[ RadSafe ] Airport Whole Body Scanner Risks

Wed Nov 24 12:14:12 CST 2010

Full Disclosure: I did not post the link to the letter: I was commenting
on how impressive I found the letter.  The link was posted by Barbara.  

Prof. Rabbe,

I agree that there may well be problems in using models based on bomb
survivors to predict risk in very different exposure scenarios.  All
other models I am aware of also have problems, though.  They are based
on animals, or cell cultures, or no data at all (the anti-everything
advocates like those ones).  The choice seems to be between using the
most defensible model available and paralysis because you can't know the
long term effects of a particular exposure upon a large population
without exposing a large population to that particular for a long time
(and possibly not even then).  

While it is possible that weak x-rays may be more important in skin
cancer induction than higher energy gammas, I see a problem with then
arguing that, because they are higher energy, they may also be more
important in inducing skin cancer than UV.  If one is going to posit
that weak x-ray occupy a particular window of effectiveness in inducing
skin cancer, one is going to have to provide some pretty good evidence.

And, in any event, the question should be (in my opinion), are the risks
and inconveniences of the scan less than the risks and inconveniences of
the things the scans are supposed to prevent?  There are a great many
assumptions that have to go into both sides of this expression in order
to determine if it is an inequality, and which is the "less than" side.
I don't claim to know the answer, but there are a lot of people being
interviewed who don't seem to be asking all of the question.     

-----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: Wednesday, November 24, 2010 7:19 AM
To: The International Radiation Protection (Health Physics) Mailing List
Subject: Re: [ RadSafe ] Airport Whole Body Scanner Risks

At 02:53 PM 11/22/2010, Brennan, Mike  (DOH) wrote:

>I don't know if this has been posted here yet or not, but here is a
link
>to FDA's response to the UCSF concerns:
>www.whitehouse.gov/sites/default/files/microsites/ostp/fda-backscatter-
response.pdf

***********************************************
The important letter above to Dr. Holden from the Department of 
Health and Human Services lays out in detail the radiation dosimetry 
issues associated with the whole body x ray scanners. Please read it.

An important sentence on page 4 that I don't quite understand is "The 
dose to the skin from one screening would be approximately 0.56 uSv 
when the effective dose for that same screening would be 
approximately 0.25 uSv." The tissue weighting factor for skin is 
0.01, so this sentence makes no sense to me. However, the letter is 
clear that they like to use the "effective dose" in describing these 
exposures.

However, the use of a tissue weighting factor of 0.01 based on the 
atomic bomb survivor studies to calculate the either 56 urem or 25 
urem effective dose per screening to skin may not be appropriate. The 
high energy gamma radiation received by the atomic bomb survivors my 
not have the same biological effectiveness per unit of dose as weak x 
rays in the case of the skin. Also, cancer  promotion from weak x ray 
exposures may be more important than cancer induction in the case of the
skin.

I presume that the actual absorbed dose to skin per screening is 5.6 
mrem or 2.5 mrem based on the information in the letter to Dr. 
Holden. Therefore, it is safe to assume that the skin absorbed dose 
per scan is a few mrem.

The main issue related to skin irradiation is skin cancer. Skin 
cancer including some life-threatening forms, have been clearly 
associated with ultraviolet light exposures. UV light is less 
energetic than x rays and we can presume that ionizing weak x rays 
are more effective than UV light in promoting skin cancer. The 
promotional effect of repeated skin x ray exposures at airports 
rather than the cancer initiation by x rays may be the most important 
issue for people with high risk of skin cancer. People from southern 
states where UV exposure is high and skin cancer is common might be 
more affected by repeated whole body skin exposures to x rays that
others.

Comments please......

Otto

**********************************************
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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