Abstract: A patient immobilization system and method for patient immobilization prior to radiation therapy is described. An adjustable anchor including a slidable base plate between left and right sides of the anchor, provides for utilizing the same patient immobilizing device for head and neck, chest, and pelvis areas requiring radiation treatment. The adjustable anchor accommodates varying sizes of customized posterior molds forming the "mattress" portion of the patient immobilization system, while customized anterior molds secured in a holder are fitted over the patient area to be directly exposed to radiation. The holder is then firmly, but easily releasably secured to the adjustable holder. A hook and loop fastener or compression clip assembly provides for quick release of the anterior mold from the patient when required for difficult or emergency situations.