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 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 forced detection (FD) and convolution-based forced detection (CFD) with multiple projection sampling, 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 article is focused on the implementation and validation of these aforementioned developments. The results show a good agreement between the FD and CFD versus analog GATE simulations for Tc-99m SPECT. These combined developments accelerate GATE by three orders of magnitude in the case of FD. CFD is an additional two orders of magnitude faster than FD. This renders realistic simulations feasible within minutes on a single CPU. Future work will extend our framework to higher energy isotopes, which will require the inclusion of a septal penetration and collimator scatter model.