In defense of linear, no-threshold model for carcinogenesis

[dj_strom@ccmail.pnl.gov]

Reply to 
>Date: Thu, 17 Aug 1995 08:45:33 -0400 (EDT) >From: Bernard L Cohen 
<blc+@pitt.edu>
>Subject: linear, no threshold theory in the low dose region

>Does anyone know of references that defend the linear, no-threshold >theory for
radiation-induced cancer in the low dose region? 

A news report on a review of the linear, no-threshold dose-response relationship
for carcinogenesis has been published recently by scientists at the U.K. 
National Radiological Protection Board (NRPB; Stather et al. 1995).  They 
reviewed the current state of knowledge in some of the major fields relevant to 
the assessment of the risk of radiation-induced cancer at low doses and low dose
rates for radiation protection purposes.  The review considered the results of 
epidemiological investigations and fundamental studies on the cellular and 
molecular mechanisms involved in radiation damage and response, supplemented by 
studies with experimental animals which provide further guidance on the form of 
the dose-response relationship for cancer induction, as well as the effect of 
dose rate on tumor yield.  They conclude that "the data relating to the role of 
gene mutations in tumorigenesis, the monoclonal origin of tumors, and the 
relationship between DNA damage repair, gene/chromosomal mutation and neoplasia 
are well established and broadly consistent with the thesis that, at low doses 
and low dose rates, the risk of induced neoplasia rises as a simple function of 
dose and does not have a DNA damage or DNA repair related threshold-like 
component.  Whilst adaptive responses or other protective mechanisms may 
influence the risk of tumor development, they do not provide a sound basis for 
judgement that tumorigenic response at low doses and low dose rates of radiation
is likely to have a non-linear component which might result in a dose threshold 
below which the risk may approach zero.  These mechanistic studies, in addition 
to the epidemiological information, indicate that for radiation protection 
purposes there is little basis for arguing that low radiation doses (about 10 
mGy) would have no associated cancer risk and that, in the present state of 
knowledge, it is appropriate to assume an increasing risk with increasing dose."

Reference:

Stather, J.; Muirhead, C.; Cox, R.  Radiation-induced cancer at low doses and 
low dose rates.  National Radiological Protection Board (NRPB)'s Radiological 
Protection Bulletin (ISSN 0308-4272) No. 167, pp. 8-12, July 1995.

Note: 
National Radiological Protection Board, Chilton, Didcot, Oxfordshire OX11 0RQ, 
UK; Tel: 01235 831600 Fax: 01235 833891.  To my knowledge, NRPB has resisted 
connecting to the Internet.

- Dan Strom <dj_strom@pnl.gov>