Why The Link Between Childhood Cancer and CT Scans May Be Overblown

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Another study is adding to the growing body of evidence that CT scans in childhood can be linked to cancer later on.

The new study, published in the journal JAMA Pediatrics, looked at seven U.S. health care systems and the use of CT scans on the head, abdomen, pelvis, chest and spine in kids under age 15.

According to the researchers, CT scan use for this population doubled from 1996 to 2005 and tripled for kids ages 5 to 14. CT scan usage remained unchanged from 2006 to 2007; since then, the numbers have started to drop. The authors say the numbers are still concerning since kids are more sensitive to the cancer-causing effects of radiation exposure.

The location of cancers associated with radiation varied depending on the focus of the CT scans. In the breakdown of results, the study authors from Group Health Research Institute and University of California, Davis note that the risk of developing leukemia was highest from head scans for kids under age 5 with a rate of 1.9 cases per 10,000 CT scans. Younger children and girls seemed more susceptible to solid cancers than older kids and boys. Every 300 to 390 scans of a girl’s abdomen or pelvis was associated with the development of one solid cancer. The study estimates that 4,870 future cancers may be caused by the 4 million pediatric CT scans each year. Cutting radiation doses for the top quarter of exposures may prevent 43% of those cancer diagnoses.

(MORE: To Scan or Not to Scan: Largest Study to Date Links Childhood CTs to Increased Cancer Risk)

CT scans are considered one of the greatest medical innovations in the last 50 years. The powerful tests can diagnose internal injuries from major accidents and illnesses in the internal abdomen area that physicians cannot see during a check-up.

Other studies have also linked the increasing rates of CT scans to cancer risks, but some doctors argue that today’s CT scan is very different from earlier versions. Lower radiation doses mean that some previous studies that look at CT scans from 20 years ago don’t accurately reflect today’s CT scan usage and risks for kids.

“I think one of the things that struck me from this study is that they talked about how CT utilization is going up, but actually in the last five or six years, utilization of CT is going down and is being replaced more frequently with ultrasound and MRI,” says Dr. George Bisset, the chief of pediatric radiology at Texas Children’s Hospital and president of the Radiological Society of North America. “If you were to poll any children’s hospital around the country and ask them about utilization in the last four years, I guarantee you they would say that CT use is going down at children’s facilities. At Texas Children’s Hospital, each year for the last three years we’ve had decreased utilization of CT.”

(MORE: Too Many Scans? Use of CT Scans Triples, Study Finds)

That’s largely because patients and families have expressed concern over radiation exposure, and both hospitals and imaging technology manufacturers have responded. “Over the last 5 years, we have substantially reduced our radiation dose use as a whole. What used to be a 5-millisieverts scan is now a 1-millisievert scan. So we have reduced the dose by 70 to 80% over the last five years,” says Bisset. “So now if you were to say, Should I be concerned if my child is getting a CT scan?, the answer would be no. You should always have it in the back of your mind. It is a dose of radiation. But if they needed it, I would say let’s do it. With doses less than a millisievert, I think the risks are really low.”

Parents should always ask if there are other ways to assess their child’s injury besides a CT Scan; ultrasounds or MRIs, for example, have no ionizing radiation. But the method used may depend on the circumstances. MRIs can take anywhere from a half hour to a full hour, whereas CT scans can be done in a few minutes. “It really depends on the scenario. If the child is not very sick, an MRI may work, but if the child is 3 years old, they still might not be able to sit still for 30 minutes. In some of those cases, you might think the risk of doing the CT is less than doing sedation, which is what we would do to keep the child still during an MRI,” says Dr. Bisset.

Clinics are also starting to use different forms of imaging that can cut back even further on radiation exposure. For instance, PET/MRI (positron emission tomography/magnetic resonance imaging)  scans are cutting-edge technology that can diagnose a variety of cancers, heart diseases and neurologic disorders using low doses of radiation. Texas Children’s Hospital is the first children’s hospital in the U.S. to start using one.

“We are hopeful that it will be another radiation dose reduction,” says Dr. Bisset. “PET is another source of ionizing radiation, but using MRI with PET instead of CT with PET will substantially reduce the dose.”

The less radiation children are exposed to, regardless of the source, the better off they are, note study authors, who are calling for a decrease in CT radiation dosages — which will hopefully yield a decrease in CT-related cancers.

MORE: CT Scans in Childhood Can Triple the Risk of Cancer

4 comments
jennmetz15
jennmetz15

I've worked in both adult and children emergency departments. In either ED, it is impossible to get an MRI approved to do emergently unless someone has very strong evidence of a spinal cord injury. MRIs are a very very expensive study and until insurance companies or individuals agree to pick up the tab to an essentially unnecessary study in comparison to the quick, cheap, and easy CT scan, this will never change. That being said, in the children's ED ultra sounds are used frequently to try to diagnose appendicitis instead of a CT scan, however the appendix is very rarely ever actually seen. This leads to making the child sit through not only the US but also bloodwork and a CT scan as well.

jennmetz15
jennmetz15

I've worked in both adult and children emergency departments. In either ED, it is impossible to get an MRI approved to do emergently unless someone has very strong evidence of a spinal cord injury. MRIs are a very very expensive study amd until

ElizabethMcBride-Lilleg
ElizabethMcBride-Lilleg

This really oversimplifies the situation.  Sure, ultrasound and MRI are alternative imaging techniques, but they do not show the same things as a CT.  CT scans are good for identifying high-density structures: bone-breaks or swallowed objects, which are common in kids.  MRIs essentially image water, so soft tissues and areas of swelling will show up, but bones and solid objects are virtually invisible.  MRIs also take much longer than CTs to perform, and require the child to be perfectly still for an extended period of time, rather than just for a few second with a CT.  Ultrasound relies on changes in density, which is useful for finding foreign objects and seeing the edges of organs, but also misses a lot due to lower resolutions, more "noise" and being only 2-D.  It also takes longer to perform.

So, there is a lot more to consider when deciding whether or not to perform CT on a child who is injured or ill.  Risking cancer is bad, but in emergency situations, it is likely worse to miss the problem by insisting on an imaging technique that isn't going to work anyway.  Delaying diagnosis and therefore the right treatment puts the child at risk right then and there.