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Hello<BR>
<BR>
As far as I know each material border, be it a voxel(border) in a voxelised phantom ar a conventional geometry<BR>
imposes an mandotory step.<BR>
This is coming from the underlying geant4. and has something to do with how particles are tracked.<BR>
<BR>
Cheers,<BR>
Hermann<BR>
<BR>
On Fri, 2013-08-09 at 15:21 +0000, Chiavassa Sophie wrote:
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Hello,<BR>
<BR>
<BR>
<BR>
</BLOCKQUOTE>
<BLOCKQUOTE TYPE=CITE>
Using GateV6.2 we obtained strange results for geometries with interfaces (like voxelized geometry).<BR>
<BR>
To investigate this point, we performed very simple simulation (main.mac):<BR>
<BR>
<BR>
<BR>
- Mono energetic photon source (80 keV) and a dose actor in a box of water (cuve)<BR>
<BR>
<BR>
<BR>
We compare results with the same box adding a second water box (Interface), daughter of the first water box (cuve) (interface water/water).<BR>
<BR>
Theoretically, results should be similar. In fact we obtain a peak in each interface (results.jpg).<BR>
<BR>
<BR>
<BR>
Various hypothesis were explored: <BR>
<BR>
- Same results were obtain for all Electromagnetic processes and models.<BR>
<BR>
- Global Edep is similar with and without interfaces.<BR>
<BR>
- Same results were obtain with Geant4 (geant4.zip)<BR>
<BR>
<BR>
<BR>
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.<BR>
<BR>
<BR>
<BR>
Could you reproduce this behavior from your side ?<BR>
<BR>
Results obtained with and without interfaces should be similar for homogeneous media.<BR>
<BR>
What do you think about that ?<BR>
<BR>
<BR>
<BR>
Best regards<BR>
<BR>
<BR>
<BR>
<BR>
</BLOCKQUOTE>
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<BR>
<BR>
<B>Sophie Chiavassa</B><BR>
<BR>
<B>Radiophysicienne</B><BR>
<BR>
<B>Service de physique médicale</B><BR>
<BR>
<B>Centre de Lutte Contre le Cancer Nantes Atlantiques – </B><BR>
<BR>
<B>René Gauducheau</B><BR>
<BR>
<B>Site Hospitalier Nord Bd J. Monod</B><BR>
<BR>
<B>44805 ST HERBLAIN CEDEX</B><BR>
<BR>
<B>0240679963</B><BR>
<BR>
<B> </B><IMG SRC="cid:image001.jpg@01CE9524.9CBC4AF0" WIDTH="190" HEIGHT="95" ALIGN="bottom" ALT="cid:193052914@09082012-3151" BORDER="0"><BR>
<BR>
<BR>
<BR>
<BR>
<BR>
</BLOCKQUOTE>
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<BR>
<BR>
<BR>
</BLOCKQUOTE>
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<PRE>
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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. <A HREF="mailto:hermann.fuchs@meduniwien.ac.at">hermann.fuchs@meduniwien.ac.at</A>
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