Abstract: An oral appliance may be used to stabilize a subject during radiation therapy. The body of the oral appliance may be configured to be secured within the subject's mouth in an as-used position. A handle of the oral appliance may extend from the subject's mouth during use. The body may comprise a first portion configured to engage maxillary teeth, a second portion configured to engage mandibular teeth, a tongue positioning component, and/or other components. The tongue positioning component may be configured to receive the subject's tongue when the oral appliance is in the as-used position and to facilitate positioning the subject's tongue in a predetermined location and/or orientation with respect to the oral appliance when in use. One or both of the first portion or second portion may be configured to displace corresponding mandibular teeth or maxillary teeth away from the body and/or tongue positioning component in the as-used position.