Dissertation Abstract

Cause-Specific Cancer Mortality and Incident Hematopoietic Malignancies Among Radiation Technologists in the United States.

The main objective of this study was to evaluate risk for all-cause and cause-specific mortality, and incident hematopoietic malignancies in a large, primarily female (73%) cohort of radiologic technologists. A cohort of 146,022 radiologic technologists certified during 1926-1982 were followed through 1997 to evaluate mortality risks. Causes of death were obtained from death certificates prior to 1979 and subsequently from the National Death Index Plus.

Significantly low standardized mortality ratios (SMRs) were observed for deaths from all causes (0.76) and all cancers (0.82), while elevated risks were observed for breast cancer, associated with certification before 1940 (SMR 1.55, 95% CI 1.24-1.91), and certification durations of 20-29 (SMR 1.21, 95% CI 1.06-1.37) and 30+ years (SMR 1.77, 95% CI 1.54-2.02), and for leukemia, associated with certification duration of 20 & 29 (SMR = 1.35, 95% CI = 1.00-1.77) and 30+ years (SMR = 1.36, 95% CI = 0.97-1.85). Among 90,305 technologists who responded to a self-administered questionnaire, risks for breast cancer mortality were significantly increased among women (n = 69,525) with an earlier year of first employment (RR = 2.75 and RR = 2.20 for women first employed before 1940 and during 1940-49, respectively, versus 1960 or later) and with longer duration of employment before 1950 (p-trend = 0.04), after adjusting for age at first birth, age at menopause, and family history of breast cancer. Increasing breast cancer risks were also linked with earlier calendar year but not with duration of use of fluoroscopy (p-trend = 0.04) and multi-film procedures (p-trend = 0.06). Breast cancer risks were not related to estimated cumulative radiation exposures. Poisson regression analysis of incident hematopoietic malignancies among respondents to the baseline questionnaire who either responded to a follow-up questionnaire administered during 1994-1996 to ascertain cancer incidence and exposure updates or died after completion of the baseline questionnaire (n = 71,925), did not show any significant association with the calendar year and total duration of employment, employment with specific procedures or the estimated life-time cumulative exposure measure. The risk for acute myeloid and monocytic leukemia (n = 12) was significantly higher (RR = 6.3, 95% CI = 1.1-86.2) among radiologic technologists employed for 5 years or more prior to 1950. Acute myelogenous and monocytic leukemia was also significantly higher (2-fold) among technologists who held patients 50 times or more while being x-rayed compared to technologists who held patients less frequently.

This study suggests an increased breast cancer risk associated with occupational radiation exposures prior to 1950, when radiation doses were probably the highest. There is also some suggestion of an increased risk for acute myelogenous and monocytic leukemia among radiologic technologists employed for longer durations prior to 1950. Given large differences in exposure over time, calendar time period of employment may be a more important predictor of occupational radiation exposure than total number of years worked.

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