Low-dose Ionizing Radiation in Infancy May Affect Cognitive Functioning

Abstract

Source: Hall P, Hans-OlovA, Trichopoulos D, et al. Effect of low doses of ionising radiation in infancy on cognitive function in adulthood: Swedish population based cohort study. BMJ. 2004;328:19–24.Researchers in Sweden performed a retrospective analysis of 2,211 young men who had received radiation for cutaneous cranial hemangiomas from 1930–1959 before age 18 months. Radiation dose to the frontal and posterior parts of the brain was estimated and correlated with high school attendance and military service tests of cognitive ability administered at age 18 or 19 years. The mean age of the men at first treatment was 7 months, median 6 months. The average estimated absorbed dose to the brain was 52 mGy (median 20 mGy, range 0–2,800 mGy). With increasing doses of radiation to the brain there was a decreasing likelihood of high school attendance (P for trend <.0001) and decreasing performance on tests for concept discrimination (P=.03) and technical comprehension (P=.003) but not spatial recognition (P=.50). With no radiation exposure, high school attendance was ~32%; with exposure >250 mGy, attendance fell to ~17%. The probability of attending high school was reduced by about 50% in the >100mGy category compared with 1–20 mGy, and it decreased by 11–14% per 50 mGy increment in dose in multivariate analysis. The authors conclude that irradiation of the brain with doses that overlap those of diagnostic radiological studies are done at some risk to the developing brain. They recommend that the risks and benefits of computed tomography (CT) scans in minor head trauma be re-evaluated. (See also AAP Grand Rounds, October 2002;8:41–42).1High doses of ionizing radiation have been shown to adversely affect the developing brain. In utero radiation exposure at Hiroshima and Nagasaki caused an increase in mental retardation;2 and x-ray therapy of tinea capitis in Israel led to lower intelligence quotients (IQs) and fewer completed school grades.3 What this study adds is that the effective dose may be much lower than expected. The estimated dose of radiation from a head CT to an infant is about 120 mGy,4 more than twice the average dose in this study. If these retrospective results from Sweden can be replicated, then the relative ease with which head CTs are ordered for minor head trauma (sometimes more for legal than for cogent medical reasons) must be changed.In recent years, considerable attention has been directed towards the possible development of cancer in children receiving low-dose radiation during CT scans. The use of multidetector scanners and an increasing use of CT for diagnosis of children with abdominal pain, trauma, neurologic abnormality, and pulmonary problems has increased the potential radiation exposure of children individually and as a population group and, consequently, the potential long-term effect of carcinogenesis. The study reviewed above indicates another potentially more immediate complication of diagnostic levels of radiation adversely affecting the level of cognitive function. The children in the study received radiation in infancy with inclusion of parts of their brains. The resultant impairment of cognitive ability, which the authors document in this population in their late teens-early adulthood, adds another cautionary note regarding the potential harm of CT scanning the brain. While CT is a valuable and sensitive tool for diagnosis, there is a risk that warrants constant consideration of the justification of CT studies in children.