1. A patient positioning system for positioning a patient in an irradiation position by a radiation therapy system, the system comprising: a patient supporting module having a patient supporting device for keeping the patient in a posture intended in the radiation treatment planning, the patient supporting device being disposed above a bearing at a base unit rotatably about an axis, and the base unit having a coupling element, and a positioning arm, which has a plurality of joints and a coupling point for coupling the coupling element, and the positioning arm providing positioning of the patient with adjustment of a rotary angle of the patient supporting module in an arbitrarily predeterminable irradiation position.