is also incorporating advanced robotic systems. cyberknife is such a system that has a lightweight linear accelerator mounted on the robotic arm. it is guided towards tumor processes, using the skeletal structures as a reference system (stereotactic radiosurgery system). during the procedure, real time x-ray is used to accurately position the device before delivering radiation beam. the robot can compensate for respiratory motion of the tumor in real-time. advantages cas starts with the premise of a much better visualization of the operative field, thus allowing a more accurate preoperative diagnostic and a well-defined surgical planning, by using surgical planning in a preoperative virtual environment. this way, the surgeon can easily assess most of the surgical difficulties and risks and have a clear idea about how to optimize the surgical approach and decrease surgical morbidity. during the operation, the computer guidance improves the geometrical accuracy of the surgical gestures and also reduce the redundancy of the surgeon’s acts. this significantly improves ergonomy in the operating theatre, decreases the risk of surgical errors, reduces the operating time and improves the surgical outcome. disadvantages there are several disadvantages of computer-assisted surgery. many systems have costs in the millions of dollars, making them a large investment for even big hospitals. some people believe that improvements in technology, such as haptic feedback, increased processor speeds, and more complex and capable software will increase the cost of these systems. another disadvantage is the size of the systems. these systems have relatively large footprints. this is an important disadvantage in today's already crowded-operating rooms. it may be difficult for both the surgical team and the robot to fit into the operating room.