Acceleration of GATE SPECT simulations

GEANT4 application for tomographic emission (GATE) is a geometry and tracking 4 (GEANT4) application toolkit for accurate simulation of positron emission tomography (PET) and single photon emission computed tomography (SPECT) scanners. GATE simulations with realistic count levels are very CPU-intensive as they take up to several days with single-CPU computers. Therefore, we implemented both standard (FD) and convolution based forced detection (CFD) with multiple projection sampling (MPS) which allows the simulation of all projections simultaneously in GATE. In addition, a FD and CFD specialized Geant4 navigator was developed to overcome the detailed but slow tracking algorithms in Geant4. This paper is focussed on the implementation and validation of these aforementioned developments. The results show a good agreement between the FD and CFD versus analog GATE simulations. These combined developments accelerate GATE from three to six orders of magnitude and render realistic simulations feasible within clinically acceptable simulation times.