PROBLEM TO BE SOLVED: To provide a particle therapy planning system for creating therapy plan data with improved uniformity of dose distribution.SOLUTION: In a therapy planning system for creating therapy plan data for performing a particle therapy, movement of a patients affected area (target) is extracted from plural tomography images including the target, and the direction of scanning is determined by projecting the extracted movement on a scanning plane of scanning electromagnets. Irradiation positions arranged on straight lines parallel with the scanning direction enable calculation of a scanning path for scanning mainly in the target direction.
