Downloaded from http://oem.bmj.com/ on January 13, 2015 - Published by group.bmj.com
Workplace
ORIGINAL ARTICLE
Work history and mortality risks in 90 268 US radiological technologists Jason J Liu,1 D Michal Freedman,1 Mark P Little,1 Michele M Doody,1 Bruce H Alexander,2 Cari M Kitahara,1 Terrence Lee,1 Preetha Rajaraman,1 Jeremy S Miller,3 Diane M Kampa,2 Steven L Simon,1 Dale L Preston,4 Martha S Linet1 1
Division of Cancer Epidemiology and Genetics, National Cancer Institute, Rockville, Maryland, USA 2 Division of Environmental Health Sciences, University of Minnesota School of Public Health, Minneapolis, Minnesota, USA 3 Information Management Services, Inc., Rockville, Maryland, USA 4 Hirosoft International, Eureka, California, USA Correspondence to Dr Jason J Liu, Division of Cancer Epidemiology and Genetics, Radiation Epidemiology Branch, 9609 Medical Center Drive, Room 7E520, Rockville, MD 20850, USA; [email protected] Received 17 September 2013 Revised 17 April 2014 Accepted 2 May 2014 Published Online First 22 May 2014
ABSTRACT Objectives There have been few studies of work history and mortality risks in medical radiation workers. We expanded by 11 years and more outcomes our previous study of mortality risks and work history, a proxy for radiation exposure. Methods Using Cox proportional hazards models, we estimated mortality risks according to questionnaire work history responses from 1983 to 1989 through 2008 by 90 268 US radiological technologists. We controlled for potential confounding by age, birth year, smoking history, body mass index, race and gender. Results There were 9566 deaths (3329 cancer and 3020 circulatory system diseases). Mortality risks increased significantly with earlier year began working for female breast ( p trend=0.01) and stomach cancers ( p trend=0.01), ischaemic heart ( p trend=0.03) and cerebrovascular diseases ( p trend=0.02). The significant trend with earlier year first worked was strongly apparent for breast cancer during baseline through 1997, but not 1998–2008. Risks were similar in the two periods for circulatory diseases. Radiological technologists working ≥5 years before 1950 had elevated mortality from breast cancer (HR=2.05, 95% CI 1.27 to 3.32), leukaemia (HR=2.57, 95% CI 0.96 to 6.68), ischaemic heart disease (HR=1.13, 95% CI 0.96 to 1.33) and cerebrovascular disease (HR=1.28, 95% CI 0.97 to 1.69). No other work history factors were consistently associated with mortality risks from specific cancers or circulatory diseases, or other conditions. Conclusions Radiological technologists who began working in early periods and for more years before 1950 had increased mortality from a few cancers and some circulatory system diseases, likely reflecting higher occupational radiation exposures in the earlier years.
INTRODUCTION
To cite: Liu JJ, Freedman DM, Little MP, et al. Occup Environ Med 2014;71:819–835.
There are more than 2 million medical radiation workers worldwide with potential occupational exposures to protracted low-dose ionising radiation.1 Clinical reports of leukaemia in early medical radiation workers established ionising radiation as a carcinogen more than 100 years ago.2 3 However, there have been relatively few large epidemiological studies of medical radiation workers with long-term follow-up, and most of these have not evaluated disease risks in substantial numbers of female workers. Previous studies have primarily focused on cancers,4–10 although some investigations have examined other outcomes.11–14
What this paper adds ▸ This analysis of the largest medical radiation worker cohort addresses the previously little-studied topic of work history and long-term mortality risks from cancers, circulatory system diseases and a broad range of other serious non-malignant diseases among medical radiation workers. ▸ Based on internal analyses, US radiological technologists who began working in earlier calendar years had increasing risks of dying from female breast cancer, stomach cancer, ischaemic heart disease and cerebrovascular disease. ▸ Risks of breast cancer, leukaemia, ischaemic heart disease and cerebrovascular disease rose significantly with increasing number of years worked before 1950. ▸ The findings suggest that protracted occupational exposure to radiation before the implementation of more stringent radiation protection measures in the late 1950s may be linked with mortality from specific cancers and circulatory system diseases. ▸ To our knowledge, this is the only cohort of medical radiation workers with a large number of radiation-exposed female workers, questionnaire-derived work history and extensive information on potential confounding factors, and our findings contribute to the knowledge of long-term mortality risks among medical radiation workers, particularly women.
A few studies of medical radiation workers and other radiation-exposed populations have suggested that low- and moderate-dose radiation exposure may also increase mortality from diseases of the circulatory,14 15 digestive16 17 and respiratory16 17 systems. The United States Radiologic Technologists (USRT) study represents the largest cohort study of medical radiation workers with fractionated low-dose rate radiation exposures that have likely cumulated to low-to-moderate levels, and one of only a small number of such cohorts that includes substantial numbers of female medical radiation workers.10 We previously conducted a mortality
Liu JJ, et al. Occup Environ Med 2014;71:819–835. doi:10.1136/oemed-2013-101859
819
Downloaded from http://oem.bmj.com/ on January 13, 2015 - Published by group.bmj.com
Workplace follow-up in this cohort through 1997 that examined only a few outcomes in relation to work history factors.7 14 We found that those who worked before 1950 had elevated mortality risks for breast cancer, leukaemia7 and circulatory system diseases, particularly cerebrovascular diseases.14 Using updated mortality data through 2008, we have extended our previous 16-year follow-up of the USRT to include an additional 11 years and have examined a broader range of cancers, as well as circulatory, digestive, respiratory and infectious diseases. The USRT is the only cohort of medical radiation workers to have completed questionnaires inquiring about work history, job practices, and other risk factors for cancer and other diseases. Work history data obtained from the cohort are a surrogate for estimated occupational radiation exposure and captures the variability in work practices that contribute to differences in radiation exposures over time. In this paper, we assess the work history factors as a proxy for occupational radiation exposure.
codes in online supplementary table A1). We examined mortality from all causes, all and specific cancers as well as circulatory, digestive, respiratory and infectious diseases. We analysed specific cancers that have been commonly associated with radiation exposure in studies of exposed populations1 (table 2), as well as other types of cancer (table 3). The rationale for assessing risks for circulatory system diseases was that some of these were previously associated with work history in the US radiological technologists,14 and because these conditions have been linked with radiation exposure in the atomic bomb survivors and other populations with low-to-moderate radiation exposure.15 We conducted exploratory analyses of certain malignant and nonmalignant diseases based on reports of elevated risks in the atomic bomb survivors (tables 3 and 4).16 17 Underlying causes of death were obtained from death certificates or the National Death Index Plus and coded according to the ICD revision in use at the time of death.19 20
METHODS Study population
Potential confounders
Details of the study population, methods for tracing the technologists, content of the questionnaires, and information about the work history and job practices have been previously published7 14 18 and can be found online (). A brief description of the study methods is provided below. The USRT cohort consists of 146 022 US residents certified for two or more years by the American Registry of Radiologic Technologists (ARRT) during 1926–1982. The ARRT certifies technologists in radiography, nuclear medicine, radiation therapy and, more recently, in other subspecialties. Follow-up is conducted through annual ARRT certification renewals. Technologists who drop their certification are linked with the records of the Social Security Administration and, if reported to be deceased, are linked with the National Death Index Plus to determine cause of death. A baseline questionnaire was mailed to 133 298 cohort members who were believed to be alive and for whom a current address was available (93% of the target population) during 1983–1989. The 90 268 technologists (68% participation rate) who responded were included in the current analysis focusing on internal comparisons within the cohort. The baseline questionnaire included questions about work history and practices, cigarette smoking history, and other known or potential chronic disease risk factors. This study has been approved annually by the human subjects review boards of the National Cancer Institute and the University of Minnesota.
Work history factors Work history information examined in this study was based on responses to the baseline questionnaire. We evaluated year first worked as a radiological technologist (
Workplace
ORIGINAL ARTICLE
Work history and mortality risks in 90 268 US radiological technologists Jason J Liu,1 D Michal Freedman,1 Mark P Little,1 Michele M Doody,1 Bruce H Alexander,2 Cari M Kitahara,1 Terrence Lee,1 Preetha Rajaraman,1 Jeremy S Miller,3 Diane M Kampa,2 Steven L Simon,1 Dale L Preston,4 Martha S Linet1 1
Division of Cancer Epidemiology and Genetics, National Cancer Institute, Rockville, Maryland, USA 2 Division of Environmental Health Sciences, University of Minnesota School of Public Health, Minneapolis, Minnesota, USA 3 Information Management Services, Inc., Rockville, Maryland, USA 4 Hirosoft International, Eureka, California, USA Correspondence to Dr Jason J Liu, Division of Cancer Epidemiology and Genetics, Radiation Epidemiology Branch, 9609 Medical Center Drive, Room 7E520, Rockville, MD 20850, USA; [email protected] Received 17 September 2013 Revised 17 April 2014 Accepted 2 May 2014 Published Online First 22 May 2014
ABSTRACT Objectives There have been few studies of work history and mortality risks in medical radiation workers. We expanded by 11 years and more outcomes our previous study of mortality risks and work history, a proxy for radiation exposure. Methods Using Cox proportional hazards models, we estimated mortality risks according to questionnaire work history responses from 1983 to 1989 through 2008 by 90 268 US radiological technologists. We controlled for potential confounding by age, birth year, smoking history, body mass index, race and gender. Results There were 9566 deaths (3329 cancer and 3020 circulatory system diseases). Mortality risks increased significantly with earlier year began working for female breast ( p trend=0.01) and stomach cancers ( p trend=0.01), ischaemic heart ( p trend=0.03) and cerebrovascular diseases ( p trend=0.02). The significant trend with earlier year first worked was strongly apparent for breast cancer during baseline through 1997, but not 1998–2008. Risks were similar in the two periods for circulatory diseases. Radiological technologists working ≥5 years before 1950 had elevated mortality from breast cancer (HR=2.05, 95% CI 1.27 to 3.32), leukaemia (HR=2.57, 95% CI 0.96 to 6.68), ischaemic heart disease (HR=1.13, 95% CI 0.96 to 1.33) and cerebrovascular disease (HR=1.28, 95% CI 0.97 to 1.69). No other work history factors were consistently associated with mortality risks from specific cancers or circulatory diseases, or other conditions. Conclusions Radiological technologists who began working in early periods and for more years before 1950 had increased mortality from a few cancers and some circulatory system diseases, likely reflecting higher occupational radiation exposures in the earlier years.
INTRODUCTION
To cite: Liu JJ, Freedman DM, Little MP, et al. Occup Environ Med 2014;71:819–835.
There are more than 2 million medical radiation workers worldwide with potential occupational exposures to protracted low-dose ionising radiation.1 Clinical reports of leukaemia in early medical radiation workers established ionising radiation as a carcinogen more than 100 years ago.2 3 However, there have been relatively few large epidemiological studies of medical radiation workers with long-term follow-up, and most of these have not evaluated disease risks in substantial numbers of female workers. Previous studies have primarily focused on cancers,4–10 although some investigations have examined other outcomes.11–14
What this paper adds ▸ This analysis of the largest medical radiation worker cohort addresses the previously little-studied topic of work history and long-term mortality risks from cancers, circulatory system diseases and a broad range of other serious non-malignant diseases among medical radiation workers. ▸ Based on internal analyses, US radiological technologists who began working in earlier calendar years had increasing risks of dying from female breast cancer, stomach cancer, ischaemic heart disease and cerebrovascular disease. ▸ Risks of breast cancer, leukaemia, ischaemic heart disease and cerebrovascular disease rose significantly with increasing number of years worked before 1950. ▸ The findings suggest that protracted occupational exposure to radiation before the implementation of more stringent radiation protection measures in the late 1950s may be linked with mortality from specific cancers and circulatory system diseases. ▸ To our knowledge, this is the only cohort of medical radiation workers with a large number of radiation-exposed female workers, questionnaire-derived work history and extensive information on potential confounding factors, and our findings contribute to the knowledge of long-term mortality risks among medical radiation workers, particularly women.
A few studies of medical radiation workers and other radiation-exposed populations have suggested that low- and moderate-dose radiation exposure may also increase mortality from diseases of the circulatory,14 15 digestive16 17 and respiratory16 17 systems. The United States Radiologic Technologists (USRT) study represents the largest cohort study of medical radiation workers with fractionated low-dose rate radiation exposures that have likely cumulated to low-to-moderate levels, and one of only a small number of such cohorts that includes substantial numbers of female medical radiation workers.10 We previously conducted a mortality
Liu JJ, et al. Occup Environ Med 2014;71:819–835. doi:10.1136/oemed-2013-101859
819
Downloaded from http://oem.bmj.com/ on January 13, 2015 - Published by group.bmj.com
Workplace follow-up in this cohort through 1997 that examined only a few outcomes in relation to work history factors.7 14 We found that those who worked before 1950 had elevated mortality risks for breast cancer, leukaemia7 and circulatory system diseases, particularly cerebrovascular diseases.14 Using updated mortality data through 2008, we have extended our previous 16-year follow-up of the USRT to include an additional 11 years and have examined a broader range of cancers, as well as circulatory, digestive, respiratory and infectious diseases. The USRT is the only cohort of medical radiation workers to have completed questionnaires inquiring about work history, job practices, and other risk factors for cancer and other diseases. Work history data obtained from the cohort are a surrogate for estimated occupational radiation exposure and captures the variability in work practices that contribute to differences in radiation exposures over time. In this paper, we assess the work history factors as a proxy for occupational radiation exposure.
codes in online supplementary table A1). We examined mortality from all causes, all and specific cancers as well as circulatory, digestive, respiratory and infectious diseases. We analysed specific cancers that have been commonly associated with radiation exposure in studies of exposed populations1 (table 2), as well as other types of cancer (table 3). The rationale for assessing risks for circulatory system diseases was that some of these were previously associated with work history in the US radiological technologists,14 and because these conditions have been linked with radiation exposure in the atomic bomb survivors and other populations with low-to-moderate radiation exposure.15 We conducted exploratory analyses of certain malignant and nonmalignant diseases based on reports of elevated risks in the atomic bomb survivors (tables 3 and 4).16 17 Underlying causes of death were obtained from death certificates or the National Death Index Plus and coded according to the ICD revision in use at the time of death.19 20
METHODS Study population
Potential confounders
Details of the study population, methods for tracing the technologists, content of the questionnaires, and information about the work history and job practices have been previously published7 14 18 and can be found online (). A brief description of the study methods is provided below. The USRT cohort consists of 146 022 US residents certified for two or more years by the American Registry of Radiologic Technologists (ARRT) during 1926–1982. The ARRT certifies technologists in radiography, nuclear medicine, radiation therapy and, more recently, in other subspecialties. Follow-up is conducted through annual ARRT certification renewals. Technologists who drop their certification are linked with the records of the Social Security Administration and, if reported to be deceased, are linked with the National Death Index Plus to determine cause of death. A baseline questionnaire was mailed to 133 298 cohort members who were believed to be alive and for whom a current address was available (93% of the target population) during 1983–1989. The 90 268 technologists (68% participation rate) who responded were included in the current analysis focusing on internal comparisons within the cohort. The baseline questionnaire included questions about work history and practices, cigarette smoking history, and other known or potential chronic disease risk factors. This study has been approved annually by the human subjects review boards of the National Cancer Institute and the University of Minnesota.
Work history factors Work history information examined in this study was based on responses to the baseline questionnaire. We evaluated year first worked as a radiological technologist (
