http://www.npr.org/assets/news/2010/05/17/concern.pdf(i included the text below):
University of California
San Francisco
John W. Sedal, Ph.D.
Professor Emeritus
Department of Biochemistry
and Biophysics
600 16th Street
N412D. MC 2240
San Francisco. CA 94158-2517
tel: 415/476-4156
fax: 415/514-4242
e-mail: sedat@msg.ucsf.edu
April 6, 2010
Dr. John P. Holdren
Assistant to the President for Science and Technology
Dear Dr. Holdren:
We, a number of University of California, San Francisco faculty, are writing-see
attached memo--to call your attention to our concerns about the potential serious
health risks of the recently adopted whole body back scatter 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.
By way of introduction one of us (John Sedat) met you recently when he and his
wife Dr. Elizabeth Blackburn, a 2009 Nobel Laureate; talked with President Obama
last December. Dr. Sedat is Professor Emeritus in Biochemistry and Biophysics at
the University of California, San Francisco, with expertise in imaging. He is also a
member of the National Academy of Sciences. The other cosigners include Dr.
Marc Shuman, an internationally well known and respected cancer expert and UCSF
professor, as well as Drs. David Agard and Robert Stroud, who are UCSF
Professors, X-ray crystallographers, imaging experts and NAS members.
Sincerely yours,
~~
(signatures of)
John Sedat, Ph.D
David Agard, Ph.D.
Marc Shuman, M.D.
Robert Stroud, PhD
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 Xrays
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
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 mutagenesisprovoking
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.
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