[ RadSafe ] DOE workshop presentation
Scott, Bobby
BScott at lrri.org
Mon May 16 17:58:31 CDT 2011
Hi All:
In case it may be of interest, my presentation given last week at the
DOE Low Dose Radiation Research Program Investigators' Workshop X is
available at the link below:
"Differential epigenetic changes in the lung after low and high
carcinogen doses and implications for designing molecular epidemiology
and other studies of radiation-induced lung cancer"
http://dspace.lrri.org:8080/xmlui/handle/123456789/1064
In the presentation, I point out the need for new terminology related to
discussing consequences to humans from low-level exposure to low- or
low- plus high-LET radiation (e.g., radiation exposure in the home from
radon progeny). I introduce the adaptive protection function, A(x), and
benefit function B(x) = 1 - exp[-A(x)], which respectively correspond to
the high-dose hazard function H(x) and related risk function R(x) = 1-
exp[-H(x)], widely used in risk assessment. B(x) is the probability of
radiation activated natural protection (ANP) against cancer (e.g.,
against smoking-related lung cancer). The independent variable x is the
dose or exposure level. Interestingly, for low-level exposure to radon
progeny and for lung cancer, the benefit B(x) can be close to 1 (e.g.,
for protecting against smoking-related lung cancer) while the risk R(x)
for radiogenic cancer is close to zero. This indicates that the
probability B(x) can be orders of magnitude greater than the probability
R(x), while much of the current focus is unfortunately on R(x) (usually
under the invalid LNT hypothesis). At the EPA's action level of 4
picocuries/L (approximately 150 Bq/cubic meter), B(x) = 1 for ANP
against sporadic lung cancer (i.e., everyone expected to benefit from
natural protection against lung cancer). The natural protection when
maintained over a prolonged period prevents a future cancer with
probability PROFAC (the protection factor, a population average which
varies with different populations). PROFAC is the average over the
at-risk population of individual-specific protection factors "profac".
For x close to zero, cancer relative risk (RR; population average) is
given by RR = 1 - B(x)PROFAC (hormetic zone where RR < 1). For large
values of x, B(x) goes to zero (no benefit) and H(x) can be >> 1
(serious hazard with R(x) close to 1).
Bobby R. Scott
Senior Scientist
Lovelace Respiratory Research Institute
2425 Ridgecrest Drive SE
Albuquerque, NM 87108 USA
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