Implications of radiation dose and exposed populations on radiation protection in the 21st century

The Use of Computerized Tomography Scans in Elective Knee and Hip Arthroplasty—What Do They Tell Us and at What Risk?

The average background radiation exposure in the United States has nearly doubled over the previous quarter century, with almost all the increase derived from medical imaging. Nearly 2% of all cancers in the United States may be attributable to radiation from computerized tomography (CT) scans. Given the nondiagnostic nature of CT scans that are used in elective knee and hip arthroplasty today, special consideration should be given to the inherent risk of radiation exposure with routine use of this technology. Methods to decrease radiation exposure including modulating the settings of the CT machine and using alternative non-CT-based systems can decrease patient exposure to radiation from CT scans. The rapid evolution of CT technology in arthroplasty has allowed for expanded clinical applications, the benefits of which remain controversial.

Blood RNA Integrity is a Direct and Simple Reporter of Radiation Exposure and Prognosis: A Pilot Study

In the event of a mass casualty radiation scenario, rapid assessment of patients' health and triage is required for optimal resource utilization. Identifying the level and extent of exposure as well as prioritization of care is extremely challenging under such disaster conditions. Blood-based biomarkers, such as RNA integrity numbers (RIN), could help healthcare personnel quickly and efficiently determine the extent and effect of multiple injuries on patients' health. Evaluation of the effect of different radiation doses, alone or in combination with burn injury, on total RNA integrity over multiple time points was performed. Total RNA integrity was tallied in blood samples for potential application as a marker of radiation exposure and survival. Groups of aged mice (3-6 mice/group, 13-18 months old) received 0.5, 1, 5, 10 or 20 Gy ionizing radiation. Two additional mouse groups received low-dose irradiation (0.5 or 1 Gy) with a 15% total body surface area (TBSA) burn injury. Animals were euthanized at 2 or 12 h and at day 1, 2, 3, 7 or 14 postirradiation, or when injury-mediated mortality occurred. Total RNA was isolated from blood. The quality of RNA was evaluated and RNA RIN were obtained. Analysis of RIN indicated that blood showed the clearest radiation effect. There was a time- and radiation-dose-dependent reduction in RIN that was first detectable at 12 h postirradiation for all doses in animals receiving irradiation alone. This effect was reversible in lower-dose groups (i.e., 0.5, 1 and 5 Gy) that survived to the end of the study (14 days). In contrast, the effect persisted for 10 and 20 Gy groups, which showed suppression of RIN values <4.5 with high mortalities. Radiation doses of 20 Gy were lethal and required euthanasia by day 6. A low RIN (<2.5) at any time point was associated with 100% mortality. Combined radiation-burn injury produced significantly increased mortality such that no dually-injured animals survived beyond day 3, and no radiation dose >1 Gy resulted in survival past day 1. More modest suppression of RIN was observed in the surviving dually challenged mice, and no statistically significant changes were identified in RIN values of burn-only mice at any time point. In this study of an animal model, a proof of concept is presented for a simple and accurate method of assessing radiation dose exposure in blood which potentially predicts lethality. RIN assessment of blood-derived RNA could form the basis for a clinical decision-support tool to guide healthcare providers under the strenuous conditions of a radiation-based mass casualty event.

Radiation Emergency Readiness Among US Medical Toxicologists: A Survey

INTRODUCTION

Large scale radiologic and nuclear disasters are rare; however, recent events such as the Fukushima Daiichi nuclear reactor emergency in Japan and current global political tensions have highlighted the need for health-care providers with expertise in managing radiation injuries. Medical Toxicologists have the ability to collaborate with other specialists in filling this critical role.

METHODS

We conducted a cross-sectional survey to assess the attitudes, experiences, and knowledge of medical toxicologists through the assistance of the American College of Medical Toxicology.

RESULTS

The survey was completed by 114 medical toxicologists during the enrollment period. Medical toxicologists who had a willingness to participate in radiologic or nuclear emergencies or who had taken care of patients contaminated with radioactive material were more likely to perform well on the knowledge assessment.

CONCLUSION

We identified that there is a group of medical toxicologists who have the willingness, experience, and knowledge to help manage patients in the event of a radiologic or nuclear emergency.

Radiation epidemiology and health effects following low-level radiation exposure

Radiation epidemiology is the study of human disease following radiation exposure to populations. Epidemiologic studies of radiation-exposed populations have been conducted for nearly 100 years, starting with the radium dial painters in the 1920s and most recently with large-scale studies of radiation workers. As radiation epidemiology has become increasingly sophisticated it is used for setting radiation protection standards as well as to guide the compensation programmes in place for nuclear weapons workers, nuclear weapons test participants, and other occupationally exposed workers in the United States and elsewhere. It is known with high assurance that radiation effects at levels above 100-150 mGy can be detected as evidenced in multiple population studies conducted around the world. The challenge for radiation epidemiology is evaluating the effects at low doses, below about 100 mGy of low-linear energy transfer radiation, and assessing the risks following low dose-rate exposures over years. The weakness of radiation epidemiology in directly studying low dose and low dose-rate exposures is that the signal, i.e. the excess numbers of cancers associated with low-level radiation exposure, is so very small that it cannot be seen against the very high background occurrence of cancer in the population, i.e. a lifetime risk of incidence reaching up to about 38% (i.e. 1 in 3 persons will develop a cancer in their lifetime). Thus, extrapolation models are used for the management of risk at low doses and low dose rates, but having adequate information from low dose and low dose-rate studies would be highly desirable. An overview of recently conducted radiation epidemiologic studies which evaluate risk following low-level radiation exposures is presented. Future improvements in risk assessment for radiation protection may come from increasingly informative epidemiologic studies, combined with mechanistic radiobiologic understanding of adverse outcome pathways, with both incorporated into biologically based models.

Mortality among military participants at the 1957 PLUMBBOB nuclear weapons test series and from leukemia among participants at the SMOKY test

Health effects following low doses of ionizing radiation are uncertain. Military veterans at the Nevada test site (NTS) during the SMOKY atmospheric nuclear weapons test in 1957 were reported to be at increased risk for leukemia in 1979, but this increase was not evaluated with respect to radiation dose. The SMOKY test was one of 30 tests in 1957 within the PLUMBBOB test series. These early studies led to public laws where atomic veterans could qualify for compensation for presumptive radiogenic diseases. A retrospective cohort study was conducted of 12219 veterans at the PLUMBBOB test series, including 3020 at the SMOKY nuclear test. Mortality follow-up was through 2010 and observed causes of death were compared with expected causes based on general population rates. Radiation dose to red bone marrow was based on individual dose reconstructions, and Cox proportional hazards models were used to evaluate dose response for all leukemias other than chronic lymphocytic leukemia (non-CLL leukemia). Vital status was determined for 95.3% of the 12 219 veterans. The dose to red bone marrow was low (mean 3.2 mGy, maximum 500 mGy). Military participants at the PLUMBBOB nuclear test series remained relatively healthy after 53 years and died at a lower rate than the general population. In contrast, and in comparison with national rates, the SMOKY participants showed significant increases in all causes of death, respiratory cancer, leukemia, nephritis and nephrosis, and accidents, possibly related in part to lifestyle factors common to enlisted men who made up 81% of the SMOKY cohort. Compared with national rates, a statistically significant excess of non-CLL leukemia was observed among SMOKY participants (Standardized Mortality Ratio  =  1.89, 95% 1.24-2.75, n  =  27) but not among PLUMBBOB participants after excluding SMOKY (SMR  =  0.87, 95% 0.64-1.51, n  =  47). Leukemia risk, initially reported to be significantly increased among SMOKY participants, remained elevated, but this risk diminished over time. Despite an intense dose reconstruction, the risk for leukemia was not found to increase with increasing levels of radiation dose to the red bone marrow. Based on a linear model, the estimated excess relative risk per mGy is  -0.05 (95% CI -0.14, 0.04). An explanation for the observed excess of leukemia remains unresolved but conceivably could be related to chance due to small numbers, subtle biases in the study design and/or high tobacco use among enlisted men. Larger studies should elucidate further the possible relationship between fallout radiation, leukemia and cancer among atomic veterans.

Preoperative Mapping in Unicompartmental Knee Arthroplasty Using Computed Tomography Scans Is Associated with Radiation Exposure and Carries High Cost

Robotic-assisted knee arthroplasty with some systems requires the use of computed tomography (CT) scans. The associated radiation dose has not been studied. The effective dose (ED, mSv) of radiation was calculated for 236 preoperative CT scans used for planning of robotic assisted surgery. The mean ED was 4.8±3.0 mSv. There was a 3-fold difference in ED between institutions. One or more additional CT scans were obtained in 25% of patients, amounting to a cumulative ED per patient up to 103 mSv. Preoperative CT is a disadvantage of some robotic-assisted knee arthroplasty systems due to additional cost and radiation exposure. Newer image-free robotic technologies are an alternative to CT-dependent surgery if accuracy and safety are not compromised.

Capturing opportunities and meeting challenges in radiation protection

This summary of the 2014 Annual Meeting of the National Council on Radiation Protection and Measurement (NCRP) captures the opportunities presented during the Warren K. Sinclair Keynote Address, the Lauriston S. Taylor Lecture, and the six scientific sessions including the subsequent questions and answers. It captures the important issues that emerge in these opportunities and discusses the challenges that they bring to radiation protection. These opportunities arise in the basic sciences; in operational areas such as emerging technologies, preparing for the improbable but possible event, industry and medicine; and in education, communication and policy. The challenges include identifying the most important aspects of radiation protection and measurement, prioritizing them in accordance with the NCRP mission, and gaining support for the activities of the NCRP to address these issues in the fulfillment of its charter.

Application of an informatics-based decision-making framework and process to the assessment of radiation safety in nanotechnology

The National Council on Radiation Protection and Measurements (NCRP) established NCRP Scientific Committee 2-6 to develop a report on the current state of knowledge and guidance for radiation safety programs involved with nanotechnology. Nanotechnology is the understanding and control of matter at the nanoscale, at dimensions between ∼1 and 100 nm, where unique phenomena enable novel applications. While the full report is in preparation, this paper presents and applies an informatics-based decision-making framework and process through which the radiation protection community can anticipate that nano-enabled applications, processes, nanomaterials, and nanoparticles are likely to become present or are already present in radiation-related activities; recognize specific situations where environmental and worker safety, health, well-being, and productivity may be affected by nano-related activities; evaluate how radiation protection practices may need to be altered to improve protection; control information, interpretations, assumptions, and conclusions to implement scientifically sound decisions and actions; and confirm that desired protection outcomes have been achieved. This generally applicable framework and supporting process can be continuously applied to achieve health and safety at the convergence of nanotechnology and radiation-related activities.

Potential for adult-based epidemiological studies to characterize overall cancer risks associated with a lifetime of CT scans

Recent epidemiological studies have suggested that radiation exposure from pediatric CT scanning is associated with small excess cancer risks. However, the majority of CT scans are performed on adults, and most radiation-induced cancers appear during middle or old age, in the same age range as background cancers. Consequently, a logical next step is to investigate the effects of CT scanning in adulthood on lifetime cancer risks by conducting adult-based, appropriately designed epidemiological studies. Here we estimate the sample size required for such studies to detect CT-associated risks. This was achieved by incorporating different age-, sex-, time- and cancer type-dependent models of radiation carcinogenesis into an in silico simulation of a population-based cohort study. This approach simulated individual histories of chest and abdominal CT exposures, deaths and cancer diagnoses. The resultant sample sizes suggest that epidemiological studies of realistically sized cohorts can detect excess lifetime cancer risks from adult CT exposures. For example, retrospective analysis of CT exposure and cancer incidence data from a population-based cohort of 0.4 to 1.3 million (depending on the carcinogenic model) CT-exposed UK adults, aged 25-65 in 1980 and followed until 2015, provides 80% power for detecting cancer risks from chest and abdominal CT scans.