Head and neck radiation therapy for the treatment of cancer or the like is carried out using a mask which comprises a heat-softenable, conformable and perforate plastic sheet and a frame which can be secured to the surface of a treatment table or chair to immobilize the patient's head and neck. An inhaler is placed on the patient's face prior to molding the thermoplastic sheet over the patient's face such that the resulting contoured sheet captures the inhaler and produces a unitary assembly. Inlet and outlet hoses can be attached to the inhaler for administering an anesthetic or soporific in gaseous form, such as nitrous oxide, for the purpose of calming and tranquilizing the patient for reducing feelings of claustrophobic anxiety during the treatment. A separate scavenging unit may be added.
