[ RadSafe ] Bystander Effect" Hints at Dangers of Low-Dose Radiation

[John Jacobus]

I would think the article would have this type of information,  Scatter is somewhat dependent to the energy and characteristics ("hardness") of the beam.
+++++++++++++++++++
"Part of human nature resents change, loves equilibrium, while another part welcomes novelty, loves the excitement of disequilibrium. There is no formula for the resolution of this tug-of-war, but it is obvious that absolute surrender to either of them invites disaster."
-J. Bartlet Brebner 

-- John
John Jacobus, MS
Certified Health Physicist
e-mail: crispy_bird at yahoo.com

--- On Wed, 8/20/08, Glenn R. Marshall <GRMarshall at philotechnics.com> wrote:

From: Glenn R. Marshall <GRMarshall at philotechnics.com>
Subject: RE: [ RadSafe ] Bystander Effect" Hints at Dangers of Low-Dose Radiation
To: "ROY HERREN" <royherren2005 at yahoo.com>, radsafe at radlab.nl
Date: Wednesday, August 20, 2008, 10:28 AM

I don't deal with x-ray machines at all, so here's a question for the
medical HPs out there:  Assuming a newborn baby mouse's head is less than an
inch from the part that was x-rayed, what would the dose be to the head due to
scatter in the scenario described below?  The article implies the head received
zero exposure; obviously that's not true. 

Glenn Marshall, CHP, RRPT


-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On Behalf Of
ROY HERREN
Sent: Wednesday, August 20, 2008 12:11 AM
To: radsafe at radlab.nl
Subject: [ RadSafe ] Bystander Effect" Hints at Dangers of Low-Dose
Radiation

http://sciencenow.sciencemag.org/cgi/content/full/2008/818/3
 
Bystander Effect" Hints at Dangers of Low-Dose Radiation
 
By Jocelyn Kaiser
ScienceNOW Daily News
18 August 2008That lead apron you wear during a dental x-ray is supposed to
protect the rest of you from radiation. But it may not work very well, according
to a new study. When cancer-prone mice were placed in lead containers and
irradiated on just the lower half of their bodies, they developed brain tumors.
The results suggest that radiation could be riskier than scientists thought. 
The study builds on a surprising effect, first observed 16 years ago. When
cells in culture are exposed to ionizing radiation, even those not directly hit
sustain damage to chromosomes. Apparently, the irradiated cells pass on a
distress signal or emit some chemical that breaks the DNA of neighboring cells
(ScienceNOW, 7 September 2005). Although this "bystander effect" has
been observed in tissue culture and recently in living animals, no experiments
have yet linked it to the main reason for concern: Bystander effects might
trigger cancer. Some scientists even suspect the opposite--that the bystander
responses could protect against the disease by killing damaged cells. 
Now it seems that the cancer risk is real. Radiation oncologist Anna Saran at
the Italian National Agency for New Technologies, Energy and the Environment in
Rome and colleagues studied mice with a mutation in a gene called Patched that
makes them susceptible to brain tumors early in life. They placed newborn mice
in lead shields that protected their heads and upper bodies, then zapped them
with high-dose x-rays, or about 12,000 times the dose of a dental or chest
x-ray. The scientists found that the cerebellums of these animals had higher
than normal amounts of DNA damage and apoptosis, or programmed cell death. By 40
weeks of age, 39% of the shielded mice had developed brain tumors. That's a
lot considering that the rate was 62% in Patched mice that were irradiated all
over, including their heads. Patched mice that weren't irradiated did not
develop brain cancer. 
When the team injected the shielded mice with a chemical that blocks
cell-to-cell communication before irradiating them, they detected no DNA breaks
and the amount of apoptosis decreased more than threefold. Even though the
irradiated tissues are far away from the brain, they are connected by neurons
that could be passing on bystander signals, Saran says. The results appear
online this week in the Proceedings of the National Academy of Sciences. 
"This is a milestone paper," says Columbia University radiation
physicist David Brenner. He suggests that current estimates of cancer risk from
low doses of radiation--say, from naturally occurring radon and diagnostic
tests--may underestimate the danger by failing to take into account bystander
effects. To learn more, however, the mouse work should be repeated with lower
doses of radiation, Saran says.


      
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