During a linac SRS procedure, the patient is carefully positioned so that the intracranial lesion is located at the linear accelerator's isocenter.  Special radiosurgery hardware and software are used to achieve a high degree of conformation to the tumor's 3-dimensional shape, thus delivering significantly less radiation to the brain and other structures inside the head than conventional X-ray therapy. Also, in most cases, only a single radiation treatment is required.  A relative advantage of linear accelerator radiosurgery as compared to that of the Gamma Knife is that a larger X-ray beam can be used, allowing larger lesions to be treated with better dose homogeneity and with less repositioning of the patient.

Emory's Stereotactic Radiosurgery Program

     The SRS program at Emory has been active since 1989, and we have treated more than 1000 patients during this period.  Our SRS program  uses a dedicated and modified 6 MV linear accelerator with the BrainLAB M3 micro-multileaf collimator.  Images from one of several state-of-the-art CT and MRI scanners are transferred over the computer network to be used for treatment planning. This planning is performed on a graphics workstation with the BrainScan treatment planning software.  

Radiosurgery Procedure & Treatment

     These patients typically have an MRI scan performed as part of the diagnostic workup in the weeks prior to radiosurgical treatment.  The images from this diagnostic MRI scan are used for the initial treatment planning a day or two before the radiosurgery is performed.  On the morning of the actual radiosurgery procedure, the patient is admitted to the Neurosurgery service where a stereotactic frame is applied to the patient's skull under local anesthesia.  This stereotactic frame is the apparatus that enables the physicians to localize the tumor in three-dimensional space with extreme accuracy.  A detailed CT scan with the headframe in place is obtained in the Radiation Oncology department.  The patient is then returned to his or her room while the remainder of the treatment planning is performed.     

     Rigid attachment of the frame to the skull allows the location of structures seen on the imaging studies to be determined in reference to the external frame itself, a process known as stereotaxis.  Images from the CT scan are transferred over the Department of Radiation Oncology's computer network for treatment planning.  These CT images (with the headframe in place) are precisely fused to the diagnostic MRI images using radiosurgery planning software.  This approach enables the physicians to incorporate both the highly detailed pathology (tumor) information from the MRI scan, as well as the accurate normal anatomy and stereotactic positional information from the headframe CT scan.  The neuroradiologist, neurosurgeon, and radiation oncologist, with the aid of magnified, computer-displayed images, precisely determine the location of the target lesion and sensitive brain structures.  A unique treatment plan then is developed for that patient.

     The patient then is brought to the treatment room, placed on the linac table, and accurately positioned via the stereotactic frame.  The treatment is typically delivered over a period of 30 to 40 minutes.  Once the treatment is completed, the stereotactic headframe is removed.  Nearly all of these procedures are performed on an outpatient basis; after the headframe is removed, the patient is observed for an hour or so and then is able to return home.

     The entire procedure is very much a team effort.  Physicians and radiation physicists work together throughout the planning and treatment process.