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

Abstract

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.

Keywords:

• Medical workers
• radiation epidemiology
• million person study
• cancer
• heart disease

Acknowledgments

Special thanks to Chris Passmore, Mark Salasky and colleagues at Landauer Inc. who provided essential advice and guidance in understanding, using and accessing the dosimetry database used for defining the cohort selected for study, including the recording of personal dose equivalents (badge doses) over the more than 50 y of individual dosimetry data available for dose reconstruction. We are grateful for the detailed expert guidance on the dosimetric aspects of this work as provided by the members of the National Council on Radiation Protection and Measurements Scientific Committees SC 6-9 (NCRP, Report 178) and SC 6-11 (NCRP Commentary 30). We especially thank Daniel Miowdownik, Memorial Sloan Kettering Cancer Center for his assistance in the validation efforts. We also are indebted to the Department of Energy (Nimi Rao), the Nuclear Regulatory Commission (Doris Lewis), Oak Ridge Associated Universities (Derek A. Hagemeyer) and the Naval Dosimetry Center (CAPT Thad Sharp and LCDR Nakima McCormack) for facilitating linkages with their respective dosimetry files. The results presented herein represent the conclusions and opinions solely of the authors. Its publication does not imply endorsement by the National Council on Radiation Protection and Measurements, Vanderbilt University or any of the acknowledged agencies.

Disclosure statement

Most of the data used to reconstruct doses for the medical radiation worker cohort arose from measurements made by Landauer, Inc. and its predecessors over a period in excess of 50 y. Dr. R. Craig Yoder, a former long-term employee of Landauer, Inc and now retired was chair of the NCRP Scientific Committee that recently completed Commentary 30 on dosimetry guidance for medical workers. He contributed to the assembling, evaluation and interpretation of the recorded doses used in the analyses as well as assuring the historical accuracy of both technical and administrative data, His participation does not reflect any endorsement of the commercial offerings of Landauer by the NCRP, and he received no compensation from Landauer with regard to any aspect of the research reported herein. Further, he attests that his former associations had no influence on the scientific accuracy, or any other aspect of the work reported here. The other authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Additional information

Funding

The study of the medical workers, a component of the Million Person Study, was supported in part by a research grant from the U.S. Department of Energy (DOE) [Grant No. DE-SC0008944] awarded to the National Council on Radiation Protection and Measurements, which included interagency support from the U.S. Nuclear Regulatory Commission (NRC), the U.S. Environmental Protection Agency and the National Aeronautics and Space Administration (NASA); and two more recent DOE Grants [No. DE-AU0000042 and DE-AU0000046]. Additional support included grants from the NRC [NRC-HQ‐60‐14‐G‐0011]; the Centers for Disease Control and Prevention [5UE1EH000989, 5NUE1EH001315]; NASA [NNX15AU88G, 80NSSC17M0016]. Contract support also was received from the Naval Sea Systems Command [N00024-17-C-4322] for dosimetry linkages.

Notes on contributors

John D. Boice

John D. Boice Jr is past President of the National Council on Radiation Protection and Measurements and Professor of Medicine at Vanderbilt University. He is an international authority on radiation effects and served on the Main Commission of the International Commission on Radiological Protection and the United Nations Scientific Committee on the Effects of Atomic Radiation. He directs the Million Person Study of Low-Dose Health Effect.

Sarah S. Cohen

Sarah S. Cohen is a Senior Managing Epidemiologist at EpidStrategies, a Division of ToxStrategies, where she directs observational research studies in the areas of pharmacoepidemiology, nutritional epidemiology, and occupational epidemiology as well as leads large data management projects and statistical analyses. She is an Adjunct Assistant Research Professor of Medicine in the Department of Medicine at Vanderbilt University School of Medicine. She has been a collaborator on the Million Person Study of Low-Dose Health Effects for nearly twenty years, providing analytic support as well as coauthoring numerous publications.

Michael T. Mumma

Michael T. Mumma is the Director of Information Technology at the International Epidemiology Institute and the International Epidemiology Field Station for Vanderbilt University Medical Center. He has over 20 y of experience in data analysis and conducting epidemiologic investigations. He has published on methodological topics, including geocoding and comprehensive radiation exposure assessment, and is currently developing methods to determining socioeconomic status based on residential history.

Sara C. Howard

Sara C. Howard is a research associate at Oak Ridge Associated Universities. She has a masters degree in epidemiology and is pursuing a PhD in epidemiology with a focus on chronic diseases and occupational exposure. She has been a collaborator on the Million Person Study of Low-Dose Health Effects for nearly three years.

R. Craig Yoder

R. Craig Yoder directed the technical activities and programs at Landauer, Inc. from 1983 through his retirement in 2015. In this capacity, he influenced the technologies and measurement protocols used by the Company as it delivered dosimetry services around the world. He currently is using his historical knowledge to advise the MPS epidemiologists regarding the methods to translate personal monitoring information into mean absorbed doses to various organs. He is a Council member of the National Council on Radiation Protection and Measurements.

Lawrence T. Dauer

Lawrence T. Dauer is an Attending Physicist specializing in radiation protection at Memorial Sloan Kettering Cancer Center in the Departments of Medical Physics and Radiology. Previously, he was a Radiological Engineering Supervisor in the nuclear power industry. He is a Council and former Board member of the NCRP and served as a member of the ICRP Committee 3, Protection in Medicine.