Health Protection Agency, Centre for Radiation, Chemical and Environmental Hazards  January 2010 – Axel MacDonald, Phil Tattersall, John O’Hagan, Jill Meara, Richard Paynter, Peter Shaw.

The Government may require airport operators to use enhanced screening techniques using x-ray scanning equipment to safeguard flights from UK airports. The Justification of Practices Involving Ionising Radiation Regulations 2004 (SI 2004/1769)(Justification Regulations) came into force on 2 August 2004. These regulations are applied to new practices utilising ionising radiation that arose after May 2000. Those practices in use prior to May 2000 are regarded as existing practices and are not required to go through the justification process required of new practices, although any important new information on their effectiveness and potential doses may prompt a review of their justification. X-ray backscatter scanning systems to detect concealed items were in use prior to May 2000 and this is listed as an existing practice¹.

This assessment addresses exposures and risks from the use of an x-ray backscatter body scanner, specifically a model that has been trialled in the UK in both a single scan and double scan (single pose) set-up. X-ray transmission body scanning systems, for instance those used by customs on those suspected of smuggling narcotics within their body, are not considered and it is thought that the use of such systems for routinely scanning passengers would be considered as a new practice. The Department of Energy and Climate Change hold a register of applications for new practices under the Justification Registrations².

The effective dose from one scan from an x-ray backscatter unit (single or double scan) is 0.02 micro Sv or less (worst case scenario). Effective dose is a quantity that integrates radiation dose across the whole body. This dose is a small fraction of the annual background radiation.

People are constantly exposed to ionising radiation, most of which is from natural sources and medical exposures wherever they live. In the UK, the average dose to a member of the public from all sources (natural and artificial) is 2700 micro Sv/year. Natural radiation sources include cosmic rays, for which the radiation exposure increases with altitude; the typical dose rate during a commercial flight is approximately 5 micro Sv/h. In comparison, the dose rate from terrestrial and cosmic radiation sources at ground level is approximately 0.08 – 0.12 micro Sv/h.

Therefore the total radiation dose from an examination (which might involve 2 or 3 scans) is less than that received from two minutes flying at cruising altitude, or from one hour at ground level. However, it must be emphasised that these figures are based on the two variants (single and double scan) of the scanner model that HPA has assessed, and rely on the correct installation, operation and maintenance of the unit.  Significantly higher doses may occur if these criteria are not satisfied.

HPA recommends a dose constraint of 300 micro Sv/year to a member of the public from practices involving the deliberate use of ionising radiation sources³. A passenger would need to be examined 5000 times before exceeding this constraint value (based on three scans per examination). It is concluded that the potential doses received from the use of a correctly installed and used x-ray backscatter body scanner are likely to be very low.  Even in the case of frequent fliers the doses are unlikely to exceed 20 micro Sv/year.

It is important to note that the installation and use of this equipment will be subject to the requirements of the relevant radiation protection legislation⁴. 

Comparative risks

The radiation doses from backscatter scanners are so low that the traditional radiation risk comparators, for example cancer risk may not provide the best illustration. A range of traditional and other comparators are given below. The data are taken from Office for National Statistics accident figures as presented on the ROSPA website⁵ and the JPNM “risk list” ⁶.

Whilst there are stages of pregnancy where a fetus is considered to be more susceptible to harm from radiation, the backscatter technology ensures that negligible doses are absorbed into the body (where the fetus is) and the fetal dose is thus much lower than the dose to a pregnant woman. Therefore for this comparison, which due to uncertainties only provides indicative risks, maternal and fetal dose can be considered the same. Similarly, because of the uncertainties at these low levels of exposure the risks to children, people with any type of illness or people undergoing any type of medical treatment are considered to be comparable to the risks to adults.
Therefore this risk assessment applies to the whole human population.

Activity	Cause of death	Fatality risk
Activities with a similar fatality risk to backscatter body scanning
6 Rapiscan Secure 1000 x-ray backscatter body scans (return flight with one set of scans at each embarkation) Effective radiation dose = 0.12 micro Sv	Fatal lifetime cancer risk induced by the scan (assumed to be 0.05 (5%) per Sv)	0.000,000,006 = 0.000,000,6 % = 1 in 166,000,000
1.4 minutes flying at airline cruising height Effective radiation dose = 0.12 micro Sv	Fatal lifetime cancer risk induced by the scan (assumed to be 0.05 (5%) per Sv)	0.000,000,006 = 0.000,000,6 % = 1 in 166,000,000
Travelling 6 miles by commercial jet. (ref. Harvard  risk list)	Fatal accident	0.000,000,006 = 0.000,000,6 % = 1 in 166,000,000
Travelling 0.3 miles by car (ref. Harvard  risk list)	Fatal accident	0.000,000,006 = 0.000,000, 6% = 1 in 166,000,000
Travelling 1.8 miles by car (ref. ROSPA UK data)	Fatal accident	0.000,000,006 = 0.000,000,6 % = 1 in 166,000,000
Activities with a much higher fatality risks than backscatter body scanning
Risk of accidental death in a school pupil while at school (UK annual rate, ref. ROSPA data)	Fatal accident	0.000,000,44 =0.000,044 % = 1 in 2,300,000 Risk = x70 backscatter scan risk
Average annual background radiation in the UK Effective radiation dose = 2,700 µSv	Fatal lifetime cancer risk induced by exposure to background radiation (assumed to be 0.05 (5%) per Sv)	0.000,1 = 0.01 % = 1 in 10,000 Risk = x 16,600 backscatter scan risk
Risk of a mother dying during pregnancy or soon after in the UK (UK Office for National Statistics)	All causes directly and indirectly related to the pregnancy	0.000,15 = 0.015 % =1 in 6,700 Risk = x 25,000 backscatter scan risk
All causes	Lifetime fatal cancer risk	0.25 = 25 % = 1 in 4

References

1. The Justification of Practices Involving Ionising Radiation Regulations 2004 (SI 2004 No 1769), Guidance on their application and administration, Department for Environment Food and Rural Affairs, Version May 2008.

2. Justification Register, Department of Energy and Climate Change

3. Application of the 2007 Recommendations of the ICRP to the UK. Advice from the Health Protection Agency, Documents of the Health Protection Agency, RCE-12, ISBN 978-0-85951-647-1

4. The Ionising Radiations Regulations 1999 (SI 1999 No 3232)

5. Royal Society for the Prevention of Accidents (ROSPA) Accident statistics 2007 (PDF)

6. JPNM Physics Risk List From Robert Zamenhof, January