Patients with inoperable tumors too young to immobilize for frame-based radiosurgery, or patients in danger of radiation overdose, now have hope. Robot technology is combining with precise diagnostic X-Ray beams to allow a stereotactic radiosurgery system from Accuray (www.accuray.com) to match CT images with live images to accurately target tumors with cancer-destroying radiation beams.

The CyberKnife© system requires no incisions, draws no blood, requires no anesthetic and is performed in an outpatient setting.  An option to the system compensates for patient breathing using a new respiratory tracking system.  These tight targeting tolerances allow treatment close to critical organs and treatment of some tumors not treatable by traditional forms of radiotherapy, and treatment for patients who have already received the maximum allowed dose of radiation to certain organs.

How it Works
A Kuka robot (www.kukacontrols.com) is used to precisely position the radiation beams during the surgical procedure. The robot’s control software uses VxWorks to control real-time operation, but also co-exists on the same machine with Windows XP which provides the operator interface.

John Patchkin, an applications specialist for Kuka, says the system utilizes a six-axis robot with a 200 kilogram payload capability.  The robot controller uses VxWin® software to provide a software extension to VxWorks, and eliminate the need for additional control hardware or intelligent co-processor boards.  The user interface is Windows XP embedded written in C#.  All of the system’s control system is handled by VxWorks including I/O, trajectory generation and motion control.

The VxWin® software extension offers the stability and real-time performance that enabled the Accuray CyberKnife system to gain FDA approval. Patchkin says that positioning accuracies for the system are sub-millimeter during dynamic motion operations.  Plus, the openness of the VxWin software allows easy integration of DeviceNet I/O with the robot and Ethernet-based communication with an external Silicon Graphics workstation.

System Operation
Traditional stereotaxy is a method used in neurosurgery for locating points within the brain using an external frame.  Until recently, this type of surgery used an external frame to locate and treat tumors and lesions with radiation.  Its advantage is that it focuses the radiation tightly on the treatment site while limiting radiation exposure in adjacent tissue and eliminates the rigid stereotactic frame.

The Accuray system relies on the cranium or small metallic markers implanted in the tumor to serve as the frame of reference.  X-Ray cameras are mounted underneath and on both sides of the patient, and a moveable table is used to position the patient during the treatment.  The system continuously updates the target position of the miniaturized linear accelerator by comparing real-time diagnostic X-Ray images with previously generated CT scans.  The updated target position is continually fed to the robot control system that re-positions the linear accelerator attached to the robot.

The linear accelerator shoots hundreds of tightly focused high energy radiation beams during the course of the treatment.  This enables the rigid stereotactic frame used by traditional methods of radiotherapy to be discarded in favor of a non-invasive flexible mask for intracranial tumors.  The non-invasive mask eliminates the need for anesthesia, is more comfortable for the patient and provides greater flexibility for breaking-up the treatment.

“Of necessity, we set very high standards for the reliability and accuracy of the robot controlling the linear accelerator positioning,” notes Dr. Euan Thomson, President and CEO of Accuray. “We were impressed by the performance of the system and Kuka’s commitment to assist in the systems integration of the CyberKnife system.”

Thomson says the system is unique because it uses a robot to position the linear accelerator, which offers increased maneuverability for more complete coverage of complex target volumes while minimizing effects on surrounding healthy tissue and organs.  He says the six-axis robot arm also makes previously unreachable tumors accessible for treatment.

The diagnostic X-Ray cameras are used to snap real-time pictures of the target volume.  A workstation compares these pictures against previously generated CT scans and locates the spatial position of the target volume.  This information is fed to the robot, which continually updates the position of the linear accelerator.  Whenever movement of the tumor is measured, the position of the robot is updated within milliseconds.