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Cyberknife (device)

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Cyberknife based on Kuka 250

CyberKnife is the name of a frameless robotic radiosurgery system invented by John R. Adler, a Stanford University Professor of Neurosurgery and Radiation Oncology. The two main elements of the CyberKnife are (1) the energy source produced by 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 CyberKnife system is sold by the company Accuray, located in Sunnyvale California. The CyberKnife system is used for treating benign tumors, malignant tumors and other medical conditions.[1] [2]

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

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 methods.

Robotic Mounting

The first is the fact that the radiation source is mounted on a precisely controlled industrial robot. The original CyberKnife used a Fanuc robot[3], however the more modern systems use a Kuka 240.[4] 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. The radiation is collimated using tungsten collimators (also referred to as “cones”) which produce circular radiation fields. At present the radiation field sizes range from 5mm to 60mm (in roughly 5mm intervals). Mounting the radiation source on the robot allows complete freedom to position the radiation within a sphere about the patient. The robotic mounting allows very fast repositioning of the source, which allows the system to deliver radiation from many different directions, which is impossible using a conventional gantry based linear accelerator system due to the mechanical limitations of the gantry as compared to a 6 degree of freedom robot.

Image Guidance

The image guidance system is the other essential item in the CyberKnife system. X-ray 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 patients skull.[5] 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.

Xsight

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[6] 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[7] which allows tracking of some lung tumors without the need to implant fiducials.

Fiducial

For soft tissue tumors, a method known as fiducial tracking can be utilized.[8] 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.[9][10]

Synchrony

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.[11] 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 patients 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 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 there motion will reflect the internal motion of the diaphragm, and the lungs.

RoboCouch

A new robotic six degree of freedom patient treatment couch called RoboCouch[12] has been added to the CyberKnife which provides the capability for significantly improving patient positioning options for treatment.

Frameless

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. 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 Neurosurgeon, 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.

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.[13] 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.[14] This can allow a larger dose to be delivered to the tumor compared to a single treatment.

Usage

CyberKnife systems have been installed in hospitals in the United States. For example: the Stanford Blake Wilbur CyberKnife Center and the Comprehensive Cancer Center at Stanford University; Georgetown University Hospital; UCSF Medical Center; Kennestone Hospital in Georgia; and the University of Pittsburgh. Stanford University has treated over 2,500 patients using the CyberKnife system, and worldwide over 15,000 patients have been treated.[15] Several CyberKnife video clips can be found on YouTube.[16][17][18]

Other CyberKnife systems have been installed in Korea,Japan, Italy, China and Vietnam.

Comparison with other Stereotactic systems

Gamma Knife

One of the most widely known stereotactic radiosurgery systems is the Gamma Knife. The Gamma Knife was originally developed by Lars Leksell, and is manufactured by Elekta. 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 a series of 4 collimators of 4mm, 8mm, 12mm and 16mm diameter, and is capable of accuracies of greater than a millimeter. 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 tumors. The Gamma Knife accuracy is solely dependent upon the frame placement, and has no real time imaging capability. Many people erroneously believe the Gamma Knife system is more accurate than Cyber Knife.[19] The Cyberknife Society and Accuray maintain that there are no peer-reviewed published papers that establish GammKnife as being more accurate than CyberKnife.[20][21]

Novalis

Another popular Stereotactic system is the Novalis produced by Brainlab.[22] 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 100 mm x 100 mm, and the minimum is 3mm x 3mm allowing a considerable range of tumors to be treated. The Novalis system also has x-ray camera imaging using amorphous silicon x-ray cameras, and it can be operated framelessly. The Novalis system is equipped with an implanted marker based respiratory tracking unit known as ExacTrac Gating.

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 micro MLC system. Examples of removable micro MLC units are the Ergo from 3D line],[23] the mMLC manufactured by Brainlab,[24] and the AccuKnife produced by Direx.[25]

Utilizing a conventional therapy linac has several difficulties, not the least of which that the system is not usually mechanically accurate to within 1mm. A conventional linac will also not have the image guided ability of a CyberKnife system, and will therefore require a treatment frame.

Clinical uses

The CyberKnife system has FDA clearance for treatment of tumors in any location of the body. Some of the tumors treated include: pancreas,[26][27] liver,[28] prostate,[29] Spinal Lesions,[30] head and neck cancers,[31] and benign tumors.[32]

See also

References

  1. ^ http://med.stanford.edu/neurosurgery/patient_care/radiosurgery.html Stanford Neurosurgery
  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. ^ Fanuc Robotics http://www.fanucrobotics.com/
  4. ^ Kuka Roboter GmbH http://www.kuka.com/en/
  5. ^ An Analysis of the Accuracy of the 6D Tracking With CyberKnife Inoue M, Sato K, Koike I International Journal of Radiation Oncology, Biology, Physics 01 November 2006 (Vol. 66, Issue 3 (Supplement), Page S611)
  6. ^ Accuray::Xsight® Spine Tracking System
  7. ^ Accuray::Xsight® Lung Tracking System
  8. ^ CyberKnife Radiosurgery - Fiducial Overview
  9. ^ Fuller CD, and Scarbrough TJ, MD Fiducial Markers in Image-guided Radiotherapy of the Prostate. U S ONCOLOGICAL DISEASE 2006 75-78
  10. ^ Murphy MJ. Fiducial-based targeting accuracy for external-beam radiotherapy. Medical Physics March 2002 Volume 29, Issue 3, pp. 334-344
  11. ^ 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)
  12. ^ Accuray::RoboCouch® Patient Positioning System
  13. ^ http://biz.yahoo.com/bw/070115/20070115005165.html?.v=1
  14. ^ Radiobiology for the Radiologist Eric J. Hall Lippincott Williams & Wilkins; 5th edition (2000)
  15. ^ Maverick in a mind field - Silicon Valley / San Jose Business Journal:
  16. ^ YouTube - 數碼導航刀 Accuray CyberKnife System
  17. ^ YouTube - Packard Children's Opens First Pediatric-Focused Cyberknife
  18. ^ YouTube - Broadcast Yourself
  19. ^ Gamma Knife vs. CyberKnife :: Gamma Knife Center :: Wake Forest University Baptist Medical Center
  20. ^ Radiosurgery CyberKnife Overview
  21. ^ 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
  22. ^ Brainlab http://www.brainlab.com/
  23. ^ 3D line http://www.3dline.com/
  24. ^ Brainlab http://www.brainlab.com/
  25. ^ Direx http://www.direx.co.il/accu.htm
  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. ^ 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, 01 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, 01 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, 01 November 2006 (Vol. 66, Issue 3 (Supplement), Pages S324-S325)
  30. ^ 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, 01 October 2003 (Vol. 57, Issue 2 (Supplement), Pages S370-S371)
  31. ^ 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, 01 October 2005 (Vol. 63, Issue (Supplement 1), Page S381)
  32. ^ 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)

External links

Example treatment centers in the U.S.

Example treatment centers in Europe

Competitors

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