Blockchain Papers

Lloyd W. Klein, James A. Goldstein, David E. Haines, Charles E. Chambers · 8 authors

Renewed attention has focused on the occupational health hazards posed by working in the fluoroscopic laboratory.1-6 Accumulated occupational radiation exposure is associated with health risks to physicians, nurses, and technologists working in this environment. Health care workers are subject to insidious health effects of radiation exposure over many years. Adverse effects include the established predilection to posterior subcapsular cataracts, as well as worrisome signals of lifetime risks of cancer induction, particularly in the unprotected brain.7-12 A further consequence is the extensively documented incidence of orthopedic illnesses reported in physicians as well as nurses and technologists and injuries linked to the cumulative burden of bearing the weight of only partly protective lead aprons mandatory to reduce radiation risk.13-16 The increased volume and complexity of procedures, together with the physical stresses inherent in procedural performance, have exacerbated the prevalence and magnitude of such orthopedic injuries.17 The high prevalence of orthopedic afflictions not only affects individual health but also could be potential career ending, with workforce implications for both the profession as well as for society.15 Advances in interventional imaging techniques and treatments over the last three decades have achieved significant success with clear benefits to our patients18; yet protective measures for workers have unfortunately lagged the pace, magnitude, and impact of this therapeutic progress. The purpose of this position statement is to review the data documenting occupational health injuries, summarize current equipment and processes that can be widely applied to optimize protection, emphasize the importance of investment by hospitals and health systems in protective equipment established to enhance workplace safety, examine barriers that need to be overcome to spur advances to enhance the occupational safety of the fluoroscopic laboratory environment, and propose enhanced advocacy for innovation. Future processes and proposals to improve the fluoroscopic laboratory environment should be based on the following precepts: (a) there is ample clinical data documenting the prevalence of serious occupational health risks engendered by the fluoroscopic laboratory environment; (b) sufficient attention to these occupational health issues has been drawn in annual meetings and published clinical scientific studies; (c) despite these data and advocacy efforts, advances to improve worker safety in the fluoroscopic laboratory remain inadequate; and (d) a concerted effort by all stakeholders (physicians, catheterization laboratory nurses, and technologists, sonographers, hospitals, professional societies, and industry) in the fluoroscopic laboratory is necessary to further advance occupational safety and health. Radiation exposure is inherent to procedural performance in the fluoroscopic laboratory. Exposure to ionizing radiation imposes health risks to both patients and operators, resulting in an increased likelihood of numerous illnesses and diseases.1-8 The association with posterior subcapsular cataracts is well documented.11, 12 There are growing concerns for cancer induction,7, 8 with recent reports of a cluster of predominantly left-sided brain cancers in interventionists,9, 10 as well as a signal for increased breast19-22 and skin cancers.23-26 Radiation exposure generally, not necessarily as part of occupational exposure, is associated with leukemia/lymphoma, myeloma, numerous gastrointestinal and bone cancers, and thyroid and parathyroid adenomas. These disquieting signals fuel the increasing anxiety regarding radiation exposure-related oncogenesis, though no mortality impact has been proven.27 Recent studies have also suggested that occupational radiation exposure is associated with hypertension, hypercholesterolemia, and possibly atherosclerosis.28-30 Evidence of lengthening sarcomere length and early vascular aging in epidemiologic studies suggests that workers who are occupationally exposed to radiation during interventional procedures may be at increased risk to develop these same illnesses.30, 31 There is now overwhelming evidence demonstrating that working in the interventional laboratory is associated with an increased incidence of orthopedic illnesses, particularly those related to the cervical and lumbar spine. These orthopedic injuries have been linked to the cumulative effects of bearing the weight of leaded aprons.5, 15, 16 Additionally, the design of the catheterization laboratory environment promotes awkward orthopedic ergonomic postures (e.g., monitors placed out of the line of natural working sight views). As procedures become increasingly complex and prolonged, and their volume increase in number, it should not be surprising that interventional practice is attended by a high rate (40–50%) of occupational-induced orthopedic injuries.15-17 Over a career's duration, the likelihood of suffering such illnesses are 2–7 times27, 28 higher than other medical occupations. Studies report substantial differences in orthopedic injuries between those wearing lead aprons working in the fluoroscopic laboratory compared to colleagues working in the same department not working in the fluoroscopic laboratory and thus not bearing the burden of wearing lead aprons.27-29 These occupational-related injuries not uncommonly result in missed days of work, surgery, and, in some cases, curtailed careers. This issue has significant implications for the interventional workforce, particularly in view of the aging of the population and anticipated increased procedural demand concomitant with aging of the operators who pioneered these advances.17, 27-29 These occupational health concerns potentially affect several medical specialties, including cardiologists, radiologists, and surgeons working with fluoroscopy, as well as pain management specialists performing nonvascular fluoroscopic procedures. Importantly, all such issues also pertain to the other personnel who are essential members of the “interventional team” (e.g., nurses and technologists, interventional imagers, and cardiac anesthesiologists) who are exposed to the harmful effects of scattered ionizing radiation.30-33 Electrophysiologists and their team are also exposed to radiologic risks and orthopedic injury34 and perhaps even more so, given the duration of their procedures and lack of upper torso shielding during device cases (e.g., implantable defibrillators and cardiac resynchronization therapy). These issues also have particular importance to women; although radiation effects on the fetus have not been demonstrated, women report concerns for adverse effects during reproduction as an obstacle to choice of an interventional career. These radiation exposure concerns have sometimes been considered a reason for disproportionately low representation of women in the field.35 As noninvasive cardiologists specialized in imaging are now required to guide interventions in the catheterization and electrophysiology laboratories, pursuing career in imaging is no longer radiation free and a safer choice for women. This may result in shifts in gender distribution in various cardiology subspecialties, further impacting strategies to improve diversity and inclusion in out profession. The past three decades have witnessed astounding progress in interventional equipment, technique, therapeutics, and the clinical research that catalyzed these advances. Progress in interventional laboratory protection and safety has comparatively lagged, despite the growing mounting data emphasizing occupational health concerns. A paradigm shift to dramatically improve the occupational safety for all stakeholders in the fluoroscopic laboratory (members of the interventional team, professional societies, hospitals, and industry) is required. In particular, there is an opportunity and obligation for industry and hospitals, who clearly benefit from the workers' commitment to their profession, to play a leadership role in correcting these deficiencies. A template exists based on the collaboration established by recent FDA-led efforts aimed to reduce patient exposure.36 Leveraging the concept and practice of the “Image Wisely” and “Image Gently” campaigns codified by Radiological Society of North America37 and Pediatric Cardiology community38 to minimize radiation exposure to patients, in 2010, the FDA Center for Devices and Radiological Health launched an Initiative to Reduce Unnecessary Radiation Exposure from Medical Imaging. As part of this initiative, the FDA held a public meeting on ways to improve devices to reduce unnecessary radiation exposure to help the agency decide on any new, targeted requirements for manufacturers of computed tomographic and fluoroscopic devices. This effort resulted in an industry-driven enhanced awareness, with mandates to recognize both the needs for and market potential of innovations focused on minimizing patient radiation exposure. These initiatives rapidly resulted in dramatic changes to improve the X-ray systems. Examples of these improvements include minimizing radiation exposure through lower emission X-ray systems as well as monitoring, recording of each procedure's patient exposure, and standardization in laboratory reports and patient charts. These efforts have also stimulated industry to develop X-ray systems that provide high-quality imaging at low-radiation exposure dose levels. Hospitals should be encouraged to invest in adopting such platforms that have potential to mitigate occupational risk. Physicians working with our professional societies should strive to establish a culture of safety encompassing both patients and catheterization laboratory personnel (Table 1). The pathway forward should be focused to assure: (1) consistent application and adherence to established and procedural processes; (2) widespread adoption and utilization of novel commercially available protection systems; and (3) encouragement and support to further develop even more effective equipment and processes that facilitate enhanced safety and protection in the workspace. Our professional societies must support individual physicians, teams, and practices, especially those that are hospital owned. It is critical that clinician leaders speak authoritatively to hospital administration and industry partners regarding these concerns without fear of reprisal; societal support could be influential in these situations. The following specific steps should be endorsed by our professional societies to enhance hospital and physician compliance: Whether or not to comply with appropriate shielding and other safety measures should not be at the discretion of the operator. The imaging team (physician, sonographer, radiologic technologist, physicist, and other medical personnel) should be responsible for developing optimized protocols, implementing regular equipment quality control tests, and monitoring radiation doses to patients and members of the team. This group and their products should be recognized as an essential part of the quality assurance program, present in all laboratories, for emphasizing radiation management. Operator dose is directly proportional to patient dose; thus, reducing the dose to the patient will benefit the operator. Knowledge of radiation and methods to reduce risk should be stressed to all operators who perform fluoroscopically guided interventions, practiced routinely, and all staff educated in these measures and assuring they are adhered. These methods and concepts have been well described previously.1-7 Recently, publications from the Society of Cardiovascular Angiography and Interventions, The Heart Rhythm Society, and the American College of Cardiology/multi-society consensus document18 articulate detailed procedural systems and processes, as well as practical approaches, to assist cardiac catheterization laboratories in establishing optimal radiation safety program. The components of a radiation safety program include essential personnel, radiation monitoring, protective shielding (at minimum strict adherence to protective aprons and leaded glasses), imaging equipment, and training/education.39-41 Fundamental principles of radiation safety teach the tenet that radiation exposure should be “as low as reasonably achievable (ALARA)”, with monitoring to assure individuals do not exceed annual or lifetime “safe limits.” Unfortunately, the term “reasonably achievable” is ambiguous and not actionable, and may unintentionally inhibit innovative strides to improve safety both for patients who require medically necessary procedures and for workers in radiation-exposed environments. The phrase might incorrectly imply that as long as one's exposure is “minimized,” then that is all that need to be accomplished. Rather, the ultimate goal of innovation efforts should strive to achieve a completely safe environment wherein the ultimate definition of ALARA translates to as close to a zero radiation exposure work environment as possible. Meticulous application of established prudent radiation techniques is obvious and essential. Standard shielding combines laboratory based (e.g., movable ceiling suspended and fixed table-side shielding). Personal protective aprons and eyewear should be properly fitted and maintained, and hospitals should finance these protective devices for all of their employees, including trainees. Newer personal protective choices, including two-piece aprons that are much lighter, may be beneficial; accessory sleeves for arm protection are also available. Despite these advances, the orthopedic burden of only partially protective leaded apparel continues. Institutions and operators must partner to develop a program specific for their laboratory that will result in the adoption of appropriate recent innovations to reduce radiation exposure. Strategies should also include usage of adjunctive devices for which there is substantial data documenting their capability to reduce exposure. Specifically, there is now compelling data demonstrating reductions in exposure with accessory drapes42 (Supplementary Tables); such disposable radiation shielding pads should NOT be refused by hospitals due to their expense. The use of leaded caps has been proposed with mixed results regarding reduction in exposure.43, 44 Simple accessory mobile shields afford significant protection to both nurses and technologists45 as well as to the interventional imaging team.30 More expansive and encompassing lead shielding systems are commercially available,46 and there is a need for more clinical research data supporting their capabilities to reduce exposure. Robotic systems developed to enhance procedural performance also provide protection from radiation exposure to the physician and reduce leaded apron orthopedic burden.47 Thus far, robotics has had limited adoption, due mostly to cost considerations but also fear from the loss of a “hands-on” sensibility. In electrophysiology, intracardiac navigation systems48 have shown efficacy to navigate catheters for ablation procedures with lesser exposure. Simultaneously, industry and physicians must partner to expedite development of a fluoroless catheterization laboratory, using echocardiography, magnetic resonance imaging, 3D mapping, or other technologies. Removing the necessity of lead aprons should be the ultimate goal. Although the proximate cause of many orthopedic complications may be wearing lead, there are other important factors, such as screen height and position, and other ergonometric considerations, which may account for much cervical spine pathology.49 This growing portfolio of enhanced/innovative protective technology will continue to yield a growing pipeline of solutions providing optimism for a healthier work environment. Table 1 summarizes the responsibilities of professional societies going forward. A direct role is a necessity to coordinate the policy matters raised in this document. Table 2 lists the specific future directions recommended for all stakeholders to achieve. It is essential to emphasize that the operator has the responsibility to understand how to use protective equipment optimally to minimize exposure to both patients and personnel.50 Education in this area is already part of cardiology trainee education and is tested in certification exams. Nevertheless, formal training for those who are planning to be interventional operators and imagers should be considered, and compliance monitored on site. Real-time radiation dose monitoring should become standard. Further, physicians must accept the challenge to adopt new technologies for the reduction of occupational hazards. Expense is one reason that new innovations are often not adopted, as it is difficult to advocate for expensive nonrevenue-enhancing equipment in the current fiscal environment. Other obstacles to overcome include potential discomfort with the design modifications and the resistance to making changes in familiar techniques even if there are improvements. The question always arises as to “proof” as to whether the changes are really beneficial, which sometimes become a justification to maintain an unsatisfactory status quo. Therefore, it is incumbent on our profession to continue to produce high-quality clinical research that documents the capabilities of novel imaging equipment, protective devices, and processes designed to improve workplace safety and health. As previously discussed, structural heart interventions depend on procedural image guidance/interventional echocardiography using transthoracic (TTE) or transesophageal echocardiography (TEE) in addition to fluoroscopy. Interventional imagers who operate the TTE or TEE probe and echo console are highly exposed to the harmful effects of scattered ionizing radiation. Protection for these workers also needs to be incorporated and mandated.30, 45, 46 Professional societies should develop programs to assist hospitals and health systems to address occupational safety. It is in everyone's interest to assure the health of medical caregivers.17 The establishment of new, and coordination with existing, comprehensive programs for clinician health in the catheterization and electrophysiology laboratories consistent with recommended wellness programs are an opportunity to highlight this problem. This may include an on-site physical or massage therapist, programs for core strengthening and stretching, and improved posture techniques to prevent orthopedic injury.34 Moreover, this issue can be an opportunity for societies to share and collaborate with international colleagues, who face similar problems. Since the inception of radiologic imaging, the biomedical industry has taken primary responsibility for development and refinement of catheterization laboratory equipment with associated financial benefits. As this equipment engenders intrinsic radiation exposure hazards, industry should assume a level of fiduciary responsibility to optimize the safety of the equipment they design and sell. It is our role to communicate the cardiology community's widespread support for innovations and catheterization laboratory design reformation. Though definite progress has occurred in the past two decades, particularly the advent of high-quality X-ray systems that produce high-quality imaging at lower radiation dose, further innovations are needed to achieve maximal operator radiation protection. The goal is a laboratory design that achieves a completely environment that the need for personal protective apparel and the orthopedic progress has been by the FDA to industry and medical to improve equipment and processes designed to achieve radiation exposure to are that efforts can be to enhance operator safety by providing a template by which this may be innovation will be that market are to such of worker health to increase worker is both the to and a workforce (physicians, nurses, and Hospitals and health care systems should recognize that protective equipment and wellness processes to at the of the health of their workers is more it increased more and increased training Hospitals have the responsibility to and assure worker safety and optimal occupational radiation exposure. radiation provide training and monitoring of personnel and It that hospitals have a responsibility for those working in their and an responsibility not only to maintain and present imaging systems but also to catheterization laboratories with the equipment and established to benefits to the safety and of their of the X-ray with of imaging and equipment are the responsibilities of the will if (e.g., Health and might in on these occupational safety issues and issue that require a for of imaging and protective In this of and commitment on the part of hospitals is critical to industry to invest in research and development of in the that there is an and In our professional societies play a role to help establish is considered and necessary for practice in radiation safety and clinician The is not responsible for the or of any supporting by the than should be to the for the

Robert L. Dixon, John M. Boone

PURPOSE: Knowledge of the complete axial dose profile f(z), including its long scatter tails, provides the most complete (and flexible) description of the accumulated dose in CT scanning. The CTDI paradigm (including CTDIvol) requires shift-invariance along z (identical dose profiles spaced Sat equal intervals), and is therefore inapplicable to many of the new and complex shift-variant scan protocols, e.g., high dose perfusion studies using variable (or zero) pitch. In this work, a convolustion-based beam model developed by Dixon et al. [Med. Phys. 32, 3712-3728, (2005)] updated with a scatter LSF kernel (or DSF) derived from a Monte Carlo simulation by Boone [Med. Phys. 36, 4547-4554 (2009)] is used to create an analytical equation for the axial dose profile f(z) in a cylindrical phantom. Using f(z), equations are derived which provide the analytical description of Sconventional (axial and helical) dose, demonstrating its physical underpinnings; and likewise for the peak axial dose f(0) appropriate to stationary phantom cone beam CT, (SCBCT). The methodology can also be applied to dose calculations in shift-variant scan protocols. This paper is an extension of our recent work Dixon and Boone [Med. Phys. 37, 2703-2718 (2010)], which dealt only with the properties of the peak dose f(0), its relationship to CTDI, and its appropriateness to SCBCT. METHODS: The experimental beam profile data f(z) of Mori et al. [Med. Phys. 32, 1061-1069 (2005)] from a 256 channel prototype cone beam scanner for beam widths (apertures) ranging from a = 28 to 138 mm are used to corroborate the theoretical axial profiles in a 32 cm PMMA body phantom. RESULTS: The theoretical functions f(z) closely-matched the central axis experimental profile data for all apertures (a = 28 -138 mm). Integration of f(z) likewise yields analytical equations for all the (CTDI-based) dosimetric quantities of conventional CT (including CTDIL itself) in addition to the peak dose f(0) relevant to SCBCT (allowing direct cross-comparison between CT scan modes and mathematical proofs of several hypotheses of practical utility in CT dosimetry). A fast, analytical dose simulator6 is also demonstrated-successfully matching complex dose distributions measured using OSL and film dosimetry. CONCLUSIONS: The model described allows one to obtain analytical functions describing both the primary and scatter components of the axial dose profile. This model (using no empirical functions or adjustable fit parameters) provides a good match to the experimental data, as well as a complete analytical description of dose for both conventional (axial and helical) CT and cone beam CT. An efficient method whereby the complete data set for both modalities can be obtained from a single measurement of either CTDI100 or f(0) is illustrated. This method is also flexible--allowing calculation of heretofore unattainable doses for recently-introduced shift-variant protocols [e.g., variable pitch (irregular scan spacing), variable aperture, shuttle mode acquisition, and mA modulation schemes].

Dale P. Sandler

What does an anecdote about John Snow have to do with modern-day epidemiology? And why use it to introduce an issue of the Journal highlighting the challenges of studying disease risks associated with low dose environmental exposures? In this issue, Lilienfeld describes John Snow giving expert-witness testimony on behalf of industry (1). Besides being interesting on a historical basis, this incident raises several issues that are pertinent today. Lilienfeld's paper and the accompanying commentary by Vandenbroucke (2) deal directly or indirectly with the role and responsibilities of expert witnesses, the extrapolation of data on health effects from high dose exposures to low dose exposures, the importance of epidemiology to the development of public health policy, the current debates on environmental justice (3), and the use of the precautionary principle (4) in standard-setting. Furthermore, if faced with an issue similar to that faced by Snow—namely, local residents' being worried about health consequences associated with emanations from factories—would modern-day environmental epidemiologists be any better positioned to carry out appropriate studies and reach sound conclusions? Snow can be seen at once as victim and perpetrator of sins that are common in epidemiology in general and in environmental epidemiology in particular. Was Snow victimized by the medical establishment, including The Lancet, for expressing views that were not commonly held by the scientists of the day? Were his peers outraged because of the reactionary social position he was taking (as suggested by Vandenbroucke)? On the other hand, was he as guilty as proponents of the miasma theory for trying to apply his theory of disease transmission to all situations without allowing for the possibility of multiple disease pathways? Did he fall into the trap of equating the absence of data with an absence of effect? When Snow contended that emanations from the bone-boiling factories were not causing ill health in the community at large, he invoked arguments that are often raised when unexpected health effects are encountered following supposed low dose exposures. One argument is that such health effects are implausible given what we know about high dose exposures. In this instance, Snow noted that the factory workers were not dying and therefore health effects in the community at large were not plausible. A related argument is that, even if workers are dying or suffering other health effects, because of the distance from the exposure source, the exposure levels in the community are probably too low to plausibly affect health. Health effects of low dose exposures are often seen as implausible, even in the face of accumulated consistent evidence. Such arguments have frequently been invoked in environmental epidemiology. Examples of low dose exposures that have been deemed implausible contributors to disease risk based on what is known about high dose exposures include passive smoking, residential radon exposure, childhood lead exposure, electromagnetic fields, and residence near nuclear facilities. If one begins with a fixed idea of what is plausible, arguments regarding susceptible subgroups, inverse dose rate, hormesis, multiple pathways, multifactor etiologies, and complex exposures (e.g., the different constituents of sidestream and mainstream smoke) are untenable. But how do we know that the factory workers were not dying or suffering other ill effects? Snow cited no studies. All too often the absence of data is argued as proof of no effect. This issue becomes especially difficult when regulatory decisions are being made. In the absence of evidence, can something be considered safe? While science is important, it is ultimately social forces, as much as science, that guide regulators in decision-making. Snow's statements and the questions that were put to him call to mind some of the fundamental difficulties inherent in environmental epidemiology. Today, there are numerous examples of residents who live near potential environmental hazards claiming health effects that can never be proven beyond a reasonable doubt. Although the “gold standard” is an unbiased risk estimate with precise confidence limits, studies focused on overt health effects are invariably underpowered because of the small numbers of residents in the neighborhoods of interest. Other creative approaches to assessment of subclinical health effects are more costly and difficult to implement, but even these studies are often too small for conclusive results. Yet, what is the right thing to do? If we wait for strong scientific evidence before we act—if we require proof that workers are dying or evidence of overt illness in the community—have we waited too long? Few clusters are ever resolved with the identification of a causal link between some localized exposure and disease. While many apparent clusters may be artifacts, what is the real cost of the true hazards that cannot be proven? These were the issues facing Parliament when Snow testified on behalf of industry. What is the role of the epidemiologist in this quagmire? In Snow's London, the living conditions of people near the factories were likely to have been dismal. There were no doubt residents who perceived their symptoms as being related to the smells—smells that, if nothing else, impacted the quality of life. Policy-makers must balance “doing the right thing” with regard to human suffering and quality of life with the financial costs of doing so. Epidemiology can only go so far in providing the answers. It is this political and social tug-of-war that makes environmental epidemiology especially difficult. On the one hand, there are well—funded industries with a financial stake in the outcome of such research. As Vandenbroucke notes (2), these industries often are in a position to exploit the many weaknesses that epidemiologists are trained to identify in their own studies and in the work of others to cast potentially damaging results in a more favorable light. On the other hand, there are environmental groups committed to proving that a particular environmental exposure can be linked to a variety of personal complaints; these groups may be motivated by the possibility of effecting social change through science or by the prospect of receiving needed medical attention or financial compensation. Those who attempt to work in this arena often find themselves and their research attacked from all directions. Environmental epidemiology is difficult to conduct today for other reasons as well. Adequate tools with which to measure and quantify exposures are lacking. Studies are often unable to detect meaningful effects because exposures are low, infrequent, or difficult to measure with certainty. How many investigators are willing to tackle this problem? In the case of the bone-boiling factories, would research linking questionnaire data on symptoms to factory releases be believed? Would a study relating distance from the factory to disease be sufficient evidence of effect? What health effects would be plausible based on known biologic mechanisms? How well could those effects be measured, and could they be measured objectively? Is there a biomarker of exposure? If a biomarker exists, does it measure relevant past exposures? Is the measure unaffected by current health status—particularly the disease under study? In addition to Lilienfeld's historical report and Vandenbroucke's commentary, this issue of the Journal features papers that illustrate various aspects of the difficulties faced in studying health effects of environmental exposures. Several of these include innovative attempts to improve the quality of such research. The paper by Viel et al. (5) may come closest to what many may think of as environmental epidemiology. The authors have examined the spatial distribution of soft tissue sarcomas and non-Hodgkin's lymphomas around an incinerator with high dioxin emissions. Their results are suggestive but need to be followed by studies incorporating more rigorous exposure assessment—perhaps a biologic measure of exposure such as that used in the study of polychlorinated biphenyls and breast cancer reported by Zheng et al. (6). Other studies described in this issue used a variety of approaches to exposure assessment. Rondeau et al. (7) linked estimates of levels of aluminum and silica in drinking water to risks of dementia and Alzheimer's disease. Laden et al. (8) used questionnaire data on use of electric blankets to estimate exposure to electromagnetic fields, and Gustavsson et al. (9) used questionnaire data and expert assessment by industrial hygienists to classify environmental and occupational exposures. Radiation workers are one of the few groups for which historical records of personal exposure typically are available. Dupree-Ellis et al. (10) took advantage of such records to estimate cumulative external radiation exposure. Several of the papers evaluate methods for assessing exposure. For example, Oglesby et al. (11) average individual-level annoyance scores to estimate community-level exposure to air pollution. The authors propose that this measure better accounts for exposure variability than data from fixed-site monitoring stations. This is an interesting twist in a field where much work is based on linking data from monitoring stations with population-level mortality statistics. The measure seems to be easy to operationalize, and it correlates well with monitoring station data, although its ultimate utility may be limited. The real gold standard—a more precise direct measure of individual exposure, rather than another indirect measure—is what is needed. Hwang et al. (12) propose an alternative modeling approach whereby air pollution monitoring station data are used to ascribe exposures to individuals with and without school absences due to respiratory disease. Auvinen et al. (13) compare several possible methods for measuring and classifying exposure to electromagnetic fields. This is a topic that has been hurt by the lack of consensus on the best and most appropriate exposure measure, and results tend to vary for studies employing different exposure metrics. The paper by Karagas et al. (14) attempts to link a biologic measure, arsenic in toenails, with an environmental measure of arsenic in water. The toenail measure is likely to reflect total body burden, but it appears to correlate with water only when water levels are high. This presents an interesting regulatory dilemma. The best epidemiologic research may be based on a direct measure of body burden such as levels in toenails, whereas it is water levels that need to be regulated. Studies of toenail arsenic levels may not shed direct light on the link between water levels and disease. As these papers demonstrate, technological advances are making possible a wide range of new study designs and strategies to better assess both exposures and outcomes. Although progress has been made, research in environmental epidemiology is far from perfect. As epidemiologists face pressures and criticisms from industry, regulatory bodies, and other scientific disciplines, it is important to not lose sight of the lessons from John Snow.