[ RadSafe ] LNT may or may not be scientific- Regulators need numbers

parthasarathy k s ksparth at yahoo.co.uk
Sun May 10 19:29:18 CDT 2009

Kai Kaletesch, 

You have aptly summarized various views on LNT. In all probability, there appears to be threshold doses for each and every end point.Till there is satisfactory agreement on the lowest value of these thresholds, we have difficulties in arriving at practical ways of enforcing radiological protection. Regulators need some numbers as dose limits. 
Discussions on whether or not  LNT has irrefutable scientific basis is interesting and rewarding. It is clear that we need not lose sleep on the possibility of induction of cancer and other effects at low level radiation.State of the art technologies may help us to detect a single interaction in cells or tissues; however we need not worry, as, such "picoscopic" changes which occur with unpredictable rates, seldom lead to macroscopic cellular changes that lead to effects such as cancer.


From: Kai Kaletsch <eic at shaw.ca>
To: al at solidsurfacealliance.org; radsafe at radlab.nl
Sent: Sunday, 10 May, 2009 21:48:38
Subject: [ RadSafe ] LNT

Hi Al,

you wrote:

"If LNT is the generally accepted theory..." I think we have to look at what "generally accepted" means. If I understand the LNT debate correctly, the differing thoughts can be summarized like this:

1) Some people believe that LNT is a pretty good model and is no worse than other models (hormesis/threshold). So, we might as well keep it.
2) Some people believe that  LNT has significant shortcomings and is probably not the correct scientific model, but it is easy and convenient to use for making policy. So, we might as well keep it, as the basis for making policy.
3) Some people believe that LNT is either incorrect or irrelevant at very low doses and the use of LNT at very low doses should be restricted. See for example the HPS position statement http://hps.org/documents/risk_ps010-1.pdf , which explicitly states : " the Health Physics Society recommends against quantitative estimation of health risks below an individual dose of 5 rem in one year or a lifetime dose of 10 rem above that received from natural sources."
4) Some people believe that there is strong evidence that LNT fails. Some of these people think that it is time to adjust public policy accordingly. Others think that this should be a scientific debate and public policy should not be an issue.

While some of the politically appointed bodies still cling to 1), it seems to be the minority position among scientists. The HPS states: "There is, however, substantial scientific evidence that this model is an oversimplification. It can be rejected for a number of specific cancers, such as bone cancer and chronic lymphocytic leukemia, and heritable genetic damage has not been observed in human studies. However, the effect of biological mechanisms such as DNA repair, bystander effect, and adaptive response on the induction of cancers and genetic mutations are not well understood and are not accounted for by the linear, no-threshold model."

There used to be people who thought that LNT was actually a correct description of the organism's response to radiation. This was before we knew about biological mechanisms such as DNA repair, bystander effect, and adaptive response. I have not heard any credible scientist state, in the last 10 years, that he/she personally believes that LNT is the scientifically correct model and that it describes the dose response 100% correctly for all types of ionizing radiation.

It would be extremely easy to prove me wrong on this. All it would take is for someone on this list to state that they personally believe that LNT is the scientifically correct model that it describes the dose response 100% correctly for all types of ionizing radiation.

It will be interesting to see if there is still anyone out there who truly accepts LNT as a scientific theory.

Best Regards,

----- Original Message ----- From: <al at solidsurfacealliance.org>
To: <radsafe at radlab.nl>
Sent: Thursday, May 07, 2009 4:45 PM
Subject: [ RadSafe ] Re: radsafe Digest, Vol 196, Issue 3

"I listen with interest when people talk about hormesis
and/or thresholds, and await models and studies that would elevate one
of those concepts to the dominant paradigm status."

Excellent point and one that if logic rules the discussion, ends the discussion. If LNT is the generally accepted theory, any claims to the contrary have the burden of proof. If the BEIR committee changes their position on LNT, I will be convinced. Prior to that, right or wrong, the radiation is chocolate crowd will lack credibility.


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