Observations on the Chernobyl Disaster and LNT

Thyroid Cancer in Regions Most Contaminated after the Chernobyl Disaster

Exposure to ionizing radiation, especially during childhood, is a well-established risk factor for thyroid cancer. Following the 1986 Chernobyl nuclear power plant accident the total number of cases of thyroid cancer registered between 1991 and 2015 in males and females who were less than 18 years old exceeded 19,000 (in Belarus and Ukraine, and in the most contaminated oblasts of the Russian Federation). However, as indicated by the United Nations Scientific Committee on the Effects of Atomic Radiation the fraction of the incidence of thyroid cancer attributable to radiation exposure among the non-evacuated residents of the contaminated regions of Belarus, Ukraine and Russia is of the order of 0.25. Apparently, the increased registration of thyroid neoplasms in the parts of these countries is a classical 'screening effect', i.e., massive diagnostic examinations of the risk-aware populations performed with modern eqipment resulting in detection of many occult neoplasms (incidentalomas). Moreover, one type of thyroid cancer previously called 'encapsulated follicular variant of papillary thyroid carcinoma' is non-invasive and instead of 'carcinoma' should now be recognized as 'noninvasive follicular thyroid neoplasm with papillary-like nuclear features.' Other potential causes of overdiagnosing of thyroid tumors include increase of the spontaneous incidence rate of this disease with age, iodine deficiency among children from Belarus, Russia and Ukraine, and/or consumption by these children of drinking water containing high levels of nitrates that likely coincides with the carcinogenic effect of radiation on the thyroid gland.

Pestilence, Plague and Pandemics: A Troubled History

Humankind has lived with the danger of endemic, epidemic and pandemic disease for thousands of years. The effects of these outbreaks have often devastated human populations. Sixteen pandemic events causing an estimated 147 million deaths have occurred since the eighth century, The Black Death and the influenza pandemic of 1918-1920 probably having the greatest impact. Animal populations, both wild and domestic, have similarly suffered devastating outbreaks of disease which, on occasions, have translated into serious effects on human health. The deliberate or accidental introduction of animals into virgin areas has given rise to unforeseen disease events occasionally leading to extinction. Similarly, human intent or negligence and the vagaries of nature itself has resulted in ill health and loss of life. This paper describes the history of pandemics, epidemics and disasters, and the attempts to bring them under control.

Unlaid Eggs: Ovarian Damage after Low-Dose Radiation

The total body irradiation of lymphomas and co-irradiation in the treatment of adjacent solid tumors can lead to a reduced ovarian function, premature ovarian insufficiency, and menopause. A small number of studies has assessed the radiation-induced damage of primordial follicles in animal models and humans. Studies are emerging that evaluate radiation-induced damage to the surrounding ovarian tissue including stromal and immune cells. We reviewed basic laboratory work to assess the current state of knowledge and to establish an experimental setting for further studies in animals and humans. The experimental approaches were mostly performed using mouse models. Most studies relied on single doses as high as 1 Gy, which is considered to cause severe damage to the ovary. Changes in the ovarian reserve were related to the primordial follicle count, providing reproducible evidence that radiation with 1 Gy leads to a significant depletion. Radiation with 0.1 Gy mostly did not show an effect on the primordial follicles. Fewer data exist on the effects of radiation on the ovarian microenvironment including theca-interstitial, immune, endothelial, and smooth muscle cells. We concluded that a mouse model would provide the most reliable model to study the effects of low-dose radiation. Furthermore, both immunohistochemistry and fluorescence-activated cell sorting (FACS) analyses were valuable to analyze not only the germ cells but also the ovarian microenvironment.

Assessment of probable scenarios of radiological emergency and their consequences

PURPOSE

Despite the vast amount of literature on radiological emergencies, to the best of our knowledge there is no systematic review of probable scenarios and their consequences. This work aimed for compiling such review.

MATERIALS AND METHODS

The authors comprised a Red Team - that is, simulated best efforts to inflict maximal damage to the society by various means of radiological attacks. Nuclear warfare including improvised nuclear devices is beyond the scope of this work.

RESULTS

The direct radiogenic health consequences of any conceivable radiological accident, natural or man-made, are much less dangerous than those which are usually perceived. In each scenario, direct health effects are only a small part of the damage caused by fear and over-reaction; the damage is somewhat independent of the small health effect predicted for most of the scenarios. The reason is that nuclear radiation has become perceptually connected with nuclear apocalypses. This connection has caused the emotional description of radiological emergencies to frequently substitute quantitative considerations. For example, Chernobyl and Fukushima became major humanitarian disasters not because of the radiation itself but because of the over-reaction of both the authorities and the public, that led to the unjustified relocation of hundreds of thousands of people. In Fukushima, the evacuation was not justified at all and in Chernobyl the evacuated zone should have been re-populated after 1 month.

CONCLUSIONS

It is vital to educate decision makers, first responders and the public about the factual extent of possible radiological consequences, as well as about the very real danger of over-reaction. Since the extent of the countermeasures deployed is unavoidably connected, in the eye of the public, with the extent of the danger, we suggest launching educational campaigns that explain the factual extent of the radiation risk, followed by easing regulations and narrowing safety margins. Such measures will probably be the most efficient method of countering radiological terrorism: by depriving any adversary of the most important ability which is to cause an over-reaction.

Slavutych atomograd as the last ideal city of the USSR: Challenges and adaptation mechanisms of resilience

Urban resilience implies the ability of all components of a city system to maintain or restore their functions following unforeseen events, and the ability to adapt to external changes. We apply the concept of resilience and adaptation to Slavutych atomograd following the Chornobyl Nuclear Power Station explosion. Challenges and responses facing the urban management and planning systems are examined. Perceptions of Slavutych's resilience capacity are integrated into research based on a survey of residents. The main challenges faced were lack of targeted financing; insufficient economic diversification and professional employment opportunities; an aging population and outmigration of youth and professionals; physical remoteness from the Kyiv Region; declining quality of municipal infrastructure, poor housing and community services; and slow introduction of market mechanisms. Resilience potential formation is used in effective municipal management practices, stimulating innovations in nuclear/alternative energy, IT, and cultural/artistic events. Urban management and planning systems remain active and are ongoing.

Bounce Forward: Economic Recovery in Post-Disaster Fukushima

After the cascading disaster—earthquake, tsunami, and nuclear accident—in Fukushima on 11 March 2011, the Fukushima region is facing a significant reconstruction challenge. Contamination, economic downturn, depopulation, labor shortage, a damaged reputation, and public distrust must be overcome in order to ensure the future economic recovery of Fukushima. Based on field surveys of the affected areas and unstructured interviews with key informants such as local residents, government officials, and local businesses, this study analyses economic recovery in Fukushima. By exploring four key “pillar” areas of Fukushima’s economic recovery—renewable energy, manufacturing, agriculture, and tourism—this paper gives an overview of how to rebuild industry in the shadow of nuclear pollution. The results show how the economic recovery in Fukushima has required adaptation and innovation by the local people, and the economic downturn has been reversed and subsequently improved. Across the pillar industries, innovative reconstruction projects have been pioneered and led by local residents and businesses. Fukushima’s industrial recovery has been facilitated by the efforts to make the livelihoods of local residents sustainable. It is argued that creative and sustainable economic recovery makes full use of people’s and businesses’ existing resources to transform the disadvantages caused by disasters into opportunities.

Long-Term Consequences of the Chernobyl Radioactive Fallout: An Exploration of the Aggregate Data

Policy Points Policymakers should invest more on researching the long-term health effects of low-ionizing radiation exposure, as we are far from reaching a consensus on a topic that is of enormous importance for public health and safety. Public policies such as those limiting the import of contaminated food from areas hit by a radioactive disaster or those regulating the resident population's access to such areas should follow a precautionary approach. Neoplasm diagnosis and medical care should be designed in order to take into account the possible role of long-term, low-dose radiation exposure. Health care policies should provide effective screening and prevention strategies with a specific focus on the regions that were hit most severely by the Chernobyl nuclear fallout. Health care expenditure should be targeted, taking into account the geographical dispersion of the fallout in order to attenuate its possible effect on neoplasm incidence.

CONTEXT

This study investigates the association between the radioactive ¹³⁷ Cesium fallout originated by the 1986 Chernobyl nuclear accident and dispersed over Western Europe, as a result of a combination of radioactive cloud passage days and rainy days over a 10-day period, and long-term health patterns and related costs. Since the half-life of ¹³⁷ Cesium is 30.17 years, part of the radioactivity in the affected regions is still present today, and it is usually still detected in the food chain, although at lower concentration levels.

METHODS

We match longitudinal data on neoplasm incidence over the time span 2000-2013 in a number of European regions not immediately adjacent to Chernobyl with the randomly distributed levels of cesium deposition after the nuclear disaster in order to assess whether we can detect an association with the long-term health effects on the European population through a random effects model.

FINDINGS

Considering 3 levels of fallout deposition-low, medium, and high-hospital discharges after treatment for neoplasms are, respectively, 0.36, 0.44, and 0.98 discharges over 100 inhabitants higher compared to regions with no fallout, with the population average being around 1.7 hospital discharges by neoplasms over 100 inhabitants. We checked the robustness of our findings to a number of tests including a placebo simulation and different model specifications.

CONCLUSIONS

Radioactive fallout is positively associated with a higher incidence of hospital discharges after treatment for neoplasms almost 30 years after its release, with larger effects in regions where the radioactivity was more intense. Our estimates are comparable to the findings of the largest-scale study on the long-term health effects of continuous low levels of radiation exposure among workers in the nuclear industry and suggest that more research is needed on this topic, given its enormous importance for public health and safety.

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.

Hormesis and radiation safety norms: Comments for an update

Hormesis can be explained by evolutionary adaptation to the current level of a factor present in the natural environment or to some average from the past. This pertains also to ionizing radiation as the natural background has been decreasing during the time of the life existence. DNA damage and repair are normally in a dynamic balance. The conservative nature of the DNA repair suggests that cells may have retained some capability to repair damage from higher radiation levels than that existing today. According to this concept, the harm caused by radioactive contamination would tend to zero with a dose rate tending to a wide range level of the natural radiation background. Existing evidence in favor of hormesis is substantial, experimental data being partly at variance with results of epidemiological studies. Potential bias, systematic errors, and motives to exaggerate risks from low-dose low-rate ionizing radiation are discussed here. In conclusion, current radiation safety norms are exceedingly restrictive and should be revised on the basis of scientific evidence. Elevation of the limits must be accompanied by measures guaranteeing their observance.

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.

Reconsidering Health Consequences of the Chernobyl Accident

The Chernobyl accident led to major human suffering caused by the evacuation and other counter-measures. However, the direct health consequences of the accident-related radiation exposures, besides the acute effects and small number of thyroid cancers, have not been observed. This absence is challenged by some influential groups affecting public policies who claim that the true extent of radiogenic health consequences is covered up. We consider such claims. The most conservative (in this case - overestimating) linear no-threshold hypothesis was used to calculate excess cancer expectations for cleanup workers, the population of the contaminated areas and the global population. Statistical estimations were performed to verify whether such expected excess was detectable. The calculated cancer excess for each group is much less than uncertainties in number of cancer cases in epidemiological studies. Therefore the absence of detected radiation carcinogenesis is in full correspondence with the most conservative a priori expectations. Regarding the cover-up claims, rational choice analysis was performed. Such analysis shows that these claims are ill-founded. The present overcautious attitude to radiological hazards should be corrected in order to mitigate the present suffering and to avoid such suffering in the future.

Radiation-hormesis phenotypes, the related mechanisms and implications for disease prevention and therapy

Humans are continuously exposed to ionizing radiation throughout life from natural sources that include cosmic, solar, and terrestrial. Much harsher natural radiation and chemical environments existed during our planet's early years. Mammals survived the harsher environments via evolutionarily-conserved gifts ̶ a continuously evolving system of stress-induced natural protective measures (i.e., activated natural protection [ANP]). The current protective system is differentially activated by stochastic (i.e., variable) low-radiation-dose thresholds and when optimally activated in mammals includes antioxidants, DNA damage repair, p53-related apoptosis of severely-damaged cells, reactive-oxygen-species (ROS)/reactive-nitrogen-species (RNS)- and cytokine-regulated auxiliary apoptosis that selectively removes aberrant cells (e.g., precancerous cells), suppression of disease promoting inflammation, and immunity against cancer cells. The intercellular-signaling-based protective system is regulated at least in part via epigenetic reprogramming of adaptive-response genes. When the system is optimally activated, it protects against cancer and some other diseases, thereby leading to hormetic phenotypes (e.g., reduced disease incidence to below the baseline level; reduced pain from inflammation-related problems). Here, some expressed radiation hormesis phenotypes and related mechanisms are discussed along with their implications for disease prevention and therapy.

Using an Ecosystem Approach to complement protection schemes based on organism-level endpoints

Radiation protection goals for ecological resources are focussed on ecological structures and functions at population-, community-, and ecosystem-levels. The current approach to radiation safety for non-human biota relies on organism-level endpoints, and as such is not aligned with the stated overarching protection goals of international agencies. Exposure to stressors can trigger non-linear changes in ecosystem structure and function that cannot be predicted from effects on individual organisms. From the ecological sciences, we know that important interactive dynamics related to such emergent properties determine the flows of goods and services in ecological systems that human societies rely upon. A previous Task Group of the IUR (International Union of Radioecology) has presented the rationale for adding an Ecosystem Approach to the suite of tools available to manage radiation safety. In this paper, we summarize the arguments for an Ecosystem Approach and identify next steps and challenges ahead pertaining to developing and implementing a practical Ecosystem Approach to complement organism-level endpoints currently used in radiation safety.

Chernobyl-Related Cancer and Precancerous Lesions: Incidence Increase vs. Late Diagnostics

The reported incidence of thyroid cancer in children and adolescents in Soviet Union before the Chernobyl accident was lower than in other developed countries. This is not clearly recognizable from the literature because comparisons of the high incidence figures 4 years after the accident and later have been made with those from the first years after the accident, when the registered incidence had already started to increase. Considering the low pre-accident registered incidence, there was an accumulated pool of undiagnosed thyroid tumors before the accident. The percentage of more advanced cancers, larger in size and less differentiated, was higher after the accident, when the pool of neglected cancers was diagnosed due to the screening and improved diagnostics. Some of these advanced tumors found by screening were interpreted as aggressive radiogenic cancers. The same tendency might be true also for other cancers, e.g. renal cell carcinoma. Furthermore, the screening-effect, false-positivity and registration of non-exposed patients as Chernobyl victims has obviously contributed to the registered incidence increase of malignancy.

Potential treatment of inflammatory and proliferative diseases by ultra-low doses of ionizing radiations

Ultra-low doses and dose- rates of ionizing radiation are effective in preventing disease which suggests that they also may be effective in treating disease. Limited experimental and anecdotal evidence indicates that low radiation doses from radon in mines and spas, thorium-bearing monazite sands and enhanced radioactive uranium ore obtained from a natural geological reactor may be useful in treating many inflammatory conditions and proliferative disorders, including cancer. Optimal therapeutic applications were identified via a literature survey as dose-rates ranging from 7 to 11μGy/hr or 28 to 44 times world average background rates. Rocks from an abandoned uranium mine in Utah were considered for therapeutic application and were examined by γ-ray and laser-induced breakdown fluorescence spectroscopy. The rocks showed the presence of transuranics and fission products with a γ-ray energy profile similar to aged spent uranium nuclear fuel (93% dose due to β particles and 7% due to γ rays). Mud packs of pulverized uranium ore rock dust in sealed plastic bags delivering bag surface β,γ dose-rates of 10-450 μGy/h were used with apparent success to treat several inflammatory and proliferative conditions in humans.

Theoretical increase of thyroid cancer induction from cervical spine multidetector computed tomography in pediatric trauma patients

BACKGROUND

The trend of increasing cervical spine multidirectional computed tomography (MDCT) imaging of pediatric trauma patients is characteristic of the overall dramatic increase in computed tomography utilization in the United States. The purpose of this study is to compare the amount of radiation a pediatric trauma patient absorbs to the thyroid from plain radiographs and MDCT of the cervical spine and to express risk by calculation of theoretical thyroid cancer induction.

METHODS

A retrospective evaluation of pediatric trauma patients admitted from October 1, 2004, to October 31, 2009, was performed at an academic, Level I trauma center. Inclusion criteria were Level I/II trauma patients, cervical spine imaging performed at our institution, and age <18 years. Absorbed thyroid radiation was calculated for patients receiving plain radiographs or MDCT. Thyroid cancer risk was calculated using the 2006 Biological Effects on Ionizing Radiation VII report.

RESULTS

Six hundred seventeen patients met inclusion criteria: 224 received cervical spine radiographs and 393 received cervical spine MDCT. The mean thyroid radiation absorbed from radiographs was 0.90 mGy for males and 0.96 mGy for females compared with 63.6 mGy (males) and 64.2 mGy (females) receiving MDCT (p < 0.001). The median excess relative risk of thyroid cancer induction from one cervical spine MDCT in males was 13.0% and females was 25.0%, compared with 0.24% (males) and 0.51% (females) for radiographs (p < 0.001).

CONCLUSIONS

The significant difference in radiation that MDCT delivers to the pediatric trauma patient when compared with plain radiographs should temper routine use of computed tomography in pediatric cervical spine clearance algorithms.

Debate on the Chernobyl disaster: response to Dr. Sergei V. Jargin

The author responds, point by point, to Dr. Jargin's critique in this Journal issue of A. V. Yablokov, V. B. Nesterenko, and A. B. Nesterenko, Chernobyl: consequences of the catastrophe for people and the environment, published in 2009 by the New York Academy of Sciences.

Shifting the paradigm in radiation safety

The current radiation safety paradigm using the linear no-threshold (LNT) model is based on the premise that even the smallest amount of radiation may cause mutations increasing the risk of cancer. Autopsy studies have shown that the presence of cancer cells is not a decisive factor in the occurrence of clinical cancer. On the other hand, suppression of immune system more than doubles the cancer risk in organ transplant patients, indicating its key role in keeping occult cancers in check. Low dose radiation (LDR) elevates immune response, and so it may reduce rather than increase the risk of cancer. LNT model pays exclusive attention to DNA damage, which is not a decisive factor, and completely ignores immune system response, which is an important factor, and so is not scientifically justifiable. By not recognizing the importance of the immune system in cancer, and not exploring exercise intervention, the current paradigm may have missed an opportunity to reduce cancer deaths among atomic bomb survivors. Increased antioxidants from LDR may reduce aging-related non-cancer diseases since oxidative damage is implicated in these. A paradigm shift is warranted to reduce further casualties, reduce fear of LDR, and enable investigation of potential beneficial applications of LDR.

Hormesis and radiation safety norms

Today's radiation safety norms are based on the linear no-threshold theory (LNT): extrapolation of the dose-response relationships down to the minimal doses, where such relationships are unproven and can be inverse due to hormesis. The most promising way to obtaining reliable data on the dose-effect relationships for low radiation doses would be large-scale animal experiments. Outstanding published data on carcinogenic effects of the doses e.g. below 100 mSv should be verified by experiments. Arguments against applicability of the LNT to the doses comparable to those from the natural radiation background are discussed. Furthermore it is stressed that medical consequences of the Chernobyl accident have been overestimated; and this theme has been exploited to strangle development of atomic energy and to elevate prices for fossil fuels. Worldwide introduction of nuclear energy will be possible only after a concentration of authority within a powerful international executive. It would enable the construction of nuclear reactors in optimally suitable places, considering all sociopolitical, geographical, and geological conditions, which would contribute to the prevention of accidents like in Japan in 2011. A concluding point is that radiation safety norms are exceedingly restrictive and should be revised to become more realistic and workable. Elevation of the limits must be accompanied by measures guaranteeing their strict observance. It is also concluded that there are no evidence-based contraindications to fivefold elevation of the total equivalent effective doses to individual members of the public (up to 5 mSv/year), and doubling of the limits for professional exposures.

Debate on the Chernobyl Disaster: On the Causes of Chernobyl Overestimation

The Journal is pleased to publish an exchange of articles on the nuclear catastrophe at Chernobyl that has special importance in the light of the Fukushima situation in Japan.

After the Chernobyl accident, many publications appeared that overestimated its medical consequences. Some of them are discussed in this article. Among the motives for the overestimation were anti-nuclear sentiments, widespread among some adherents of the Green movement; however, their attitude has not been wrong: nuclear facilities should have been prevented from spreading to overpopulated countries governed by unstable regimes and regions where conflicts and terrorism cannot be excluded. The Chernobyl accident has hindered worldwide development of atomic industry. Today, there are no alternatives to nuclear power: nonrenewable fossil fuels will become more and more expensive, contributing to affluence in the oil-producing countries and poverty in the rest of the world. Worldwide introduction of nuclear energy will become possible only after a concentration of authority within an efficient international executive. This will enable construction of nuclear power plants in optimally suitable places, considering all sociopolitical, geographic, geologic, and other preconditions. In this way, accidents such as that in Japan in 2011 will be prevented.

On the RET Rearrangements in Chernobyl-Related Thyroid Cancer

There is a consensus that Chernobyl accident has induced thyroid cancer increase in children and adolescents. The UNSCEAR report concluded that no somatic disorders other than thyroid cancer were caused by radiation exposure due to the accident except for acute radiation sickness occurred to the people within the Power Plant at the time of the accident. A hypothesis is discussed in this paper that the increase of thyroid cancer was caused predominantly by the screening, overdiagnosis, and registration of nonirradiated persons as Chernobyl victims. A mechanism of thyroid cancer overdiagnosis is described that can be active even today, causing hypertherapy. Older neglected tumors found by the screening shortly after the Chernobyl accident or brought from noncontaminated areas were misclassified as aggressive radiation-induced cancers. Therefore, supposed markers of the radiation-induced thyroid cancer, such as the RET rearrangements, are probably associated with disease duration and tumor progression. The screening effect is obviously dependent on the basis level of medical surveillance: the higher the level, the smaller the screening effect. Absence of any significant increase of thyroid cancer after the Fukushima accident in spite of the vigorous screening would certify the high level of health care in Japan especially for children.

Regulatory-Science: Biphasic Cancer Models or the LNT-Not Just a Matter of Biology!

There is no doubt that prudence and risk aversion must guide public decisions when the associated adverse outcomes are either serious or irreversible. With any carcinogen, the levels of risk and needed protection before and after an event occurs, are determined by dose-response models. Regulatory law should not crowd out the actual beneficial effects from low dose exposures-when demonstrable-that are inevitably lost when it adopts the linear non-threshold (LNT) as its causal model. Because regulating exposures requires planning and developing protective measures for future acute and chronic exposures, public management decisions should be based on minimizing costs and harmful exposures. We address the direct and indirect effects of causation when the danger consists of exposure to very low levels of carcinogens and toxicants. The societal consequences of a policy can be deleterious when that policy is based on a risk assumed by the LNT, in cases where low exposures are actually beneficial. Our work develops the science and the law of causal risk modeling: both are interwoven. We suggest how their relevant characteristics differ, but do not attempt to keep them separated; as we demonstrate, this union, however unsatisfactory, cannot be severed.

Validity of thyroid cancer incidence data following the Chernobyl accident

The only clearly demonstrated cancer incidence increase that can be attributed to radiation from the Chernobyl accident is thyroid carcinoma in patients exposed during childhood or adolescence. Significant increases in thyroid disease were observed as soon as 4 y after the accident. The solid/follicular subtype of papillary carcinoma predominated in the early period after the accident. Morphological diagnosis of cancer in such cases, if no infiltrative growth is clearly visible, depends mainly on the nuclear criteria. Outdated equipment and insufficient quality of histological specimens impeded reliable evaluation of the nuclear criteria. Access to foreign professional literature has always been limited in the former Soviet Union. The great number of advanced tumors observed shortly after the accident can be explained by the screening effect (detection of previously neglected cancers) and by the fact that many patients were brought from non-contaminated areas and registered as Chernobyl victims. It is also worth noting that exaggeration of the Chernobyl cancer statistics facilitated the writing of dissertations, financing of research, and assistance from outside the former Soviet Union. "Chernobyl hysteria" impeded nuclear energy production in some countries, thus contributing to higher prices for fossil fuel. The concluding point is that since post-Chernobyl cancers tend on average to be in a later stage of tumor progression, some published data on molecular or immunohistochemical characteristics of Chernobyl-related cancers require reevaluation.

Pooled Bayesian analysis of twenty-eight studies on radon induced lung cancers

The influence of ionizing radiation of (222)Rn and its progeny on lung cancer risks that were published in 28 papers was re-analyzed using seven alternative dose-response models. The risks of incidence and mortality were studied in two ranges of low annual radiation dose: 0-70 mSv per year (391 Bq m(-3)) and 0-150 mSv per year (838 Bq m(-3)). Assumption-free Bayesian statistical methods were used. The analytical results demonstrate that the published incidence and mortality data do not show that radiation dose is associated with increased risk in this range of doses. This conclusion is based on the observation that the model assuming no dependence of the lung cancer induction on the radiation doses is at least ∼90 times more likely to be true than the other models tested, including the linear no-threshold (LNT) model.

Toward improved ionizing radiation safety standards

Ionizing radiation safety standards developed by the International Commission on Radiological Protection (ICRP) during the past 50-plus years have provided guidance for effective protection of workers and the public from the potentially harmful effects of exposure to ionizing radiation, including cancer. Earlier standards were based primarily on radiation dose rate to organs of the body. More recent recommendations have calculated cancer risk as a function of cumulative dose using a linear no-threshold cancer risk model based on the acute high dose rate exposures received by the Japanese atomic bomb survivors. The underlying assumption in these current recommendations is that risk of radiation-induced cancer is proportional to cumulative dose without threshold. In conflict with this position are the studies of protracted exposures from internally-deposited radionuclides in people and laboratory animals that have demonstrated that cancer induction risk is a function of average dose rate for protracted exposures to ionizing radiation. At lower average dose rates, cancer latency can exceed natural lifespan leading to a virtual threshold. This forum statement proposes that the conflict of these two cancer risk models is explained by the fact that the increased risk of cancer observed in the atomic bomb survivor studies was primarily the result of acute high dose rate promotion of ongoing biological processes that lead to cancer rather than cancer induction. In addition, ionizing radiation-induced cancer is not the result of a simple stochastic event in a single living cell but rather a complex deterministic systemic effect in living tissues. It is recommended that the ICRP consider revising its position in light of this important distinction between cancer promotion and cancer induction.