1. Monte Carlo Simulation on Performance of Double–scattering Compton Camera J. H. Park a, H. Seo a, Y. S. Kim a, C. H. Kim a, *, J. H. Lee b, C. S. Lee b, S. M. Kim c, J. S. Lee c a Department of Nuclear Engineering, Hanyang University, Seoul 133-791, Korea b Department of Physics, Chung-Ang University, Seoul 156-756, Korea c Department of Nuclear Medicine, College of Medicine, Seoul National University, Seoul 110-744, Korea MATERIALS AND METHODS ConclusionsConclusions AbstractAbstract Compared with conventional gamma-ray emission imaging, the Compton imaging technique could provide better performance in terms of imaging resolution and sensitivity when the gamma-ray source to be imaged has relatively high energy. We have developed a prototype double-scattering Compton camera which consists of two double-sided silicon strip detectors (DSSDs) for scatter detectors and a cylindrical NaI(Tl) scintillation detector for absorber detector for nuclear decommissioning applications and particle therapy applications both of which involve imaging high energy gamma-ray sources. The basic idea of the double-scattering Compton camera is to maximize the imaging resolution by measuring two successive interaction positions of Compton scattering very accurately because the imaging resolution is mostly limited by the spatial resolution of the component detectors which consequently affects the accuracy in determining the axis of the reconstruction cone. In the present study, the performance of the double-scattering Compton camera was compared with that of a single-scattering Compton camera with similar dimensions as a function of the source energy by using Geant4 Monte Carlo simulations. The optimal geometry of the multiple-detector-type double-scattering Compton camera was also studied by comparing the performance of the Compton camera. In addition, the performance of the double-scattering Compton camera was evaluated when additional side absorber detectors were used to register the double-scattered photon in the backward direction. We hope that the results of this simulation study will provide a guideline to researchers to find a proper design of Compton camera for a given objective. INTRODUCTIONINTRODUCTION Contact Information Chan Hyeong Kim, Ph. D., E-mail: chkim@hanyang.ac.kr, Tel: +82-2-2220-0513 Based on gamma-ray tracking  3-D imaging at a fixed position  Small-size and light-weight  Non-correlation between resolution and sensitivity  High-quality imaging for high-E gamma- ray Wide field of view  Multitracing capability axis of the reconstruction cone 3-D Compton imaging using double scattering compton camera: 137 Cs and 60 Co(left), 22 Na(right) Prototype double scatt- ering Compton camera Monte Carlo simulation study using Geant4 toolkit  The performance of the double-scattering Compton camera was compared with that of a single-scattering Compton camera with similar dimensions as a function of the source energy  The optimal geometry of the multiple-detector-type double-scattering Compton camera was studied by comparing the performance of the Compton camera for two extreme cases. Below figures show that of the two cases  The performance of the double-scattering Compton camera was evaluated when additional side absorber detectors were used to register the double- scattered photon in the backward direction RESULTSRESULTS Comparison performance between double-scattering Compton cam- era and single -scattering Compton camera  The figures show simulation results that is sensitivity (left), ARM (middle) and FOM (right). With low energy gamma source, single-scattering Compton camera showed better performance than double-scattering Compton camera however with a high energy gamma source (~ 2 MeV) double scattering Compton camera showed better performance The optimal geometry of the multiple-detector type in double-scatte- ring Compton camera 662 keV1332 keV typeefficiency(×10 -7 )ARM [°]FOMefficiency(×10 -7 )ARM [°]FOM SC1 wide12.1±0.603.80±0.122.03±1.097.24±0.763.68±0.0414.5±1.52 SC2 wide12.7±1.164.14±0.0118.02±1.658.25±0.503.82±0.0314.7±0.89 SC1 stack22.9±1.014.21±0.0330.66±1.358.50±0.764.02±0.0513.04±1.16 SC2 stack17.4±0.314.72±0.116.68±0.297.25±0.624.50±0.097.83±0.67  The results showed that wide scatterer is proper for the high resolution purpose and stack scatterer is proper for the high sensitivity purpose Evaluation the performance of the double-scattering Compton came- ra with side absorber  Figure left shows geometry of the double-scattering Compton camera with side absorber  Figure middle shows simulation result to determine thickness of the side absorber. As you can see 2.5 cm is enough for practical application  Figure right shows performance of the side absorber. The sensitivity was increased up to 59%, 68%, 80%, and 86% for source energy of 364 keV, 662 keV, 1173 keV, and 1332 keV, respectively In the present simulation study, we evaluated performance of the double- scattering Compton camera We hope that the results of this simulation study will provide a guideline to researchers to find a proper design of Compton camera for a given objective