Stereotactic radiosurgery (SRS) is a treatment modality capable of delivering high radiation dose to one or more cranial lesions. Current approaches include frame-based and frameless techniques. The former involves the use of a rigid metal frame to ensure patient positioning, and the latter uses a thermoplastic mask and patient motion monitoring to determine when patient movement exceeds clinical thresholds. Recent studies have also shown that the rotational motion of the patient can hinder target coverage and degrade the treatment plan, particularly in cases where lesions are a distance away from the treatment isocenter, such as when multiple targets are treated with a single isocenter. Our goal is to achieve sub-millimeter and sub-degree patient head motion control for patients undergoing frameless and maskless intracranial SRS using an approach which improves upon conventional treatment protocols. Our solution is to monitor and compensate for intrafraction head motion in 6 degrees-of-freedom (6DOF) in real-time using an in-house designed and built parallel kinematics robotic motion compensation system. To that end, we present the research and set of experiments required to reach this goal in this dissertation.,The research to achieve this objective is presented in six chapters, focusing first on the the theory behind parallel robot control and the design and construction of a 6DOF robotic system, then the development of a general calibration methodology and first use of the robot as a phantom to evaluate clinical motion tracking systems, and finally the creation and implementation of a motion compensation algorithm for use with human subjects. Additional experiments help support these goals, which include the collection and analysis of both volunteer and real patient motion to better inform the control algorithms and system design, and target dose coverage improvements when using the robot for real-time head motion stabilization for a single-isocenter multi-target SRS treatment.,This work presents a novel approach to SRS treatments through the development of a robotic motion compensation system. By integrating real-time robotic head motion correction into frameless and maskless SRS, it may be possible to improve upon the current SRS treatment regimes by streamlining clinical workflow, minimizing patient discomfort, and achieving target dose coverage with accuracy as good or better than traditional frame-based intracranial SRS.