[ 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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