Projecting the lifetime risk of cancer from exposure to diagnostic ionizing radiation for adolescent idiopathic scoliosis.

Adolescent idiopathic scoliosis (AIS) is a disorder characterized by lateral curvature of the spine and is the most prevalent orthopedic disorder in this age group. The diagnosis and management of AIS requires multiple full-spinal radiographs, leading to potentially high doses of ionizing radiation. The purpose of this study was to estimate in a cohort of subjects with AIS the organ-specific doses of x-ray radiation from spinal radiographs and to calculate the lifetime number of cancers attributable to these exposures. The cohort consisted of AIS patients referred from 1960 to 1979 to a large pediatric hospital in Montreal, Quebec. Organ-specific x-ray doses were estimated using a Monte Carlo procedure that accounted for the radiant energy of the x-ray beam. Cumulative doses for each subject were obtained by summing the estimated doses over all radiographs. These estimates of dose and published estimates of risk from the U.S. National Academy of Sciences Fifth Committee on the Biological Effects of Ionizing Radiation were then incorporated into a life table procedure to project the excess lifetime risk of cancer. About 85% of the 2,181 subjects in the cohort were first referred for scoliosis between the ages of 11 and 17 y. The mean number of radiographs over an average 3-y follow-up period was 12. Organs receiving the highest mean cumulative doses (about 0.03 Gy) were the thyroid gland and the female breast. About 10 excess incident cancer cases (out of a total of 399 projected) and about four excess deaths (out of a total of 247 projected) were estimated to occur over the lifetime of the 1,847 women in the cohort. This is equivalent to an excess lifetime risk of about 1 to 2% (12-25/1,000) among women. Although doses today from spinal radiographs are considerably lower than two decades ago, doses and risks can be further reduced through the use of the posteroanterior view in place of the more traditional anteroposterior view.