Immobilization devices such as thermoplastic masks are used routinely in the radiation treatment of head and neck cancer patients. It is important to assess how well they function at preventing patient motion while the radiation treatment is being delivered. (i.e. isocentre set-up margins, patient motion with the mask). If these new thermoplastic masks such as MedTec S-frame allow less movement, then smaller margins are needed during radiation therapy which, in turn, would decrease side effects from the treatment.