Hi Bosky, We encountered exactly the same problem and the problem comes from Geant4. As I know the particles are "born" in a certain volume (here the phantom) and they move to a second volume only when they reach a boundary of the first one, so even if the particles are both in the phantom (i.e. first volume) and the second one (overlapping, here your scanner), they behave as they are in the first one. And unfortunately there is no solution ... except to resize your phantom if it's possible ... Cheers, Simon <div class="gmail_quote">On Thu, May 15, 2008 at 5:14 PM, Ravindranath, Bosky <<a href="mailto:bosky@bnl.gov">bosky@bnl.gov</a>> wrote: <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> Hello Gate users, I'm using voxellized phantoms to test my scanner performance, however due to the positioning of the scanner, there is bound to be overlapping regions between the scanner and the image that is read in as the phantom. The regions in the phantom that overlap with the scanner has material properties set to vacuum. When I run my simulations, I do not see any gamma interactions with the overlapping detector regions. Is there a way to work around this? I tried to define the scanner as a daughter of the phantom, GATE did not allow me to do that (I set the type as parameterized box matrix), I tried defining the phantom first and then the geometry, but the result was the same. Any suggestions appreciated. Thank you, Bosky _______________________________________________ Gate-users mailing list <a href="mailto:Gate-users@lists.healthgrid.org">Gate-users@lists.healthgrid.org</a> <a href="http://lists.healthgrid.org/mailman/listinfo/gate-users" target="_blank">http://lists.healthgrid.org/mailman/listinfo/gate-users</a> </blockquote></div>