Science and LNT

[niton@mchsi.com]

J Radiol Prot. 2002 Sep;22(3A):A129-35.   



Uncertainty, low-dose extrapolation and the threshold hypothesis.



Land CE.



Radiation Epidemiology Branch, Division of Cancer Epidemiology and Genetics, 

National Cancer Institute, Bethesda, MD, USA.



Risk-based radiation protection policy is influenced by estimated risk and by 

the uncertainty of that estimate. Thus, if the upper limit, at (say) 95% 

probability, of risk associated with a given radiation dose is at 

an 'acceptable' level, it is unlikely (or not credible) that the true level of 

risk associated with the dose is at an unacceptable level. Central estimates 

presented alone, in the absence of probability limits, lack this safety 

factor. Estimating cancer risks from low doses of ionising radiation involves 

extrapolation of risk estimates based on high-dose data to the much lower dose 

levels that characterize the vast majority of exposures of regulatory concern. 

Proof of a universal low-dose threshold, below which there is no radiation-

related risk, would revolutionise radiation protection. Available data fail to 

provide such proof and, in fact, leave considerable room for the possibility 

that DNA damage from a single photon can contribute to the carcinogenic 

process. Allowing for the possibility of a threshold would, however, remove 

very little of the regulatory burden associated with the so-called linear, no-

threshold hypothesis, unless that possibility were a virtual certainty.





INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF RADIOLOGICAL PROTECTION

J. Radiol. Prot. 23 (2003) 263–268 PII: S0952-4746(03)65206-7



The LNT model is the best we can do—today



R Julian Preston

Environmental Carcinogenesis Division, National Health and Environmental 

Effects Research Laboratory, US Environmental Protection Agency (MD B143-06), 

Research Triangle Park, NC 27711, USA



E-mail: preston.julian@epa.gov



Received 10 February 2003, in final form and accepted for publication

27 May 2003

Published 8 September 2003

Online at stacks.iop.org/JRP/23/263



Abstract

The form of the dose–response curve for radiation-induced cancers, particularly

at low doses, is the subject of an ongoing and spirited debate. The present

review describes the current database and basis for establishing a low dose,

linear no threshold (LNT) model. The requirement for a dose–response model

to be used for risk assessment purposes is that it fits the great majority of 

data derived from epidemiological and experimental tumour studies. Such is the

case for the LNT model as opposed to other nonlinear models. This view is

supported by data developed for radiation-induced mutations and chromosome

aberrations. Potential modifiers of low dose cellular responses to radiation

(such as adaptive response, bystander effects and genomic instability) have not

been shown to be associated with tumour development. Such modifiers tend

to influence the slope of the dose–response curve for cellular responses at low

doses and not the shape—thereby resulting in a quantitative modification rather

than a qualitative one. Additional data pertinent to addressing the shape of 

the tumour dose–response relationship at low doses are needed.

> From: Ted Rockwell [mailto:tedrock@starpower.net]

>  

> >I don't know of any good data that show deleterious effects from LDR.  

>  

> But there is some evidence, and some logical arguments, that create a

> reasonable doubt about dose and effect at low levels, IMHO.

>  

> >And they rely only on the demonstrably false argument that it is

> prudent to assume the worst.  That is not science.  It is transparently

> politics.

>  

> I guess "they" here are the NCRP and ICRP. What they are doing is

> transparently setting policy. These policies are based on science, but

> no, they are not "science". I think it is good policy to be prudent

> until we have the clear evidence or a unified and well confirmed model

> that eliminates this reasonable doubt. I agree that funding should be

> fairly distributed to different groups, although I've never seen real

> fairness in funding in any area of science. The burden is and should be

> on those who believe in a threshold to show convincingly that it exists



> and what its numerical value is, before public policy should be shifted

> away from prudence. I found Mossman's "the debate is over" unpalatable,

> as I do the arguments of those who say "low levels are clearly

> harmless". This scientific discussion is clearly not resolved, and my

> point (in the context of this thread) was that we should be honest about

> that among ourselves and when dealing with the public and others.

>  

> Mike

>  

> 

> Michael G. Stabin, PhD, CHP

> Assistant Professor of Radiology and Radiological Sciences

> Department of Radiology and Radiological Sciences

> Vanderbilt University

> 1161 21st Avenue South

> Nashville, TN 37232-2675

> Phone (615) 343-0068

> Fax   (615) 322-3764

> Pager (615) 835-5153

> e-mail     michael.g.stabin@vanderbilt.edu

> internet   www.doseinfo-radar.com

> 

>  

> 

> 



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