Image-Guided Frameless Robotic Radiosurgery for Treatment of Spinal Cord Tumors

Spinal cord tumors are not as common as brain tumors; however, about 100,000 Americans each year develop primary or metastatic (secondary growth) spinal cord tumors, according to the National Institute of Neurological Disorders and Stroke. Spinal cord tumors, most common in young and middle-aged adults, often result in significant pain, deterioration of the spinal column, mental instability, and other numerous neurological defects. A recent study, "CyberKnife Radiation Delivery System for Frameless Stereotactic Radiosurgery for Spinal Lesions: A Series of 50 Patients," is being presented by Peter Gerszten, MD, of the University of Pittsburgh Medical Center, during the 71st Annual Meeting of the American Association of Neurological Surgeons (AANS) in San Diego.

The study finding stereotactic radiosurgery a feasible and safe delivery system for treatment of debilitating spinal cord tumors, will be presented by Peter Gerszten, MD, MPH; Steven A. Burton, MD; Cihat Ozhasoglu, PhD; William C. Welch, MD, FACS; and Shalom Kalnicki, MD, all of the University of Pittsburgh Medical Center on Monday, April 28, from 4:45 to 5 p.m.

"The purposes of the study were to compare conventional frame-based radiosurgery with frameless image-guided stereotactic radiosurgery and to evaluate the safety and efficacy of the systems," said Peter Gerszten, MD, MPH, a co-author of the study and AANS member. "The image-guided treatment system is a logical advance of the current state-of-the-art radiation therapy, and proving new technologies safe and effective is a critical step for clinical adoption."

Radiosurgery, pioneered in the 1950s, directs radiation--X-rays or gamma rays--at tumors to destroy them without ever making an incision. Because radiation can destroy healthy, as well as diseased tissue, delivery systems that allow precise targeting are crucial to success. To achieve this level of accuracy, conventional radiosurgery systems require the use of a metal head frame to immobilize the patient during the procedure. However, such frames are cumbersome and uncomfortable for the person being treated and more importantly limit treatment to tumors and lesions in the head. Radiosurgery for areas outside of the head, such as the spine, was difficult if not impossible to perform with conventional systems because of the frame.

Researchers used a new image-guided frameless stereotactic radiosurgery delivery system, the CyberKnife(r) Real-Time Image-Guided Radiosurgery System, to treat spinal lesions with a single-fraction radiosurgical technique. The CyberKnife consists of a lightweight computer-controlled linear accelerator that is mounted on a robotic arm. X-ray cameras provide real-time imaging that tracks patient movement and enables delivery of the treatment dose to within 1 mm of the target.

In the study, 67 spinal lesions in 50 patients were treated with single fraction radiosurgery (27 cervical, 22 thoracic, 14 lumbar and 4 sacral). There were a total of 12 benign tumors and 55 metastatic lesions. Using the X-ray imaging system and robot-mounted linear accelerator, the authors were able to guide the radiation beams to the intended target without the use of a frame-based fixation system. This targeted method minimizes the irradiation of the surrounding healthy tissue, potentially decreasing the rate of complications. As a result, overall pain had improved in all patients who were symptomatic prior to treatment.

"This study proves that spinal stereotactic radiosurgery using a frameless image-guided system is now both feasible and safe," said Dr. Gerszten. "The major benefits of radiosurgical removal of spinal cord tumors are non-invasive short treatment times in an outpatient setting, with both rapid recovery and symptomatic response."

This new technique offers a successful alternative for the treatment of a variety of spinal tumors not eligible for open surgical techniques, such as those in medically inoperable patients or previously irradiated sites. This technique may also serve as an adjunct to surgery.

The CyberKnife spinal radiosurgery treatment consists of the following main steps: (1) implantation of small bone fiducials near the tumor (2) computed tomography (CT) image acquisition of pertinent anatomy including the bone fiducials, (3) treatment planning, and (4) the treatment itself.

During the actual treatment, real-time digital X-ray images of the patient are taken to track the implanted fiducials, which serve as reference points for tumor location. The robotic arm is automatically repositioned if a change in position is detected to ensure accurate radiation delivery. The patient is observed throughout treatment by a closed-circuit television.

Each radiosurgical treatment plan should involve a team comprised of a neurosurgeon, a radiation oncologist, and a radiation physicist. In each individual case, the radiosurgical treatment plan is designed based primarily on tumor size and shape, proximity to the spinal cord, and location within the body. The radiation dose is based on tumor tissue structure, location, and history of previous fractionated radiotherapy. The duration of treatment is usually one to two hours.

"This study revealed that image-guided stereotactic radiosurgery for spinal tumors is a safe and feasible treatment option and introduces the opportunity for irradiation to be completed in a single day," said Dr. Gerszten.

Most importantly, the study found there is greater potential for local control of the tumor, with minimal risk of side effects. Although these are the results of only one study, this outcome could evolve into further reduction of postoperative patient symptoms and a longer survival period.

Founded in 1931 as the Harvey Cushing Society, the American Association of Neurological Surgeons (AANS) is a scientific and educational association with more than 6,500 members worldwide. The AANS is dedicated to advancing the specialty of neurological surgery in order to provide the highest quality of neurosurgical care to the public. All active members of the AANS are certified by the American Board of Neurological Surgery, the Royal College of Physicians and Surgeons (Neurosurgery) of Canada or the Mexican Council of Neurological Surgery, AC. Neurological surgery is the medical specialty concerned with the prevention, diagnosis, treatment and rehabilitation of disorders that affect the entire nervous system including the spinal column, spinal cord, brain and peripheral nerves.