Cyberknife

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The CyberKnife is a robotic robotic radiosurgery system used to treat benign tumors, malignant tumors and other medical conditions. The system was invented by John R. Adler, a professor of neurosurgery and radiation oncology at Stanford University, and Peter and Russell Schonberg of Schonberg Research Corporation. It's made by the Accuray company headquartered in Sunnyvale, California.

The CyberKnife system is a method of radiotherapy delivery, with the goal of targeting treatments more accurately than standard radiotherapy. The two main elements of CyberKnife are:

radiation generated from a small linear particle accelerator (linac)
a robotic arm that allows energy to be directed to any body part from any direction

Video Cyberknife

Key features

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

Robot installation

The first is that the radiation source is installed in a general purpose industrial robot. Original CyberKnife uses Japanese Fanuc robot; However, the more modern system uses KUKA KR 240 Germany. Installed on Robot is a compact X-band linac that produces 6MV X-ray radiation. Linac is capable of delivering approximately 600 cGy of radiation every minute - the new 800 cGy/min model is announced at ASTRO 2007. The radiation is colonized using a fixed tungsten collector (also called a "cone") that produces a circular radiation field. Current radiation field sizes are: 5, 7.5, 10, 12.5, 15, 20, 25, 30, 35, 40, 50 and 60 mm. ASTRO 2007 also sees the launch of the IRIS variable-aperture collarator that uses two offset banks of six prismatic tungsten segments to form a regular dodecagon field that is blurred from variable sizes that eliminates the need to change fixed collimators. Installing a radiation source on the robot allows almost perfect freedom to place the source inside the patient room. The installation of the robot allows rapid source repositioning, allowing the system to transmit radiation from multiple directions without the need to move the patient and the resources required by the current gantry configuration.

Image guide

The second is that the CyberKnife system uses an image guidance system. The X-ray imaging camera is located in support around the patient allowing instant X-ray images to be obtained.

6D skull

The original method (and still used) is called tracking based on 6D or skull. X-ray camera images are compared to computer libraries that produce patient anatomical images. Digital Reconstruction Radiography (or DRR) and computer algorithms determine what motion correction should be given to the robot because of the patient's movement. This imaging system allows CyberKnife to provide radiation with a 0.5mm accuracy without the use of mechanical clamps attached to the patient's skull. The use of image-guided techniques is referred to as without frames stereotactic radiosurgery. This method is referred to as 6D because the correction is made for 3 translational movements (X, Y and Z) and three rotational motions. It should be noted that it is necessary to use some anatomical or artificial features to direct the robot to provide X-ray radiation, since the tumor is never well-defined (if seen at all) on an X-ray camera image.

Xsight

Additional image guidance methods are available for spinal tumors and for tumors located in the lungs. For tumors located in the spine, a variant of the image guide called Xsight-Spine is used. The main difference here is that instead of taking pictures of the skull, images of the spinal process are used. While the skull is effectively rigid and non-deformed, the spinal cord can move relative to each other, this means that the image warping algorithm should be used to correct the distortion of X-ray camera images.

The recent increase to Xsight is Xsight-Lung which allows tracking of several lung tumors without the need to embed fiduciary markers.

Fiduciary

For soft-tissue tumors, a method known as fiduciary tracking can be used. Gold markers (fiducials) made of gold for bio-compatibility and high density to provide good contrast to X-ray images are implanted surgically in patients. This is done by an interventional radiologist, or neurosurgeon. Placement of fiducials is an important step if fiduciary tracking is to be used. If the fiduciary is too far from the location of the tumor, or is not sufficiently dispersed from each other then it is impossible to transmit radiation accurately. Once these markers are placed, they are placed on a CT scan and the image guidance system is programmed in position. When an X-ray camera image is taken, the location of the tumor relative to the fiducials is determined, and radiation can be sent to any part of the body. Thus fiduciary tracking requires no bony anatomy to position the radiation. Fiduciary is known to migrate and this can limit the accuracy of treatment if sufficient time is not allowed between implantation and care for fiduciary to be stable.

Sync

Another technology of image guidance that can be used by the CyberKnife system is called the Synchrony system or the Synchrony method. This method uses a combination of internal fiduciaries placed in surgery (usually small gold markers, clearly visible in x-ray imaging), and light-emitting optical fibers (LED markers) mounted on the patient's skin. The LED marker is tracked by an infrared tracking camera. As the tumor moves continuously, continuously depicting its location using an X-ray camera will require very large amounts of radiation to be sent to the patient's skin. The Synchrony system overcomes this by periodically taking pictures of the internal fiducial, and computing the correlation model between the motion of the external LED marker and the internal fiduciary. The time stamp of two sensors (x-rays and infrared LEDs) is required to synchronize the two data streams, hence the name Synchrony.

Motion prediction is used to overcome latency of motion robot and shooting latency. Prior to treatment, computer algorithms created a correlation model that represents how internal fiduciary markers move compared to external markers. During treatment, the system continually enters the internal fiduciary movement, and therefore the tumor, based on the movement of the skin marker. The correlation model is updated at a fixed time step during maintenance. Thus, the synchrony tracking method does not make assumptions about the regularity or reproducibility of the patient's breathing patterns.

To function properly, the system requires that for any given correlation model there is a functional relationship between the marker and the internal fiduciary. The placement of external markers is also important, and markers are usually placed on the patient's abdomen so that their movements will reflect the internal movements of the diaphragm and lungs. This method was discovered in 1998. The first patient was admitted to the Cleveland Clinic in 2002. Sync is used primarily for tumors that move while being treated, such as lung tumors and pancreatic tumors.

Borderless

The borderless nature of CyberKnife also improves clinical efficiency. In conventional frame-based radiosurgery, the accuracy of delivery of treatment is determined simply by connecting a rigid frame for patients who are anchored to a patient's skull with an invasive aluminum or titanium screws. CyberKnife is the only radiosurgery device that does not require a framework for proper targeting. After the frame is connected, the patient's relative anatomical position should be determined by making a CT scan or MRI. After a CT scan or MRI has been made, the radiation oncologist must plan for radiation delivery using a special computer program, after which treatment can be delivered, and the frame removed. The use of frames therefore requires a linear sequence of events to be done in sequence before other patients can be treated. The establishment of CyberKnife radiosurgery is of particular benefit to patients who have previously received large doses of conventional radiation therapy and patients with gliomas located near the critical area of â€‹â€‹the brain. Unlike whole brain radiotherapy, which should be done daily for several weeks, radiosurgery treatments can usually be completed within 1-5 treatment sessions. Radiosurgery can be used alone to treat brain metastases, or in relation to surgery or radiotherapy of the entire brain, depending on the specific clinical situation.

For comparison, using a borderless system, CT scans can be performed daily before convenient treatment. Treatment planning can also be done at any time before treatment. During treatment, the patient only needs to be positioned on the treatment table and predetermined plan. This allows clinical staff to plan many patients at the same time, devoting as much of the time as necessary to complicated cases without delaying treatment. When a patient is being treated, other doctors may consider treatment options and plans, and others can perform CT scans.

In addition, very young patients (pediatric cases) or patients with brittle heads due to prior brain surgery can not be treated using a skeletal system. Also, by being borderless, CyberKnife can efficiently treat back the same patient without repeating the preparatory steps required by a framework-based system.

Submission of radiation treatment for several days or even weeks (referred to as fractionation) can also be useful from a therapeutic point of view. Cell tumors usually have poor repair mechanisms compared to healthy tissue, so by dividing the radiation dose into fractions, a healthy tissue has time to repair itself among treatments. This may allow larger doses to be sent to the tumor compared to a single treatment.

Maps Cyberknife

Clinical use

Since August 2001, the CyberKnife system has FDA clearance for tumor treatment at every body location. Some of the tumors treated include: pancreas, liver, prostate, spinal lesions, head and neck cancer, and benign tumors.

None of these studies demonstrate general survival benefits compared to conventional methods of treatment. By improving the accuracy of the given handling, there is potential for dose escalation, and potentially a subsequent increase in effectiveness, especially in local control levels. But the research cited thus far is limited in scope, and broader research will need to be completed to demonstrate the effect on survival.