The invention relates to a miniature X-ray source device connected to a distal end of a guiding wire for insertion towards a desired location within an animal body for effecting radiation therapy, said X-ray source device at least comprising a vacuum tube accommodated in said housing containing a cathode and an anode spaced apart at some distance from each other; electron freeing means for freeing electrons from the cathode; electric field means for applying during use a high-voltage electric field between said cathode and said anode for accelerating said free electrons; said vacuum tube being at least partly transparent to X-ray radiation emitted by said anode, as well as cooling means for cooling at least said anode. It is an object to provide a miniature X-ray source device having further limited constructional dimensions and an improved control of the working temperature of at least the anode and hence the working conditions of the miniature X-ray source device. According to the invention the miniature X-ray source device is hereto characterised in that said cooling means are cryogenic cooling means. More in particular in a specific embodiment of said miniature X-ray source device said cooling means comprise at least one supply passageway for supplying pressurized gas towards said anode and at least one exhaust passageway for exhausting said pressurized gas from said anode, said supply passageway and said exhaust passageway being interconnected by means of an expansion chamber surrounding at least partly said anode.