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Dose-rate effects in radiation biology and radiation protection
Annals of the ICRP, 2016
Quantification of biological effects (cancer, other diseases, and cell damage) associated with exposure to ionising radiation has been a major issue for the International Commission on Radiological Protection (ICRP) since its foundation in 1928. While there is a wealth of information on the effects on human health for whole-body doses above approximately 100 mGy, the effects associated with doses below 100 mGy are still being investigated and debated intensively. The current radiological protection approach, proposed by ICRP for workers and the public, is largely based on risks obtained from high-dose and high-dose-rate studies, such as the Japanese Life Span Study on atomic bomb survivors. The risk coefficients obtained from these studies can be reduced by the dose and dose-rate effectiveness factor (DDREF) to account for the assumed lower effectiveness of low-dose and low-dose-rate exposures. The 2007 ICRP Recommendations continue to propose a value of 2 for DDREF, while other int...
Dose and dose-rate effectiveness of radiation: first objectivity then conclusions
Journal of Environmental and Occupational Science
This letter comments on the ongoing re-evaluation of the dose and dose rate effectiveness factor (DDREF) equal to 2.0, currently recommended by the International Commission on Radiological Protection. The topics of DDREF and threshold are related to the linear no-threshold theory (LNT), which does not take into account that DNA damage and repair are in dynamic equilibrium probably reached in a long term. Living organisms must have been adapted by natural selection to the today's background level of radiation or to some average from the past, when the radiation background was higher. Dosedependent self-selection of exposed people and other biases common in epidemiological studies, cited in support of the DDREF lowering, are discussed here. In conclusion, the LNT and underestimation of DDREF tend to exaggerate radiationrelated health risks at low dose and dose rates exposures. Future risk estimates should be based on direct comparisons of experimental data from acute and protracted exposures.
Radiation and Environmental Biophysics, 2015
The biological effects on humans of low-dose and low-dose-rate exposures to ionizing radiation have always been of major interest. The most recent concept as suggested by the International Commission on Radiological Protection (ICRP) is to extrapolate existing epidemiological data at high doses and dose rates down to low doses and low dose rates relevant to radiological protection, using the socalled dose and dose-rate effectiveness factor (DDREF). The present paper summarizes what was presented and discussed by experts from ICRP and Japan at a dedicated workshop on this topic held in May 2015 in Kyoto, Japan. This paper describes the historical development of the DDREF concept in light of emerging scientific evidence on dose and dose-rate effects, summarizes the conclusions recently drawn by a number of international organizations (e.g., BEIR VII, ICRP, SSK, UNSCEAR, and WHO), mentions current scientific efforts to obtain more data on low-dose and low-dose-rate effects at molecular, cellular, animal and human levels, and discusses future options that could be useful to improve and optimize the DDREF concept for the purpose of radiological protection.
Journal of radiation research, 2018
In order to quantify radiation risks at exposure scenarios relevant for radiation protection, often extrapolation of data obtained at high doses and high dose rates down to low doses and low dose rates is needed. Task Group TG91 on 'Radiation Risk Inference at Low-dose and Low-dose Rate Exposure for Radiological Protection Purposes' of the International Commission on Radiological Protection is currently reviewing the relevant cellular, animal and human studies that could be used for that purpose. This paper provides an overview of dose rates and doses typically used or present in those studies, and compares them with doses and dose rates typical of those received by the A-bomb survivors in Japan.
A hypothesis to derive the shape of the dose–response curve for teratogenic radiation effects
Environmental Health, 2022
Reports of adverse pregnancy outcomes after in utero exposure to very low levels of ionizing radiation are inconsistent with a threshold dose of 100 mSv for teratogenic effects in humans. In the present study, it is hypothesized that the shape of the dose-response relationship for teratogenic effects is a cumulative lognormal distribution without threshold. This hypothesis relies on the assumption that both doses and radiosensitivities in human populations exposed to ionizing radiation are random variables, modeled by lognormal density functions. Here, radiosensitivity is defined as the dose limit up to which radiation damage can be repaired by the cellular repair systems, in short, the repair capacity. Monte Carlo simulation is used to generate N pairs of individual doses and repair capacities. Radiation damage occurs whenever the dose exceeds the related repair capacity. The rate of radiation damage is the number of damages, divided by the number N of pairs. Monte Carlo simulation is conducted for a sufficient number of ascending median doses. The shape of the dose-response relationship is determined by regression of damage rates on mean dose. Regression with a cumulative lognormal distribution function yields a perfect fit to the data. Acceptance of the hypothesis means that studies of adverse health effects following in-utero exposure to low doses of ionizing radiation should not be discarded primarily because they contradict the concept of a threshold dose for teratogenic effects.
TH-E-213AB-02: Review of the Radiobiological Principles of Radiation Protection
Medical Physics, 2012
Learning Objectives 1. To understand the radiobiological basis of radiation protection standards. 2. To define the radiation protection magnitudes and units, their values and their practical measurement. 3. To distinguish between stochastic and deterministic effects. 2 3 Radiation Effects Ionizing radiation interacts at the cellular level: • ionization • chemical changes • biological effect cell nucleus chromosomes incident radiation http://rpop.iaea.org/ Interaction of ionizing radiation with DNA, the critical target 4 DIRECT ACTION INDIRECT ACTION http://rpop.iaea.org/ Outcomes after Cell Exposure 5 Cell survives but mutated Cancer? Cell dies Cell mutates but mutation is repaired Unviable Cell Viable Cell Radiation hits cell nucleus! http://rpop.iaea.org/ There are qualitative and quantitative differences in initial DNA damage caused by radiation DNA damage caused by radiation exhibits multiply damaged sites and clustered legions Double strand breaks are more common in radiation-induced damage than single strand breaks, which are more common in normal endogenous DNA damage. DNA Damage http://lowdose.energy.gov/pdf/Powerpoint\_WEBBystander.pdf 6 How does radiation interact with cells? Past Theory Hit theory Radiation causes free radicals to damage only the cell that is "hit" by direct ionization Present Theories Bystander effects Radiation causes free radicals to trigger cell-cell communication and cellmatrix communication to cells other than those which are "hit" by the direct ionization.