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

[Richard Smart]

For radioimmunotherapy using alpha emitters, the RBE is often chosen to be 
5, not 20. As stated below, the radiation weighting factor of 20 for alphass 
is for stochastic effects.

Richard

----- Original Message ----- 
From: "Ronald Frick" <rfrick at gammacorp.com>
To: <radsafe at radlab.nl>
Sent: Thursday, November 30, 2006 6:46 AM
Subject: Re: [ RadSafe ] Sv (and rems) are NOT restricted to stochastic 
effects


ICRP 60 states: "The equivalent dose is not always the appropriate quantity 
for use in relation to deterministic effects because the values of radiation 
weighting factors have been chosen to reflect the relative biological 
effectiveness (RBE) of the different types and energies of radiation in 
producing stochastic effects.  For radiations with a radiation weighting 
factor larger than 1, the values of RBE for deterministic effects are 
smaller than those for stochastic effects.  The use of the equivalent dose 
to predict deterministic effects for high LET radiations, e.g. neutrons, 
will thus lead to overestimates."

See also ICRP 58, "RBE for Deterministic Effects".

Ron Frick

>>> Douglas Simpkin <dsimpkin at wi.rr.com> 11/29/2006 8:21 AM >>>
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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