[ RadSafe ] BEIR VII Report

[Scott, Bobby]

On 7/2/05, John Jacobus wrote:

"Maybe I not looking at this issue as you are.  I
really do not consider the LNT to be the issue in
developing safey regulations..."

Reply from B.R. Scott:
Thanks John for sharing your views on this topic. In section 13 of the
BEIR VII prepublication draft, it is stated that the primary task of the
BEIR VII committee was "to develop the best possible risk estimate for
exposure to low-dose, low-LET radiation in human subjects."  Thus,
developing safety regulations was not the primary focus.  My view is
that the "best possible risk estimate" cannot be obtained solely based
on epidemiological studies.  One has to first have a basic understanding
of the underlying stochastic biological effects associated with
low-dose, low-LET radiation induced cancer. These stochastic effects
include induced mutations, neoplastic transformation, and apoptosis.
Fortunately, ongoing basic research around the world is focusing on
low-dose-induced stochastic radiobiological effects and results obtained
have led to nonlinear dose-response relationships more as a rule then an
exception.  The new journal, Nonlinearity in Biology, Toxicology and
Medicine features a number of publications of nonlinear dose-response
relationships for low-dose, radiation-induced stochastic biological
effects.

Note that the stated primary task of the BEIR VII committee was not to
determine if a risk of radiation-induced harm actually exists after low
doses of low-LET radiation.  Implied in the stated primary task was the
assumption that elevated cancer risk always exists (after any
irradiation) and their task is to quantify the assumed elevated risk.
Research results obtained by my research group indicate that for persons
already bearing precancerous cells (e.g. heavy, long-time smokers), low
doses (or low dose rates) of low-LET radiation could activate a
protective process that selectively eliminates precancerous cells
thereby reducing the risk of cancer.  The selective cell killing is via
apoptosis and has been named the "protective apoptosis mediated (PAM)
process".  Animal studies have shown that low doses of low-LET radiation
can extend the cancer latent period for spontaneous cancers. Both
epidemiological and animal studies have shown that protracted exposure
to low-LET radiation can reduce the cancer incidence below the
spontaneous level.  Our in-press paper (Nonlinearity in Biology,
Toxicology and Medicine) shows evidence for low-dose rate gamma
radiation suppressing lung cancer induction in Mayak workers by alpha
irradiation (from inhaled Pu-239).  Some of the indicated data are
discussed in the Low Dose Research section of my webpage:
http://www.radiation-scott.org.  See for example the subsection on
"Stochastic Thresholds and Nonlinearity" (plenary session presentation
at the BELLE 2005 Conference).

Bobby R. Scott
Lovelace Respiratory Research Institute