Extracranial radiosurgery using the CyberKnife

Several technical drawbacks can limit the clinical applications of conventional stereotactic radiosurgery: It requires the attachment of a rigid frame that immobilizes the patient and provides a frame of reference for aiming radiation beams, which is uncomfortable to patients, complicates fractional treatment, can impede beam aiming and introduce image artifacts, and generally restricts the application of stereotactic radiosurgery to the cranium and the high cervical spine. The CyberKnife solves these problems by using real-time, computer-based image guidance technology to aim a lightweight LINAC with a highly maneuverable robotic arm to deliver conformal radiation doses to tumors of all shapes, all without a rigid frame. Navigation is accomplished using skeletal features or implanted fiducials, and the system adjusts the aim of radiation beams frequently based on changes in patient position. Recent improvements in the system (ie, the introduction of flat-panel amorphous silicon X-ray cameras) have made it applicable to the treatment of tumors throughout the body, including in organs (eg, lungs and pancreas) that move with respiration. The authors summarize the characteristics of the CyberKnife system, describe their recent work adapting the system to treat extracranial tumors, and provide a brief update of their experience treating adenocarcinoma of the pancreas using the system.