[Gate-users] voxellized phantom attenuation (no) problem

[Richard Taschereau]

Hi Ahmet,

Here is what I did.  I used standard Gate code (not your stepping action).
I defined a spherical shell detector, large enough to contain the phantom
and I ³attached² a phantomSD to the voxel phantom (uncompressed).  I
collected ³singles² in a root file and I looked at the distribution of
scattered/unscattered photons using the field ³comptonPhantom².  Here¹s my
results with 5000 photons:

                                        %unscattered
All Bone phantom:                   3.1
All water phantom:                  7.1
MCAT phantom:                       9.0
All Lung phantom:                  48.3

These results make sense to me.  I did have one problem though: since the
phantom has an even number of voxels in each direction, the source at
(0,0,0) is at the corner of 8 voxels, and the GEANT4 navigator couldn¹t
determine in which voxels the particle was.  I moved the source by 1 micron
in each direction.  You may want to try this approach (spherical shell
detector) instead of using GateSteppingAction.

Richard
-- 
Richard Taschereau, Ph.D.
Crump Institute for Molecular Imaging
University of California Los Angeles
700 Westwood Plaza, A222
Los Angeles, CA 90095-1770
Phone: (310) 825-0697
Fax:     (310) 206-8975
email: RTaschereau at mednet.ucla.edu



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