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The CyberKnife is a frameless robotic radiosurgery system used for treating benign tumors, malignant tumors and other medical conditions.[1][2] The system was invented by John R. Adler, a Stanford University professor of neurosurgery and radiation oncology, and Peter and Russell Schonberg of Schonberg Research Corporation. It is made by the Accuray company headquartered in Sunnyvale, California.

The CyberKnife system is a method of delivering radiotherapy, with the intention of targeting treatment more accurately than standard radiotherapy.[3] The two main elements of the CyberKnife are (1) the radiation produced from a small linear particle accelerator and (2) a robotic arm which allows the energy to be directed at any part of the body from any direction.

The main features of the CyberKnife system, shown on a Fanuc robot

Main features[edit]

Several generations of the CyberKnife system have been developed since its initial inception in 1990. There are two major features of the CyberKnife system that are different from other stereotactic therapy methods.

Robotic mounting[edit]

The first is that the radiation source is mounted on a general purpose industrial robot. The original CyberKnife used a Japanese Fanuc robot,[4] however the more modern systems use a German KUKA KR 240.[5] Mounted on the Robot is a compact X-band linac that produces 6MV X-ray radiation. The linac is capable of delivering approximately 600 cGy of radiation each minute - a new 800 cGy / minute model was announced at ASTRO[6][7] 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. ASTRO 2007 also saw the launch of the IRIS[7] 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[edit]

The CyberKnife system uses an image guidance system. X-ray imaging cameras are located on supports around the patient allowing instantaneous X-ray images to be obtained.

6D skull[edit]

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.[8] 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.

6D Skull tracking


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[9] 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[10] which allows tracking of some lung tumors without the need to implant fiducial markers.[11]


For soft tissue tumors, a method known as fiducial tracking can be utilized.[12] 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.[13][14]


The final technology of image guidance that the CyberKnife system can use is called the Synchrony system or Synchrony method. The synchrony method uses a combination of surgically placed internal fiducials (typically small gold markers, well visible in x-ray imaging), and light emitting optical fibers (LED markers) mounted on the patient skin. LED markers are tracked by an infrared tracking camera. 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 patient's skin. The Synchrony system overcomes this by periodically taking images of the internal fiducials, and computing a correlation model between the motion of the external LED markers and the internal fiducials. Time stamps from the two sensors (x-ray and infrared LED) are needed to synchronize the two data streams, hence the name Synchrony. Motion prediction is used to overcome the motion latency of the robot and the latency of image acquisition. Before treatment, a computer algorithm creates a correlation model that represents how the internal fiducial markers are moving compared to the external markers. During treatment, the system continuously infers the motion of the internal fiducials, and therefore the tumor, based on the motion of the skin markers. The correlation model is updated at fixed time steps during treatment. Thus, the Synchrony tracking method makes no assumptions about the regularity or reproducibility of the patient breathing pattern. 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. The synchrony method was invented in 1998.[15][16] The first patients were treated at Cleveland Clinic in 2002. Synchrony is utilized primarily for tumors that are in motion while being treated, such as lung tumors and pancreatic tumors.[17] [18]


A new robotic six degree of freedom patient treatment couch called RoboCouch[19] 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.[20] 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 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.[21]

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.[22] 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.[23] This can allow a larger dose to be delivered to the tumor compared to a single treatment.[24]

Clinical uses[edit]

Since August 2001, the CyberKnife system has FDA clearance for treatment of tumors in any location of the body.[25] Some of the tumors treated include: pancreas,[26][27] liver,[28] prostate,[29][30] spinal lesions,[31] head and neck cancers,[32] and benign tumors.[33]

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.[27]

In 2008 actor Patrick Swayze was among the people to be treated with CyberKnife radiosurgery.[34]

Worldwide locations[edit]

CyberKnife systems have been installed in over 150 locations worldwide,[35] including 100 hospitals in the United States.[36]

Recently - April 2014 - CyberKnife has been installed at Sir Charles Gairdner Hospital, Perth, Australia. (More Information)

Stanford University has treated over 2,500 patients using the Cyberknife system, and worldwide over 40,000 patients have been treated.[37][38]

The CyberKnife Centre at the Harley Street Clinic in London was the first in the UK to offer this treatment performed by Professor Christopher Nutting in 2009. The Freemasons in London, UK, have paid for a CyberKnife to be placed in Barts Hospital, and it is available to all on the National Health Service. The Queen Elizabeth Hospital in Birmingham have recently bought a CyberKnife, the first NHS hospital outside of London to acquire one. The Royal Marsden NHS Foundation Trust has a CyberKnife at their Chelsea, London site.

Overlook Hospital in Summit, New Jersey 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 with the CyberKnife in the world.[39] Anova Cancer Care in Denver, Colorado, has been acknowledged as the world leader in prostate cancer radiosurgery as of 2013.

Recently - Nov 2013 - CyberKnife VSI has been installed in Hermitage Medical Clinic, Dublin Ireland

There is a CyberKnife machine in Hong Kong Adventist Hospital (private service and expensive price) in Hong Kong.

The first next generation CyberKnife VSI in Asia at BLK CyberKnife in New Delhi India.

SRS Cyberknife is also available in Pakistan at Jinnah Post-Graduate Medical Centre Karachi, the only place where it is offered free of cost.

In January 2013, the first patients were treated with the new generation CyberKnife M6 in Munich, Germany, at the European CyberKnife Center Munich.

In Malaysia, Beacon Hospital (Beacon International Specialist Centre) which specialises in oncology, provides Cybernknife treatment as one of their few treatments on cancer. It has been operating since 2005 as a boutique medical centre.[40] Beacon Hospital also provides Corporate Social Responsibilities (CSR) programme to help underprivileged patients who cannot afford radiotherapy treatments.[41]

See also[edit]


  1. ^ Stanford Neurosurgery[dead link]
  2. ^ Robotic Whole Body Stereotactic Radiosurgery: Clinical Advantages of the CyberKnife Integrated System. . . . Reprinted by permission from The International Journal of Medical Robotics and Computer Assisted Surgery - Robotics Online
  3. ^ Dr Nick Plowman, Senior Clinical Oncologist, London HCA - How CyberKnife Works
  4. ^ Fanuc Robotics
  5. ^ Kuka Roboter GmbH
  6. ^ ASTRO annual meeting website
  7. ^ a b Accuray announce 4 new products at ASTRO
  8. ^ An Analysis of the Accuracy of the 6D Tracking With CyberKnife Inoue M, Sato K, Koike I International Journal of Radiation Oncology, Biology, Physics 1 November 2006 (Vol. 66, Issue 3 (Supplement), Page S611)
  9. ^ Accuray::Xsight Spine Tracking System
  10. ^ Accuray::Xsight Lung Tracking System
  11. ^ Schweikard, A., H. Shiomi, and J. Adler. "Respiration tracking in radiosurgery without fiducials." The International Journal of Medical Robotics and Computer Assisted Surgery 1.2 (2005): 19-27, PMID 17518375
  12. ^ CyberKnife Radiosurgery - Fiducial Overview
  13. ^ Fuller CD, and Scarbrough TJ, MD Fiducial Markers in Image-guided Radiotherapy of the Prostate. U S ONCOLOGICAL DISEASE 2006 75-78
  14. ^ Murphy MJ. Fiducial-based targeting accuracy for external-beam radiotherapy. Medical Physics March 2002 Volume 29, Issue 3, pp. 334–344
  15. ^ Schweikard, A., Glosser, G., Bodduluri, M., Murphy, M. J., & Adler, J. R. (2000). Robotic motion compensation for respiratory movement during radiosurgery. Computer Aided Surgery, 5(4), 263-277, PMID 11029159
  16. ^ Schweikard, Achim, Hiroya Shiomi, and John Adler. "Respiration tracking in radiosurgery." Medical physics 31.10 (2004): 2738-2741, PMID 15543778
  17. ^ Alexander Muacevic , Markus Kufeld , B. Wowra , H. Winter , H. T. Hofmann: Single-Session Lung Radiosurgery Using Robotic Image-Guided Real-Time Respiratory Tumor Tracking. Cureus ( 9 December 2009
  18. ^ Phase I study of stereotactic radiosurgery in patients with locally advanced pancreatic cancer Koong AC, Le QT, Ho A, Fong B, Fisher G, Cho C, Ford J, Poen J, Gibbs IC, Mehta VK, Kee S, Trueblood W, Yang G, Bastidas JA International Journal of Radiation Oncology*Biology*Physics 15 March 2004 (Vol. 58, Issue 4, Pages 1017–1021)
  19. ^ Accuray::RoboCouch Patient Positioning System
  20. ^ Rocky Mountain CyberKnife Center - Brain Metastases
  21. ^ Chang SD, Min W, Martin DP, Gibbs IC, Heilbrun MP. An analysis of the accuracy of the CyberKnife: A robotic frameless stereotactic radiosurgical system. Neurosurgery. 2003; 52: 140-147.
  22. ^
  23. ^ Radiobiology for the Radiologist Eric J. Hall Lippincott Williams & Wilkins; 5th edition (2000)
  24. ^ Comparisons between Gamma Knife, Novalis by Brainlab and Cyberknife
  25. ^ "CyberKnife::Reimbursement Information." CyberKnife. Web. 10 Mar. 2010.<>
  26. ^ Phase I study of stereotactic radiosurgery in patients with locally advanced pancreatic cancer. Koong AC, Le QT, Ho A, Fong B, Fisher G, Cho C, Ford J, Poen J, Gibbs IC, Mehta VK, Kee S, Trueblood W, Yang G, Bastidas JA. International Journal of Radiation Oncology*Biology*Physics, 15 March 2004 (Vol. 58, Issue 4, Pages 1017–1021)
  27. ^ a b Phase II study to assess the efficacy of conventionally fractionated radiotherapy followed by a stereotactic radiosurgery boost in patients with locally advanced pancreatic cancer. Koong AC, Christofferson E, Le QT, Goodman KA, Ho A, Kuo T, Ford JM, Fisher GA, Greco R, Norton J, Yang GP. International Journal of Radiation Oncology*Biology*Physics, 1 October 2005 (Vol. 63, Issue 2, Pages 320-323)
  28. ^ Phase I Dose Escalation Study of CyberKnife Stereotactic Radiosurgery for Liver Malignancies. Lieskovsky YC, Koong A, Fisher G, Yang G, Ho A, Nguyen M, Gibbs I, Goodman K.International Journal of Radiation Oncology*Biology*Physics, 1 October 2005 (Vol. 63, Issue (Supplement 1), Page S283)
  29. ^ 2206: Hypofractionated Stereotactic Radiotherapy for Prostate Cancer: Early Results. Hara W, Patel D, Pawlicki T, Cotrutz C, Presti J, King C. International Journal of Radiation Oncology, Biology, Physics, 1 November 2006 (Vol. 66, Issue 3 (Supplement), Pages S324-S325)
  30. ^ Wall street Journal - November 2008 - Is CyberKnife Ready for Prime Time in Prostate Cancer?
  31. ^ Cyberknife frameless real-time image-guided stereotactic radiosurgery for the treatment of spinal lesions. Gerszten PC, Ozhasoglu C, Burton SA, Vogel WJ, Atkins BA, Kalnicki S, Welch WC. International Journal of Radiation Oncology*Biology*Physics, 1 October 2003 (Vol. 57, Issue 2 (Supplement), Pages S370-S371)
  32. ^ CyberKnife Fractionated Stereotactic Radiosurgery for the Treatment of Primary and Recurrent Head and Neck Cancer. Liao JJ, Judson B, Davidson B, Amin A, Gagnon G, Harter K. International Journal of Radiation Oncology*Biology*Physics, 1 October 2005 (Vol. 63, Issue (Supplement 1), Page S381)
  33. ^ Cyberknife frameless radiosurgery for the treatment of benign tumors. Bhatnagar AK, Gerzsten PC, Agarwal A, Ozhasoglu CW, Vogel WJ, Kalnicki S, Welch WC, Burton SA. International Journal of Radiation Oncology*Biology*Physics, September 2004 (Vol. 60, Issue 1 (Supplement), Page S548)
  34. ^ Patrick-Swayze has Cyberknife radiotherapy
  35. ^ Reuters -December 2008 - Accuray Achieves Milestone of 150th CyberKnife System Installed Worldwide
  36. ^ Accuray Reaches 100th U.S. CyberKnife System Installation
  37. ^ Cutland, Laura (25 September 2005). "Maverick in a mind field - Silicon Valley / San Jose Business Journal:". 
  38. ^ Accuray FAQ
  39. ^ Atlantic Health
  40. ^
  41. ^


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