[ RadSafe ] Airport Whole Body Scanner Risks

Mon Nov 22 15:25:21 CST 2010

Isn't this why we have a weighting factor from ICRP for skin? So we can
normalize the dose (risk) for comparison and protection purposes?

If the effective dose was calculated using accepted methodology and
weighting factors and really is about 10 microrem per scan (the number I
have seen reported) then it's as good a number as we have for any other
radiation dose out there.

It seems to me that the pertinent questions are:

1.  Do you accept the reported dose at face value?  Why or why not?

1a. What methodology and measurement techniques were used to determine
the reported dose?

1b. Do you accept ICRP weighting factors for determining the effective
dose once the absorbed dose to all tissues of interest - including of
course skin - is determined? 

So, there are really two discussion to have:
1.  What is the dose (and therefore risk) - really? This is an
interesting scientific question and goes directly to the point the UC
researchers brought up.  I seem to recall reading somewhere that
measurements were taken free-in-air with an ionization chamber.  Somehow
this was converted to effective dose.  It seems that the UC researchers
are saying that they have a problem with the method used- whatever that
may be.

2.  Is such a dose/risk appropriate for population screening?  This is
an entirely different question - but I can tell you this: given the
choice between the scan and the pat down, I will take the scan thank you
very much.

Bryan Lemieux

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Brennan, Mike
(DOH)
Sent: Monday, November 22, 2010 1:46 PM
To: The International Radiation Protection (Health Physics) MailingList
Subject: Re: [ RadSafe ] Airport Whole Body Scanner Risks

I've seen other references to this letter, and none of them have
addressed what I consider to be a key technical issue in the contention:

"Specifically, even though the backscatter machines operate at low beam
powers, the majority of their radiation is directed at the skin and
underlying tissue, not the entire body. The report says because the
X-ray energy is not absorbed by the entire body, the skin dosage may be
dangerously high in localized areas, exposure that's very different than
a chest X-ray."

Is this in fact true?  

I am not an x-ray guy, but it seems that just because one system looks
at backscatter and the other looks at the photons that make it through
the target doesn't mean that the photons behave differently (aside from
fairly minor differences due to some materials absorbing some
frequencies better than others).  It seems to me that the skin at the
entry point of a diagnostic is exposed to a greater amount of radiation
than the skin at the exit point, or the tissue anywhere between.  I
recall stories about the "bad old days" where people would get burns on
their skin from x-ray procedures.  

Given that the backscatter images I've seen show the shin bones better
than the surrounding tissue, it is clear that the x-rays used in
backscatter have penetrating power.  I assume that if one put film on
the other side of the target, it would fog, and if the geometry was
right you could image (although poorly) the bones of the target. So it
seems to me that there is no qualitative difference between the x-rays
used for diagnostic and security: both beams deposit their energy in the
way that we are familiar with, and the big difference is where we put
the detectors, and how much energy is needed to get a usable number of
photons to the detector.  

If I am wrong in my reasoning, I would appreciate someone pointing it
out to me.  I am a general rad guy, and I could easily be overlooking
something.  

But if I am right, it raises an interesting question as to why the UC
researchers either didn't see it, or chose not to consider it.  And if I
am right, their entire position is undermined. 

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Otto G. Raabe
Sent: Monday, November 22, 2010 10:26 AM
To: The International Radiation Protection (Health Physics) Mailing List
Subject: [ RadSafe ] Airport Whole Body Scanner Risks

Researchers: TSA Misleads Public on Scanner Safety

As the Transportation Security Administration's 
deployment of backscatter X-ray machines at 
airports draws increasing public resistance, four 
University of California researchers say the 
ionizing radiation used in these devices pose 
serious health concerns. In early April of 2010, 
the researchers-all medical and biology 
specialists- 
<http://www.scribd.com/doc/35498347/UCSF-letter-to-Holdren-concerning-he
alth-risks-of-full-body-scanner-TSA-screenings-4-6-2010>wrote 
the White House's science and technology 
assistant, John Holdren, expressing "urgent" 
concerns about the safety of so-called Advanced 
Imaging Technology. TSA has claimed that the 
scanners expose passengers to less than the 
equivalent of a chest X-ray, but the researchers 
say this claim is misleading because of the way backscatter X-rays work.

In a detailed paper submitted to the White House, 
the researchers identified a number of red flags 
associated with the use of this technology. 
Specifically, even though the backscatter 
machines operate at low beam powers, the majority 
of their radiation is directed at the skin and 
underlying tissue, not the entire body. The 
report says because the X-ray energy is not 
absorbed by the entire body, the skin dosage may 
be dangerously high in localized areas, exposure 
that's very different than a chest X-ray. 
Furthermore, they say no independent data exists 
on the safety of routine use of backscatter 
machines. The TSA appears to have accepted data 
from the manufacturers, without benefit of 
conducting independent risk assessment buttressed by peer-reviewed data.

The researchers' report indentified several 
categories of at-risk passengers, including 
people over 65, women who may be sensitive to 
mutagenesis provoking radiation, a breast cancer 
risk and immunocompromised individuals. The 
scientists urged the administration to assemble 
an independent panel to evaluate the scanner 
risk, but thus far, this hasn't been done, 
although TSA did engage Johns Hopkins University 
of Applied Physics Laboratory 
<http://blog.tsa.gov/2010/03/advanced-imaging-technology-radiation.html>
to 
perform an engineering assessment. The university 
claimed the radiation exposure is within safe 
limits published by the American National 
Standards Institute. Similarly, it posted 
<http://www.acr.org/MainMenuCategories/media_room/FeaturedCategories/Pre
ssReleases/StatementonAirportFullbodyScanners.aspx>a 
statement from the American College of Radiology 
claiming that the backscatter machines represent 
less radiation risk than the flight itself. 
Neither of those reports addresses the 
researchers' point about concentration of 
radiation on the skin.At least two airline unions 
aren't buying TSA's assurances. The U.S. Airline 
Pilots Association and the Allied Pilots 
Association are advising their members to avoid the scanners.

**********************************************
Prof. Otto G. Raabe, Ph.D., CHP
Center for Health & the Environment
University of California
One Shields Avenue
Davis, CA 95616
E-Mail: ograabe at ucdavis.edu
Phone: (530) 752-7754   FAX: (530) 758-6140
*********************************************** 
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