An X-ray computer tomography (CT) apparatus according to an embodiment includes processing circuitry. The processing circuitry an operation to change information relating to a range of a part that is defined based on a plurality of anatomical landmarks in any one of image data of a subject and image data of a virtual patient image. The processing circuitry performs any one of a first setting processing and a second setting processing, the first setting processing of changing a part of the anatomical landmarks to define the range of the part, the second setting processing of setting, for a part of the anatomical landmarks, a position departed therefrom by a predetermined length in a predetermine direction as an actual anatomical landmark.
