CyberKnife technology, first developed in 1990, has been through several incarnations, becoming quite prevalent in recent years. With about 150 systems available worldwide, the technology offers radiation treatment to patients with inoperable tumors and tumors that are in areas not accessible with conventional radiation therapy. The system consists of a small linear accelerator and a robotic arm that allows radiation to be directed at tumors anywhere in the body.

Stereotactic radiosurgery commonly has been used for treatment of vascular abnormalities and benign and malignant brain lesions for years. The Gamma Knife and Novalis are two popular systems for radiosurgery. Other options include linac-based radiosurgery like mMLC and Accuknife.  

The most common application of these systems is arteriovenous malformations and brain tumors. Treating lesions in the head typically requires head frames to be bolted to the skull for localization and immobilization. The CyberKnife is a frameless system, using a sophisticated image guidance system that consists of X-ray imaging cameras mounted around the patient. The system tracks the tumor, ensuring accurate delivery of radiation to the targeted area. These cameras are used with some anatomical or artificial feature to orient the robotic arm to deliver the radiation to the tumor.

As is true with other types of portal imaging, the images from these X-ray cameras often don't have the resolution to actually visualize the tumor. The CyberKnife system uses several different methods to align the beam, including fiducial tracking.

In addition to lesions in the brain, the CyberKnife system has FDA clearance for treatment of tumors anywhere in the body. The system has been used on lung, brain, head and neck, liver, pancreas and prostate cancer. While currently, studies have not shown any survival benefit, it's hoped that the improved accuracy will allow for dose escalation that may ultimately have a positive impact on local control rates.

The use of this tool has an impact on radiation oncology personnel and other clinical professionals. Most patients require multimodality imaging, and the radiation oncologist will typically consult with other specialists to identify targets and critical structure. Once these structures have been identified, the medical physicist devises the treatment plan with input from the radiation oncologist.

After a plan is finalized and approved by the physician, the patient is scheduled for treatment. It is crucial to match the patient position with the position used throughout the imaging process. The tracking mechanisms search for a perfect match and treatment may not be possible if the positioning does not agree. The treatment couch is also robotic, which helps align the patient with the digitally reconstructed radiographs (DRRs).  

During the set-up phase, images are taken for every beam. This allows the robot to terminate the exposure if the planned location doesn't correlate with the DRRs. In this case, the couch would be realigned before proceeding. The technology used when treating lung lesions is even more sophisticated. With this system, the robot looks for respiratory motion. With patients wearing a vest equipped with light-emitting diodes (LED), a camera watches the movement of the lights and takes images throughout the respiratory cycle. These images correlate the position of the lesion with the lights, and develop a model to allow the robot's motion to follow the target as it moves.

As one might expect, treatment times for these procedures are quite lengthy, averaging about an hour. After alignment, the images and the accuracy of the tracking system must be constantly verified. If there's tracking difficulty, the treatment may take three hours or longer.

Radiation therapists (RTTs) are an integral part of the treatment team. Once the patient is aligned, treatment challenges are more technical than clinical. It's important for the RTT to be aware of the planning process and technical aspects of the system since they monitor the algorithms in real time.

While more extensive research is required to demonstrate effects on survival rates, it appears the use of this technology will continue to increase.

Amy Freshley Lebkuecher, MS, RT(R)(T), is a radiation therapist living in Ashland City, Tenn.