![]() ![]() Pending any definitive answer to these questions, the LNT model is applied through the precautionary principle. Because the current data is inconclusive, scientists disagree on which model should be used. A 2016 peer-reviewed meta-analysis rejected the LNT on the basis of a lack of empirical evidence supporting it, and that it ignores biological effects, especially the self-correcting mechanisms in DNA which are effective up to a certain level of mutagenic agent. The LNT model opposes two competing schools of thought: the threshold model, which assumes that very small exposures are harmless, and the radiation hormesis model, which claims that radiation at very small doses can be beneficial. NRC rejected the petitions in 2021 because "they fail to present an adequate basis supporting the request to discontinue use of the LNT model". Whether the LNT model describes the reality for small-dose exposures is disputed, and challenges to the LNT model used by NRC for setting radiation protection regulations were submitted. Nonetheless, regulatory bodies, such as the Nuclear Regulatory Commission (NRC), commonly use LNT as a basis for regulatory dose limits to protect against stochastic health effects, as found in many public health policies. LNT is a common model to calculate the probability of radiation-induced cancer both at high doses where epidemiology studies support its application, but controversially, also at low doses, which is a dose region that has a lower predictive statistical confidence. Because of the inherent differences, LNT is not a model for deterministic effects, which are instead characterized by other types of dose-response relationships. Deterministic effects reliably occur above a threshold dose and their severity increases with dose. In contrast, deterministic health effects are radiation-induced effects such as acute radiation syndrome, which are caused by tissue damage. In other words, LNT assumes that radiation has the potential to cause harm at any dose level, however small, and the sum of several very small exposures is just as likely to cause a stochastic health effect as a single larger exposure of equal dose value. The LNT model assumes there is no lower threshold at which stochastic effects start, and assumes a linear relationship between dose and the stochastic health risk. Stochastic health effects are those that occur by chance, and whose probability is proportional to the dose, but whose severity is independent of the dose. One of the organizations for establishing recommendations on radiation protection guidelines internationally, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) that previously supported the LNT model, no longer supports the model for very low radiation doses. For example, the US Nuclear Regulatory Commission and United States Environmental Protection Agency endorse the model, while a number of other bodies deprecate it. ĭifferent organizations take different approaches to the LNT model. It has been argued that the LNT model may have created an irrational fear of radiation. Whenever the cancer risk is estimated from real data at low doses, and not from extrapolation of observations at high doses, the supra-linear model is verified. The validity of the LNT model, however, is disputed, and other significant models exist: the threshold model, which assumes that very small exposures are harmless, the radiation hormesis model, which says that radiation at very small doses can be beneficial, and the supra-linear model based on observational data. ![]() The model has also been used in the assessment of cancer risks of mutagenic chemicals. The LNT model is commonly used by regulatory bodies as a basis for formulating public health policies that set regulatory dose limits to protect against the effects of radiation. The LNT model lies at a foundation of a postulate that all exposure to ionizing radiation is harmful, regardless of how low the dose is, and that the effect is cumulative over lifetime. The model statistically extrapolates effects of radiation from very high doses (where they are observable) into very low doses, where no biological effects may be observed. The linear no-threshold model ( LNT) is a dose-response model used in radiation protection to estimate stochastic health effects such as radiation-induced cancer, genetic mutations and teratogenic effects on the human body due to exposure to ionizing radiation. radiation dose to low-dose levels, given a known risk at a high dose: Different assumptions on the extrapolation of the cancer risk vs. ![]()
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