Radiotherapy of the craniospinal axis in young children is frequently complicated by the need for access to the patient's airway for sedation and anesthesia delivery or by frequent, unanticipated movement. Positioning the patient supine, instead of in the conventional prone position, allows the use of immobilization facemasks with body molds and more positive patient fixation, and improved airway access. The procedure for establishing the various fields differs from the prone approach. In this paper, we describe the methodology to achieve successful supine positioning.