Radiation risk of incident colorectal cancer by anatomical site among atomic bomb survivors: 1958-2009

Colorectal Cancer: Epidemiology, Risk Factors, and Prevention

Colorectal cancer (CRC) is the third most common cancer and the second most common cause of cancer mortality worldwide. There are disparities in the epidemiology of CRC across different populations, most probably due to differences in exposure to lifestyle and environmental factors related to CRC. Prevention is the most effective method for controlling CRC. Primary prevention includes determining and avoiding modifiable risk factors (e.g., alcohol consumption, smoking, and dietary factors) as well as increasing protective factors (e.g., physical activity, aspirin). Further studies, especially randomized, controlled trials, are needed to clarify the association between CRC incidence and exposure to different risk factors or protective factors. Detection and removal of precancerous colorectal lesions is also an effective strategy for controlling CRC. Multiple factors, both at the individual and community levels (e.g., patient preferences, availability of screening modalities, costs, benefits, and adverse events), should be taken into account in designing and implementing CRC screening programs. Health policymakers should consider the best decision in identifying the starting age and selection of the most effective screening strategies for the target population. This review aims to present updated evidence on the epidemiology, risk factors, and prevention of CRC.

Non-targeted effects and space radiation risks for astronauts on multiple International Space Station and lunar missions

Future space travel to the earth's moon or the planet Mars will likely lead to the selection of experienced International Space Station (ISS) or lunar crew persons for subsequent lunar or mars missions. Major concerns for space travel are galactic cosmic ray (GCR) risks of cancer and circulatory diseases. However large uncertainties in risk prediction occur due to the quantitative and qualitative differences in heavy ion microscopic energy deposition leading to differences in biological effects compared to low LET radiation. In addition, there are sparse radiobiology data and absence of epidemiology data for heavy ions and other high LET radiation. Non-targeted effects (NTEs) are found in radiobiology studies to increase the biological effectiveness of high LET radiation at low dose for cancer related endpoints. In this paper the most recent version of the NASA Space Cancer Risk model (NSCR-2022) is used to predict mission risks while considering NTEs in solid cancer risk predictions. I discuss predictions of space radiation risks of cancer and circulatory disease mortality for US Whites and US Asian-Pacific Islander (API) populations for 6-month ISS, 80-day lunar missions, and combined ISS-lunar mission. Model predictions suggest NTE increase cancer risks by about ∼2.3 fold over a model that ignores NTEs. US API are predicted to have a lower cancer risks of about 30% compared to US Whites. Cancer risks are slightly less than additive for multiple missions, which is due to the decease of risk with age of exposure and the increased competition with background risks as radiation risks increase. The inclusion of circulatory risks increases mortality estimates about 25% and 37% for females and males, respectively in the model ignoring NTEs, and 20% and 30% when NTEs are assumed to modify solid cancer risk. The predictions made here for combined ISS and lunar missions suggest risks are within risk limit recommendations by the National Council on Radiation Protection and Measurements (NCRP) for such missions.

Residual radiation risk disparities across sex and race or ethnic groups for lifetime never-smokers on lunar missions

Missions to the Earth's moon are of scientific and societal interest, however pose the problem of risks of late effects for returning crew persons, most importantly cancer and circulatory diseases. In this paper, we discuss NSCR-2022 model risk estimates for lunar missions for US racial and ethnic groups comparing never-smokers (NS) to US averages for each group and sex. We show that differences within groups between men and women are reduced for NS compared to the average population. Race and ethnic group dependent cancer and circulatory disease risks are reduced by 10% to 40% for NS with the largest decrease for Whites. Circulatory disease risks are changed by less than 10% for NS and in several cases modestly increased due to increased lifespan for NS. Asian-Pacific Islanders (API) and Hispanics NS are at lower risk compared to Whites and Blacks. Differences between groups are narrowed for NS compared to predictions for average populations, however disparities remain especially for Blacks and to a lesser extent Whites compared to API or Hispanic NS groups.

Association of low-dose ionising radiation with site-specific solid cancers: Chinese medical X-ray workers cohort study, 1950-1995

BACKGROUND

The dose-response relationship between cancers and protracted low-dose rate exposure to ionising radiation is still uncertain. This study aims to estimate quantified relationships between low-dose radiation exposures and site-specific solid cancers among Chinese medical X-ray workers.

METHODS

This cohort study included 27 011 individuals who were employed at major hospitals in 24 provinces in China from 1950 to 1980 and had been exposed to X-ray equipment, and a control group of 25 782 physicians who were not exposed to X-ray equipment. Person-years of follow-up were calculated from the year of employment to the date of the first diagnosis of cancer or the end of follow-up, whichever occurred first. All cancers were obtained from medical records during 1950-1995. This study used Poisson regression models to estimate the excess relative risk (ERR) and excess absolute risk (EAR) for incidence of site-specific solid cancers associated with cumulative dose.

RESULTS

1643 solid cancers were developed, the most common being lung, liver and stomach cancer. Among X-ray workers, the average cumulative colon dose was 0.084 Gy. We found a positive relationship between cumulative organ-specific dose and liver (ERR/Gy=1.48; 95% CI 0.40 to 2.83), oesophagus (ERR/Gy=18.1; 95% CI 6.25 to 39.1), thyroid (ERR/Gy=2.96; 95% CI 0.44 to 8.18) and non-melanoma skin cancers (ERR/Gy=7.96; 95% CI 2.13 to 23.12). We found no significant relationship between cumulative organ-specific doses and other cancers. Moreover, the results showed a statistically significant EAR for liver, stomach, breast cancer (female), thyroid and non-melanoma skin cancers.

CONCLUSIONS

These findings provided more useful insights into the risks of site-specific cancers from protracted low-dose rate exposure to ionising radiation.

Colorectal Cancer: From Risk Factors to Oncogenesis

Colorectal cancer is the second leading cause of cancer-related mortality worldwide. Numerous pathophysiological mechanisms, such as abnormal cell proliferation, cell differentiation, resistance to apoptosis, invasion of structures adjacent to colorectal tumor cells, and distant metastasis, are involved in colorectal carcinogenesis. These processes are initiated by the complex interaction of a number of genetic and environmental factors, including sedentary lifestyle, obesity, alcohol consumption, smoking, or gut microbiota. Despite the significant progress achieved in the diagnostic and therapeutic management of patients with colorectal cancer, there has been recently a noteworthy increase in the incidence of colorectal cancer in individuals below the age of 50 years. Early-onset colorectal cancer has a different frequency of oncogenic mutations, a higher prevalence of mucinous histology, a distinct deoxyribonucleic acid (DNA) methylation profile, a more distal location, and lower survival rates. A significant improvement in the prognosis of these patients can be achieved through the detection and removal of modifiable risk factors, along with the implementation of personalized screening strategies for individuals at high risk for this malignancy. Furthermore, gaining comprehension of the pathophysiological mechanisms by which these risk factors contribute to the process of oncogenesis may facilitate the discovery of novel therapeutic targets.

The scientific basis for the use of the linear no-threshold (LNT) model at low doses and dose rates in radiological protection

The linear no-threshold (LNT) model was introduced into the radiological protection system about 60 years ago, but this model and its use in radiation protection are still debated today. This article presents an overview of results on effects of exposure to low linear-energy-transfer radiation in radiobiology and epidemiology accumulated over the last decade and discusses their impact on the use of the LNT model in the assessment of radiation-related cancer risks at low doses. The knowledge acquired over the past 10 years, both in radiobiology and epidemiology, has reinforced scientific knowledge about cancer risks at low doses. In radiobiology, although certain mechanisms do not support linearity, the early stages of carcinogenesis comprised of mutational events, which are assumed to play a key role in carcinogenesis, show linear responses to doses from as low as 10 mGy. The impact of non-mutational mechanisms on the risk of radiation-related cancer at low doses is currently difficult to assess. In epidemiology, the results show excess cancer risks at dose levels of 100 mGy or less. While some recent results indicate non-linear dose relationships for some cancers, overall, the LNT model does not substantially overestimate the risks at low doses. Recent results, in radiobiology or in epidemiology, suggest that a dose threshold, if any, could not be greater than a few tens of mGy. The scientific knowledge currently available does not contradict the use of the LNT model for the assessment of radiation-related cancer risks within the radiological protection system, and no other dose-risk relationship seems more appropriate for radiological protection purposes.

Interstitial deletion of the Apc locus in β-catenin-overexpressing cells is a signature of radiation-induced intestinal tumors in C3B6F1 ApcMin/+ mice†

Recent studies have identified interstitial deletions in the cancer genome as a radiation-related mutational signature, although most of them do not fall on cancer driver genes. Pioneering studies in the field have indicated the presence of loss of heterozygosity (LOH) spanning Apc in a subset of sporadic and radiation-induced intestinal tumors of ApcMin/+ mice, albeit with a substantial subset in which LOH was not detected; whether copy number losses accompany such LOH has also been unclear. Herein, we analyzed intestinal tumors of C3B6F1 ApcMin/+ mice that were either left untreated or irradiated with 2 Gy of γ-rays. We observed intratumor mosaicism with respect to the nuclear/cytoplasmic accumulation of immunohistochemically detectable β-catenin, which is a hallmark of Apc+ allele loss. An immunoguided laser microdissection approach enabled the detection of LOH involving the Apc+ allele in β-catenin-overexpressing cells; in contrast, the LOH was not observed in the non-overexpressing cells. With this improvement, LOH involving Apc+ was detected in all 22 tumors analyzed, in contrast to what has been reported previously. The use of a formalin-free fixative facilitated the LOH and microarray-based DNA copy number analyses, enabling the classification of the aberrations as nondisjunction/mitotic recombination type or interstitial deletion type. Of note, the latter was observed only in radiation-induced tumors (nonirradiated, 0 of 8; irradiated, 11 of 14). Thus, an analysis considering intratumor heterogeneity identifies interstitial deletion involving the Apc+ allele as a causative radiation-related event in intestinal tumors of ApcMin/+ mice, providing an accurate approach for attributing individual tumors to radiation exposure.

Insights into radiation carcinogenesis based on dose-rate effects in tissue stem cells

PURPOSE

Increasing epidemiological and biological evidence suggests that radiation exposure enhances cancer risk in a dose-dependent manner. This can be attributed to the 'dose-rate effect,' where the biological effect of low dose-rate radiation is lower than that of the same dose at a high dose-rate. This effect has been reported in epidemiological studies and experimental biology, although the underlying biological mechanisms are not completely understood. In this review, we aim to propose a suitable model for radiation carcinogenesis based on the dose-rate effect in tissue stem cells.

METHODS

We surveyed and summarized the latest studies on the mechanisms of carcinogenesis. Next, we summarized the radiosensitivity of intestinal stem cells and the role of dose-rate in the modulation of stem-cell dynamics after irradiation.

RESULTS

Consistently, driver mutations can be detected in most cancers from past to present, supporting the hypothesis that cancer progression is initiated by the accumulation of driver mutations. Recent reports demonstrated that driver mutations can be observed even in normal tissues, which suggests that the accumulation of mutations is a necessary condition for cancer progression. In addition, driver mutations in tissue stem cells can cause tumors, whereas they are not sufficient when they occur in non-stem cells. For non-stem cells, tissue remodeling induced by marked inflammation after the loss of tissue cells is important in addition to the accumulation of mutations. Therefore, the mechanism of carcinogenesis differs according to the cell type and magnitude of stress. In addition, our results indicated that non-irradiated stem cells tend to be eliminated from three-dimensional cultures of intestinal stem cells (organoids) composed of irradiated and non-irradiated stem cells, supporting the stem-cell competition.

CONCLUSIONS

We propose a unique scheme in which the dose-rate dependent response of intestinal stem cells incorporates the concept of the threshold of stem-cell competition and context-dependent target shift from stem cells to whole tissue. The concept highlights four key issues that should be considered in radiation carcinogenesis: i.e. accumulation of mutations; tissue reconstitution; stem-cell competition; and environmental factors like epigenetic modifications.

Heavy-ion radiation-induced colitis and colorectal carcinogenesis in Il10-/- mice display co-activation of β-catenin and NF-κB signaling

Space radiation-induced gastrointestinal (GI) cancer risk models for future interplanetary astronauts are being developed that primarily rely on quantitative animal model studies to assess radiation-quality effects of heavy-ion space radiation exposure in relation to γ-rays. While current GI-cancer risk estimation efforts are focused on sporadic GI-cancer mouse models, emerging in-vivo data on heavy-ion radiation-induced long-term GI-inflammation are indicative of a higher but undetermined risk of GI-inflammation associated cancers, such as colitis-associated cancer (CAC). Therefore, we aimed to assess radiation quality effects on colonic inflammation, colon cancer incidence, and associated signaling events using an in-vivo CAC model i.e., Il10-/- mice. Male Il10-/- mice (8-10 weeks, n = 12/group) were irradiated with either sham, γ-rays or heavy-ions (28Si or 56Fe), and histopathological assessments for colitis and CAC were conducted at 2.5 months post-exposure. qPCR analysis for inflammation associated gene transcripts (Ptges and Tgfb1), and in-situ staining for markers of cell-proliferation (phospho-histone H3), oncogenesis (active-β-catenin, and cyclin D1), and inflammation (phospho-p65NF-κB, iNOS, and COX2) were performed. Significantly higher colitis and CAC frequency were noted after heavy-ion exposure, relative to γ and control mice. Higher CAC incidence after heavy-ion exposure was associated with greater activation of β-catenin and NF-κB signaling marked by induced expression of common downstream inflammatory (iNOS and COX2) and pro-proliferative (Cyclin D1) targets. In summary, IR-induced colitis and CAC incidence in Il10-/- mice depends on radiation quality and display co-activation of β-catenin and NF-κB signaling.

DOSE-RATE EFFECT OF RADIATION ON RAT MAMMARY CARCINOGENESIS AND AN EMERGING ROLE FOR STEM CELL BIOLOGY

The uncertain cancer risk of protracted radiation exposure at low dose rates is an important issue in radiological protection. Tissue stem/progenitor cells are a supposed origin of cancer and may contribute to the dose-rate effect on carcinogenesis. The authors have shown that female rats subjected to continuous whole body γ irradiation as juveniles or young adults have a notably reduced incidence of mammary cancer as compared with those irradiated acutely. Experiments using the mammosphere formation assay suggested the presence of radioresistant progenitor cells. Cell sorting indicated that basal progenitor cells in rat mammary gland were more resistant than luminal progenitors to killing by acute radiation, especially at high doses. Thus, the evidence indicates a cell-type-dependent inactivation of mammary cells that manifests only at high acute doses, implying a link to the observed dose-rate effect on carcinogenesis.

Age effects on radiation response: summary of a recent symposium and future perspectives

One of the principal uncertainties when estimating population risk of late effects from epidemiological data is that few radiation-exposed cohorts have been followed up to extinction. Therefore, the relative risk model has often been used to estimate radiation-associated risk and to extrapolate risk to the end of life. Epidemiological studies provide evidence that children are generally at higher risk of cancer induction than adults for a given radiation dose. However, the strength of evidence varies by cancer site and questions remain about site-specific age at exposure patterns. For solid cancers, there is a large body of evidence that excess relative risk (ERR) diminishes with increasing age at exposure. This pattern of risk is observed in the Life Span Study (LSS) as well as in other radiation-exposed populations for overall solid cancer incidence and mortality and for most site-specific solid cancers. However, there are some disparities by endpoint in the degree of variation of ERR with exposure age, with some sites (e.g., colon, lung) in the LSS incidence data showing no variation, or even increasing ERR with increasing age at exposure. The pattern of variation of excess absolute risk (EAR) with age at exposure is often similar, with EAR for solid cancers or solid cancer mortality decreasing with increasing age at exposure in the LSS. We shall review the human data from the Japanese LSS cohort, and a variety of other epidemiological data sets, including a review of types of medical diagnostic exposures, also some radiobiological animal data, all bearing on the issue of variations of radiation late-effects risk with age at exposure and with attained age. The paper includes a summary of several oral presentations given in a Symposium on "Age effects on radiation response" as part of the 67th Annual Meeting of the Radiation Research Society, held virtually on 3-6 October 2021.

Comparison of All Solid Cancer Mortality and Incidence Dose-Response in the Life Span Study of Atomic Bomb Survivors, 1958-2009

Recent analysis of all solid cancer incidence (1958-2009) in the Life Span Study (LSS) revealed evidence of upward curvature in the radiation dose response among males but not females. Upward curvature in sex-averaged excess relative risk (ERR) for all solid cancer mortality (1950-2003) was also observed in the 0-2 Gy dose range. As reasons for non-linearity in the LSS are not completely understood, we conducted dose-response analyses for all solid cancer mortality and incidence applying similar methods [1958-2009 follow-up, DS02R1 doses, including subjects not-in-city (NIC) at the time of the bombing] and statistical models. Incident cancers were ascertained from Hiroshima and Nagasaki cancer registries, while cause of death was ascertained from death certificates throughout Japan. The study included 105,444 LSS subjects who were alive and not known to have cancer before January 1, 1958 (80,205 with dose estimates and 25,239 NIC subjects). Between 1958 and 2009, there were 3.1 million person-years (PY) and 22,538 solid cancers for incidence analysis and 3.8 million PY and 15,419 solid cancer deaths for mortality analysis. We fitted sex-specific ERR models adjusted for smoking to both types of data. Over the entire range of doses, solid cancer mortality dose-response exhibited a borderline significant upward curvature among males (P = 0.062) and significant upward curvature among females (P = 0.010); for solid cancer incidence, as before, we found a significant upward curvature among males (P = 0.001) but not among females (P = 0.624). The sex difference in magnitude of dose-response curvature was statistically significant for cancer incidence (P = 0.017) but not for cancer mortality (P = 0.781). The results of analyses in the 0-2 Gy range and restricted lower dose ranges generally supported inferences made about the sex-specific dose-response shape over the entire range of doses for each outcome. Patterns of sex-specific curvature by calendar period (1958-1987 vs. 1988-2009) and age at exposure (0-19 vs. 20-83) varied between mortality and incidence data, particularly among females, although for each outcome there was an indication of curvature among 0-19-year-old male survivors in both calendar periods and among 0-19-year-old female survivors in the recent period. Collectively, our findings indicate that the upward curvature in all solid cancer dose response in the LSS is neither specific to males nor to incidence data; its evidence appears to depend on the composition of sites comprising all solid cancer group and age at exposure or time. Further follow up and site-specific analyses of cancer mortality and incidence will be important to confirm the emerging trend in dose-response curvature among young survivors and unveil the contributing factors and sites.

Extended analysis of solid cancer incidence among the Nuclear Industry Workers in the UK: 1955-2011

Radiation worker studies provide direct estimates of cancer risk after protracted low-dose exposures to external X-ray and gamma-ray irradiations. The National Registry for Radiation Workers (NRRW) started in 1976 and has become the largest epidemiological program of research on nuclear workers in the UK. Here, we report on the relationship between solid cancer incidence and external radiation at the low-dose levels in 172,452 NRRW cohort members of whom (90%) were men. This study is based on 5.25 million person-years of follow-up from 1955 through the end of 2011. In the range of accumulated low doses two-thirds of workers have doses of less than 10 mSv. This study is an updated analysis of solid cancer incidence data with an additional 10 years of follow-up over the previous analysis of the NRRW cohort (NRRW-3). A total of 18,310 cases of solid cancers based on a 10-year lag were registered and of these 43% of the solid cancer cases occurred during the latest 10 years. Poisson regression was used to investigate the relationship between solid cancers risk and protracted chronic low-dose radiation exposure. This study demonstrated for solid cancers a rapid decrease of risk at high external doses that appeared to be driven by the workers who were monitored for potential exposure to internal emitters and who had also received relatively high external doses. Among cohort members only exposed to external radiation, a strong association was found between external dose and solid cancers (ERR/Sv = 0.52, 95% CI: 0.11; 0.96, based on 13,199 cases). A similar pattern is also seen for lung cancer. Excluding lung cancer from the grouping of all solid cancers resulted in evidence of a linear association with external radiation dose (ERR/Sv = 0.24, 95% CI: 0.01; 0.49, based on 15,035 cases), so suggesting some degree of confounding by smoking. Statistically significantly increasing trends with dose were seen for cancers of the colorectal, bladder and pleura cancer. Some of these results should be treated with caution because of the limited corroborating evidence from other published studies. Information on internal doses as well as non-radiation factors such smoking would be helpful to make more definitive inferences.

Molecular Biologic and Epidemiologic Insights for Preventability of Colorectal Cancer

The etiology of colorectal cancer (CRC) has been informed from both a molecular biology perspective, which concerns the study of the nature, timing, and consequences of mutations in driver genes, and epidemiology, which focuses on identifying risk factors for cancer. For the most part, these fields have developed independently, and it is thus important to consider them in a more integrated manner. The molecular mutational perspective has stressed the importance of mutations due to replication of adult stem cells, and the molecular fingerprint of most CRCs does not suggest the importance of direct carcinogens. Epidemiology has identified numerous modifiable risk factors that account for most CRCs, most of which are not direct mutagens. The distribution of CRCs across the large bowel is not uniform, which is possibly caused by regional differences in the microbiota. Some risk factors are likely to act through or interact with the microbiota. The mutational perspective informs when risk factors may begin to operate in life and when they may cease to operate. Evidence from the mutational model and epidemiology supports that CRC risk factors begin early in life and may contribute to the risk of early-onset CRC. Later in carcinogenesis, there may be a "point of no return" when sufficient mutations have accumulated, and some risk factors do not affect cancer risk. This period may be at least 5-15 years for some risk factors. A more precise knowledge of timing of risk factor to cancer is required to inform preventive efforts.

Race and ethnic group dependent space radiation cancer risk predictions

Future space missions by national space agencies and private industry, including space tourism, will include a diverse makeup of crewmembers with extensive variability in age, sex, and race or ethnic groups. The relative risk (RR) model is used to transfer epidemiology data between populations to estimate radiation risks. In the RR model cancer risk is assumed to be proportional to background cancer rates and limited by other causes of death, which are dependent on genetic, environmental and dietary factors that are population dependent. Here we apply the NSCR-2020 model to make the first predictions of age dependent space radiation cancer risks for several U.S. populations, which includes Asian-Pacific Islanders (API), Black, Hispanic (white and black), and White (non-Hispanic) populations. Results suggest that male API and Hispanic populations have the overall lowest cancer risks, while White females have the highest risk. Blacks have similar total cancer rates than Whites, however their reduced life expectancy leads to modestly lower lifetime radiation risks compared to Whites. There are diverse tissue specific cancer risk ranking across sex and race, which include sex specific organ risks, female’s having larger lung, stomach, and urinary-bladder radiation risks, and male’s having larger colon and brain risks.

Cancer risk following low doses of ionising radiation - Current epidemiological evidence and implications for radiological protection

Recent studies suggest that every year worldwide about a million patients might be exposed to doses of the order of 100 mGy of low-LET radiation, due to recurrent application of radioimaging procedures. This paper presents a synthesis of recent epidemiological evidence on radiation-related cancer risks from low-LET radiation doses of this magnitude. Evidence from pooled analyses and meta-analyses also involving epidemiological studies that, individually, do not find statistically significant radiation-related cancer risks is reviewed, and evidence from additional and more recent epidemiological studies of radiation exposures indicating excess cancer risks is also summarized. Cohorts discussed in the present paper include Japanese atomic bomb survivors, nuclear workers, patients exposed for medical purposes, and populations exposed environmentally to natural background radiation or radioactive contamination. Taken together, the overall evidence summarized here is based on studies including several million individuals, many of them followed-up for more than half a century. In summary, substantial evidence was found from epidemiological studies of exposed groups of humans that ionizing radiation causes cancer at acute and protracted doses above 100 mGy, and growing evidence for doses below 100 mGy. The significant radiation-related solid cancer risks observed at doses of several 100 mGy of protracted exposures (observed, for example, among nuclear workers) demonstrate that doses accumulated over many years at low dose rates do cause stochastic health effects. On this basis, it can be concluded that doses of the order of 100 mGy from recurrent application of medical imaging procedures involving ionizing radiation are of concern, from the viewpoint of radiological protection.

Radiation concerns in frequent flyer patients: Should imaging history influence decisions about recurrent imaging?

Radiation risks from diagnostic imaging have captured the attention of patients and medical practitioners alike, yet it remains unclear how these considerations can best be incorporated into clinical decision making. This manuscript presents a framework to consider these issues in a potentially at-risk population, the so called "frequent flyer" patients undergoing a large amount of recurrent imaging over time. Radiation risks from the low-dose exposures of diagnostic imaging are briefly reviewed, as applied to recurrent exposures. Some scenarios are then explored in which it may be helpful to incorporate knowledge of a patient's imaging history. There is no simple or uniformly applicable approach to these challenging and often nuanced clinical decisions. The complexity and variability of the underlying disease states and trajectories argues against alerting mechanisms based on a simple cumulative dose threshold. Awareness of imaging history may instead be beneficial in encouraging physicians and patients to take the long view, and to identify those populations of frequent flyers that might benefit from alternative imaging strategies.

Radiation Risks for the Incidence of Kidney, Bladder and Other Urinary Tract Cancers: 1958-2009

As part of the recent series of articles to create a comprehensive description of the radiation risks of solid cancer incidence after ionizing radiation exposure, based on the atomic bomb survivors' Life Span Study (LSS), this work focuses on the risks of urinary tract cancer (UTC) and kidney cancer. Analyses covered a 52-year period of follow-up, through 2009, among 105,444 eligible survivors who were alive and cancer free in 1958. This represents an additional 11 years of follow-up since the last comprehensive report, with a total of 3,079,502 person-years. We observed 790 UTC and 218 kidney cancer cases. Adjusted for smoking, there was a strong linear radiation dose response for UTC. The sex-averaged excess relative risk per 1 Gy (ERR/Gy) was 1.4 (95% confidence interval, CI: 0.82 to 2.1). Both males and females showed significantly increased ERRs/Gy with female point estimates at a factor of 3.4 (95% CI: 1.4 to 8.6) greater than male estimates. UTC radiation risks were largely unmodified by age at exposure or attained age. The attributable fraction of UTC to radiation exposure was approximately 18% while that attributed to smoking was 48%. Kidney cancer showed an increased ERR due to smoking (0.56 per 50 pack-years; 95% CI -0.007 to 1.6; P = 0.054), but we did not observe any strong associations of kidney cancer with radiation exposure, although sex-specific dose responses were found to be statistically different.

Gastrointestinal Cancer Survival and Radiation Exposure among Atomic Bomb Survivors: The Life Span Study

BACKGROUND

Radiation exposure is an established risk factor for the development of several forms of cancer, including gastrointestinal cancers. However, few studies have investigated the relationship between prediagnostic radiation exposure and survival after cancer diagnosis.

METHODS

Participants in the Life Span Study (LSS) of atomic bomb survivors who were diagnosed with a first primary invasive stomach, colon, or rectal cancer between 1958 and 2009 were followed for mortality during 1958-2014. Cox regression models were used to calculate HRs and 95% confidence intervals (CI) for associations of radiation dose from atomic bomb exposure with survival (cancer-specific and overall) after cancer diagnosis. Analyses were adjusted for city of primary exposure, sex, age at diagnosis, and year of diagnosis.

RESULTS

We identified 7,728 eligible patients with cancer for analysis. We observed no statistically significant associations between radiation dose and cancer-specific survival among LSS participants with a gastrointestinal cancer. Higher radiation doses (≥1 Gy) were suggestively, but not significantly, associated with modestly poorer cancer-specific survival for colon cancer only (HR, 1.38; 95% CI, 0.90-2.12), and were associated with poorer overall survival regardless of cancer site.

CONCLUSIONS

Although radiation exposure is associated with increased risk of gastrointestinal cancer incidence and mortality, study results are inconclusive about an association between prediagnostic radiation exposure and survival after gastrointestinal cancer diagnosis.

IMPACT

Radiation exposure from the atomic bomb before gastrointestinal cancer diagnosis was not associated with cancer survival, but should be evaluated in relation to survival for other cancer types.

ProZES: the methodology and software tool for assessment of assigned share of radiation in probability of cancer occurrence

ProZES is a software tool for estimating the probability that a given cancer was caused by preceding exposure to ionising radiation. ProZES calculates this probability, the assigned share, for solid cancers and hematopoietic malignant diseases, in cases of exposures to low-LET radiation, and for lung cancer in cases of exposure to radon. User-specified inputs include birth year, sex, type of diagnosed cancer, age at diagnosis, radiation exposure history and characteristics, and smoking behaviour for lung cancer. Cancer risk models are an essential part of ProZES. Linking disease and exposure to radiation involves several methodological aspects, and assessment of uncertainties received particular attention. ProZES systematically uses the principle of multi-model inference. Models of radiation risk were either newly developed or critically re-evaluated for ProZES, including dedicated models for frequent types of cancer and, for less common diseases, models for groups of functionally similar cancer sites. The low-LET models originate mostly from the study of atomic bomb survivors in Hiroshima and Nagasaki. Risks predicted by these models are adjusted to be applicable to the population of Germany and to different time periods. Adjustment factors for low dose rates and for a reduced risk during the minimum latency time between exposure and cancer are also applied. The development of the methodology and software was initiated and supported by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) taking up advice by the German Commission on Radiological Protection (SSK, Strahlenschutzkommission). These provide the scientific basis to support decision making on compensation claims regarding malignancies following occupational exposure to radiation in Germany.

Analyses of cancer incidence and other morbidities in gamma irradiated B6CF1 mice

With increasing medical radiation exposures, it is important to understand how different modes of delivery of ionizing radiation as well as total doses of exposure impact health outcomes. Our lab studied the risks associated with ionizing radiation by analyzing the Northwestern University Radiation Archive for animals (NURA). NURA contains detailed data from a series of 10 individual neutron and gamma irradiation experiments conducted on over 50,000 mice. Rigorous statistical testing on control mice from all Janus experiments enabled us to select studies that could be compared to one another and uncover unexpected differences among the controls as well as experimental animals. For controls, mice sham irradiated with 300 fractions died significantly earlier than those with fewer sham fractions and were excluded from the pooled dataset. Using the integrated dataset of gamma irradiated and control mice, we found that fractionation significantly decreased the death hazard for animals dying of lymphomas, tumors, non-tumors, and unknown causes. Gender differences in frequencies of causes of death were identified irrespective of irradiation and dose fractionation, with female mice being at a greater risk for all causes of death, except for lung tumors. Irradiated and control male mice were at a significantly greater risk for lung tumors, the opposite from observations noted in humans. Additionally, we discovered that lymphoma deaths can occur quickly after exposures to high doses of gamma rays. This study systematically cross-compared outcomes of different modes of fractionation evaluated across different Janus experiments and across a wide span of total doses. It demonstrates that protraction modulated survival and disease status differently based on the total dose, cause of death, and sex of an animal. This novel method for analyzing the Janus datasets will lead to insightful new mechanistic hypotheses and research in the fields of radiation biology and protection.

Gastric and rectal cancers in workers exposed to asbestos: a case series

BACKGROUND

The Occupational Safety and Health Research Institute (OSHRI) of the Korea had not recognized gastrointestinal cancer as work-related disease during their evaluation. However, in 2018 OSHRI recognized gastric and rectal cancers as work-related disease in asbestos-exposed workers. We present 2 such cases along supportive evidence of causation.

CASE PRESENTATION

Patient A: A 57-year-old man had worked for about 40 years since 1978 as an oxygen cutter at workplaces that dismantle ships, buildings, boilers, and thermal power plants. In November 2016, endoscopy and biopsy confirmed the diagnosis of advanced gastric cancer, for which he underwent subtotal gastrectomy and chemotherapy; however, he later died of the cancer. Patient B: A 71-year-old man had worked in shipbuilding and repair workplaces for approximately 49 years, being employed in pipe laying, asbestos insulation installation, grinding, and other ship repair work. In 2003, he was diagnosed of rectal cancer by abdominal computed tomography. He accordingly underwent surgical removal of the cancer. Based on the occupational history of the 2 patients and our review of the relevant literature addressing the occupational environment, we concluded that both patients had continuous exposure to high levels of asbestos while performing their jobs for 40 and 49 years, respectively.

CONCLUSION

Both patients had a history of smoking and drinking (non-occupational personal risk factors). However, the possibility of an increased risk of gastric and rectal cancers from asbestos exposure cannot be excluded. Therefore, we considered that occupational exposure to asbestos had contributed to the cancer diagnosis in these cases. Workers exposed to asbestos should be made aware of the possibility of gastric or rectal cancer, and should undergo monitoring and medical examinations. Appropriate compensation for gastric and rectal cancers that occur in workers exposed to asbestos are anticipated in future.

Radiation and Risk of Liver, Biliary Tract, and Pancreatic Cancers among Atomic Bomb Survivors in Hiroshima and Nagasaki: 1958-2009

The Life Span Study (LSS) of atomic bomb survivors has consistently demonstrated significant excess radiation-related risks of liver cancer since the first cancer incidence report. Here, we present updated information on radiation risks of liver, biliary tract and pancreatic cancers based on 11 additional years of follow-up since the last report, from 1958 to 2009. The current analyses used improved individual radiation doses and accounted for the effects of alcohol consumption, smoking and body mass index. The study participants included 105,444 LSS participants with known individual radiation dose and no known history of cancer at the start of follow-up. Cases were the first primary incident cancers of the liver (including intrahepatic bile duct), biliary tract (gallbladder and other and unspecified parts of biliary tract) or pancreas identified through linkage with population-based cancer registries in Hiroshima and Nagasaki. Poisson regression methods were used to estimate excess relative risks (ERRs) and excess absolute risks (EARs) associated with DS02R1 doses for liver (liver and biliary tract cancers) or pancreas (pancreatic cancer). We identified 2,016 incident liver cancer cases during the follow-up period. Radiation dose was significantly associated with liver cancer risk (ERR per Gy: 0.53, 95% CI: 0.23 to 0.89; EAR per 10,000 person-year Gy: 5.32, 95% CI: 2.49 to 8.51). There was no evidence for curvature in the radiation dose response (P=0.344). ERRs by age-at-exposure categories were significantly increased among those who were exposed at 0-9, 10-19 and 20-29 years, but not significantly increased after age 30 years, although there was no statistical evidence of heterogeneity in these ERRs (P = 0.378). The radiation ERRs were not affected by adjustment for smoking, alcohol consumption or body mass index. As in previously reported studies, radiation dose was not associated with risk of biliary tract cancer (ERR per Gy: -0.02, 95% CI: -0.25 to 0.30). Radiation dose was associated with a nonsignificant increase in pancreatic cancer risk (ERR per Gy: 0.38, 95% CI: <0 to 0.83). The increased risk was statistically significant among women (ERR per Gy: 0.70, 95% CI: 0.12 to 1.45), but not among men.

Effect of Heterogeneity in Background Incidence on Inference about the Solid-Cancer Radiation Dose Response in Atomic Bomb Survivors

A recent analysis of solid cancer incidence in the Life Span Study of atomic bomb survivors (Hiroshima and Nagasaki, Japan) found evidence of a nonlinear, upwardly curving radiation dose response among males but not among females. Further analysis of this new and unexpected finding was necessary. We used two approaches to investigate this finding. In one approach, we excluded individual cancer sites or groups of sites from all solid cancers. In the other approach, we used joint analysis to allow for heterogeneity in background-rate parameters across groups of cancers with dissimilar trends in background rates. Exclusion of a few sites led to the disappearance of curvature among males in the remaining collection of solid cancers; some of these influential sites have unique features in their background age-specific incidence that are not captured by a background-rate model fit to all solid cancers combined. Exclusion of a few sites also led to an appearance of curvature among females. Misspecification of background rates can cause bias in inference about the shape of the dose response, so heterogeneity of background rates might explain at least part of the all solid cancer dose-response difference in curvature between males and females. We conclude that analysis based on all solid cancers as a single outcome is not the optimal method to assess radiation risk for solid cancer in the Life Span Study; joint analysis with suitable choices of cancer groups might be preferable by allowing for background-rate heterogeneity across sites while providing greater power to assess radiation risk than analyses of individual sites.