Re: Linear-no threshold question

["John Moulder" <jmoulder@post.its.mcw.edu>]

> >BTW:  For the general case of protracted exposure to low-LET 
> >radiation, it is relatively easy to show that linear no threshold 
> >model, as applied in BEIR V, predicts that no statistically 
> >significant effects will be seen in human populations below a total 
> >dose of around 1000 mSv.  
>  
> 	Hmm. John. Is this true also for the relatively rare cancers?

You can get the detection threshold a bit lower for rare cancers, but not a 
lot lower, because with rare cancers you have a problem getting an accurate 
measure of the rate in the control population.

You can also get the detection threshold lower for cancers that are easier to 
induce (more cancer/rad).

You can also lower the detection threshold a bit lower for the general 
population if you were to do separate studies of all the radiosensitive groups 
(e.g., children) and radiosensitive tumors (e.g., multiple myeloma) and sum 
all these groups.

You could get a much lower detection threshold for the general population if 
you could identify all the sensitive subpopulations (e.g., AT and XT 
heterozygotes).

The thing to keep in mind is that the detection threshold is determined by the 
epidemiological statistics plus the fact that radiation-induced cancers have 
no unique signature (at least none that we know of), not by any feature of 
radiation induced cancer.

> 	From my recollection, no statistically significance was seen 
> 	in the Hiroshima/ Nagasaki survivors, even up near lethal 
> 	doses.

If you look at the "raw" Hiroshima/Nagasaki data in Thompson et al (Rad Res 
137:S26, 1994) with a magnifying glass, you find that:
- breast cancer incidence is significantly (p<0.05) elevated in the 0.25 Sv 
bin
- total solid, lung and urinary system tumor incidence is significantly (p<
0.05)  elevated in the 0.75 Sv bin
The LD50 for that population is about 3 Sv, so yes, to find a significant 
elevation in cancer in the Hiroshima/Nagasaki data you need a dose near 10% of 
the lethal dose.

> If its also true for low doses, dang we're wasting LOTS of money. 

I suspect we are wasting a lot of money, and not just in ionizing radiation. 
We are regulating lots to things to risk levels that are orders of magnitude 
below where health effects would expected to be seen (even assuming that the 
risk estimates and modeling are correct).