Ultrasonic Motor as a Drive of a Multileaf Collimator

A multileaf collimator (MLC) is used on a radiation therapy machine to provide conformal shaping of radiation treatment beams. An MLC is an assembly of individual leaves of a high atomic-numbered material, usually tungsten. The leaves can move independently in and out of the path of the radiation beam in order to block a portion of it, thereby altering the shape of the radiation field to closely match the shape of a tumor. All current MLC leaf drive mechanisms are electro-mechanical assemblies that still employ conventional electro-magnetic motors with gear mechanisms or drive screws. Therefore, they can suffer from some drawbacks such as mechanical backlash which limits the positioning accuracy. Furthermore, gear mechanisms add additional weight and complexity to the system. Employing ultrasonic motors as the drive of the multileaf collimator leaves can eliminate the above-mentioned drawbacks. An MLC drive prototype based on PI Line (R) RodDrive linear motor was built and studied. The irradiation effects on piezoceramics were reviewed.