Work history and mortality risks in 90 268 US radiological technologists

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.

Occupational exposure to radiation among health workers: Genome integrity and predictors of exposure

The current study aimed to investigate genomic instabilities in healthcare workers who may experience varying levels of radiation exposure through various radiological procedures. It also sought to determine if factors related to the work environment and dosimeter reading could effectively explain the observed genomic instabilities. Utilizing the cytokinesis-block micronucleus assay (CBMN) on peripheral blood lymphocytes, we assessed a spectrum of genomic aberrations, including nucleoplasmic bridge (NPB), nuclear budding (NBUD), micronucleus (MN) formation, and total DNA damage (TDD). The study uncovered a statistically significant increase in the occurrence of distinct DNA anomalies among radiology workers (with a significance level of P < 0.0001 for all measurements). Notably, parameters such as total working hours, average work duration, and time spent in projection radiography exhibited significant correlations with MN and TDD levels in these workers. The dosimeter readings demonstrated a positive correlation with the frequency of NPB and NBUD, indicating a substantial association between radiation exposure and these two genomic anomalies. Our multivariable models identified the time spent in projection radiography as a promising parameter for explaining the overall genomic instability observed in these professionals. Thus, while dosimeters alone may not fully explain elevated total DNA damage, intrinsic work environment factors hold potential in indicating exposure levels for these individuals, providing a complementary approach to monitoring.

The challenges of defining hormesis in epidemiological studies: The case of radiation hormesis

In the current radiation protection system, preventive measures and occupational exposure limits for controlling occupational exposure to ionizing radiation are based on the linear no-threshold extrapolation model. However, currently an increasing body of evidence indicates that this paradigm predicts very poorly biological responses in the low-dose exposure region. In addition, several in vitro and in vivo studies demonstrated the presence of hormetic dose response curves correlated to ionizing radiation low exposure. In this regard, it is noteworthy that also the findings of different epidemiological studies, conducted in different categories of occupationally exposed workers (e.g., healthcare, nuclear industrial and aircrew workers), observed lower rates of mortality and/or morbidity from cancer and/or other diseases in exposed workers than in unexposed ones or in the general population, then suggesting the possible occurrence of hormesis. Nevertheless, these results should be considered with caution since the identification of hormetic response in epidemiological studies is rather challenging because of a number of major limitations. In this regard, some of the most remarkable shortcomings found in epidemiological studies performed in workers exposed to ionizing radiation are represented by lack or inadequate definition of exposure doses, use of surrogates of exposure, narrow dose ranges, lack of proper control groups and poor evaluation of confounding factors. Therefore, considering the valuable role and contribution that epidemiological studies might provide to the complex risk assessment and management process, there is a clear and urgent need to overcome the aforementioned limits in order to achieve an adequate, useful and more real-life risk assessment that should also include the key concept of hormesis. Thus, in the present conceptual article we also discuss and provide possible approaches to improve the capacity of epidemiological studies to identify/define the hormetic response and consequently improve the complex process of risk assessment of ionizing radiation at low exposure doses.

Mortality among medical radiation workers in the United States, 1965-2016

BACKGROUND

Estimates of radiation risks following prolonged exposures at low doses and low-dose rates are uncertain. Medical radiation workers are a major component of the Million Person Study (MPS) of low-dose health effects. Annual personal dose equivalents, H_P(10), for individual workers are available to facilitate dose-response analyses for lung cancer, leukemia, ischemic heart disease (IHD) and other causes of death.

MATERIALS AND METHODS

The Landauer, Inc. dosimetry database identified 109,019 medical and associated radiation workers first monitored 1965-1994. Vital status and cause of death were determined through 2016. Mean absorbed doses to red bone marrow (RBM), lung, heart, and other organs were estimated by adjusting the recorded H_P(10) for each worker by scaling factors, accounting for exposure geometry, the energy of the incident photon radiation, sex of the worker and whether an apron was worn. There were 4 exposure scenarios: general radiology characterized by low-energy x-ray exposure with no lead apron use, interventional radiologists/cardiologists who wore aprons, nuclear medicine personnel and radiation oncologists exposed to high-energy photon radiation, and other workers. Standardized mortality ratio (SMR) analyses were performed. Cox proportional hazards models were used to estimate organ-specific radiation risks.

RESULTS

Overall, 11,433 deaths occurred (SMR 0.60; 95%CI 0.59,0.61), 126 from leukemia other than chronic lymphocytic leukemia (CLL), 850 from lung cancer, and 1654 from IHD. The mean duration of monitoring was 23.7 y. The excess relative rate (ERR) per 100 mGy was estimated as 0.10 (95% CI -0.34, 0.54) for leukemia other than CLL, 0.15 (0.02, 0.27) for lung cancer, and -0.10 (-0.27, 0.06) for IHD. The ERR for lung cancer was 0.16 (0.01, 0.32) among the 55,218 male workers and 0.09 (-0.19, 0.36) among the 53,801 female workers; a difference that was not statistically significant (p-value = 0.23).

CONCLUSIONS

Medical radiation workers were at increased risk for lung cancer that was higher among men than women, although this difference was not statistically significant. In contrast, the study of Japanese atomic bomb survivors exposed briefly to radiation in 1945 found females to be nearly 3 times the radiation risk of lung cancer compared with males on a relative scale. For medical workers, there were no statistically significant radiation associations with leukemia excluding CLL, IHD or other specific causes of death. Combining these data with other cohorts within the MPS, such as nuclear power plant workers and nuclear submariners, will enable more precise estimates of radiation risks at relatively low cumulative doses.

Reproductive factors, hormone use, and incidence of melanoma in a cohort of US Radiologic Technologists

STUDY QUESTION

Are reproductive factors and exogenous hormone use associated with incidence of cutaneous melanoma while accounting for ultraviolet radiation (UVR) exposure across different life periods and sun sensitivity factors?

SUMMARY ANSWER

Earlier age at menarche and late age at first birth, but not other estrogen-related factors were associated with an increased incidence rate of melanoma, with higher risks observed for earlier age at menarche and light hair color at age 15 years.

WHAT IS KNOWN ALREADY

Although estrogens have been recognized as photosensitizing, previous studies have reported inconsistent findings for the association of melanoma with estrogen-related factors. Most have not collected detailed skin cancer risk factors and have not thoroughly investigated effect modification by ambient UVR and sun sensitivity.

STUDY DESIGN, SIZE, DURATION

Participants in the US Radiologic Technologists study, an occupational cohort of 146 022 radiologic technologists (73% women), were included and followed during the four time periods (1983-1989, 1994-1998, 2003-2005 and 2012-2014).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Non-Hispanic white female participants who completed both the second (baseline) and third questionnaires, and did not report having cancer (except keratinocyte carcinoma) at baseline, were included and followed from their age at completion of the second (baseline) questionnaire until the earlier of first primary cancer diagnosis, including invasive melanoma of the skin, or completion of either the third or fourth questionnaire. Reproductive and exogenous hormonal factors were ascertained from the second (baseline) questionnaire, which also collected information on demographic, lifestyle factors and sun sensitivity factors. Ambient UVR was assigned by linking geocoded residential locations, based on self-reported residential history information collected from the third questionnaire to satellite-based ambient UVR data from the National Aeronautics and Space Administration's Total Ozone Mapping Spectrometer database. To examine the association of reproductive factors, exogenous hormone use, and first primary invasive melanoma of the skin, we used Poisson regression to calculate rate ratios (RRs) and 95% likelihood-based CIs, adjusting for attained age, birth cohort, lifetime average annual ambient UVR, contraceptives and menopausal hormone therapy use. To address the effect modification of ambient UVR exposure and sun sensitivities on melanoma risk, we conducted likelihood-ratio tests for multiplicative interaction.

MAIN RESULTS AND THE ROLE OF CHANCE

Over a median follow-up time of 17.1 years, 0.95% of eligible participants had an incident first primary melanoma (n = 444). Higher melanoma incidence rates were observed in participants with older attained age, blue/green/gray eye color, blonde/red/auburn natural hair color at age 15, fair skin complexion, and higher UVR. We found an increased incidence rate of melanoma in women who experienced menarche at an earlier age (13, 12 and <12 years vs ≥14 years: RR = 1.48, 95% CI = 1.11-1.98; 1.19, 0.89-1.61; 1.26, 0.93-1.73), and in women with older age at first birth (25-29 and ≥30 years vs <25 years; 1.09, 0.86-1.39; 1.48, 1.12-1.95; P-value for trend = 0.006). However, no significant association was observed for other reproductive factors, and for all exogenous hormone use. The associations of melanoma incidence for most reproductive factors and exogenous hormone use were not modified by ambient UVR, eye color, natural hair color at age 15 and skin complexion. The exception was that natural hair color at age 15 modified the associations of melanoma for age at menarche (P-value for interaction = 0.004) and age at first birth among parous women (0.005). In participants with blonde/red/auburn natural hair color at age 15, we found increased risk of melanoma among women who experienced menarche at age 13, 12 and <12 years (vs ≥14 years: RR = 3.54, 95% CI = 1.98-6.90; 2.51, 1.37-4.98; 2.66, 1.41-5.36, respectively; P-value for trend = 0.10). However, the association between age at menarche and melanoma was null in participants with brown/black natural hair color at age 15.

LIMITATIONS, REASONS FOR CAUTION

Information on reproductive history and exogenous hormone use was self-reported. We did not have information on specific doses or formulations of exogenous hormone medications or breastfeeding.

WIDER IMPLICATIONS OF THE FINDINGS

Women residing in areas of high ambient UVR and those with blonde/red/auburn natural hair color may constitute an additional high-risk group in need of more frequent skin cancer screening. Identifying susceptible periods of exposure or factors that modify UVR susceptibility may aid in guiding more targeted guidelines for melanoma prevention.

STUDY FUNDING/COMPETING INTEREST(S)

This research was supported by the Intramural Research Program, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, US Department of Health and Human Services. Authors declare no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Breast Cancer Risk Among Female Health Professionals: A 35-Year Population-Based Longitudinal Cohort Study in Taiwan

INTRODUCTION

Breast cancer is the most frequently diagnosed cancer among women worldwide. Previous studies have found a higher risk in nurses but no clear relationship among other health professionals. This study aims to investigate the risks of incident breast cancer among female health professionals compared with that among nonhealth professionals in Taiwan.

METHODS

This longitudinal observational cohort study included >35 years (1979-2016) of data from 4 nationwide population-based databases in Taiwan and identified matched cohorts with 1-to-2 propensity score matching between 277,543 health professionals and 555,086 nonhealth professionals. This study calculated total person-years for study subjects and compared breast cancer incidence between matched health and nonhealth professionals. Multivariable Cox proportional hazards and competing risk analyses were used, stratified by birth age, job tenure categories, and types of health professional license. Statistical analyses were conducted in 2019-2020.

RESULTS

Health professionals had a significantly higher risk of breast cancer (hazard ratio=1.34, 95% CI=1.28-1.41; subdistribution hazard ratio=1.36, 95% CI=1.30, 1.42). Elevated risk of breast cancer incidence was associated with birth age, job tenure, and several health professional license types, including physician, pharmacist, registered nurse, midwife, medical technologist, and psychologist.

CONCLUSIONS

Elevated breast cancer risk was found overall in female health professionals. Regular ultrasonography for younger women and mammography for those aged >45 years may be necessary in the annual labor physical examination for female health professionals.

Occupational radiation and haematopoietic malignancy mortality in the retrospective cohort study of US radiologic technologists, 1983-2012

OBJECTIVES

To evaluate cumulative occupational radiation dose response and haematopoietic malignancy mortality risks in the US radiologic technologist cohort.

METHODS

Among 110 297 radiologic technologists (83 655 women, 26 642 men) who completed a baseline questionnaire sometime during 1983-1998, a retrospective cohort study was undertaken to assess cumulative, low-to-moderate occupational radiation dose and haematopoietic malignancy mortality risks during 1983-2012. Cumulative bone marrow dose (mean 8.5 mGy, range 0-430 mGy) was estimated based on 921 134 badge monitoring measurements during 1960-1997, work histories and historical data; 35.4% of estimated doses were based on badge measurements. Poisson regression was used to estimate excess relative risk of haematopoietic cancers per 100 milligray (ERR/100 mGy) bone-marrow absorbed dose, adjusting for attained age, sex and birth year.

RESULTS

Deaths from baseline questionnaire completion through 2012 included 133 myeloid neoplasms, 381 lymphoid neoplasms and 155 leukaemias excluding chronic lymphocytic leukaemia (CLL). Based on a linear dose-response, no significant ERR/100 mGy occurred for acute myeloid leukaemia (ERR=0.0002, 95% CI <-0.02 to 0.24, p-trend>0.5, 85 cases) or leukaemia excluding CLL (ERR=0.05, 95% CI <-0.09 to 0.24, p-trend=0.21, 155 cases). No significant dose-response trends were observed overall for CLL (ERR<-0.023, 95% CI <-0.025 to 0.18, p-trend=0.45, 32 cases), non-Hodgkin lymphoma (ERR=0.03, 95% CI <-0.2 to 0.18, p-trend=0.4, 201 cases) or multiple myeloma (ERR=0.003, 95% CI -0.02 to 0.16, p-trend>0.5, 112 cases). Findings did not differ significantly by demographic factors, smoking or specific radiological procedures performed.

CONCLUSION

After follow-up averaging 22 years, there was little evidence of a relationship between occupational radiation exposure and myeloid or lymphoid haematopoietic neoplasms.

Occupational low-dose irradiation and cancer risk among medical radiation workers

Background

Medical workers are the largest group of workers occupationally exposed to low doses of ionizing radiation (IR) worldwide.

Aims

This review presents all the cohorts of medical workers exposed in the world and summarizes cancer risks associated with radiation exposure in this population.

Methods

Epidemiological studies on health professionals exposed to IR published from 1975 to 2019 were reviewed. Strength of evidence was assessed according to the modified Royal College of General Practitioners three-star system.

Results

Among the 16 epidemiological studies focusing on cancers from 11 cohorts among medical staff exposed to radiation, higher risks of cancer were observed for pre-1950 exposure and for medical workers who performed fluoroscopically guided interventional procedures or radionuclides procedures compared to those who did not. However, strength of evidence supporting the associations remains moderate as several methodological limits including the lack of dosimetry data, lifestyle factors and recent updates may obscure the link between medical occupational exposure and cancer occurrence.

Conclusions

Excess risk of cancer is suspected for high and former exposures. The more highly exposed professions, i.e. interventional physicians and nuclear medicine workers, should be monitored carefully. Collaborative projects aiming to increase the quantity and quality of information of the studied populations would be a key point

Lung cancer mortality associated with protracted low-dose occupational radiation exposures and smoking behaviors in U.S. radiologic technologists, 1983-2012

In the Japanese atomic bomb survivors, risk of lung cancer has been shown to increase with greater acute exposure to ionizing radiation. Although similar findings have been observed in populations exposed to low-dose, protracted radiation, such studies lack information on cigarette smoking history, a potential confounder. In a cohort of 106 068 U.S. radiologic technologists, we examined the association between estimated cumulative lung absorbed dose from occupational radiation exposure and lung cancer mortality. Poisson regression models, adjusted for attained age, sex, birth cohort, pack-years smoked and years since quitting smoking, were used to calculate linear excess relative risks (ERR) per 100 mGy, using time-dependent cumulative lung absorbed dose, lagged 10 years. Mean cumulative absorbed dose to the lung was 25 mGy (range: 0-810 mGy). During the 1983 to 2012 follow-up, 1090 participants died from lung cancer. Greater occupational radiation lung dose was not associated with lung cancer mortality overall (ERR per 100 mGy: -0.02, 95% CI: <0-0.13). However, significant dose-response relationships were observed for some subgroups, which might be false-positive results given the number of statistical tests performed. As observed in other studies of radiation and smoking, the interaction between radiation and smoking appeared to be sub-multiplicative with an ERR per 100 mGy of 0.41 (95% CI: 0.01-1.15) for those who smoked <20 pack-years and -0.03 (95% CI: <0-0.15) for those who smoked ≥20 pack-years. Our study provides some evidence that greater protracted radiation exposure in the low-dose range is positively associated with lung cancer mortality.

Occupational radiation exposure and morbidity of circulatory disease among diagnostic medical radiation workers in South Korea

Objectives

We investigated the association between low-dose external occupational radiation exposure and circulatory disease morbidity among diagnostic medical radiation workers.

Methods

A cohort of 11 500 diagnostic medical radiation workers was linked with the National Dosimetry Registry data and the National Health Insurance Service data. Relative risks (RRs) were calculated to explore the association between occupational factors and circulatory disease morbidity, and excess relative risks per 100 milligray (ERR/100 mGy) were estimated to quantify the radiation dose-response relationship.

Results

Overall, there were 2270 cases of circulatory diseases during 93 696 person-years of observation (average follow-up=8.1 years). RRs for hypertension were significantly increased for individuals who started working before 2000 compared with those who started in 2005 and later. ERR/100 mGy for all circulatory diseases was 0.14 (95% CI −0.57 to 0.99). Radiation risks of cerebrovascular diseases and ischaemic heart disease were non-significantly increased with estimates of individual cumulative doses to the heart (ERR/100 mGy=3.10 (−0.75 to 11.59) and 1.22 (−0.71 to 4.73), respectively). However, ERR estimates were generally more strongly positive for female versus male workers and for younger workers versus more than 50-year-old workers.

Conclusions

This study provides little evidence in support of a positive association between occupational radiation exposure and the overall risk of circulatory disease over a short follow-up period among medical radiation workers in South Korea. However, significantly increased RR with earlier year first worked, elevated ERR in female workers and young workers should be further followed up.

Fetal radiation exposure risk in the pregnant neurointerventionalist

BACKGROUND

The prevalence of women physicians is steadily rising, but the field of neurointervention remains one of the most male-dominated subspecialties in medicine. A fear of radiation exposure, particularly during pregnancy and childbearing years, may be responsible for deterring some of the best and brightest. This is the first study to examine the amount of maternal and fetal radiation exposure during a pregnant neurointerventional fellow's training.

METHODS

We retrospectively analyzed the radiation exposure of a neurointerventional fellow prior to and during pregnancy from February 2018 to May 2019 in 758 neurointerventional cases. The collar dosimeter was used to measure overall maternal exposure and an additional fetal dosimeter was worn under two lead apron skirts to estimate fetal radiation exposure.

RESULTS

There was not a significant difference between pre- and post-pregnancy overall maternal radiation exposure as measured by the collar dosimeter (151 mrem pre-pregnancy and 105 mrem during pregnancy, p=0.129). Mean fluoroscopy time and fluoroscopy emission per procedure also did not differ prior to and during pregnancy. Fetal radiation exposure measurements from both the Mirion Genesis Ultra TLD dosimeter as well as the Mirion Instadose dosimeters worn under double lead apron skirts were 0 mrem for all 6 months.

CONCLUSION

These findings suggest that, when optimal radiation safety practices are implemented, the fetal dose of a pregnant neurointerventionalist is negligible. Further studies and education are necessary to encourage women to choose neurointervention and allow practicing women neurointerventionalists to maintain their productivity during their reproductive years.

EYE LENS DOSES OF RADIOLOGY TECHNOLOGISTS WHO ASSIST PATIENTS DURING RADIOGRAPHY

The International Commission on Radiological Protection (ICRP) revised a drastic decrease of the annual eye equivalent dose limit. The present study aimed to evaluate the amounts of radiation to which the eye lenses of radiological technologists (RT) become exposed and the effects of wearing lead glasses on dose reduction while assisting patients during radiographic assessments. Lens equivalent doses (Hp(3)) were measured at the neck using personal dosemeter. In addition, Hp(3) was estimated by converting air kerma determined using small optically stimulated luminescence (OSL) dosemeters at six positions on lead glasses near the eyes and at the neck. The estimated mean Hp(3) from personal dosemeter at the neck varied from 3.92 to 18.6 mSv/y. Compare to OSL for which the dose varies from 8.95 to 54.75 mSv/y, personal dosimeter underestimate Hp(3).Therefore, Hp(3) for RT might exceed the revised eye equivalent dose limit 20 mSv/y recommended by the ICRP.

Radiation epidemiology and health effects following low-level radiation exposure

Radiation epidemiology is the study of human disease following radiation exposure to populations. Epidemiologic studies of radiation-exposed populations have been conducted for nearly 100 years, starting with the radium dial painters in the 1920s and most recently with large-scale studies of radiation workers. As radiation epidemiology has become increasingly sophisticated it is used for setting radiation protection standards as well as to guide the compensation programmes in place for nuclear weapons workers, nuclear weapons test participants, and other occupationally exposed workers in the United States and elsewhere. It is known with high assurance that radiation effects at levels above 100-150 mGy can be detected as evidenced in multiple population studies conducted around the world. The challenge for radiation epidemiology is evaluating the effects at low doses, below about 100 mGy of low-linear energy transfer radiation, and assessing the risks following low dose-rate exposures over years. The weakness of radiation epidemiology in directly studying low dose and low dose-rate exposures is that the signal, i.e. the excess numbers of cancers associated with low-level radiation exposure, is so very small that it cannot be seen against the very high background occurrence of cancer in the population, i.e. a lifetime risk of incidence reaching up to about 38% (i.e. 1 in 3 persons will develop a cancer in their lifetime). Thus, extrapolation models are used for the management of risk at low doses and low dose rates, but having adequate information from low dose and low dose-rate studies would be highly desirable. An overview of recently conducted radiation epidemiologic studies which evaluate risk following low-level radiation exposures is presented. Future improvements in risk assessment for radiation protection may come from increasingly informative epidemiologic studies, combined with mechanistic radiobiologic understanding of adverse outcome pathways, with both incorporated into biologically based models.

Are We Approaching the End of the Linear No-Threshold Era?

The linear no-threshold (LNT) model for radiation-induced cancer was adopted by national and international advisory bodies in the 1950s and has guided radiation protection policies worldwide since then. The resulting strict regulations have increased the compliance costs for the various uses of radiation, including nuclear medicine. The concerns about low levels of radiation due to the absence of a threshold have also resulted in adverse consequences. Justification of the LNT model was based on the concept that low levels of radiation increase mutations and that increased mutations imply increased cancers. This concept may not be valid. Low-dose radiation boosts defenses such as antioxidants and DNA repair enzymes. The boosted defenses would reduce the endogenous DNA damage that would have occurred in the subsequent period, and so the result would be reduced DNA damage and mutations. Whereas mutations are necessary for causing cancer, they are not sufficient since the immune system eliminates cancer cells or keeps them under control. The immune system plays an extremely important role in preventing cancer, as indicated by the substantially increased cancer risk in immune-suppressed patients. Hence, since low-dose radiation enhances the immune system, it would reduce cancers, resulting in a phenomenon known as radiation hormesis. There is considerable evidence for radiation hormesis and against the LNT model, including studies of atomic bomb survivors, background radiation, environmental radiation, cancer patients, medical radiation, and occupational exposures. Though Commentary 27 published by the National Council on Radiation Protection and Measurements concluded that recent epidemiologic studies broadly support the LNT model, a critical examination of the studies has shown that they do not. Another deficiency of Commentary 27 is that it did not consider the vast available evidence for radiation hormesis. Other advisory body reports that have supported the LNT model have similar deficiencies. Advisory bodies are urged to critically evaluate the evidence supporting both sides and arrive at an objective conclusion on the validity of the LNT model. Considering the strength of the evidence against the LNT model and the weakness of the evidence for it, the present analysis indicates that advisory bodies would be compelled to reject the LNT model. Hence, we may be approaching the end of the LNT model era.

Implications of recent epidemiologic studies for the linear nonthreshold model and radiation protection

The recently published NCRP Commentary No. 27 evaluated the new information from epidemiologic studies as to their degree of support for applying the linear nonthreshold (LNT) model of carcinogenic effects for radiation protection purposes (NCRP 2018 Implications of Recent Epidemiologic Studies for the Linear Nonthreshold Model and Radiation Protection, Commentary No. 27 (Bethesda, MD: National Council on Radiation Protection and Measurements)). The aim was to determine whether recent epidemiologic studies of low-LET radiation, particularly those at low doses and/or low dose rates (LD/LDR), broadly support the LNT model of carcinogenic risk or, on the contrary, demonstrate sufficient evidence that the LNT model is inappropriate for the purposes of radiation protection. An updated review was needed because a considerable number of reports of radiation epidemiologic studies based on new or updated data have been published since other major reviews were conducted by national and international scientific committees. The Commentary provides a critical review of the LD/LDR studies that are most directly applicable to current occupational, environmental and medical radiation exposure circumstances. This Memorandum summarises several of the more important LD/LDR studies that incorporate radiation dose responses for solid cancer and leukemia that were reviewed in Commentary No. 27. In addition, an overview is provided of radiation studies of breast and thyroid cancers, and cancer after childhood exposures. Non-cancers are briefly touched upon such as ischemic heart disease, cataracts, and heritable genetic effects. To assess the applicability and utility of the LNT model for radiation protection, the Commentary evaluated 29 epidemiologic studies or groups of studies, primarily of total solid cancer, in terms of strengths and weaknesses in their epidemiologic methods, dosimetry approaches, and statistical modelling, and the degree to which they supported a LNT model for continued use in radiation protection. Recommendations for how to make epidemiologic radiation studies more informative are outlined. The NCRP Committee recognises that the risks from LD/LDR exposures are small and uncertain. The Committee judged that the available epidemiologic data were broadly supportive of the LNT model and that at this time no alternative dose-response relationship appears more pragmatic or prudent for radiation protection purposes.

Work history and radioprotection practices in relation to cancer incidence and mortality in US radiologic technologists performing nuclear medicine procedures

INTRODUCTION

Technologists working in nuclear medicine (NM) are exposed to higher radiation doses than most other occupationally exposed populations. The aim of this study was to estimate the risk of cancer in NM technologists in relation to work history, procedures performed and radioprotection practices.

METHODS

From the US Radiologic Technologists cohort study, 72 755 radiologic technologists who completed a 2003-2005 questionnaire were followed for cancer mortality through 31 December 2012 and for cancer incidence through completion of a questionnaire in 2012-2013. Multivariable-adjusted models were used to estimate HRs for total cancer incidence and mortality by history of ever performing NM procedures and frequency of performing specific diagnostic or therapeutic NM procedures and associated radiation protection measures by decade.

RESULTS

During follow-up (mean=7.5 years), 960 incident cancers and 425 cancer deaths were reported among the 22 360 technologists who worked with NM procedures. We observed no increased risk of cancer incidence (HR 0.96, 95% CI 0.89 to 1.04) or death (HR 1.05, 95% CI 0.93 to 1.19) among workers who ever performed NM procedures. HRs for cancer incidence but not mortality were higher for technologists who began performing therapeutic procedures in 1960 and later compared with the 1950s. Frequency of performing diagnostic or therapeutic NM procedures and use of radioprotection measures were not consistently associated with cancer risk. No clear associations were observed for specific cancers, but results were based on small numbers.

CONCLUSION

Cancer incidence and mortality were not associated with NM work history practices, including greater frequency of procedures performed.

State of the evidence 2017: an update on the connection between breast cancer and the environment

BACKGROUND

In this review, we examine the continually expanding and increasingly compelling data linking radiation and various chemicals in our environment to the current high incidence of breast cancer. Singly and in combination, these toxicants may have contributed significantly to the increasing rates of breast cancer observed over the past several decades. Exposures early in development from gestation through adolescence and early adulthood are particularly of concern as they re-shape the program of genetic, epigenetic and physiological processes in the developing mammary system, leading to an increased risk for developing breast cancer. In the 8 years since we last published a comprehensive review of the relevant literature, hundreds of new papers have appeared supporting this link, and in this update, the evidence on this topic is more extensive and of better quality than that previously available.

CONCLUSION

Increasing evidence from epidemiological studies, as well as a better understanding of mechanisms linking toxicants with development of breast cancer, all reinforce the conclusion that exposures to these substances - many of which are found in common, everyday products and byproducts - may lead to increased risk of developing breast cancer. Moving forward, attention to methodological limitations, especially in relevant epidemiological and animal models, will need to be addressed to allow clearer and more direct connections to be evaluated.

The Comparison of Health Status Between Male and Female Medical Radiation Workers in China

To assess the health statue of chronically exposed Chinese medical radiation workers. A cross-sectional study of 530 medical radiation workers in a city of China was conducted to document the health status and the monitored annually absorbed doses. Long-term and low-dose radiation exposure can affect a number of health indicators in the individuals, which covered the cardiovascular system, hematologic system, ophthalmology, liver and kidney's functions, chromosome aberration and micronucleus. The differences in the health status between male and female individuals were associated with job types and exposed years of service. The monitored doses of individuals were lower than the limit value of the national standard. The health status in chronically exposed individuals demonstrated some gender difference associated with length of exposure and work type. This study provides some evidence to understand the health status of medical radiation workers in China and have the potentially to inform screening and clinical diagnosis.

The work-relatedness at a case of acute lymphoblastic leukemia in a radiation oncologist

Background

Clinicians who perform radiation therapy (RT) are exposed to radiation, which may negatively affect their health. The present study reports a case of acute lymphoblastic leukemia in a healthcare provider who was exposed to radiation at work; we also present a literature review of this topic.

Case presentation

A 45-year-old patient, who had been a radiation oncologist and had been exposed to radiation while performing brachytherapy 10 years ago, complained of chest pain and was suspected of having leukemia based on the results of a blood test in an outpatient clinic. He was diagnosed with acute lymphoblastic leukemia, and subsequently underwent chemotherapy. However, the case died during treatment. Through epidemiological investigation, it was found that the case’s cumulative exposure dose based on personal exposure and spatial dose measured during the work period was in the range of 6.08–12.15 mSv.

Conclusions

Based on the following considerations, acute lymphoblastic leukemia was highly correlated with the level of radiation to which the case was exposed while performing brachytherapy on patients with cancer. Firstly, the latent period of acute lymphoblastic leukemia in the case closely matched the latency time reported in previous published studies (5–10 years). In addition, numerous studies have reported significantly higher relative risks of cancer among clinicians who perform RT compared with the general population. The case was also atypically exposed to radiation through his hands, despite wearing protective equipment. Lastly, the case’s coworkers were also found to have been exposed to high levels of radiation. Investigation into the influence of radiation exposure through atypical routes during RT on the health of clinicians is recommended.

Reliability of self-reported questionnaire on occupational radiation practices among diagnostic radiologic technologists

BACKGROUND

We aimed to assess the reliability of a self-reported questionnaire on occupational radiation practices among radiologic technologists.

METHODS

We enrolled 941 participants who had repeatedly completed the questionnaire from the 2012-2013 radiologic technologists' health study in South Korea. We used percentage agreement, kappa statistics, and intraclass correlation coefficient (ICC) to assess the reliability of responses on work practices.

RESULTS

Overall agreement for ever-never diagnostic radiation procedures was high (87.5-97.5%), and κ values indicated substantial agreement (0.66-0.86) in all procedures except cephalometric and intraoral radiography. For the information of year of work start and working duration, high agreement was obtained (ICC: 0.99 and 0.98, respectively). However, use of a worn dosimeter and of personal protective equipment showed only moderate to substantial agreement.

CONCLUSIONS

Self-reported information on working practices regarding radiation exposure in radiologic technologists was reliable enough for epidemiologic studies. Am. J. Ind. Med. 60:377-385, 2017. © 2017 Wiley Periodicals, Inc.

Occupational Radiation Exposure and Deaths From Malignant Intracranial Neoplasms of the Brain and CNS in U.S. Radiologic Technologists, 1983-2012

OBJECTIVE

Childhood exposure to acute, high-dose radiation has consistently been associated with risk of benign and malignant intracranial tumors of the brain and CNS, but data on risks of adulthood exposure to protracted, low-to-moderate doses of radiation are limited. In a large cohort of radiologic technologists, we quantified the association between protracted, low-to-moderate doses of radiation and malignant intracranial tumor mortality.

MATERIALS AND METHODS

The study population included 83,655 female and 26,642 male U.S. radiologic technologists who were certified for at least 2 years as of 1982. The cohort was followed from the completion date of the first or second survey (1983-1989 or 1994-1998) to the date of death, loss to follow-up, or December 31, 2012, whichever was earliest. Occupational brain doses through 1997 were based on work history, historical data, and, for most years after the mid 1970s, individual film badge measurements. Radiation-related excess relative risks (ERRs) and 95% CIs were estimated from Poisson regression models adjusted for attained age and sex.

RESULTS

Cumulative mean absorbed brain dose was 12 mGy (range, 0-290 mGy). During follow-up (median, 26.7 years), 193 technologists died of a malignant intracranial neoplasm. Based on models incorporating a 5-year lagged cumulative brain dose, cumulative brain dose was not associated with malignant intracranial tumor mortality (overall ERR per 100 mGy, 0.1; 95% CI, < -0.3 to 1.5). No effect modification was observed by sex or birth cohort.

CONCLUSION

In this nationwide cohort of radiologic technologists, cumulative occupational radiation exposure to the brain was not associated with malignant intracranial tumor mortality.

Occupational Health Risks in Cardiac Catheterization Laboratory Workers

BACKGROUND

Orthopedic strain and radiation exposure are recognized risk factors in personnel staff performing fluoroscopically guided cardiovascular procedures. However, the potential occupational health effects are still unclear. The purpose of this study was to examine the prevalence of health problems among personnel staff working in interventional cardiology/cardiac electrophysiology and correlate them with the length of occupational radiation exposure.

METHODS AND RESULTS

We used a self-administered questionnaire to collect demographic information, work-related information, lifestyle-confounding factors, all current medications, and health status. A total number of 746 questionnaires were properly filled comprising 466 exposed staff (281 males; 44±9 years) and 280 unexposed subjects (179 males; 43±7years). Exposed personnel included 218 interventional cardiologists and electrophysiologists (168 males; 46±9 years); 191 nurses (76 males; 42±7 years), and 57 technicians (37 males; 40±12 years) working for a median of 10 years (quartiles: 5-24 years). Skin lesions (P=0.002), orthopedic illness (P<0.001), cataract (P=0.003), hypertension (P=0.02), and hypercholesterolemia (P<0.001) were all significantly higher in exposed versus nonexposed group, with a clear gradient unfavorable for physicians over technicians and nurses and for longer history of work (>16 years). In highly exposed physicians, adjusted odds ratio ranged from 1.7 for hypertension (95% confidence interval: 1-3; P=0.05), 2.9 for hypercholesterolemia (95% confidence interval: 1-5; P=0.004), 4.5 for cancer (95% confidence interval: 0.9-25; P=0.06), to 9 for cataract (95% confidence interval: 2-41; P=0.004).

CONCLUSIONS

Health problems are more frequently observed in workers performing fluoroscopically guided cardiovascular procedures than in unexposed controls, raising the need to spread the culture of safety in the cath laboratory.

Occupational radiation procedures and doses in South Korean dentists

OBJECTIVES

Dentistry is among the occupations involving chronic exposure to ionizing radiation. Although several cohort studies on medical radiation workers have been conducted in some countries, only a few epidemiological studies on dentists have been performed to examine occupational radiation exposure worldwide. The aim of this study was to investigate occupational characteristics and radiation exposures in South Korean dentists.

METHODS

A total of 658 dentists were surveyed from April 2012 to May 2013, and survey data were linked with dosimetry data from the National Dose Registry. Multiple linear regression analysis was used to identify the relationship between demographic or occupational factors and individual radiation doses.

RESULTS

Of the dentists sampled, 78% were men, 51% were younger than age 40, and 61% began employment after 2000. The most frequent procedures performed by dentists were panoramic radiography, followed by intraoral and portable dental radiography. Male dentists were more frequently involved in radiation procedures, and a higher proportion of male than female dentists wore a lead apron for diagnostic radiology. The average annual effective dose was 0.18 mSv for male and 0.13 mSv for female dentists. Female dentists working in provincial areas had significantly higher average annual and cumulative effective doses than those in metropolitan areas. The cumulative effective doses were significantly greater for older dentists, those who entered the field in the 1990s, and those with longer employment duration.

CONCLUSIONS

Our findings provided detailed information on work practices, number of procedures performed on a weekly basis, and occupational radiation doses, which enabled in-depth evaluation of occupational radiation exposure and work status among dentists.

Ionising radiation and risk of death from leukaemia and lymphoma in radiation-monitored workers (INWORKS): an international cohort study

BACKGROUND

There is much uncertainty about the risks of leukaemia and lymphoma after repeated or protracted low-dose radiation exposure typical of occupational, environmental, and diagnostic medical settings. We quantified associations between protracted low-dose radiation exposures and leukaemia, lymphoma, and multiple myeloma mortality among radiation-monitored adults employed in France, the UK, and the USA.

METHODS

We assembled a cohort of 308,297 radiation-monitored workers employed for at least 1 year by the Atomic Energy Commission, AREVA Nuclear Cycle, or the National Electricity Company in France, the Departments of Energy and Defence in the USA, and nuclear industry employers included in the National Registry for Radiation Workers in the UK. The cohort was followed up for a total of 8.22 million person-years. We ascertained deaths caused by leukaemia, lymphoma, and multiple myeloma. We used Poisson regression to quantify associations between estimated red bone marrow absorbed dose and leukaemia and lymphoma mortality.

FINDINGS

Doses were accrued at very low rates (mean 1.1 mGy per year, SD 2.6). The excess relative risk of leukaemia mortality (excluding chronic lymphocytic leukaemia) was 2.96 per Gy (90% CI 1.17-5.21; lagged 2 years), most notably because of an association between radiation dose and mortality from chronic myeloid leukaemia (excess relative risk per Gy 10.45, 90% CI 4.48-19.65).

INTERPRETATION

This study provides strong evidence of positive associations between protracted low-dose radiation exposure and leukaemia.

FUNDING

Centers for Disease Control and Prevention, Ministry of Health, Labour and Welfare of Japan, Institut de Radioprotection et de Sûreté Nucléaire, AREVA, Electricité de France, National Institute for Occupational Safety and Health, US Department of Energy, US Department of Health and Human Services, University of North Carolina, Public Health England.