The role of radiation therapy for the treatment of tumors of the brain and spine has been well established. Conventional external beam radiotherapy currently lacks the ability to allow for the delivery of large doses of radiation near radiosensitive structures such as the optic nerve or spinal cord. It is the low tolerance of these structures to radiation that often limits the treatment dose to a level that is far below the optimal therapeutic dose. If the radiation dose could be confined more precisely to the treatment volume, the likelihood of successful tumor control should increase at the same time that the risk of spinal cord injury is minimized. A device called the CyberKnife® has the ability to do just that.
The CyberKnife, manufactured by Accuray, Inc. of Sunnyvale, CA, is operational at UPMC Shadyside. This device is an image-guided stereotactic radiosurgery delivery system that does not require the application of a head frame for cranial radiosurgery. It also has the ability to deliver fractionated radiosurgical treatment plans for larger lesions and also provide radiosurgery for spinal lesions. UPMC has one of the largest experiences in the world in treating spine tumors with radiosurgery.
What is the CyberKnife?
The CyberKnife consists of a lightweight linear accelerator mounted on a robotic arm. Near real-time image allows for patient movement tracking within 1mm spatial accuracy. The CyberKnife references the position of the treatment target to internal radiographic features such as the skull or body landmarks or implanted fiducials rather than a frame that is fixed to a patients skull. The CyberKnife uses real-time x-rays to establish the position of the lesion during treatment and then dynamically brings the radiation beam into alignment with the observed position of the treatment target. The CyberKnife aims each beam independently, without a fixed isocenter. If the target moves, the process detects the change and corrects the beam pointing in near real-time.
The CyberKnife is currently available for treatment of lesions throughout the brain, skull base and spine. These lesions may be either benign or malignant including metastases, meningiomas, neurofibromas, schwannomas, and vascular malformations. The CyberKnife has been used to successfully treat lesions in patients who are otherwise not candidates for surgery or for lesions that are not amenable to open surgical techniques.
How does the treatment process work?
CyberKnife patients with cranial lesions undergo the necessary imaging which may consist of CT, MRI or PET scans. The images are fused together and the lesion is contoured in 3-dimensions. The treatment plan including the total dose, number of beams and total number of fractions is finalized.
CyberKnife patients with cervical lesions undergo a CT scan as an outpatient. For thoracic and lumbar lesions, patients first undergo the percutaneous placement of fiducial bony markers as an outpatient. The patient then returns for a CT scan of the tumor. The imaging is transferred to a work station where a treatment plan is developed.
Once the CyberKnife treatment plan has been finalized, the patient returns several days later for the actual treatment. The treatment time takes approximately one to three hours. No sedation is necessary as the patient is able to comfortably lie on the table throughout the procedure.
Spinal stereotactic radiosurgery using a framelessimage-guided system can now be performed safely, accurately, and effectively. The CyberKnife technique offers a successful alternative therapeutic modality for the treatment of a variety of spinal lesions not amenable to open surgical techniques, in medically inoperable patients, lesions located in previously irradiated sites, or as an adjunct to surgery. The major potential benefits of radiosurgical ablation of spinal lesions are short treatment time in an outpatient setting with no recovery time and good treatment effect.
The Department of Neurological Surgery works in concert with members of the Department of Radiation Oncology, including Dwight Heron, MD, and Steven Burton, MD, in defining the treatment plans for the CyberKnife.
Potential candidates for cranial-based CyberKnife radiosurgery should call (412) 647-7614. Spine-related candidates should be referred to Peter C. Gerszten, MD, at (412) 647-1700