This invention relates to a fixation device and a method for immobilizing a head of a patient relative a treatment unit or medical device during treatment of the head. The fixation device is provided with an interface unit adapted to be fixated in relation to an adaptor unit for connection to the treatment unit, or to a frame for connection to the medical device. Furthermore, the fixation device is provided with a bite-block for being inserted into a mouth of a patient and a positioning arrangement movably connecting the bite-block to the interface unit. The positioning arrangement is adapted to be fixated by means of an adhesive for fixation of the bite-block such that the head of a patient can be immobilized relative said adaptor unit or frame.
