Radiation Impacts on Human Health: Certain, Fuzzy, and Unknown
Shore, Roy E.*
*Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815, Japan.
The author declares no conflicts of interest.
For correspondence contact the author at the above address, or email at firstname.lastname@example.org.
Supplemental Digital Content is available in the HTML and PDF versions of this article on the journal’s Web site (www.health-physics.com).
(Manuscript accepted 27 August 2013)
Abstract: The atomic bomb and other studies have established with certainty that moderate-to-high doses of radiation cause many types of solid cancer and leukemia. Moving down the dose range to the vicinity of 100–200 mSv, the risks become fuzzy and then unknown at low doses on the order of 10–20 mSv. Nor have low-dose experimental studies provided definitive answers: some have suggested there may be adverse biological effects in the range of 5–50 mSv, while others support a “no risk” interpretation. Epidemiologic data contain intrinsic “noise” (variation by known and unknown factors related to genetics, lifestyle, other environmental exposures, sociodemographics, diagnostic accuracy, etc.) so are generally too insensitive to provide compelling answers in the low-dose range. However, there have been recent provocative reports regarding risk from relatively low-dose occupational and medical radiation exposures that warrant careful consideration. Summaries of the largest studies with low-dose or low dose-rate radiation exposure provide suggestive evidence of risk for solid cancer and stronger evidence for leukemia risk. Recently, interest in health endpoints other than cancer also has risen sharply, in particular the degree of cardiovascular and cataract risk following doses under 1 Sv. Data regarding cardiovascular disease are limited and fuzzy, with suggestions of inconsistencies, and the risk at low doses is essentially unknown. The evidence of cataract risk after low dose-rate exposures among those conducting interventional medical radiological procedures is becoming strong. The magnitude of radiation impacts on human health requires fuller documentation, especially for low-dose or low dose-rate exposures. From the epidemiologic vantage point, this will require longer observation of existing irradiated cohorts and development of new informative cohorts, improved accuracy in dose assessments, more attention to confounding variables, and more biosamples from irradiated groups to enable translational radiobiological studies. Introduction of Radiation Impacts on Human Health (Video 2:02, http://links.lww.com/HP/A35)
RADIATION AND CANCER: CERTAIN TO UNKNOWN
THE ATOMIC bomb Life Span Study (LSS) and other studies have long shown that moderate-to-high doses of radiation cause leukemia and many types of solid cancer. The lack of knowledge regarding cancer effects at the dawn of the atomic era 60–70 y ago has clearly been changed to where there is little doubt that most of the major types of cancer are increased by acute radiation doses of at least 200–500 mGy. In particular, the LSS of atomic bomb survivors provides strong data at higher doses, but risks become fuzzy at ∼100–200 mSv and are unknown at doses on the order of 5–20 mSv. When cumulative doses are received at a low dose rate or as a large series of small exposures, the degree of risk becomes fuzzy in the vicinity of 100–200 mSv. There is a pressing need for better information on the health effects of cumulative low-dose or low dose-rate exposures, such as from medical or occupational sources. For instance, it has been estimated that 80 million computed tomography (CT) scans per year are being performed in the United States, of which about six million are scans of children (Goodman 2013). A study of the history of multiple CT scans allows one to extrapolate that over a million persons in the United States probably have received sufficient multiple CT scans to have had effective doses of >250 mSv (Sodickson et al. 2009).
To date, experimental studies have not provided definitive answers regarding low-dose risks: some data have implied there may be adverse biological effects in the range of 5–50 mSv, with suggestions that induced genomic instability or bystander effects may accentuate risk, while other data support a “no risk” interpretation due to adaptive responses, high-fidelity low-dose DNA repair, and other protective systems. There are also large uncertainties in extrapolating from homogeneous, and often genetically modified, animal models or in vitro cellular systems to human populations that have considerable variability in both genetic and environmental exposure cofactors.
Even though there is still much uncertainty about the magnitude of risk, if any, from low cumulative doses on the order of 5–50 mSv, that is not to say that nothing is known about the risk. It can be assumed reasonably that those risks are small: the weight of evidence indicates that larger risks can be ruled out, such as might be associated with doses of several hundred millisievert. Nevertheless, at least three types of factors work against obtaining precise epidemiologic estimates of low-dose risks in the 5–50 mSv range:
1. Many epidemiologic studies have fairly substantial dose uncertainties. While that tends to pose fairly minor problems for studies with a high, broad range of doses, the magnitude of dose uncertainties may approach or exceed the imputed doses in low-dose studies with a consequent large impact on any risk estimates from them;
2. Similarly, variations in study subjects’ levels of exposure from extraneous radiation sources such as background radiation and especially medical radiation exposures, produce random “noise” that introduces more variability into the dose-response estimates and may even produce bias in the dose response estimate if the levels of background or medical radiation exposure happen to be substantially correlated with the doses of interest. Again, the extraneous radiation exposure has relatively little impact on high-dose studies but can substantially weaken or bias low-dose studies; and
3. The impact of variation among individuals in known and unknown factors related to genetics, lifestyle, other environmental exposures, sociodemographics, diagnostic accuracy, medical care adequacy, etc., potentially has a greater effect on low-dose studies and their risk estimates.
All these factors tend to introduce random statistical noise, and possibly bias, into the risk estimates. Thus, the intrinsic uncertainties in epidemiologic studies mean that most individual studies have insufficient statistical power and precision to provide compelling answers regarding low dose risks.
STUDIES OF LOW DOSE, PROTRACTED, OR HIGHLY FRACTIONATED (LDPF) RADIATION EXPOSURES AND CANCER RISK
LDPF radiation exposure and total solid cancer
There have been recent provocative reports regarding risk based on studies with LDPF radiation exposures from occupational, environmental, or medical sources that warrant careful consideration. For instance, Jacob et al. (2009) summarized results from a series of occupational or environmental radiation studies and estimated that the weighted average risk for total solid cancers was slightly higher than for the corresponding age-gender matched subsets of the LSS atomic bomb data: the ratio of the average LDPF risk compared to the LSS risk was 1.2 [90% confidence interval (CI) 0.5, 1.9]. The authors concluded that, “The present analysis does not confirm that the cancer risk per dose for [LDPF] exposures is lower than for the atomic-bomb survivors.”
Data and analyses in addition to those reported by Jacob et al. (2009) are available. Of particular note, a recent widely publicized study by Mathews et al. (2013) reported heightened cancer risk after pediatric CT scans based on 680,000 children or adolescents who received CT scans and 10,000,000 with no record of such exposures. They reported an excess of total cancers, with special note of brain cancers and leukemia. Although the study was well conducted, certain partly unavoidable issues introduced extra uncertainties in the results: the potential for reverse causation (cancers were caused by the medical indications for the CT scans rather than by the CT dose), missing doses (CT retakes and CT exams outside the age- and time-period of the study), and implausible radiation-tumor associations (e.g., associations of radiation with melanoma and Hodgkin lymphoma but not with breast cancer).
This report updates the analyses of Jacob et al. (2009) with a broader, semi-quantitative assessment. To avoid unclear selection criteria that might bias the conclusions, an objective criterion was used to assess the literature. Specifically, for total solid cancers, an attempt was made to locate all the English language LDPF studies that met the criteria of having at least 400 deaths or incident cases of total solid cancer and some assessment of dose and risk. This number was chosen subjectively as a minimum because risk estimates from large studies tend to be more precise and have better statistical power. In some cases, total solid cancer data were not available, so a fairly good approximation to that (e.g., all cancers except leukemia) was used.
A brief summary of the estimated risks in those studies is presented in Table 1. Because of the diversity of types of study analyses, adequacy of dose estimates, varying ages at exposure and follow-up, and noncalculable lower confidence bounds, a formal meta-analysis could not be conducted. However, the table shows that seven out of 19 studies had a statistically significant excess associated with LDPF exposure. If there were no association at all, one would expect only about one in 20 studies (5%) to show a statistically significant excess by chance. The fact that a third of the largest available studies showed an excess indicates that there is probably at least a small excess risk of solid cancers from LDPF exposures. It seems unlikely that the relatively large percentage of positive studies is due to publication bias, because large radiation studies that have >400 cancer cases are virtually always reported in the literature whether the results are statistically significant or not. However, for most of the studies, information on other exposures and risk factors, such as smoking and obesity, was not available. To the degree that those exposures and risk factors may have been correlated with cumulative radiation exposure, some bias (whether positive or negative) could have been introduced into the results of individual studies. For the occupational studies that used standardized mortality (incidence) ratios (SMRs/SIRs) for risk estimates, there probably was some negative bias in the results due to the “healthy worker effect” (Arrighi and Hertz-Picciotto 1994).
LDPF radiation exposure and leukemia
Besides the Mathews et al. (2013) study of CT examination risk (see above), another widely noted finding regarding leukemia incidence after CT scans was reported by Pearce et al. (2012). They estimated individualized doses to the red bone marrow and brain for 178,000 patients who had received CT scans and found an excess relative risk (ERR) for leukemia incidence of 36 (90% CI 5, 120) per gray, although questions have been raised about potential random and systematic uncertainties in that study (NCRP 2012).
Using a strategy to evaluate leukemia risk similar to that for solid cancers, all the LDPF studies that could be found that had at least 30 leukemia cases or deaths and risk estimates were compiled, usually excluding chronic lymphoid leukemia. A brief summary of risk estimates is presented in Table 2 from studies of LDPF occupational or environmental radiation exposures. Studies of leukemia risk after diagnostic radiation exposures also were examined, and even those without dose estimates were included so as to minimize study-selection bias. Considering occupational or environmental radiation exposures, 10 out of 16 studies (63%) showed statistically significant positive results. Adding in the medical radiation studies, of which seven out of 17 were significant, yields a total of 17 of the 33 LDPF leukemia studies (52%) that showed statistically significant excess risk, again indicating an effect from LDPF exposures. Since a substantial number and a high percentage of the leukemia studies showed a positive effect, the case for leukemia risk after LDPF exposures appears stronger than that for total solid cancers.
In summary, the LDPF epidemiologic studies of total solid cancer and leukemia provide evidence that is not unequivocal but for which the weight of evidence is in the direction of cancer risk occurring in association with LDPF exposures. It seems appropriate to regard the cancer risk from LDPF exposures as fuzzy rather than unknown. For leukemia, the studies of childhood leukemia subsequent to prenatal diagnostic medical exposure (not reviewed here) also provide support for risk from LDPF radiation exposure (Wakeford 2008).
LOW DOSE RADIATION EXPOSURE AND CARDIOVASCULAR DISEASE
Recently, interest in health endpoints other than cancer also has risen sharply; in particular, the degree of cardiovascular risk following doses under 1 Sv. The study of Japanese atomic bomb survivors showed a dose response curve for heart disease that appeared essentially linear, although the authors believed the risk below ∼0.5 Gy was quite uncertain because of the substantial variability around the lower-dose part of the regression line and the finding that a dose response analysis for the range 0–0.5 Gy was not statistically significant (Shimizu et al. 2010). However, a recent meta-analysis by Little et al. (2012) of ischemic heart disease risk at primarily mean doses under ∼0.5 Gy reported that two out of eight studies showed statistically significant positive associations, and the combined meta-analysis showed a significant positive association [ERR at 1 Sv of 0.10 (95% CI 0.04, 0.15) taking into account heterogeneity in risk among studies]. The authors also reported a statistically significant association for cerebrovascular disease [ERR at 1 Sv of 0.21 (95% CI 0.02, 0.39) accounting for study-risk heterogeneity]. However, several caveats need to be mentioned: Even though mean doses were under 0.5 Sv for most studies, for several the dose-response data were driven by the subset of doses above 0.5 Sv; most were occupational studies and had no ability to determine whether smoking, obesity, or other risk factors may have been confounders. A variety of other LDPF studies for cardiovascular disease have been reported (McGale and Darby 2005, 2008; UNSCEAR 2008) that could not be included in the aforementioned meta-analysis, mainly because insufficient dose information was available to estimate risk per Sievert. A number of these are shown in Table 3. Most are null (negative), even though the average cumulative doses were considerable for some of them. So at this point, risks of circulatory disease after LDPF exposure probably should be regarded as in the fuzzy category.
LOW-DOSE RADIATION EXPOSURE AND CATARACT RISK
Most studies of cataract risk have used ophthalmological screening as their methodology; in such studies, the vast majority of positive findings are small opacities of limited clinical significance (Ainsbury et al. 2009; Shore et al. 2010). However, two recent studies of atomic bomb survivors have documented that both the prevalence and incidence of cataracts that required surgical removal are increased in relation to radiation dose at doses below 1 Gy (Neriishi et al. 2007, 2012). In the cataract incidence study, an estimated 32% (95% CI 9%, 53%) excess of cataract extractions was found at 1 Gy based on a linear dose response (Fig. 1). Though the nonlinear dose response term was not statistically significant, the best estimate of a dose threshold was at ∼0.5 Gy (95% CI 0.10 to 0.95 Gy). Based on these data and other supporting studies, the International Commission on Radiological Protection (ICRP) recently revised their estimate of the threshold dose for cataract induction downward from 5 Gy to 0.5 Gy for acute exposures (ICRP 2011). Hence, cataract risk for doses above ∼0.5 Gy is moving in the direction from fuzzy to certain, but for doses on the order of 0.2 Gy or below, the risk is fuzzy or unknown.
Of concern has been the ophthalmological risk for occupations where LDPF doses to the lens of the eye are considerable, especially medical specialists conducting interventional procedures under fluoroscopic guidance. A number of studies have been conducted of interventional cardiologists, catheterization laboratory personnel, radiologists, or radiologic technicians (Chodick et al. 2008; Kleiman et al. 2009; Milacic 2009; Ciraj-Bjelac et al. 2010, 2012; Vano et al. 2010, 2013; Mrena et al. 2011; Jacob et al. 2013). A summary of the results in Table 4 suggests there is occupational radiation cataract risk among interventional cardiologists and associated nurses/technicians, who receive the largest cumulative doses. However, those studies have been difficult to conduct and have potential sample selection biases, small sample sizes, and very uncertain dosimetry. The consistency in positive findings by the several medical worker studies that had substantial estimated cumulative doses but were below the previously ICRP-recommended dose threshold for cataract induction of 5 Gy of acute exposure suggests that a reduction in threshold dose was warranted.
The magnitude of radiation impacts on human health require fuller documentation, especially for low dose or low dose rate exposures. From the epidemiologic vantage point, that will require longer observation of existing irradiated cohorts and sometimes more accurate dose assessments. Additional studies of new cohorts also can be of value if the cohorts have characteristics to make them statistically informative:
* appropriate study designs and subject selection;
* a sufficient range of doses and a large enough cohort size to be able to detect risks;
* reasonably accurate individual dose information;
* an infrastructure that permits complete and accurate ascertainment of the diseases of interest;
* information on potential confounding or effect-modifying risk factors; and
* appropriate analyses and interpretations of the data.
Biosamples from subgroups of the irradiated cohorts could permit genomic, epigenetic, and functional biological assessments that provide a bridge to the many advances in experimental radiation biology and that also can be used to identify subsets of persons who are particularly susceptible to radiation-related cancer or other diseases.
To develop more clarity on cardiovascular disease risk from low-to-moderate radiation doses, current and future cohorts need to obtain information on other important exposures (e.g., smoking) and endogenous factors that might be confounding or effect-modifying variables. To improve our understanding of the biology of radiogenic cardiovascular disease, especially after whole-body exposures, more information is needed on the potential cardiovascular impact of damage to the liver, kidney, pituitary, and other organs, as well as to the microvasculature and endothelial tissue of the heart.
Regarding radiation-induced lens opacities from occupational or other LDPF radiation exposures, criteria for adequate and standardized lens photos would permit a uniform review of ophthalmological findings and increase comparability across studies. Current studies of cataract in interventional cardiologists and allied personnel have large intrinsic uncertainties in their retrospective dose estimates, even with the best dosimetric efforts (Jacob et al. 2013). Protocols for better dose information are needed to assure health protection of medical radiation workers and to provide more accurate future quantitative risk assessments. There currently is little information on the association of low-to-moderate radiation exposures with vision-impairing cataracts, which constitute the ocular health impact of greatest concern. Most studies have documented largely small, subclinical opacities; little is known from radiation studies about the frequency and rate with which those progress to vision-impairing cataracts.
In summary, there is much more to learn about the cancer risks from low-dose and low dose-rate exposures and about risks of cardiovascular and ophthalmologic diseases. To inform the radiation protection community regarding the impact of these health risks, there will be a need to give priority to epidemiologic studies that are carefully designed and conducted to address the issues, and to the parallel development of translational and radiobiological research to shed light on radiation-disease mechanisms and modifying factors.
The Radiation Effects Research Foundation (RERF), Hiroshima and Nagasaki, Japan, is a public interest foundation funded by the Japanese Ministry of Health, Labour and Welfare and the U.S. Department of Energy (DOE). The research was also funded in part through DOE award DE-HS0000031 to the National Academy of Sciences. This publication was supported by RERF Research Protocols RP1-75 and RP3-00. The views of the author do not necessarily reflect those of the two governments.
Ainsbury EA, Bouffler SD, Doerr W, Graw J, Muirhead CR, Edwards AA, Cooper J. Radiation cataractogenesis: a review of recent studies. Radiat Res 172: 1–9; 2009.
Aoyama T. Radiation risk of Japanese and Chinese low dose-repeatedly irradiated population. J Univ Occup Environ Health Jpn 11 (Suppl): 432–442; 1989.
Arrighi HM, Hertz-Picciotto I. The evolving concept of the healthy worker survivor effect. Epidemiol 5: 189–196; 1994.
Bartley K, Metayer C, Selvin S, Ducore J, Buffler P. Diagnostic x-rays and risk of childhood leukaemia. Int J Epidemiol 39: 1628–1637; 2010.
Bauer S, Gusev BI, Pivina LM, Apsalikov KN, Grosche B. Radiation exposure due to local fallout from Soviet atmospheric nuclear weapons testing in Kazakhstan: solid cancer mortality in the Semipalatinsk historical cohort, 1960–1999. Radiat Res 164: 409–419; 2005.
Berrington A, Darby SC, Weiss HA, Doll R. 100 years of observation on British radiologists: mortality from cancer and other causes 1897–1997. Br J Radiol 74: 507–519; 2001.
Boice JD, Morin M, Glass A, Friedman G, Stovall M, Hoover R, Fraumeni J. Diagnostic x-ray procedures and risk of leukemia, lymphoma, and multiple myeloma. J Am Med Assoc 265: 1290–1294; 1991.
Boice JD Jr, Cohen SS, Mumma MT, Ellis ED, Eckerman KF, Leggett RW, Boecker BB, Brill AB, Henderson BE. Updated mortality analysis of radiation workers at Rocketdyne (Atomics International), 1948–2008. Radiat Res 176: 244–258; 2011.
Cardis E, Vrijheid M, Blettner M, Gilbert E, Hakama M, Hill C, Howe G, Kaldor J, Muirhead CR, Schubauer-Berigan M, Yoshimura T, Bermann F, Cowper G, Fix J, Hacker C, Heinmiller B, Marshall M, Thierry-Chef I, Utterback D, Ahn Y-O, Amoros E, Ashmore P, Auvinen A, Bae J-M, Bernar J, Biau A, Combalot E, Deboodt P, Diez Sacristan A, Eklof M, Engels H, Engholm G, Gulis G, Habib RR, Holan K, Hyvonen H, Kerekes A, Kurtinaitis J, Malker H, Martuzzi M, Mastauskas A, Monnet A, Moser M, Pearce MS, Richardson DB, Rodriguez-Artalejo F, Rogel A, Tardy H, Telle-Lamberton M, Turai I, Usel M, Veress K. The 15-country collaborative study of cancer risk among radiation workers in the nuclear industry: estimates of radiation-related cancer risks. Radiat Res 167: 396–416; 2007.
Chodick G, Bekiroglu N, Hauptmann M, Alexander BH, Freedman DM, Doody MM, Cheung LC, Simon SL, Weinstock RM, Bouville A, Sigurdson AJ. Risk of cataract after exposure to low doses of radiation: a 20-year prospective cohort study among US radiologic technologists. Am J Epidemiol 168: 620–631; 2008.
Ciraj-Bjelac O, Rehani MM, Sim KH, Liew HB, Vano E, Kleiman NJ. Risk for radiation-induced cataract for staff in interventional cardiology: is there reason for concern? Catheter Cardiovasc Interv 76: 826–834; 2010.
Ciraj-Bjelac O, Rehani M, Minamoto A, Sim KH, Liew HB, Vano E. Radiation-induced eye lens changes and risk for cataract in interventional cardiology. Cardiol 123: 168–171; 2012.
Daniels RD, Schubauer-Berigan MK. A meta-analysis of leukaemia risk from protracted exposure to low-dose gamma radiation. Occup Environ Med 68: 457–464; 2011.
Davis F, Boice J, Hrubec Z, Monson R. Cancer mortality in a radiation-exposed cohort of Massachusetts. Cancer Res 49: 6130–6136; 1989.
Davis S, Day RW, Kopecky KJ, Mahoney MC, McCarthy PL, Michalek AM, Moysich KB, Onstad LE, Stepanenko VF, Voillequé PG, Chegerova T, Falkner K, Kulikov S, Maslova E, Ostapenko V, Rivkind N, Shevchuk V, Tsyb AF. Childhood leukaemia in Belarus, Russia and Ukraine following the Chernobyl power station accident: results from an international collaborative population-based case-control study. Int J Epidemiol 35: 386–396; 2006.
Gibson R, Graham S, Lilienfeld A, Schuman L, Dowd J, Levin M. Irradiation in the epidemiology of leukemia among adults. J Natl Cancer Inst 48: 301–311; 1972.
Goodman DM. Initiatives focus on limiting radiation exposure to patients during CT scans. J Am Med Assoc 309: 647–648; 2013.
Gunz FW, Atkinson H. Medical radiations and leukaemia: a retrospective survey. Br Med J 1: 389–393; 1964.
Hauptmann M, Mohan AK, Doody MM, Linet MS, Mabuchi K. Mortality from diseases of the circulatory system in radiologic technologists in the United States. Am J Epidemiol 157: 239–248; 2003.
Holm L. Cancer risks after diagnostic doses of 131
I with special reference to thyroid cancer. Cancer Detect Prev 15: 27–30; 1991.
Holm LE, Wiklund K, Lundell G, Bergman N, Bjelkengren G, Ericsson U, Cederquist E, Lidberg M, Lindberg R, Wicklund H, Boice J. Cancer risk in population examined with diagnostic doses of 131-I. J Natl Cancer Inst 81: 302–306; 1989.
Holm L, Hall P, Wiklund K, Lundell G, Berg G, Bjelkengren G, Cederquist E, Ericsson U, Hallquist A, Larsson L, Lidberg M, Lindberg S, Tennvall J, Wicklund H, Boice J. Cancer risk after iodine-131 therapy for hyperthyroidism. J Natl Cancer Inst 83: 1072–1077; 1991.
International Commission on Radiological Protection. Statement on tissue reactions [online]. ICRP ref 4825-3093-1464; 2011. Available at www.icrp.org/page.asp?id=123
. Accessed 24 May 2013.
Infante-Rivard C. Diagnostic x rays, DNA repair genes and childhood acute lymphoblastic leukemia. Health Phys 85: 60–64; 2003.
Ivanov VK. Late cancer and noncancer risks among Chernobyl emergency workers of Russia. Health Phys 93: 470–479; 2007.
Jacob P, Ruhm W, Walsh L, Blettner M, Hammer G, Zeeb H. Cancer risk of radiation workers larger than expected? Occup Environ Med 66: 789–796; 2009.
Jacob S, Boveda S, Bar O, Brézin A, Maccia C, Laurier D, Bernier M-O. Interventional cardiologists and risk of radiation-induced cataract: results of a French multicenter observational study. Int J Cardiol 167: 1843–1847; 2013. doi:10.1016/j.ijcard.2012.04.124.
Jacob S, Donadille L, Maccia C, Bar O, Boveda S, Laurier D, Bernier M-O. Eye lens radiation exposure to interventional cardiologists: a retrospective assessment of cumulative doses. Radiat Protect Dosim 153: 282–298; 2013.
Kendall GM, Little MP, Wakeford R, Bunch KJ, Miles JCH, Vincent TJ, Meara JR, Murphy MFG. A record-based case-control study of natural background radiation and the incidence of childhood leukaemia and other cancers in Great Britain during 1980–2006. Leukemia 27: 3–9; 2013.
Kleiman NJ, Cabrera M, Duran G, Ramirez R, Duran A, Vano E. Occupational risk of radiation cataract in interventional cardiology. Invest Ophthalmol Vis Sci 49 (Suppl): 511; 2009.
Krestinina L, Preston DL, Davis FG, Epifanova S, Ostroumova E, Ron E, Akleyev A. Leukemia incidence among people exposed to chronic radiation from the contaminated Techa River, 1953–2005. Radiat Environ Biophys 49: 195–201; 2010.
Krestinina LY, Epifanova S, Silkin S, Mikryukova L, Degteva M, Shagina N, Akleyev A. Chronic low-dose exposure in the Techa River Cohort: risk of mortality from circulatory diseases. Radiat Environ Biophys 52: 47–57; 2013.
Kreuzer M, Dufey F, Sogl M, Schnelzer M, Walsh L. External gamma radiation and mortality from cardiovascular diseases in the German WISMUT uranium miners cohort study, 1946–2008. Radiat Environ Biophys 52: 37–46; 2013.
Little MP, Azizova TV, Bazyka D, Bouffler SD, Cardis E, Chekin S, Chumak VV, Cucinotta FA, de Vathaire F, Hall P, Harrison JDG, G Ivanov V, Kashcheev VV, Klymenko SV, Kreuzer M, Laurent O, Ozasa K, Schneider T, Tapio S, Taylor AM, Tzoulaki I, Vandoolaeghe WL, Wakeford R, Zablotska L, Zhang W, Lipshultz SE . Systematic review and meta-analysis of circulatory disease from exposure to low-level ionizing radiation and estimates of potential population mortality risks. Environ Health Perspect 120: 1503–1511; 2012.
Logue JN, Barrick M, Jessup G. Mortality of radiologists and pathologists in the radiation registry of physicians. J Occup Med 28: 91–99; 1986.
Matanoski GM. Health effects of low-level radiation in shipyard workers. Baltimore, MD: Johns Hopkins University; Final Report, DOE Contract: DE-AC02-79EV10095; 1991.
Matanoski GM, Sartwell P, Elliott E, Tonascia J, Sternberg A. Cancer risks in radiologists and radiation workers. In: Boice J, Fraumeni J, eds. Radiation carcinogenesis: epidemiology and biological significance. New York: Raven Press; 1984: 83–96.
Matanoski GM, Sternberg A, Elliott E. Does radiation exposure produce a protective effect among radiologists? Health Phys 52: 637–643; 1987.
Mathews JD, Forsythe AV, Brady Z, Butler MW, Goergen SK, Byrnes GB, Giles GG, Wallace AB, Anderson PR, Guiver TA, McGale P, Cain TM, Dowty JG, Bickerstaffe AC, Darby SC. Cancer risk in 680,000 people exposed to computed tomography scans in childhood or adolescence: data linkage study of 11 million Australians. Br Med J 346: 2360; 2013.
McGale P, Darby SC. Low doses of ionizing radiation and circulatory diseases: a systematic review of the published epidemiological evidence. Radiat Res 163: 247–257; 2005.
McGale P, Darby SC. Commentary: a dose-response relationship for radiation-induced heart disease—current issues and future prospects. Int J Epidemiol 37: 518–523; 2008.
Meinert R, Kaletsch U, Kaatsch P, Schuz J, Michaelis J. Associations between childhood cancer and ionizing radiation. Results of a population-based case-control study in Germany. Cancer Epidemiol Biomark Prev 8: 793–799; 1999.
Metz-Flamant C, Samson E, Caer-Lorho S, Acker A, Laurier D. Solid cancer mortality associated with chronic external radiation exposure at the French Atomic Energy Commission and Nuclear Fuel Company. Radiat Res 176: 115–127; 2011.
Milacic S. Risk of occupational radiation-induced cataract in medical workers. Med Lav 100: 178–186; 2009.
Mrena S, Kivela T, Kurttio P, Auvinen A. Lens opacities among physicians occupationally exposed to ionizing radiation—a pilot study in Finland. Scand J Work Environ Health 37: 237–243; 2011.
Muirhead CR, O’Hagan JA, Haylock RGE, Phillipson MA, Willcock T, Berridge GLC, Zhang W. Mortality and cancer incidence following occupational radiation exposure: third analysis of the National Registry for Radiation Workers. Br J Cancer 100: 206–212; 2009.
Nair RRK, Rajan B, Akiba S, Jayalekshmi P, Nair MK, Gangadharan P, Koga T, Morishima H, Nakamura S, Sugahara T. Background radiation and cancer incidence in Kerala, India—Karunagappally cohort study. Health Phys 96: 55–66; 2009.
NCRP. Uncertainties in the estimation of radiation risks and probability of disease causation. Bethesda, MD: National Council on Radiation Protection and Measurements; Report No. 171; 2012.
Neriishi K, Nakashima E, Minamoto A, Fujiwara S, Akahoshi M, Mishima HK, Kitaoka T, Shore RE. Postoperative cataract cases among atomic bomb survivors: radiation dose response and threshold. Radiat Res 168: 404–408; 2007.
Neriishi K, Nakashima E, Akahoshi MH, A Grant EJ, Masunari N, Funamoto S, Minamoto A, Fujiwara S, Shore RE . Radiation dose and cataract surgery incidence in atomic-bomb survivors, 1986–2005. Radiol 265: 167–174; 2012.
Ozasa K, Shimizu Y, Suyama A, Kasagi F, Soda M, Grant EJ, Sakata R, Sugiyama H, Kodama K. Studies of the mortality of atomic bomb survivors, Report 14, 1950–2003: an overview of cancer and noncancer diseases. Radiat Res 177: 229–243; 2012.
Pearce MS, Salotti JA, Little MP, McHugh K, Lee C, Kim KP, Howe NL, Ronckers CM, Rajaraman P, Craft AW, Parker L, Berrington de Gonzalez A. Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. Lancet 380: 499–505; 2012.
Pogoda JM, Nichols PWR, R K Stram DO, Thomas DC, Preston-Martin S. Diagnostic radiography and adult acute myeloid leukemia: an interview and medical chart review study. Br J Cancer 104: 1482–1486; 2011.
Preston-Martin S, Thomas D, Yu M, Henderson B. Diagnostic radiography as a risk factor for chronic myeloid and monocytic leukaemia (CML). Br J Cancer 59: 639–644; 1989.
Preston DL, Ron E, Tokuoka S, Funamoto S, Nishi N, Soda M, Mabuchi K, Kodama K. Solid cancer incidence in atomic bomb survivors: 1958–1998. Radiat Res 168: 1–64; 2007.
Rajaraman P, Simpson J, Neta G, Berrington de Gonzalez A, Ansell P, Linet MS, Ron E, Roman E. Early life exposure to diagnostic radiation and ultrasound scans and risk of childhood cancer: case-control study. Br Med J 342: d472; 2011.
Richardson DB, Wing S, Wolf S. Mortality among workers at the Savannah River Site. Am J Indust Med 50: 881–891; 2007.
Romanenko AY, Finch SC, Hatch M, Lubin JH, Bebeshko VG, Bazyka DA, Gudzenko ND, I S Reiss RF, Bouville A, Chumak VV, Trotsiuk NK, Babkina NG, Belyayev YM I, Ron E, Howe GR, Zablotska LB. The Ukrainian-American study of leukemia and related disorders among Chornobyl cleanup workers from Ukraine: III. Radiation risks. Radiat Res 170: 711–720; 2008.
Ron E, Doody MM, Becker DV, Brill A, Curtis R, Goldman M, Harris B, Hoffman D, McConahey W, Maxon H, Preston-Martin S, Warshauer E, Wong F, Boice J. Cancer mortality following treatment for adult hyperthyroidism. J Am Med Assoc 280: 347–355; 1998.
Schonfeld SJ, Krestinina LY, Epifanova S, Degteva MO, Akleyev AV, Preston DL. Solid cancer mortality in the Techa River cohort (1950–2007). Radiat Res 179: 183–189; 2013.
Schubauer-Berigan MK, Daniels RD, Fleming DA, Markey AM, Couch JR, Ahrenholz SH, Burphy JS, Anderson JL, Tseng C-Y. Risk of chronic myeloid and acute leukemia mortality after exposure to ionizing radiation among workers at four U.S. nuclear weapons facilities and a nuclear naval shipyard. Radiat Res 167: 222–232; 2007.
Shilnikova NS, Preston DL, Ron E, Gilbert ES, Vassilenko EK, Romanov SA, Kuznetsova IS, Sokolnikov ME, Okatenko PV, Kreslov VV, Koshurnikova NA. Cancer mortality risk among workers at the Mayak nuclear complex. Radiat Res 159: 787–798; 2003.
Shimizu Y, Kodama K, Nishi N, Kasagi F, Suyama A, Soda M, Grant EJ, Sugiyama H, Sakata R, Moriwaki H, Hayashi M, Konda M, Shore RE. Radiation exposure and circulatory disease risk: Hiroshima and Nagasaki atomic bomb survivor data, 1950–2003. Br Med J 340: b5349; 2010.
Shore RE, Neriishi K, Nakashima E. Epidemiologic studies of cataract risk at low-to-moderate radiation doses: (not) seeing is believing. Radiat Res 174: 889–894; 2010.
Shu XO, Potter JD, Linet MS, Severson RK, Han DH, Kersey JH, Neglia JP, Trigg ME, Robison LL. Diagnostic x-rays and ultrasound exposure and risk of childhood acute lymphoblastic leukemia by immunophenotype. Cancer Epidemiol Biomark Prev 11: 177–185; 2002.
Sodickson A, Baeyens PF, Andriole KP, Prevedello LM, Nawfel RD, Hanson R, Khorasani R. Recurrent CT, cumulative radiation exposure, and associated radiation-induced cancer risks from CT of adults. Radiol 251: 175–184; 2009.
Stewart A, Pennybacker W, Barber R. Adult leukaemias and diagnostic x-rays. Br Med J 2: 882–890; 1962.
Tao Z, Akiba S, Zha Y, Sun Q, Zou J, Li J, Liu Y, Yuan Y, Tokonami S, Morishima H, Koga T, Nakamura S, Sugahara T, Wei L. Cancer and non-cancer mortality among inhabitants in the high background radiation area of Yangjiang, China (1979–1998). Health Phys 102: 173–181; 2012.
UNSCEAR. Annex B: epidemiological evaluation of cardiovascular disease and other non-cancer diseases. In: UNSCEAR 2006 report to the general assembly, with scientific annexes. New York: United Nations; 2008: 325–383.
Vano E, Kleiman NJ, Duran A, Rehani MM, Echeverri D, Cabrera M. Radiation cataract risk in interventional cardiology personnel. Radiat Res 174: 490–495; 2010.
Vano E, Kleiman NJ, Duran A, Romano-Miller M, Rehani MM. Radiation-associated lens opacities in catheterization personnel: results of a survey and direct assessments. J Vasc Interv Radiol 24: 197–204; 2013.
Wakeford R. Childhood leukaemia following medical diagnostic exposure to ionizing radiation in utero or after birth. Radiat Protect Dosim 132: 166–174; 2008.
Wang JX, Zhang LA, Li BX, Zhao YC, Wang ZQ, Zhang JY, Aoyama T. Cancer incidence and risk estimation among medical x-ray workers in China, 1950–1995. Health Phys 82: 455–466; 2002.
Wiggs LD, Johnson E, Cox-DeVore C, Voelz G. Mortality through 1990 among white male workers at the Los Alamos National Laboratory: considering exposures to plutonium and external ionizing radiation. Health Phys 67: 577–588; 1994.
Wing S, Richardson DB. Age at exposure to ionising radiation and cancer mortality among Hanford workers: follow up through 1994. Occup Environ Med 62: 465–472; 2005.
Yuasa H, Hamajima N, Ueda R, Ohno R, Asou N, Utsunomiya A, Ogura M, Takigawa N, Ueda T, Hiraoka A, Matsuda S, Kuraishi Y, Nishikawa K, Uike N, Takeshita A, Takemoto Y, Shimazaki C, Sakamaki H, Ino T, Matsushima T, Kuriyama K, Hirai H, Naoe T, Tsubaki K, Takahashi M, Takeyama K, Morishima Y, Itoh K, Omoto E, Hodohara K, Takahashi I. Case-control study of leukemia and diagnostic radiation exposure. Int J Hematol 65: 251–261; 1997.
Zaridze D, Li N, Men T, Duffy S. Childhood cancer incidence in relation to distance from the former nuclear testing site in Semipalatinsk, Kazakhstan. Int J Cancer 59: 471–475; 1994.
Zielinski JM, Garner MJ, Band PR, Krewshi D, Shilnikova NS, Jiang H, Ashmore JP, Sont WN, Fair ME, Letourneau EG, Semenciw R. Health outcomes of low-dose ionizing radiation exposure among medical workers: a cohort study of the Canadian National Dose Registry of Radiation Workers. Int J Occup Med Environ Health 22: 149–156; 2009.
cancer; dose, low; health effects; National Council on Radiation Protection and Measurements
Supplemental Digital Content
© 2014 by the Health Physics Society
Highlight selected keywords in the article text.