Vacuum cushions for positioning patients for radiation therapy procedures are well known and widely used. These cushions are comprised of several common elements: a gas-impermeable outer cover, valve-stem and closeable valve, and expanded polystyrene beads that fill the cushion. In use, the patient is positioned on the cushion while it is in its semi-inflated, loose state. A source of vacuum, usually a vacuum pump, is attached to the closeable valve. As the cushion is evacuated, the expanded polystyrene beads are forced together to form a rigid support that conforms to the body contour of the patient. If desired, the expanded polystyrene beads may be bunched-up around a portion of the patient's anatomy, a thigh for example, so that when the beads become rigid they will hold that portion of the patient's anatomy in the desired position.
Such vacuum cushions come in a variety of sizes, fill rates, and configurations to fit the sizes and contours for different body portions, including a size large enough to hold the entire patient. A problem arises, however, in that it becomes difficult to correctly elevate and/or position some body parts like thighs and knees without over-filling the cushion with polystyrene beads, which would make it difficult to position other body elements like the torso that do not need elevation. This can lead to the need to position a solid or rigid positioner such as a wedge or other form underneath the vacuum cushion to properly elevate and position knees and thighs.