BACKGROUND:
The Radiation Epidemiology Branch and the University of Minnesota have followed a nationwide cohort of 146,022 U.S. radiologic technologists (USRT) since 1982 to assess cancer and other disease risks associated with long-term repeated low doses of ionizing radiation. The USRT Study is the largest cohort of medical radiation workers studied to date and the only one with substantial numbers of women, extensive covariate data, incident and fatal cancer and other outcomes, estimates of individual historical occupational radiation doses, personal medical radiation doses, and personal and residential solar ultraviolet radiation (UVR) doses, and biospecimens for breast and thyroid cancer cases and comparison subjects. This cohort is uniquely suited for addressing outstanding scientific questions about differences in risk related to the nature of radiation exposure, specifically whether risks are the same from a single or a few high-dose exposures (e.g. atomic bomb, radiotherapy) or from many small exposures over time that might be mitigated by DNA repair or other mechanisms. The nationwide distribution of the cohort, with wide-ranging UVR exposures, also offers a rare opportunity to evaluate risks for non-melanoma skin cancer with UVR, which will be a major focus of study during the next few years.
OBJECTIVES:
1. Assess risks of cancer and other diseases from long-term low-dose occupational and personal medical exposures.
2. Assess risks of cancer and other diseases from occupational exposure to emerging and evolving radiologic modalities (i.e. nuclear medicine, fluoroscopically-guided procedures).
3. Assess risks of skin and other cancers from solar ultraviolet radiation exposures.
4. Conduct discovery of genetic determinants for thyroid cancer and rapid replication of main genotype effects for breast cancer.
5. Evaluate gene-radiation and ionizing radiation-ultraviolet radiation interactions.
ELIGIBILITY:
All radiologic technologists certified by the American Registry of Radiologic Technologists for at least two years during 1926-1982 were eligible for study. Excluded were technologists who resided outside the U.S.
DESIGN:
Cohort study: The full USRT cohort consists of 146,022 radiologic technologists. The cohort is predominantly female (73%), Caucasian (93%), and presently 67 years old on average; 83% are living and 16% are deceased or presumed deceased. Three questionnaire surveys were conducted during 1983-2005 to collect information on occupational, personal medical, and personal and ambient residential ultraviolet radiation exposures, other cancer risk factors, and cancer and other disease outcomes. More than 110,000 technologists participated in the first and/or second surveys. The most recent follow-up (third survey) was conducted during 2003-2005 to obtain detailed work history information for improving occupational dosimetry. Enhanced estimates of individual annual badge dose (personal dose equivalent) and radiation absorbed doses to 12 organs and tissues (breast, thyroid, brain, red bone-marrow, lung, heart, ovary, colon, testes, skin of extremities, skin of head and neck, and lens of eye) were recently completed for survey participants. Linear dose-response analyses are underway to quantify risks from protracted low-dose radiation for cancers (e.g., breast, thyroid) and other radiation-related diseases (e.g., cardiovascular, cataracts). A fourth questionnaire survey is under development and will collect information on cancer and other disease outcomes, work history with nuclear medicine and fluoroscopically-guided procedures, and other risk factors. Fourth survey outcomes will be used to assess incident cancer risks with UVR exposure data collected on the third survey. Collection of blood or buccal cell samples from breast and thyroid cancer cases and comparison subjects continues. Future plans include a case-control study of basal cell carcinoma to assess risks with ultraviolet and ionizing radiation exposure, genetic variants, and interactions.
