Re: Low-level Rn exposure and lung cancer

[Kai Kaletsch <eic@shaw.ca>]

Steven,



I'll let others address possible biological mechanisms. I'll just point out

a simple mathematical fact:



If you have a LNT dose response and your measured dose rate has some random

error, then, once you bin the data by total exposure, you will observe an

inverse dose rate relationship very much like that observed by Lubin, even

though there is absolutely no relationship between dose rate and cancer.

Here is an example.



Assume the true exposure rate is constant at 10 WLM per year, but 1/2 the

people are assigned a dose that is 50% too low and the other half are

assigned a dose that is 50% too high. Also assume one group of miners works

for 5 years and another one for 20 years. LNT says that the 20 year group

will have 4 times the excess cancer rate.



The researchers will assign exposures of 25 and 100 WLM to people that

worked for 5 years and 100 and 400 WLM to miners that worked for 20 years.

They then bin the results by ASSIGNED exposure and graph cancer incidence vs

exposure rate. In our primitive example, only the 100 WLM bin can be used in

this way.



Cancer incidence will be related to TRUE exposure, rather than OBSERVED

exposure, so the people who received their observed 100 WLM in 20 years (200

WLM true exposure) will show 4 times the excess cancer rate of the people

who received their observed 100 WLM in 5 years (50 WLM true exposure).



Looking at the errors associated with exposure assessments associated with

the early mines, I am not convinced that the observed inverse dose rate

effect is not entirely a mathematical artifact.



(I think that this argument can be extended to controlled experiments as

well, but don't have time to get into it.)



Regards,



Kai





----- Original Message ----- 

From: "Steven Dapra" <sjd@swcp.com>

To: <radsafe@list.vanderbilt.edu>

Sent: Wednesday, March 31, 2004 9:34 PM

Subject: Low-level Rn exposure and lung cancer





> March 31

>

> One of the fundamental rules of toxicology (if not <the> fundamental rule)

> is that "the dose makes the poison."  It seems that this is generally true

> of exposure to radiation as well.

>

> While doing some library research on radon and lung cancer I found that

> this rule might not apply for radon exposure and lung cancer.  According

to

> Lubin (1994), " . . . the exposure-response relation declined with

> increasing exposure rate or decreasing exposure duration, implying that

for

> equal total exposure, a higher risk for lung cancer is experienced by

those

> who accumulate exposure at a lower exposure rate and over a longer period

> of time."  (This is quoted from p. 324, col. 2 of an "Invited Commentary"

> wherein Lubin analyzed and discussed approximately 20 papers studying lung

> cancer and radon exposure.  He also drew on other germane research

findings.)

>

> In another paper (Darby et al. 1998) we read (p. 405, col. 1):  " . . .

> greater risks are associated with exposures occurring at a low exposure

> rate and spread over a long duration than for exposures occurring at a

high

> exposure rate with short duration [citations omitted]."

>

> Why does it seem - at least for radon exposure - that lower exposure

> levels lead to a higher risk of cancer?  Does this phenomenon show up for

> exposure to any other type of radiation exposure?  Please note that I do

> not want to instigate a debate about LNT.  I only would like to know why

> this anomaly shows up in the case of radon exposure.  You may reply via

> RADSAFE or via private e-mail, whichever is more convenient.

>

> Steven Dapra

> sjd@swcp.com

>

> REFERENCES

>

> Darby, S. et al.  Risk of lung cancer associated with residential radon

> exposure in south-west England:  a case-control study.  British Journal of

> Cancer.  78(3):394-408; 1998.

>

> Lubin, J. H.  Invited Commentary:  Lung Cancer and Exposure to Residential

> Radon.  American Journal of Epidemiology.  140(4):323-332; 1994.

>

>

>

>

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