After assessing several decades’ worth of survey data on more than 110,000 radiologic technologists, researchers have all but ruled out a dose-response association between cumulative protracted occupational radiation and death by brain tumor.  

In fact, the absence of positive-association evidence proved consistent even among techs who assisted with fluoroscopically guided interventions (FGIs). These procedures emit higher radiation doses, typically leave the tech’s head and extremities unshielded—and have long been a particular source of concern for FGI-performing physicians as well as techs.

The study was published online March 28 in the American Journal of Roentgenology.

Cari Kitahara, PhD, of the National Cancer Institute and colleagues looked at survey responses from 83,655 female and 26,642 male U.S. radiologic technologists.

The cohort was followed from the completion date of the first or second survey (1983 to 1989 or 1994 to 1998) to the date of death, last survey returned (“loss to follow-up”) or December 31, 2012, whichever was earliest, the authors report.

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 percent confidence intervals were estimated from Poisson regression models adjusted for attained age and sex.

The researchers found that, during follow-up (median, 26.7 years), 193 technologists died of a malignant intracranial neoplasm. However, based on models incorporating a five-year lagged cumulative brain dose, cumulative brain dose was not associated with malignant intracranial tumor mortality (overall ERR per 100 mGy, 0.1; 95 percent confidence interval).  

They also found that cumulative mean absorbed brain dose was 12 mGy (range, 0 to 290 mGy), and no effect modification was observed by sex or birth cohort.

“In this large nationwide cohort of U.S. radiologic technologists, all of whom were first certified for at least two years as of 1982 and were prospectively followed for mortality outcomes for nearly 30 years, we found no evidence of a dose-response association between cumulative protracted occupational radiation and malignant intracranial tumor mortality,” Kitahara et al. write in their discussion. “We also found no evidence of a dose-response association among radiologic technologists who reported having assisted with FGI procedures despite consistently higher doses compared with radiologic technologists who never assisted with FGI procedures.”

Among the study limitations the authors acknowledge is the unknowability of the extent to which nonresponse may have biased their results, “but we have no evidence that it was systematic by dose.”

Further, they write, their findings are “limited by uncertainties in the dose reconstruction, particularly for the earliest workers, who lacked dose information from film badges and who were also estimated to have much higher cumulative organ-specific doses compared with cohort participants who began working more recently.”

Among the strengths of their study, the authors note its large sample size, long length of follow-up, “nearly complete ascertainment of mortality including causes of death, and individualized estimates of absorbed brain doses for all individuals in the cohort that have been corroborated by a dose-response evaluation of chromosomal translocation rate.”