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

[garyi at trinityphysics.com]

Assuming that "less than an inch" is about 2 cm, the dose should be about 15% of the direct 
beam dose.

I'm taking that from a paper by Felmlee et al, 1990, which is commonly used to estimate fetal 
dose from CT when the conceptus is outside the beam.  I've normalized some of his data, 
below, to show the scattered radiation as a fraction of the direct beam dose.  Its a very 
ballpark estimate, but I would guess that the actual value will be in the range of 10% to 30%.  
The Felmlee data is for CT energies and tissue depths of about 10 cm, but I don't know of 
any published data that would be applicable to a mouse.

The quoted reference doesn't give enough information to make any meaningful critique of the 
paper.  However, just reading the quote, it sounds like the author really just went looking for 
something that would help them say, "Now it seems that the cancer risk is real."  I'll 
remember that the next time I go get 12,000 dental x-rays.  Anybody that thinks 12,000 
dental x-rays should be risk free should go get their head examined.  Maybe by x-ray.

-Gary Isenhower

1.000	direct beam
0.184	1 cm offset
0.144	2 cm offset
0.112	3 cm offset
0.088	4 cm offset
0.072	5 cm offset
0.060	6 cm offset
0.044	7 cm offset
0.036	8 cm offset
0.032	9 cm offset
0.028	10 cm offset


On 20 Aug 2008 at 10:28, Glenn R. Marshall wrote:

Subject:        	RE: [ RadSafe ] Bystander Effect" Hints at Dangers of Low-Dose
	Radiation
Date sent:      	Wed, 20 Aug 2008 10:28:17 -0400
From:           	"Glenn R. Marshall" <GRMarshall at philotechnics.com>
To:             	"ROY HERREN" <royherren2005 at yahoo.com>, <radsafe at radlab.nl>

[ Double-click this line for list subscription options ] 

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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