Test of the linear-no threshold theory of radiation carcinogenesis for inhaled radon decay products

Evaluating county-level lung cancer incidence from environmental radiation exposure, PM2.5, and other exposures with regression and machine learning models

Characterizing the interplay between exposures shaping the human exposome is vital for uncovering the etiology of complex diseases. For example, cancer risk is modified by a range of multifactorial external environmental exposures. Environmental, socioeconomic, and lifestyle factors all shape lung cancer risk. However, epidemiological studies of radon aimed at identifying populations at high risk for lung cancer often fail to consider multiple exposures simultaneously. For example, moderating factors, such as PM2.5, may affect the transport of radon progeny to lung tissue. This ecological analysis leveraged a population-level dataset from the National Cancer Institute's Surveillance, Epidemiology, and End-Results data (2013-17) to simultaneously investigate the effect of multiple sources of low-dose radiation (gross [Formula: see text] activity and indoor radon) and PM2.5 on lung cancer incidence rates in the USA. County-level factors (environmental, sociodemographic, lifestyle) were controlled for, and Poisson regression and random forest models were used to assess the association between radon exposure and lung and bronchus cancer incidence rates. Tree-based machine learning (ML) method perform better than traditional regression: Poisson regression: 6.29/7.13 (mean absolute percentage error, MAPE), 12.70/12.77 (root mean square error, RMSE); Poisson random forest regression: 1.22/1.16 (MAPE), 8.01/8.15 (RMSE). The effect of PM2.5 increased with the concentration of environmental radon, thereby confirming findings from previous studies that investigated the possible synergistic effect of radon and PM2.5 on health outcomes. In summary, the results demonstrated (1) a need to consider multiple environmental exposures when assessing radon exposure's association with lung cancer risk, thereby highlighting (1) the importance of an exposomics framework and (2) that employing ML models may capture the complex interplay between environmental exposures and health, as in the case of indoor radon exposure and lung cancer incidence.

Radon level in groundwater in Kwara State, Nigeria, and the potential radiation dose due to intake

Radon in groundwater for domestic purposes contributes to indoor radon and at high concentration levels could be hazardous to inhabitants. Rn-222 concentrations in 101 groundwater samples from some Local Government Areas (LGAs) of Kwara State, Nigeria, were determined by AlphaGUARD portable radon monitor. The mean activity concentrations for the LGAs varied from 4.28 ± 2.29 to 14.59 ± 8.92 Bq.l-1. Radon concentrations were <100 Bq.l-1 guidance level recommended by CEC and WHO. Eighteen percent exceeded the recommended 11.1 Bq.l-1 by the United States Environmental Protection Agency. All the samples exceeded the 0.1 Bq.l-1 Maximum Permitted Level of the Standard Organization of Nigeria for radionuclide contaminant. Mean effective dose from ingestion was estimated for adults, children and infants. Inhalation dose was also estimated. The mean annual effective doses in five LGAs were higher than the 0.1 mSv reference dose level of committed effective dose from the intake of drinking water for 1 y as recommended by the ICRP.

HIGHLIGHTS

Can Low-Level Ionizing Radiation Do Us Any Harm?

The current system of radiological protection relies on the linear no-threshold (LNT) hypothesis of cancer risk due to humans being exposed to ionizing radiation (IR). Under this tenet, effects of low doses (i.e. of those not exceeding 100 mGy or 0.1 mGy/min. of X- or γ-rays for acute and chronic exposures, respectively) are evaluated by downward linear extrapolation from regions of higher doses and dose rates where harmful effects are actually observed. However, evidence accumulated over many years clearly indicates that exposure of humans to low doses of radiation does not cause any harm and often promotes health. In this review, we discuss results of some epidemiological analyses, clinical trials and controlled experimental animal studies. Epidemiological data indicate the presence of a threshold and departure from linearity at the lowest dose ranges. Experimental studies clearly demonstrate the qualitative difference between biological mechanisms and effects at low and at higher doses of IR. We also discuss the genesis and the likely reasons for the persistence of the LNT tenet, despite its scientific implausibility and deleterious social consequences. It is high time to replace the LNT paradigm by a scientifically based dose-effect relationship where realistic quantitative hormetic or threshold models are exploited.

Radon and Lung Cancer: Current Trends and Future Perspectives

Simple Summary

Radon represents the main risk factor of lung cancer in non-smokers and the second one in smoking patients. In Europe, there are several radon-prone areas, but regulatory policies may vary between countries. Radon causes DNA damage and high genomic tumor instability, but its exact carcinogenesis mechanism in lung cancer remains unknown. Molecular drivers in NSCLC are more often described in non-smoker patients and a potential association between radon exposure and oncogenic-driven NSCLC has been postulated. This is an updated review on indoor radon exposure and its role in lung cancer carcinogenesis, especially focusing on its potential relation with NSCLC with driver genomic alterations. We want to contribute to rising knowledge and awareness on this still silent but preventable lung cancer risk factor.

Abstract

Lung cancer is a public health problem and the first cause of cancer death worldwide. Radon is a radioactive gas that tends to accumulate inside homes, and it is the second lung cancer risk factor after smoking, and the first one in non-smokers. In Europe, there are several radon-prone areas, and although the 2013/59 EURATOM directive is aimed to regulate indoor radon exposition, regulating measures can vary between countries. Radon emits alpha-ionizing radiation that has been linked to a wide variety of cytotoxic and genotoxic effects; however, the link between lung cancer and radon from the genomic point of view remains poorly described. Driver molecular alterations have been recently identified in non-small lung cancer (NSCLC), such as somatic mutations (EGFR, BRAF, HER2, MET) or chromosomal rearrangements (ALK, ROS1, RET, NTRK), mainly in the non-smoking population, where no risk factor has been identified yet. An association between radon exposure and oncogenic NSCLC in non-smokers has been hypothesised. This paper provides a practical, concise and updated review on the implications of indoor radon in lung cancer carcinogenesis, and especially of its potential relation with NSCLC with driver genomic alterations.

Correlative links between natural radiation and life expectancy in the US population

The linear no-threshold (LNT) hypothesis is still the ruling concept which dictates the radiation protection health policy and regulations. However, more and more studies show that not only that low dose radiation pose no danger to our health, but also exhibits clear beneficial health effects. Here, we evaluated the correlative links of the natural sources of radiation-terrestrial radiation (TR), cosmic radiation (CR), and Radon-222, with life expectancy, the most integrative index of population health. The results of this study show that the different sources of natural radiation display positive correlative links to life expectancy, which is in line with the hypothesis of radiation hormesis.

Radiobiology in my life

The fate of radiobiology and in particular radiation genetics in the Soviet Union was difficult and dramatic. In the period of 1948-1965, a political campaign, based on the theory of T. D. Lysenko, rejected classical genetics, banned such research and persecuted "classical" geneticists. After the Nuclear Test-Ban Treaty was signed on August 5, 1963, Belarusian authorities started closing down radiobiological centers. Many radiobiologists were obliged to go abroad. Then the Chernobyl disaster in May 1986 changed the political direction - research on radiobiology and radiation genetics became relevant again. The only medical effect of the Chernobyl disaster was thyroid cancer, but radiation was not the only reason for that. A lot of criminal mistakes of the Soviet government and the Ministry of Health increase the cancer rate. The history of science is always complicated, and nowadays there are some unanswered questions and contradictory issues in the field of radiobiology, for instance, uncertainties in estimating radiation risks. It is necessary to keep in mind a lot of limitations and qualifications that demonstrates that there are no simple answers in this science.

Designing an Indoor Radon Risk Exposure Indicator (IRREI): An Evaluation Tool for Risk Management and Communication in the IoT Age

The explosive data growth in the current information age requires consistent new methodologies harmonized with the new IoT era for data analysis in a space-time context. Moreover, intuitive data visualization is a central feature in exploring, interpreting, and extracting specific insights for subsequent numerical data representation. This integrated process is normally based on the definition of relevant metrics and specific performance indicators, both computed upon continuous real-time data, considering the specificities of a particular application case for data validation. This article presents an IoT-oriented evaluation tool for Radon Risk Management (RRM), based on the design of a simple and intuitive Indoor Radon Risk Exposure Indicator (IRREI), specifically tailored to be used as a decision-making aid tool for building owners, building designers, and buildings managers, or simply as an alert flag for the problem awareness of ordinary citizens. The proposed methodology was designed for graphic representation aligned with the requirements of the current IoT age, i.e., the methodology is robust enough for continuous data collection with specific Spatio-temporal attributes and, therefore, a set of adequate Radon risk-related metrics can be extracted and proposed. Metrics are summarized considering the application case, taken as a case study for data validation, by including relevant variables to frame the study, such as the regulatory International Commission on Radiological Protection (ICRP) dosimetric limits, building occupancy (spatial dimension), and occupants' exposure periods (temporal dimension). This work has the following main contributions: (1) providing a historical perspective regarding RRM indicator evolution along time; (2) outlining both the formulation and the validation of the proposed IRREI indicator; (3) implementing an IoT-oriented methodology for an RRM indicator; and (4) a discussion on Radon risk public perception, undertaken based on the results obtained after assessment of the IRREI indicator by applying a screening questionnaire with a total of 873 valid answers.

Analysis of Indoor Radon Data Using Bayesian, Random Binning, and Maximum Entropy Methods

Three statistical methods: Bayesian, randomized data binning and Maximum Entropy Method (MEM) are described and applied in the analysis of US radon data taken from the US registry. Two confounding factors-elevation of inhabited dwellings, and UVB (ultra-violet B) radiation exposure-were considered to be most correlated with the frequency of lung cancer occurrence. MEM was found to be particularly useful in extracting meaningful results from epidemiology data containing such confounding factors. In model testing, MEM proved to be more effective than the least-squares method (even via Bayesian analysis) or multi-parameter analysis, routinely applied in epidemiology. Our analysis of the available residential radon epidemiology data consistently demonstrates that the relative number of lung cancers decreases with increasing radon concentrations up to about 200 Bq/m³, also decreasing with increasing altitude at which inhabitants live. Correlation between UVB intensity and lung cancer has also been demonstrated.

Full Analysis of Lung Cancer Mortality/Radon Relationship with Simple Nonlinear Concepts

We analyze the relationship between the lung cancer mortality and the indoor radon intensity from the viewpoint of nonlinear mathematics. We conclude that their relationship is governed by the proportionality law where the cumulative lung cancer mortality Y is negatively proportional to the cumulative radon intensity X; or specifically, the nonlinear change of nonlinear face value (qYu - qY) is negatively proportional to the nonlinear change of nonlinear face value (X - Xb). The author obtained a set of data from late Professor Cohen on the lung-cancer mortality rate versus indoor radon level collected from 1,597 counties and territory of the USA. We initially presented the data as various primitive elementary graphs; then extended them to the primary graphs, leading graphs, and the proportionality graphs. The article emphasizes the building of a straight-line proportionality relationship for the dose-response data in a log-linear and/or log-log graphs. It demonstrates a straightforward methodology for solving the key upper asymptotes (Yu) for the proportionality equation using the Microsoft Excel via determining the "coefficient of determination". (Note: q = log, Yu = upper asymptote of Y, Xb = bottom asymptote of X).

Background radiation impacts human longevity and cancer mortality: reconsidering the linear no-threshold paradigm

The current linear no-threshold paradigm assumes that any exposure to ionizing radiation carries some risk, thus every effort should be made to maintain the exposures as low as possible. We examined whether background radiation impacts human longevity and cancer mortality. Our data covered the entire US population of the 3139 US counties, encompassing over 320 million people. This is the first large-scale study which takes into account the two major sources of background radiation (terrestrial radiation and cosmic radiation), covering the entire US population. Here, we show that life expectancy, the most integrative index of population health, was approximately 2.5 years longer in people living in areas with a relatively high vs. low background radiation. (≥ 180 mrem/year and ≤ 100 mrem/year, respectively; p < 0.005; 95% confidence interval [CI]). This radiation-induced lifespan extension could to a great extent be associated with the decrease in cancer mortality rate observed for several common cancers (lung, pancreas and colon cancers for both genders, and brain and bladder cancers for males only; p < 0.05; 95% CI). Exposure to a high background radiation displays clear beneficial health effects in humans. These hormetic effects provide clear indications for re-considering the linear no-threshold paradigm, at least within the natural range of low-dose radiation.

A review of studies of childhood cancer and natural background radiation

PURPOSE

The projected existence and magnitude of carcinogenic effects of ionizing radiation at low doses and low-dose rates is perhaps the most important issue in radiation protection today. Studies of childhood cancer and natural background radiation have the potential to throw direct light on this question, into a dose range below a few tens of mSv. This paper describes the studies that have been undertaken and their context, discusses some problems that arise and summarizes the present position.

CONCLUSIONS

Many such studies have been undertaken, but most were too small to have a realistic chance of detecting the small effects expected from such low doses, based on risk projections from higher exposures. Case-control or cohort studies are to be preferred methodologically to ecological studies but can be prone to problems of registration/participation bias. Interview-based studies of the requisite size would be prohibitively expensive and would undoubtedly also run into problems of participation bias. Register-based studies can be very large and are free of participation bias. However, they need to estimate the radiation exposure of study subjects using models rather than individual measurements in the homes of those concerned. At present, no firm conclusions can be drawn from the studies that have been published to date. Further data and perhaps pooled studies offer a way forward.

Methodological Considerations for Epidemiological Studies of Air Pollution and the SARS and COVID-19 Coronavirus Outbreaks

BACKGROUND

Studies have reported that ambient air pollution is associated with an increased risk of developing or dying from coronavirus-2 (COVID-19). Methodological approaches to investigate the health impacts of air pollution on epidemics should differ from those used for chronic diseases, but the methods used in these studies have not been appraised critically.

OBJECTIVES

Our study aimed to identify and critique the methodological approaches of studies of air pollution on infections and mortality due to COVID-19 and to identify and critique the methodological approaches of similar studies concerning severe acute respiratory syndrome (SARS).

METHODS

Published and unpublished papers of associations between air pollution and developing or dying from COVID-19 or SARS that were reported as of 10 May 2020 were identified through electronic databases, internet searches, and other sources.

RESULTS

All six COVID-19 studies and two of three SARS studies reported positive associations. Two were time series studies that estimated associations between daily changes in air pollution, one was a cohort that assessed associations between air pollution and the secondary spread of SARS, and six were ecological studies that used area-wide exposures and outcomes. Common shortcomings included possible cross-level bias in ecological studies, underreporting of health outcomes, using grouped data, the lack of highly spatially resolved air pollution measures, inadequate control for confounding and evaluation of effect modification, not accounting for regional variations in the timing of outbreaks' temporal changes in at-risk populations, and not accounting for nonindependence of outcomes.

DISCUSSION

Studies of air pollution and novel coronaviruses have relied mainly on ecological measures of exposures and outcomes and are susceptible to important sources of bias. Although longitudinal studies with individual-level data may be imperfect, they are needed to adequately address this topic. The complexities involved in these types of studies underscore the need for careful design and for peer review. https://doi.org/10.1289/EHP7411.

The downfall of the linear non-threshold model

The linear non-threshold model (LNTM) is a theoretical dose-response function as a result of extrapolating the late effects of high-dose exposure to ionizing radiation to the low-dose range, but there is great uncertainty about its validity. The acceptance of LNTM as the dominant probabilistic model have survived to the present day and it is actually the cornerstone of current radiation protection policies. In the last decades, advances in molecular and evolutive biology, cancer immunology, and many epidemiological and animal studies have cast serious doubts about the reliability of the NLTM, as well as suggesting alternative models, like the hormetic theory. Considering the given evidences, a discussion between the involved scientific societies and the regulatory commissions is promtly required in order to to reach a redefiniton of theradiation protection basis, as it would be specially crucial in the medical field.

Multiple Stressor Effects of Radon and Phthalates in Children: Background Information and Future Research

The present paper reviews available background information for studying multiple stressor effects of radon (222Rn) and phthalates in children and provides insights on future directions. In realistic situations, living organisms are collectively subjected to many environmental stressors, with the resultant effects being referred to as multiple stressor effects. Radon is a naturally occurring radioactive gas that can lead to lung cancers. On the other hand, phthalates are semi-volatile organic compounds widely applied as plasticizers to provide flexibility to plastic in consumer products. Links of phthalates to various health effects have been reported, including allergy and asthma. In the present review, the focus on indoor contaminants was due to their higher concentrations and to the higher indoor occupancy factor, while the focus on the pediatric population was due to their inherent sensitivity and their spending more time close to the floor. Two main future directions in studying multiple stressor effects of radon and phthalates in children were proposed. The first one was on computational modeling and micro-dosimetric studies, and the second one was on biological studies. In particular, dose-response relationship and effect-specific models for combined exposures to radon and phthalates would be necessary. The ideas and methodology behind such proposed research work are also applicable to studies on multiple stressor effects of collective exposures to other significant airborne contaminants, and to population groups other than children.

Are Restrictive Medical Radiation Imaging Campaigns Misguided? It Seems So: A Case Example of the American Chiropractic Association's Adoption of "Choosing Wisely"

Since the 1980s, increased utilization of medical radiology, primarily computed tomography, has doubled medically sourced radiation exposures. Ensuing fear-mongering media headlines of iatrogenic cancers from these essential medical diagnostic tools has led the public and medical professionals alike to display escalating radiophobia. Problematically, several campaigns including Image Gently, Image Wisely, and facets of Choosing Wisely propagate fears of all medical radiation, which is necessary for the delivery of effective and efficient health care. Since there are no sound data supporting the alleged risks from low-dose radiation and since there is abundant evidence of health benefits from low-doses, these imaging campaigns seem misguided. Further, thresholds for cancer are 100 to 1000-fold greater than X-rays, which are within the realm of natural background radiation where no harm has ever been validated. Here, we focus on radiographic imaging for use in spinal rehabilitation by manual therapists, chiropractors, and physiotherapists as spinal X-rays represent the lowest levels of radiation imaging and are critical in the diagnosis and management of spine-related disorders. Using a case example of a chiropractic association adopting "Choosing Wisely," we argue that these campaigns only fuel the pervasive radiophobia and continue to constrain medical professionals, attempting to deliver quality care to patients.

MODELLING THE INDOOR RADIATION DOSES: A REVIEW AND PERSPECTIVE

Theoretical models to calculate the indoor gamma and radon doses are reviewed, refined and applied. The model for gamma doses is built based on the relative effects of the different room elements that control the amount of radiation. The relative doses are calculated by the MCNP5 simulation software. The gamma sources are due to the natural radiation from the 238U series, 232Th series and the radionuclide 40K. An application of the model that involves all the considered elements is demonstrated. The elements are the thickness of the walls, the density of the building material, the dimensions of the room, the existence of other rooms surrounding the room under study, the split of some walls into two portions, the existence of internal thin partial walls inside the room, the existence of windows and doors, and the incompleteness of the secular equilibrium in the 238U decay series due to radon release from the building materials. The model for radon doses is built based on Fick's laws. The radon surface exhalation rate from a wall and that from a building material sample are calculated from a one-dimension and three-dimension diffusion description by Fick's second law, respectively. The two rates are compared, and the radon indoor concentration and inhalation doses are formulated.

Low-level radon exposure and lung cancer mortality

BACKGROUND

It is agreed that high level radon exposure is harmful to humans. However, some published literature suggests that low levels of radon show no adverse effects or may even be protective. Claims made using traditional methods of analysis on observational data often fail to replicate. Here, we use a simple, alternative data-analytic strategy for examining effects of low-level indoor radon exposure on lung cancer mortality. One objective will be to demonstrate that local population characteristics can alter expected effects.

METHODS

Observational data on indoor radon exposure levels and lung cancer mortality for 2881 U.S. counties were obtained from federal and state governmental agencies. A new "statistical thinking" step-by-step analysis strategy called Local Control (LC) allows us to perform analyses of observational data that are more objective and "fair" than regression-like methods. LC analytical strategy makes as few and as realistic assumptions as possible. As a result, key LC inferences are nonparametric, and estimates of potentially heterogeneous treatment effect-sizes are robust.

RESULTS

Our LC analyses suggest that lung cancer mortality usually tends to decrease as background radon exposure increases. Local rank correlation (LRC) effect-sizes are shown to be predictable from confounding local characteristics like percentage of residents over 65, percentage of residents who currently smoke and percentage of obese residents.

CONCLUSIONS

At low indoor radon exposure levels, reverse (negative) LRCs between radon exposure level and lung cancer mortality predominate. The strengths of these associations vary with local demographics.

Modeling Cell Reactions to Ionizing Radiation: From a Lesion to a Cancer

This article focuses on the analytic modeling of responses of cells in the body to ionizing radiation. The related mechanisms are consecutively taken into account and discussed. A model of the dose- and time-dependent adaptive response is considered for 2 exposure categories: acute and protracted. In case of the latter exposure, we demonstrate that the response plateaus are expected under the modelling assumptions made. The expected total number of cancer cells as a function of time turns out to be perfectly described by the Gompertz function. The transition from a collection of cancer cells into a tumor is discussed at length. Special emphasis is put on the fact that characterizing the growth of a tumor (ie, the increasing mass and volume), the use of differential equations cannot properly capture the key dynamics-formation of the tumor must exhibit properties of the phase transition, including self-organization and even self-organized criticality. As an example, a manageable percolation-type phase transition approach is used to address this problem. Nevertheless, general theory of tumor emergence is difficult to work out mathematically because experimental observations are limited to the relatively large tumors. Hence, determination of the conditions around the critical point is uncertain.

Meta-analysis of case-control studies on the relationship between lung cancer and indoor radon exposure

Indoor exposure to natural radon is a factor that influences lung cancer risk worldwide. The present study includes a meta-analysis of epidemiological data on the relationship between lung cancer and indoor radon. Altogether, 31 case-control studies with 20,703 cases, 34,518 controls and 140 individual odds ratio (OR) estimates are included in the meta-analysis. Weighted median OR was calculated for five radon intervals. The following parameters were used for the weighting: standard error of OR, duration of radon concentration measurement, and relative number of controls in reference intervals. The dependence of the weighted median OR on the radon concentration was estimated applying linear non-threshold and threshold models. The results obtained suggest a significant linear no-threshold exposure-effect relationship for radon concentrations above 100 Bq/m³, with a slope of 0.14 (95% confidence interval 0.08-0.21) per 100 Bq/m³.

Epidemiologic Studies Cannot Reveal the True Shape of the Dose-Response Relationship for Radon-Induced Lung Cancer

A long-standing controversy is the correct shape of the dose-response relationship for lung cancer induction by inhaled radon (eg, residential radon) at low levels. A probabilistic approach is used in this commentary to show that cohort and case-control epidemiologic studies cannot reveal the true shape of the dose-response relationship for radon-induced lung cancer. Using the indicated approach, it is found that while the dose response for radon-induced lung cancer is expected to be threshold-increasing, the dose-response curve for the cancer incidence when cancers caused by smoking and other carcinogens are included is expected to be threshold-decreasing (ie, threshold-hormetic), as low-level radon can protect from cancer induction by other carcinogens via stimulating the body's natural defenses against cancer. These defenses include DNA damage repair, removal of aberrant cells via apoptosis, suppression of cancer promoting inflammation, and anticancer immunity.

Adverse Childhood Experiences and the Presence of Cancer Risk Factors in Adulthood: A Scoping Review of the Literature From 2005 to 2015

Exposure to Adverse Childhood Experiences (ACEs) is associated with a host of harmful outcomes, including increased risk for cancer. A scoping review was conducted to gain a better understanding of how ACEs have been studied in association with risk factors for cancer. This review includes 155 quantitative, peer-reviewed articles published between 2005 and 2015 that examined associations between ACEs and modifiable cancer risk factors, including alcohol, environmental carcinogens, chronic inflammation, sex hormones, immunosuppression, infectious agents, obesity, radiation, ultraviolet (UV) radiation, and tobacco, among U.S. adults. This review highlights the growing body of research connecting ACEs to cancer risk factors, particularly alcohol, obesity, and tobacco. Fewer studies investigated the links between ACEs and chronic inflammation or infectious agents. No included publications investigated associations between ACEs and environmental carcinogens, hormones, immunosuppression, radiation, or ultraviolet radiation. Mitigating the impact of ACEs may provide innovative ways to effect comprehensive, upstream cancer prevention.

Are We Approaching the End of the Linear No-Threshold Era?

The linear no-threshold (LNT) model for radiation-induced cancer was adopted by national and international advisory bodies in the 1950s and has guided radiation protection policies worldwide since then. The resulting strict regulations have increased the compliance costs for the various uses of radiation, including nuclear medicine. The concerns about low levels of radiation due to the absence of a threshold have also resulted in adverse consequences. Justification of the LNT model was based on the concept that low levels of radiation increase mutations and that increased mutations imply increased cancers. This concept may not be valid. Low-dose radiation boosts defenses such as antioxidants and DNA repair enzymes. The boosted defenses would reduce the endogenous DNA damage that would have occurred in the subsequent period, and so the result would be reduced DNA damage and mutations. Whereas mutations are necessary for causing cancer, they are not sufficient since the immune system eliminates cancer cells or keeps them under control. The immune system plays an extremely important role in preventing cancer, as indicated by the substantially increased cancer risk in immune-suppressed patients. Hence, since low-dose radiation enhances the immune system, it would reduce cancers, resulting in a phenomenon known as radiation hormesis. There is considerable evidence for radiation hormesis and against the LNT model, including studies of atomic bomb survivors, background radiation, environmental radiation, cancer patients, medical radiation, and occupational exposures. Though Commentary 27 published by the National Council on Radiation Protection and Measurements concluded that recent epidemiologic studies broadly support the LNT model, a critical examination of the studies has shown that they do not. Another deficiency of Commentary 27 is that it did not consider the vast available evidence for radiation hormesis. Other advisory body reports that have supported the LNT model have similar deficiencies. Advisory bodies are urged to critically evaluate the evidence supporting both sides and arrive at an objective conclusion on the validity of the LNT model. Considering the strength of the evidence against the LNT model and the weakness of the evidence for it, the present analysis indicates that advisory bodies would be compelled to reject the LNT model. Hence, we may be approaching the end of the LNT model era.

Overview of Biological, Epidemiological, and Clinical Evidence of Radiation Hormesis

The effects of low-dose radiation are being increasingly investigated in biological, epidemiological, and clinical studies. Many recent studies have indicated the beneficial effects of low doses of radiation, whereas some studies have suggested harmful effects even at low doses. This review article introduces various studies reporting both the beneficial and harmful effects of low-dose radiation, with a critique on the extent to which respective studies are reliable. Epidemiological studies are inherently associated with large biases, and it should be evaluated whether the observed differences are due to radiation or other confounding factors. On the other hand, well-controlled laboratory studies may be more appropriate to evaluate the effects of low-dose radiation. Since the number of such laboratory studies is steadily increasing, it will be concluded in the near future whether low-dose radiation is harmful or beneficial and whether the linear-no-threshold (LNT) theory is appropriate. Many recent biological studies have suggested the induction of biopositive responses such as increases in immunity and antioxidants by low-dose radiation. Based on recent as well as classical studies, the LNT theory may be out of date, and low-dose radiation may have beneficial effects depending on the conditions; otherwise, it may have no effects.

It Is Time to Move Beyond the Linear No-Threshold Theory for Low-Dose Radiation Protection

The US Environmental Protection Agency (USEPA) is the primary federal agency responsible for promulgating regulations and policies to protect people and the environment from ionizing radiation. Currently, the USEPA uses the linear no-threshold (LNT) model to estimate cancer risks and determine cleanup levels in radiologically contaminated environments. The LNT model implies that there is no safe dose of ionizing radiation; however, adverse effects from low dose, low-dose rate (LDDR) exposures are not detectable. This article (1) provides the scientific basis for discontinuing use of the LNT model in LDDR radiation environments, (2) shows that there is no scientific consensus for using the LNT model, (3) identifies USEPA reliance on outdated scientific information, and (4) identifies regulatory reliance on incomplete evaluations of recent data contradicting the LNT. It is the time to reconsider the use of the LNT model in LDDR radiation environments. Incorporating the latest science into the regulatory process for risk assessment will (1) ensure science remains the foundation for decision making, (2) reduce unnecessary burdens of costly cleanups, (3) educate the public on the real effects of LDDR radiation exposures, and (4) harmonize government policies with the rest of the radiation scientific community.

Health Impacts of Low-Dose Ionizing Radiation: Current Scientific Debates and Regulatory Issues

Health impacts of low-dose ionizing radiation are significant in important fields such as X-ray imaging, radiation therapy, nuclear power, and others. However, all existing and potential applications are currently challenged by public concerns and regulatory restrictions. We aimed to assess the validity of the linear no-threshold (LNT) model of radiation damage, which is the basis of current regulation, and to assess the justification for this regulation. We have conducted an extensive search in PubMed. Special attention has been given to papers cited in comprehensive reviews of the United States (2006) and French (2005) Academies of Sciences and in the United Nations Scientific Committee on Atomic Radiation 2016 report. Epidemiological data provide essentially no evidence for detrimental health effects below 100 mSv, and several studies suggest beneficial (hormetic) effects. Equally significant, many studies with in vitro and in animal models demonstrate that several mechanisms initiated by low-dose radiation have beneficial effects. Overall, although probably not yet proven to be untrue, LNT has certainly not been proven to be true. At this point, taking into account the high price tag (in both economic and human terms) borne by the LNT-inspired regulation, there is little doubt that the present regulatory burden should be reduced.

Meta-analysis of thirty-two case-control and two ecological radon studies of lung cancer

A re-analysis has been carried out of thirty-two case-control and two ecological studies concerning the influence of radon, a radioactive gas, on the risk of lung cancer. Three mathematically simplest dose-response relationships (models) were tested: constant (zero health effect), linear, and parabolic (linear-quadratic). Health effect end-points reported in the analysed studies are odds ratios or relative risk ratios, related either to morbidity or mortality. In our preliminary analysis, we show that the results of dose-response fitting are qualitatively (within uncertainties, given as error bars) the same, whichever of these health effect end-points are applied. Therefore, we deemed it reasonable to aggregate all response data into the so-called Relative Health Factor and jointly analysed such mixed data, to obtain better statistical power. In the second part of our analysis, robust Bayesian and classical methods of analysis were applied to this combined dataset. In this part of our analysis, we selected different subranges of radon concentrations. In view of substantial differences between the methodology used by the authors of case-control and ecological studies, the mathematical relationships (models) were applied mainly to the thirty-two case-control studies. The degree to which the two ecological studies, analysed separately, affect the overall results when combined with the thirty-two case-control studies, has also been evaluated. In all, as a result of our meta-analysis of the combined cohort, we conclude that the analysed data concerning radon concentrations below ~1000 Bq/m3 (~20 mSv/year of effective dose to the whole body) do not support the thesis that radon may be a cause of any statistically significant increase in lung cancer incidence.

Radon, smoking and HPV as lung cancer risk factors in ecological studies

OBJECTIVES

Cohen's ecological analyses revealed negative correlation between the lung cancer mortality and average indoor radon concentration in the US counties, that contradicts to linear non-threshold (LNT) model and is inconsistent with results of case-control studies. The aim of this study was to analyze dependence between radon exposure and lung cancer mortality rate taking into account more complete data on smoking and new findings on association of the lung cancer with human papillomavirus (HPV) infection.

MATERIALS AND METHODS

Information on the cancer rates in the US counties and Russian oblasts, smoking prevalence and indoor radon concentration was found in literature. The cervix cancer incidence rate was used as surrogate of the HPV infection prevalence. The analysis included calculation of the coefficients of linear dependence between radon exposure and lung cancer mortality rate with adjustment to smoking and HPV infection prevalence.

RESULTS

After adjustment for the most relevant data on smoking and HPV infection, correlation between the lung cancer mortality and indoor radon was found to be consistent with results of the case control studies.

CONCLUSIONS

Analysis of geographically aggregated data on the lung cancer mortality and radon concentration in dwellings with adjustment to the significant risk factors confirms both the linear non-threshold dependency and results obtained in studies with individual accounting for the smoking and radon.

Cancer immunotherapy: how low-level ionizing radiation can play a key role

The cancer immunoediting hypothesis assumes that the immune system guards the host against the incipient cancer, but also "edits" the immunogenicity of surviving neoplastic cells and supports remodeling of tumor microenvironment towards an immunosuppressive and pro-neoplastic state. Local irradiation of tumors during standard radiotherapy, by killing neoplastic cells and generating inflammation, stimulates anti-cancer immunity and/or partially reverses cancer-promoting immunosuppression. These effects are induced by moderate (0.1-2.0 Gy) or high (>2 Gy) doses of ionizing radiation which can also harm normal tissues, impede immune functions, and increase the risk of secondary neoplasms. In contrast, such complications do not occur with exposures to low doses (≤0.1 Gy for acute irradiation or ≤0.1 mGy/min dose rate for chronic exposures) of low-LET ionizing radiation. Furthermore, considerable evidence indicates that such low-level radiation (LLR) exposures retard the development of neoplasms in humans and experimental animals. Here, we review immunosuppressive mechanisms induced by growing tumors as well as immunomodulatory effects of LLR evidently or likely associated with cancer-inhibiting outcomes of such exposures. We also offer suggestions how LLR may restore and/or stimulate effective anti-tumor immunity during the more advanced stages of carcinogenesis. We postulate that, based on epidemiological and experimental data amassed over the last few decades, whole- or half-body irradiations with LLR should be systematically examined for its potential to be a viable immunotherapeutic treatment option for patients with systemic cancer.

A preliminary study for conducting a rational assessment of radon exposure levels

The aim of this study was to determine the factors that go into a highly reliable estimate of radon exposure levels for use in setting up the case-control study. To this end, the present study conducted a multi-faceted investigation of the distribution of radon concentrations in the bedrooms and living rooms of 400 households in the target areas during the winter months from December 2014 to February 2015. We determined that taking the mean value of the radon concentration levels detected in the bedroom and living room as the representative value of residential concentration is appropriate, given the usability of previous research data and the difference in the concentration levels between the two. In terms of detector placement, we found that detectors should not inconvenience residents or be affected by an air current. Further, we found that housing type should distinguish between regular housing (single-detached, row, and multiplex housing) and apartments but that the building type was not a key factor in the assessment of radon exposure levels. Houses should be classified into those constructed with soil (red clay) and those with constructed with general building materials for the assessment of radon exposure levels.

Radon Release and Its Simulated Effect on Radiation Doses

One of the main factors that affect the uncertainty in calculating the gamma-radiation absorbed dose rate inside a room is the variation in the degree of secular equilibrium of the considered radioactive series. A component of this factor, considered in this paper, is the release of radon (Rn) from building materials to the living space of the room. This release takes place through different steps. These steps are represented and mathematically formulated. The diffusion of radon inside the material is described by Fick's second law. Some of the factors affecting the radon release rate (e.g. covering walls, moisture, structure of the building materials, etc.) are discussed. This scheme is used to study the impact of radon release on the gamma-radiation absorbed dose rate inside a room. The investigation is carried out by exploiting the MCNP simulation software. Different building materials are considered with different radon release rates. Special care is given to Rn due to its relatively higher half-life and higher indoor concentration than the other radon isotopes. The results of the presented model show that the radon release is of a significant impact in some building materials.

Residential radon and COPD. An ecological study in Galicia, Spain

PURPOSE

Radon is a human lung carcinogen but it might be linked with other respiratory diseases. We aimed to assess the relationship between residential radon exposure and COPD (chronic obstructive pulmonary disease) prevalence and hospital admissions at a municipal level.

MATERIALS AND METHODS

We designed an ecological study where we included those municipalities with at least three radon measurements. Using mixed Poisson regression models, we calculated the relative risk (RR) for COPD for each 100 Bq/m³ of increase in radon concentration and also the relative risk for COPD using a cut-off point of 50 Bq/m³. We did not have individual data on cigarette smoking and therefore we used a proxy (bladder cancer standardized mortality rate) that has proved to account for tobacco consumption. We performed separate analyses for sex and also sensitivity analysis considering age and rurality.

RESULTS

A total of 3040 radon measurements and 49,393 COPD cases were included. The relative risk for COPD prevalence was 0.95 (95% CI: 0.92-0.97) while for hospital admissions the RR was 1.04 (95% CI: 1.00-1.10) for each 100 Bq/m³. Relative risks were higher for women compared to men. Using a categorical analysis with a cut-off point of 50 Bq/m³, the RR for COPD prevalence was 1.06 (95% CI: 1.02-1.10) and for hospital admissions it was 1.08 (95% CI: 1.00-1.17) for women living in municipalities with more than 50 Bq/m³. All risks were also higher for women. No relevant differences were observed for age, rurality or other categories for radon exposure.

CONCLUSION

While the influence of radon on COPD prevalence is unclear depending on the approach used, it seems that residential radon might increase the risk of hospital admissions in COPD patients. Women have a higher risk than men in all situations. Since this is an ecological study, results should be interpreted cautiously.

Variation with socioeconomic status of indoor radon levels in Great Britain: The less affluent have less radon

We demonstrate a strong correlation between domestic radon levels and socio-economic status (SES) in Great Britain, so that radon levels in homes of people with lower SES are, on average, only about two thirds of those of the more affluent. This trend is apparent using small area measures of SES and also using individual social classes. The reasons for these differences are not known with certainty, but may be connected with greater underpressure in warmer and better-sealed dwellings. There is also a variation of indoor radon levels with the design of the house (detached, terraced, etc.). In part this is probably an effect of SES, but it appears to have other causes as well. Data from other countries are also reviewed, and broadly similar effects seen in the United States for SES, and in other European countries for detached vs other types of housing. Because of correlations with smoking, this tendency for the lower SES groups to experience lower radon levels may underlie the negative association between radon levels and lung cancer rates in a well-known ecological study based on US Counties. Those conducting epidemiological studies of radon should be alert for this effect and control adequately for SES.

Look Different: Effect of Radiation Hormesis on the Survival Rate of Immunosuppressed Mice

BACKGROUND

Hormesis is defined as the bio-positive response of something which is bio-negative in high doses. In the present study, the effect of radiation hormesis was evaluated on the survival rate of immunosuppressed BALB/c mice by Cyclosporine A.

MATERIAL AND METHODS

We used 75 consanguine, male, BALB/c mice in this experiment. The first group received Technetium-99m and the second group was placed on a sample radioactive soil of Ramsar region (800Bq) for 20 days. The third group was exposed to X-rays and the fourth group was placed on the radioactive soil and then injected Technetium-99m. The last group was the sham irradiated control group. Finally, 30mg Cyclosporine A as the immunosuppressive agent was orally administered to all mice 48 hours after receiving X-rays and Technetium-99m. The mean survival rate of mice in each group was estimated during time.

RESULTS

A log rank test was run to determine if there were differences in the survival distribution for different groups and related treatments. According to the results, the survival rate of all pre-irradiated groups was more than the sham irradiated control group (p < .05). The highest survival time was related to the mice which were placed on the radioactive soil of Ramsar region for 20 days and then injected Technetium-99m.

CONCLUSION

This study confirmed the presence of hormetic models and the enhancement of survival rate in immunosuppressed BALB/c mice as a consequence of low-dose irradiation. It is also revealed the positive synergetic radioadaptive response on survival rate of immunosuppressed animals.

Establishing a radon management program for public university facilities

Purpose

The purpose of this paper is to elucidate best approaches for facility radon management in a resource-limited environment such as a public university. Radon exposures are believed to be a risk factor for lung cancer. However, the degree to which typical indoor radon levels within settings such as the university campus contribute to lung cancer risk is controversial. The authors sought to develop a risk-balancing approach to safe and cost-efficient facility radon management.

Design/methodology/approach

The authors collected pilot monitoring data to determine radon activity levels at a large public university within a projected high-radon region of the southeastern USA, then reviewed scientific literature, trade literature and regulatory guidance to determine radon risk knowledge and best practices for mitigation. From this body of data and information, the authors determined the safest and most resource-effective means for campus radon management.

Findings

The developed program for comprehensive radon management included guidance on building selection for most effective use of monitoring, tiered response and mitigation strategies based on radon activity levels and faculty, staff and student education.

Research Limitations/implications

The radon management strategies might not be generalizable to facilities with usage patterns that differ from a public university, and should be extrapolated with caution.

Practical Implications

This paper shows how building managers can address indoor radon in a manner that maximizes both safety and cost-efficiency.

Originality/value

This paper fulfills a need for evidence-based and prudent approaches to radon management for campuses with mixed residential, educational and occupational contexts and limited resources.

Epidemiology Without Biology: False Paradigms, Unfounded Assumptions, and Specious Statistics in Radiation Science (with Commentaries by Inge Schmitz-Feuerhake and Christopher Busby and a Reply by the Authors)

Radiation science is dominated by a paradigm based on an assumption without empirical foundation. Known as the linear no-threshold (LNT) hypothesis, it holds that all ionizing radiation is harmful no matter how low the dose or dose rate. Epidemiological studies that claim to confirm LNT either neglect experimental and/or observational discoveries at the cellular, tissue, and organismal levels, or mention them only to distort or dismiss them. The appearance of validity in these studies rests on circular reasoning, cherry picking, faulty experimental design, and/or misleading inferences from weak statistical evidence. In contrast, studies based on biological discoveries demonstrate the reality of hormesis: the stimulation of biological responses that defend the organism against damage from environmental agents. Normal metabolic processes are far more damaging than all but the most extreme exposures to radiation. However, evolution has provided all extant plants and animals with defenses that repair such damage or remove the damaged cells, conferring on the organism even greater ability to defend against subsequent damage. Editors of medical journals now admit that perhaps half of the scientific literature may be untrue. Radiation science falls into that category. Belief in LNT informs the practice of radiology, radiation regulatory policies, and popular culture through the media. The result is mass radiophobia and harmful outcomes, including forced relocations of populations near nuclear power plant accidents, reluctance to avail oneself of needed medical imaging studies, and aversion to nuclear energy-all unwarranted and all harmful to millions of people.

[Tremendous Human, Social, and Economic Losses Caused by Obstinate Application of the Failed Linear No-threshold Model]

The linear no-threshold model (LNT) was recommended in 1956, with abandonment of the traditional threshold dose-response for genetic risk assessment. Adoption of LNT by the International Commission on Radiological Protection (ICRP) became the standard for radiation regulation worldwide. The ICRP recommends a dose limit of 1 mSv/year for the public, which is too low and which terrorizes innocent people. Indeed, LNT arose mainly from the lifespan survivor study (LSS) of atomic bomb survivors. The LSS, which asserts linear dose-response and no threshold, is challenged mainly on three points. 1) Radiation doses were underestimated by half because of disregard for major residual radiation, resulting in cancer risk overestimation. 2) The dose and dose-rate effectiveness factor (DDREF) of 2 is used, but the actual DDREF is estimated as 16, resulting in cancer risk overestimation by several times. 3) Adaptive response (hormesis) is observed in leukemia and solid cancer cases, consistently contradicting the linearity of LNT. Drastic reduction of cancer risk moves the dose-response curve close to the control line, allowing the setting of a threshold. Living organisms have been evolving for 3.8 billion years under radiation exposure, naturally acquiring various defense mechanisms such as DNA repair mechanisms, apoptosis, and immune response. The failure of LNT lies in the neglect of carcinogenesis and these biological mechanisms. Obstinate application of LNT continues to cause tremendous human, social, and economic losses. The 60-year-old LNT must be rejected to establish a new scientific knowledge-based system.

Hormetic effect induced by depleted uranium in zebrafish embryos

The present work studied the hormetic effect induced by uranium (U) in embryos of zebrafish (Danio rerio) using apoptosis as the biological endpoint. Hormetic effect is characterized by biphasic dose-response relationships showing a low-dose stimulation and a high-dose inhibition. Embryos were dechorionated at 4h post fertilization (hpf), and were then exposed to 10 or 100μg/l depleted uranium (DU) in uranyl acetate solutions from 5 to 6 hpf. For exposures to 10μg/l DU, the amounts of apoptotic signals in the embryos were significantly increased at 20 hpf but were significantly decreased at 24 hpf, which demonstrated the presence of U-induced hormesis. For exposures to 100μg/l DU, the amounts of apoptotic signals in the embryos were significantly increased at 20, 24 and 30 hpf. Hormetic effect was not shown but its occurrence between 30 and 48 hpf could not be ruled out. In conclusion, hormetic effect could be induced in zebrafish embryos in a concentration- and time-dependent manner.

A message to Fukushima: nothing to fear but fear itself

INTRODUCTION

The linear no-threshold model (LNT) has been the basis for radiation protection policies worldwide for 60 years. LNT was fabricated without correct data. The lifespan study of Atomic bomb survivors (LSS) has provided fundamental data to support the NLT. In LSS, exposure doses were underestimated and cancer risk was overestimated; LSS data do not support LNT anymore. In light of these findings, radiation levels and cancer risk in Fukushima are reexamined.

RESULTS

Soon after the Fukushima accident, the International Commission on Radiological Protection issued an emergency recommendation that national authorities set reference highest levels in the band of 20-100 mSv and, when the radiation source is under control, reference levels are in the band of 1-20 mSv/y. The Japanese government set the limit dose as low as 1 mSv for the public and stirred up radiophobia, which continues to cause tremendous human, social, and economic losses. Estimated doses in three areas of Fukushima were 0.6-2.3 mSv/y in Tamura City, 1.1-5.5 mSv/y in Kawauchi Village, and 3.8-17 mSv/y in Iitate Village. Since even after acute irradiation, no significant differences are found below 200 mSv for leukemia and below 100 mSv for solid cancers. These data indicate that cancer risk is negligible in Fukushima. Moreover, beneficial effects (lessened cancer incidence) were observed at 400-600 mSv in LSS. Living organisms, which have established efficient defense mechanisms against radiation through 3.8 billion years of evolutionary history, can tolerate 1000 mSv/y if radiation dose rates are low. In fact, people have lived for generations without adverse health effects in high background radiation areas such as Kelara (35 mSv/y), India, and Ramsar (260 mSv/y), Iran. Low dose radiation itself is harmless, but fear of radiation is vitally harmful.

CONCLUSIONS

When people return to the evacuation zones in Fukushima now and in the future, they will be exposed to such low radiation doses as to cause no physical effects. The most threatening public health issue is the adverse effect on mental health caused by undue fear of radiation.

Time to Reject the Linear-No Threshold Hypothesis and Accept Thresholds and Hormesis: A Petition to the U.S. Nuclear Regulatory Commission

On February 9, 2015, I submitted a petition to the U.S. Nuclear Regulatory Commission (NRC) to reject the linear-no threshold (LNT) hypothesis and ALARA as the bases for radiation safety regulation in the United States, using instead threshold and hormesis evidence. In this article, I will briefly review the history of LNT and its use by regulators, the lack of evidence supporting LNT, and the large body of evidence supporting thresholds and hormesis. Physician acceptance of cancer risk from low dose radiation based upon federal regulatory claims is unfortunate and needs to be reevaluated. This is dangerous to patients and impedes good medical care. A link to my petition is available: http://radiationeffects.org/wp-content/uploads/2015/03/Hormesis-Petition-to-NRC-02-09-15.pdf, and support by individual physicians once the public comment period begins would be extremely important.