Leveraging Advances in Modern Science to Revitalize Low-Dose Radiation Research in the United States (2022) / Chapter Skim
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Pages 65-85
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From page 65... ...
. The key data on these observations derive from the Japanese atomic bombing survivor cohorts for individuals of all ages (see Section 4.5.6)
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From page 66... ...
of the survivors exposed in utero had died at the end of follow-up, so this cohort is expected to continue to provide valuable information on the effects of in utero exposure and cancer mortality later in life. Long-term excess occurrences of leukemia following in utero exposure in the atomic bombing survivor cohorts have not been observed, but these results need to be interpreted cautiously due to the shorter latency period between radiation exposure and leukemia compared with solid tumors.
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From page 67... ...
However, the effects of postnatal radiation exposure on neurological disorders including cognitive impairment at low doses and low dose rates are poorly characterized in part because of the difficulty in exploring cognitive deficits in experimental animals and because of the difficulty in discerning the subtle changes that need to be measured at low doses. Studies funded by the National Aeronautics and Space Administration documented some evidence of cognitive dysfunction in rodent systems, predominantly following high linear energy transfer (LET)
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. A recent review of the literature on possible cognitive impairment at low doses of radiation concluded that both biological and epidemiological research provide evidence for an effect, but a better characterization of the effects and improved understanding of the mechanisms are needed (Pasqual et al., 2021)
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. However, among the elderly atomic bombing survivors, response to vaccination did not appear to be impaired by radiation exposure early in life (Hayashi et al., 2018)
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(2018) that included data from the Japanese atomic bombing survivors, Chernobyl cleanup workers, medical workers, and radiotherapy patients suggested that the evidence of an increase in cataract formation at doses below 500 mGy was inconclusive.
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. 2.2.6 Heritable Genetic Effects A main concern of populations exposed to radiation, including the Japanese atomic bombing survivors, those exposed to radiation from the Chernobyl and Fukushima nuclear power plant accidents (Suzuki et al., 2018)
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. The investigators discuss that harsh living conditions and the limited socioeconomic resources available to heavily exposed atomic bombing survivors after the war might have led to an overestimate of genetic effects of radiation and suggest that additional insights on radiation and reproduction might be gained by using contemporary genomic methods to compare the DNA of parents irradiated by the bombings with that of their children (Yamada et al., 2021)
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From page 73... ...
. Today, in the absence of a mechanistic understanding of different low-dose and dose-rate radiation sources and their direct health effects, estimation of risks and decisions related to exposures from substantially different sources are often made using the same generic approach -- by relying on risk estimates derived from higher, acute, external exposures to radiation, largely of the Japanese atomic bombing survivors, and applying appropriate correction factors.
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In addition, this program can identify mechanisms for induction of these health effects, develop improved risk models for doses and dose rates at which direct measure ment of risks is not currently possible, and ultimately develop more individualized risk estimates.
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The committee explains why it cannot provide a quantitative assessment of the economic impacts. Instead, the committee offers its assessment of whether knowledge from low-dose radiation research can affect the decision-making frameworks in the federal regulatory system and how (Section 3.4)
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. Exposures to low levels of radiation may carry low levels of risk to an exposed individual; nonetheless they are a high priority for the radiation protection system, and the vast majority of regulations and guidance in the radiation protection system tend to address low-dose radiation exposures.
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From page 77... ...
The LNT model has provided an adequate fit to the data from several major epidemiological studies of cancer risk following radiation exposures, including the Life Span Study of the Japanese atomic bomb survivors. Although no alternative model has convincingly been shown to provide a better fit to these data (Hauptmann et al., 2020; NCRP, 2018a; UNSCEAR, 2020a)
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. The only dose-response curve that predicts more risk at low doses than the linear model is curve "b." Any divergences from the LNT model imply that the current radiation protection system either overestimates or underestimates risks at low doses.
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, but radiation dose estimates were not available in that study.3 3 As discussed in Chapter 5, genome sequencing studies have identified genomic signatures in cancers that suggest specific, non-radiation causative agents for individual tumors (Alexandrov et al., 2020)
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is the lead federal agency responsible for establishing human health and environmental radiation standards for air, surface water, drinking water, uranium mill tailings sites, and deep geologic repositories.4 Various laws authorize other federal agencies to set regulatory limits and issue guidelines to protect the public and workers from exposure to ionizing radiation. The authority of a federal agency to administer those limits and guidance is rooted in statute and tends to vary depending on the setting in which radiation exposure occurs.
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NRC or other federal agencies, such as X-ray equipment, some accelerators, and some naturally occurring radioactive material. OSHA's limits for workers vary by industry.9 The Department of Defense is responsible for military exposure and remediation as well as for setting requirements to operate in environments that could expose personnel to low doses of ionizing radiation.
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. Both the National Academies and UNSCEAR periodically review the available scientific literature of epidemiological and mechanistic studies of radiation exposure and develop models for calculating 10 Seehttp://www.iscors.org.
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Uncertainties in low-dose radiation risks raise questions about whether dose limits and guidance levels are set appropriately or whether they are set too high and therefore do not sufficiently protect workers and members of the public or too low and therefore result in unnecessary costs to reduce radiation exposure. Federal agencies have been formally challenged by members of the public about the use of LNT to set radiation protection standards at least twice in the recent past.
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radiation protection regulations relates to the allowable exposure to radiation workers and to the lens of the eye. ICRP recommends limiting the annual exposure to radiation workers to 20 mSv (ICRP, 2007)
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3.3.2 Decision-Making Frameworks for Radiation Protection Risk-based regulation is a particular strategy or set of strategies that regulators use to target their resources at those sites and activities that present threats to their ability to achieve their objectives. Economic analysis of the impacts of the proposed change (Step 1 in the regulatory development process described in the previous section)
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