Robot-directed radiation eradicates lung tumors

A linear accelerator, mounted on a robotic arm, destroys lung tumors in some patients within four months post-treatment, according to study results unveiled at the American Association of Physicists in Medicine meeting in Orlando, FL, on Wednesday. The University of Pittsburgh Medical Center researchers have also successfully used the technology to treat tumors in the thorax and abdomen.

Lung tumors are particularly difficult to treat because they move during respiration. Even tumors in the thorax and abdomen are problematic, as breathing causes them to change size by as much as 4 cm.

The device, called CyberKnife with Synchrony, tracks these tumors and adjusts the stream of radiation using a linear accelerator mounted on a robotically controlled mechanical arm. Three optical CCD cameras follow LED markers attached to a tracking vest worn by the patient. Two flat-panel detectors, mounted below the patient, visualize the tumors in real-time. Computers process the data, keeping the accelerator aligned with the tumors despite the motion encountered during patient respiration.

The University of Pittsburgh is among 76 active CyberKnife sites in operation; 45 of these are in the U.S. Another 62 units are scheduled for installation worldwide.

The number of CyberKnife systems has more than doubled in the U.S. over the past year, according to the privately held Sunnyvale, CA, company. The paper discussed by the Pittsburgh team is just one of several being presented on the CyberKnife at the AAPM meeting this week.

CyberKnife irradiates a tumor from all sides, typically delivering 100 to 150 highly focused x-ray beams, causing the tumor to absorb approximately 10 times more radiation than in a conventional radiotherapy session. CyberKnife can deliver so much more radiation than other techniques because its robotic arm aims the x-rays precisely and avoids the surrounding healthy tissue.

The Synchrony add-on to the device adjusts the robotic arm to stay in line with tumors that move due to respiration. To track the moving tumor, the CyberKnife takes real-time x-ray pictures of the patient while using external markers attached to the patient's chest or abdomen to follow tumors in real-time within a few millimeters of accuracy.

Treating lung tumors with the enhanced CyberKnife can be accomplished with one to three sessions lasting 60 to 90 minutes each. This compares to the dozens of conventional radiation treatments otherwise prescribed.

Dr. John R. Adler, professor of neurosurgery and radiation oncology at Stanford University Medical Center, developed the CyberKnife in 1987 after completing a fellowship in Sweden with Dr. Lars Leksell, the founder of radiosurgery. At that time, the field of radiosurgery was restricted to the treatment of intracranial tumors. Adler founded AccuRay in 1990. Nine years later, the FDA cleared the CyberKnife for the treatment of head, neck, and upper spine tumors. In 2001, AccuRay received FDA clearance for enhancements that allow the system to treat tumors anywhere in the body.