A method and a system for x-ray treatment of, for example, cancer or restenosis prevention inside a living body is disclosed. A miniature x-ray tube (1) is provided with at least one pair of electrodes (6, 8), the electrodes alternatingly serving as anode and cathode, respectively. A power supply (13) is connected to the electrodes, and a switching unit of the power supply alternates the electrical potential across the electrodes. With the x-ray tube according to the invention the temperature increase at the site of treatment is limited, thereby providing an effective treatment without unduly prolonged treatment duration.