[ RadSafe ] RE: Calculated Health Impacts of Reducing Natural Background Ionizing Radiation

[Scott, Bobby]

Thanks Dan for your comment and question. Hope that things are going
well for you. You are correct regarding the 8 orders-of-magnitude. The
local cellular community participates in the protection activation
rather than an individual cell.  Reactive oxygen and nitrogen species
and specific cytokines (e.g., transforming growth factor beta-1)
participate in the intercellular communications that lead to selective
removal of genomically unstable cells (e.g., mutants, precancerous
cells, etc.) via the auxiliary apoptosis process.  Photon doses as low
as 0.01 to 0.02 mGy appear sufficient for activation of the protective
system based on mutation studies in mice exposed to 250-kVp X rays.
Moderate and high doses inhibit protection.  When the photon radiation
dose is protracted and delivered at a very low rate over years, doses as
high as 400 mGy may not inhibit protection based on epidemiological
studies.  For such protracted exposure, the protection can be quite
dramatic (e.g., greater than a 50% reduction in spontaneous cancers).
For brief exposure at a very high rate, as occurred for a-bomb
survivors, gamma-ray doses above about 100 mGy may inhibit protection
and the level of protection associated with lower gamma-ray doses may be
quite small.

Bobby

-----Original Message-----
From: Strom, Daniel J [mailto:strom at pnl.gov] 
Sent: Friday, April 07, 2006 10:10 AM
To: Scott, Bobby
Cc: radsafe at radlab.nl
Subject: Re: Calculated Health Impacts of Reducing Natural Background
Ionizing Radiation

Bobby,

Thanks for the interesting post.

I assume that by "(eight-fold lower)" you meant "8-decade" or "8
orders-of-magnitude" lower.

Does this activation of the transient system have to occur repeatedly in
each cell, or can cells activate bystander cells when they themselves
are activated?

- Dan Strom