CyberKnife Radiosurgery Treatment Process

Treatment Setup

Setup is the initial process that allows a physician to plan and deliver a CyberKnife® treatment. For a typical cranial tumor, a custom-fit plastic mask is made for each patient. This mask, unlike the conventional metal head frame, is noninvasive and painless. This immobilization device is molded to the patient’s face quickly and the process is quite painless. The mesh mask is allowed to dry and will be ready for the patient’s use on the day of treatment. When tumors elsewhere in the body are treated, a foam body cradle is custom-fit for the individual patient instead of the mask. With the mask or body cradle in place, the patient undergoes a CT scan with contrast (iodinated dye), which is then used to precisely plan delivery of radiation to the tumor. In some instances, an MRI or PET scan may also be necessary in order to fully visualize the tumor and adjacent critical anatomy.

If the condition being treated is not intracranial, but elsewhere in the body, special markers may need to be placed in the body. These metal markers, called fiducials, are 3 to 4 mm long and are used to accurately target radiation from the CyberKnife. These markers must be implanted during a short 10 to 15 minute outpatient procedure prior to the CT scan and may remain in the body permanently without harm.

Each patient receives an individualized treatment plan and treatments are specific to the condition being targeted. Consequently treatment times may vary. Some patients require only a single treatment, while others will require multiple treatments, depending on the size and location of their lesion. Fractionated treatments are typically given in two to five sessions over a period of two to five days.

Treatment Planning

CyberKnife® treatment planning utilizes both physician and physicist experience to use the computing power of high-speed computers to develop an optimal pattern of radiation. During the CyberKnife® treatment planning process, once the physician/physicist team has determined the volume and dose of radiation, the CyberKnife® computer performs millions of calculations to determine the best radiation delivery plan.

The CyberKnife’s treatment planning system exploits the robot's high degree of maneuverability to allow a much more conformal delivery of radiation throughout a tumor than can be achieved by older frame-based radiosurgical systems, particularly as the size and complexity of the lesion(s) increase.

Treatment Delivery

When patient returns for treatment delivery, he/she puts on the custom plastic mask or body cradle and lies on the treatment table. Prior to beginning the actual radiation treatment, the imaging system acquires digital x-rays of the patient position. This information is used to move the linear accelerator to the appropriate position then it delivers a small dose of radiation. The robot moves and re-targets the linear accelerator at a large number of positions around the patient. At each position or "node”, a small radiation beam is delivered.

This process is repeated at 50 to 300 different positions around the patient to complete the treatment. At pre-programmed intervals, the linear accelerator stops and additional pictures are obtained of the patient, allowing the CyberKnife® to track and compensate for small amounts of patient movement. These intervals can be as frequent as every node, and translate to sub-millimeter tracking accuracy throughout the entire treatment.

The entire process is painless, and it typically takes between 30 to 120 minutes to deliver all radiation beams. Most typically a patient can go home immediately upon completion and return to normal activities. If the treatment prescription is for fractionated radiosurgery, the patient will return up to a total of five visits for the additional treatment delivery.