Standard stereotactic techniques rely on a rigid metal frame fixed to a patient’s skull for head immobilization and target localization. However, such frame-based systems have numerous limitations, including:

1) restricting treatment to the brain,
2) limiting the possible angles which radiation could be delivered,
3) causing considerable discomfort for the patient.

In contrast to the standard frame-based radiosurgical instruments, the CyberKnife uses noninvasive image-guided localization, and a robotic delivery system. This combination of technologies enables the CyberKnife to overcome the limitations of older frame-based radiosurgery such as the Gamma Knife and LINAC.

The robot is instrumental in precisely aiming this device. When a patient moves during treatment, the change in position is detected by the cameras, and the robot compensates by re-targeting the linear accelerator before administering the radiation beam. This process of continually checking and correcting ensures accurate radiation targeting throughout treatment.

In summary, the CyberKnife replaces the stereotactic head frame with a patient-friendly image-guided localization system. This technology has the added benefit of enabling the CyberKnife to be used for radiosurgical applications outside the brain and for staged radiosurgery. It is difficult if not impossible to perform these other procedures with standard frame-based radiosurgical systems

The Synchrony System is an enhancement that works together with the CyberKnife System to deliver dynamic radiosurgery - the ability to irradiate a tumor or other target while it is moving. The advantage of the Synchrony System is that patients can breathe normally throughout treatment while the CyberKnife robot actively compensates for the breathing motion during irradiation - this allows extremely accurate radiation delivery without the need for breath holding. Treatment is thus more comfortable for patients and significantly faster.

The Synchrony System records the breathing movements of a patient's chest and combines that information with sequential x-ray pictures of tiny radiopaque markers implanted in or near the tumor, to enable the CyberKnife robot to precisely follow the moving tumor as it delivers each radiation beam. The increased accuracy of the CyberKnife System with Synchrony, which is the only radiosurgery device capable of targeting tumors in this manner, reduces normal tissue exposure by requiring smaller irradiation margins. The Synchrony System is used in conjunction with the CyberKnife to treat patients with tumors and lesions in areas of the body such as the lung, liver, kidney and pancreas.

By using digital radiographic images of anatomical features or implanted fiducials to localize the position of a tumor, the CyberKnife eliminates the need for a stereotactic frame. Although frameless and therefore non-invasive, the accuracy of the CyberKnife is comparable if not superior to frame-based systems.

In a recently published manuscript (Yu, C, Main W, Taylor D, Kuduvalli G, Apuzzo M, Adler J, Wang M: An Anthropomorphic Phantom Study of the Accuracy of CyberKnife Spinal Radiosurgery. Neurosurgery, 55(5):1138-1149, 2004) showed the mean clinically relevant error, as measured at three different CyberKnife facilities, was determined to be 0.7 + 0.3 mm, which did not vary with computed tomographic slice thickness in a range of 0.625 to 1.5 mm. The average treatment delivery precision was 0.3 + 0.1 mm. Fiducial tracking error was less than 0.3 mm for radial translations up to 14 mm and less than 0.7 mm for rotations up to 4.5 degrees.

(Note: there have been no medical publications showing that any existing radiosurgery system has or is more accurate than the CyberKnife. Many medical centers performing radiosurgery will make oftentimes undocumented accuracy claims about narrow portions of their technology. If you or a loved one is considering radiosurgical treatment, it is advisable that you ask the radiosurgical facility for published documentation regarding the “OVERALL” accuracy of their entire system.)

1) Treatment setup,
2) Treatment planning,
3) Treatment delivery.

These steps can be performed on the same day or separate days, depending on the combined schedule preferences of the CyberKnife team and patient.

Unlike frame-based procedures, where the entire process must be performed in a single day, a CyberKnife patient does not need to wait in the hospital while the treatment plan is being developed. As a result, a patient can go home after setup and return on a separate day for treatment delivery.

Treatment setup
Setup is the initial process that allows a physician to plan and deliver a CyberKnife treatment. For a typical cranial tumor, a custom-fit plastic mask is made for each patient. This mask, unlike the conventional metal head frame, is noninvasive and painless. With the mask in place, the patient undergoes a CT scan with contrast (iodinated dye), which is then used to precisely plan delivery of radiation to the tumor. In some instances, a MRI scan may also be necessary in order to fully visualize the tumor and adjacent critical anatomy.

When spinal tumors are treated, a foam body cradle is custom-fit for the individual patient instead of the mask. Most spine tumor patients require placement of small metal fiducials prior to treatment set-up. These implanted metal fiducials are 3 to 4 mm long and are used to accurately target radiation from the CyberKnife. These markers must be implanted during a short 10 to 15 minute outpatient procedure prior to the CT scan.

Treatment planning
Treatment planning is the process through which physicians and the medical physicist plan the details of radiation delivery to a tumor or other lesion. With most frame-based radiosurgical systems, the physician relies on his prior experience and intuition to design an effective treatment dose for a specific target.

In contrast, CyberKnife treatment planning utilizes both physician and physicist experience, but also harnesses the massive computing power of high-speed computers to develop an optimal pattern of radiation. During the CyberKnife treatment planning process, once the physician/physicist has determined the volume and dose of radiation, the CyberKnife computer performs millions of calculations to determine the best radiation delivery plan.

The CyberKnife’s treatment planning system exploits the robot's high degree of maneuverability to allow a more even delivery of radiation throughout a tumor than can be achieved by older frame-based radiosurgical systems.

Treatment Delivery
At some point after planning, the patient returns for treatment delivery. The CyberKnife treatment follows the following basic format. The patient is fitted with the custom plastic mask (for cranial tumors) or body cradle (for spinal tumors) and lies on the treatment table. Prior to beginning the actual radiation treatment, the imaging system acquires digital x-rays of the patient position.

This information is used to move the linear accelerator to the appropriate position. Subsequently, the robot moves and re-targets the linear accelerator at a large number of positions around the patient. At each position or “node”, a small radiation beam is delivered.

This process is repeated at 50 to 300 different positions around the patient to complete the treatment. At various intervals, the linear accelerator stops and additional pictures are obtained of the patient, thereby allowing the CyberKnife to track and compensate for small amounts of patient movement. These intervals can be as frequent as every node.

The entire process is painless, and it typically takes between 30 to 90 minutes to deliver all radiation beams. Most typically a patient can go home immediately upon completion and return to normal activities. If the treatment prescription is for staged (fractionated) radiosurgery, the patient will return on a separate visit and repeat the above process for treatment delivery.

Perhaps most importantly, CyberKnife technology is finally making it possible to perform radiosurgery at almost any location within the body.