Thyroid cancer after exposure to external radiation: a pooled analysis of seven studies

The thyroid gland of children is especially vulnerable to the carcinogenic action of ionizing radiation. To provide insights into various modifying influences on risk, seven major studies with organ doses to individual subjects were evaluated. Five cohort studies (atomic bomb survivors, children treated for tinea capitis, two studies of children irradiated for enlarged tonsils, and infants irradiated for an enlarged thymus gland) and two case-control studies (patients with cervical cancer and childhood cancer) were studied. The combined studies include almost 120,000 people (approximately 58,000 exposed to a wide range of doses and 61,000 nonexposed subjects), nearly 700 thyroid cancers and 3,000,000 person years of follow-up. For persons exposed to radiation before age 15 years, linearity best described the dose response, even down to 0.10 Gy. At the highest doses (>10 Gy), associated with cancer therapy, there appeared to be a decrease or leveling of risk. For childhood exposures, the pooled excess relative risk per Gy (ERR/Gy) was 7.7 (95% CI = 2.1, 28.7) and the excess absolute risk per 10(4) PY Gy (EAR/10(4) PY Gy) was 4.4 (95% CI = 1.9, 10.1). The attributable risk percent (AR%) at 1 Gy was 88%. However, these summary estimates were affected strongly by age at exposure even within this limited age range. The ERR was greater (P = 0.07) for females than males, but the findings from the individual studies were not consistent. The EAR was higher among women, reflecting their higher rate of naturally occurring thyroid cancer. The distribution of ERR over time followed neither a simple multiplicative nor an additive pattern in relation to background occurrence. Only two cases were seen within 5 years of exposure. The ERR began to decline about 30 years after exposure but was still elevated at 40 years. Risk also decreased significantly with increasing age at exposure, with little risk apparent after age 20 years. Based on limited data, there was a suggestion that spreading dose over time (from a few days to >1 year) may lower risk, possibly due to the opportunity for cellular repair mechanisms to operate. The thyroid gland in children has one of the highest risk coefficients of any organ and is the only tissue with convincing evidence for risk at about 0.10 Gy.     

Thyroid cancer risk in areas of Ukraine and Belarus affected by the Chernobyl accident

The purpose of the present study was to analyze the thyroid cancer incidence risk after the Chernobyl accident and its degree of dependence on time and age. Data were analyzed for 1034 settlements in Ukraine and Belarus, in which more than 10 measurements of the (131)I content in human thyroids had been performed in May/June 1986. Thyroid doses due to the Chernobyl accident were assessed for the birth years 1968-1985 and related to thyroid cancers that were surgically removed during the period 1990-2001. The central estimate for the linear coefficient of the EAR dose response was 2.66 (95% CI: 2.19; 3.13) cases per 10(4) PY-Gy; for the quadratic coefficient, it was -0.145 (95% CI: -0.171; -0.119) cases per 10(4) PY-Gy(2). The EAR was found to be higher for females than for males by a factor of 1.4. It decreased with age at exposure and increased with age attained. The central estimate for the linear coefficient of the ERR dose response was 18.9 (95% CI: 11.1; 26.7) Gy(-1); for the quadratic coefficient, it was -1.03 (95% CI: -1.46; -0.60) Gy(-2). The ERR was found to be smaller for females than for males by a factor of 3.8 and decreased strongly with age at exposure. Both EAR and ERR were higher in the Belarusian settlements than in the Ukrainian settlements. In contrast to ERR, EAR increases with time after exposure. At the end of the observation period, excess risk estimates were found to be close to those observed in a major pooled analysis of seven studies of childhood thyroid cancer after external exposures.     

Long-term follow-up for brain tumor development after childhood exposure to ionizing radiation for tinea capitis

Ionizing radiation is an established risk factor for brain tumors, yet quantitative information on the long-term risk of different types of brain tumors is sparse. Our aims were to assess the risk of radiation-induced malignant brain tumors and benign meningiomas after childhood exposure and to investigate the role of potential modifiers of that risk. The study population included 10,834 individuals who were treated for tinea capitis with X rays in the 1950s and two matched nonirradiated groups, comprising population and sibling comparison groups. The mean estimated radiation dose to the brain was 1.5 Gy. Survival analysis using Poisson regression was performed to estimate the excess relative and absolute risks (ERR, EAR) for brain tumors. After a median follow-up of 40 years, an ERR/Gy of 4.63 and 1.98 (95% CI = 2.43-9.12 and 0.73-4.69) and an EAR/Gy per 10(4) PY of 0.48 and 0.31 (95% CI = 0.28-0.73 and 0.12-0.53) were observed for benign meningiomas and malignant brain tumors, respectively. The risk of both types of tumors was positively associated with dose. The estimated ERR/Gy for malignant brain tumors decreased with increasing age at irradiation from 3.56 to 0.47 (P = 0.037), while no trend with age was seen for benign meningiomas. The ERR for both types of tumor remains elevated at 30-plus years after exposure.     

Analysis of solid cancer mortality in the techa river cohort using the two-step clonal expansion model

In this study the solid cancer mortality data in the Techa River Cohort in the Southern Urals region of Russia was analyzed. The cohort received protracted exposure in the 1950s due to the releases of radioactive materials from the Mayak plutonium complex. The Extended Techa River Cohort includes 29,849 people who resided along the Techa River between 1950 and 1960 and were followed from January 1, 1950 through December 31, 1999. The analysis was done within the framework of the biologically based two-stage clonal expansion (TSCE) model. It was found that about 2.6% of the 1854 solid cancer deaths (excluding 18 bone cancer cases) could be related to radiation exposure. At age 63, which is the mean age for solid cancer deaths, the excess relative risk (ERR) and excess absolute risk (EAR) were found to be 0.76 Gy(-1) (95% CI 0.23; 1.29) and 33.0 (10(4) PY Gy)(-1) (95% CI 9.8; 52.6), respectively. These risk estimates are consistent with earlier excess relative risk analyses for the same cohort. The change in the ERR with age was investigated in detail, and an increase in risk with attained age was observed. Furthermore, the data were tested for possible signs of genomic instability, and it was found that the data could be described equally well by a model incorporating effects of genomic instability. Results from the TSCE models indicated that radiation received at older ages might have stronger biological effects than exposure at younger ages.     

Risk of second primary thyroid cancer after radiotherapy for a childhood cancer in a large cohort study: an update from the childhood cancer survivor study

Previous studies have indicated that thyroid cancer risk after a first childhood malignancy is curvilinear with radiation dose, increasing at low to moderate doses and decreasing at high doses. Understanding factors that modify the radiation dose response over the entire therapeutic dose range is challenging and requires large numbers of subjects. We quantified the long-term risk of thyroid cancer associated with radiation treatment among 12,547 5-year survivors of a childhood cancer (leukemia, Hodgkin lymphoma and non-Hodgkin lymphoma, central nervous system cancer, soft tissue sarcoma, kidney cancer, bone cancer, neuroblastoma) diagnosed between 1970 and 1986 in the Childhood Cancer Survivor Study using the most current cohort follow-up to 2005. There were 119 subsequent pathologically confirmed thyroid cancer cases, and individual radiation doses to the thyroid gland were estimated for the entire cohort. This cohort study builds on the previous case-control study in this population (69 thyroid cancer cases with follow-up to 2000) by allowing the evaluation of both relative and absolute risks. Poisson regression analyses were used to calculate standardized incidence ratios (SIR), excess relative risks (ERR) and excess absolute risks (EAR) of thyroid cancer associated with radiation dose. Other factors such as sex, type of first cancer, attained age, age at exposure to radiation, time since exposure to radiation, and chemotherapy (yes/no) were assessed for their effect on the linear and exponential quadratic terms describing the dose-response relationship. Similar to the previous analysis, thyroid cancer risk increased linearly with radiation dose up to approximately 20 Gy, where the relative risk peaked at 14.6-fold (95% CI, 6.8-31.5). At thyroid radiation doses >20 Gy, a downturn in the dose-response relationship was observed. The ERR model that best fit the data was linear-exponential quadratic. We found that age at exposure modified the ERR linear dose term (higher radiation risk with younger age) (P < 0.001) and that sex (higher radiation risk among females) (P = 0.008) and time since exposure (higher radiation risk with longer time) (P < 0.001) modified the EAR linear dose term. None of these factors modified the exponential quadratic (high dose) term. Sex, age at exposure and time since exposure were found to be significant modifiers of the radiation-related risk of thyroid cancer and as such are important factors to account for in clinical follow-up and thyroid cancer risk estimation among childhood cancer survivors.     

Mortality among the liquidators of the Chernobyl accident: dose dependences and groups of the potential risk

Dynamics of the mortality and the mortality radiation risks among male emergency workers of 1986-1987 years of entrance to the Chernobyl zone is analyzed. The average dose of external gamma-exposure for this cohort equals 128 mGy. The size of the cohort at the beginning of the follow-up in 1992 was 47820 persons. For the follow-up period 1992-2006 statistically significant radiation risks of death rates have been estimated: for the mortality from all causes, the excess relative risk per Gy (ERR/Gy) equals 0.42 with 95% confidence interval (95% CI) (0.14-0.72); for the mortality from solid cancers ERR/Gy = 0.74, 95% CI (0.03-1.76); and for the mortality from the circulatory system diseases ERR/Gy = 1.01, 95% CI (0.51-1.57). Based on these estimates the risk groups were ranked among all Russian emergency workers (160 thousand persons): the group of the potential radiation risk with doses more than 150 mGy (33488 persons) and the group of the high radiation risk with doses more than 240 mGy (6054 persons).     

Lung cancer risk of Mayak workers: modelling of carcinogenesis and bystander effect

Lung cancer mortality in the period of 1948-2002 has been analysed for 6,293 male workers of the Mayak Production Association, for whose information on smoking, annual external doses and annual lung doses due to plutonium exposures was available. Individual likelihoods were maximized for the two-stage clonal expansion (TSCE) model of carcinogenesis and for an empirical risk model. Possible detrimental and protective bystander effects on mutation and malignant transformation rates were taken into account in the TSCE model. Criteria for non-nested models were used to evaluate the quality of fit. Data were found to be incompatible with the model including a detrimental bystander effect. The model with a protective bystander effect did not improve the quality of fit over models without a bystander effect. The preferred TSCE model was sub-multiplicative in the risks due to smoking and internal radiation, and more than additive. Smoking contributed 57% to the lung cancer deaths, the interaction of smoking and radiation 27%, radiation 10%, and others cause 6%. An assessment of the relative biological effectiveness of plutonium was consistent with the ICRP recommended value of 20. At age 60 years, the excess relative risk (ERR) per lung dose was 0.20 (95% CI: 0.13; 0.40) Sv(-1), while the excess absolute risk (EAR) per lung dose was 3.2 (2.0; 6.2) per 10(4) PY Sv. With increasing age attained the ERR decreased and the EAR increased. In contrast to the atomic bomb survivors, a significant elevated lung cancer risk was also found for age attained younger than 55 years. For cumulative lung doses below 5 Sv, the excess risk depended linearly on dose. The excess relative risk was significantly lower in the TSCE model for ages attained younger than 55 than that in the empirical model. This reflects a model uncertainty in the results, which is not expressed by the standard statistical uncertainty bands.     

The radiation risks of cerebrovascular diseases among the liquidators

The work concerns the assessment of radiation risks for non-cancer diseases of circulatory system among the Chernobyl liquidators. The medical and dosimetric data from Russian National Medical and Dosimetric Registry were used. The cohort data from 1986 to 2000 years of 61017 liquidators are discussed. Radiation risks are established for the cerebrovascular diseases and for the essential hypertension the significant. ERR =0.45/Gy, with 95% CI = (0.11; 0.80) for the cerebrovascular diseases and ERR = 0.36/Gy, with 95% CI = (0.005; 0.71) for the essential hypertension. It approves the results which were established by authors for the similar cohort in 1986-1996. The cerebrovascular diseases (CVD) are considered in greater details. The significant heterogeneity of the radiation risks by working time in Chernobyl zone is shown for the first time. ERR = 0.89/Gy for the working time less then 6 weeks, and ERR = 0.39/Gy in average for all periods of working in the zone. Among the liquidators entered Chernobyl zone during the first year after the accident (29003 liquidators), the CVD's risk group consists of persons accumulated more then 150 mGy from external sources in less, then 6 weeks (RR = 1.18 with 95% CI = (1.00; 1.40)). The significant CVD's risk from averaged dose rate was defined for external doses greater then 150 mGy (ERR for 100 mGy/day = 2.17, with 95% CI = (0.64; 3.69)).     

Cancer mortality following in utero exposure among offspring of female mayak worker cohort members

Little is known about long-term cancer risks following in utero radiation exposure. We evaluated the association between in utero radiation exposure and risk of solid cancer and leukemia mortality among 8,000 offspring, born from 1948-1988, of female workers at the Mayak Nuclear Facility in Ozyorsk, Russia. Mother's cumulative gamma radiation uterine dose during pregnancy served as a surrogate for fetal dose. We used Poisson regression methods to estimate relative risks (RRs) and 95% confidence intervals (CIs) of solid cancer and leukemia mortality associated with in utero radiation exposure and to quantify excess relative risks (ERRs) as a function of dose. Using currently available dosimetry information, 3,226 (40%) offspring were exposed in utero (mean dose = 54.5 mGy). Based on 75 deaths from solid cancers (28 exposed) and 12 (6 exposed) deaths from leukemia, in utero exposure status was not significantly associated with solid cancer: RR = 0.94, 95% CI 0.58 to 1.49; ERR/Gy = -0.1 (95% CI < -0.1 to 4.1), or leukemia mortality; RR = 1.65, 95% CI 0.52 to 5.27; ERR/Gy = -0.8 (95% CI < -0.8 to 46.9). These initial results provide no evidence that low-dose gamma in utero radiation exposure increases solid cancer or leukemia mortality risk, but the data are not inconsistent with such an increase. As the offspring cohort is relatively young, subsequent analyses based on larger case numbers are expected to provide more precise estimates of adult cancer mortality risk following in utero exposure to ionizing radiation.     

Cancer morbidity and mortality among the liquidators of the Chernobyl accident: estimation of radiation risks

The work focuses on the results of the analysis of the cancer incidence among the Chernobyl emergency workers residing in Russia during 1991-2001. The analysis is based on the data for the cohort of male emergency workers from 6 regions of Russia including 55718 persons with documented external radiation doses in the range of 0.001-0.3 Gy who worked within the 30-km zone in 1986-1987. The mean age at exposure for these persons was 34.8 years old and the mean external radiation dose 0.13 Gy. In this cohort 1370 cases of solid cancer were diagnosed. Three follow-up periods were considered: 1991-1995, 1996-2001 and 1991-2001. The second follow-up period was chosen to allow for a minimum latency period of 10 years. Risk assessments were performed for two control groups: the first control group ("external") represented incidence rates for corresponding ages in Russia in general and the second control group ("internal") consisted of emergency workers. The estimated standardized incidence ratio (SIR) is in good agreement with that of the control within 95% CI. The values of the excess relative risk per unit dose 1 Gy (ERR/Gy) for solid malignant neoplasms have been estimated to be 0.33 (95% CI: -0.39, 1.22) (internal control) for the follow-up period 1991-2001 and 0.19 (95% CI: -0.66, 1.27) for 1996-2001. The analysis of cancer morbidity was carried out for the cohort of 29003 emergency workers who took part in liquidation of the consequences of the Chernobyl accident from 26 April 1986 to 25 April 1987. It was shown that the excess relative risk of cancer deaths per unit dose 1 Sv (ERR/Sv) is equal to 1.52 (95% CI: 0.20, 2.85).     

Dose-response relationship for parathyroid adenoma after exposure to ionizing radiation in infancy

Several authors have suggested that there is an excess risk of hyperparathyroidism, adenomas or hyperplasia after exposure to ionizing radiation. There is still, however, some uncertainty about this association, because these diseases are often asymptomatic and escape clinical detection if not specially searched for. This study is based on a pooled Swedish cohort of 27,925 persons with skin hemangiomas. The majority received radiation treatment in infancy between 1920 and 1965 in Stockholm and Gothenburg. The mean age at treatment was 6 months and the median thyroid dose was 0.20 Gy (range 0-28.5 Gy). Record linkage with the Swedish Cancer Register for the period 1958-1997 gave 43 cases of parathyroid adenoma in the cohort. Analyses of excess relative risk (ERR) models were performed using Poisson regression methods. Clinical records were scrutinized to determine if the childhood radiation exposure was known (biased cases) at the time of diagnosis. Seven of the cases of parathyroid adenoma were classified as biased cases. The standardized incidence ratio (SIR) was 2.10 (95% confidence interval 1.52-2.82) when all cases were included and 1.76 (95% CI 1.23-2.43) with the biased cases excluded. A linear dose-response model with stratification for sex fitted the data best. The ERR per gray was 3.84 (95% CI 1.56-8.99) with all cases and 1.56 (95% CI 0.36-4.45) with the biased cases excluded. There was a significant difference in the ERR per gray between the two subcohorts, probably because of different diagnostic activity in the regions. Our findings confirm that there is a dose-response relationship for radiation-induced parathyroid adenomas.     

Effects of radiation and lifestyle factors on risks of urothelial carcinoma in the Life Span Study of atomic bomb survivors

Among the Life Span Study (LSS) of Atomic-bomb survivors, recent estimates showed that unspecified bladder cancer had high radiation sensitivity with a notably high female-to-male excess relative risk (ERR) per radiation dose ratio and were the only sites for which the ERR did not decrease with attained age. These findings, however, did not consider lifestyle factors, which could potentially confound or modify the risk estimates. This study estimated the radiation risks of the most prevalent subtype of urinary tract cancer, urothelial carcinoma, while accounting for smoking, consumption of fruit, vegetables, alcohol and level of education (a surrogate for socioeconomic status). Eligible study subjects included 105,402 (males = 42,890) LSS members who were cancer-free in 1958 and had estimated radiation doses. Members were censored due to loss of follow-up, incident cancer of another type, death, or the end of calendar year 2001. Surveys (by mail or clinical interview) gathered lifestyle data periodically for 1963-1991. There were 63,827 participants in one or more survey. Five hundred seventy-three incident urothelial carcinoma cases occurred, of which 364 occurred after lifestyle information was available. Analyses were performed using Poisson regression methods. The excess relative risk per weighted gray unit (the gamma component plus 10 times the neutron component, Gy(w)) was 1.00 (95% CI: 0.43-1.78) but the risks were not dependent upon age at exposure or attained age. Lifestyle factors other than smoking were not associated with urothelial carcinoma risk. Neither the magnitude of the radiation ERR estimate (1.00 compared to 0.96), nor the female-to-male (F:M) ERR/Gy(w) ratio (3.2 compared to 3.4) were greatly changed after accounting for all lifestyle factors. A multiplicative model of gender-specific radiation and smoking effects was the most revealing though there was no evidence of significant departures from either the additive or multiplicative joint effect models. Among the LSS cohort members with doses greater than 0.005 Gy(w) (average dose 0.21 Gy(w)), the attributable fraction of urothelial carcinoma due to radiation was 7.1% in males and 19.7% in females. Among current smokers, the attributable fraction of urothelial carcinoma due to smoking was 61% in males and 52% in females. Relative risk estimates of smoking risk were approximately two for smokers compared to nonsmokers. After adjustment for lifestyle factors, gender-specific radiation risks and the F:M ERR/Gy(w), the ratios of excess urothelial carcinoma risk were similar to the estimates without adjusting for lifestyle factors. Smoking was the primary factor responsible for excess urothelial carcinoma in this cohort. These findings led us to conclude that the radiation risk estimates of urothelial carcinoma do not appear to be strongly confounded or modified by smoking, consumption of alcohol, fruits, or vegetables, or level of education.     

Projection of cancer risks from the Japanese atomic bomb survivors to the England and Wales population taking into account uncertainty in risk parameters

Generalized relative risk models, with adjustments to the relative risk for time after exposure and age at exposure and incorporating a linear-quadratic dose response, were fitted to the latest (Life Span Study Report 12) Japanese atomic bomb survivor cancer mortality data using Bayesian Markov Chain Monte Carlo methods, taking account of random errors in the DS86 dose estimates. The resulting uncertainty distributions in the relative risk model parameters were used to derive uncertainties in population cancer risks for a current UK population. Following an assumed administered dose of 1 Sv, leukaemia mortality risks were estimated to be 1.93×10^–2 Sv^–1 (95% CI 1.14, 3.38), or 0.44 years of life lost Sv^–1 (95% CI 0.22, 0.94). Following an assumed administered dose of 1 Sv, solid cancer mortality risks were calculated to be 10.36×10^–2 Sv^–1 (95% CI 8.41, 12.42), or 1.38 years of life lost Sv^–1 (95% CI 1.11, 1.68). In general, solid cancer risks were very similar to those predicted by classical likelihood-based methods; however, leukaemia risks were somewhat higher, by 10–35%, than those predicted by classical likelihood-based methods. This is so in both cases, irrespective of whether or not adjustments are made in these likelihood-based fits for the effects of measurement errors, and the discrepancy for leukaemia tends to be greater at higher doses. Overall, cancer risks predicted by Bayesian Markov Chain Monte Carlo methods are similar to those derived by classical likelihood-based methods and which form the basis of established estimates of radiation-induced cancer risk. Received: 28 September 1999 / Accepted: 21 August 2000     

Solid cancer incidence in atomic bomb survivors: 1958-1998

This is the second general report on radiation effects on the incidence of solid cancers (cancers other than malignancies of the blood or blood-forming organs) among members of the Life Span Study (LSS) cohort of Hiroshima and Nagasaki atomic bomb survivors. The analyses were based on 17,448 first primary cancers (including non-melanoma skin cancer) diagnosed from 1958 through 1998 among 105,427 cohort members with individual dose estimates who were alive and not known to have had cancer prior to 1958. Radiation-associated relative risks and excess rates were considered for all solid cancers as a group, for 19 specific cancer sites or groups of sites, and for five histology groups. Poisson regression methods were used to investigate the magnitude of the radiation-associated risks, the shape of the dose response, how these risks vary with gender, age at exposure, and attained age, and the evidence for inter-site variation in the levels and patterns of the excess risk. For all solid cancers as a group, it was estimated that about 850 (about 11%) of the cases among cohort members with colon doses in excess of 0.005 Gy were associated with atomic bomb radiation exposure. The data were consistent with a linear dose response over the 0- to 2-Gy range, while there was some flattening of the dose response at higher doses. Furthermore, there is a statistically significant dose response when analyses were limited to cohort members with doses of 0.15 Gy or less. The excess risks for all solid cancers as a group and many individual sites exhibit significant variation with gender, attained age, and age at exposure. It was estimated that, at age 70 after exposure at age 30, solid cancer rates increase by about 35% per Gy (90% CI 28%; 43%) for men and 58% per Gy (43%; 69%) for women. For all solid cancers as a group, the excess relative risk (ERR per Gy) decreases by about 17% per decade increase in age at exposure (90% CI 7%; 25%) after allowing for attained-age effects, while the ERR decreased in proportion to attained age to the power 1.65 (90% CI 2.1; 1.2) after allowing for age at exposure. Despite the decline in the ERR with attained age, excess absolute rates appeared to increase throughout the study period, providing further evidence that radiation-associated increases in cancer rates persist throughout life regardless of age at exposure. For all solid cancers as a group, women had somewhat higher excess absolute rates than men (F:M ratio 1.4; 90% CI 1.1; 1.8), but this difference disappears when the analysis was restricted to non-gender-specific cancers. Significant radiation-associated increases in risk were seen for most sites, including oral cavity, esophagus, stomach, colon, liver, lung, non-melanoma skin, breast, ovary, bladder, nervous system and thyroid. Although there was no indication of a statistically significant dose response for cancers of the pancreas, prostate and kidney, the excess relative risks for these sites were also consistent with that for all solid cancers as a group. Dose-response estimates for cancers of the rectum, gallbladder and uterus were not statistically significant, and there were suggestions that the risks for these sites may be lower than those for all solid cancers combined. However, there was emerging evidence from the present data that exposure as a child may increase risks of cancer of the body of the uterus. Elevated risks were seen for all of the five broadly classified histological groups considered, including squamous cell carcinoma, adenocarcinoma, other epithelial cancers, sarcomas and other non-epithelial cancers. Although the data were limited, there was a significant radiation-associated increase in the risk of cancer occurring in adolescence and young adulthood. In view of the persisting increase in solid cancer risks, the LSS should continue to provide important new information on radiation exposure and solid cancer risks for at least another 15 to 20 years.     

Thyroid cancer incidence among liquidators of the Chernobyl accident

The increase of thyroid cancer incidence rate among children living in the Chernobyl contaminated territories of Belarus, Russia and Ukraine has widely been accepted. Our current work deals with thyroid cancer incidence in the cohort of liquidators (99024 persons) living in 6 regions of Russia: North-West, Volgo-Vyatsky, Central-Chernozemny, Povolzhsky, North-Caucasus and Urals. In the period 1986-1998, a total of 58 thyroid cancer cases were detected in this cohort. We found a statistically significant increase of the thyroid cancer incidence rate in liquidators as compared to the baseline (male population of Russia) level (SIR=4.33, 95% CI: 3.29; 5.60). It was demonstrated that there is no dependence of incidence rates due to external radiation exposure (ERR/Gy=-2.23, 95% CI: -4.67; 0.22).     

Radiation exposure and cancer incidence in a cohort of nuclear power industry workers in the Republic of Korea, 1992–2005

This study examines for the first time cancer incidence between radiation and non-radiation workers in nuclear power facilities in the Republic of Korea. Radiation workers were defined as persons who were issued with a dosimeter at nuclear power facilities, until 2005. All analyses were conducted on male workers only (in total 16,236 individuals) because of the sparseness of females. Statistical analyses were carried out using the standardized incidence ratio (SIR), to compare the cancer risks of radiation and non-radiation workers with those of the general population, and the χ² trend test was used to investigate any increase in cancer rates with dose. Poisson regression was also used to estimate the rate ratio (RR) and the excess relative risk (ERR) after considering the confounding effect due to smoking. During 1992–2005, 99 cancer cases in 63,503 person-years were observed among 8,429 radiation workers, while 104 cancer cases were observed in 48,301 person-years among 7,807 non-radiation workers. When compared with the site- and age-specific cancer rates for the male population of Korea, the SIR for all cancers combined was 1.07 [95% confidence interval (CI) 0.87–1.30] for radiation workers, and 0.88 (95% CI 0.72–1.06) for non-radiation workers, respectively. The RR for radiation workers compared with non-radiation workers was 1.18 (95% CI 0.89–1.58) for all cancers combined. The SIRs for thyroid cancer were noticeably high for both radiation and non-radiation workers, possibly due to the screening effect, but analysis of the RR showed that there was no statistically significant difference in thyroid cancer incidence rates between the two groups. For lung cancer, radiation workers showed a higher incidence rate as compared to non-radiation workers, with the RR being 3.48 (95% CI 1.19–11.48). A χ² trend test showed that there was no evidence for an increase in cancer rate with increasing cumulative dose for all cancers combined (p = 0.5108). The ERR per Sievert was estimated to be 1.69 (95% CI −2.07 to 8.21) for all cancers combined assuming a 10 years lag time. Consequently, a significant excess of cancer incidence among radiation workers in the nuclear power industry in Korea was not observed. Further follow-up and an expansion of the cohort are needed to overcome the lack of statistical power in the study.     

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

A nested case-control study was conducted among workers at five U.S. nuclear facilities to evaluate leukemia mortality risk (excluding chronic lymphocytic) from ionizing radiation using worksite doses and adjusting for potential confounding. Conditional logistic regression was used to estimate the relative risk (RR) of exposed workers and the excess relative risk (ERR) per unit of radiation among 206 cases and 823 age-matched controls. Adjusting for sex and benzene, the RR of leukemia for workers receiving more than 10 mSv was higher compared to those receiving lower or no dose; however, the risk increase was attenuated in the highest dose group. The ERR per 10 mSv was 1.44% (95% CI: < -1.03%, 7.59%) but was higher for workers born after 1921 compared to workers born earlier or when excluding leukemias of uncertain type. Excluding the 7% who were high-dose workers (> 100 mSv), the sex- and benzene-adjusted ERR per 10 mSv was 6.82% (95% CI: -2.87%, 24.1%). The results suggest that risks among these nuclear workers are comparable to those observed in high-dose populations, although no evidence was observed of a positive quadratic dose-response term in this study. This large study is among the first to jointly evaluate benzene and ionizing radiation risk.     

Radiation dose associated with renal failure mortality: a potential pathway to partially explain increased cardiovascular disease mortality observed after whole-body irradiation

Whole-body and thoracic ionizing radiation exposure are associated with increased cardiovascular disease (CVD) risk. In atomic bomb survivors, radiation dose is also associated with increased hypertension incidence, suggesting that radiation dose may be associated with chronic renal failure (CRF), thus explaining part of the mechanism for increased CVD. Multivariate Poisson regression was used to evaluate the association of radiation dose with various definitions of chronic kidney disease (CKD) mortality in the Life Span Study (LSS) of atomic bomb survivors. A secondary analysis was performed using a subsample for whom self-reported information on hypertension and diabetes, the two biggest risk factors for CRF, had been collected. We found a significant association between radiation dose and only our broadest definition of CRF among the full cohort. A quadratic dose excess relative risk model [ERR/Gy(2) = 0.091 (95% CI: 0.05, 0.198)] fit minimally better than a linear model. Within the subsample, association was also observed only with the broadest CRF definition [ERR/Gy(2) = 0.15 (95% CI: 0.02, 0.32)]. Adjustment for hypertension and diabetes improved model fit but did not substantially change the ERR/Gy(2) estimate, which was 0.17 (95% CI: 0.04, 0.35). We found a significant quadratic dose relationship between radiation dose and possible chronic renal disease mortality that is similar in shape to that observed between radiation and incidence of hypertension in this population. Our results suggest that renal dysfunction could be part of the mechanism causing increased CVD risk after whole-body irradiation, a hypothesis that deserves further study.