A method is provided to select a value of a voltage to be set at an x-ray tube of a computer tomography for scanning a patient before an acquisition of x-ray projections of a body region of the patient so as to reduce the dose of x-ray radiation to be applied to the patient in the course of the scan. According to the method, the selection of the value of the voltage takes place under consideration of at least one item of information that can be learned from a topogram of the patient and at least one item of information about the patient that can be learned from a patient file of the patient. The invention also encompasses a computer tomography apparatus with a computer for the execution of the method, as well as a data medium on which is stored a computer program that can be executed on a computer device to perform the method.
