[ RadSafe ] Article: Heavy ions damage DNA

[John Jacobus]

This appeared in PhysicsWeb at
http://physicsweb.org/articles/news/9/10/8
You may have to subscribe to see this article, but the
ciation is given at the end of the first paragraph.

Question: Does anyone have an idea if these effects
compare to the decay alpha particles of radon progeny?

Note there is a related article "How particles can be
therapeutic" from August 2003 at
http://physicsweb.org/articles/world/16/8/9

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Heavy ions damage DNA
14 October 2005

Medical physicists in Canada have discovered that
heavy-ion-beam cancer therapy can cause more damage to
healthy DNA than previously believed. The harm is
caused by low-energy secondary particles rather than
the heavy ions themselves. The results could help
medical physicists develop more accurate dose models
for heavy-ion therapy (Phys. Rev. Lett. 95 153201).

Heavy-ion-beam cancer therapy employs protons or ions
such as argon and neon that have energies of about 1
MeV per nucleon. One advantage of heavy-ion therapy
over other techniques is that most of the energy is
deposited in a small region of space, known as the
Bragg peak, whereas X-rays, for example, deposit their
energy continuously once they enter the body. However,
little is known about how heavy-ion radiation damages
DNA on the molecular scale, especially in the region
beyond the Bragg peak. This damage might be caused by
the heavy ions after they have lost most of their
energy or by low-energy secondary ions. This is a
worry because the tissue beyond the Bragg peak is
often healthy. 

Previously it was thought that heavy ions caused the
same amount of damage as the conventional X-ray or
gamma-ray radiation routinely used in medicine. These
types of radiation cause damage by simple ionisation
of atoms in cells, cleavage of single bonds in
molecules, and attack by chemical radicals. 

Michael Huels and colleagues at the University of
Sherbrooke decided to look into this issue in more
detail. They fired low-energy ions onto a film of
biomolecules in an ultrahigh vacuum and analysed the
ions that desorb from the film with a mass
spectrometer. The results show that the initial damage
caused by the ions at their track ends is
significantly more complex, clustered and lethal than
that induced by X- or gamma-rays. Severe damage can be
caused by energies as low as 0.25 eV per nucleon --
which is very low when compared with the energy of a
typical heavy-ion beam. 

The new work was prompted by previous experiments by
Thomas Schlathölter and colleagues at Gröningen in the
Netherlands. In 2003 Schlathölter noticed that low
energy (1 to 200 eV) secondary particles could be
produced by firing high-energy MeV-range heavy ions at
DNA fragments. The latest experiments were made
possible by the development of a machine that is
capable of producing heavy ions with energies as low
as just 1 eV in the Sherbrooke lab. 

The team is now investigating how secondary ions,
created by the primary ions inside DNA, can also cause
damage although they have even lower energies than
primary ions. "Our dream is that some day doctors will
be able to manipulate the heavy-particle radiation
effects at the molecular level - for example, by
developing DNA 'radiosensitisers' that are specific to
the secondary particles created in DNA during ion
therapy," says Huels.

About the author
Belle Dumé is science writer at PhysicsWeb



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On Oct. 5, 1947, in the first televised White House address, President Truman asked Americans to refrain from eating meat on Tuesdays and poultry on Thursdays to help stockpile grain for starving people in Europe. 

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


		
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