SCOTTSDALE, ARIZ. — Radiation exposure from the diagnostic imaging of children greatly increases their risk of cancer and death decades later, according to speakers at a pediatric update sponsored by Phoenix Children's Hospital.
Dr. Thomas L. Slovis and Dr. Alan H. Friedman urged pediatricians to be judicious, limiting their use of chest x-rays and computerized tomography to essential studies. They also called on pediatricians to insist that radiologists adjust radiation doses to minimize future harm to children.
Among the alarming statistics reported in their separate talks were the following:
▸ A 1-year-old infant is 10–15 times as likely to develop malignancy as is a 50-year-old adult given the same dose of radiation, according to the International Commission on Radiological Protection.
▸ The equivalent natural-radiation exposure ranges from 2.4 days of natural exposure during one chest x-ray to 4.3 years of natural exposure during one 30-minute cardiac catheterization. Within this range are one upper-gastrointestinal x-ray (equivalent to 1 year of natural exposure), one barium enema (equivalent to 2.3 years), and one abdominal CT scan (equivalent to 3.3 years).
▸ The risk of dying of complications from an abdominal CT scan performed in the first year of life is 1:1,000. This is greater than the risk of death from a bicycle accident, drowning, or a medical complication, according to the National Safety Council.
▸ Low doses of radiation comparable to a CT dose are associated with excess cancers and excess deaths in an ongoing 50-year study of 50,000 atomic bomb survivors (Radiation Research 2000:154:178–86).
The issue is not whether to image, but when and how often and which test to use, said Dr. Friedman, director of the pediatric echocardiography laboratory at Yale University, New Haven, Conn.
“If we're not careful and thoughtful in the use of the technology, we may be exposing our youngest and most vulnerable patients to potentially dangerous and worrisome doses of radiation,” he said in an interview. “It may not have an effect in the short term, but we may really start to realize deleterious effects decades down the road.”
Along with more judicious use of tests, pediatricians should ask radiologists whether they tailor radiation doses for children, said Dr. Slovis, of the division of pediatric imaging at Wayne State University, Detroit.
He advocated wider application of the concept of ALARA (“as low as reasonably achievable”) to radiation dosing in children. “You want the proper dose. If the dose is too low, you can't make the diagnosis,” he said.
Various factors make children more susceptible to radiation. Dr. Friedman listed tissue weighting, the exposure of more organs, longer life expectancy, and more rapid cell division.
Dr. Slovis said that children receive more radiation than do adults when the same dose of radiation is used. Radiation doses are measured with a phantom and set at a fixed midpoint, he said. This measurement is based on 14 slices, but is independent of the thickness of those slices.
Studies of the effects of radiation in the survivors of the atomic bombings of Hiroshima and Nagasaki include data specific to children.
Among the findings noted by Dr. Friedman is an increased incidence of leukemia, breast cancer, colon cancer, thyroid cancer, and lung cancer. These do not occur immediately, but at the times that would be expected for the specific cancer to develop.
Girls are more radiosensitive than boys, he said, and the risk of cancer development varies dramatically with the patient's age at exposure.
Dr. Slovis said some children with hereditary diseases—including ataxia-telangiectasia, basal cell nevus syndrome, Cockayne's syndrome, Down syndrome, Fanconi's anemia, Gardner's syndrome, Nijmegen breakage syndrome, and Usher's syndrome—are extremely sensitive to radiation and should not be exposed at all, if possible.
He also discouraged the use of radiation in children with hereditary syndromes that have been associated with childhood cancers.
Fetuses and premature babies are especially vulnerable, added Dr. Slovis. He hailed the late Dr. Alice Stewart's work for establishing that radiation in utero increases the relative risk of leukemia and other malignancies.
“How much radiation does a 25-week surviving preemie get?” he asked, comparing them to third-trimester fetuses and urging limited testing in infants. “I don't say don't get an indicated CT,” he said. “I say get the indications, and work it through.” Physicians should be sure each test they order is necessary, should use “the least invasive modality that gives a high certainty of success,” and should discuss the case with a pediatric radiologist whenever they are unsure.
'We may be exposing our … most vulnerable patients to dangerous doses of radiation. DR. FRIEDMAN