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

Mon Aug 19 10:26:48 CEST 2013

Hello Andrew,

Thanks for this answer.
But, the command "/gate/actor/dose/stepHitType random" was present yet in our tests .
Indeed, you are right, this command allows a better energy deposition along the step. It's clearly visible in the attached file.
Unfortunately, this command does not remove artefacts from boundaries.
Best regards
Sophie Chiavassa

De : gate-users-bounces at lists.opengatecollaboration.org [mailto:gate-users-bounces at lists.opengatecollaboration.org] De la part de Andrew Green
Envoyé : lundi 12 août 2013 12:49
À : <gate-users at lists.opengatecollaboration.org>
Objet : Re: [Gate-users] Gate-users Digest, Vol 87, Issue 13

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<mailto:gate-users-request at lists.opengatecollaboration.org>>
 wrote:

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Today's Topics:

  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<mailto:hermann.fuchs at meduniwien.ac.at>>
To: gate-users at lists.opengatecollaboration.org<mailto: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<mailto:1376298045.8816.3.camel at strahlen41.strahlen.meduniwien.ac.at>>
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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

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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<mailto:hermann.fuchs at meduniwien.ac.at>
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