CyberKnife Information for Physicians

Why is CyberKnife Radiosurgery Different?


Using image-guidance, robotics and dynamic respiratory motion tracking, the CyberKnife® System delivers superior accuracy and conformality to lesions throughout the body. Developed by Accuray and FDA approved for full body use in 2001, it is the first device to enable full-body dynamic radiosurgery. CyberKnife® is making possible effective new treatments in clinical areas such as spine, lung, liver, pancreas and prostate lesions.


The CyberKnife® System utilizes a robotic manipulator to move the compact linear accelerator with six degrees of freedom. With this range of motion, the robotic manipulator is capable of positioning the linear accelerator to an infinite number of beam positions and orientations. This creates the ability to accurately adjust the beam to react to three-dimensional translational and rotational target volume displacements, providing treatment flexibility and accuracy that is unsurpassed in radiosurgery. Such versatility allows both non-isocentric and isocentric treatment of lesions and enables superior conformality.


The CyberKnife® System tracks position in tumors that move with respiration in real time, by synchronizing radiation delivery to the motion of the respiratory cycle, using a sophisticated combined optical and radiographic tracking system. This 4D tracking capability is unique to the CyberKnife® and not only makes treatment with the CyberKnife® significantly more comfortable for patients, but safer, faster and more accurate as well.


Image-guided CyberKnife® radiosurgery is non-invasive and 100% frameless. Since treatments can be delivered in single or fractionated sessions, CyberKnife® offers optimum protection for adjacent critical structures. Unlike traditional radiosurgery devices, the CyberKnife® systems tracks internal reference points. In this way the CyberKnife® automatically detects and compensates for patient and tumor movement in real time, with updated image guidance at every beam position.

CyberKnife Radiosurgery Benefits

  • Extremely accurate radiation targeting means a biologically ablative dose of radiation can be used, offering the patient a better chance for a cure
  • No invasive head frame or other rigid immobilization device is required
  • The ability to perform radiosurgery (1-5 fractions) on targets throughout the body, not just the brain
  • Precise targeting (within 1 mm) of selected lesions in the brain and body
  • A unique ability to provide real time monitoring of the treated target throughout treatment using an advanced image-guidance system
  • Continually checks and compensates for any movement made during treatments, ensuring accuracy
  • The capacity to perform fractionated radiosurgery
  • Eliminates risks related to surgery, including potential infection, complication from anesthesia and post-operative bleeding
  • Requires no recovery time. Treatments are done on an outpatient basis
  • Patients undergo their treatment and immediately resume normal daily activities
  • Painless treatment
  • Requires minimal or no sedation
  • No Incisions
  • Low risk of complications
  • Improved quality of life

Technical Information


The compact X-band linear accelerator emits circular beams with secondary collimation ranging from 5 mm to 60 mm. This compact lightweight system allows for precisely delivered pencil-shaped beams of radiation in almost any direction, providing superior conformality when treating patients.


The robotic manipulator used by the CyberKnife® System is made by Kuka™, one of the leading robot manufactures in the world. This high-precision robot is capable of delivering a repeatability accuracy of less than 0.2 mm.


The low-energy x-ray sources generate two perpendicular, oblique diagnostic x-rays that determine the location of bony landmarks or implanted radiopaque markers throughout the entire treatment.


The high-resolution image detectors capture x-ray images and generate digital images of the anatomy. These images which are taken throughout the treatment are compared to the digitally reconstructed radiographs (DRRs) generated from the CT scans used for treatment planning. The imaging system then determines the patient’s position and sends a command to the robotic manipulator to correct for movement.


The AXUM™ Automatic Patient Positioning System automatically and accurately aligns patients in one simple step, significantly reducing patient setup times and increasing patient throughput.


The Synchrony Respiratory Tracking System is the first technology in the world capable of delivering radiosurgery to targets that move with respiration. The CyberKnife® System synchronizes the Robotic Delivery System to the motion of the tumor so margins of less than a millimeter are needed in order to compensate for respiratory motions.


CyRIS™ Treatment Planning includes fast, multi-modality image fusion with simplified contouring. Supports forward and inverse planning methods and achieves desired plan results quickly andefficiently. Streamlines overall planning process to maximize the capabilities of CyberKnife® System.


With CyRIS InView, physicians are able to perform fusion, contouring and dose review in the comfort of their own office or other remote location.

Treatment Process

We believe CyberKnife® technology has revolutionized stereotactic radiosurgery and we are committed to serving the needs of physicians looking to give their patients the most effective treatment options available.

Communication is key at the CyberKnife Centers of San Diego. We work closely with referring physicians to keep them up-to-date on their patients.

Contact us with questions or to arrange a tour

For questions about how CyberKnife® may benefit your patients, how to arrange a consultation or referral, or how to schedule a personalized tour of one of our centers please call us at 858-505-4100 or 800-470-1256.


Fiducial markers are gold seeds or stainless steel screws that are implanted in and/or around a soft tissue tumor, or within the bony spine, to act as a radiologic landmark, to define the target lesion’s position with millimeter precision. They are typically placed using a CT  or other image-guided percutaneous method. There may be other appropriate fiducial placement methods as well, including endoscopic or surgical approaches, if determined best by the participating physicians. To track lesions in 6 degrees (translational and rotational movements), fiducials may be recommended, depending upon the exact circumstance and lesion. Fiducials must be fixed relative to other fiducials and relative to the tumor to ensure targeting accuracy

Approved Fiducials

    • Stainless Steel Screw (2.0 x 5.0mm) embedded within bone. Self-drilling and self-tapping screws provide optimal contrast again the bone and minimize migration. These are typically used for spine applications.
    • Gold Seeds ( 0.8 mm x 5 mm) are typically used for soft tissue lesions

Specific Clinical Situations Potentially Requiring Fiducial Placement

    • Spine lesions – In cases where spine fiducials are required, we will normally recommend 3-6 Stainless Steel Screws, placed by a neurosurgeon or interventional radiologist. In some cases, only one screw may be required, and in still other cases, due to an advanced CyberKnife® software feature known as X-Sight®, there may be no fiducials required. The patient’s attending doctors will individualize the recommended fiducial approach for each CyberKnife® spine case. If neurosurgical spine stabilization is required, any required fiducial screws may be integrated into that same surgical procedure, eliminating a separate fiducial placement step for the patient.
    • Head and Neck soft tissue lesions – In these cases, 3-6 fiducial seeds may be placed under anesthesia by the participating head and neck surgeon, or percutaneously by a radiologist under CT or other radiologic guidance. Depending upon the initial clinical presentation, it may be feasible for the head and neck surgeon or radiologist to place the CyberKnife® targeting fiducials at the time of the patient’s original biopsy, if clinical suspicion is high and potential CyberKnife® use is anticipated, avoiding the need for a separate fiducial placement procedure.
    • Intrathoracic lesions (e.g. NSCLC) – The majority of Intrathoracic lesions will be lung cancers but the specific fiducial requirement will vary according to the specific clinical presentation.
      • Peripheral pulmonary nodules – Typically, these lesions will be targeted using 3-6 transthoracically placed CT-guided fiducials. In certain clinical situations where the nodule is small and the medical risk high, it may be acceptable to place a single fiducial for translational motion tracking only. Because there is a pneumothorax risk with the transthoracic CT-guided approach, this will ordinarily be done in a hospital setting, and the patient observed for a period of time. If no pneumothorax ensues the patient will be discharged the same day and treatment planning will ensue approximately one week later. If a pneumothorax does ensue, depending upon its severity, an overnight hospital stay with a chest tube may be required for stabilization, after which the patient will be discharged and CT +/- PET based CyberKnife® treatment planning will then ensue approximately 7 days later.
      • Central or recurrent lesions – Central intrathoracic lesions such as endobronchial or mediastinal presentations may be effectively targeted for fiducial placement bronchoscopically or transesophageally, greatly reducing the pneumothorax risk. Depending upon the initial clinical presentation, it may also be feasible for the pulmonologist or thoracic surgeon to place the CyberKnife® targeting fiducials at the time of the patient’s original biopsy, if clinical suspicion is high and potential CyberKnife® use is anticipated, avoiding the need for a separate fiducial placement procedure. CT +/- PET based CyberKnife® treatment planning will then ensue approximately 7 days after fiducial placement.
    • Liver, Pancreatic, Retroperitoneal and Kidney Lesions – These will ordinarily be marked using CT-guided fiducial placement technique, delivering 3-6 seed fiducials in and around the target lesion. If surgical exploration is otherwise indicated then open or laparoscopic fiducial placement may also be accomplished at the time of surgical exploration in lieu of scheduling a separate invasive CT procedure. CT +/- PET based CyberKnife® treatment planning will then ensue approximately 7 days later.
    • Prostate Cancer – Typically, 3-6 seed fiducials will be placed in the prostate using ultrasound guidance, either transrectally or transperineally, by the urologist or radiation oncologist. CT +/- co-registered MRI CyberKnife® treatment planning will then ensue approximately 7 days later.
    • Miscellaneous – Invariably, there will arise some sort of tumor situation that is not specifically addressed by any of the fiducial placement protocols described above.  In such a case the patient’s participating physicians will decide the most effective fiducial placement and treatment planning approach.
    • Technology note – Over time, as the CyberKnife® device continues to evolve, improved software and image-processing capability may eliminate the need for fiducials in some cases, though at present, fiducials are required for all non-cranial lesions, except for X-Sight targeted spine lesions.
  • Key Fiducial Placement Principles
    • Implant 3 – 6 fiducials with a minimum of 2.0 cm spacing between fiducials to minimize uncertainty in measuring rotation. They should be placed no more than 5 -6 cm from lesion (20 cm FOV for live images)
    • There must be at least a 15° angle between any grouping of 3 fiducials – not collinear –  encompassing the tumor volume
    • In soft tissue, use gold seeds and place 3 – 6 fiducials around the perimeter of the tumor, 2 -3 cm apart.
    • If hardware or other radio-opaque materials are present, place the fiducial above, below or lateral to and not along the axis of the X-ray tracking system (i.e. – Do not place fiducial(s) at or near 45 degrees axial orientation from the potentially obstructing hardware).


Any fiducial migration will degrade the accuracy of fiducial-based targeting. If CyberKnife® targeting fiducials migrate more than 1.5 mm from time of CyberKnife® CT planning to actual CyberKnife® treatment, it may render the patient untreatable without repeating the entire CyberKnife® treatment planning process.

As there may be some migration or “settling” of fiducials for up to 7 days following their placement into soft tissue, it is recommended that the CyberKnife® planning CT study be obtained approximately 7 days after fiducial placement for soft tissue lesions, to allow them to settle into stable position. For spine lesions, where fiducials are anchored into bone, the planning CT may be accomplished as soon as the following day. Once the CyberKnife® planning CT has been accomplished, the time to the actual CyberKnife® treatment itself should be minimized, to reduce the probability of fiducial mis-registration between the planning and treatment stage due to additional potential fiducial migration.

Written by Donald B. Fuller, M.D. – Radiation Oncologist – Genesis Healthcare – 2012 © All Rights Reserved