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Multiple childhood CT scans increased risk for brain tumors, leukemia
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Children aged younger than 15 years who undergo two to three CT scans to the head could have nearly triple the risk of developing brain cancer, depending on cumulative radiation exposure, according to study results.
The cumulative radiation exposure from five to 10 CT scans could nearly triple the same patients’ risk of developing leukemia, researchers said.
“Because these cancers are relatively rare, the cumulative absolute risks are small,” Mark S. Pearce, PhD, and colleagues wrote. “Although clinical benefits should outweigh the small absolute risks, radiation doses from CT scans ought to be kept as low as possible, and alternative procedures [that] do not involve ionizing radiation should be considered, if appropriate.”
Pearce, a reader in lifecourse epidemiology at the Institute of Health and Society at Newcastle University in the United Kingdom, and colleagues conducted a retrospective study in which they evaluated nearly 180,000 patients without previous malignancy who underwent CT scans while aged younger than 22 years. All patients underwent the scans between 1985 and 2002 at one of 81 National Health Service (NHS) centers in Great Britain.
The researchers determined the number and type of CT scans each patient underwent, and then used Poisson RR models to estimate the radiation doses absorbed by the brain and bone marrow in each scan.
The researchers obtained data about cancer incidence, mortality and loss to follow-up from the NHS Central Register.
The researchers included 176,587 patients in the brain tumor analysis, and 135 of them were later diagnosed with brain cancer. The RR of developing a brain tumor increased by 0.023 for each additional milligray (mGy) of radiation the patients received (95% CI, 0.01-0.049).
Patients who received a cumulative dose of 50 mGy to 74 mGy had nearly three times the risk of developing primary brain tumors than patients who received a cumulative dose of less than 5 mGy (RR=2.82; 95% CI, 1.33-6.03), according to study findings.
The researchers included 178,604 patients in the leukemia analysis, and 74 of them were later diagnosed with leukemia. The RR of developing leukemia increased by 0.036 for each additional mGy of radiation the patients received (95% CI, 0.005-0.12).
Patients who received cumulative doses of at least 30 mGy had about three times the risk of developing leukemia than patients who received a cumulative dose of less than 5 mGy (RR=3.18; 95% CI, 1.46-6.94), the results showed.
Based on dose estimates, if 10,000 patients aged 0 to 10 years underwent one CT scan to the head, study findings suggest one excess case of leukemia and one excess brain tumor would occur within 10 years.
“Because of CT’s diagnostic accuracy and speed of scanning, notably removing the need for anesthesia and sedation in young patients, it will and should remain in widespread practice for the foreseeable future,” Pearce said in a press release. “Further refinements to allow reduction in CT doses should be a priority, not only for the radiology community but also for manufacturers. Alternative diagnostic procedures that do not involve ionizing radiation exposure, such as ultrasound and MRI, might be appropriate in some clinical settings. Of utmost importance is that, where CT is used, it is only used where fully justified from a clinical perspective.”
In an accompanying editorial, Andrew J. Einstein, MD, PhD, assistant professor of medicine in the division of cardiology at Columbia University Medical Center and a cardiologist at New York Presbyterian Hospital, said the results should quiet the debate about whether the risks from CT scans are real.
“The specialty has anyway changed strikingly in the past decade, even while the risk debate continued,” Einstein wrote. “New CT scanners all now have dose-reduction options, and there is far more awareness among practitioners about the need to justify and optimize CT doses — an awareness that will surely be bolstered by Pearce and colleagues’ study.”
Perspective
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S. Pinar Karakas, MD
The ordering clinician can talk to the radiologist to see if there are other techniques we can perform that do not use radiation. At our institution, if patients come into the emergency room with common conditions — such as appendicitis — we always start with an ultrasound. If we cannot see the appendix, and if the clinician is worried enough, we proceed to the CT. That requires communication between the clinician and the radiologist. We are aware of the risks created by radiation. As a pediatric radiologist, that is an important part of our job. We try to use the minimum dose of radiation in whatever we do, including X-rays or CT scans. The doses we apply today are much lower than 10 years ago or even 5 years ago, and they are continuing to get lower. We even use technologies to improve the image quality of low-dose techniques, making the image smoother and easier to look at.
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