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)
