Cleveland Clinic was, in 1989, one of the early adopters of Medical Linear Accelerator based stereotactic radiosurgery in the United States. Stereotactic Radiosurgery specifically refers to a procedure whereby x-ray or gamma-ray radiation is aimed at a focal point (e.g. an arteriovenous malformation, a tumor, the site of a functional disorder, etc.). The dose distributions achieved by these stereotactic radiosurgery techniques assure large doses to the target volume and much lower doses to the surrounding normal tissues.
Further, Stereotactic Radiosurgery is typically given as a single treatment (single fraction) whereas Stereotactic Radiotherapy is given as a course of treatments (multiple fractions).
Stereotactic procedures (Stereotactic Radiosurgery and Radiotherapy) are a joint effort of the departments of Neurosurgery and Radiation Oncology at the Clinic. Stereotactic radiosurgery and radiotherapy are implemented by a team that includes Neurosurgeons, Radiation Oncologists, Medical Physicists, Dosimetrists, Special Procedures Technologists, Accelerator Engineers, Nurses and other highly-skilled practitioners.
Gamma Knife
The stereotactic radiosurgery treatment system presently available at Cleveland Clinic is a Gamma Knife system. A Leksell Gamma Knife (Elekta Instrument AB, Stockholm, Sweden) is operating at our Cleveland Clinic Health System Gamma Knife Center where it is made available to properly credentialed Cleveland Clinic and Northern Ohio Neurosurgeons and Radiation Oncologists. It functions by delivering beams from 201 Cobalt-60 sources to a focal point (with the patient's lesion already positioned at that focal point). Cleveland Clinic Health System's Gamma Knife began stereotactic radiosurgery operations on January 27, 1997.
Stereotactic Radiosurgery Process
A patient arrives early in the day prior to stereotactic radiosurgery and a rigid ring (usually called a "frame") is attached to their skull with four "pins." This frame provides a solid reference for both targeting and treatment during stereotactic radiosurgery.
The stereotactic radiosurgery patient is then sent for CT and/or angiographic and/or MRI imaging. Just prior to each imaging procedure, an "indicator-box," with fiducial markers, is attached to the frame. The resulting images contain marks that enable the stereotactic radiosurgery team to very accurately determine the position of the target (relative to the head-frame).
While the stereotactic radiosurgery patient relaxes in a waiting room, the team members use a sophisticated computer system to produce a detailed and optimized plan of treatment (maximizing radiation dose-to-target while minimizing the dose-to-normal-tissue). This is accomplished when the team members interactively view a detailed map of the dose deposited within the patient and adjust plan parameters for the most beneficial distribution. When the preferred plan is selected, it will specify how to position the patient for stereotactic radiosugery treatment, the blocking of any of the 201 beams, and the treatment time for each "shot" of the several that might be needed for a plan.
Once the plan of treatment is ready, the required treatment unit accessories and treatment aids are prepared for the procedure. A lengthy set of quality assurance (QA) and alignment steps are implemented to assure high accuracy and precision for the treatment.
Once the QA is done, the patient is positioned for stereotactic radiosurgery treatment with the head-frame affixed in a very precise and accurate way to the treatment couch. The treatment is then delivered as per the computer-derived plan.
Immediately at the end of the stereotactic radiosurgery treatment the patient is freed from the couch and the frame is removed. After a roughly one hour observation period, the patient departs.
Stereotactic radiosurgery is considered an alternative to surgical resection in selected patients. Current indications include metastatic brain tumors, primary and recurrent malignant gliomas, arteriovenous malformations (AVMs), acoustic neuromas, meningiomas, pituitary adenomas, and some functional diseases.
The stereotactic radiosurgery treatment method (Gamma Knife) used for any particular patient will depend upon that persons requirements. Each of these treatment systems has their strengths. Cleveland Clinic is among a very few institutions that can offer two different, optimized, approaches to stereotactic radiosurgery.
