A medical apparatus and method of operating a medical apparatus are disclosed. The apparatus includes a radiation source for emitting radiation towards an area to be treated of a patient； a mount element arranged to be worn by the patient for positioning the radiation source in a predetermined position relative to the area to be treated； a sensor element arranged to provide a signal indicative of whether the apparatus is being worn by the patient； and at least one controller arranged to receive the signal from the sensor, and to determine whether the apparatus is being worn by the patient, and to determine duration data indicative of the duration for which the radiation source emits radiation whilst the apparatus is being worn by the patient.
