[Gate-users] Gate-users Digest, Vol 87, Issue 13

[Andrew Green]

Hello,

Geant4 deals with boundaries by stepping onto them, and then stepping away again, so yes, each interface will cause a mandatory step. If this is causing problems, try adding the line: 

/gate/actor/dose/stepHitType random

(assuming you have a dose actor called 'dose'). This tells GATE to deposit energy from each step at a random point along the step, and ought to remove any artefacts from boundaries/step limits.

Hope that helps,
Andrew


On 12 Aug 2013, at 11:00, <gate-users-request at lists.opengatecollaboration.org>
 wrote:

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>   1. Re: the consequences of interface in particle tracking
>      (Hermann Fuchs)
> 
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Mon, 12 Aug 2013 11:00:45 +0200
> From: Hermann Fuchs <hermann.fuchs at meduniwien.ac.at>
> To: gate-users at lists.opengatecollaboration.org
> Subject: Re: [Gate-users] the consequences of interface in particle
> 	tracking
> Message-ID:
> 	<1376298045.8816.3.camel at strahlen41.strahlen.meduniwien.ac.at>
> Content-Type: text/plain; charset="utf-8"
> 
> 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 m?dicale
>> 
>> Centre de Lutte Contre le Cancer Nantes Atlantiques ? 
>> 
>> Ren? Gauducheau
>> 
>> Site Hospitalier Nord Bd J. Monod
>> 
>> 44805 ST HERBLAIN CEDEX
>> 
>> 0240679963
>> 
>> cid:193052914 at 09082012-3151
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> _______________________________________________
>> Gate-users mailing list
>> Gate-users at lists.opengatecollaboration.org
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> 
> 
> -- 
> -------------
> DI Hermann Fuchs
> Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology
> Department of Radiation Oncology
> Medical University Vienna
> W?hringer G?rtel 18-20
> A-1090 Wien
> 
> Tel.  + 43 / 1 / 40 400 7271
> Mail. hermann.fuchs at meduniwien.ac.at
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