[ RadSafe ] Article: Heavy ions damage DNA

Wed Oct 19 16:47:52 CDT 2005

John R.
I was not expecting any replies directly, but I seem
to be getting them.  And I do think it is good to
discuss the science involved with this paper.

As for your comment 1:  In therapy, you do see a
continual deposition of energy along the path of the
primary beam.  While single photon infrequently
interacts in the media, for the entire irradiation
beam the energy deposition, based on the dose or kerma
measurements, demonstrate a build up to a peak at some
depth and then a continual trailing off.  In other
words, you get a continual depositing along the beam
axis.  For 8 MeV photons, the D(max) is about 2 cm
into the tissuem, and for 22 MeV photons it is about
4.5 cm. For Co-60, D(max) is about 0.5 cm. 

The advantage of heavy-ion therapy is that the
majority of the energy deposited around the Bragg
peak.  Very elegant.

As for the paper, I am not clear as to how they made
their determination of effects at depth.  But I am
always willing to learn.

--- John R Johnson <idias at interchange.ubc.ca> wrote:

> 
> John et al
> 
> My comments follow
> 
> Item 1
> 
> "X-rays, for example, deposit their energy
> continuously once they enter the
> body."
> This is true for electrons, but X-ray interact
> differently with tissue, and
> this depends on their energy.
> 
> Item 2
> 
> "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."
> 
> I agree that this is the usual "thought", but anyone
> who has worked with
> radiation biophysists have been told it is more
> complicated.
> 
> Item 3
> 
> I agree with Rainer Facius's posting this morning
> that "the article is
> confusing"; but then I was confused when I first
> heard about the "bystander
> effect". I look forward to reading other articles
> about the effects of low
> energy heavy ions.
> 
> John
> 
> -----Original Message-----
> From: radsafe-bounces at radlab.nl
> [mailto:radsafe-bounces at radlab.nl]On
> Behalf Of John R Johnson
> Sent: October 16, 2005 5:59 PM
> To: John Jacobus; radsafe;
> know_nukes at yahoogroups.com
> Cc: John R Johnson (TRIUMF)
> Subject: RE: [ RadSafe ] Article: Heavy ions damage
> DNA
> 
> 
> 
> John
> 
> Thanks for this intersecting "article" I plan on
> reviewing it and commenting
> later.
> 
> John
>  _________________
> John R Johnson, Ph.D.
> *****
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> -----Original Message-----
> From: radsafe-bounces at radlab.nl
> [mailto:radsafe-bounces at radlab.nl]On
> Behalf Of John Jacobus
> Sent: October 16, 2005 5:32 PM
> To: radsafe; know_nukes at yahoogroups.com
> Subject: [ RadSafe ] Article: Heavy ions damage DNA
> 
> 
> 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
> 
> ------------------
> 
> 
> 
> 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
> 
> 
> 
> +++++++++++++++++++
> 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
> 
=== message truncated ===

+++++++++++++++++++
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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