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

[Andy Hull <hull@mail.sep.bnl.gov>]

At 11:56 AM 6/19/97 -0500, you 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.
>
>In a way - it IS.  Kinda sorta.
>
>>I think Ted's comment above in fact is agreeing with this underlying
>>presumption. He is pointing out that the external field is not the same as
>>that at the cells.
>
>yes
>
>>But I saw no comments on what I was trying to find out - Is the total
>>number of cells  in the body that are possible proginators for cancer a
>>constant across adults of widely varying sizes?  Or a constant to a
>>reasonable approximation?
>
>Oh I see - cell COUNT not cell MASS.  ie. do all humans have the same CELL
>COUNT regardlessof mass??  I don't know but I don't think so.
>
>I'd also suspect MASS is more important than NUMBER.
>
>BUT what I was trying to say was:
>
>IFF one takes LNT to be true ...... THEN the risk to the population
>- be it the population of cells in and organism or individuals in a
>community - is the SAME if all the cells (using the organism model) are
>exposed to 1x rads or 1/2 to 2x or 1/1000 to 1000x.
>
>LNT says this would hold, up to prompt effects.
>
>So - when one calculates EDE one is calculating the risk to the organism AS
>IF ALL CELLS WERE UNIFORMLY IRRADIATED - thus assuming the local variations
>were within the realm of linearity - ie - no prompt cell mortalities since
>dead cells cannot become cancerous (I think).
>
>So - EDE DOES in fact mathematically attempt to weight TOTAL energy
>deposited in TOTAL mass - ie, the Fluence to each and every cell - BUT
>expresses this in units that are a "concentration unit" and thus averaging
>over the organism/population is mathematically the same thing.
>
>For what it may be worth, the following quotation from a 1977 paper "Repair
and Dose-Response at Low Doses" by  J. R. Totter and A. M. Weinberg,
ORAU/IEA(0)-77-11, may be relevant:

"Yet the simplest considerations strongly suggest that repair, at some
level, at least of low LET radiation, must exist. With some 2-4E14
ionizations from background radiation (a large dose from the standpoint of
the strictly no-threshold linear hypothesis) occurring within the DNA of the
~10E13 cells of the human body during the first 30 years of life, it is
difficult to explain why everyone does not die of cancer unless very
effective mechanisms for removing the damage are a dominant factor". 

Andrew P. Hull
S&EP Div. Bldg 51
Brookhaven National Laboratory
Upton, N.Y. 11973

>