This study estimated the performance of a multiple-scattering Compton camera (MSCC) in monitoring the dose distribution of therapeutic photons on a Korean Typical Man-2 (KTMAN-2) phantom. The MSCC was constructed with two CZT semiconductor detectors as scatter detectors and a CWO scintillator detector as an absorber detector. The two planar semiconductor arrays consisted of 40 × 40 pixels, each with a size of 1 × 1 × 10 mm3, and the other CWO array consisted of 40 × 40 pixels, each with a size of 1 × 1 × 10 mm3. The optimized designed parameters such as an inter-detector distance of 3 cm, and a detector thickness of 1cm, were used in this system. The distance between the phantom and first scattering detector was wet to 17 cm to maximize the detection efficiency for scattered photons. When 6-MV photons interacted with voxel in the KTMAN phantom, some photons deposited part of their energy on the voxels and scattered out of the KTMAN phantom. The 3D distribution of therapeutic photons detected by MSCC was simulated by using a Monte Carlo simulation. The reconstructed Compton images were combined with the cross-sectional images of the phantom, and all combined images were well-matched with the predetermined conditions of the simulation. Our simulation showed the feasibility of using the Compton imaging to monitor the 3D interaction position in 3D radiation therapy.