[Gate-users] Radiationtherapy - Strange Multiple Scattering

[Hermann Fuchs]

Hello

I forgot to mention, the simulations where done with monoenergetic
helium ion beams at 150MeV/Nucleon.
To help the interpretation of the graphics: The Bragg Peak is at 160.2
mm.

Any help is welcome,
Hermann
On Mon, 2011-09-26 at 11:54 +0200, Hermann Fuchs wrote:
> Hello
> 
> I am trying to simulate simple gaussian shaped helium ion beams in a
> homogeneous water phantom. The setup is more or less the same as in the
> proton therapy benchmark.
> Analyzing the simulated data I got strange results regarding the beams
> lateral shape.
> One would expect a continuous beam broadening due to Multiple
> Scattering.
> 
> I have found that using a point beam (e.g from a point source) the beam
> broadening looks ok (e.g. according to MS theory).
> 
> However, using a gaussian shaped beam the broadening of the beam rises
> linearly, decreases again until at the point of the bragg peak the
> correct (as expected from MS theory) beam broadening is reached.
> 
> I can not explain this. Using 10^7 particles it should not be a
> statistics issue.
> To illustrate I've attached pictures. I used the recommended Carbon
> Physics list, the recommended proton physics list and the
> standardhadrontherapy physics list. The effect remains the same although
> the pronunciation is slightly different.
> 
> Point beam code:
> /gate/source/mybeam/gps/particle alpha
> /gate/source/mybeam/gps/pos/type Point
> /gate/source/mybeam/gps/pos/rot1 0 1 0
> /gate/source/mybeam/gps/pos/rot2 1 0 0
> /gate/source/mybeam/gps/centre 0. 0. 0.0 cm
> 
> Gaussian shaped code:
> /gate/source/mybeam/gps/particle alpha
> /gate/source/mybeam/gps/pos/type Beam
> /gate/source/mybeam/gps/pos/rot1 0 1 0
> /gate/source/mybeam/gps/pos/rot2 1 0 0
> /gate/source/mybeam/gps/pos/shape Circle
> /gate/source/mybeam/gps/pos/centre 0 0 0 cm
> /gate/source/mybeam/gps/pos/sigma_x 10 mm
> /gate/source/mybeam/gps/pos/sigma_y 10 mm
> /gate/source/mybeam/gps/direction 0 0 1
> 
> Can anybody explain this effect?
> 
> Cheers,
> Hermann
> _______________________________________________
> Gate-users mailing list
> Gate-users at lists.opengatecollaboration.org
> http://lists.opengatecollaboration.org/mailman/listinfo/gate-users