The projected lifetime attributable risk of leukemia was highest among the youngest children who received head scans, and decreased with increasing age of the patient. For children younger than 5 years who underwent head CT scanning, leukemia was projected to develop in 1.9 patients/10,000 scans, while the rate was only 0.5 cases/10,000 for patients older than 10 years. Abdominal and pelvic CT scans also raised the risk of later leukemia.
"A case of leukemia was projected to result from 1 in 5,250 head scans performed for children younger than 5 years of age and from 1 in 21,160 scans for children 10-14 years of age. The risk of leukemia was 0.8-1.0 cases/10,000 abdomen and pelvic scans and 0.4-0.7 cases/10,000 chest and spine scans," the researchers said.
"Conservatively assuming that 4.25 million pediatric CT scans are performed each year in the United States, 4.0 million CT scans would be of the head, abdomen/pelvis, chest, or spine, based on our observed distribution. If radiation doses from those CT scans parallel our observed dose distributions, approximately 4,870 future cancers could be induced by pediatric CT scans each year," they wrote (JAMA Pediatr. 2013 June 10 [doi:10.1001/jamapediatrics.2013.311]).
"Cases of breast, thyroid, and lung cancers and cases of leukemia account for 68% of projected cancers in exposed girls, whereas cases of brain, lung, and colon cancers and cases of leukemia account for 51% of future cancers in boys."
The number of radiation-induced cancers could be markedly reduced if standard dose-reduction CT protocols were implemented more uniformly across the country. "Reducing the highest 25% of doses within age groups and anatomic regions to the median dose could prevent 2,090 (43%) of these cancers," Dr. Miglioretti and her colleagues said
The benefits of medically necessary CT scans far exceed the increase in cancer risk to a given patient, but CT scans that are not necessary place patients at risk for no reason. Some studies suggest that as many as one-third of pediatric CT scans are not medically necessary and eliminating them would reduce future cancers by another 33%.
"Combining these two strategies could prevent 3,020 (62%) of these cancers," Dr. Miglioretti and her colleagues said.
"It is important for both the referring physician and the radiologist to consider whether the risks of CT exceed the diagnostic value it provides over other tests," they noted.
For example, the indications for most of the abdominal and pelvic scans in this study were pain (40%), possible appendicitis (11%), or possible infection (6%). Ultrasound, which doesn’t use ionizing radiation, is a reasonable alternative for such assessments, with CT reserved for patients whose findings are equivocal or negative on ultrasonography.
Similarly, 23% of the head scans in this study were to evaluate trauma, 22% to assess upper respiratory issues, and 17% to evaluate headache. The use of CT for trauma can be reduced if highly sensitive prediction rules are used to select only the most appropriate patients, and CT has not been established as having value in the pediatric population for assessing headache or sinusitis, the researchers said.
They cautioned that their risk projections "are only estimates based on the best available evidence and are in no way definitive."
This study was supported by the National Cancer Institute. No financial conflicts of interest were reported.