Monte Carlo simulations on performance of double-scattering Compton camera

A double-scattering Compton camera that can effectively obtain three-dimensional emission images in high-energy gamma-ray applications such as nuclear decommissioning and particle therapy monitoring has been developed. The double-scattering Compton camera utilizes two position-sensitive detectors as scatter detectors to determine the trajectory of a scattered gammaray, and a scintillation detector as absorber detector to measure the remaining energy of the double-scattered gamma-ray. The benefit of using two scatter detectors is the accurate determination of the gamma-ray trajectory after the scattering at the first scatter detector, which makes possible higher imaging resolution. In the present study, Geant4 Monte Carlo simulations were conducted to compare the performance of the double-scattering Compton camera with that of a similarly dimensioned single-scattering Compton camera for different source energies. Further, the optimal geometry of the multiple-detector-type double-scattering Compton camera was investigated for the purposes of increasing its imaging sensitivity. The results showed that the double-scattering Compton camera offers superior angular resolution over the entire energy range considered in the present study, whereas the single-scattering Compton camera provides greater sensitivity. The results also showed that, in general, the placement of additional detectors in the axial direction (i.e., stacking) is more effective for sensitivity improvement than doing so in the planar direction. This axial placement, however, lowers the imaging resolution. The double-scattering Compton camera exhibited the highest sensitivity when the additional scatter detectors were added to the first scatter detector in the axial direction, and exhibited the highest imaging resolution when the additional detectors were added to first scatter detector in the planar direction. Therefore, the results generally indicated that the first scatter detector is more important than the second not only for improving the sensitivity but also for maintaining a high imaging resolution. We believe that the present study's findings will provide valuable guidelines to researchers looking for the best Compton camera designs for certain objectives.