[ RadSafe ] protraction enhancement effect

[Otto G. Raabe]

At 11:27 AM 8/31/2010, Brennan, Mike  (DOH) wrote:
>Has anyone heard of "protraction enhancement effect", apparently 
>also called "inverse exposure-rate effect"?  I ran across it in an 
>ICRP document, and I just want to see if other, more knowledgeable 
>people think it means what I think it means.
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September 1, 2010

The inverse dose-rate effect and its low-dose-rate limitations are 
explained in my March HPJ paper:  Health Physics 98: 515-536; 2010.

Here are some quotes from my paper:

Page 519, RESULTS , Paragraph 3:

"Alpha radiation is seen to be about 10 times more
effective at the low dose-rate than at the high dose-rate in
inducing bone cancer based on the calculated cumulative
dose. This demonstrates the so-called inverse dose-rate
effect and shows that the calculated cumulative dose is an
unreliable indicator of cancer risk for protracted exposures
to ionizing radiation. This phenomenon can distort
response relationships based on cumulative dose."


Page 531, First full paragraph:

"Because the negative slopes of these distributions
are less than unity, the cumulative absorbed dose required
to yield a specified level of cancer risk is less at
lower dose-rates than at higher dose-rates (relative dose-rate
effectiveness, RDE, up to a factor of 10 for high LET
radiation and a factor of 2 for low LET radiation), but the
time required for tumors to manifest is much longer at
lower dose-rates and can exceed the natural lifespan,
yielding a lifespan virtual threshold for fatal radiation-induced
cancer."

Page 533, labeled paragraph 3:

"3. The calculated cumulative dose required to yield any
given level of induced cancer risk is less at lower
dose-rates (up to a factor of 10 for high LET alpha
radiation and a factor of 2 for low LET beta radiation)
than at higher dose-rates, indicating differences in RDE;"

Page 534, first paragraph:

"Inverse dose-rate effect
For radiation induction of cancer the inverse dose-rate
effect is quite pronounced for the high LET alpha
radiation but only weakly exists for the low LET beta
radiation. This effect has previously been observed for
high LET neutron radiation and for high LET alpha
radiation for inhaled radon and the associated decay
products that deposit in the lungs. This phenomenon has
sometimes been used to suggest that low dose-rate
radiation is more effective in producing cancer than high
dose radiation because it has been previously assumed
that radiation carcinogenicity is proportional to cumulative
dose, but it is not. This is an artifact of a wrong
dose-response conceptual model. The cancer risk for
protracted radiation exposures is dependent on the lifetime
average dose-rate to the sensitive tissues rather than
on the cumulative dose."

Otto

**********************************************
Prof. Otto G. Raabe, Ph.D., CHP
Center for Health & the Environment
University of California
One Shields Avenue
Davis, CA 95616
E-Mail: ograabe at ucdavis.edu
Phone: (530) 752-7754   FAX: (530) 758-6140
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