There is no question that the CT scan has revolutionized medicine since its introduction in the 1970s. However the fact that it delivers ionizing radiation doses that are 100 to 500 times higher than those of conventional X-rays poses the potential significant risk of developing cancer as a result of the test itself.
Children are especially vulnerable because their organs are still developing and they have a longer period for cancer to form.
Three new reports document these dangers.
A June report in JAMA Pediatrics estimates that because so many children in the US have had CT scans (and many have had more multiple such scans), in future there be as many as 4,870 cancers developing in these patients.
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 estimate that conservatively 4.25 million pediatric CT scans are performed each year in this country.
Looking at boys and girls aged 15 years and younger (with a third under age 5) enrolled in 7 health care systems across the US between 1996 to 2010, she found an increased use of scans in children over the years, 95 percent of which were of the head, chest, abdomen/pelvis, and spine which tend to deliver high doses of radiation.
In addition Miglioretti discovered that even for the same type of scan, doses of radiation varied considerably from one radiology center to another.
What many people don’t realize, is that radiation is cumulative. That means that with every scan or conventional Xray you have, the total dose you’ve been exposed to adds up. The higher the dose of radiation, the greater the the risk of developing all kinds of cancers.
According to projections based on the CT data analyzed in the JAMA study, breast, thyroid, and lung cancers as well as leukemia account for more than two thirds of the cancers expected in exposed girls, while brain, lung, and colon cancers and cases of leukemia account for about half of future cancers expected in boys.
In another two decade study of more than 600,000 Australians under age 19 reported online in May in the British Medical Journal, John D. Mathews, MBBS, MD, PhD, the study’s lead author from the University of Melbourne, found that for every 1,800 people who underwent CT scans before the age of 20, one extra case of cancer occurred over the following 10 years. Overall the cancer incidence was almost 25 percent greater for those children who had been exposed to radiation from CT scans as opposed to those who had not.
The incidence was significantly increased for urinary tract cancer and six other solid tumors (digestive organs, melanoma, soft tissue, female genital, brain, and thyroid). As with the American study, the risk of cancer was greater for those exposed at younger ages and increased with the number of CT scans.
Both studies highlight the overuse of CT scans in children, asserting that as many as one-third of pediatric CT scans are not medically necessary.
While CT scans can be crucial in making the diagnosis of serious medical conditions, they must be used judiciously and not always as the first test done. For example, medical evidence suggests that children with suspected appendicitis should get an ultrasound, which doesn’t use radiation before a CT scan.
A third study published in the July issue of Pediatrics pointed out the dangers of the overuse of CT scans in children with headaches. Researchers looked at almost 16,000 children age 3 to 12 seen in Emergency Rooms around the country who had more than 2 CT scans for headache complaints during 2008.
Paul Young, MD, professor of pediatrics at the University of Utah School of Medicine and study co-author stated “It’s ironic that providers sometimes use CT scans to rule out brain tumors or brain abnormalities because parents are concerned about this possibility–which is the cause of less than one percent of those with pediatric headache–when overuse of CT scans can increase the risk of brain tumors.”
All three studies emphasized both the need to eliminate the number of unnecessary CT scans and to use the lowest possible dose of radiation whenever a CT scan is performed.
Dr. Maglioretti stated that these two strategies together could lower the risk of cancers from CT scans by as much as 62 percent.
Some of these changes will have to come from parents who are willing to take a “wait and see” approach in certain cases where the potential risk of the CT scan could outweigh the benefits.
Finally, there is a push (albeit very slow) to begin to accurately measure patients’ lifetime exposure to radiation from all kinds of diagnostic imaging.
Starting in the last quarter of 2012, Salt Lake City-based Intermountain Healthcare launched a program to compile the cumulative radiation patients receive from about 220,000 higher-dose procedures and imaging exams each year. That information plus access to educational materials on the risks and benefits of medical radiation is now readily available to both physicians and patients electronically.
If every radiology facility did the same, this would go a long way to empower individual patients to keep track of their own risks and make decisions about whether to have a particular test based on the risk/benefit.