The use of computed tomography (CT) scans has increased dramatically over the last two decades and Radiation-induced cancers have tripled in that time. Diagnostic imaging has been already been admitted as a cause by the U.S. government.
CT scans deliver higher radiation doses than other tests. Therefore, radiation protection is a concern, especially among children, who may receive higher radiation doses, are more susceptible to radiation-related malignancies than adults and have more time to show effects from the potential risk.
The increased use of CT in pediatrics, combined with the wide variability in radiation doses, has resulted in many children receiving a high-dose examinations. The Food and Drug Administration (FDA) has warned radiologists in the past that the scan expose children to doses of radiation far greater than is safe for their age and weight -- by some estimates, up to six times more than what is needed to produce clear images.
The most common malignancies caused by radioactivity among children and young adults are leukemia and brain tumors. Researchers therefore evaluated leukemia and brain tumor risks following exposure to radiation from CT scans in childhood.
The reason is children are much more sensitive to radiation because of the way their cells divide. Their DNA is much more susceptible to damage. While the risk of an adult developing cancer from a CT scan is about 1 in 2000, for a child the risk goes up to 1 in 500. Compounding the problem, it's not always easy to tell when a CT scan's levels are in the danger zone.
Researchers at the National Cancer Institute estimate that 29,000 future cancer cases could be attributed to the millions of CT scans performed. That increase is linked to a growing percentage of cancers diagnosed nationwide every year. A 2009 study of medical centers in the San Francisco Bay Area also calculated an elevated risk: one extra case of cancer for every 400 to 2,000 routine chest CT exams.
The average yearly environmental exposure to radiation is approximately 3000mSv. One CT scan of the abdomen is equal to 15,000mSv. That's 5 times the yearly dose of exposure in one sitting.
Radiation doses of more than 5000 mrem/year are considered unsafe, regardless of source. You can use our radiation dose calculator to measure the amounts you are exposed to yearly.
The projected lifetime attributable risks of solid cancer are higher for younger patients and girls than for older patients and boy. The risks are also higher for patients who underwent CT scans of the abdomen/pelvis or spine than for patients who underwent other types of CT scans.
For a nationwide group of 168,394 Dutch children who received one or more CT scans between 1979 and 2012, researchers obtained cancer incidence and vital status by record linkage. They surveyed all Dutch hospital-based radiology departments to ascertain eligibility and participation. In the Netherlands, pediatric CT scans are only performed in hospitals.
Overall cancer incidence was 1.5 times higher than expected. For all brain tumors combined, and for malignant and nonmalignant brain tumors separately, dose-response relationships were observed with radiation dose to the brain. Relative risks increased to between two and four for the highest dose category. The researchers observed no association for leukemia. Radiation doses to the bone marrow, where leukemia originates, were low.
The researchers caution that this pattern of excess cancer risk may be partly due to confounding by indication, because the incidence of brain tumors was higher in the cohort than in the general population. CT scans are sometimes used to identify conditions associated with an increased tumor risk; the reason these children had CT scans may be associated with their risk of developing cancer.
"Epidemiological studies of cancer risks from low doses of medical radiation are challenging, said the study's principal investigator, Michael Hauptmann. "Nevertheless, our careful evaluation of the data and evidence from other studies indicate that CT-related radiation exposure increases brain tumor risk. Careful justification of pediatric CT scans and dose optimization, as done in many hospitals, are essential to minimize risks."