Exposure to postnatal diagnostic x-rays may be associated with an increased risk of childhood acute lymphoid leukemia (ALL), according to a study published in the October issue of the International Journal of Epidemiology .
While the relationship between high doses of radiation and cancer has been established, Karen Bartley, a doctoral student in the department of epidemiology at the School of Public Health at the University of California, Berkeley, and colleagues noted that the potential association between low dose diagnostic x-ray exposures early in life and increased risk of childhood leukemia remains unclear.
"The general clinical impression has been that the level of radiation a child would be exposed to today from a conventional x-ray would not confer an additional risk for cancer," said the study's senior author Patricia Buffler, PhD. "The results of our study were not what we expected."
The researchers selected 711 children between the ages of 0 to 14 years with ALL and 116 with acute myeloid leukemia (AML) between 1995 and 2008 for inclusion in the Northern California Childhood Leukemia Study, a population-based case-control study. The children with leukemia were compared with a control group of children randomly selected from the California birth registry who were matched by factors such as age, gender, ethnicity and maternal race.
Bartley and colleagues interviewed mothers of children diagnosed with leukemia within four months of diagnosis for information concerning the number of x-rays the child underwent at least 12 months or more before the leukemia diagnosis, in addition to their own exposure to x-rays during pregnancy and the year prior to pregnancy, excluding dental x-rays.
Conditional logistic regression analyses were utilized to determine whether ALL or AML could be associated with self-reported post-natal x-rays, including number of x-rays, region of the body x-rayed and age at first x-ray, as well as maternal preconception and prenatal x-ray exposure.
The researchers reported that following the exclusion of x-rays in the year prior to diagnosis (reference date for matched controls), risk of ALL was elevated in children exposed to three or more postnatal x-rays. For B-cell ALL specifically, exposure to one or more x-rays resulted in a moderately increased risk. Body region exposed was not an independent risk factor in multivariable analyses and no associations were observed between number of postnatal x-rays and AML or T-cell ALL.
Additionally, the prevalence of exposure to prenatal and preconception x-rays was low, and no associations with ALL or AML could be observed, the authors wrote.
While the results suggest that exposure to postnatal diagnostic x-rays is associated with increased risk of childhood ALL, specifically B-cell ALL, but not AML or T-cell ALL, Bartley and colleagues suggested that due to the “imprecise measures of self-reported x-ray exposure,” the findings should be interpreted with caution and warrant further research.