Linear Non-threshold Hypothesis Research Articles

The Linear Non-Threshold Hypothesis-A Failed Concept

Bevelacqua Resources 7531 Flint Crossing Circle SE, Owens Cross Roads, AL 35753 USA bevelresou@aol.com The linear non-threshold (LNT) hypothesis is based on the premise that the smallest amount of ionizing radiation produces a biological detriment. It implies that exposure to low-dose radiation be minimized. The LNT approach causes fear and anxiety regarding the beneficial use of radiation and radioactive materials. Contrary to its intended goal of protecting workers and the public, the LNT premise causes physical and economic harm by encouraging radiophobia. KEYWORDS: LNT hypothesis, Hormesis, Dose Thresholds, Radiobiology, Immune System, DNA Repair Mechanisms

Progress in low dose health risk research: Novel effects and new concepts in low dose radiobiology.

People are more often exposed to low as opposed to high doses of ionising radiation (IR). Knowledge on the health risks associated with exposures to ionising radiation above 100 mGy is quite well established, while lower dose risks are inferred from higher level exposure information (ICRP). The health risk assessments are mainly based on epidemiological data derived from the atomic bombing of Hiroshima and Nagasaki, medical exposure studies and follow-up studies after nuclear accidents. For the estimation of long-term stochastic radiation health effects (such as cancer) and radiation protection purposes, a linear non-threshold (LNT) model is applied. However, the general validity of the LNT hypothesis for extrapolations from effects of high to low doses (<100 mGy) and low dose-rates (<6 mGy/h) has been questioned as epidemiological studies are statistically limited at low doses and unable to evaluate low dose and low dose-rate health risks (UNSCEAR). Thus, uncertainties on health risks need to be clarified with the help of mechanistic studies. The European Network of Excellence DoReMi (2010-2016) was designed to address some of the existing uncertainties and to identify research lines that are likely to be most informative for low dose risk assessment. The present review reports the results obtained from studies addressing the induction of cancer and non-cancer effects by low dose IR as well as on individual radiation sensitivity. It is shown that low dose and low dose-rate effects are the result of complex network responses including genetic, epigenetic, metabolic and immunological regulation. Evidence is provided for the existence of nonlinear biological responses in the low and medium dose range as well as effects other than the classical DNA damage. Such effects may have a bearing on the quantitative and qualitative judgements on health effects induced by low dose radiations.

Linear Non-Threshold: Separating Facts from Fiction

The Linear Non-Threshold (LNT) process is used by virtually all governmental agencies to compute incidence of cancer as a consequence of exposure to a carcinogen. This comment applies the concept of Best Available Science (BAS) Metrics for Evaluation of Scientific Claims (MESC) derived from BAS to issues related to reliability of LNT hypothesis. This paper identifies the level of maturity of the LNT hypothesis and the associated uncertainties.

Observations on the Chernobyl Disaster and LNT.

The Chernobyl accident was probably the worst possible catastrophe of a nuclear power station. It was the only such catastrophe since the advent of nuclear power 55 years ago. It resulted in a total meltdown of the reactor core, a vast emission of radionuclides, and early deaths of only 31 persons. Its enormous political, economic, social and psychological impact was mainly due to deeply rooted fear of radiation induced by the linear non-threshold hypothesis (LNT) assumption. It was a historic event that provided invaluable lessons for nuclear industry and risk philosophy. One of them is demonstration that counted per electricity units produced, early Chernobyl fatalities amounted to 0.86 death/GWe-year), and they were 47 times lower than from hydroelectric stations ( approximately 40 deaths/GWe-year). The accident demonstrated that using the LNT assumption as a basis for protection measures and radiation dose limitations was counterproductive, and lead to sufferings and pauperization of millions of inhabitants of contaminated areas. The projections of thousands of late cancer deaths based on LNT, are in conflict with observations that in comparison with general population of Russia, a 15% to 30% deficit of solid cancer mortality was found among the Russian emergency workers, and a 5% deficit solid cancer incidence among the population of most contaminated areas.

UPDATE ON LINEAR NON-THRESHOLD DOSE-RESPONSE MODEL AND IMPLICATIONS FOR DIAGNOSTIC RADIOLOGY PROCEDURES

Cancer risk estimates are used in the setting of radiation protection standards by international and national organizations, and for this purpose need to be developed for low doses of radiation. The approach has involved extrapolation from cancer mortality and incidence values at higher doses to predict the low-dose estimates. Such an extrapolation has generally involved the use of the linear non-threshold (LNT) theory. Recent reports from the National Research Council (BEIR VII) and the International Commission on Radiological Protection (ICRP) have considered the appropriateness of the use of LNT for the purposes of radiation protection standard setting. The overall conclusion from both committees was that current scientific evidence remains consistent with the LNT hypothesis, while appreciating that this might not rule out the possibility that other extrapolation models might well be valid but require further evaluation and additional research to establish their validity. The dose and dose-rate effectiveness factor (DDREF) is used for adjustment in the extrapolation from high to low doses and from high to low dose rates. The BEIR VII committee proposed a new Bayesian approach for estimating DDREF and concluded that a value of 1.5 best fit the data. This is a departure from the previously used value of 2, which is still proposed by ICRP in its most recent recommendations. The current cancer risk estimation process as utilized by ICRP and BEIR VII is used here to assess the potential risks from annual whole-body computed tomography (CT) screens using information and an approach published by Brenner and Ellington. The major conclusion is that potential radiation risks need to be considered along with the pros and cons of the detection limits of the procedure and the impact of false positives.

Changing views on ionising radiation-induced cellular effects

Low dose and low dose-rate effects of ionising radiation (IR) are important issues in radiation protection. For these low exposures, radiation-induced double-strand breaks (DSB) and locally multiply damaged sites (LMDS) are considered very deleterious for cells, leading to lethality, mutations, genetic instability and cancer. However, recent results suggest that LMDS are much less frequent than generally thought. DNA lesions are recognised by sensor proteins which activate cellular IR responses such as cell cycle arrest, DNA repair or cell death. These processes clearly differ with dose and dose-rate, challenging the linear non-threshold hypothesis for radiation risk assessments.

The fetal dose limit for flight personnel should be 1 mSv over the gestation period, rather than 5 mSv as recommended by the NCRP

The fetal dose limit for flight personnel should be 1 mSv over the gestation period, rather than 5 mSv as recommended by the NCRP

Implications of health risk of radiation exposures less than 100 mGy: focused on the linear non-threshold hypothesis

Implications of health risk of radiation exposures less than 100 mGy: focused on the linear non-threshold hypothesis

Health Effects of High Radon Environments in Central Europe: Another Test for the LNT Hypothesis?

Among the various "natural laboratories" of high natural or technical enhanced natural radiation environments in the world such as Kerala (India), Brazil, Ramsar (Iran), etc., the areas in and around the Central European Ore Mountains (Erzgebirge) in the southern parts of former East Germany, but also including parts of Thuringia, northern Bohemia (now Czech Republic), and northeastern Bavaria, are still relatively little known internationally.Although this area played a central role in the history of radioactivity and radiation effects on humans over centuries, most of the valuable earlier results have not been published in English or quotable according to the current rules in the scientific literature and therefore are not generally known internationally. During the years 1945 to 1989, this area was one of the world's most important uranium mining areas, providing the former Soviet Union with 300,000 tons of uranium for its military programs. Most data related to health effects of radon and other carcinogenic agents on miners and residents became available only during the years after German reunification. Many of the studies are still unpublished, or more or less internal reports.By now, substantial studies have been performed on the previously unavailable data about the miners and the population, providing valuable insights that are, to a large degree, in disagreement with the opinion of various international bodies assuming an increase of lung cancer risk in the order of 10% for each 100 Bq/m(3) (or doubling for 1000 Bq/m(3)), even for small residential radon concentrations. At the same time, other studies focusing on never-smokers show little or no effects of residential radon exposures. Experiments in medical clinics using radon on a large scale as a therapeutic against various rheumatic and arthritic disease demonstrated in randomized double-blind studies the effectiveness of such treatments.The main purpose of this review is to critically examine, including some historical references, recent results primarily in three areas, namely the possible effects of the inhalation of very high radon concentrations on miners; the effect of increased residential radon concentrations on the population; and the therapeutic use of radon. With many of the results still evolving and/or under intense discussion among the experts, more evidence is emerging that radon, which has been inhaled at extremely high concentrations in the multimillion Bq/m(3) range by many of older miners (however, with substantial confounders, and large uncertainties in retrospective dosimetry), was perhaps an important but not the dominating factor for an increase in lung cancer rates. Other factors such as smoking, inhalation of quartz and mineral dust, arsenic, nitrous gases, etc. are likely to be more serious contributors to increased miner lung cancer rates. An extrapolation of miner data to indoor radon situations is not feasible.Concerning indoor radon studies, the by far dominating effect of smoking on the lung cancer incidence makes the results of some studies, apparently showing a positive dose-response relationship, questionable. According to recent studies in several countries, there are no, or beneficial, residential radon effects below about 600 to 1000 Bq/m(3) (the extensive studies in the U.S., in particular by B. Cohen, and the discussions about these data, will not be part of this review, because they have already been discussed in detail in the U.S. literature). As a cause of lung cancer, radon seems to rank - behind active and passive smoking, and probably also air pollution in densely populated and/or industrial areas (diesel exhaust soot, etc.) - as a minor contributor in cases of extremely high residential radon levels, combined with heavy smoking of the residents.As demonstrated in an increasing number of randomized double-blind clinical studies for various painful inflammatory joint diseases such as rheumatism, arthritic problems, and Morbus Bechterew, radon treatments are beneficial, with the positive effect lasting until at least 6 months after the normally 3-week treatment by inhalation or bathes. Studies on the mechanism of these effects are progressing. In other cases of extensive use of radon treatment for a wide spectrum of various diseases, for example, in the former Soviet Union, the positive results are not so well established. However, according to a century of radon treatment experience (after millenniums of unknown radon therapy), in particular in Germany and Austria, the positive medical effects for some diseases far exceed any potential detrimental health effects.The total amount of available data in this field is too large to be covered in a brief review. Therefore, less known - in particular recent - work from Central Europe has been analyzed in an attempt to summarize new developments and trends. This includes cost/benefit aspects of radon reduction programs. As a test case for the LNT (linear non-threshold) hypothesis and possible biopositive effects of low radiation exposures, the data support a nonlinear human response to low and medium-level radon exposures.

Nonlinearity of radiation health effects.

The prime concern of radiation protection policy since 1959 has been to protect DNA from damage. In 1994 the United Nations Scientific Community on the Effects of Atomic Radiation focused on biosystem response to radiation with its report Adaptive Responses to Radiation of Cells and Organisms. The 1995 National Council on Radiation Protection and Measurements report Principles and Application of Collective Dose in Radiation Protection states that because no human data provides direct support for the linear nonthreshold hypothesis (LNT), confidence in LNT is based on the biophysical concept that the passage of a single charged particle could cause damage to DNA that would result in cancer. Several statistically significant epidemiologic studies contradict the validity of this concept by showing risk decrements, i.e., hormesis, of cancer mortality and mortality from all causes in populations exposed to low-dose radiation. Unrepaired low-dose radiation damage to DNA is negligible compared to metabolic damage. The DNA damage-control biosystem is physiologically operative on both metabolic and radiation damage and effected predominantly by free radicals. The DNA damage-control biosystem is suppressed by high dose and stimulated by low-dose radiation. The hormetic effect of low-dose radiation may be explained by its increase of biosystem efficiency. Improved DNA damage control reduces persistent mis- or unrepaired DNA damage i.e., the number of mutations that accumulate during a lifetime. This progressive accumulation of gene mutations in stem cells is associated with decreasing DNA damage control, aging, and malignancy. Recognition of the positive health effects produced by adaptive responses to low-dose radiation would result in a realistic assessment of the environmental risk of radiation.