AW: [ RadSafe ] query

[John Jacobus]

Rainer,
Thank you for your comments.  Like Mike, I do not
subscribe to the LNT, but what I believe is not really
that important to the discussion.  

I have considered the LNT to be the simplest model
that mathematically fits the data points. 
Unfortunately, it tries to fit all the data, both
epidemiological, animal, and cellular data.  I believe
that cellular data is useful as it study what
radiation effects are occuring and how the cells
respond to the effects that occur.  

However, organisms are made up of many highly
differeniated cells that evolved to defend the whole
organism.  When individual cells are damage, by
radiation, chemicals or age, they release compounds
that signal distress.  Cells may die, be repaired by
cellular response, or killed by other cells. Thus,
cells in isolation do not represent the whole
organism. (I assume that you know most of this
already.)

In separate studies, animal and human populations are
studied.  Unfortuately, may such studies are based on
acute doses and high dose rates.  To me it is obvioius
that radiation effects occur at both high and low
doses, and high and low dose rates.  However, at low
doses and dose rates, which may workers are exposed
to, biological systems (cellular and the whole
integrated system of tissue) repair damaged cells or
kill those that are defective.  That is why there are
no observed radiation effects below 100 mSv.

Again, when you combine all of this data, cellular and
epidemiological, and try to fit it to a simple dose
response curve, you get a linear plot.  It may not
reflect what is really going on, but it is the
simplest relationship that can be made.  This is what
the BEIR committee was tasked to do.

My understanding for studing the ATB survivors is that
they represent a large population whose exposures are
well known.  Also, the low dose group provide a
control to the higher dose groups.  This eliminates
the problem of comparing the highly exposed population
to some other group, like the rest of the Japanese
population who may not have non-radiation bomb
effects.  

--- Rainer.Facius at dlr.de wrote:

> Mike:
> 
> Despite my serious disagreement with BEIR VII-2's
> endorsement of the LNT postulate as a scientific
> fact, I concur that conspiracy theories like biased
> committee selection are unreasonable or worse. 
> 
> The rows stirred by several anti-nuclear activist
> organisations and which accompanied the assembly of
> the committee testify that many members to be were
> villainised as minions of the nuclear establishment
> since they were accused of NOT subscribing to LNT.
> In fact, several of the epidemiologists which are
> (rightly) renowned for their empirical work on human
> carcinogenesis from occupational radiation exposure
> could be quoted as stating that their data on
> radiation workers are compatible with anything from
> hormesis to LNT. 
> 
> They also often emphasised the relevancy if not the
> pre-eminence - as far as radiation protection
> standards are concerned - of findings from studies
> on truly chronically exposed worker populations
> above findings from high dose rate studies such as
> therapeutic or ATB exposures. Yet, from the
> beginning of their professional career these
> epidemiologists appear to have been conditioned to
> somehow regard the ATB survivor findings as the
> 'gold-standard' of radiation epidemiology. The fact
> that in the 1970s and 1980s only data from the ATB
> survivor studies could boast error bars which at
> least above 200 mSv excluded the y-axis may have
> biased them to rest content if their own data
> admitted a LNT line which within the confidence
> limits did not contradict the ATB LNT line. 
> 
> Then, and even more so in the 90s, their data (at
> least from that handful of really large studies
> which I happen to know) would have been equally well
> - and from the parsimony principle even better -
> represented by a 'no-effect' model, up to say 500
> mSv. Still, and without an attempt to justify this
> self-restraint, the only answer sought from their
> data was again whether they would be compatible with
> the then current ATB LNT line. The rationale
> occasionally given that the ATB data yielded more
> definite (alias accurate) risk estimates was at
> least as weak as the DDREF uncertainty was large,
> not to speak of the other imponderabilities of
> extrapolating from the ATB survivors to non Japanese
> worker populations. 
> 
> Why despite of their own professional expertise they
> subscribed to the LNT postulate can only be guessed.
> One reason may be - in line with still much of
> contemporary biology - the - with hindsight peculiar
> - preoccupation with initial DNA damage as the sole
> determinant of an organism's response to genotoxic
> substances, among which radiation is just one. In
> conjunction with their report also the protocols of
> BEIR VII-2's proceedings back the assumption that
> this outdated notion might have been influential.
> 
> Another, and as I speculate, probably decisive
> reason might have been the import of the disastrous
> Brenner et. al. paper published in PNAS
> 100#24(2003)13761-66. Authored by an excerpt from
> "Who is Who in radiation biology" it still appears
> mysterious how that manuscript could make it into
> the pages of PNAS. Classified by another luminary in
> radiation research (actually a doyen) as "a horrible
> paper" and "shoddy work" at least in one detail it
> is outright fraudulent, i.e., in asserting that in
> Cardis et al. 1995 a significant increase in
> leukaemia mortality had been demonstrated. Other
> aspects such as the design of their figure 2 have
> again by some most knowledgeable experts been
> classified as "misleading" where I once more would
> prefer fraudulent. 
> 
> (As an aside: another really strange aspect with
> this paper - as with all PNAS publications - is that
> once it has been printed it effectively is immunized
> against public professional criticism. In contrast
> to all other scientific journals I know, the NAS
> offers no manuscript category "Letters to the
> Editor" or "Correspondence" or "Matters Arising"
> where controversial aspects of a paper could be
> publicized. At least at that time I was unable to
> find a section where I could submit the commentary
> which I had prepared already.)
> 
> So, at least as far the compliance of the
> 'epidemiology members' of the committee is
> concerned, my guess is that a mixture of (self-)
> conditioning, of DNA-'obsession', and the imposing
> author list of the PNAS paper was instrumental in
> winning their consent to a conclusion which
> continues the tradition of leaning on a perceived
> overriding predominance of the ATB survivor data.
> 
> Fortunately, another at least as distinguished
> scientific body, the French Academy of Sciences
> nearly simultaneously voiced its opposite appraisal
> of the biomedical effects of chronic low dose
> radiation exposures and anybody interested in taking
> part in the cutting-edge of the respective
> scientific development is urged to study their
> report and the references they drew upon (quite a
> few PNAS papers among them!).
> 
. . .

+++++++++++++++++++
"Every now and then a man's mind is stretched by a new idea and never shrinks back to its original proportion." -- Oliver Wendell Holmes, Jr.

-- John
John Jacobus, MS
Certified Health Physicist
e-mail:  crispy_bird at yahoo.com


		
____________________________________________________
Start your day with Yahoo! - make it your home page 
http://www.yahoo.com/r/hs