[ RadSafe ] bakscatter xray
Mark Ramsay
mark.ramsay at ionactive.co.uk
Mon Nov 15 00:25:54 CST 2010
Interesting, thanks for posting that.
A key thing I think is the correct use of terminology here. For example, many suppliers (or folks like myself even) might fall into the habit of quoting a dose such as '0.06 micro Sv/scan' without clearly expressing the dose quantity involved - in this case 'whole body effective dose'. Then, if this is compared to cosmic radiation then no wonder there are concerns from physicists as outlined in the letter below.
However, if the science and physics is done correctly, then the whole body effective dose is useful, and is after all a comparator of risks.
After the Alexander Litvinenko incident in London, the 'experts' at the time (e.g. HPA etc) may well have been considering the impact of the internal exposure to various organs from alpha radiation. During the biological sampling programme for members of the public they would have been considering exposure pathways, excretion criteria, equivalent dose to organs, ages and so on. However, in the end what was required was to quote the 'risk' to those members of public who may have been exposed to Po-210 in a way they would understand and accept. For example, this might have been exposure to so many days background radiation, or a certain number of back x-rays. This was only valid because of the way that effective whole body dose is expressed (and indeed derived).
Clearly the temptation to compare cosmic radiation exposure and back scatter screening is high - for the very reason that once you understand what you are receiving when flying, it 'should' help you accept / understand the 'risk' before you get on the aircraft.
One could take the approach of discussing skin doses, in the same way that for Litvinenko one might have discussed the quality factors employed / the dose to the spleen etc etc. However, we know that is a turn off - that is why effective whole body dose for the masses is used.
I am visiting quite a few users / suppliers of x-ray equipment this coming week. I am going to make a point of looking at the equipment documentation - I wonder how often I will see the nature of the dose quantity described in the safety section explicitly defined - not much I would guess.
Mark
www.ionactive.co.uk
-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu [mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of conrad sherman
Sent: 15 November 2010 02:57
To: radsafe at health.phys.iit.edu
Subject: [ RadSafe ] bakscatter xray
here is the letter from ucsf and response
LETTER OF CONCERN
We are writing to call your attention to serious concerns about the
potential health risks of the recently adopted whole body backscatter
X-ray airport security scanners.This is an urgent situation as these
X-ray scanners are rapidly being implemented as a primary screening step
for all air travel passengers.
Our overriding concern is the extent to which the safety of this
scanning device has been adequately demonstrated.This can only be
determined by a meeting of an impartial panel of experts that would
include medical physicists and radiation biologists at which all of the
available relevant data is reviewed.
An important consideration is that a large fraction of the population
will be subject to the new X-ray scanners and be at potential risk, as
discussed below.This raises a number of 'red flags'.Can we have an
urgent second independent evaluation?
The Red Flags
The physics of these X-rays is very telling: the X-rays are
Compton-Scattering off outer molecule bonding electrons and thus
inelastic (likely breaking bonds).
Unlike other scanners, these new devices operate at relatively low beam
energies
(28keV).The majority of their energy is delivered to the skin and the
underlying
tissue. Thus, while the dose would be safe if it were distributed
throughout the volume of the entire body, the dose to the skin may be
dangerously high.
The X-ray dose from these devices has often been compared in the media
to the cosmic ray exposure inherent to airplane travel or that of a
chest X-ray. However, this comparison is very misleading: both the air
travel cosmic ray exposure and chest X- rays have much higher X-ray
energies and the health consequences are appropriately understood in
terms of the whole body volume dose.In contrast, these new airport
scanners are largely depositing their energy into the skin and
immediately adjacent tissue, and since this is such a small fraction of
body weight/vol, possibly by one to two orders of magnitude, the real
dose to the skin is now high.
In addition, it appears that real independent safety data do not exist.A
search, ultimately finding top FDA radiation physics staff, suggests
that the relevant radiation quantity, the Flux [photons per unit area
and time (because this is a scanning device)] has not been
characterized.Instead an indirect test (Air Kerma) was made that
emphasized the whole body exposure value, and thus it appears that the
danger is low when compared to cosmic rays during airplane travel and a
chest X-ray dose.
In summary, if the key data (flux-integrated photons per unit values)
were available, it would be straightforward to accurately model the dose
being deposited in the skin and
Letter of Concern -- Page 2
adjacent tissues using available computer codes, which would resolve the
potential concerns over radiation damage.
Our colleagues at UCSF, dermatologists and cancer experts, raise
specific important concerns:
.A) The large population of older travelers, >65 years of age, is
particularly at risk from the mutagenic effects of the X-rays based on
the known biology of melanocyte aging.
.B) A fraction of the female population is especially sensitive to
mutagenesis- provoking radiation leading to breast cancer.Notably,
because these women, who have defects in DNA repair mechanisms, are
particularly prone to cancer, X-ray mammograms are not performed on
them.The dose to breast tissue beneath the skin represents a similar risk.
.C) Blood (white blood cells) perfusing the skin is also at risk.
.D) The population of immunocompromised individuals--HIV and cancer
patients (see above) is likely to be at risk for cancer induction by the
high skin dose.
.E) The risk of radiation emission to children and adolescents does not
appear to have been fully evaluated.
.F) The policy towards pregnant women needs to be defined once the
theoretical risks to the fetus are determined.
.G) Because of the proximity of the testicles to skin, this tissue is at
risk for sperm mutagenesis.
.H) Have the effects of the radiation on the cornea and thymus been
determined? Moreover, there are a number of 'red flags' related to the
hardware itself. Because this
device can scan a human in a few seconds, the X-ray beam is very
intense. Any glitch in power at any point in the hardware (or more
importantly in software) that stops the device could cause an intense
radiation dose to a single spot on the skin.Who will oversee problems
with overall dose after repair or software problems?The TSA is already
complaining about resolution limitations; who will keep the
manufacturers and/or TSA from just raising the dose, an easy way to
improve signal-to-noise and get higher resolution?Lastly, given the
recent incident (on December 25th), how do we know whether the
manufacturer or TSA, seeking higher resolution, will scan the groin area
more slowly leading to a much higher total dose?
After review of the available data we have already obtained, we suggest
that additional critical information be obtained, with the goal to
minimize the potential health risks of
Letter of Concern -- Page 3
total body scanning. One can study the relevant X-ray dose effects with
modern molecular tools.Once a small team of appropriate experts is
assembled, an experimental plan can be designed and implemented with the
objective of obtaining
information relevant to our concerns expressed above, with attention
paid to completing the information gathering and formulating
recommendations in a timely fashion.
We would like to put our current concerns into perspective.As
longstanding UCSF scientists and physicians, we have witnessed critical
errors in decisions that have seriously affected the health of thousands
of people in the United States.These unfortunate errors were made
because of the failure to recognize potential adverse outcomes of
decisions made at the federal level.Crises create a sense of urgency
that frequently leads to hasty decisions where unintended consequences
are not recognized. Examples include the failure of the CDC to recognize
the risk of blood transfusions in the early stages of the AIDS epidemic,
approval of drugs and devices by the FDA without sufficient review, and
improper standards set by the EPA, to name a few. Similarly, there has
not been sufficient review of the intermediate and long-term effects of
radiation exposure associated with airport scanners. There is good
reason to believe that these scanners will increase the risk of cancer
to children and other vulnerable populations. We are unanimous in
believing that the potential health consequences
need to be rigorously studied before these scanners are
adopted.Modifications that reduce radiation exposure need to be explored
as soon as possible.
In summary we urge you to empower an impartial panel of experts to
reevaluate the potential health issues we have raised before there are
irrevocable long-term consequences to the health of our country.These
negative effects may on balance far outweigh the potential benefit of
increased detection of terrorists.
October 12, 2010
Dr. John P. Holdren
Assistant to the President for Science and Technology
Director, Office of Science and Technology Policy
Executive Office of the President
New Executive Office Building
725 17th St. NW
Washington, DC 20502
Dear Dr. Holdren,
Thank you for sharing the April 6 letter you received regarding
general-use full-body x-ray screening systems used for airport security.
As with all x-ray security products, justified application demands a
balancing act: The radiation dose delivered must be sufficient to do the
job---in this case to identify security threats---while presenting no
more than a miniscule risk to people being scanned, including special
populations.
The overriding concern expressed in the letter is the extent to which
the safety of the security devices has been adequately demonstrated.
Since 1990, the Food and Drug Administration (FDA) has regulated
manufacturers to ensure the radiation safety of full-body x-ray security
screening systems. The FDA consulted its Technical Electronic Product
Radiation Safety Standards Committee (TEPRSSC) about these products
during several meetings from 1998 through 2003. TEPRSSC is the
independent advisory committee to FDA with expertise in electronic
product radiation issues. This expert committee raised several issues
during these meetings and FDA responded by initiating work on a
consensus radiation safety standard through the American National
Standards Institute (ANSI) and Health Physics Society (HPS). FDA
assembled a working group of experts that included representatives from
manufacturers, security agencies, and other regulatory agencies. The
working group produced a national standard, /Radiation Safety for
Personnel Security Screening Systems Using X-rays/^1
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn1>
/, /which was published in July 2002. The 2002 standard required
facilities to ensure that no individual scanned received an effective
dose in excess of 0.25 mSv (25 mrem) in any 12-month period. The
standard also provided other guidelines specific to the radiation safety
aspects of the design and operation of these systems. This annual dose
limit is based on the National Council of Radiation Protection and
Measurements^2
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn2>
(NCRP) recommendations for the annual effective dose limit for
individual members of the general public^3
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn3>
. NCRP's dose limitation recommendations for the general public were
made with the understanding that the general public includes special
populations that are more sensitive to radiation, such as children.
In September 2002 FDA asked the NCRP to undertake a study that led to
NCRP Commentary No. 16 (2003/), Screening of Humans for Security
Purposes Using Ionizing Radiation Scanning Systems/. The committee that
prepared this commentary included representatives from the Milton S.
Hershey Medical Center, Columbia University, FDA's Center for Devices
and Radiological Health, the U.S. Environmental Protection Agency, and
the /NCRP Secretariat /consulting staff. This commentary introduced the
concept of general-use and limited-use systems. Commentary No. 16
recommended g eneral-use systems should not exceed the dose limit set in
the 2002 standard and can be used mostly^4
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn4>
without regard to the number of individuals scanned or the number of
scans per individual in a year.
FDA brought the issue of consistent federal evaluation and justification
of security screening practices that used ionizing radiation to the
Interagency Steering Committee on Radiation Standards (ISCORS)^5
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn5>
. ISCORS was established to foster early resolution and coordination of
regulatory issues associated with radiation standards and guidelines.
ISCORS published /Guidance for Security Screening of Humans Utilizing
Ionizing Radiation /(2008) to assist Federal agencies in determining
when the use of ionizing radiation for security screening of humans is
warranted and to provide guidelines for establishing a radiation safety
program. The Transportation Security Administration (TSA), FDA,
Occupational Safety and Health Administration, National Institute of
Standards and Technology (NIST), U.S. Army Center for Health Promotion
and Preventive Medicine, Nuclear Regulatory Commission, Environmental
Protection Agency, Federal Bureau of Prisons, Department of Energy,
Customs and Border Protection, Central Intelligence Agency, Maryland
Department of the Environment, and Pennsylvania Bureau of Radiation
Protection collaborated in developing this federal guidance.
Since publication of the original 2002 standard, a number of new system
designs have been developed, including portal systems, multi-source
systems, vehicle scanners meant for screening occupied vehicles,
scanners for inspecting casts and prosthetic devices, and scanners using
a radioisotope as the source of radiation. New uses for these systems
include the use of vehicle and cargo scanners to inspect people and the
limited use of higher-dose systems as defined in NCRP Commentary No. 16.
Consequently, FDA and NIST chaired a working group to revise the
national standard^6
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn6>
. The revised standard, /Radiation Safety for Personnel Security
Screening Systems Using X-Ray or Gamma Radiation/^7
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn7>
, was published November 2009. It includes requirements that cover these
new designs and uses. This standard applies to security screening
systems in which people are intentionally exposed to primary beam x-rays
and provides guidelines specific to radiation safety in the design and
operation of these systems.The standard covers doses to individuals
scanned, safety systems, operational procedures, information to provide
to screened individuals, training for operators, and other issues. The
revised standard retained the annual effective dose limit for members of
the public of 0.25 mSv (25 mrem). This standard defines a /general-use
/x-ray screening system as one that delivers less than 1/1000 of this
dose per screening (0.25 µSv (25 µrem)). The rationale for the annual
and per screening dose limits is presented in the standard^8
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn8>
.
TSA requires that the full-body x-ray security systems approved for
deployment (Advanced Imaging Technology (AIT)) conform to the
requirements in the 2009 standard for general-use systems. Surveys of
the recently deployed backscatter x-ray personnel security screening
systems have been performed by an independent party to confirm
compliance with the radiation dose-per-screening limits for general-use
of the 2009 standard. All systems surveyed to date have been found to
comply with the general-use dose-per-screening limit in that standard.
In addition, our independent survey teams are gathering area radiation
dose data by mounting dosimeters on (within the inspection zone) select
systems.
Regarding the specific "Red Flag" issues raised in the letter:
First, the letter is correct to note that the TSA-deployed product is a
recent model. However, the specification for the x-ray tube for the
deployed model is almost identical to the original 1991 product. The
stated concern was, "The majority of their energy is delivered to the
skin and the underlying tissue." We agree. However, the concern that
"the dose to the skin may be dangerously high" is not supported. The
recommended limit for annual dose to the skin for the general public is
50,000 µSv^9
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn9>
. The dose to the skin from one screening would be approximately 0.56
µSv^10
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn10>
when the effective dose for that same screening would be 0.25 µSv^11
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn11>
. Therefore the dose to skin for the example screening is at least
89,000 times lower than the annual limit.
Second, radiation safety protection quantities are stated as 'effective
dose'^12
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn12>
. NCRP Commentary No. 16 says, "The purpose of effective dose^13
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn13>
is to place on a common scale the radiation doses: (1) from different
types of ionizing radiation that have different biological
effectiveness, and (2) in different organs or tissues that have
different radiation sensitivities." Comparing effective doses from
different sources is appropriate. The comparison between the effective
dose from cosmic ray exposure or a medical diagnostic chest x-ray and
the effective dose from a security screening is intended to be a clear
means of risk communication.
The third point relates to a concern "that real independent safety data
do not exist." In fact, independent safety data do exist. Independent
measurements have been made on various versions of this product and all
results are consistent with the dose specified by the manufacturer.
Examples include:
* Sandia National Laboratories, measurements made July 1991.
Published as Sandia Report: /Evaluation Tests of the SECURE 1000
Scanning System/ (1992), National Technical Information Service,
DE92013773
* FDA, dose measurements re-verified via computational evaluation,
September 15, 1998
* N43.17 working group, measurements made at Folsom State Prison on
November 15, 1999
* FDA & NIST, Assessment for TSA, July 21, 2006
* Johns Hopkins University Applied Physics Laboratory (JHU APL),
Assessment for TSA, October 2009
Fourth is the concern that "the relevant radiation quantity, the Flux
[photons per unit area and time (because this is a scanning device)] has
not been characterized." We disagree that flux is the appropriate
quantity. The air kerma (or skin entrance exposure) for one screening
can be determined by a direct measurement of the total charge produced
in the air contained in an ion chamber during one complete screening
when the meter is correctly calibrated^14
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn14>
. Additionally, measurements to determine the amount of material
required to reduce the intensity of the x-ray exposure by half^16
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn16>
are necessary to convert air kerma (or exposure) to effective dose^15
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn15>
. These measurements can most practically be made ---and indeed have
been repeatedly made--- at locations where these products are installed
and can be made without altering a scanner's normal operation. These are
the same sorts of measurements made to characterize the output of
medical x-ray systems^17
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn17>
.
Fifth is the assertion that "if the key data (flux-integrated photons
per unit values) were available, it would be straightforward to
accurately model the dose being deposited in the skin and adjacent
tissues using available computer codes [. . .]" In fact, we have done
better. FDA and NIST used software called PCXMC^18
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn18>
to estimate the individual organ doses and to calculate effective dose.
This analysis was part of an evaluation performed under contract for
TSA. The input information required by the PCXMC program required
considerably more information than simply the x-ray flux. Its parameters
include 1) the x-ray tube anode angle, 2) anode voltage, 3) total
filtration, 4) x-ray field size, 5) location of the field on the body,
6) focus-to-skin distance (FSD), and 7) entrance skin exposure. Every
parameter was measured, calculated, or verified by indirect measurement.
The modeling results revealed that the dose to the skin is approximately
twice the effective dose^19
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn19>
.
The letter continues: "[. . .] which would resolve the potential
concerns over radiation damage." Direct measurements of the exposure or
air kerma from one screening combined with measurements to determine the
half-value layer provide sufficient information to adequately estimate
the effective dose. There are a number of available publications by
groups of recognized experts regarding the biological effects of
ionizing radiation and the risk of detriment related to the effective
dose. These documents include /Health Risks from Exposure to Low Levels
of Ionizing Radiation/ : BEIR VII Phase 2 (2006) and NCRP report no. 115
/Risk Estimates for Radiation Protection/, as well as the documents that
specifically address security screening of people with ionizing
radiation mentioned in this letter.
Other specific concerns expressed in the letter are based on the
assumption that a screening results in skin or other organ doses that
are orders of magnitude higher than the effective dose per screening.
The dose to other organs is less than, equal to, or at most
approximately three times the effective dose^20
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn20>
for the deployed product. The annual dose limit for security screening
is the same as the NCRP recommendations for the annual effective dose
limit for the general public including special populations^21
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn21>
. An individual would have to receive more than 1000 screenings to begin
to approach the annual limit.
With regard to concerns about the hardware itself, the standard requires
that products have safety systems to terminate emission of the primary
beam in the event of any system problem that could result in abnormal or
unintended radiation emission. The scan motion cannot be adjusted. If
the scan motion were intentionally redesigned and changed to scan the
groin at a slower rate than the rest of the body, the point of
measurement to determine the dose per screening would also change. The
dose per screening measurement must be made at the point of maximum
exposure in order to comply with the standard. Manufacturers are
required to report changes to a product's performance specifications
when those changes can affect radiation safety, as would be the case
with any change to dose per screening.
These products have been available commercially in the United States
since 1992. Manufacturers of any type of electronic product that emits
radiation -- including full-body x-ray security systems -- are required
to notify FDA immediately upon discovery of any accidental radiation
occurrence or radiation safety defect. TSA policy is to require a survey
of x-ray systems annually, after any maintenance that could affect
radiation shielding, and after any impacts that could affect radiation
shielding. FDA regulations require notifications if the manufacturer or
FDA determines that an electronic product emits radiation unnecessary to
the accomplishment of its primary purpose creating a risk of injury,
including genetic injury, to any person. Such a product is then
considered to have a radiation safety defect. Unless a manufacturer can
provide evidence that a significant risk to public health is not created
by a defect, the manufacturer is required to repair, repurchase, or
replace its products. Raising the dose delivered without gaining a
commensurate increase in safety could be grounds to declare that a
product emits radiation unnecessary to the accomplishment of its primary
purpose and thus has a radiation safety defect. Products and practices
that comply with the American national radiation safety standard^22
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm231857.htm#_ftn22>
do not present a significant risk to public health.
In summary, the potential health risks from a full-body screening with a
general-use x-ray security system are miniscule. Several groups of
recognized experts have been assembled and have analyzed the radiation
safety issues associated with this technology. These experts have
published recommendations, commentaries, technical reports, and an
American national radiation safety standard as a result of their
analyses. This technology has been available for nearly two decades and
we have based our evaluation on scientific evidence and on the
recommendations of recognized experts. Public meetings were held to
discuss these products with FDA's advisory panel (TEPRSSC), and the
American national radiation safety standard was available for public
comment both before its initial publication and before its recently
published revision. There are numerous publications regarding the
biological effects of radiation and the appropriate protection limits
for the general public that apply to these products. As a result of
these evidence-based, responsible actions, we are confident that
full-body x-ray security products and practices do not pose a
significant risk to the public health.
We enclose a list of references to some of the relevant reports,
commentaries, and the current safety standard. If you have any further
questions or concerns, please contact either of the individuals listed
below.
Sincerely yours,
John L. McCrohan
Deputy Director for Technical and Radiological Initiatives
Office of Communication, Education, and Radiation Programs
Center for Devices and Radiological Health
Food and Drug Administration
Karen R. Shelton Waters
Deputy Assistant Administrator / Chief Administrative Officer
Designated Safety and Health Official
Transportation Security Administration
Enclosure
*REFERENCES *
* ANSI/HPS N43.17-2009 /Radiation Safety for Personnel Security
Screening Systems Using X-Ray or Gamma Radiation/
(http://hps.org/hpssc/)
o More information on the ANSI standards setting process is
available on the ANSI website
(http://www.ansi.org/standards_activities/overview/overview.aspx?menuid=3
)
* Interagency Steering Committee on Radiation Standards (ISCORS),
/Guidance on Security Screening of Humans Using Ionizing Radiation
(GSSHUIR) /Report
(http://www.iscors.org/doc/GSSHUIR%20July%202008.pdf)
* NCRP commentary 16, /Screening of humans for security purposes
using ionizing radiation scanning systems/ (2003)
(http://www.ncrppublications.org/Commentaries/16)
o Press release regarding commentary no. 16 (May 26, 2010)
(http://www.ncrponline.org/Press_Rel/Commentaries/Comm_16_Press_Release.pdf)
* /NCRP Statement 10, Recent Applications of the NCRP Public Dose
Limit Recommendation for Ionizing Radiation/(2004)
(http://www.ncrponline.org/Publications/Statements/Statement_10.pdf)
* NCRP report no. 115 /Risk Estimates for Radiation Protection /(1993)
* NCRP report no. 116 /Limitation of Exposure to Ionizing Radiation/
(1993)
(http://www.ncrppublications.org/index.cfm?fm=Product.AddToCart&pid=9143114606
<http://www.ncrppublications.org/index.cfm?fm=Product.AddToCart&pid=9143114606>)
* /NCRP rep/ort no. 160, /Ionizing Radiation Exposure of the
Population of the United States (2009)/
(http://www.ncrppublications.org/Reports/160)
* HPS Position Statement /Use of Ionizing Radiation for Security
Screening Individuals/
(http://hps.org/documents/securityscreening_ps017-1.pdf)
* American College of Radiology (ACR) /Statement on Airport
Full-body Scanners and Radiation
/(http://www.acr.org/SecondaryMainMenuCategories/NewsPublications/
FeaturedCategories/CurrentACRNews/archive/StatementonAirportFullbodyScanners.aspx
<http://www.acr.org/SecondaryMainMenuCategories/NewsPublications/FeaturedCategories/CurrentACRNews/archive/StatementonAirportFullbodyScanners.aspx>).
* U.S. Transportation Security Administration's (TSA) web site
regarding advanced imaging technology
(http://www.tsa.gov/approach/tech/imaging_technology.shtm).
* Information on laws and regulations applicable to manufacturers of
people screening security systems that use x-rays is available on
FDA's /X-Ray & Particulate Products other than Medical Diagnostic
or Cabinet/ page (http://www.fda.gov/Radiation-EmittingProducts/
RadiationEmittingProductsandProcedures/HomeBusinessandEntertainment/ucm116416.htm
<http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/HomeBusinessandEntertainment/ucm116416.htm>
)
* The concept of justification based on a societal benefit appears
in the International Commission on Radiological Protection (ICRP)
report 60 (see paragraph S14).
(http://www.icrp.org/downloadDoc.asp?document=docs/Summary_B-scan_ICRP_60_Ann_ICRP_1990_Recs.pdf)
* Health Physics Society fact sheet on Environmental radiation
(http://hps.org/documents/environmental_radiation_fact_sheet.pdf)
* Security screening with x-rays was discussed at several Technical
Electronic Product Radiation Safety Standards Committee (TEPRSSC)
meetings
(http://www.fda.gov/AdvisoryCommittees/CommitteesMeetingMaterials/Radiation-EmittingProducts/TechnicalElectronicProductRadiationSafetyStandardsCommittee/default.htm).
The last discussion took place during the October 1, 2003 meeting
(http://www.fda.gov/ohrms/dockets/ac/cdrh03.html#TechnicalElectronicProduct).
* Sandia Report: Evaluation Tests of the SECURE 1000 Scanning System
(http://www.ntis.gov/search/product.aspx?ABBR=DE92013773)
* Health Risks from Exposure to Low Levels of Ionizing Radiation:
BEIR VII Phase 2 (2006)
(http://www.nap.edu/openbook.php?record_id=11340&pag
<http://www.nap.edu/openbook.php?record_id=11340&pag>)
* Assessment of the /Rapiscan Secure 1000 ® Body Scanner for
Conformance with Radiological Safety Standards/. July 21, 2006,
produced for TSA, measurements made at FDA, report completed at
NIST (http://www.tsa.gov/research/reading/index.shtm)
* /Radiation Safety Engineering Assessment Report for the Rapiscan
Secure 1000 in Single Pose Configuration/,Johns Hopkins University
Applied Physics Laboratory, Assessment for TSA, October 2009 and
revised August 2010 (http://www.tsa.gov/research/reading/index.shtm)
------------------------------------------------------------------------
^1 ANSI/HPS N43.17-2002 /Radiation Safety For Personnel Security
Screening Systems Using X-rays/
^2 NCRP was founded in 1964 by the U.S. Congress to "cooperate with the
International Commission on Radiological Protection, the Federal
Radiation Council, the International Commission on Radiation Units and
Measurements, and other national and international organizations,
governmental and private, concerned with radiation quantities, units and
measurements and with radiation protection."
^3 NCRP report no. 116 /Limitation of exposure to ionizing radiation/
(1993); pages 45-47, 56
^4 "Mostly" refers to the unlikely situation where individuals are
routinely screened so many times in one 12-month period that the annual
dose limit would be exceeded. For example, an individual can be screened
19 times each week and would not receive more than the annual dose limit.
^5 Initial presentation October 20, 2003
^6 1st work group meeting May 11, 2006
^7 ANSI/HPS N43.17-2009 /Radiation Safety for Personnel Security
Screening Systems Using X-Ray or Gamma Radiation/
^8 Ibid (ANSI/HPS N43.17-2009): "Various organizations have studied the
biological effects of ionizing radiation exposure. The National Council
on Radiation Protection and Measurements (NCRP) reviewed two independent
studies, one by the United Nations Scientific Committee on the Effects
of Atomic Radiation (UNSCEAR 1988) and the other by the National Academy
of Sciences/National Research Council, Committee on the Biological
Effects of Ionizing Radiation, known as BEIR V (NAS/NRC 1990). Based on
this review, the NCRP recommends that, for radiation protection
purposes, an incremental lifetime risk of fatal cancer of 5% per sievert
be used for the general population (NCRP 1993). The 5% per sievert risk
is also consistent with the more recent BEIR VII report (NAS/NRC 2006).
Application of this risk estimate means that each 0.01 ?Sv (1 ?rem) of
effective dose received is considered to contribute 5 × 10^-10 (one
chance in two billion) to an individual's risk of contracting a fatal
cancer during his or her lifetime. These low-dose estimates assume a
"linear no-threshold" relationship between radiation exposure and health
effects.
Both the NCRP and the International Commission on Radiological
Protection (ICRP) recommend that members of the general population who
are frequently exposed to ionizing radiation not exceed an annual
effective dose of 1 mSv (100 mrem) from all man-made, non-medical
sources (NCRP 1993; ICRP 2007). Further, the NCRP recommends that
institutions ensure that the individuals they expose do not repeatedly
exceed the 1 mSv yearly limit from all non-medical sources. Information
relating to other sources of radiation exposure may be difficult to
obtain, so institutions have the option to ensure that the radiation
sources under their own control do not contribute to an individual more
than an annual effective dose of 0.25 mSv (25 mrem).
General-use systems operating in accordance with this standard produce a
maximum reference effective dose of 0.25 ?Sv (25 ?rem) per screening.
Therefore, an individual may be screened up to 1,000 times each year
without exceeding the annual 0.25 mSv (25 mrem) limit. The associated
incremental risk of death is 1 in 80,000,000 per screening."
^9 NCRP report no. 116 /Limitation of exposure to ionizing radiation/
(1993), page 56
^10 FDA & NIST Assessment of the /Rapiscan Secure 1000® Body Scanner for
Conformance with Radiological Safety Standards/. July 21, 2006, produced
for TSA. This skin dose is an estimate based on dose modeling. This
estimate is only for products with very similar x-ray output. The
difference between skin and effective dose is smaller for products that
use higher energy or more filtration.
^11 The actual dose per screening specification is 0.05 µSv or less
http://www.rapiscansystems.com/rapiscan-secure-1000-single-pose-health.html.
The JHU APL assessment report confirms that the product meets this
specification.
^12 NCRP report no. 158/Uncertainties in the Measurement and Dosimetry
of External Radiation/, page 22
^13 Radiation doses from exposures that may result in delayed stochastic
effects are expressed in the quantity effective dose (/E/):
E =
?/w/_T /H/_T ,
^T
where /H/_T is the equivalent dose in an organ or tissue T, and /w/_T is
the tissue weighting factor that accounts for the radiation sensitivity
of organ or tissue T.
^14 ANSI/HPS N43.17-2009 /Radiation Safety for Personnel Security
Screening Systems Using X-Ray or Gamma Radiation,/ section 'C.3.2
Calibration'
^15 This quantity is called the half-value layer (HVL). HVL is often
expressed in terms of the thickness of aluminum required.
^16 ANSI/HPS N43.17-2009 /Radiation Safety for Personnel Security
Screening Systems Using X-Ray or Gamma Radiation,/ section '6.0 Dose
Limitation' and 'A.1 Reference Effective Dose'
^17 Nationwide Evaluation of X-Ray Trends (NEXT)
(http://www.fda.gov/Radiation-EmittingProducts/RadiationSafety/
NationwideEvaluationofX-RayTrendsNEXT/default.htm
<http://www.fda.gov/Radiation-EmittingProducts/RadiationSafety/NationwideEvaluationofX-RayTrendsNEXT/default.htm>)
^18 Servomaa, A. and Tapiovaara, M. Organ dose Calculation in Medical X
Ray Examinations by the Program PCXMC. Radiation Protection Dosimetry
80, 213-219 (1998).
^19 FDA & NIST Assessment of the /Rapiscan Secure 1000® Body Scanner for
Conformance with Radiological Safety Standards/. July 21, 2006, produced
for TSA.
^20 FDA & NIST Assessment (2006); Our dose modeling reveals that a
screening that delivers 0.25 µSv effective dose would deliver
approximately 0.12 µSv to the uterus or 0.69 µSv to the testes. This
estimate applies to products with very similar x-ray output.
^21 NCRP Statement 10/, Recent Applications of the NCRP Public Dose
Limit Recommendation for Ionizing Radiation/ (2004) and NCRP report no.
116 /Limitation of exposure to ionizing radiation/ (1993).
^22 ANSI/HPS N43.17-2009 /Radiation Safety for Personnel Security
Screening Systems Using X-Ray or Gamma Radiation/
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