The risk to any one person of developing cancer from airport X-rays is extremely small, but given the large number of people that go through the machines each day, a small number of people, especially those who are particularly vulnerable or who fly often, could develop cancer, one scientist says.

The Transportation Security Administration currently uses two types of X-rays to scan travelers at airports. One type uses millimeter wave technology, in which an image is generated using energy that is reflected from the body. The energy is 10,000 times less than a cell-phone transmission , according to the TSA.

The second type is the backscatter X-ray, in which ionizing energy is reflected back from the body and objects on the body and converted into an image. The energy is equivalent to the radiation absorbed during 2 minutes of flying in an airplane, the TSA said. These types of X-ray scans have become more frequently used in airports in recent years.

The chance of developing cancer from two 1-microsievert X-ray scans (what a passenger would receive before and after a round-trip flight) is one in 10 million, said researcher David J. Brenner, director of the Center for Radiological Research at Columbia University Medical Center in New York. (American National Standards Institute dose limits are currently 0.25 microsieverts per scan, and the National Council on Radiation Protection and Measurements recommends a limit of 0.1 microsieverts per scan.)

But "given the very large numbers of scans involved, potentially up to 1 billion each year in the U.S., there is a significant likelihood that, amongst the scanned population, there will be some cancers produced by the associated radiation exposure," Brenner told MyHealthNewsDaily.

However, the risk is so small that it's still highly unlikely any one person would develop cancer from going through an airport scan, he said.

Researcher David A. Schauer, executive director of the National Council on Radiation Protection and Measurements, says that there is no scientific evidence that an individual's small risk of cancer can change based on others' exposure to the same radiation.

Both researchers will publish their views in the April issue of the journal Radiology.

Individual vs. population risk

Brenner uses what is called the theory of population risk to assess cancer risks associated with backscatter X-rays. According to the theory, if 100 people are exposed to the radiation, then it would be unlikely that any of the 100 people would develop a cancer as a cause of the radiation, he said.

But if 1 billion people are exposed to the radiation (which causes cancer in one in 10 million people) then about 100 people might develop cancer from that radiation, Brenner said.

"It is reasonable to say that, for an average individual, the scanners are 'safe,'" Brenner said. But individual lifetime cancer risks could be somewhat higher for children , people who are sensitive to radioactivity and people who spend a lot of time flying, like flight attendants, pilots and frequent fliers, he said.

Weighing risks and benefits

But just because the risk of developing cancer from backscatter X-rays is about one in 10 million doesn't mean that a person's individual risk of developing cancer is more than one in 10 million, Schauer said.

"The collective dose increases with the increasing size of the exposed population, but the benefits and risks to individuals remain nearly constant," Schauer wrote in the article.

The benefits of avoiding terrorism or security breaches at airports far outweigh the small cancer risks associated with X-ray radiation, he added.

"The risk of health effects from backscatter x-ray systems used for security screening is very small as long as their use is justified (appropriate), optimized (as low as reasonably achievable) and complies with applicable dose limits," Schauer told MyHealthNewsDaily.

Both Brenner and Schauer said that transportation security officials should prefer to use X-rays with millimeter wave technology over the backscatter X-rays when possible.

Pass it on: Even though individual risks of cancer from backscatter X-rays are very low, the population risks how many people will develop cancer out of millions or billions of people exposed to radiation still exist. But, the benefits of screening still outweigh the potential risks.

Follow MyHealthNewsDaily staff writer Amanda Chan on Twitter @AmandaLChan.