Systems for immobilizing a patient are disclosed. The system includes at least one preform formed from a low melting temperature thermoplastic, the preform being configured to be formed to the anatomy of the patient, at least one frame coupled to the at least one preform, and at least one support configured to support the anatomy of the patient. The system also includes at least one lock mechanism coupled to at least one of the frame and the support and configured to couple the at least one frame to the at least one support, and at least one adjuster mechanism coupled to at least one of the at least one frame and the at least one support and configured to selectively adjust a distance between the at least one frame and the at least one support while the at least one frame is coupled to the at least one support.