An estimated 4,870 future cancers are induced each year because so many children are exposed to high radiation doses from CT scans, according to a report published online June 10 in JAMA Pediatrics.
Currently, the doses of radiation vary dramatically among radiologists, even for the same type of scan in children of the same age and size. Reducing the highest 25% of radiation doses to the median dose for that type of scan would prevent nearly half of these cancers from developing, said Diana L. Miglioretti, Ph.D., of the biostatistics unit at the Group Health Research Institute and the department of public health sciences at the University of Washington, Seattle, and her associates.
Noting that the ionizing radiation doses delivered by CT are 100-500 times higher than those of conventional radiography and fall within ranges that have been linked to increased cancer risk, Dr. Miglioretti and her colleagues examined time trends in CT imaging of pediatric patients from 1996 to 2010. CT exposure "is especially concerning for children because they are more sensitive to radiation-induced carcinogenesis [than are adults] and have many remaining years of life left for cancer to develop," they noted.
The researchers used data from the HMO Research Network to retrospectively assess randomly selected CT scans in children aged 15 years and younger enrolled in six health care systems covering diverse racial/ethnic and socioeconomic populations across the country. Between 152,419 and 371,095 patients were included for each year, for a total of 4,857,736 child-years of observation.
Radiation doses were calculated for a subset of 744 pediatric CTs of the head, chest, abdomen/pelvis, and spine. These regions together account for more than 95% of all pediatric CT scans. The study population was equally divided among boys and girls, and 29% of the patients were younger than 5 years at the time of their CT scans.
For children aged 5-15 years, the use of CT nearly tripled during the first decade of the study period, from 10.5 scans/1,000 in 1996 to 27.0/1,000 in 2006, then decreased somewhat to 23.9/1,000 in 2010, Dr. Miglioretti and her colleagues reported
The pattern was similar in children aged 0-5 years: CT scanning doubled from 11/1,000 in 1996 to 20/1,000 in 2006, and then dropped somewhat to 15.8/1,000 in 2010. This trend was seen across all six health care systems.
The stabilization and slight decline in pediatric CT scanning may have resulted from increased awareness about the cancer risks from pediatric imaging, particularly given the Image Gently campaign that began in 2007, they said.
Among the anatomic locations for CT scans, increases in the number of scans were greatest for abdominal and pelvic imaging, which happen to deliver the highest doses of radiation. The head was the most commonly scanned region for children of all ages, and head CTs increased by approximately 50% during the study period. Chest CTs also rose by 50%, and the number of spinal scans increased as much as ninefold, depending on the age of the patient.
Thus, the greater use of CT scans overall and the increased use of scans for regions that required higher radiation doses both contributed to the increase in radiation doses to the pediatric population, Dr. Miglioretti and her colleagues said.
However, variability in the radiation dose administered for a given type of scan also accounted for much of the increased exposure, and targeting the highest 25% of doses would yield the largest population benefits, the investigators said.
For example, radiation doses were highest for abdominal/pelvic scans, with a mean effective dose of 14.8 mSv for the oldest and largest children. But, as many as one-fourth of all the children who underwent a single abdominal/pelvic CT scan received a dose of 20 mSv or higher, Dr. Miglioretti and her associates said.
In another example, up to 14% of all head CTs delivered radiation doses of 50 mGy to the brain in a single examination and many children who require head CT undergo multiple such examinations. Reports in the literature cite 50 mGy of exposure as raising the risk of brain cancer by two- to threefold.
The investigators used the data on radiation exposure to estimate the lifetime attributable risks of various cancers nationwide.
One radiation-induced solid cancer was projected to arise from every 300-390 abdominal or pelvic scans among girls and for every 670-760 such scans among boys. For girls, one solid cancer was projected to arise from every 330-480 chest scans and from every 270-800 spinal scans, depending on the age of the child, Dr. Miglioretti and her colleagues said