AUDIE CORNISH, HOST:
New research out today indicates that a popular medical test may increase the risk for some forms of cancer. A large international study found that CAT scans, which are also known as CT scans, can increase the risk for leukemia and brain cancer in children.
NPR's Rob Stein joins us now to talk about the new findings. And, Rob, I understand the concerns about these scans have been building for a long time. So what's the specific source of worry here?
ROB STEIN, BYLINE: Well, the concern, really, is about radiation. X-rays emit very low levels of radiation, but CT scans use a lot of X-rays. And so that can build up and accumulate over time and expose people to fairly significant amount of radiation. And if you get enough CT scans, you get exposed to a significant amount of radiation and can potentially boost your risk for cancer.
CORNISH: So this is the first study really, directly, to look at the safety of CT scans. And tell us exactly how they did this.
STEIN: That's right. Previous studies that have tried to take a look at it are really based on extrapolations of data collected for other reasons. It really was based mostly on data collected from the survivors of the bombings in Hiroshima and Nagasaki in World War II. And they would extrapolate from that data to try to determine what their radiation risk was.
In this study, for the first time, they looked directly at patients who are getting CT scans and then followed up to see if they developed any kinds of cancers, in this case, the - it was based on 180,000 patients in Britain who got CT scans.
CORNISH: And these findings are pretty alarming. I mean, what exactly did they find out?
STEIN: Right. What they found was that for kids, it seemed to increase the risk for two types of cancer: leukemia and brain cancers. And based on the findings, they calculated that kids who got two or three CT scans of the head would have three times the risk of brain cancer than people got exposed to less radiation than that. And if you got five to 10 CT scans of the head, your increased risk for leukemia would be tripled.
CORNISH: Now, the takeaway from this hasn't been that people shouldn't do CT scans, but why is that?
STEIN: Well, there are really two reasons. One is that the risk, even though it is - seems to be elevated, is still very low. Leukemia and brain tumors are fairly rare cancers. So even if you increased the risk by a factor of three, the risk is still very, very low. And on the other side of the ledger sheet is the fact that CT scans are very valuable medical tools, and they can save a lot of lives by being - enabling doctors to diagnose and treat patients very quickly.
CORNISH: So, Rob, in the end, what should we understand about the study?
STEIN: Well, really, the take-home message is that doctors should be much more selective in how to use CT scans. Like everything else, CT scans can have a lot of benefits, but they can have a potential downside. And so doctors should just think twice about CT scans when they order one. There's an estimate that maybe 80 million CT scans are done each year in the United States, and maybe half of those may be unnecessary.
So their thinking is that doctors could just pick and choose a little bit more carefully and think, do I really need to do this test? Or is there another test that I could use that has less radiation? And that way, everybody will be safer.
CORNISH: NPR's Rob Stein, thank you.
STEIN: Oh, thank you, Audie. Transcript provided by NPR, Copyright National Public Radio.