Localization of radiation sources is an essential task for decontamination. For radiation sources that are inside of structures, it is hard to estimate an accurate position. In this paper, we propose an approach to estimate accurate localization of radiation sources using the gamma-ray CT method. Gamma-ray CT method estimates inner structures from the data obtained numbers of position and pose of detector surrounding objects. Therefore, location of radiation sources surrounded structures can be estimated. In conclusion, our approach successfully detects sources which are placed inside of structures.