Presented by: Steven D. Chang, MD
Stanford University Medical Center
October 30, 2014
There is a delicate balance when it comes to treating brain tumors. How do you effectively destroy the cancer cells while avoiding damage to the nearby normal cells? How can you operate on such a complex organ without causing neurological problems?
The answer lies in new tools and technologies that involve less invasive procedures that use computers and robotics, and more refined use of radiologic imaging, said Steven D. Chang, MD, a professor of neurosurgery, who spoke at a presentation sponsored by the Stanford Health Library. The optimal strategy depends on the individual and the type of brain cancer that needs to be treated, and is individualized for each patient.
Glioblastoma, for example, is an extremely aggressive form of brain cancer that affects more than 15,000 people each year. These tumors are highly malignant, and because the cells reproduce quickly patients usually survive only a few months without treatment.
In the past, glioblastoma was treated solely with basic surgical techniques. Today an innovation known as an interoperative MRI scanner (iMRI) allows a surgeon to conduct an imaging scan while the patient is still in the operating room to ensure that all visible cancerous cells have been removed. The OR team can access the MRI images during the procedure without having to move the patient out of the operating room. This process maximizes the chance of removing as much tumor as possible and improves patient outcome.
The system can be set up in several ways, with the imaging instruments on a sliding mechanism on the ceiling, in an adjacent room, or integrated into the operating room bed. “We can take a picture of the skull to see if we have done the best job possible,” Dr. Chang said. “It’s a powerful tool to have available.”
A recent study of 44 glioblastoma patients found that almost half had a residual tumor after the surgeon thought the procedure was complete. The iMRI allows the surgeon to continue to resect the tumor after the scan for the complete removal of all radiographically visible cancer cells before the skull is closed up.
Another advanced surgical strategy is an awake craniotomy, in which language function directly tested during the procedure by having the patient speak to the surgical team during the tumor resection. This procedure is used when the tumor lies close to the language center of the brain as a way to preserve speech. The patient is sedated without a general anesthesia for initial comfort and then awakened once the brain is exposed.
Since the brain has no pain receptors, there is no discomfort during the actual surgery. The neurosurgeon is able to map the brain’s speech areas as the patient speaks and interacts. If speech is affected during the electrical stimulation and mapping that area of the brain is marked and preserved. This approach is especially useful since many tumors look like normal brain tissue, said Dr. Chang.
Diffusion tensor imaging (DTI) is a type of magnetic resonance imaging that maps the internal structure of the brain. The brain’s neurons are intrinsically interconnected like the branches of a major highway. DTI creates a complex and detailed map of the white matter tracts, which are the internal neurological pathways of the brain. The resulting image shows where the neurons intersect so the surgeon can avoid critical areas.
Dr. Chang showed an image of a tumor that abutted the neurological pathways involved in motor function; DTI enabled the team to plan the surgical approach in a direction that avoided these crucial nerve tracts. In another example, DTI was used to identify and avoid the neural tracks in the back of the brain essential to vision, preserving the patient’s sight.
Another useful technique is a functional MRI (fMRI), which depicts the patterns of activity and creates detailed maps that show which parts of the brain are involved in a particular neurologic process. During the MRI scan, the patient performs a series of tasks, such as speaking, answering questions, and moving the hands to activate the parts of the brain involved in motor, speech reception, and expressive function. The MRI shows the patterns of activation so critical function can be spared while removing the tumor. This powerful tool is especially helpful for patients who have had a previous injury or for those who are bilingual since the site of activity may be moved from its normal location.
The CyberKnife is a robotic radiosurgery system that delivers beams of high-dose radiation with extreme accuracy to treat tumors. It combines computerized imaging with radiation therapy from a linear accelerator to precisely deliver radiation in the three-dimensional pattern of a tumor.
This noninvasive technology is used as an outpatient procedure so patients are back to work or school almost immediately. It is also often more cost-effective compared to surgery or traditional radiotherapy and does not interfere with other treatments such as chemotherapy.
“It is extremely precise and can be used to treat inaccessible tumors,” said Dr. Chang. “It can be used as an alternative to conventional surgery or radiation therapy, and in conjunction with these strategies as part of a multimodality treatment plan.”
The CyberKnife, which was invented by Stanford neurosurgeon Dr John Adler, incorporates a robotic delivery system that can deliver images in real time, which means it can accommodate a patient’s movements during treatment. Multiple radiation beams are used, with each beam focused on the target for an accrued impact. Originally designed to treat brain tumors, it is now used for prostate, pancreas, spine, lungs, and liver. More than 7,000 patients have been treated with the two CyberKnifes at Stanford.
This type of radiosurgery is also an important tool for peri-optic tumors, which are difficult to treat because of their location so close to the optic nerve. Studies have shown that vision is preserved—and in some cases improved—after treatment with the CyberKnife. A similar challenge is addressed with acoustic neuromas, which are accessible for surgery but located right alongside the hearing nerve.
Dr. Chang said that these advances are due in large part because Stanford’s experienced neurosurgeons work as a team with specialists in radiology, pathology, oncology, radiation oncology, and other professionals to improve outcomes and quality of life for people with brain cancer.
About the Speaker
Steven D. Chang, MD, is the Robert C. and Jeannette Powell Professor in the Neurosciences, director of the Stanford Neurogenetics Program and the Stanford Neuromolecular Innovation Program, and co-director of the Stanford Cyberknife Program. A noted expert in radiosurgery technology, Dr. Chang is at the forefront of refining new strategies for using radiation to treat brain cancer. He received his MD and completed his internship, residency, and fellowship at Stanford. He is board certified by the American Board of Neurological Surgery.
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