Japanese pediatric and adult atomic bomb survivor dosimetry: potential improvements using the J45 phantom series and modern Monte Carlo transport

The radiation exposure estimates for the atomic bomb survivors at Hiroshima and Nagasaki have evolved over the past several decades, reflecting a constant strive by the Radiation Effects Research Foundation (RERF) to provide thorough dosimetry to their cohort. Recently, a working group has introduced a new series of anatomical models, called the J45 phantom series, which improves upon those currently used at RERF through greater age resolution, sex distinction, anatomical realism, and organ dose availability. To evaluate the potential dosimetry improvements that would arise from their use in an RERF Dosimetry System, organ doses in the J45 series are evaluated here using environmental fluence data for 20 generalized survivor scenarios pulled directly from the current dosimetry system. The energy- and angle-dependent gamma and neutron fluences were converted to a source term for use in MCNP6, a modern Monte Carlo radiation transport code. Overall, the updated phantom series would be expected to provide dose improvements to several important organs, including the active marrow, colon, and stomach wall (up to 20, 20, and 15% impact on total dose, respectively). The impacts were especially significant for neutron dose estimates (up to a two-fold difference) and within organs which were unavailable in the previous phantom series. These impacts were consistent across the 20 scenarios and are potentially even greater when biological effectiveness of the neutron dose component is considered. The entirety of the dosimetry results for all organs are available as supplementary data, providing confident justification for potential future DS workflows utilizing the J45 phantom series.

Lifetime Risk Assessment of Lung Cancer Incidence for Nonsmokers in Japan Considering the Joint Effect of Radiation and Smoking Based on the Life Span Study of Atomic Bomb Survivors

Background: The lifetime risk of lung cancer incidence due to radiation for nonsmokers is overestimated because of the use of the average cancer baseline risk among a mixed population, including smokers. In recent years, the generalized multiplicative (GM)-excess relative risk (ERR) model has been developed in the life span study of atomic bomb survivors to consider the joint effect of radiation and smoking. Based on this background, this paper discusses the issues of radiation risk assessment considering smoking in two parts.Materials and Methods: In Part 1, we proposed a simple method of estimating the baseline risk for nonsmokers using current smoking data. We performed sensitivity analysis on baseline risk estimation to discuss the birth cohort effects. In Part 2, we applied the GM-ERR model for Japanese smokers to calculate lifetime attributable risk (LAR). We also performed a sensitivity analysis using other ERR models (e.g., simple additive (SA)-ERR model).Results and Discussion: In Part 1, the lifetime baseline risk from mixed population including smokers to nonsmokers decreased by 54% (44%–60%) for males and 24% (18%–29%) for females. In Part 2, comparison of LAR between SA- and GM-ERR models showed that if the radiation dose was ≤200 mGy or less, the difference between these ERR models was within the standard deviation of LAR due to the uncertainty of smoking information.Conclusion: The use of mixed population for baseline risk assessment overestimates the risk for lung cancer due to low-dose radiation exposure in Japanese males.

Incidence of lymphoid neoplasms among atomic bomb survivors by histological subtype: 1950-1994

Epidemiological data have provided limited and inconsistent evidence on the relationship between radiation exposure and lymphoid neoplasms. We classified 553 lymphoid neoplasm cases diagnosed between 1950 and 1994 in the Life Span Study (LSS) cohort of atomic bomb survivors into WHO subtypes. Mature B-cell neoplasms represented 58%, mature T-cell and NK-cell neoplasms 20%; precursor cell neoplasms, 5%, and Hodgkin lymphoma, 3%; with the remaining 15% classified as non-Hodgkin lymphoid neoplasms or lymphoid neoplasms, not otherwise specified. We used Poisson regression methods to assess the relationship between radiation exposure and the more common subtypes. As in earlier reports, a significant dose response for non-Hodgkin lymphoid neoplasms as a group was seen for males but not females. However, subtype analyses showed that radiation dose was strongly associated with increased precursor cell neoplasms rates, with an estimated excess relative risk per Gy of 16 (95% Confidence interval: 7.0, >533) at age 50. The current data based primarily of tissue-based diagnoses suggest that the association between radiation dose and lymphoid neoplasms as a group is largely driven by the radiation effect on precursor cell neoplasms while presenting no evidence of a radiation dose response for major categories of mature cell neoplasms, either B- or T-/NK-cell, or more specific disease entities (diffuse large B-cell lymphoma, plasma cell myeloma, adult T-cell leukemia/lymphoma) or Hodgkin lymphoma.

Congenital Malformations and Perinatal Deaths among the Children of Atomic Bomb Survivors: A Reappraisal

From 1948 to 1954, the Atomic Bomb Casualty Commission conducted a study of pregnancy outcomes of children of atomic bomb survivors who had received radiation doses from zero to near-lethal levels. Past reports (1956, 1981, and 1990) on the cohort did not identify significant associations of radiation exposure with untoward pregnancy outcomes such as major congenital malformations, stillbirths, or neonatal deaths, individually or in aggregate. We have re-examined the risk of major congenital malformations and perinatal deaths in the children of the atomic bomb survivors (N=71,603) using fully reconstructed data to minimize the potential for bias, with refined estimates of the gonadal dose from the Dosimetry System 2002 and refined analytical methods for characterizing dose-response relationships. The analyses show that parental exposure is associated with increased risk for major congenital malformations and perinatal deaths, but the estimates are imprecise for direct radiation effects and most are not statistically significant. Nonetheless, the uniformly positive estimates for untoward pregnancy outcomes among children of both maternal and paternal survivors are useful for risk assessment purposes, although extending them to circumstances other than atomic bomb survivors comes with uncertainty as to the generalizability of the Hiroshima and Nagasaki populations.

Radiation effects on atherosclerosis in atomic bomb survivors: a cross‐sectional study using structural equation modeling

Past reports indicated that total-body irradiation at low to moderate doses could be responsible for cardiovascular disease risks, but the mechanism remains unclear. The purpose of this study was to investigate the association between radiation exposure and atherosclerosis, an underlying pathology of cardiovascular diseases, in the Japanese atomic bomb survivors. We performed a cross-sectional study measuring 14 clinical-physiological atherosclerosis indicators during clinical exams from 2010 to 2014 in 3274 participants of the Adult Health Study cohort. Multivariable analyses were performed by using a structural equation model with latent factors representing underlying atherosclerotic pathologies: (1) arterial stiffness, (2) calcification, and (3) plaque as measured with indicators chosen a priori on the basis of clinical-physiological knowledge. Radiation was linearly associated with calcification (standardized coefficient per Gy 0.15, 95 % confidence interval: CI [0.070, 0.23]) and plaque (0.11, 95 % CI [0.029, 0.20]), small associations that were comparable to about 2 years of aging per Gy of radiation exposure, but not with arterial stiffness (0.036, 95 % CI [− 0.025, 0.095]). The model fitted better and had narrower confidence intervals than separate ordinary regression models explaining individual indicators independently. The associations were less evident when the dose range was restricted to a maximum of 2 or 1 Gy. By combining individual clinical-physiological indicators that are correlated because of common, underlying atherosclerotic pathologies, we found a small, but significant association of radiation with atherosclerosis.