Patients undergoing radiation therapy for head and neck (HN) or intracranial (IC) targets are immobilized using a thermoplastic mesh mask. One anterior and two lateral points marked on the mask are aligned with the treatment room lasers to position the patient relative to the machine isocentre. Following alignment, a cone-beam computed tomography (CBCT) dataset is acquired for verification of patient position prior to treatment. Any errors in patient position are corrected with couch motions (in 3 translation and 3 rotation axes) determined from matching the CBCT with the plan CT. A recently acquired optical skin monitoring system (OSMS) shows promise in aiding the patient setup, however these systems do not work when the skin is obscured by the mask. The purpose of this study is to determine if using OSMS to position the patient’s head prior to fitting the mask reduces the magnitude of corrections indicated by CBCT to plan CT matching. Secondly, this study seeks to determine whether the use of OSMS prior to mask fitting aids in reproducing the posture of HN patients. Lastly, this study reports therapists’ perception of the utility of using OSMS in this way.