[Gate-users] the consequences of interface in particle tracking

[Hermann Fuchs]

Hello

As far as I know each material border, be it a voxel(border) in a
voxelised phantom ar a conventional geometry
imposes an mandotory step.
This is coming from the underlying geant4. and has something to do with
how particles are tracked.

Cheers,
Hermann

On Fri, 2013-08-09 at 15:21 +0000, Chiavassa Sophie wrote:
> Hello,
> 
>  
> 
> 
> Using GateV6.2 we obtained strange results for geometries with
> interfaces (like voxelized geometry).
> 
> To investigate this point, we performed very simple simulation
> (main.mac):
> 
>  
> 
> -         Mono energetic photon source (80 keV) and a dose actor in a
> box of water (cuve)
> 
>  
> 
> We compare results with the same box adding a second water box
> (Interface), daughter of the first water box (cuve) (interface
> water/water).
> 
> Theoretically, results should be similar. In fact we obtain a peak in
> each interface (results.jpg).
> 
>  
> 
> Various hypothesis were explored: 
> 
> -         Same results were obtain for all Electromagnetic processes
> and models.
> 
> -         Global Edep is similar with and without interfaces.
> 
> -         Same results were obtain with Geant4 (geant4.zip)
> 
>  
> 
> Moreover, when max step size parameter is reduced, we obtain similar
> peak at each step. It seems that interface create an artificial step
> in the simulation process.
> 
>  
> 
> Could you reproduce this behavior from your side ?
> 
> Results obtained with and without interfaces should be similar for
> homogeneous media.
> 
> What do you think about that ?
> 
>  
> 
> Best regards
> 
>  
> 
> 
> 
>  
> 
> Sophie Chiavassa
> 
> Radiophysicienne
> 
> Service de physique médicale
> 
> Centre de Lutte Contre le Cancer Nantes Atlantiques – 
> 
> René Gauducheau
> 
> Site Hospitalier Nord Bd J. Monod
> 
> 44805 ST HERBLAIN CEDEX
> 
> 0240679963
> 
>  cid:193052914 at 09082012-3151
> 
>  
> 
>  
> 
> 
>  
> 
> 
> 
> _______________________________________________
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-- 
-------------
DI Hermann Fuchs
Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology
Department of Radiation Oncology
Medical University 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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