The present invention relates to the field of radiation therapy. In particular, the relates to a system for measuring the position of a head of a patient during neurological diagnosis, therapy or surgery, in particular during radiation therapy relatively a frame adapted to be fixated to a radiation therapy unit. The invention also relates to a head cap and a measurement tool for use in such a system, and to a method measuring the position of a head of a patient by means of a system mentioned above during neurological diagnosis, therapy or surgery, in particular during radiation therapy relatively a frame adapted to be fixated to a radiation therapy unit. The measurement tool is adapted to measure a distance between the head and the head cap via a through hole by means of an elongated element having an end being adapted to abut against the head during a measurement, wherein the measurement tool is adapted to obtain at least one measurement value indicating a position of the head in relation to the head cap substantially without operator interaction.