Re: Re[4]: how many sensitive cells?

[JMUCKERHEIDE@delphi.com]

> The following is the closest to addressing my question of whether risk is
> proportional (i.e., not necessarily linear) to the number of cell exposed.
> 
> "In biology, cells don't exist in isolation. By using data from hits on
> cells in cultures that do not have functional response capability, it is
> easy to show "linear" responses. As soon as you take 4 cells with
> communication, the response will not, can not be "linear". All the
> framework of the biological assessment of "dose" as energy concentration
> falls. This is part of the biological work that has been judiciously
> ignored by the ICRP et al for the last 15-20 years, and longer if you go
> back to the work of Brues and others. 
> 
> Regards, Jim Muckerheide"
> 
> This is easy to accept for cells within an organ or a limits region.  Is
> it true for the whole organism, i.e., the whole body?  Is 1 cm2 of the
> foot is exposed will the body reaction in effect make the response the
> same as if 1 cm2 of each foot were exposed or does the later in fact
> double the risk?

As Vic Bond, Feinendegen, Sondhaus, Weilopolski and others have shown, it is
valid for any population, from cells to organs to organisms to populations
(see eg their treatment of the Japanese survivor population. Beyond that
however, your concern about "non-lineear proportionality" must also, further,
include consideration of adaptive response that is clearly demonstrated in
viable cell populations. 

The response must certainly be positive because a small radiation dose causes
a stimulative response. This stmulative response acts on all the DNA damage
and cellular repair functions. The normal background of DNA damage is 10+5 -
10+6 times higher than background radiation damage, and unrepaired DNA damage
(mutations) is at least 10+4 times higher than the DNA damage from background
radiation. 

Many multiples of background radiation can not add any significant increment
to the normal damage/repair process! But the stimulated response acts on all
the damage, not just the radiation damage. Therefore, a net benefit up to a
level sufficient to adversely affect the repair processes. (This is still not
high enough to be significant compared to the normal DNA damage rate, but it
is high enough to have adverse effects on the repair processes, eg, 100 times
background = 30 rad, which is still only 1% of annual backround, but if you
get it acutely instead of chronically then it can have adverse effects.) 

Thanks.

Regards, Jim Muckerheide
jmuckerheide@delphi.com
Radiation, Science, and Health, Inc.

> If the former is the case then the body reaction would seem to be one that 
> must be communicated very the blood circulatory system as opposed to an
> intracellular repair response.  I guess it is time to do some radiobiology
> remedial reading. This sure is not addressed in the books I have.
> 
> -- 
> the above are the personal musing of the author,
> and do not represent any past, current, or future
> position of NIST, the U.S. Government, or anyone else
> who might think that they are in a position of authority.
> NBSR Health Physics
> NIST
> Gaithersburg, MD 20899
> 301 975-5810
> -----------------------------------------------------------
> Lester.Slaback@nist.gov
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