Re: how many sensitive cells?

[Wes Van Pelt <VanPeltW@IDT.NET>]

Lester.Slaback@nist.gov wrote:
> 
> The question was (in a left handed way) why is not risk proportional
> to
> the total number of cells subject to irradiation times the actual
> fluence
> at the cells.
> 
> Assuming one does the corrections for partial exposures, depth
> distribution, and all the other things that affect the number of cells
> that might be exposed at a particular fluence, why is this not the
> starting point for a risk estimate.
> 
> 

Les and All,

This is a very interesting line of reasoning.

Suppose that a mouse and a horse are exposed for equal times in a
uniform gamma field of high energy per photon (e.g., Co-60). Ignore for
a moment the self attenuation in the horse and assume both animals got,
say, 200 rad.  That is, 200x100 = 20,000 ergs/gram. The horse has, say,
10,000 times more mass (and cells) than the mouse. If each cell gets 200
rad, then the horse should have a cancer risk 10,000 times that of the
mouse.  That is, if each irradiated cell has an equal chance of going
cancerous. Clearly this is not so, because the cancer risk per rad is
nearly the same for all/most mammals (I think).

This is a very interesting line of reasoning.

I look forward to other comments.

Best regards, Wes
-- 
Wesley R. Van Pelt, Ph.D., CIH, CHP                KF2LG
President, Van Pelt Associates, Inc.     
Consulting in radiological health and safety.
mailto:VanPeltW@IDT.net        
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