[Gate-users] Radiationtherapy - Strange Multiple Scattering

[Loic Grevillot]

Dear Hermann,

Knowing the fact that the transverse dose spreading works for a point like
source, I do not understand why the behavior is not similar for a pencil
beam of a few milimeters in diameter (you should have the same effect).

My first guess is an issue in the data analysis, i.e. a mistake in the GATE
macro file or in the routine used for the Gaussian fit.

Did you try this test case with protons or other ions?



Loïc Grevillot, Ph.D. Student
PARTNER project, CERN

IBA Particle Therapy / Creatis-LRMN
Tel (IBA):         +32 10 487 729



2011/9/26 Hermann Fuchs <hermann.fuchs at meduniwien.ac.at>

> 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
> --
> -------------
> DI Hermann Fuchs
> Div. Medical Radiation Physics
> Department of Radiotherapy
> Med. Univ. Vienna / AKH Vienna
> Währinger Gürtel 18-20
> A-1090 Wien
>
> Tel.  + 43 / 1 / 40 400 7271
> Mail. hermann.fuchs at meduniwien.ac.at
>
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