Yttrium-90 (Y-90) is almost exclusively a high-energy beta-particle emitting radionuclide used in radiotherapy. Generally, Y-90 are imaged by bremsstrahlung SPECT. However, the images demonstrate a low quality. Thus, we considered using a Compton camera. 30 MBq of Y-90 was encapsulated in a glass bottle. The bottle was set at the center of a water filled NEMA phantom. A Si/CdTe Compton camera was set under the bottle and the distance was 10 cm. Then the bremsstrahlung X-ray was measured for six hours. We found that the image quality depended on the energy window of the Compton camera. The Y-90 source was clearly imaged with 300-400 keV energy window and the spatial resolution was highest. ; 第111回日本医学物理学会学術大会