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2 Background T his chapter contains background factual information, much of which was distilled from remarks made by workshop committee members and workshop presenters. 2.1 TRENDS IN DIAGNOSTIC IMAGING Dr. Hedvig Hricak, workshop committee vice-chair and chairman, Department of Radiology, Memorial Sloan-Kettering Cancer Center, explained the workshop’s scope and discussed the current advances and trends in diagnostic imaging. Advances in medical imaging in the past few decades using procedures such as computed tomography (CT), fluoroscopy, and nuclear medicine imaging exams have dramatically improved health care. Tissues deep within the body can be easily accessed using these procedures, permitting radiolo- gists to make diagnoses that previously would have necessitated exploratory surgery (Wittenberg et al., 1978). Other direct benefits of modern imaging procedures include more effective surgical treatment (Godoy et al., 2011), potentially shorter hospital stays (Batlle et al., 2010), safer discharge of patients (Litt et al., 2012), better diagnosis and treatment of cancer (Wagner and Conti, 1991), more efficient treatment after injury (Philipp et al., 2003), better treatment of stroke and cardiac conditions (Saini and Butcher, 2009; Winchester et al., 2010), and rapid diagnosis of life-threatening vascular conditions (Furukawa et al., 2009). Today in the United States, medical 5
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6 TRACKING RADIATION EXPOSURE imaging occurs in hospitals and imaging centers, as well as free-standing private physician, dental, and chiropractor practices. A report released in early 2009 by the National Council on Radiation Protection and Measurements (NCRP)1 titled Ionizing Radiation Exposure of the Population of the United States indicated that in 2006 Americans were exposed to more than six times as much ionizing radiation from medi- cal diagnostic procedures than in 1980 (NCRP, 2009). The average effective radiation dose2 to which the U.S. population is now exposed is estimated to be 3 mSv,3 which is comparable to the annual exposure from natural background radiation which has remained unchanged for the past 20 years. The most significant changes in medical diagnostic imaging were attrib- uted to rapid increases in usage of higher-dose procedures particularly CT and nuclear medicine (especially nuclear cardiology [Mettler, 2009]). Close to 82 million CT exams are now performed annually in the United States (IMV, 2011), up from 46 million in 2000 and 13 million in 1990 (Brenner and Hall, 2007). Cardiac diagnostic nuclear procedures increased from 1 percent of the total number of diagnostic nuclear medicine examinations performed in 1973 to 57 percent in 2005 (Mettler et al., 2009). Many factors have been suggested as explanations for the sharp increase in CT use (Baker et al., 2008; Iglehart, 2009), such as advances in CT technology that have increased ease of use for physicians and comfort for patients during testing; increased CT scanner availability; favorable financial reimbursements for imaging procedures; and shifts in the practice of medicine including more time constraints and promotion of defensive medicine. Newer radiographic imaging modalities such as positron-emis- sion tomography/CT (PET/CT), single-photon emission CT (SPECT/CT), and potentially CT for screening of high-risk asymptomatic patients (for example, smokers screened for early lung cancer detection) are likely to further increase the population’s exposure (Brenner and Hricak, 2010). 1 The NCRP is a congressionally chartered organization that formulates and disseminates information and research data related to radiation exposure and protection. 2 Effective dose is a dose parameter used to normalize partial-body radiation exposures relative to whole-body exposures to facilitate radiation protection activities (ICRP, 1991). Effective dose can also be used to enable comparison of risks between procedures that utilize ionizing radiation. The International Commission on Radiological Protection (ICRP) does not recommend use of effective dose for estimating population or individual risks. Effective dose is expressed in sieverts (Sv). 3 The exposures of particular individuals could be higher or lower than these reported aver- ages depending on how many medical imaging procedures that use ionizing radiation they undergo. As discussed in Section 2.2, a number of individuals undergo multiple imaging exams in their lifetime. Others may not undergo any. Therefore, their exposure would be higher or lower than the estimated average.
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7 BACKGROUND 2.2 POTENTIAL HEALTH RISKS FROM DIAGNOSTIC IMAGING Although the growing use of medical diagnostic procedures is corre- lated with tremendous and undeniable benefits in care of most patients, it comes with growing concerns about risks associated with the use of ionizing radiation. A 2001 article in USA Today generated visibility and publicity and became a critical component in changing the prioritization of image quality alone to image quality balanced with radiation dose in both adults and children (Sternberg, 2001). Dr. David Brenner (Columbia University) noted that ionizing radiation is an initiator and promoter of carcinogenesis. In the absence of sufficient empirical knowledge regarding radiation effects at low doses4 typically encountered in medical diagnostic procedures, it is assumed that the probabilistic (stochastic) risk of cancer proceeds in a linear fashion at lower doses without a threshold. Scientific groups such as the International Commission on Radiological Protection (ICRP), the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), NCRP, and the National Research Council Committee on the Biological Effects of Ionizing Radiation (BEIR), repeatedly review and endorse the use of the linear-no-threshold (LNT) model for assessing risk (NCRP, 1993; ICRP, 2005; NRC, 2006; UNSCEAR 2008). The LNT model is often considered to be conservative and gives emphasis to public health and is currently used to set radiation protection standards and operating policies, such as the “as low as reasonably achievable” (ALARA) policy. There is large scientific debate, however, on the nature of the shape of the dose-response curve for radiation-induced cancers at low doses. Assuming a linear relationship between dose and cancer risk at low doses, a potential small increase in the chance of developing cancer is the main health effect of concern associated with the use of medical diagnostic procedures. The level of risk depends on the type of imaging procedure. For example, the typical radiation exposure from a CT examination is ~100 times larger than that from an x-ray examination.5 The theoretical individual risk of fatal cancer from a single CT for a dose of 10 mSv is estimated to be around 1 in 2000 (Mettler et al., 2000).6 For comparison, the natural occurrence of fatal cancer in the U.S. population is about 1 in 5. When a diagnostic procedure is medically justified (e.g., in a symptom- 4 There is near-universal agreement that epidemiologic studies have demonstrated that radia- tion doses above 100 mSv are associated with increased risk of developing cancer. However, scientific debate on the potential cancer risks exists at low doses (< 100 mSv). 5 The average effective dose for a typical chest CT exam is 7 mSv and for a chest x-ray 0.1 mSv; an x-ray of the shoulder is around 0.01 mSv; the average effective dose for most nuclear medicine procedures varies between 0.3 and 20 mSv (Mettler et al., 2008). 6 See also: http://www.fda.gov/radiationemittingproducts/radiationemittingproductsand procedures/medicalimaging/medicalx-rays/ucm115329.htm.
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8 TRACKING RADIATION EXPOSURE atic patient), it is apparent that the likely benefit to the patient is greater than the risk, although the imaging exam should be optimized to the low- est dose that provides acceptable diagnostic information (ICRP, 2008). Special care is needed, however, for evaluating nonsymptomatic screening protocols, such as for CT lung screening, where the estimated annual risk from low-dose protocols is ~1.8 percent (upper limit is 5 percent) (Brenner, 2004) and the estimated benefit (measured as reduction in mortality from lung cancer) among current or former heavy smokers is ~20 percent (NLST Research Team et al., 2011). Because large numbers of individuals receive radiation doses from medical imaging, whether for screening or diagnostic purposes, the possibility exists that even small potential risks per individual attributed to these exams could translate into many cases of cancer. Not surprisingly, because CT is used to not only diagnose disease but also follow the course of therapy and complications, a number of individu- als have multiple CT scans in their lifetime. Wiest et al. (2002) reported that in 2001 approximately 30 percent of their patients had more than three CT exams in their medical histories, 7 percent had more than five, and 4 percent had more than nine. The percentages of repeated exams were higher in a more recent study at one institution (33 percent of patients had 5 or more lifetime CT exams and 5 percent had between 22 and 132) (Sodickson et al., 2009). The patients who underwent large amounts of recurrent imag- ing in the study generally had substantial underlying disease such as cancer diagnosis (Sodickson et al., 2009). Irrespective of the presence or severity of underlying disease, multiple CT scans of a patient can result in absorbed doses that have been empirically shown to increase the risk of cancer. This may be one of the reasons why for tracking radiation exposure from medi- cal diagnostic procedures, CT scanning has received the majority of interest. In contrast to the stochastic effects following radiation (e.g., develop- ment of cancer and some cardiovascular diseases), accidental exposure to very high levels of radiation can cause acute effects such as skin red- dening, skin necrosis, hair loss, and severe tissue damage. These acute effects are known as “deterministic” or “non- stochastic” radiation effects. The problem of skin reactions following fluoroscopy were reported and summarized by Shope (1996). Recently, several unfortunate and highly publicized radiation overexposure events have been reported, especially involving CT exams. In 2009 officials of the Cedars-Sinai Medical Center in California notified the Food and Drug Administration (FDA) of acci- dental overexposure of about 200 patients undergoing brain-perfusion CT examination, resulting in hair loss and skin redness. The FDA identified additional patients who received overexposures at other hospitals7 and has subsequently issued advisory warnings to initiate preventive actions 7 See: http://www.fda.gov/MedicalDevices/Safety/AlertsandNotices/ucm185898.htm.
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9 BACKGROUND (Kuehn, 2010). These events have heightened the awareness of radiation dose among radiologists, technologists, patient populations, regulators, and international agencies. Assuming compliance from both the medical provider and patient, confirming and reporting the visible events of direct radiation injury may be a relatively straightforward task. However, measuring the potential long- term risks associated with low-level radiation doses from medical diagnostic procedures is challenging and therefore the risks have not been fully quanti- fied. This is because the number of excess cancer cases expected to result from exposure to ionizing radiation from medical diagnostic procedures is low and difficult to differentiate from background cancer rates, which normally affect 42 out of every 100 persons.8 Studies to assess these small risks would require very large numbers of individuals and long follow-up periods (Land, 1980). Because any radiation-induced cancer would not appear for years, it would be difficult, if not impossible, to relate it to past imaging procedures. Results from large-scale epidemiologic studies assess- ing the risks of medical diagnostic procedures that utilize ionizing radiation are not available yet. However, a number of epidemiologic studies of risks associated with CT exams are underway (see Section 3.5.1). CT exams are likely the high-dose medical diagnostic imaging exams associated with the easiest exposures and dose parameters to collect both in terms of equipment output and in terms of estimation of actual patient doses. An alternative to directly examining cancer occurrence or death from cancer in the exposed populations is use of risk projection models. Such models use population dose estimates and existing risk coefficients to extrapolate the effects of medical diagnostic procedures. Typically popula- tion risk estimates are derived from the atomic-bombing survivors cohort in Hiroshima and Nagasaki; today, this cohort is widely considered the “gold standard” in the assessment of radiation-induced cancer risks at low doses.9 Medically exposed cohorts are also used to provide risk estimates for risk projection studies. The risks determined from projection models represent theoretical risks rather than empirical observed risks and rely upon the assumption of a linear relationship between radiation dose and risk at low doses. A study with frequency data from Medicare claims and data from the IMV Medical Information Division estimated that 29,000 future cancers could be related to CT scan use in the United States in 2007 (Berrington de González et al., 8 See: http://www.cancer.org/Cancer/CancerBasics/lifetime-probability-of-developing-or- dying-from-cancer. 9 The effective dose from a typical CT exam is estimated to be about 8 mSv. This dose is comparable to the lowest doses of 5 to 20 mSv received by some of the Japanese atomic- bombing survivors.
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10 TRACKING RADIATION EXPOSURE 2009). Fifty-seven million CT scans were used for the calculation of the potential future cancers. A second study showed that the lifetime cancer risk estimates for standard cardiac scans varied widely depending on age and gender, from 1 in about 3,000 for an 80-year-old man to 1 in about 140 for a 20-year-old woman (Einstein et al., 2007). The risk estimates in the projection models used in the above-mentioned studies deal with particularly challenging problems related to uncertainty from various sources, in terms of both the dose for a given examination and the cancer risk per unit dose in the estimations. Moreover, the magnitude of cumulative individual doses from single or multiple procedures has not been fully characterized because of limited medical recording and the lack of sharing of medical information across different health care facilities. 2.3 APPROPRIATENESS OF DIAGNOSTIC IMAGING The appropriateness of diagnostic imaging in terms of justification and optimization were discussed by Dr. Donald (Don) Miller, acting chief, Diag- nostic Devices Branch, Division of Mammography Quality and Radiation Programs, Center for Devices and Radiological Health, FDA, and other workshop participants. There are two ways to reduce doses from diagnostic imaging: (1) do imaging only when justified and appropriate and (2) for any given examina- tion, use dose reducing approaches consistent with acceptable image quality and diagnostic performance. Although based on limited data, one in four procedures is believed to be unjustified and therefore associated with unnecessary potential radia- tion risk. Examples include unnecessary CT scanning of the chest both with and without contrast or multi-phase scanning for patients undergoing abdominal and pelvic CTs (Guite et al., 2011). It is estimated that each year approximately 75,000 patients across the country have unnecessary pre- and post-contrast chest CT scans (Bogdanich and McGinty, 2011). A straw poll among pediatric radiologists indicated that about 30 percent of CT examinations in children were unnecessary or could have been replaced by imaging exams not using ionizing radiation such as ultrasound-based imaging modalities (Berdon and Slovis, 2002). Although the outcome of the straw poll does not constitute scientific evidence, it is an indicator that the issue of unnecessary exams is recognized by the medical community. Lack of training regarding clinical decisions is one cause of the use of inappropriate examinations. In addition, ordering physicians may be unaware that recommended criteria can guide them in particular clinical decisions. Various professional organizations (e.g., the American College of Radiology [ACR]) have produced evidence-based guidelines, but several studies suggest that these guidelines have not been widely adopted by the
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11 BACKGROUND medical community. In a retrospective study of 200 trauma patients, for whom imaging decisions were made without the use of formal decision rules, 169 of 200 patients underwent one or more CT scans, resulting in an overall total of 660 CT scans. The authors found that application of the ACR appropriateness criteria could have prevented 44 percent of those CT scans from being ordered (Hadley et al., 2006). Other studies have found that similar percentages (20-40 percent) of CT scans could be avoided by following decision guidelines (Garcia Pena et al., 2004; Kuppermann et al., 2009; Holmes et al., 2009; Stein et al., 2009). A pilot study showed that two out of three nuclear cardiology scans performed were appropriate according to the American College of Cardiology criteria, while the remain- der were either inappropriate or of uncertain appropriateness (Hendel, 2009). A successful approach to increasing the use of decision guidelines has been to incorporate them into computerized imaging order entry systems (Sistrom et al., 2009). However, even when decision guidelines are readily accessible, a variety of factors may contribute to the ordering of unjustified CT scans such as emergency department patient throughput, fear of liability for a missed diagnosis, lack of information from other sources, and patient and physician self-referrals (Dunnick et al., 2005). 2.4 REDUCTION IN RADIATION DOSES Reducing the dose per exam is the second way to reduce unnecessary exposure to radiation from medical diagnostic procedures, and this is dis- cussed in the context of optimization10 and the need to create reference values based on best practices (ICRP, 2008). Interest in this area has arisen because wide variations have been observed among radiation doses associ- ated with particular imaging exams both within and across medical centers. Again, there is a specific interest in CT scanning, because of its amenability to significant dose reductions (or increases) by the ease of manipulation of technical factors during protocol adjustments. One study in four San Francisco Bay Area institutions showed that radiation doses varied significantly among different types of CT studies performed on adult patients. A mean 13-fold variation between the highest and lowest doses for routine head CT exams and multiphase abdomen and pelvis CT exams was reported (Smith-Bindman et al., 2009). The authors state that this observed variation cannot be entirely explained by differ- ences in patient size (which were not accounted for in the analysis) or the specifics of the clinical question that was being addressed. Large variability 10 Radiation dose is optimized when imaging is performed with as low as possible amount of radiation required to provide adequate image quality for diagnosis or intervention.
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12 TRACKING RADIATION EXPOSURE in doses was also observed in a recent multicenter study in France that included children aged 0-5 years undergoing at least one CT scan between 2000 and 2006 (Bernier et al., 2012). In regard to nuclear medicine, a survey of 13 pediatric hospitals in North America identified a broad range of administered doses from institution to institution; these administered doses would directly lead to variability in radiation-absorbed doses to the pediatric patients (Treves et al., 2008). Optimization of the techniques is viewed as a joint responsibility and effort of the radiology facilities and equipment designers. For example, manufacturers of CT scanners and fluoroscopy equipment have made many successful attempts to reduce the doses associated with particular exam types. These reductions have been accomplished through technological advances in equipment design, implementation of features such as auto- matic exposure control, and efforts to educate physicians and technologists and create awareness of potential adverse radiation effects. A comprehen- sive review of dose reduction efforts in nuclear medicine is presented else- where (Hricak et al., 2011). One of the earliest success stories of procedure optimization was an effort to improve technical aspects of mammography, which culminated in the passage of the Mammography Quality Standards Act in 1992 (Spelic et al., 2007). This legislation set national standards for high-quality mammog- raphy, including standards for mammographic x-ray equipment, patient dose, and image quality and ensured that facilities in the United States would meet those standards. Radiologists attempt to reduce dose through use of optimized protocols in accordance with national and international guidelines (ICRP 2000a,b, 2007a; McCollough, 2011). However, the information available to them is frequently inadequate. For example, on the technical side, although new CT and fluoroscopic devices include displays of dose metrics, some lack other safeguards, such as default parameter settings that optimize radiation dose or alerts when the radiation dose in a given exam exceeds a particular reference level or range. Even when these safeguards are in place, users may not have received adequate training in the proper use of these features and the importance of optimizing radiation dose. Additionally, training often takes place in the hospital or imaging center with all the concomitant dis- tractions and without a verification of acquisition of knowledge at the end of the training sessions (Slovis, 2002) or quality assurance practices within the imaging facility. On the dose side, Lee and colleagues (2004) performed a survey to determine the awareness of emergency department physicians and radiolo- gists of the radiation exposure from the CT scans that they order. About 75 percent of the entire group significantly underestimated the radiation dose from a CT scan, and 53 percent of radiologists and 91 percent of
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13 BACKGROUND emergency department physicians did not believe that CT scans increase the lifetime risk of cancer. The risks and benefits of imaging procedures are rarely communicated to patients (Lee et al., 2004) and are not recorded in the patient’s medical record. In addition, many medical imaging devices that communicate with radiology information systems do not forward data on radiation dose despite recommendations to the contrary from the ACR (Amis et al., 2007). 2.5 RECENT PROGRESS IN RADIATION SAFETY IN MEDICINE A number of initiatives in radiation safety in medicine have taken place in the United States and internationally and were discussed by the work- shop invited speakers. Each of these initiatives serves different purposes. The ultimate goal is to provide better quality clinical management of the patient and to reduce dose by adhering to the ALARA principle, without compromising diagnostic efficacy (ICRP, 2007b). 2.5.1 Image Gently and Step Lightly Campaigns The Alliance for Radiation Safety in Pediatric Imaging11 launched the Image Gently (in 2008) and Step Lightly (in 2009) campaigns aiming to reduce unnecessary exposure to radiation during pediatric imaging and interventional radiology, respectively. The campaigns’ goal is to promote the special precautions required for children who undergo medical imag- ing that utilizes ionizing radiation (Sidhu et al., 2009; Goske et al., 2010). Through separate education material directed to patients, the health care team (radiologists, technologists, and pediatricians), physicists, and the news media, the Image Gently campaign has successfully disseminated its message by partnering with prominent medical organizations and agencies. 2.5.2 Image Wisely Campaign In 2010, the ACR and the Radiological Society of North America (RSNA), together with the American Association of Physicists in Medi- cine and the American Society of Radiologic Technologists, established the Image Wisely campaign for minimizing radiation exposure in adults. The campaign resembles but does not exactly mirror the Image Gently campaign. The mission of the Image Wisely campaign is to raise aware- ness of opportunities to eliminate unnecessary imaging examinations and 11 The Alliance for Radiation Safety in Pediatric Imaging is an organization of more than 60 national and international professional societies and agencies with the goal of promoting radiation safety for children.
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14 TRACKING RADIATION EXPOSURE to optimize the amount of radiation used in imaging examinations to only what is necessary to acquire appropriate medical images. Image Wisely has developed a web site with selected and logically indexed educational material for imaging professionals, referring practitioners, and the public and has partnered with imaging equipment vendors through the creation of vendor-specific web pages to provide the most current information on dose reduction techniques available on specific equipment. Participants in the program are asked to demonstrate their commitment to the Image Wisely principles by taking a pledge, pursuing accreditation, and participating in national dose index registries (Brink and Amis, 2010). 2.5.3 ACR’s Dose Index Registry The ACR launched the Dose Index Registry in May 2011 to address the lack of a substantial database for determining the average dose indices for a CT exam in the United States. Once these are determined, the data can be used to establish national benchmarks and practice patterns in dose indices and provide feedback to the participating facilities as to where they stand compared to those benchmarks and how far they are from achiev- ing optimal practices. The Dose Index Registry collects and compares CT dose index information from facilities across the country and internation- ally. Information is collected using automated standardized techniques and includes exposure parameters (kVp, mAs) and dose indices (CT index vol- ume [CTDIvol],12 dose length product [DLP]13). Currently the Dose Index Registry does not collect information on dose estimates because they are not available. 2.5.4 IAEA Smart Card In 2006 the International Atomic Energy Agency (IAEA) initiated an ambitious program named Smart Card with the purpose of tracking the radiological procedures of individual patients and radiation dose. The pro- gram, launched in 2009, will be implemented in some countries in three to five years. Until the program was launched, the only way to track a patient’s lifetime (cumulative) exposures was by manual search of physical or elec- tronic records in a hospital or hospitals or reliance on the patient’s memory. The Smart Card program emphasizes the need for a more systematic track- ing method resulting from the substantial increase in the use of high-dose radiation exams (Rehani and Frush, 2011). The major goals of tracking are 12 CTDI describes the amount of radiation that machines emit during one scan; that is, CTDI is not the amount of radiation that enters the body. 13 DLP combines all the scans from an examination into one value.
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15 BACKGROUND stated in the recent Joint Position Statement on patient exposure tracking14 and include: supporting accountability for patient safety, justification, and optimization; providing information for assessment of radiation risks; and establishing a tool for use in research and epidemiology. The original name of the Smart Card program tended to give the impression that the card would contain the patient’s estimated dose data; thus, the name Smart Card/SmartRadTrack was subsequently adopted to place the emphasis on tracking. The estimated patient doses are not avail- able on the card. Instead, like an ATM card or a credit card, the card simply provides the methodology (digital signature) to access dose information, which is available online. The IAEA Smart Card/SmartRadTrack is con- sidered to be an improvement over a more basic tracking approach such as a vaccination card, which stays in the possession of the patient. Such a method would rely fully upon compliance and maintenance by the patient and may not have an impact on the quality of radiation dose management. 2.5.5 National Institutes of Health Clinical Center Initiative The National Institutes of Health (NIH) Clinical Center has mandated that imaging equipment manufacturers provide for electronic reporting of patients’ radiation exposures from their equipment in this setting. The information on radiation exposure reports will be logged into the patient’s electronic medical record (EMR). Exposures from CT and PET/CT will be the first to be recorded using this system, because CT and PET/CT scan- ners already output this information (Neumann and Bluemke, 2010). The goal of this policy within the NIH Clinical Center is to achieve an accurate assessment of whether low-dose radiation exposure from medical imaging exams increases the patient’s risk of developing cancer. It is understood that steps taken within a single institution will not be sufficient to allow a precise population-based assessment of cancer risk from lose-dose radiation and that tracking of medical imaging doses from a truly large number of individuals in the United States will ultimately be necessary. This initiative is, however, necessary to begin building a prototypical data set (Neumann and Bluemke, 2010). Besides building a database for population-based risk assessment, the NIH Clinical Center will require that vendors ensure that radiation expo- 14 The joint statement was endorsed by the World Health Organization, FDA, the European Society of Radiology, the International Organization for Medical Physics, the International Society of Radiographers and Radiological Technologists, and the Board of Directors of the Conference of Radiation Control Program Directors. See: https://rpop.iaea.org/RPOP/RPoP/ Content/Documents/Whitepapers/iaea-smart-card-position-statement.pdf.
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16 TRACKING RADIATION EXPOSURE sure can be tracked by patients via personal electronic health record plat- forms such as Google Health and Microsoft HealthVault. 2.5.6 California Legislation California became the first state in the United States to regulate CT scans.15 The law dictates that facilities with CT systems capable of cal- culating and displaying radiation dose index document the dose index of each CT exam within the patient’s radiology exam report. (The deadline for meeting the requirement is July 2012.) The law also requires that a medical physicist verify annually the dose index for each protocol and that any reported errors are communicated to patients and physicians. (The law does not set a limit as to what the dose indices should be.) For the purposes of this bill, the radiation dose that should be recorded is defined as any metrics such as CTDIvol and DLP or a dose unit as recommended by the American Association of Physicists in Medicine (AAPM).16 This legislation was enacted in response to multiple events where patients were exposed to excessive radiation by diagnostic CT scanners, with the intent to prevent such events.17 15 Florida, New York, and Texas are also considering similar legislation (Schmidt, 2012). 16 AAPM is a member society concerned with the topics of medical physics, radiation oncol- ogy, and imaging physics with a primary goal of identifying and implementing improvements in patient safety for the medical use of radiation in imaging and radiation therapy. 17 See: http://www.leginfo.ca.gov/pub/09-10/bill/sen/sb_1201 1250/sb_1237_bill_20100929_ chaptered.html.