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RE: Damage stays from low-dose X-rays



New Scientist reports



Routine X-ray safety called into question



22:00 31 March 03 NewScientist.com news service



http://www.newscientist.com/news/news.jsp?id=ns99993568





The safety of routine X-rays has been called into question following

the unexpected discovery that cells exposed to low doses avoid or

delay repairing damaged DNA.



Puzzlingly, cells given higher doses of X-rays were faster and more

efficient at patching up any damage. But the German researchers who

made the discovery say it is not clear whether the sloppy repairs

that follow low level exposure is a good or bad thing.



Kai Rothkamm and Markus Löbrich, at the University of Saarland in

Homburg, acknowledge that unrepaired breaks in DNA could well lead to

cells becoming cancerous. But it is equally possible, they say, that

the failure to repair low-level DNA damage has evolved as a safety

measure.



"Repairing a DNA break is dangerous, as the repair could itself be

faulty," says Rothkamm. "If, say, only one in ten cells has received

DNA damage, it may be safer just to let it die and be replaced."



It makes sense that cells must repair themselves after exposure to

higher doses, because more cells are damaged. "Tissue can't eliminate

every cell, so repair becomes a necessity," he says.



The discovery was made by exposing human lung cells to a range of X-

ray doses. The lowest dose of 1.2 milligrays was typical of routine

medical and dental X-rays. The highest - 200 milligrays - is 10 times

higher than the doses received by patients undergoing computer

tomography scans.



The variation in DNA repair efficiency was totally unexpected. High

dose cells repaired 95 per cent of their damage within a day. At

doses of 5.0 milligrays, the DNA repaired fell to 80 per cent. But

cells exposed to the lowest doses avoided repairs altogether, or

delayed it for days.



Rothkamm suggests there may be a threshold level below which damage

is ignored. Chemical signals within or between cells could determine

when damage has reached such a level that repairs are essential. But

more research is needed, he says.



Michael Clark, scientific spokesman for the UK's National

Radiological Protection Board, agrees. "This needs to be taken

further, to see if there are implications in vivo," he says. "But we

don't feel it has any immediate effect on our risk estimates for X-

rays. People should not stop having them."



Journal reference: Proceedings of the National Academy of Sciences

(doi/10.1073/pnas.0830918100)

Andy Coghlan





========================

fwp_dawson@hotmail.com







-----Original Message-----

From: owner-radsafe@list.vanderbilt.edu

[mailto:owner-radsafe@list.vanderbilt.edu]On Behalf Of Jim Hoerner

Sent: 02 April 2003 01:12

To: Know_Nukes@yahoogroups.com

Cc: downwinders@yahoogroups.com; radsafe@list.vanderbilt.edu

Subject: Damage stays from low-dose X-rays





Well, it is April 1st, but I am not making this up...



Study: Damage stays from low-dose X-rays



Tuesday, April 1, 2003 Posted: 10:49 AM EST (1549 GMT)



WASHINGTON (Reuters) -- Low doses of X-rays such as those patients receive

in the dentist's chair may do more long-lasting damage than higher doses,

German scientists reported on Monday in a study that turns common wisdom on

its head.



Their findings, based on experiment with cell cultures, will have to be

duplicated by other labs and then repeated in living animals before doctors

can offer guidance on the effects of low-dose X-rays on humans.



The team, led by Markus Lobrich at the Universitat des Saarlandes, said its

reasearch suggests that doses of X-rays generally considered harmless may in

fact do long-lasting damage.



But they said they had developed a test that would help doctors look for

genetic damage in people exposed to low doses of X-rays, such as cancer

patients undergoing radiotherapy, patients getting X-rays and professionals

working with X-ray equipment.



Writing in the Proceedings of the National Academy of Sciences, Lobrich's

team said they exposed human cell cultures to varying X-ray doses in the

laboratory.



To their surprise, they found that damage from low radiation levels lingered

days to weeks longer than damage caused by more powerful levels.



Ionizing radiation like the kind produced by X-rays and some nuclear

breakdown products can cause leukemia and other cancers. The radiation can

cause breaks in DNA that go across both strands of its double helix

structure.



Scientists had assumed that the body moves to repair these breaks at the

same rate, no matter what the dose of radiation.



But Lobrich's team found this may not be true. It could be, they propose,

that the body simply does not recognize lower levels of damage and does not

move to repair it.



When these damaged cells divide and multiply, the unrepaired damage

multiplies along with them, they suggested.



Copyright 2003 Reuters. All rights reserved. This material may not be

published, broadcast, rewritten, or redistributed.



http://www.cnn.com/2003/HEALTH/04/01/health.xrays.reut/index.html



--

Calling All Saddam Look-Alikes!

Saddam's doctor called a meeting of all the Saddam look-alikes.

"Men, I've got some good news and I've got some bad news.

The good news is Saddam is still alive.

The bad news is he lost an arm."



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