Dynamics-based decentralized control of robotic couch and multi-leaf collimators for tracking tumor motion

Tumors in thorax region incur significant amount of motion and deformation due to respiratory and cardiac cycles. To accommodate this undesired movement, physicians incorporate a large standard margin around the tumor to delineate a Planning Target Volume (PTV), so that the Clinical Target Volume (CTV) receives the prescribed dose under any scenario. Consequently, a large volume of healthy tissue might be irradiated and sometimes it is difficult to spare critical organs adjacent to the tumor. For compensating this tumor motion, techniques such as breath-hold, gating, and Active Tracking and Dynamic Delivery (ATDD) are used. Although, ATDD is the most effective technique, it is the most challenging one. The ATDD can be accomplished in three different ways: adjusting the Multi-Leaf Collimator (MLC), adjusting the couch, and adjusting the MLC and couch simultaneously. The first two techniques have been explored and/or implemented in practice. However, the third approach has not been investigated extensively. In this study, we have proposed a novel approach for ATDD that exploits the advantages of both the MLC (or MLC-bank) and the HexaPOD™ robotic couch. In our proposed new approach, we have decomposed and allocated the tumor motion trajectory to the subsystems (MLC or MLC-bank and HexaPOD™ robotic couch) based on their natural frequency domains using wavelet technique. The efficacy of the proposed method has been investigated by extensive computer simulation and the results are presented in this paper.