Share this article on:

Radiation Dose and the Impacts on Exposed Populations: Overview Session Q&A

Cassata, James

doi: 10.1097/HP.0000000000000027

National Council on Radiation Protection and Measurements Bethesda, MD

The author declares no conflicts of interest.

Supplemental Digital Content is available in the HTML and PDF versions of this article on the journal’s Web site (

(Manuscript accepted 29 August 2013)

Back to Top | Article Outline


Has any study calculated the background radiation that was present when the Earth was formed and when living organisms first appeared on the Earth? For example, 40K must have been at a much higher level tens of millions of years ago.

I’m not personally familiar with any studies of the sort you asked about, though information is likely available elsewhere. Study of the radiation environment of the early Earth, which was well before the first organisms arose, lies within scientific disciplines not represented by myself or any of the speakers at the NCRP annual meeting. The early radiation environment of the Earth is of possible interest to paleontologists, evolutionary biologists, and other specialists, though is not considered as fundamental knowledge to present day radiation protection.

Present day science suggests the Earth is about 4.6 billion years old; organisms arose one to two billion years later, while homo sapiens arose only a few hundred thousand years ago. Modern day radiation protection provides a means to protect the health of present day human populations (though there is some interest in protection of nonhuman species as well). Consequently, radiation protection as a science has developed through studies of human populations who have lifestyles still existing today and who are generally exposed to the same types and sources of radiation.

I’m sorry I cannot answer your question more specifically.

Back to Top | Article Outline


There are cytogenetic and point mutation mechanisms to explain in part the radiation induced leukemia and solid cancers; however, what are the postulated mechanisms for producing cardiovascular diseases?

At this point, we know little about the possible mechanisms for induction of cardiovascular diseases at doses on the order of 1 Sv or less. We clearly need more translational and experimental studies to elucidate this.

Back to Top | Article Outline

Should cumulative dose or single exposure dose be treated for the risk associated with radiation situations?

It is generally believed that some function of cumulative exposure is appropriate. The concept of a dose and dose-rate effectiveness factor (DDREF) is often employed to quantitatively factor in how much the additive biological effects of cumulative small doses may be less than those from a single larger dose. However, at this time, there is a considerable range of uncertainty as to how large the DDREF may be.

Back to Top | Article Outline

I have read: (1) no solid cancers found in any epidemiological study were attributable to radiation when doses were <0.1 Sv; (2) for several sites, atomic-bomb survivor data are compared by dose group rather than to controls because cancer incidents in controls are greater; and (3) epidemiological studies of populations residing in areas with high natural background radiation do not find increased incidence of radiogenetic cancer in populations.

(1) Probably the clearest examples of solid cancers found at doses under ~0.1 Sv are for thyroid cancer, as shown in several medical irradiation studies following childhood exposures, and solid cancers seen after in utero diagnostic irradiation. The data on solid cancers in the atomic bomb studies also are suggestive of risk at doses <0.1 Sv but are limited by the studies’ low statistical power in that dose range; (2) in the atomic bomb study, the “not in city” (NIC) group is thought to differ from the distally exposed group with regard to various sociodemographic factors (e.g., urban/rural, socioeconomic) that affect baseline cancer risks. Several recent analyses of the atomic bomb cohort have used the NIC group, with statistical adjustment for the noncomparability factors. One also could cite the opposite “effect:” the distal survivors have somewhat higher rates of cancer than those of nearby Okayama prefecture, but again, in large part, this probably reflects sociodemographic and other nonradiation factors; and (3) as with those mentioned in (2), sociodemographic factors may overshadow possible radiation effects in comparing tumor rates in high- and low-background radiation areas. In addition, there may be concerns about the completeness and comparability of the cancer registries in the corresponding high and low areas.

Back to Top | Article Outline

How do your conclusions (no evidence of nonlinearity and significant dose response ranging from 0–150 mGy) account for these seemingly contradictory studies?

As stated in response to (3) above, a number of other factors impinge and lead to uncertainties, but consistent dose-response slopes tend to be less subject to bias than simple exposed/unexposed group comparisons.

Back to Top | Article Outline

Given the large and increasing growth in U.S. medical radiation exposure, how does one correct epidemiological studies of other sources such as environmental or occupational exposures? For example, nuclear power plant workers are relatively well paid and insured and are likely to be able to afford more diagnostic procedures than poorer people living in the same area

Comparing employed workers with the general population is fraught with potential biases, both in the direction the question mentions and in the opposite direction due to selection of healthy persons for employment (healthy worker effect) and further selection factors for continued employment [healthy worker survivor effect (HWSE)]. Those are reasons why exposure-response analyses based on data within the occupational group tend to be more reliable than general population comparisons, especially if special care is taken to examine potential HWSE effects.

Back to Top | Article Outline

The estimation of the percent of the epidemiological study needs to take into account the power of the study to defeat the significant effects

I’m not sure I understand the point. However, a major concern in reviewing low-dose studies is that they may have inadequate statistical power to detect effects, so that there are more false-negative studies than there would be if the studies had the same dose distributions but much larger sample sizes.

Back to Top | Article Outline

When counting the number of low-dose effects, don’t we have to consider the issue of publication bias—where negative studies are less likely to be published?

Yes, publication bias can be a concern. That is one reason why my presentation focused on only the largest studies, ones that are less likely to be unpublished even if negative.

Back to Top | Article Outline

In low dose protracted fractionated exposures, is there any evidence of protective effects?

Since more than the expected numbers of studies were significantly positive, the “weight of evidence” does not suggest protective effects.

Back to Top | Article Outline

What should the “cut line” be for radiation protection officers to limit computed tomography use by medical professionals? Should more invasive procedures (or magnetic resonance imaging) be considered?

These are obviously policy issues that need discussion by a wide array of experts.

Back to Top | Article Outline

Given that there is a concern with low-dose radiation and health effects, it is unfortunate that limited data from U.S. Department of Energy (DOE) workers (with low-dose exposures) have been presented. Dr. Shore presented three in his “literature” review—Savannah River Site, Los Alamos National Laboratory, and Oak Ridge National Laboratory. Perhaps to further look at this question, the National Institute for Occupational Safety and Health (NIOSH) should also be invited to participate on the future panel.

Actually, considerably more DOE worker studies were presented than those named in the question. Others were included in the 15-country study or in several other references, some of which were NIOSH-based references.

Back to Top | Article Outline

Looking at the high end instead of the low end of the “linear response” curve, it appears that from one of Dr. Shore’s slides on the cancer incidence versus colon dose in Japan that the curve is starting to end downward. Is there a valid observation, and is it present in relevant animal models?

A number of studies suggest that excess cancer incidence for various sites tends to plateau or taper off at high doses, perhaps due to cell killing or allied phenomena. However, the dose level at which this phenomenon begins varies considerably from study-to-study and tumor site-to-site.

Back to Top | Article Outline

There are reports, although not rigorous epidemiological studies, of post-traumatic stress disorder (PTSD) in atomic bomb survivors and Fukushima evacuees. So here are the questions: (a) What is the evidence for a link between PTSD and cardiovascular disease? (b) is there also evidence for increases in inflammatory markers in PTSD (e.g., cytokinetics and C-reactive protein)? and (c) are there any studies being done to distinguish between low-level radiation effects and psychological effects that produce physical effects?

Dr. Bromet is better qualified than I to address these questions, but a reference to a paper may be helpful regarding (a and b) (Wentworth et al. 2013).

Regarding (c), an atomic-bomb paper (Yamada and Izumi 2002) indicated that the survivors did show more psychiatric sequelae (anxiety and somatization symptoms) than those “not in city” at the time of the bombing, but the distal survivors had as much or more of those symptoms than the proximal survivors, suggesting it was not related to radiation dose per se, except for those who had had acute radiation symptoms (e.g., epilation, keratoses). That paper also summarizes some earlier reports on psychiatric sequelae of the bombings.

Back to Top | Article Outline

Are there any studies being done to distinguish between low-level radiation effects and psychological effects that produce physical effects?

I do not know of any. We once did a cross-sectional study of solvent exposure, occupational stress, and mental health. In the end, the symptoms associated with the exposures and the stressors were the same and impossible to disentangle with a cross-sectional design. There are no hypotheses at present that would indicate a mechanism to explain a relationship between low-level radiation and psychological effects. There are papers on liquidators who suffered from acute radiation syndrome, but the diagnoses were never independently verified, and the electro-encephalogram findings, if replicated independently, probably would not apply to low-level radiation exposure.

Back to Top | Article Outline


What is the effective treatment of emotional consequences?

A critical issue is early identification of highly exposed and high-risk populations so that interventions can occur at the earliest possible moment to prevent long-term mental health problems from taking root. It is also important to tailor, time, and target interventions appropriately. To date, social support and cognitive behavioral therapy are the most effective and the safest interventions for post-disaster mental health problems. However, they have to be designed as long-term, dynamic programs, given the long-term emotional toll of events like the triple disaster in northeast Japan.

Back to Top | Article Outline

What can be done proactively to insulate populations from disaster-related psychological injuries?

In the immediate aftermath, before clinically significant psychiatric symptoms emerge, the recommended prevention approaches are: (1) promote a sense of safety; (2) reduce anxiety; (3) increase self and collective senses of empowerment; (4) encourage social support; (5) instill hope; and (6) provide accurate, timely, clear, and credible information.

It is important to have professionals with good communication skills who can provide clear explanations of the disaster, explain safety procedures, describe the resources available to the population, and be available to answer questions either in person or via social media or electronic communication. It is also important that remuneration is provided promptly. High risk groups, such as pregnant women, young mothers, and elderly persons, need to have ongoing, accessible support systems in place and open lines of communication with persons in authority and with medical doctors.

Back to Top | Article Outline

How do you support community mental health before, during, and after an event?

Different countries have different systems of mental health care. Most individuals around the globe seek counseling for emotional problems from their primary care doctors, not from mental health professionals. One thing that is needed is that medical students and residents learn about the detection and treatment of common psychiatric problems that are endemic in the community and that become more prevalent (or new onsets) after disasters. These include depression, post-traumatic stress disorder or symptoms, and other forms of anxiety, especially health-related anxiety. Clergy also play a key role, depending on where the disaster occurs. There is a growing literature on post-traumatic growth, suggesting that disasters can also promote newfound resilience and strength.

It is also important to support local leaders who emerge in times of community stress. They are often the most trusted source for the community and are therefore in a position to be of great help to medical providers and other professionals in communicating ways to recover from a disaster and responding to questions from the public.

The most vulnerable, of course, are people who lost family members, friends, and neighbors. Grief counseling by experienced professionals is a critical, long-term part of the recovery process.

Back to Top | Article Outline

Do new nuclear power accidents reignite concerns of additional mental health consequences by exposing individuals to previous accidents (e.g., Chernobyl accident on Three Mile Island individuals)?

Yes. Previous trauma is a predictor of post-trauma mental health problems. This was a concern in our Three Mile Island study because the comparison group lived near another nuclear power plant in Pennsylvania that had experienced accidents, although not of similar magnitude. We therefore added a second comparison group who resided near a coal-fired plant. Anecdotally, I was told that many women in Kiev strongly identified with the terror experienced by young mothers living near Fukushima and followed news stories about Fukushima very closely.

Back to Top | Article Outline

Are there significant differences on mental health problems between the genders?

Yes. Women are more likely to develop depression, anxiety, and post-traumatic stress disorder compared to men, while men are more likely to abuse alcohol. This is true in the general population as well as in disaster-exposed populations.

Back to Top | Article Outline

Does education of the public about the disasters help reduce emotional consequences of the disasters?

Education about common reactions to disasters is recommended. Explanations about what took place, in language that is accessible, and without lies and contradictions, can also be helpful. I am not familiar with research comparing the effectiveness of different forms of educational interventions about disasters. However, the field of risk communication may have conducted such studies.

Back to Top | Article Outline

Given the mental health impacts of Fukushima and the misinformation that appears to contribute, can public education help?

This is similar to the previous question. Common sense would indicate that misinformation is never a good idea. Individuals who work in the area of risk communication emphasize that dialogue is critical, not one-sided public education. Providing information without “listening” to questions and concerns from the public is inadequate. Dialogue also allows the communicators to fine-tune their messages over time. Another reason to encourage dialogue is that, given the emotional consequences of nuclear power plant accidents, when people are fearful, they may not be able to hear the messages properly. We all engage in selective listening, but when we are afraid of something, we selectively hear “danger”’ rather than “protection.” For people who were told to evacuate (20 km zone) or to limit their daily activities (20–30 km), dialogue is especially critical. Given the long-term fear about radiation exposure and the lag time between exposure and cancer, setting up a dialogue is a long-term proposition. It is obviously also critical that messages be delivered and questions addressed by credible leaders whom the community trusts and that they be targeted to multiple risk groups.

I would also add that researchers have a moral obligation to present their findings to the public in language that is understandable and without dumbing down the data and behaving in a condescending manner. We also have an obligation to interact and answer questions. Indeed, I believe strongly that researchers should treat the people in their studies as “collaborators” and that these collaborators should be the first to learn about the findings directly from the researchers, not from the mass media. To my knowledge, this did not happen on 28 February 2013 when the World Health Organization issued their latest report (WHO 2013).

Back to Top | Article Outline

What is the possibility that the evacuees from Fukushima may suffer health effects because they have been told or believe that such effects may occur?

Physical and mental health problems are highly correlated, and epidemiologic evidence has shown clearly that prolonged anxiety and depression are associated with onset of many physical health problems later in life.

Back to Top | Article Outline

In your opinion, could more be done in the future to help the first responders, such as the “liquidators” of Chernobyl, to avoid anxiety, depression, etc.?

There are many programs for developing resilience, and responders without prior training should receive some form of “stress inoculation” before going into a traumatic situation. There is research showing that first responders who have disaster training have lower rates of post-traumatic stress disorder than nontraditional responders. After 9/11, thousands of people from various occupations worked on the pile and in other places where they experienced horrendous trauma. Several mental health reports showed significantly lower rates of post-traumatic stress disorder and depression during the decade following 9/11 among police and firefighters compared to untrained responders who came to help. Moreover, these problems were persistent over time rather than remitting.

Back to Top | Article Outline

Due to uncertainty, we cannot say there is no risk. So what can we say to explain “risk” without frightening the population?

This question is best addressed by experts in the field of risk communication. It is a very important issue. To answer this question personally, the comparator is critical. I would be reassured if I was told: “As a woman, the likelihood of developing cancer in your lifetime is 38% (i.e., one in three women develop cancer in their lifetimes). The extra risk, as someone who evacuated from the 20 km zone, is so small that it cannot be calculated exactly and will not be detectable in the future.” If that were the message, and I trusted the source (!!!), I would feel quite reassured. The problem that arose after all three accidents is that the sources of information were viewed with distrust and suspicion, which only got worse with time. And conflicting messages were delivered by the Japanese government, the World Health Organization, and other international bodies with little or no interaction with the affected populations.

Back to Top | Article Outline

Although Chernobyl and Fukushima accidents resulted in radiation exposures to the public, and the Three Mile Island accident resulted in little such exposure, they all contributed to substantial mental stresses. Please explain why a non-power plant accident, such as the Gioânia accident of 1987 (in Brazil), also caused significant emotional stresses on the public?

Gioânia was an event involving radiation exposure (a radioactive cesium teletherapy source was discarded and resulted in widespread contamination and death in a few instances), and radiation exposure tops the list of most dreaded exposures.

Back to Top | Article Outline

Can you highlight the importance of terminology (e.g., “victim” versus “survivor”) when talking to patients, the media, etc.?

The word “survivor” implies that one has actively and positively coped with an extreme stressor—hence, the importance of the term “cancer survivor.” The word “victim” implies that one has been overpowered by events. After Chernobyl, evacuees were referred to as victims. They did lose their homes and their sense of security about the future. But they have also gone on to live productive lives, raise healthy and happy children, and become integrated in their new communities. They are indeed survivors, not victims.

Back to Top | Article Outline

Is there any psychological effect (positive or negative) associated with enrolling a person in a long-term survival study? Can this increase the stress levels or encourage a healthier lifestyle?

I don’t know of any studies that examined whether being in a cohort study has beneficial effects compared to not being in a cohort study, but it is clear that there was a missed opportunity to address mental health concerns in the cohorts being followed for cancer onset after Chernobyl. There is a growing field called “mind-body medicine.” The artificial separation of physical and mental health seems more and more counterproductive to improving the population’s health.

Back to Top | Article Outline

Do you feel that local studies that showed a cognitive impairment were attempted to get increased funding from the international community, or why do you feel that their results were so different?

In my mind, the main issue is that the controls were ill matched to the cases, and the raters who collected the data were not blind to exposure status. At the time these studies were conducted, the local understanding of epidemiologic methods was not consistent with the fundamental principles practiced in the United States and Europe. Plus, there was a societal bias that radiation exposure was the root of all health problems. The investigators were a product of their era and were as invested in this belief about radiation as was the general population and the press. In the cancer studies, transparent collaborations developed over time. Unfortunately, this did not happen with the mental health and cognitive impairment studies.

Back to Top | Article Outline

Please comment on the potential financial conflict-of-interest that Ukrainian researchers have if they can show effects that can receive money from outside.

I think that this was a very real issue, and I’m not sure any of us would have behaved differently under the circumstances. After the Soviet Union broke apart, there was tremendous poverty and unemployment. Scientists worked as taxi drivers and mechanics in order to put food on the table. So yes, receiving funds from international sources was important for survival. Did some people take undue advantage? Of course, but this kind of thing happens in less obvious ways after many disasters.

Back to Top | Article Outline

Do you think it would help the mental state of the Japanese people if we held NCRP meetings and other radiation-related professional meetings inside the Fukushima exclusion zone?

We had three meetings sponsored by the Nippon Foundation and Fukushima Medical University, and some of the speakers toured the reactors. Otherwise, we were not permitted inside the exclusion zone. I thought it was important that we were in Fukushima and eating local products, because most Japanese citizens avoid buying products that come from Fukushima.

Back to Top | Article Outline

How does the Bhopal accident compare to nuclear power plant accidents?

There were no epidemiologic mental health studies after Bhopal, but the papers written by a well-known psychiatrist from India indicated that anxiety and depression were highly prevalent and persistent. Every accident is unique in the time and place of its occurrence. Each event is also unique in the secondary traumatic sequelae that they produce. Bhopal created horrific health issues, as did 9/11 for first responders. The secondary traumas from Chernobyl included evacuation, financial losses, and for some families, bereavement. Fukushima was part of a triple disaster, and the list of the secondary traumas is considerably longer.

Back to Top | Article Outline

There are reports, although not rigorous epidemiological studies, of post-traumatic stress disorder (PTSD) in atomic bomb survivors and Fukushima evacuees. The atomic bomb survivor studies indicate long-term psychosomatic and anxiety symptoms. So here are the questions: (1) What is the evidence for a link between PTSD and cardiovascular disease, and (2) is there also evidence for increases in inflammatory markers in post-traumatic stress disorder (e.g., cytokinetics and C-reactive protein)?

(1) There is a growing literature on this topic that extends to hypertension, hyperlipidemia, and cardiovascular disease. I refer you to a recent review by Coughlin (2011); and (2) there is growing evidence from both epidemiologic and epigenetic studies, starting with Uddin et al. (2010) and many papers since then.

Introduction of the Sinclair Lecture (Video 2:01,

Back to Top | Article Outline


Coughlin SS. Post-traumatic stress disorder and cardiovascular disease. Open Cardiovasc Med J 5: 164–170; 2011.
Uddin M, Aiello AE, Wildman DE, Koenen KC, Pawelec G, de Los Santos R, Goldmann E, Galea S. Epigenetic and immune function profiles associated with posttraumatic stress disorder. Proc Natl Acad Sci USA 107: 9470–9475; 2010.
Wentworth BA, Stein MB, Redwine LS, Xue Y, Taub PR, Clopton P, Nayak KR, Maisel AS. Post-traumatic stress disorder: a fast track to premature cardiovascular disease? Cardiol Rev 21: 16–22; 2013.
WHO. Health risk assessment from the nuclear accident after the 2011 Great East Japan earthquake and Tsunami based on a preliminary dose estimation. Geneva: World Health Organization; 2013. Available at Accessed 16 August 2013.
Yamada M, Izumi S. Psychiatric sequelae in atomic bomb survivors in Hiroshima and Nagasaki two decades after the explosions. Soc Psychiatry Psychiatr Epidemiol 37: 409–415; 2002.

Supplemental Digital Content

Back to Top | Article Outline
© 2014 by the Health Physics Society