The CyberKnife is a specific model of medical linear accelerator mounted on a robotic arm. It is primarily used to treat relatively small tumors with high levels of radiation in only a few sessions. This approach is referred to as “stereotactic radiosurgery” when the brain is treated and as “stereotactic body radiation therapy” when other sites are treated. Radiosurgery can also be performed with some other medical linear accelerator models or with the Gamma Knife system.

The term “stereotactic” means that a high-precision localization system is used to identify the location of the target inside the patient before (and possibly during) treatment. Stereotactic radiosurgery generally irradiates the entire cranial tumor site in a single treatment session while stereotactic body radiation therapy is usually delivered in three to five treatment sessions.

Image used with permission from Accuray Incorporated.

How does CyberKnife work?

CyberKnife combines a multi-jointed robotic radiosurgery arm with an image-guided tracking system. During treatment it uses sophisticated software and advanced x-ray imaging to track patient movement, and based on that information the system continually adjusts the timing and position of the arm-mounted linac to ensure it delivers radiation accurately.

Images used with permission from Accuray Incorporated.

What is the treatment process with CyberKnife?

The treatment process begins with CT (and possibly MRI or PET) imaging scans of the patient to determine the location, size, and shape of the tumor. Sometimes it may be necessary to implant small markers called “fiducials” near the tumor to provide a way of tracking it during treatment. The radiation oncologist, medical physicist, and dosimetrist then work as a team to create a computerized treatment plan which will deliver a therapeutic radiation dose to the tumor while minimizing unwanted dose to surrounding healthy tissue.

For CyberKnife treatment delivery, the patient lies comfortably on a treatment table and is immobilized with either a plastic mask for brain tumors or a body cradle for other treatment areas. Projection x-rays of the targeted site are taken at regular intervals to enable accurate positioning of the robotic arm with respect to the patient as it slowly moves from 50 to 200 different positions, delivering the planned radiation beams. A treatment session may last from 30 to 90 minutes, depending on the site.

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