Computerized robot arm aids in surgery.

Three-dimensional body maps that guide a robot arm offering pinpoint blasts of radiation are starting to make possible - on an outpatient basis - many brain and spinal cord surgeries that would have been impossible before, indicates Stanford University Medical Center neurosurgeon John Adler. The new technique, called computer-mediated stereotaxic radio-surgery (CMSR), draws on space-age missile tracking technology, flexible robotic manipulators, and powerful X-ray machines to destroy cancerous tumors in the brain or spine without opening the skull or risking the partial paralysis that often follows traditional spinal surgery using a knife.

With CMSR, a computer-controlled robot arm locks the radiation beam on the tumor, constantly re-adjusting its aim in response to the patient's natural small movements. Because it delivers its payload so accurately, healthy tissue surrounding the tumor remains undamaged.

Stereotaxic radiosurgery is not an uncommon treatment for brain tumors. However, older systems lack the sophisticated tracking devices of the new technology Adler and his colleagues are fine-tuning. More conventional stereotaxic units require screwing the patient's skull into a frame to prevent movement, a process that necessitates anesthesia and postsurgical hospitalization while the bolt wounds heal. "Stereotaxic radio-surgery is a natural for spinal cord tumor removal, but before the robotic tracking system, which accounts for slight, normal movement of patients undergoing surgery, we had no feasible method of holding spinal patients absolutely rigid," Adler points out.

"What's new here is extremely sophisticated computer software that stores an accurate map of the surgical target - in this case, a portion of the brain or spine - charted from a CT scan taken before the procedure. The X-ray tracking system guiding the robot arm then matches what it sees with the computer-stored map," explains Richard Cox, the radiation physicist at Stanford who prepares the individual treatment plans.

Unlike most modern procedures in radiation oncology, CMSR relies on powerful, but precisely aimed, doses that can kill malignant tumors with a few - often only one - treatment sessions. In traditional radiation therapy, physicians administer small doses of radiation over weeks or months in order to allow healthy tissue surrounding the tumor to recover from the onslaught.

CMSR attacks the tumor with short pulses of high-energy radiation from a device called a linear accelerator. "Because we cross fire in many different directions, we can minimize the radiation dose reaching healthy tissue and prevent injury," Adler notes. "The robot arm is extremely flexible and can position the beam at any of a large variety of angles to treat a small site." CMSR offers potential in the future for many other types of surgery, although "the benefits for brain and spinal cord surgery are particularly compelling. We can avoid invasive operations on the brain, and we can gain access to the surgical site without removing portions of the skull. In the spine, the opportunity to improve accuracy and avoid damage near the surgical site is equally compelling."