Simulation of complex geometries in GATE

Collimator optimization plays an important role in single photon emission computed tomography (SPECT). Nowadays complex geometries are added frequently in new designs and sometimes these geometries have no simple parametric description. The simulation of such a collimator poses a problem if one wants to use the Monte Carlo simulator GATE. A collimator in GATE can only be built using a limited set of parametric descriptions. A solution to this problem is a triangulated approximation of the structure at hand. Therefore, new functionality based on the tessellated solids in Geant4 was added to GATE. It makes the simulation of geometries with an arbitrary complexity possible if the virtual reality modeling language (VRML) description of the triangulated volume is provided. Our method was validated against standard GATE for a single knife edge pinhole collimator. The simulated difference for both sensitivity and resolution for the pinhole is lower than 0.48 % for the highest accuracy of triangulation. The major drawback of the current implementation is the computational complexity which increases linearly with the number of triangles.