With the federal government introducing new advanced imaging scanners at airports, the traveling public has become concerned about the radiation exposure they may receive when passing through scanners as well as during flight. This article offers a primer on radiation and the extent to which exposure from various sources can affect health. It also provides advice for physicians whose patients may have concerns about radiation exposure during air travel.
The catastrophic events at Japan’s tsunami-damaged Fukushima nuclear power plant and media reports about inappropriately high radiation doses delivered during medical imaging have heightened public concern about the potential long-term consequences of radiation exposure. Although we presume a positive risk-benefit ratio from diagnostic scans and medical treatments that involve radiation, there is growing concern about the health effects of the cumulative amount of radiation individuals are exposed to over the course of their lifetime. With the recent addition of more security scanners at airports around the country, the public has expressed concern about the amount of radiation they may be exposed to when passing through security and flying.
This article provides background on radiation and discusses what is known about its potential effect on biologic systems as well as the statistical risk of radiation exposure in airports and on airplanes.
The new “strip search” scanning machines at airport security checkpoints are increasingly causing furor over issues of privacy, decency and health. Over the weekend, a passenger in San Diego, software engineer John Tyner, opted out of a scan, then warned a security agent not to “touch my junk” during the enhanced pat-down check — that interaction, which Tyner recorded on his cell phone and posted online, went viral, further stoking the public’s frustration.
Whether or not you feel the new backscatter body scans (let alone the security gropes) are an overly humiliating invasion of privacy, there’s no arguing that the scans expose you to extra radiation. Many passengers and some scientists say the excess radiation exposure could pose a health hazard to frequent fliers and to young children.
The public’s No. 1 concern regarding radiation is that it may cause cancer. The probability of exposure to ionizing radiation causing cancer depends on both the dose rate and the sensitivity of the organism.
Ionizing radiation causes harm in two ways:
- It forms free radicals that may indirectly damage DNA, and
- It may directly break down DNA molecules.
The average amount of radiation a person in the United States receives from all sources is estimated to be 6.20 mSv per year.That may vary depending on the environment in which one lives, the work a person does, and the medical procedures he or she undergoes. Currently, international standards allow exposures up to 50 mSv per year for those working with and around radioactive material. Federal law mandates lower doses for women who are pregnant mSv during the entire gestational period and 0.5 mSv during any month of pregnancy.
Determining biological significance and potential damage to tissues and systems remains a challenge, however, as not all tissues (and perhaps not all individuals) react the same way to the same level of exposure. In many cases, it may be difficult if not impossible to determine the precise dose to any given tissue, and often doses are adjusted to standardized “whole-body exposures,” even though only a small portion of the body may be exposed. Adding to the confusion is the fact that medical equipment manufacturers use variable methods to quantify the dose delivered by their products.
Calculating dose is further complicated by a person’s size and percentage of body fat. Patients who have very little body fat to attenuate radiation can receive higher effective doses. As a result of these factors, some CT-dose algorithms for pediatric patients may have underestimated the delivered effective dose in neonates by as much as 300%. Recently, much-improved volumetric dose methods using phantoms (simulated targets) have been developed, substantially improving such estimates, which are now thought to be within 20% of the actual delivered dose. As medical tests and treatments deliver so much radiation, recording patient exposures and the cumulative amount delivered in the electronic health record will likely be required in the future.
Air travelers are exposed to two main sources of radiation:
- cosmic radiation during flight and
- radiation from scanners while undergoing security clearance.
Two types of modern advanced imaging technology are used for security scanning:
- backscatter X-ray (BSX) scanners and
- millimeter wave scanners (MWS).
BSX scanners, like medical imaging machines, use X-ray photons but at considerably lower doses. Unlike traditional X-ray or CT imaging, which directs higher-energy radiation through a target, BSX scanners use lower-energy radiation that reflects from a target. This technology is able to assess only one side of a target such as the front or back side of a human being, rendering a 2-D image that resembles a chalk etching.
Statistically, the risk posed by exposure to radiation from passing through BSX and MWS scanners in airports and during commercial flight is exceedingly low. Relatively speaking, the radiation people receive from medical imaging and procedures poses a much greater risk. For that reason, when physicians are counseling patients who are concerned about the amount of radiation they will receive going through airport security or during flight they might do better to focus the discussion on issues that are more likely to ensure safety such as appropriate use of medical radiation and developing habits including use of seat belts.
The American College of Radiology has developed educational materials for patients, providers, and radiologists through their Image Wisely and Image Gently campaigns in an effort to reduce the amount of medical radiation patients receive for routine procedures. In addition, manufacturers of imaging equipment are developing new technologies that will significantly reduce the amount of radiation delivered during imaging—in some cases by more than tenfold. Although the amount of radiation delivered during a CT scan may never be as low as that delivered by an airport security scan, we are likely to see substantial reductions in medical imaging radiation during the next three to five years.