The CyberKnife is a frameless robotic
Medical robots
Medical Robots are robots that allow doctors greater and more precise and less-invasive access to area of operations. They are in most telemanipulators which use doctor’s action on one side and an "effector" on the other side. Their task is to control the movements of the doctor's work and decide...

Radiosurgery is a medical procedure that allows non-invasive treatment of benign and malignant tumors. It is also known as stereotactic radiotherapy, when used to target lesions in the brain, and stereotactic body radiotherapy when used to target lesions in the body...

 system used for treating benign tumors, malignant tumors and other medical conditions. The system was invented by John R. Adler
John R. Adler
John R. Adler M.D. is a neurosurgeon, the Dorothy and Thye King Chan Endowed Professor of Neurosurgery at Stanford University School of Medicine and Vice Chair for Innovation and Technology in the Department of Neurosurgery at Stanford University School of Medicine.Clinically, Dr. Adler...

, a Stanford University
Stanford University
The Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...

 Professor of Neurosurgery and Radiation Oncology, and Peter and Russell Schonberg of Schonberg Research Corporation. The two main elements of the CyberKnife are (1) the radiation produced from a small linear particle accelerator
Linear particle accelerator
A linear particle accelerator is a type of particle accelerator that greatly increases the velocity of charged subatomic particles or ions by subjecting the charged particles to a series of oscillating electric potentials along a linear beamline; this method of particle acceleration was invented...

 and (2) a robotic arm which allows the energy to be directed at any part of the body from any direction.

The CyberKnife system is a method of delivering radiotherapy, with the intention of targeting treatment more accurately than standard radiotherapy.

Main features

Several generations of the CyberKnife system have been developed since its initial inception in 1990. There are two essential features of the CyberKnife system that set it apart from other stereotactic therapy
Stereotactic surgery
Stereotactic surgery or stereotaxy is a minimally invasive form of surgical intervention which makes use of a three-dimensional coordinates system to locate small targets inside the body and to perform on them some action such as ablation, biopsy, lesion, injection, stimulation, implantation,...


Robotic mounting

The first is that the radiation source is mounted on a general purpose industrial robot. The original CyberKnife used a Japanese Fanuc robot, however the more modern systems use a German KUKA
KUKA is a leading German producer of industrial robots for a variety of industries - from automotive and fabricated metals to food and plastics...

 KR 240. Mounted on the Robot is a compact X-band linac that produces 6MV X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

 radiation. The linac is capable of delivering approximately 600 cGy
Gray (unit)
The gray is the SI unit of absorbed radiation dose of ionizing radiation , and is defined as the absorption of one joule of ionizing radiation by one kilogram of matter ....

 of radiation each minute - a new 800 cGy / minute model was announced at ASTRO
American Society for Therapeutic Radiology and Oncology
ASTRO is the American Society for Radiation Oncology. The largest organization in its field in the world, ASTRO has a membership of over 10,000 covering a range of professions including Radiation Oncologist, Radiation Therapists, Medical Dosimetrists, Medical Physicists, Radiation Oncology Nurses...

 2007. The radiation is collimated using fixed tungsten collimators (also referred to as “cones”) which produce circular radiation fields. At present the radiation field sizes are: 5, 7.5, 10, 12.5, 15, 20, 25, 30, 35, 40, 50 and 60 mm
The millimetre is a unit of length in the metric system, equal to one thousandth of a metre, which is the SI base unit of length....

. ASTRO 2007 also saw the launch of the IRIS variable-aperture collimator which uses two offset banks of six prismatic tungsten segments to form a blurred regular dodecagon field of variable size which eliminates the need for changing the fixed collimators. Mounting the radiation source on the robot allows near-complete freedom to position the source within a space about the patient. The robotic mounting allows very fast repositioning of the source, which enables the system to deliver radiation from many different directions without the need to move both the patient and source as required by current gantry configurations.

Image guidance

The image guidance system is the other essential item in the CyberKnife system. X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

 imaging cameras are located on supports around the patient allowing instantaneous X-ray images to be obtained.

6D skull

The original (and still utilized) method is called 6D or skull based tracking. The X-ray camera images are compared to a library of computer generated images of the patient anatomy. Digitally Reconstructed Radiographs (or DRR's) and a computer algorithm determines what motion corrections have to be given to the robot because of patient movement. This imaging system allows the CyberKnife to deliver radiation with an accuracy of 0.5mm without using mechanical clamps attached to the patient's skull. The use of the image guided technique is referred to as frameless stereotactic radiosurgery. This method is referred to as 6D because corrections are made for the 3 translational motions (X,Y and Z) and three rotational motions. It should be noted that it is necessary to use some anatomical or artificial feature to orient the robot to deliver X-ray radiation, since the tumor is never sufficiently well defined (if visible at all) on the X-ray camera images.


Additional image guidance methods are available for spinal tumors and for tumors located in the lung. For a tumor located in the spine, a variant of the image guidance called Xsight-Spine is used. The major difference here is that instead of taking images of the skull, images of the spinal processes are used. Whereas the skull is effectively rigid and non-deforming, the spinal vertebrae can move relative to each other, this means that image warping algorithms must be used to correct for the distortion of the X-ray camera images.

A recent enhancement to Xsight is Xsight-Lung which allows tracking of some lung tumors without the need to implant fiduciary marker
Fiduciary marker
A fiducial marker or fiducial is an object used in the field of view of an imaging system which appears in the image produced, for use as a point of reference or a measure...



For soft tissue tumors, a method known as fiducial tracking can be utilized. Small metal markers (fiducials) made out of gold for bio-compatibility and high density to give good contrast on X-ray images are surgically implanted in the patient. This is carried out by an interventional radiologist, or neurosurgeon. The placement of the fiducials is a critical step if the fiducial tracking is to be used. If the fiducials are too far from the location of the tumor, or are not sufficiently spread out from each other it will not be possible to accurately deliver the radiation. Once these markers have been placed, they are located on a CT scan and the image guidance system is programmed with their position. When X-ray camera images are taken, the location of the tumor relative to the fiducials is determined, and the radiation can be delivered to any part of the body. Thus the fiducial tracking does not require any bony anatomy to position the radiation. Fiducials are known however to migrate and this can limit the accuracy of the treatment if sufficient time is not allowed between implantation and treatment for the fiducials to stabilize.


The final technology of image guidance that the CyberKnife system can use is called the Synchrony system. The Synchrony system is utilized primarily for tumors that are in motion while being treated, such as lung tumors and pancreatic tumors.

The synchrony system uses a combination of surgically placed internal fiducials, and light emitting optical fibers (markers) mounted on the patient skin. Since the tumor is moving continuously, to continuously image its location using X-ray cameras would require prohibitive amounts of radiation to be delivered to the patients skin. The Synchrony system overcomes this by periodically taking images of the internal fiducials, and predicting their location at a future time using the motion of the markers that are located on the patient's skin. The light from the markers can be tracked continuously using a CCD camera, and are placed so that their motion is correlated with the motion of the tumor.

A computer algorithm creates a correlation model that represents how the internal fiducial markers are moving compared to the external markers. The Synchrony system is therefore continuously predicting the motion of the internal fiducials, and therefore the tumor, based on the motion of the markers. The correlation model can be updated at any time if the patient breathing becomes in any way irregular. The advantage of the Synchrony system is that no assumptions about the regularity or reproducibility of the patient breathing have to be made.

To function properly, the Synchrony system requires that for any given correlation model there is a functional relationship between the markers and the internal fiducials. The external marker placement is also important, and the markers are usually placed on the patient abdomen so that their motion will reflect the internal motion of the diaphragm and the lungs.


A new robotic six degree of freedom patient treatment couch called RoboCouch has been added to the CyberKnife which provides the capability for significantly improving patient positioning options for treatment.


The frameless nature of the CyberKnife also increases the clinical efficiency. In conventional frame-based radiosurgery, the accuracy of treatment delivery is determined solely by connecting a rigid frame to the patient which is anchored to the patient’s skull with invasive aluminum or titanium screws. The CyberKnife is the only radiosurgery device that does not require such a frame for precise targeting. Once the frame is connected, the relative position of the patient anatomy must be determined by making a CT or MRI scan. After the CT or MRI scan has been made, a radiation oncologist
Radiation oncologist
A radiation oncologist is a doctor who specializes in the treatment of cancer patients, using radiation therapy as the main modality of treatment. Radiation can be given as a curative modality, either alone or in combination with surgery and/or chemotherapy. It may also be used palliatively, to...

 must plan the delivery of the radiation using a dedicated computer program, after which the treatment can be delivered, and the frame removed. The use of the frame therefore requires a linear sequence of events that must be carried out sequentially before another patient can be treated. Staged CyberKnife radiosurgery is of particular benefit to patients who have previously received large doses of conventional radiation therapy and patients with gliomas located near critical areas of the brain. Unlike whole brain radiotherapy, which must be administered daily over several weeks, radiosurgery treatment can usually be completed in 1-5 treatment sessions. Radiosurgery can be used alone to treat brain metastases, or in conjunction with surgery or whole brain radiotherapy, depending on the specific clinical circumstances.

By comparison, using a frameless system, a CT scan can be carried out on any day prior to treatment that is convenient. The treatment planning can also be carried out at any time prior to treatment. During the treatment the patient need only be positioned on a treatment table and the predetermined plan delivered. This allows the clinical staff to plan many patients at the same time, devoting as much time as is necessary for complicated cases without slowing down the treatment delivery. While a patient is being treated, another clinician can be considering treatment options and plans, and another can be conducting CT scans.

In addition, very young patients (pediatric cases) or patients with fragile heads because of prior brain surgery cannot be treated using a frame based system. Also, by being frameless the CyberKnife can efficiently re-treat the same patient without repeating the preparation steps that a frame-based system would require.

The delivery of a radiation treatment over several days or even weeks (referred to as fractionation) can also be beneficial from a therapeutic point of view. Tumor cells typically have poor repair mechanisms compared to healthy tissue, so by dividing the radiation dose into fractions the healthy tissue has time to repair itself between treatments. This can allow a larger dose to be delivered to the tumor compared to a single treatment.

Gamma Knife

One of the most widely known stereotactic radiosurgery systems is the Gamma Knife. The Gamma Knife was originally developed by Lars Leksell
Lars Leksell
Lars Leksell was a Swedish physician and Professor of Neurosurgery at the Karolinska Institute in Stockholm, Sweden. He was the inventor of radiosurgery.-Life and work:...

, remains the gold standard method for delivery of stereotactic radiosurgery to the brain and is manufactured by Elekta
Elekta is a swedish company that provides radiation therapy, radiosurgery, related equipment and clinical management for the treatment of cancer and brain disorders.-History:...

. John Adler, the inventor of the CyberKnife system spent time training with Lars Leksell in Stockholm at the Karolinska Institute in 1985.
The GammaKnife system uses 201 Cobalt-60 sources located in a ring around a central treatment point ("isocenter"). The Gamma Knife system is equipped with a series of 4 collimators of 4mm, 8mm, 12mm and 16mm diameter, and is capable of submillimeter accuracies. The Gamma Knife system does however require a head frame to be bolted onto the skull of the patient, and is only capable of treating cranial lesions. As a result of frame placement, treatment with Gamma Knife does not require real time imaging capability as the frame does not allow movement during treatment. This is the reason that the Gamma Knife system is likely to be more accurate than Cyber Knife. The Cyberknife Society and Accuray maintain that there are no peer-reviewed published papers that establish Gamma Knife as being more accurate than CyberKnife.


Another popular Stereotactic system is the Novalis produced by Brainlab. The Novalis radiosurgery system utilizes a small computer controlled micro Multi Leaf Collimator mMLC, that can produce many complicated shapes. The maximum radiation field size that the Novalis can produce is 98 mm x 98 mm, and the minimum is 3mm x 3mm allowing a considerable range of tumors to be treated. The Novalis system also has X-ray imaging using amorphous silicon flat panel X-ray detectors. A 2D/3D image fusion of the patient setup X-rays with digitally reconstructed radiographs from a planning CT scan quickly determines a correction vector for the patients position. Infrared fiducial markers attached to the patient then allow precise tracking of the correction vector's application to the patient's position via an infrared camera and a couch that can move in all six dimensions enables the precise positioning of the patient. Patient immobilization can also be performed framelessly using the patients internal anatomy as the frame of reference. An implanted marker based respiratory tracking option known as ExacTrac Gating is also an option. BrainLAB's Novalis has become a leading player in the world of neurosurgery.

Conventional linac

Conventional X-ray therapy linear accelerators can be utilized for radiosurgery, either by the use of additional blocking cones or by a removable or built in micro MLC system.
Examples of removable micro MLC units are the Ergo from 3D line, the mMLC manufactured by Brainlab, and the AccuKnife produced by Direx., or the Novalis TX

Clinical uses

Since August 2001, the CyberKnife system has FDA clearance for treatment of tumors in any location of the body. Some of the tumors treated include:
The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...

The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

The prostate is a compound tubuloalveolar exocrine gland of the male reproductive system in most mammals....

Spinal Lesions,
head and neck cancers,
and benign tumors.

None of these studies have shown any general survival benefit over conventional treatment methods. By increasing the accuracy with which treatment is delivered there is a potential for dose escalation, and potentially a subsequent increase in effectiveness, particularly in local control rates. However the studies cited are so far limited in scope, and more extensive research will need to be completed in order to show any effects on survival.

In 2008 actor Patrick Swayze
Patrick Swayze
Patrick Wayne Swayze was an American actor, dancer and singer-songwriter. He was best known for his tough-guy roles, as romantic leading men in the hit films Dirty Dancing and Ghost, and as Orry Main in the North and South television miniseries. He was named by People magazine as its "Sexiest...

 was among the people to be treated with Cyberknife radiotherapy.

Cyberknife worldwide locations

CyberKnife systems have been installed in over 150 locations worldwide, including 100 hospitals in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...


Stanford University has treated over 2,500 patients using the Cyberknife system, and worldwide over 40,000 patients have been treated.

Overlook Hospital in Summit, New Jersey
New Jersey
New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...

 was the first hospital in the New York metro area to offer the CyberKnife Stereotactic Radiosurgery System. Today, Overlook has performed the second most treatments of prostate cancer
Prostate cancer
Prostate cancer is a form of cancer that develops in the prostate, a gland in the male reproductive system. Most prostate cancers are slow growing; however, there are cases of aggressive prostate cancers. The cancer cells may metastasize from the prostate to other parts of the body, particularly...

 with the cyberknife in the world.


The CyberKnife was recognized as an Innovative Medical Device in the 10th Annual Innovations in HealthcareSM ABBY Awards event. These awards are given based on reducing the cost of quality healthcare. "...proven with their CyberKnife Robotic Radiosurgery System that medical technology can actually lower the cost of providing quality healthcare -- and at the same time produce a result that saves time for the patient, not to mention providing a 'scarless' result," Mimi Grant, president of the ABL Organization

See also

  • Horsley–Clarke apparatus
  • Gamma knife
  • Novalis radiosurgery
  • Robotic surgery
    Robotic surgery
    Robotic surgery, computer-assisted surgery, and robotically-assisted surgery are terms for technological developments that use robotic systems to aid in surgical procedures....

  • NCI-designated Cancer Center
    NCI-designated Cancer Center
    NCI-designated Cancer Centers are a group of approximately 66 cancer research institutions in the United States supported by the National Cancer Institute....

    s in the United States

External links

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