Occupational radiation exposure and cancer incidence in a cohort of diagnostic medical radiation workers in South Korea

Low-dose ionizing radiation and the exposure-lag response: protocol for a prospective cohort study on The Health Effects of Chongqing Occupational Radiation Workers

Introduction

Although the effects of ionizing radiation on radiation workers have been extensively studied in China, no prospective cohort study has been conducted in Chongqing. Furthermore, previous cohorts have not provided a broad-gauge assessment of the temporal relationship between low-dose occupational radiation exposure and the risk of health outcomes.

Methods

A prospective cohort study will be carried out focusing on radiation workers in Chongqing. Health examination outcomes and radiation dose monitoring data will be collected and analyzed using the distributed lag non-linear model (DLNM) combined with generalized additive model (GAM) or generalized linear model (GLM) to evaluate the exposure-lag response relationship.

Discussion

Our study will enhance our understanding of the exposure-lag response association between occupational radiation exposure and the health of radiation workers based on DLNM.

Clinical trial registration

Chinese Clinical Trials Registry, ChiCTR2400081804.

Low-Dose Ionizing Radiation and Thyroid Diseases and Functional Modifications in Exposed Workers: A Systematic Review

Background/Objectives: With technological development, ionizing radiation has found applications in numerous occupations. However, the determination and quantification of the damage resulting from exposure to it remains rather unclear, along with the damage to particular organs. The aim of this systematic review was to investigate the relationship between low-dose ionizing radiation (LDIR) in exposed workers and possible functional changes and cancer development in the thyroid gland. Methods: We included observational studies evidencing the correlation under study. Data extraction and analysis was conducted on all included studies. The research strategy included three electronic databases (PubMed, Scopus, and Web of Science). The systematic review followed PRISMA guidelines, and the research protocol was submitted to PROSPERO (CRD:42023425839). Results: The search initially yielded 166 articles and, once duplicates and irrelevant articles were removed, a total of 15 useful articles were reviewed. Qualitative analysis of the studies showed that the TSH value does not change following exposure, while a reduction in fT3 and an increase or reduction in fT4 can be observed. Furthermore, the correlation between thyroid cancer and occupational exposure to radiation was not shown with certainty, but there was some evidence of increased gland volume and nodule formation. Conclusions: Even at low doses, ionizing radiation adversely affects thyroid activity. In this regard, new studies should be carried out in order to further investigate and define this issue and, consequently, outline useful measures to ensure the protection of workers in contact with this particular physical agent.

The risk of thyroid cancer in relation to residential proximity to nuclear power plants: a systematic review and meta-analysis

INTRODUCTION

Ionizing radiation is a human carcinogen, and there is a public concern but limited evidence that it increases the incidence of cancer among those who live near nuclear power plants (NPPs). Previous analyses of thyroid cancer in these populations have been inconsistent, and the last synthesis was published nearly a decade ago. To address these gaps, we undertook a systematic review and meta-analysis.

METHODS

A search strategy was developed and applied to PubMed, Scopus, and Web of Science databases. A total of 2006 publications were identified, with 11 studies of thyroid cancer incidence that met the inclusion criteria. Study quality was assessed using the Office of Health Assessment and Translation (OHAT) tool. Summary risk estimates relating residential proximity to the NPPs and thyroid cancer were generated using a random effects model. Heterogeneity in the risk estimates was assessed for study features that included: distance to the NPP, study quality, and biological sex.

RESULTS

The 11 studies were categorized as either highly (n = 8) or plausibly (n = 3) prone to bias, primarily due to the reliance on ecological study designs. The meta-analysis summary relative risk of thyroid cancer among those who live close to NPPs (defined by ≤ 25 km distance or jurisdictional areas (e.g., community, county) relative to those who lived further away was 1.09 (95% CI: 0.93-1.29). The risk estimates were higher for studies that modelled more proximal residential distances (≤ 5 km) to NPPs than larger distances (≤ 25 km and jurisdictional areas). We found that the summary risk (RR=1.29, 95% CI: 0.77-2.16) was stronger among those studies less prone to bias. A non-significant increased risk was found among both men and women, but there was no evidence of sex differences in risk.

CONCLUSION

Overall, the findings suggest that living near a nuclear power plant increases the risk of thyroid cancer. The small number of studies on this topic, and the finding of higher risks in studies less prone to bias highlights the need for better-designed studies.

Radiation Exposure to the Brains of Interventional Radiology Staff: A Phantom Study

Numerous papers report the occurrence of head and neck tumors in interventional radiology (IR) physicians. Recently, appropriate dosimetry and protection have become much more important. To accomplish these, first, we should accurately understand how the brain is exposed. We assessed the dose distribution of the head and clarified the relationship between head exposure and brain dose. We used eight radiophotoluminescence dosimeters (RPLDs), two at the surface of the eyes and six inside the phantom head. We conducted measurements with three kinds of irradiation fields: one irradiated the whole head, the second irradiated the brain region, and the third irradiated the soft tissue of the face. The cranial bone reduced the brain dose to less than half the skin dose: about 48% at the front and less than 9% at the back of the brain. Due to the brain exposure, the soft tissues were slightly exposed to the scatter radiation from the cranial bone. We revealed the dose distribution of the head and the influence of the scatter radiation from the cranial bone and the soft tissues of the face. There are two kinds of scatter radiation: from the cranial bone to the soft tissue of the face, and from the soft tissue to the brain. Although the influence of these sources of scatter radiation is not significant, the relationship between brain exposure and the occurrence of head and neck tumors is still unclear. Therefore, some IR physicians should keep this in mind if they receive high levels of exposure in their daily practice.

Occupational radiation exposure and risk of thyroid cancer: A meta‑analysis of cohort studies

The association between occupational exposure to ionizing radiation and the risk of thyroid cancer remains unclear in medical research. The present meta-analysis assessed whether occupational radiation exposure increases the risk of thyroid cancer. The PubMed, China National Knowledge Infrastructure, Embase, ChinaInfo, Weipu and Chinese Biomedical Literature databases were comprehensively searched for cohort studies published up to January 1st, 2023, using medical subject headings and keywords. Subsequently, a meta-analysis was conducted to determine a pooled-effect estimate of the association between occupational exposure and thyroid cancer. Subgroup analyses by sex were performed. The results were presented as the overall odds ratio (OR) and 95% confidence interval (CI). A total of six studies (covering 3,409,717 individuals), which were published between 2006 and 2021 from 4 countries met the inclusion criteria. The number of participants per study ranged from 67,562 to 2,992,166 and the number of cancer events in each study ranged from 134 to 2,599 cases. Pooled analyses indicated that occupational radiation exposure was associated with a 67% higher risk of thyroid cancer (OR=1.61, 95% CI: 1.27-2.04, P<0.001). Male patients with a history of occupational radiation exposure exhibited a slightly higher risk of thyroid cancer than female patients (OR=1.74, 95% CI: 1.61-1.87, P=0.726 vs. OR=1.30, 95% CI: 1.15-1.48, P=0.032). Collectively, the data indicated that occupational exposure to ionizing radiation was associated with the risk of thyroid cancer. However, further studies are warranted to confirm these preliminary findings.

Healthy worker hire and survivor effects in a cohort of medical radiation workers

BACKGROUND

The healthy worker effect may distort the association between exposure and health effects in workers. However, few studies have investigated both the healthy worker hire and survival effects simultaneously, and they are limited to mortality studies in male workers.

METHODS

We utilized a data set comprising South Korean diagnostic medical radiation workers registered in the National Dose Registry between 1996 and 2011, and merged it with mortality and cancer incidence data. Standardized mortality ratios (SMRs) and standardized incidence ratios (SIRs) were computed for comparison with the general population. To account for time-varying confounders influenced by prior occupational radiation exposure, we applied g-estimation using structural nested accelerated failure time models and compared the outcomes with those from Weibull regression.

RESULTS

A total of 1831 deaths and 3759 first primary cancer cases were identified among 93 918 workers. Both male (SMR = 0.44; 95% CI: 0.42, 0.46) and female workers (SMR = 0.53; 95% CI: 0.46, 0.60) showed lower mortality rates compared with national rates. In the SIR analysis, male workers exhibited reduced risks of solid cancer whereas female workers had increased risks. The g-estimation-derived hazard ratios (HRs) from radiation exposure exceeded those from Weibull regression estimates for all-cause death (HR = 2.55; 95% CI: 1.97, 3.23) and all-cancer incidence (HR = 1.96; 95% CI: 1.52, 2.55) in male workers whereas female workers showed the opposite results.

CONCLUSIONS

Comprehensive consideration of the healthy worker effect by sex is essential for estimating the unbiased impact of occupational exposure on health outcomes, notably in studies focusing on male mortality.

A Historical Survey of Key Epidemiological Studies of Ionizing Radiation Exposure

In this article we review the history of key epidemiological studies of populations exposed to ionizing radiation. We highlight historical and recent findings regarding radiation-associated risks for incidence and mortality of cancer and non-cancer outcomes with emphasis on study design and methods of exposure assessment and dose estimation along with brief consideration of sources of bias for a few of the more important studies. We examine the findings from the epidemiological studies of the Japanese atomic bomb survivors, persons exposed to radiation for diagnostic or therapeutic purposes, those exposed to environmental sources including Chornobyl and other reactor accidents, and occupationally exposed cohorts. We also summarize results of pooled studies. These summaries are necessarily brief, but we provide references to more detailed information. We discuss possible future directions of study, to include assessment of susceptible populations, and possible new populations, data sources, study designs and methods of analysis.

Monte Carlo modelling of cyclotron and radioisotope center (CYRIC) at Tohoku University: a radiation protection study

Protection against ionizing radiations is important in laboratories with radioactive materials and high energy cyclotron beams. The Cyclotron and Radioisotope Center (CYRIC) located in Tohoku University in Miyagi prefecture, Japan and is a well-known nuclear science laboratory with cyclotron beams and substantial number of high activity radioactive materials. Considering this, it is important to perform complete radiation transport computations to ensure the safety of non-occupational and occupational workers. In the present work, we have developed a complete 3-dimensional model of the main cyclotron building and radiation labs using Monte Carlo method. We have found that the dispersed photons and neutrons inside and in the surrounding of the CYRIC building pose no significant risk to occupational and non-occupational workers. The present work and the developed models would be useful in the field of radiation protection.

Ionizing radiation exposure during adulthood and risk of developing central nervous system tumors: systematic review and meta-analysis

Many studies on ionizing radiation (IR) exposure during childhood have shown deleterious effects on the central nervous system (CNS), however results regarding adult exposure are inconsistent, and no systematic reviews have been performed. The objectives are to synthesize the findings and draw evidence-based conclusions from epidemiological studies on the risk of benign and malignant brain and CNS tumors in humans exposed to low-to-moderate doses (< 0.5 Gy) of IR during adulthood/young adulthood. A systematic literature search of four electronic databases, supplemented by a hand search, was performed to retrieve relevant epidemiological studies published from 2000 to 2022. Pooled excess relative risk (ERRpooled) was estimated using a random effect model. Eighteen publications were included in the systematic review and twelve out of them were included in a meta-analysis. The following IR sources were considered: atomic bombs, occupational, and environmental exposures. No significant dose-risk association was found for brain/CNS tumors (ERRpooled at 100 mGy = - 0.01; 95% CI: - 0.05, 0.04). Our systematic review and meta-analysis did not show any association between exposure to low-to-moderate doses of IR and risk of CNS tumors. Further studies with histological information and precise dose assessment are needed.

Low-Dose Radiation Can Cause Epigenetic Alterations Associated With Impairments in Both Male and Female Reproductive Cells

Humans are regularly and continuously exposed to ionizing radiation from both natural and artificial sources. Cumulating evidence shows adverse effects of ionizing radiation on both male and female reproductive systems, including reduction of testis weight and sperm count and reduction of female germ cells and premature ovarian failure. While most of the observed effects were caused by DNA damage and disturbance of DNA repairment, ionizing radiation may also alter DNA methylation, histone, and chromatin modification, leading to epigenetic changes and transgenerational effects. However, the molecular mechanisms underlying the epigenetic changes and transgenerational reproductive impairment induced by low-dose radiation remain largely unknown. In this study, two different types of human ovarian cells and two different types of testicular cells were exposed to low dose of ionizing radiation, followed by bioinformatics analysis (including gene ontology functional analysis and Ingenuity Pathway Analysis), to unravel and compare epigenetic effects and pathway changes in male and female reproductive cells induced by ionizing radiation. Our findings showed that the radiation could alter the expression of gene cluster related to DNA damage responses through the control of MYC. Furthermore, ionizing radiation could lead to gender-specific reproductive impairment through deregulation of different gene networks. More importantly, the observed epigenetic modifications induced by ionizing radiation are mediated through the alteration of chromatin remodeling and telomere function. This study, for the first time, demonstrated that ionizing radiation may alter the epigenome of germ cells, leading to transgenerational reproductive impairments, and correspondingly call for research in this new emerging area which remains almost unknown.