Health effects of security scanners for passenger screening, based on X-ray technology

Due to increased concern over terrorist attacks on aircraft, new technologies have been developed to improve the efficiency of security screening of passengers. Some of these technologies use ionising radiation such as X-rays for screening the passengers.  European Union formed a scientific committee to assess the risks related to use of security scanners for passenger screening that use ionising radiation. The X-ray based security screening technology used for the purpose relies on two techniques: backscatter or transmission. In the backscatter technique, radiation is reflected from the subject and detected to form an image of the body showing any concealed objects worn on the body. The transmission technique detects X-rays emitted by the equipment that pass through the body of the subject. Any concealed object provides an image by attenuating the radiation. While the backscatter technique can only reveal objects at the surface of the body, the transmission technique also shows objects within the body if their contrast differs sufficiently from the surrounding body fluids or tissue.

The health risk from the exposure is quantified in terms of effective dose, which takes into consideration the type of radiation and the sensitivity of the body parts exposed. The effective doses per scanned passenger are in the µSv range for the transmission technique and less than 1 µSv for the backscatter technique. The organ doses have generally the same order of magnitude. For persons scanned three times every working day, security scanning would result in an incremental effective dose of approximately 300 µSv (0.3 mSv) per year for the backscatter technique and close to 3 mSv per year for the transmission technique (assuming doses of 0.4 and 4 µSv per scan, respectively). The latter would exceed the dose limit of 1 mSv per year for the general public and hence would not comply with the current radiation protection standards for the most exposed group of frequent fliers. The risk of exposure using the backscatter technique can be considered as negligible.

Short-term (deterministic) health effects due to tissue damage cannot result from the doses delivered by security scanners. The long-term effects of ionising radiation include an increased cancer risk, which is assumed to be directly proportional to the dose received, without a safe threshold. However, direct evidence of an increased cancer risk or other stochastic risks in humans is not available at this low level exposure situations.

The potential magnitude of cancer risk from doses received from security scanners cannot be estimated, but is likely to remain so low that it cannot be distinguished from the effects of other exposures including both ionizing radiation from other sources (including natural) and background risk due to other factors. While the expected health detriment will probably be very close to zero for any single scanned person, the assessment of acceptability of the introduction of the security scanners using X-rays for passenger screening should also take into account the possible effect at the population level. Due to the substantial uncertainty regarding the potential occurrence of any health effects, risks for special groups within the population could not be evaluated meaningfully, although a higher risk related to exposure in childhood was noted (Source: Scientific Committee on Emerging and Newly Identified Health Risks, European Union, April, 2012)