Radiology and The Radiological Society of North America. Naturally-occurring “background” radiation exposure. RadiologyInfo Web site. http:// www.radiologyinfo.org/en/safety/index. cfm?pg=sfty_xray. Updated 2011. Accessed November 15, 2011. 19. Brenner DJ, Hall EJ. Computed tomogra phy—an increasing source of radiation exposure. N Engl J Med. 2007; 357(22):22772284. 20. Mueller DL, Hatab M, Al-Senan R, et al. Pediatric radiation exposure during the initial evaluation for blunt trauma. J Trauma. 2011; 70(3):724-731. 21.Brink JA, Amis ES Jr. Image Wisely: a campaign to increase awareness about adult radiation protection. Radiology. 2010; 257(3):601-602. mini-C-arm fluoroscopy. J Bone Joint Surg Am. 2009; 91(2):297-304. 28.Mehlman CT, DiPasquale TG. Radiation exposure to the orthopaedic surgical team during fluoroscopy: “how far away is far enough?” J Orthop Trauma. 1997; 11(6):392398. 29. Singer G. Occupational radiation exposure to the surgeon. J Am Acad Orthop Surg. 2005. 13(1):69-76. 30. Boraiah S, Barker JU, Lorich D. Efficacy of an aiming device for the placement of distal interlocking screws in trochanteric fixation nailing [published online ahead of print August 2, 2008]. Arch Orthop Trauma Surg. 2009; 129(9):1177-1182. 31. Krettek C, Könemann B, Miclau T, et al. A new mechanical aiming device for the placement of distal interlocking screws in femoral nails. Arch Orthop Trauma Surg. 1998; 117(3):147-152. 22. Colletti PM. Image gently: go with the guidelines. Clin Nucl Med. 2011; 36(12):e233e235. 32. Windolf M, Schroeder J, Fliri L, Dicht B, Liebergall M, Richards RG. Reinforcing the role of the conventional C-arm—a novel method for simplified distal interlocking. BMC Musculoskelet Disord. 2012; 13:8. 23. Goske MJ, Applegate KE, Bulas D, et al. Image Gently: progress and challenges in CT education and advocacy [published online ahead of print August 17, 2011]. Pediatr Radiol. 2011; 41(suppl 2):461-466. 33. Gebhard FT, Kraus MD, Schneider E, Liener UC, Kinzl L, Arand M. Does computerassisted spine surgery reduce intraoperative radiation doses? Spine (Phila Pa 1976). 2006; 31(17):2024-2027. 24. Fabricant PD, Heyworth BE, Kelly BT. Hip arthroscopy improves symptoms associated with FAI in selected adolescent athletes [published online ahead of print August 11, 2011]. Clin Orthop Relat Res. 2012; 470(1):261269. 34. Hart R, Komzák M, Bárta R, Okál F, Srůtková E. Reduction of radiation exposure by the use of fluoroscopic guidance in transpedicular instrumentation [in Czech]. Acta Chir Orthop Traumatol Cech. 2011; 78(5):447-450. 25. Miéville FA, Gudinchet F, Rizzo E, et al. Paediatric cardiac CT examinations: impact of the iterative reconstruction method ASIR on image quality—preliminary findings [published online ahead of print June 30, 2011]. Pediatr Radiol. 2011; 41(9):1154-1164. 26.Goodman BS, Carnel CT, Mallempati S, Agarwal P. Reduction in average fluoroscopic exposure times for interventional spinal procedures through the use of pulsed and low-dose image settings [published online ahead of print September 26, 2011]. Am J Phys Med Rehabil. In press. 27. Giordano BD, Baumhauer JF, Morgan TL, Rechtine GR II. Patient and surgeon radiation exposure: comparison of standard and 35.Gras F, Marintschev I, Kahler DM, Klos K, Mückley T, Hofmann GO. Fluoro-Free navigated retrograde drilling of osteochondral lesions [published online ahead of print October 7, 2010]. Knee Surg Sports Traumatol Arthrosc. 2011; 19(1):55-59. 36. Sonik A, Stein-Wexler R, Rogers KK, Coulter KP, Wootton-Gorges SL. Follow-up skeletal surveys for suspected non-accidental trauma: can a more limited survey be performed without compromising diagnostic information? Child Abuse Negl. 2010; 34(10):804-806. 37. Ndu A, Jegede KA, Bohl DD, et al. Recovery room radiographs after total hip arthroplasty tradition vs utility [published online ahead of print February 2, 2012]? J Arthroplasty. In press. Healio.com The new online home of ORTHOPEDICS | Healio.com/Orthopedics