Re: Effective Dose Equivalent

["James G. Barnes" <mail15077@pop.net>]

Dear Al,

You may be mixing apples and oranges.

My understanding of the dose limits is:

1)  Some dose effects are statistical in nature.

2)  Some dose effects are deterministic in nature (i.e., if you get a certain 
dose, you can be assured there will be a related effect).

The "Equivalent" dose is assumed to hold for statistical effects; i.e., the 
"chance" of health effect is equivalent for 4 REM to the gonads as for 1 REM to 
the "whole body."  It allows a (admittedly sloppy, hypothetical) equivalence 
between doses.

If, however, one were to expose an organ to a point where an effect would be 
expected with some certainty, the all bets are off and the equivalency no 
longer holds.  Your examples appear to clearly enter this zone as you are 
dealing with doses of several hundred REM.  As these are clearly deterministic 
doses, then the equivalency no longer applies and one has to assess the dose on 
its individual biological effect.

ICRP 30, paragraph 2.2 clearly limits the "weighting correction" to stochastic 
effects (statistical effects).  Non-stochastic effects are dealt with 
differently, using a "threshold" effect limit (50 REM).

Jim Barnes, CHP
RSO
Rocketdyne Division, Rockwell Aerospace

>  The concept of total effective dose equivalent or TEDE requires addition of
> external dose to internal dose.  The internal dose is calculated by
> multiplying the organ committed dose equivalent by an appropriate weighting
> factor.  The weighting factor is chosen so that the risk of fatal cancer or
> hereditary effects or non fatal cancer hypothetically caused by the
> committed organ dose equivalent would be the same as the hypothetical risk
> from exposure of the whole body to a dose equal to that of the organ
> multiplied by the weighting factor.  However, I have a conceptual problem
> with that idea, particularly for large doses.
> 
> For example:  Suppose the testicles receive a dose of 40 Sv and the rest of
> the body receives zero dose (remember this is hypothetical).  The equivalent
> dose is 10 Sv (weighting factor of 0.25 in 10 CFR 835).  10 Sv will almost
> certainly result in death.  40 Sv to the testicles will result in sterility,
> but probably nothing else (at least I can't find any risk numbers for fatal
> testicular cancer as a function of dose).  So, how are the 10 Sv and the 40
> Sv equivalent in risk?
> 
> A similar problem appears if the testicles are exposed to 4 Sv (equivalent
> dose of 1 Sv).  4 Sv could cause sterility.  1 Sv could have a significant
> risk of cancer.  Are those two risks equivalent?  Even worse: the DOE
> Radiological Control Manual requires establishing special control levels for
> individuals whose total lifetime dose in rem exceeds their age in years
> (based on an NCRP recommendation).  Would it make sense to establish such a
> level for such a person?
> 
> What am I missing here?
> 
> Is there an upper limit of dose above which the concept of equivalent dose
> does not apply?  Maybe 50 mSv per year?
> 
> 
>