Applying the x-ray, gamma-ray and the corpuscular ray to the affected part, to image converting the circumstances of the affected part and the remedy beam at the time of radiotherapy which it does, in order the detector ring which becomes the occasion where monitoring it does, with the multi ring to oppose to body axis direction mutually, can be less crowded, the area of interest of the irradiation field of radiotherapy, makes registration of the irradiation field which uses the PET image to be included in the range of vision of the open die PET device, and remedy monitoring possible with the open die PET device which it lays out the opening and the radiotherapy PET compound device which has with the radiotherapy device in order to do radiotherapy from the aforementioned opening,X線、ガンマ線や粒子線を患部に照射して行う放射線治療において、患部や治療ビームの様子を画像化してモニタリングする際に、マルチリングでなる検出器リングを体軸方向に互いに対向するように隙間を空けて配置した開放型PET装置と、前記隙間から放射線治療を行なうための放射線治療装置とを備えた放射線治療・PET複合装置により、放射線治療の照射野の関心領域が、開放型PET装置の視野に含まれるようにして、PET画像を用いた照射野の位置決めや治療モニタリングを可能とする。
