The CyberKnife is a specific model of medical linear accelerator mounted on a robotic arm. It is used primarily 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 “stereotactic body radiation therapy”  when other sites are treated. Radiosurgery can also be performed with other models of medical linear accelerator.

The term “stereotactic” means that a high-precision patient localization system is used to identify the physical location of the target inside the patient. Stereotactic radiation surgery is used to irradiate the entire tumor site in a single treatment session. 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 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 CyberKnife treatment process begins with CT, MRI, or PET scans to determine the location, size, and shape of the tumor. Sometimes it may be necessary to implant small markers, called fiducials, next to the tumor to provide a way of tracking the site being treated. The radiation oncologist, medical physicist, and dosimetrist work as a team to create a treatment plan to deliver therapeutic radiation doses to the tumor while minimizing dose to the surrounding normal tissue.

During treatment, the patient comfortably lies on a treatment couch and is immobilized with either a plastic mask for brain tumors or a body cradle for other treatment areas. X-rays are taken to ensure the robotic arm is accurately positioned to deliver therapeutic doses to the cancer as the robotic arm slowly moves around the patient from 50 to 200 different positions. The entire treatment is delivered in about 30 to 90 minutes.

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