The present invention provides a protection mechanism for a spectroscopic analysis system being adapted to determine a property of a biological structure in a volume of interest of a patient. The spectroscopic system preferably makes use of high power radiation, and provides a protection mechanism for preventing an accidental exposure of light sensitive tissue of a body. The invention provides a variety of approaches to detect whether a measurement head of the spectroscopic system is in a measurement position. The measurement position of the measurement head can effectively be determined by making use of e.g. a pressure sensor, a sensor measuring the electric resistance of the skin of the patient, or even by optical means analyzing the intensity or the spatial structure of a monitoring beam providing a visual image of the volume of interest.