DS02R1: Improvements to Atomic Bomb Survivors' Input Data and Implementation of Dosimetry System 2002 (DS02) and Resulting Changes in Estimated Doses.

Individual dose estimates calculated by Dosimetry System 2002 (DS02) for the Life Span Study (LSS) of atomic bomb survivors are based on input data that specify location and shielding at the time of the bombing (ATB). A multi-year effort to improve information on survivors' locations ATB has recently been completed, along with comprehensive improvements in their terrain shielding input data and several improvements to computational algorithms used in combination with DS02 at RERF. Improvements began with a thorough review and prioritization of original questionnaire data on location and shielding that were taken from survivors or their proxies in the period 1949-1963. Related source documents varied in level of detail, from relatively simple lists to carefully-constructed technical drawings of structural and other shielding and surrounding neighborhoods. Systematic errors were reduced in this work by restoring the original precision of map coordinates that had been truncated due to limitations in early data processing equipment and by correcting distortions in the old (WWII-era) maps originally used to specify survivors' positions, among other improvements. Distortion errors were corrected by aligning the old maps and neighborhood drawings to orthophotographic mosaics of the cities that were newly constructed from pre-bombing aerial photographs. Random errors that were reduced included simple transcription errors and mistakes in identifying survivors' locations on the old maps. Terrain shielding input data that had been originally estimated for limited groups of survivors using older methods and data sources were completely re-estimated for all survivors using new digital terrain elevation data. Improvements to algorithms included a fix to an error in the DS02 code for coupling house and terrain shielding, a correction for elevation at the survivor's location in calculating angles to the horizon used for terrain shielding input, an improved method for truncating high dose estimates to 4 Gy to reduce the effect of dose error, and improved methods for calculating averaged shielding transmission factors that are used to calculate doses for survivors without detailed shielding input data. Input data changes are summarized and described here in some detail, along with the resulting changes in dose estimates and a simple description of changes in risk estimates for solid cancer mortality. This and future RERF publications will refer to the new dose estimates described herein as "DS02R1 doses."

Association of Acute Radiation Syndrome and Rain after the Bombings in Atomic Bomb Survivors.

Acute radiation-induced symptoms reported in survivors after the atomic bombings in Hiroshima and Nagasaki have been suspected to be associated with rain that fell after the explosions, but this association has not been evaluated in an epidemiological study that considers the effects of the direct dose from the atomic bombs and other factors. The aim of this study was to evaluate this association using information from a fixed cohort, comprised of 93,741 members of the Life Span Study who were in the city at the time of the bombing. Information on acute symptoms and exposure to rain was collected in surveys conducted by interviewers, primarily in the 1950s. The proportion of survivors developing severe epilation was around 60% at levels of direct radiation doses of 3 Gy or higher and less than 0.2% at levels <0.005 Gy regardless of reported rain exposure status. The low prevalence of acute symptoms at low direct doses indicates that the reported fallout rain was not homogeneously radioactive at a level sufficient to cause a substantial probability of acute symptoms. We observed that the proportion of reported acute symptoms was slightly higher among those who reported rain exposure in some subgroups, however, suggestions that rain was the cause of these reported symptoms are not supported by analyses specific to the known areas of radioactive fallout. Misclassification of exposure and outcome, including symptoms due to other causes and recall bias, appears to be a more plausible explanation. However, the insufficient and retrospective nature of the available data limited our ability to quantify the attribution to those possible causes.

A report from the 2013 international symposium: the evaluation of the effects of low-dose radiation exposure in the life span study of atomic bomb survivors and other similar studies.

The RERF International Low-Dose Symposium was held on 5-6 December 2013 at the RERF campus in Hiroshima, Japan, to discuss the issues facing the Life Span Study (LSS) and other low-dose studies. Topics included the current status of low-dose risk detection, strategies for low-dose epidemiological and statistical research, methods to improve communication between epidemiologists and biologists, and the current status of radiological studies and tools. Key points made by the participants included the necessity of pooling materials over multiple studies to gain greater insight where data from single studies are insufficient; generating models that reflect epidemiological, statistical, and biological principles simultaneously; understanding confounders and effect modifiers in the current data; and taking into consideration less studied factors such as the impact of dose rate. It is the hope of all participants that this symposium be used as a trigger for further studies, especially those using pooled data, in order to reach a greater understanding of the health effects of low-dose radiation.

Invited commentary: missing doses in the life span study of Japanese atomic bomb survivors.

The Life Span Study is a long-term epidemiologic cohort study of survivors of the atomic bombs dropped on Hiroshima and Nagasaki, Japan. In this issue of the Journal, Richardson et al. (Am J Epidemiol. 2013;177(6):562-568) suggest that those who died in the earliest years of follow-up were more likely to have a missing dose of radiation exposure assigned, leading to a bias in the radiation risk estimates. We show that nearly all members of the cohort had shielding information recorded before the beginning of follow-up and that much of the alleged bias that Richardson et al. describe simply reflects the geographic distribution of shielding conditions for which reliable dosimetry was impossible.

Breast cancer risk in atomic bomb survivors from multi-model inference with incidence data 1958-1998.

Breast cancer risk from radiation exposure has been analyzed in the cohort of Japanese a-bomb survivors using empirical models and mechanistic two-step clonal expansion (TSCE) models with incidence data from 1958 to 1998. TSCE models rely on a phenomenological representation of cell transition processes on the path to cancer. They describe the data as good as empirical models and this fact has been exploited for risk assessment. Adequate models of both types have been selected with a statistical protocol based on parsimonious parameter deployment and their risk estimates have been combined using multi-model inference techniques. TSCE models relate the radiation risk to cell processes which are controlled by age-increasing rates of initiating mutations and by changes in hormone levels due to menopause. For exposure at young age, they predict an enhanced excess relative risk (ERR) whereas the preferred empirical model shows no dependence on age at exposure. At attained age 70, the multi-model median of the ERR at 1 Gy decreases moderately from 1.2 Gy(-1) (90% CI 0.72; 2.1) for exposure at age 25 to a 30% lower value for exposure at age 55. For cohort strata with few cases, where model predictions diverge, uncertainty intervals from multi-model inference are enhanced by up to a factor of 1.6 compared to the preferred empirical model. Multi-model inference provides a joint risk estimate from several plausible models rather than relying on a single model of choice. It produces more reliable point estimates and improves the characterization of uncertainties. The method is recommended for risk assessment in practical radiation protection.

Use of the individual data of the A-bomb survivors for biologically based cancer models.

All recent analyses of the data on solid cancer incidence of the atomic bomb survivors are corrected for migration and random dose errors. In the usual treatment with grouped data and regression calibration, the calibration of doses depends on the used dose response. For solid cancers, it usually is linear. Here, an individual likelihood is presented which works without further adjustment for all dose responses. When the same assumptions are made as in the usual Poisson regression, equivalent results are obtained. But, the individual likelihood has the potential to use more detailed models for dose errors and to estimate non-linear dose responses without recalibration. As an example for the potential of the individual data set for the analysis of risk at low doses, signals for a saturating bystander effect are investigated.

Methylation in p14(ARF) is frequently observed in colorectal cancer with low-level microsatellite instability.

Colorectal cancer (CRC) can be classified as high-level microsatellite instability (MSI-H), low-level MSI (MSI-L) and microsatellite stable (MSS) depending on levels of MSI. MSI-H CRC relies on a distinct molecular pathway due to the mismatch repair (MMR) deficiency and shows methylation in multiple gene promoters. The genetic pathway leading to MSI-L is unknown, although higher levels of promoter methylation are observed in this group compared with MSS CRCs. This study explored how promoter methylation affects MSI phenotype, by analysing the methylation status of eight CRC-related promoters, MSI phenotype and KRAS/BRAF mutations in a series of 234 CRCs. Promoter methylation of p14(ARF) was significantly related to MSI-L CRC with KRAS mutation. The MSI-H phenotype was related to methylation of MLH1 as expected, while the MSS phenotype was related to methylation of p16(INK4a) and O(6)-methylguanine-DNA methyltransferase, although this was not statistically significant. Thus, promoter methylation of p14(ARF) could be a significant alteration leading to CRC with MSI-L.

Prevalence of adult-onset multifactorial disease among offspring of atomic bomb survivors.

The first study to examine whether parental radiation exposure leads to increased heritable risk of common adult-onset multifactorial diseases (i.e., hypertension, diabetes mellitus, hypercholesterolemia, ischemic heart disease, and stroke) was conducted among 11,951 participants in the clinical examination program out of a potential of 24,673 mail survey subjects who were offspring of survivors born from May 1946 through December 1984. Logistic regression analyses demonstrated no evidence of an association between the prevalence of multifactorial diseases in the offspring and parental radiation exposure, after adjusting for age, city, gender and various risk factors. The odds ratio (OR) for a paternal dose of 1 Gy was 0.91 [95% confidence interval (CI) 0.81-1.01, P = 0.08], and that for a maternal dose of 1 Gy was 0.98 (95% CI 0.86-1.10, P = 0.71). There was no apparent effect of parental age at exposure or of elapsed time between parental exposure and birth, but male offspring had a low odds ratio (OR = 0.76 at 1 Gy) for paternal exposure, but cautious interpretation is needed for this finding. The clinical assessment of nearly 12,000 offspring of A-bomb survivors who have reached a median age of about 50 years provided no evidence for an increased prevalence of adult-onset multifactorial diseases in relation to parental radiation exposure.

Promoting action of radiation in the atomic bomb survivor carcinogenesis data?

The age-time patterns of risk in the atomic bomb survivor data on incidence of solid cancers suggest an action of low-LET radiation not only on the initiating event but also on promotion in a biologically motivated model that allows for both actions. The favored model indicates a decrease of radiation risks with age at exposure due to the initiating effect and with time since exposure due to the promoting effect. These result in a relative risk that depends mostly on attained age for ages at exposure above 20 years. According to the model, a dose of 100 mGy is inducing about the same number of initiating events that occur spontaneously in 1 year. Assuming that several mutations are needed to obtain intermediate cells with growth advantage does not improve the quality of fit. The estimated promoting effect could be explained if the number of intermediate cells increases by 80% at 1 Gy, e.g. due to stimulated cell repopulation.

Radiation-induced genomic instability in tandem repeat sequences is not predictive of unique sequence instability.

Tandem repeat sequences, classified as minisatellite sequences or partially duplicated genes, are inherently unstable. Radiation exposure can increase the instability of such repeat sequences, but the biological consequences of this elevated instability are not well characterized. To learn more about the characteristics of the instability at different sequences in the genome, we created mutant HT1080 cells bearing 8.4 kb of partially duplicated allele at the HPRT locus by gene targeting. The cells were then tested to determine whether repeat-sequence instability (assessed by elevated reversion rate caused by loss of one duplicated segment) accompanied increased forward mutation rates at the restored wild-type HPRT allele. After a 4-Gy X irradiation, 32 clones were selected (out of 500 clones, 6%) that showed elevated reversion rates even after many cell generations. These clones also showed general increases in the forward mutation rate, whereas the paired individual mutation rates did not correlate with each other. Furthermore, levels of intracellular reactive oxygen species (ROS) and nuclear gamma-H2AX foci, which are hallmarks for DNA damage responses, were also generally elevated, although the levels did not correlate with the individual reversion rates. It was concluded that repeat sequence instability is not predictive of unique sequence instability, probably because the instability is generated by multiple mechanisms after radiation exposure.

Oesophageal squamous cell carcinoma may develop within a background of accumulating DNA methylation in normal and dysplastic mucosa.

BACKGROUND: Oesophageal squamous cell carcinoma (OSCC) often arises from preceding dysplastic lesions in the oesophageal epithelium. However, the molecular changes occurring in premalignant lesions are not well understood. An epigenetic change is an example of OSCC that may occur within the epithelium. AIM: To investigate the methylation status of multiple promoters in cancer-derived DNA, as well as in the background epithelium of OSCC, including dysplastic lesions and non-neoplastic mucosa. The normal epithelium from patients without cancer was also examined. The findings were correlated with the mutational status of p53. PATIENTS AND METHODS: 56 patients with advanced OSCC, 21 patients with intraepithelial neoplasia (IEN), 56 patients with a background of non-neoplastic epithelium, adjacent to the OSCC, and 42 normal control epithelia from healthy volunteers were studied. The promoter methylation status of SFRP1, SFRP2, DCC, APC, p16(INK4a), p14(ARF), MINT1, MINT2, MINT31, CACNA1G, COX2, DAPK, hMLH1 and MGMT was examined by methylation-specific single polymerase chain reaction or combined bisulphite restriction analysis. The mutation of p53 by direct sequencing was assessed. RESULTS: DNA methylation was observed in OSCC and in its background epithelium. The frequency of CpG island methylation increased from a baseline level in the background non-neoplastic epithelium, through IEN, to advanced OSCC. However, mutations in p53 were almost exclusively observed in IEN and OSCC. More extensive DNA methylation was seen in the neoplastic lesions (OSCC or IEN) having a p53 mutation than in those with wild-type p53. CONCLUSION: DNA methylation is present at low levels in the non-neoplastic oesophageal epithelium and appears to contribute to the progression of the dysplasia-carcinoma sequence in OSCC carcinogenesis.

A method to differentiate between the levels of ESR signals induced by sunlight and by ionizing radiation in teeth from atomic bomb survivors.

Electron spin resonance (ESR, or electron paramagnetic resonance, EPR) analysis of tooth enamel is an effective method for the retrospective estimation of individual radiation doses. One problem with this technique is that the observed ESR signal may include a contribution from ultraviolet (UV) light exposure from sunlight, especially in front teeth. Thus there has been a need to find ways to estimate the UV-light effect in the total signal so that the net ESR dose from ionizing radiation can be determined. To examine this issue, we measured 96 teeth of various types, but with buccal and lingual parts measured separately, from a control group of atomic bomb survivors (estimated dose <5 mGy). We found that, except for molars, the mean ESR-estimated dose for the buccal halves was, on average, nearly twice that from the lingual side, which indicates that the UV-light-induced lingual dose equals the difference between the two halves. Using these corrections for UV-light exposure to front teeth that had been exposed to both ionizing radiation and UV light, it was found that the estimated radiation doses closely approximated the previously estimated ESR dose to molars from the same donors or the estimated dose arrived at with cytogenetic methods. We concluded that, when using ESR to estimate radiation dose, measuring molars is the first choice, but if only front teeth are available, separate measurements to the buccal and lingual parts can provide an estimation of the mean UV-light contribution to the ESR-determined dose.