Re: Radiation Hormesis

["Jean-Pierre Degrange" <degrange@cepn.asso.fr>]

>From: BLHamrick@AOL.COM

>Subject: Re: Radiation Hormesis

>...

>I have no argument with that - there is much theory and too little data to

>claim hormesis is substantiated sufficiently to form the basis for

>regulations.  Interestingly, one could say the same about LNT, the

>difference being that LNT is conservative.

>This is where I have an argument.  It is commonly accepted that the LNT is

>conservative, and it is used in chemical risk assessments as well as

>radiological risk assessments, but I do not believe that in either case one

can make a

>substantive case that it is, in fact, conservative.



>...

>Barbara



Regarding the argument that LNT is (always) conservative, it may be

interesting to have a look at these two recent papers, noting that the first

paper has been contributed to by a lot of well-known epidemiologists.



Jean-Pierre Degrange

CEPN, BP 48 92263 Fontenay aux Roses CEDEX France

e-mail: degrange@cepn.asso.fr

WEB: www.cepn.asso.fr





Proc Natl Acad Sci U S A. 2003 Nov 25; 100(24): 13761-6. Epub 2003 Nov 10

Cancer risks attributable to low doses of ionizing radiation: assessing what

we really know.



Brenner DJ, Doll R, Goodhead DT, Hall EJ, Land CE, Little JB, Lubin JH,

Preston DL, Preston RJ, Puskin JS, Ron E, Sachs RK, Samet JM, Setlow RB,

Zaider M.



Center for Radiological Research, Columbia University, 630 West 168th

Street, New York, NY 10032, USA. djb3@columbia.edu



High doses of ionizing radiation clearly produce deleterious consequences in

humans, including, but not exclusively, cancer induction. At very low

radiation doses the situation is much less clear, but the risks of low-dose

radiation are of societal importance in relation to issues as varied as

screening tests for cancer, the future of nuclear power, occupational

radiation exposure, frequent-flyer risks, manned space exploration, and

radiological terrorism. We review the difficulties involved in quantifying

the risks of low-dose radiation and address two specific questions. First,

what is the lowest dose of x- or gamma-radiation for which good evidence

exists of increased cancer risks in humans? The epidemiological data suggest

that it is approximately 10-50 mSv for an acute exposure and approximately

50-100 mSv for a protracted exposure. Second, what is the most appropriate

way to extrapolate such cancer risk estimates to still lower doses? Given

that it is supported by experimentally grounded, quantifiable, biophysical

arguments, a linear extrapolation of cancer risks from intermediate to very

low doses currently appears to be the most appropriate methodology. This

linearity assumption is not necessarily the most conservative approach, and

it is likely that it will result in an underestimate of some

radiation-induced cancer risks and an overestimate of others.





 J Radiol Prot. 2003 Sep; 23(3): 263-8.

The LNT model is the best we can do--today.



Preston RJ.



Environmental Carcinogenesis Division, National Health and Environmental

Effects Research Laboratory, US Environmental Protection Agency (MD

B143-06), Research Triangle Park, NC 27711, USA. preston.julian@epa.gov



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.









************************************************************************

You are currently subscribed to the Radsafe mailing list. To

unsubscribe, send an e-mail to Majordomo@list.vanderbilt.edu  Put the

text "unsubscribe radsafe" (no quote marks) in the body of the e-mail,

with no subject line. You can view the Radsafe archives at

http://www.vanderbilt.edu/radsafe/