Radiation-related ophthalmological changes and aging among Hiroshima and Nagasaki A-bomb survivors: a reanalysis.

The relationship of ionizing radiation to the age-related ophthalmological findings of the 1978-1980 ophthalmological examination of A-bomb survivors of Hiroshima and Nagasaki has been reanalyzed using DS86 eye organ dose estimates. The main purpose of this reevaluation was to determine whether age and radiation exposure, as measured using the recently revised dosimetry information (DS86), have an additive, synergistic, or antagonistic effect. The data in this study are limited to axial opacities and posterior subcapsular changes, for which a definite radiation-induced effect has been observed in Hiroshima and Nagasaki A-bomb survivors. The best model fitting for axial opacities gives a significant positive effect for both linear dose and linear age-related regression coefficients and a significant negative effect for an interaction between radiation dose and age. Such a negative interaction implies an antagonistic effect in that the relative risks in relation to radiation exposure doses become smaller with an increase in age. On the other hand, the best-fitting relationship for posterior subcapsular changes suggested a linear-quadratic dose and linear age-related effect. The estimate of the quadratic dose coefficient shows a highly negative correlation with age, but the negative quadratic dose term is extremely small and is of little biological significance.     

Immunological responses of aging Japanese A-bomb survivors

Immune response parameters were studied on 1341 A-bomb survivors residing in Hiroshima, Japan. Mononuclear cells were isolated from venous blood and tested for interleukin-2 production; lymphocytes were purified and tested for natural killer (NK) cell activity and interferon (IFN) production; and serum was tested for IFN and circulating immune complex (CIC) levels. Statistical analyses were performed for each type of assay using a linear models procedure including sex, age at the time of the bomb, radiation exposure, all the interaction variables, and the categorical variable day-of-assay in the model. The findings showed that (1) none of the immunologic variables were significantly affected by radiation exposure; (2) NK activity and CIC levels were positively associated with age; and (3) NK activity was on average higher for males than females. The data exemplify the difficulty in reaching firm conclusions concerning associations with radiation exposure when the dependent variable exhibits a large degree of interindividual and day-of-assay variability.     

Studies of the mortality of A-bomb survivors. 8. Cancer mortality, 1950-1982

This study extends an earlier one by 4 years (1979-1982) and includes mortality data on 11,393 additional Nagasaki survivors. Significant dose responses are observed for leukemia, multiple myeloma, and cancers of the lung, female breast, stomach, colon, esophagus, and urinary tract. Due to diagnostic difficulties, results for liver and ovarian cancers, while suggestive of significant dose responses, do not provide convincing evidence for radiogenic effects. No significant dose responses are seen for cancers of the gallbladder, prostate, rectum, pancreas, or uterus, or for lymphoma. For solid tumors, largely due to sex-specific differences in the background rates, the relative risk of radiation-induced mortality is greater for women than for men. For nonleukemic cancers the relative risk seen in those who were young when exposed has decreased with time, while the smaller risks for those who were older at exposure have tended to increase. While the absolute excess risks of radiation-induced mortality due to nonleukemic cancer have increased with time for all age-at-exposure groups, both excess and relative risks of leukemia have generally decreased with time. For leukemia, the rate of decrease in risk and the initial level of risk are inversely related to age at exposure.     

Selection bias in cancer risk estimation from A-bomb survivors

We consider the possible bias in cancer risk estimation from A-bomb survivors due to selection of the cohort by survival. The paper considers both relevant information from the data and basic theoretical issues involved. The most direct information from the data comes from making various restrictions on the dose-distance range, partly to reduce differential selection and partly just to reduce the magnitude of the selection. These analyses suggest that there are no serious biases, but they are not conclusive. Theoretical considerations include laying out more explicitly than usual just how biases could result from the selection. This involves heterogeneities in the ability to survive acute effects, in baseline and radiogenic cancer rates, and most importantly the correlation between survival-related and cancer-related heterogeneities. Following on this, idealized modeling is used to quantify the extent of possible bias in terms of the assumed values of the magnitude of these heterogeneities and their correlation. It is indicated that these values would need to be very large to introduce substantial bias. Based on all these considerations, it seems unlikely that the bias in cancer risk estimation could be large in relation to other uncertainties in generalizing from what is seen among A-bomb survivors; in particular, indications are that the bias in relative risks is unlikely to be as large as 0.05 to 0.07. For solid cancer this would correspond to bias in the excess relative risk at 1 Sv of at most about 15-20%.     

Incidence of female breast cancer among atomic bomb survivors, Hiroshima and Nagasaki, 1950-1990

An incidence survey of the Life Span Study (LSS) population found 1093 breast cancers among 1059 breast cancer cases diagnosed during 1950-1990. As in earlier breast cancer surveys of this population, a linear and statistically highly significant radiation dose response was found. In the analysis, particular attention was paid to modification of radiation dose response by age at exposure (e) and attained age (a). Dose-specific excess relative risk (ERR(1Sv)) decreased with increasing values of e and a. A linear dose-response model analysis, with e and a as exponential age modifiers, did not conclusively discriminate between the two variables as modifiers of dose response. A modified isotonic regression approach, requiring only that ERR(1Sv) be monotonic in age, provides a fresh perspective indicating that both e and a are important modifiers of dose response. Exposure before age 20 was associated with higher ERR(1Sv) compared to exposure at older ages, with no evidence of consistent variation by exposure age for ages under 20. ERR(1Sv) was observed to decline with increasing attained age, with by far the largest drop around age 35. Possible explanations for these observations are discussed, along with research approaches that might provide more information.     

Incidence of female breast cancer among atomic bomb survivors, Hiroshima and Nagasaki, 1950-1980

Ascertainment of breast cancer incidence among the cohort of the RERF Life Span Study extended sample identified 574 breast cancers among 564 cases diagnosed during 1950-1980 of which 412 cancers were reviewed microscopically. There were no dose-dependent differences with respect to diagnostic certainty or histological type. As in previous studies, the dose response appeared to be roughly linear and did not differ between the two cities. The most remarkable new finding was the emergence of a radiation-related excess among women under 10 years of age at exposure. The risk of radiogenic breast cancer appears to decrease with increasing age at exposure, whether expressed in relative or absolute terms. These results suggest that exposure of female breast tissue to ionizing radiation at any time during the first four decades of life, even during the premature stage, can cause breast cancer later in life, and that the length of time that tumor promoters such as endogenous hormones operate following exposure has an important influence on the development of radiation-induced breast cancer. An unresolved question is whether breast cancer risk is increased by radiation exposure at ages older than 40.     

Improved estimates of cancer site-specific risks for A-bomb survivors

Pawel, D. J., Preston, D. L., Pierce, D. A. and Cologne, J. B. Improved Estimates of Cancer Site-Specific Risks for A-Bomb Survivors. Radiat. Res. 169, 87-98 (2008). Simple methods are investigated for improving summary site-specific radiogenic risk estimates. Estimates in this report are derived from cancer incidence data from the Life Span Study (LSS) cohort of A-bomb survivors that are followed up by the Radiation Effects Research Foundation (RERF). Estimates from the LSS of excess relative risk (ERR) for solid cancer sites have typically been derived separately for each site. Even though the data for this are extensive, the statistical imprecision in site-specific (organ-specific) risk estimates is substantial, and it is clear that a large portion of the site-specific variation in estimates is due to this imprecision. Empirical Bayes (EB) estimates offer a reasonable approach for moderating this variation. The simple version of EB estimates that we applied to the LSS data are weighted averages of a pooled overall estimate of ERR and separately derived site-specific estimates, with weights determined by the data. Results indicate that the EB estimates are most useful for sites such as esophageal or bladder cancer, for which the separately derived ERR estimates are less precise than for other sites.     

Natural cell-mediated cytotoxicity among A-bomb survivors residing in the United States

Natural cell-mediated cytotoxicity (NCMC) by lymphocytes from Japanese atomic bomb survivors now living in the United States was measured. Seventy-one individuals were exposed to an estimated '0.00' Gy ('0 rads') (S0 group) and 58 to greater than '0.00 Gy' (S+ group) at the time of the bomb. Of this 58, 51 (88 per cent) received less than 0.50 Gy and 30 (52 per cent) received less than 0.10 Gy. NCMC was measured against 51Cr-labelled K562 target cells. Activity by lymphocytes from S+ group donors was significantly greater than that for the S0 group (p = 0.028 by the stratified Wilcoxon rank-sum test). This difference between the S+ and S0 populations was detected 35 years after exposure to the bomb. It is therefore feasible and important to examine appropriate biologic parameters to elucidate the effects of low doses of radiation in humans.     

Studies of the mortality of A-bomb survivors. 9. Mortality, 1950-1985: Part 3. Noncancer mortality based on the revised doses (DS86).

Deaths in the RERF Life Span Study (LSS) sample have been determined for the years 1950-1985 and an analysis of cancer mortality with the revised DS86 doses has been described separately. In this report, we examine the relationship to dose of deaths from all diseases other than cancer. Although the evidence is still limited, there seems to be an excess risk from noncancer death at high doses (2 or 3 Gy and over). Statistically, a pure quadratic or a linear-threshold model [the estimated threshold dose is 1.4 Gy (0.6-2.8 Gy)] is found to fit better than a simple linear or linear-quadratic model. This increase in noncancer mortality is statistically demonstrable, generally, after 1965 and among the younger survivors (less than 40 at the time of the bombing), suggesting a sensitivity for this age group. For specific causes of death, an excess in relative risk at the high dose level, that is, 2 Gy or more, is seen in circulatory and digestive diseases. The relative risk is, however, much smaller than that for cancer. These findings, based as they are on death certificates, have their limitations. Most significant, perhaps, is the possible erroneous attribution of radiation-related cancer deaths to other causes. At present, the contribution such errors may make to the apparent increase in non-cancer deaths at the higher doses cannot be estimated as rigorously as is obviously desirable. However, even now, this increase does not appear to be fully explicable in terms of errors in classification. Further follow-up of mortality in this LSS cohort as well as disease revealed by the biennial physical examinations of the morbidity subsample (Adult Health Study) of the LSS cohort will be needed to confirm this suggestion of a radiation-related increase in mortality from causes other than cancer, and to determine whether it results in a demonstrable life shortening among the heavily exposed A-bomb survivors.     

Model averaging in the analysis of leukemia mortality among Japanese A-bomb survivors

Epidemiological studies often include numerous covariates, with a variety of possible approaches to control for confounding of the association of primary interest, as well as a variety of possible models for the exposure–response association of interest. Walsh and Kaiser (Radiat Environ Biophys 50:21–35, 2011) advocate a weighted averaging of the models, where the weights are a function of overall model goodness of fit and degrees of freedom. They apply this method to analyses of radiation–leukemia mortality associations among Japanese A-bomb survivors. We caution against such an approach, noting that the proposed model averaging approach prioritizes the inclusion of covariates that are strong predictors of the outcome, but which may be irrelevant as confounders of the association of interest, and penalizes adjustment for covariates that are confounders of the association of interest, but may contribute little to overall model goodness of fit. We offer a simple illustration of how this approach can lead to biased results. The proposed model averaging approach may also be suboptimal as way to handle competing model forms for an exposure–response association of interest, given adjustment for the same set of confounders; alternative approaches, such as hierarchical regression, may provide a more useful way to stabilize risk estimates in this setting.     

Studies of the mortality of A-bomb survivors. 9. Mortality, 1950-1985: Part 2. Cancer mortality based on the recently revised doses (DS86)

The present study, the ninth in a series that began in 1961, extends the time of surveillance 3 more years and covers the period 1950-1985. It is based on the recently revised doses, termed the DS86. The impact of the change from the T65D to the DS86 on the dose-response relationships for cancer mortality was described in the first of this series of reports. Here, the focus is on cancer mortality among the 76,000 A-bomb survivors within the LSS sample for whom DS86 doses have been estimated, with the emphasis on biological issues associated with radiation carcinogenesis. Briefly, the following is found: The excess in leukemia mortality has continued to decline with time, but remains slightly but significantly elevated in 1981-1985 in Hiroshima. For cancers other than leukemia, as a group, excess deaths continue to increase over time in direct proportion to the normal increase in natural cancer mortality with increasing age, and the relative risk seems unchanged over time within age ATB cohorts. The single exception is the cohort under 10 years of age ATB. Within this group of survivors, where the relative risk, although based on relatively few deaths, has been quite high at the higher doses, as judged by deaths before the age of 30, the risk has fallen and has remained fairly constant at a lower level thereafter. Thus the present analysis still supports, in the main, estimation of lifetime risk based on the assumption of a constant relative risk. For the same age ATD, both the relative and absolute risks are higher for younger age ATB cohorts than older ones for cancers other than leukemia. There is no statistically significant difference in excess deaths between males and females except for leukemia, though the relative risk is higher for females than for males, significantly so for cancers of the esophagus and lung, reflecting the higher background cancer rate for males. Significant dose responses are observed for leukemia, cancers of the esophagus, stomach, colon, lung, breast, ovary, and urinary bladder and multiple myeloma, as previously observed. No significant increase is demonstrable as yet for cancers of the rectum, gallbladder, pancreas, uterus, and prostate and malignant lymphoma. In the present report, cancers of the bone, pharynx, nose, and larynx, and skin except melanoma are also examined, but none of these sites show a significant increase with dose.(ABSTRACT TRUNCATED AT 400 WORDS)     

Epidemiology and Clinical Features of Pulmonary Nontuberculous Mycobacteriosis in Nagasaki,Japan

Background and Objectives

Recent reports indicate that the incidence of nontuberculous mycobacterial-lung disease (NTM-LD) is increasing. This study aimed to investigate the epidemiology and clinical features of NTM-LD patients in Nagasaki prefecture, Japan to identify the negative prognostic factors for NTM-LD in Japan.

Methods

The medical records of patients newly diagnosed with NTM-LD in eleven hospitals in Nagasaki prefecture between January 2001 and February 2010 were reviewed. Data regarding the annual population of each region and the incidence of all forms of tuberculosis were collected to assess geographic variations in NTM-LD incidence, isolates, and radiological features.

Results

A total 975 patients were diagnosed with NTM-LD. The incidence increased over the study period and reached 11.0 and 10.1 per 100,000 population in 2008 and 2009, respectively. M. intracellulare was the most common pathogen in the southern region, and M. avium most common in other regions. The most common radiographic pattern was the nodular-bronchiectatic pattern. Age >60 years, body mass index <18.5 kg/m², underlying lung disease, and cavitary pattern were the negative prognostic factors at the 1-year follow-up.

Conclusions

The incidence of NTM-LD has been increasing in Nagasaki prefecture. The isolates and radiographic features of patients vary markedly by region.     

Experimental derivation of relative biological effectiveness of A-bomb neutrons in Hiroshima and Nagasaki and implications for risk assessment

Epidemiological data on the health effects of A-bomb radiation in Hiroshima and Nagasaki provide the framework for setting limits for radiation risk and radiological protection. However, uncertainty remains in the equivalent dose, because it is generally believed that direct derivation of the relative biological effectiveness (RBE) of neutrons from the epidemiological data on the survivors is difficult. To solve this problem, an alternative approach has been taken. The RBE of polyenergetic neutrons was determined for chromosome aberration formation in human lymphocytes irradiated in vitro, compared with published data for tumor induction in experimental animals, and validated using epidemiological data from A-bomb survivors. The RBE of fission neutrons was dependent on dose but was independent of the energy spectrum. The same RBE regimen was observed for lymphocyte chromosome aberrations and tumors in mice and rats. Used as a weighting factor for A-bomb survivors, this RBE system was superior in eliminating the city difference in chromosome aberration frequencies and cancer mortality. The revision of the equivalent dose of A-bomb radiation using DS02 weighted by this RBE system reduces the cancer risk by a factor of 0.7 compared with the current estimates using DS86, with neutrons weighted by a constant RBE of 10.