PROBLEM TO BE SOLVED: To attain faster processing by reducing the number of copies of DRR creation and reducing the calculation cost in the whole processing.SOLUTION: In automatic positioning for a patient in radiotherapy devised to calculate the amount of out of alignment between a current position of the patient and a position in treatment planning in which, in registering three-dimensional CT image data, acquired in the treatment planning, and a two-dimensional X ray perspective image to be acquired in the positioning, in order to align the positions of the three-dimensional CT image data with the two-dimensional X-ray perspective image, the geometry of the X ray photography is reproduced on a computer, by virtually executing perspective projection to the CT image data, the two-dimensional DRR is obtained, so that a valuation function for evaluating the degree of coincidence of the DRR and the X ray perspective image is maximum, the perspective projection parameter regarding rotation and parallel translation of the CT image data is optimized, optimization for the perspective projection parameter is executed by calculating the evaluation value for the degree of the coincidence of the DRR and the real perspective image only in one direction where a change in the image is greater.COPYRIGHT: (C)2013,JPO&INPIT【課題】処理全体でのDRR作成枚数を削減し、計算コストを削減して処理の高速化を図る。【解決手段】治療計画時に取得した3次元CT画像データと位置決め時に取得する2次元のX線透視像のレジストレーションを行う際に、3次元CT画像データと2次元X線透視像の位置合わせを行うために、コンピュータ上にX線撮影のジオメトリを再現し、CT画像データに対して仮想的に透視投影を行うことで、2次元DRRを得て、該DRRとX線透視像の一致度を評価する評価関数が最大となるように、CT画像データの回転・平行移動に関する透視投影パラメータを最適化し、患者の現在位置と治療計画時位置とのずれ量を算出するようにした放射線治療における患者自動位置決めに際して、前記透視投影パラメータの最適化を、画像の変化が大きい1方向でのみDRRと実透視像の一致度の評価値を算出して行う。【選択図】図10
