AW: [ RadSafe ] Sv (and rems) are NOT restricted to stochastic effects

[Rainer.Facius at dlr.de]

Douglas,

the quality/radiation weighting factor is a consensus interpretation by committees such as ICRP of RBE-max values for radiobiological data relevant for carcinogenesis ONLY such as mutation induction, malignant transformation, chromosome aberrations, tumor induction in mammalian cells or whole animals. RBE-max is the estimate of the dose dependent RBE(D) for low doses, formally RBE-max=lim(RBE(D) for D à 0). 

Cell survival data are irrelevant for the quality factor. 

I remember presenting during a congress experimental RBE values for cell killing by individual cosmic rays in the order of several hundreds and commented in my talk that this might imply that quality factors when applied to astronaut radiation protection might underestimate their risk. In the open discussion after my presentation Warren Sinclair, then (25 years ago) president of the ICRP and Michael Fry (NCRP) somewhat quizzically asked me whether I really did not know that such data as mine were irrelevant for quality factors. That was the hard way for me to learn this distinction.

Regards, Rainer
 
Dr. Rainer Facius
German Aerospace Center
Institute of Aerospace Medicine
Linder Hoehe
51147 Koeln
GERMANY
Voice: +49 2203 601 3147 or 3150
FAX:   +49 2203 61970

-----Ursprüngliche Nachricht-----
Von: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] Im Auftrag von Douglas Simpkin
Gesendet: Mittwoch, 29. November 2006 19:22
An: radsafe at radlab.nl
Betreff: [ RadSafe ] Sv (and rems) are NOT restricted to stochastic effects

Perhaps it's the neurons misfiring, but I'm confused.

In the discussion of the past couple of weeks on the Po-210 poisoning, a number of folks have indicated that the Quality Factor
(QF) or radiation weighting factor for alphas should not be considered when stating the magnitude of deterministic effects. 
Rather, they presume the QF is restricted to describing stochastic effects.

This is absolutely wrong.

The QF is based on radiobiological experiments of cell killing effects, and you can't get much more deterministic than that! The QF for alphas is 20 because the alphas dump so much more energy across the cell nucleus, and therefore cause that much more deterministic biological damage compared to sparsely ionizing x rays.

Indeed, the effective dose, or effective dose equivalent, (also confusingly in Sv or rem) is defined only for stochastic effects. But that's not the concern here.

My rough estimate of 0.12 ug = 0.53 mCi (the amount of Po-210 stated by that great repository of societal wisdom, Wikipedia, as lethal) uniformly spread through the liver yields a liver dose in the 1000-2000 rad range, or 20,000 to 40,000 rem to the liver.

Enough to mess up anyone's day.

Doug
ps. And no, I'm not apologizing for non-SI units!

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