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

[Sandra Matzkin]

I also wonder about the statement that mice which weren't irradiated 
did not develop brain cancer. Since these mice had a mutation that 
made them susceptible to brain tumors, I would have expected some of 
them to do. The article doesn't mention the size of the irradiated 
and the control groups, either.

Sandra Matzkin
Nuclear Engineering Department
INVAP SE
Bariloche
Argentina

At 11:28 08/20/2008, Glenn R. Marshall wrote:
>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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