Radiation risks and information needs of pregnant and lactating women.

This a historical review and current information regarding risks and effects of ionizing radiation in the context of human pregnancy and in particular the information needed for pregnant women to understand the type and magnitude of risks placing them in a realistic context. Much of our understanding comes from early animal studies but has been supported by studies of human exposure to medical radiation, radiation accidents and nuclear weapons.

Patient Exposure from Radiologic and Nuclear Medicine Procedures in the United States and Worldwide: 2009-2018.

The U.S. National Council on Radiation Protection and Measurements (NCRP) conducted a retrospective assessment of the U.S. data, and the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) performed a similar worldwide assessment for 2009-2018 (with most data from 2014 to 2017). Using the data from those reports, the frequency of radiologic and nuclear medicine studies, annual collective, and per capita effective dose in the United States for 2016 were compared with worldwide estimates from 2009 to 2018. There were an estimated 691 million radiologic, CT, dental, and nuclear medicine studies performed in the United States in 2016, which represented 16.5% of the 4.2 billion performed worldwide. The United States also accounted for 74 million CT procedures (18% of the world's estimated total), 275 million conventional radiology procedures (11% of the world's total), 8.1 million interventional radiologic procedures (34% of the world's total), 320 million dental radiography procedures (29% of the world's total), and 13.5 million nuclear medicine procedures (34% of the world's total). The U.S. collective effective dose was 717 000 person-sieverts (17.6% of the world's total). The average annual individual effective dose in the United States was 2.2 mSv compared with 0.56 mSv worldwide. The United States accounts for a large and disproportionate share of global medical radiation procedures and collective effective dose, but use of CT has increased more in other countries compared with the United States.

Evolution of radiation protection for medical workers.

Within a few months of discovery, X-rays were being used worldwide for diagnosis and within a year or two for therapy. It became clear very quickly that while there were immense benefits, there were significant associated hazards, not only for the patients, but also for the operators of the equipment. Simple radiation protection measures were implemented within a decade or two and radiation protection for physicians and other operators has continued to evolve over the last century driven by cycles of widening uses, new technologies, realization of previously unidentified effects, development of recommendations and regulations, along with the rise of related societies and professional organizations. Today, the continue acceleration of medical radiation uses in diagnostic imaging and in therapeutic modalities not imagined at the turn of this century, such as positron emission tomography, calls for constant vigilance and flexibility to provide adequate protection for the growing numbers of medical radiation workers.

Patient Exposure from Radiologic and Nuclear Medicine Procedures in the United States: Procedure Volume and Effective Dose for the Period 2006-2016.

Background Comprehensive assessments of the frequency and associated doses from radiologic and nuclear medicine procedures are rarely conducted. The use of these procedures and the population-based radiation dose increased remarkably from 1980 to 2006. Purpose To determine the change in per capita radiation exposure in the United States from 2006 to 2016. Materials and Methods The U.S. National Council on Radiation Protection and Measurements conducted a retrospective assessment for 2016 and compared the results to previously published data for the year 2006. Effective dose values for procedures were obtained from the literature, and frequency data were obtained from commercial, governmental, and professional society data. Results In the United States in 2006, an estimated 377 million diagnostic and interventional radiologic examinations were performed. This value remained essentially the same for 2016 even though the U.S. population had increased by about 24 million people. The number of CT scans performed increased from 67 million to 84 million, but the number of other procedures (eg, diagnostic fluoroscopy) and nuclear medicine procedures decreased from 17 million to 13.5 million. The number of dental radiographic and dental CT examinations performed was estimated to be about 320 million in 2016. Using the tissue-weighting factors from Publication 60 of the International Commission on Radiological Protection, the U.S. annual individual (per capita) effective dose from diagnostic and interventional medical procedures was estimated to have been 2.9 mSv in 2006 and 2.3 mSv in 2016, with the collective doses being 885 000 and 755 000 person-sievert, respectively. Conclusion The trend from 1980 to 2006 of increasing dose from medical radiation has reversed. Estimated 2016 total collective effective dose and radiation dose per capita dose are lower than in 2006. © RSNA, 2020 See also the editorial by Einstein in this issue.

Summary of NCRP 2019 Annual Meeting, NCRP Meeting the Challenge at 90: Providing Best Answers to Your Most Pressing Questions About Radiation.

The National Council on Radiation Protection and Measurements (NCRP) held its 55 Annual Meeting 1-2 April 2019 in Bethesda, Maryland. The 2019 meeting was a special year for NCRP as it marked the 90 Anniversary of the founding of the predecessor organization, US Advisory Committee on X-Ray and Radium Protection. Leaders for the scientific portion of the meeting were Fred A. Mettler, Jr., M.D. (Chair), University of New Mexico School of Medicine; Jerrold T. Bushberg, Ph.D. (Co-Chair), University of California Davis; and Richard J. Vetter, Ph.D. (Co-Chair), Mayo Clinic. The meeting was designed to explore important areas of inquiry associated with use of ionizing radiation relevant to radiation protection, addressing frequently asked questions and concerns from both members of the public and radiation professionals. The meeting was organized into six sessions plus three honorary lectures and a special presentation. This paper summarizes the scientific content of the six sessions and is based on the notes of the co-chairs and the slides of the speakers. The three honorary lectures are included as other papers in this issue.

Patient Radiation Exposure: Imaging During Radiation Oncology Procedures: Executive Summary of NCRP Report No. 184.

The National Council on Radiation Protection and Measurements (NCRP) recently assessed patient radiation exposure in the United States, which was summarized in its 2019 NCRP Report No. 184. This work involved an estimation of the number of medical procedures using ionizing radiation, as well as the associated effective doses from these procedures. The NCRP Report No. 184 committee elected to not incorporate radiation dose from radiotherapy into its calculated population dose exposures, as the assessment of effective dose for the population undergoing radiotherapy is more complex than that for other medical radiation exposures. However, the aim of NCRP Report No. 184 was to raise awareness of ancillary radiation exposures to patients undergoing radiotherapy. Overall, it was estimated that annually, in 2016, approximately 800,000 patients received approximately 1 million courses of radiation therapy. Each of these treatments includes various types of imaging that may not be familiar to radiologists or others. Exposures from radiotherapy planning and delivery are reviewed in the report and summarized in this executive summary. The imaging techniques, use of this imaging, and associated tissue doses are described. Imaging can contribute a few percent to the planned treatment doses (which are prescribed to specified target volumes) as well as exposing patients to radiation outside of the target volume (in the imaging field of view).

Medical Radiation Exposure in the United States: 2006-2016 Trends.

The use of radiation in medicine and the associated population dose grew very rapidly from 1980-2006 predominantly as a result of computed tomography and nuclear medicine. Over the last decade there have been significant changes in image detectors and processing with almost complete elimination of film use. Economic and reimbursement issues have also had a significant effect on usage. After about 2010, the volume of computed tomography and interventional techniques has been fairly level, plain radiography has declined slightly, and noninterventional fluoroscopy has declined dramatically. Nuclear medicine procedures have also declined significantly. Cone-beam computed tomography has expanded particularly in dental radiography. The use of several complex types of image-guided radiotherapy has increased significantly. National Council on Radiation Protection and Measurements' Scientific Committee 4-9 is currently conducting a full assessment for 2016 of collective and per caput effective dose. The report is expected to be completed in 2019, and preliminary work suggests a decrease in collective and per caput effective dose from that previously estimated for 2006.

Recent Epidemiologic Studies and the Linear No-Threshold Model For Radiation Protection-Considerations Regarding NCRP Commentary 27.

National Council on Radiation Protection and Measurements Commentary 27 examines recent epidemiologic data primarily from low-dose or low dose-rate studies of low linear-energy-transfer radiation and cancer to assess whether they support the linear no-threshold model as used in radiation protection. The commentary provides a critical review of low-dose or low dose-rate studies, most published within the last 10 y, that are applicable to current occupational, environmental, and medical radiation exposures. The strengths and weaknesses of the epidemiologic methods, dosimetry assessments, and statistical modeling of 29 epidemiologic studies of total solid cancer, leukemia, breast cancer, and thyroid cancer, as well as heritable effects and a few nonmalignant conditions, were evaluated. An appraisal of the degree to which the low-dose or low dose-rate studies supported a linear no-threshold model for radiation protection or on the contrary, demonstrated sufficient evidence that the linear no-threshold model is inappropriate for the purposes of radiation protection was also included. The review found that many, though not all, studies of solid cancer supported the continued use of the linear no-threshold model in radiation protection. Evaluations of the principal studies of leukemia and low-dose or low dose-rate radiation exposure also lent support for the linear no-threshold model as used in protection. Ischemic heart disease, a major type of cardiovascular disease, was examined briefly, but the results of recent studies were considered too weak or inconsistent to allow firm conclusions regarding support of the linear no-threshold model. It is acknowledged that the possible risks from very low doses of low linear-energy-transfer radiation are small and uncertain and that it may never be possible to prove or disprove the validity of the linear no-threshold assumption by epidemiologic means. Nonetheless, the preponderance of recent epidemiologic data on solid cancer is supportive of the continued use of the linear no-threshold model for the purposes of radiation protection. This conclusion is in accord with judgments by other national and international scientific committees, based on somewhat older data. Currently, no alternative dose-response relationship appears more pragmatic or prudent for radiation protection purposes than the linear no-threshold model.

Gilbert W. Beebe Symposium on 30 Years after the Chernobyl Accident: Current and Future Studies on Radiation Health Effects.

This commentary summarizes the presentations and discussions from the 2016 Gilbert W. Beebe symposium "30 years after the Chernobyl accident: Current and future studies on radiation health effects." The symposium was hosted by the National Academies of Sciences, Engineering, and Medicine (the National Academies). The symposium focused on the health consequences of the Chernobyl accident, looking retrospectively at what has been learned and prospectively at potential future discoveries using emerging 21st Century research methodologies.

38th Lauriston S. Taylor lecture: on the shoulders of giants - radiation protection over 50 years.

Most advances in science, technology, and radiation protection are not truly new ideas but rather build upon a foundation of prior work and achievements by earlier generations of scientists and researchers. This paper summarizes major achievements over the last 50-70 y in the various areas involved in radiation protection as well as giving information about some of those who were, and are, significant contributors.

Nuclear medicine practices in the 1950s through the mid-1970s and occupational radiation doses to technologists from diagnostic radioisotope procedures.

Data on occupational radiation exposure from nuclear medicine procedures for the time period of the 1950s through the 1970s is important for retrospective health risk studies of medical personnel who conducted those activities. However, limited information is available on occupational exposure received by physicians and technologists who performed nuclear medicine procedures during those years. To better understand and characterize historical radiation exposures to technologists, the authors collected information on nuclear medicine practices in the 1950s, 1960s, and 1970s. To collect historical data needed to reconstruct doses to technologists, a focus group interview was held with experts who began using radioisotopes in medicine in the 1950s and the 1960s. Typical protocols and descriptions of clinical practices of diagnostic radioisotope procedures were defined by the focus group and were used to estimate occupational doses received by personnel, per nuclear medicine procedure, conducted in the 1950s to 1960s using radiopharmaceuticals available at that time. The radionuclide activities in the organs of the reference patient were calculated using the biokinetic models described in ICRP Publication 53. Air kerma rates as a function of distance from a reference patient were calculated by Monte Carlo radiation transport calculations using a hybrid computational phantom. Estimates of occupational doses to nuclear medicine technologists per procedure were found to vary from less than 0.01 µSv (thyroid scan with 1.85 MBq of administered I-iodide) to 0.4 µSv (brain scan with 26 MBq of Hg-chlormerodin). Occupational doses for the same diagnostic procedures starting in the mid-1960s but using Tc were also estimated. The doses estimated in this study show that the introduction of Tc resulted in an increase in occupational doses per procedure.

Applications of justification and optimization in medical imaging: examples of clinical guidance for computed tomography use in emergency medicine.

Availability, reliability, and technical improvements have led to continued expansion of computed tomography (CT) imaging. During a CT scan, there is substantially more exposure to ionizing radiation than with conventional radiography. This has led to questions and critical conclusions about whether the continuous growth of CT scans should be subjected to review and potentially restraints or, at a minimum, closer investigation. This is particularly pertinent to populations in emergency departments, such as children and patients who receive repeated CT scans for benign diagnoses. During the last several decades, among national medical specialty organizations, the American College of Emergency Physicians and the American College of Radiology have each formed membership working groups to consider value, access, and expedience and to promote broad acceptance of CT protocols and procedures within their disciplines. Those efforts have had positive effects on the use criteria for CT by other physician groups, health insurance carriers, regulators, and legislators.

Applications of justification and optimization in medical imaging: examples of clinical guidance for computed tomography use in emergency medicine.

Availability, reliability, and technical improvements have led to continued expansion of computed tomography (CT) imaging. During a CT scan, there is substantially more exposure to ionizing radiation than with conventional radiography. This has led to questions and critical conclusions about whether the continuous growth of CT scans should be subjected to review and potentially restraints or, at a minimum, closer investigation. This is particularly pertinent to populations in emergency departments, such as children and patients who receive repeated CT scans for benign diagnoses. During the last several decades, among national medical specialty organizations, the American College of Emergency Physicians and the American College of Radiology have each formed membership working groups to consider value, access, and expedience and to promote broad acceptance of CT protocols and procedures within their disciplines. Those efforts have had positive effects on the use criteria for CT by other physician groups, health insurance carriers, regulators, and legislators.

A report from the 2013 international workshop: radiation and cardiovascular disease, Hiroshima, Japan.

Two longitudinal cohort studies of Japanese atomic bomb survivors-the life span study (LSS) and the adult health study (AHS)-from the Radiation Effects Research Foundation (RERF) indicate that total body irradiation doses less than 1 Gy are associated with an increased risk of cardiovascular disease (CVD), but several questions about this association remain.In particular, the diversity of heart disease subtypes and the high prevalence of other risk factors complicate the estimates of radiation effects. Subtype-specific analyses with more reliable diagnostic criteria and measurement techniques are needed. The radiation effects on CVD risk are probably tissue-reaction (deterministic) effects, so the dose-response relationships for various subtypes of CVD may be nonlinear and therefore should be explored with several types of statistical models.Subpopulations at high risk need to be identified because effects at lower radiation doses may occur primarily in these susceptible subpopulations. Whether other CVD risk factors modify radiation effects also needs to be determined. Finally, background rates for various subtypes of CVD have historically differed substantially between Japanese and Western populations, so the generalisability to other populations needs to be examined.Cardiovascular disease mechanisms and manifestations may differ between high-dose local irradiation and low-dose total body irradiation (TBI)-microvascular damage and altered metabolism from low-dose TBI, but coronary artery atherosclerosis and thrombotic myocardial infarcts at high localised doses. For TBI, doses to organs other than the heart may be important in pathogenesis of CVD, so data on renal and liver disorders, plaque instability, microvascular damage, metabolic disorders, hypertension and various CVD biomarkers and risk factors are needed. Epidemiological, clinical and experimental studies at doses of less than 1 Gy are necessary to clarify the effects of radiation on CVD risk.

Ninth Annual Warren K. Sinclair Keynote Address: effects of childhood radiation exposure: an issue from computed tomography scans to Fukushima.

The acute and chronic effects of radiation on children have been and will continue to be of great social, public health, scientific, and clinical importance. The focus of interest on ionizing radiation and children has been clear for over half a century and ranges from the effects of fallout from nuclear weapons testing to exposures from accidents, natural radiation, and medical procedures. There is a loosely stated notion that "children are three to five times more sensitive to radiation than adults." Is this really true? In fact, children are at greater risk for some health effects, but not all. For a few sequelae, children may be more resistant than adults. Which are those effects? How and why do they occur? While there are clear instances of increased risk of some radiation-induced tumors in children compared to adults, there are other tumor types in which there appears to be little or no difference in risk by age at exposure and some in which published models that assume the same relative increase in risks for child compared to adult exposures apply to nearly all tumor types are not supported by the scientific data. The United Nations Scientific Committee on Effects of Atomic Radiation (UNSCEAR) has a task group producing a comprehensive report on the subject. The factors to be considered include relevant radiation sources; developmental anatomy and physiology; dosimetry; and stochastic, deterministic, and hereditary effects.

Methodology for estimating cancer risks of diagnostic medical exposure: with an example of the risks associated with computed tomography.

Because of fast growing medical radiation use, estimating possible late health effects of radiation, including potential cancer risk, is an issue of substantial interest. Since physicians make the decision to order or perform a radiological procedure, it is very important to provide them with objective information about possible radiation-associated risks. Methodology for estimating cancer risks based on recommendations of ICRP Publication 103 is presented in the paper. Organ doses, age, and gender are used as basic parameters. An example of the evaluation of radiation-associated risks from computed tomography examination is presented.

Medical effects and risks of exposure to ionising radiation.

Effects and risk from exposure to ionising radiation depend upon the absorbed dose, dose rate, quality of radiation, specifics of the tissue irradiated and other factors such as the age of the individual. Effects may be apparent almost immediately or may take decades to be manifest. Cancer is the most important stochastic effect at absorbed doses of less than 1 Gy. The risk of cancer induction varies widely across different tissues; however, the risk of fatal radiation-induced cancer for a general population following chronic exposure is about 5% Sv(-1). Quantification of cancer risk at doses of less than 0.1 Gy remains problematic. Hereditary risks from irradiation that might result in effects to offspring of humans appear to be much lower and any such potential risks can only be estimated from animal models. At high doses (over 1 Gy) cell killing and modification causes deterministic effects such as skin burns, and bone marrow depression, in which case immunosuppression becomes a critical issue. Acute whole body penetrating gamma irradiation at doses in excess of 2 Gy results in varying degrees of acute radiation sickness and doses over 10 Gy are usually lethal as a result of combined organ injury.