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Are Airport Scanners Safe?
Is Very Little Risk Nothing? Or Does It Accumulate Over Time?
A major reason why one scientist can assess a particular radiation exposure as dangerous while another does not is that scientists do not know if small amounts of ionizing radiation are dangerous. One theory holds that below a certain unknown level (the threshold level), small doses of radiation pose zero risk of harm. The other theory holds that small amounts of radiation do pose a certain risk of harm, are additive over time, and that the only safe dose is zero. Both of these are theories; neither has ever been proven.
Public health officials almost all take the approach that small radiation doses carry some degree of harm. In public health, it's better to be safe than sorry.
Many studies have been published on the risk of cancer associated with large doses of radiation, and that numerical relationship is thought to be well understood. When estimating the risk of cancer from a low radiation dose, scientists extrapolate downward, assuming linearity: reduce the radiation dose 100-fold and the cancer risk is also reduced 100-fold. While it has never been proven that this is true, it's the best model available and the one generally used to calculate cancer risk from lower radiation doses.
Schauer also points out that the risk from scanners, if any, should be balanced against the good that may come from the scanning — prevention of a security threat.
The TSA does not permit independent testing of their scanners. Schauer wants tighter regulation and testing of the scanners. He argues that radiologists are the most qualified to assess whether the scanners are operating optimally and to test their safety.
Both Brenner and Schauer agree that using millimeter-wave scanners should be a first option for airports. And they also agree that the average traveler should not be concerned about being scanned with the X-ray scanners.
Estimate: Six Cancers a Year
Rebecca Smith-Bindman, M.D. is a professor in the department of radiology at UCSF. She has previously published a study that found that radiation exposure from medical imaging is higher than necessary and proposed ways to lower this exposure. She is co-author of a new study in the March 28 issue of Archives of Internal Medicine that concludes that the risk from airport X-ray scanners is negligible.
The amount of radiation received from a scan is the same as that received in three to nine minutes of daily living. It would take 50 such scans to deliver the amount of radiation that a dental X-ray delivers. People receive a much higher radiation dose while in the air during an airplane flight than they do from the scan.
One calculation assumed that 100 million passengers would take 750 million flights a year and that all would be scanned before each flight. For all passengers, this would result in six additional cancers developing over their lifetimes. Four of these would be to frequent fliers. At the same time, 600 cancers would develop in these frequent fliers from the increased radiation of flying at high altitude.
But she notes that it would be prudent for the TSA to permit independent testing of these scanners. Her calculations are based on the scanners operating properly and delivering a dose of 0.1 microsievert during each scan. It's not unheard of for radiation-emitting devices to malfunction. Or to be used improperly.
April 14, 2011