Real-time Assessment of Frameless Intrafraction Motion

The purpose of this study is to assess the ability of a modified thermoplastic mask system in keeping an individual head stationary for a predefined amount of time. The investigators hope to know if the modified mask is study enough, and also if the modification on the mask will allow the investigator see and track the individual's movement underneath the mask by means of a camera that can detect light reflected from the individual. Participants will lay down on their backs and their heads will be held in place with the mask system for approximately 1 hour.