Will I experience pain when the stereotactic frame is attached?
The Barrow Gamma Knife Center is one of only a few centers in the U.S. where patients are placed under anesthesia while the stereotactic frames are being attached. The type of anesthesia used is known as conscious sedation. The appropriate anesthetic drugs are delivered under the care of an anesthesiologist. Usually, patients wake up after about 20 minutes and have no recollection of the frame placement procedure. The pin sites where the frame is attached to the skull are injected with a local anesthetic that lasts 8 to 12 hours. If the patient later experiences pain or discomfort due to the frame placement, further administration of medication may be considered to help them get through the treatment.
Is Gamma Knife treatment painful?
No, patients do not see, hear, smell, feel, or otherwise sense the gamma radiation beams administered during treatment. When the frame is placed, some positions may be uncomfortable for the patient during treatment. If that is the case, every effort is made to make the patient comfortable, using extra pillows and padding as necessary.
How long does it take to deliver a Gamma Knife treatment?
The total treatment time depends on the size and complexity of the patient's lesion and on the dose or doses to be delivered. The treatment plan for each patient is individually custom-tailored to the patient's specific medical needs, with treatment times varying from as short as 15 minutes to as long as 4 hours.
What type of radiation does Gamma Knife treatment involve?
The Gamma Knife uses Cobalt-60 sources that emit two discrete energy levels of gamma rays. These beams, 1.17 and 1.33 MeV (megaelectronvolts) in energy, are emitted in approximately equal proportions, to create an effective treatment beam energy of 1.25 MeV. During the process of radioactive decay, a proton in the Cobalt-60 nucleus is transformed into a neutron, leaving Nickel-60 as the byproduct. To maintain radiobiologically effective dose-rate levels, the Cobalt-60 in Gamma Knife units is typically replaced soon after one Co-60 half-life, or 5.26 years, has passed.
How does the Gamma Knife deliver a high dose of radiation to the treatment target but very low doses to normal adjacent tissues?
The 201 Cobalt-60 sources direct their gamma-ray beams to converge at the center of the source distribution hemisphere. Using interchangeable collimators--devices with different-sized apertures to define the beam size--a small sphere of radiation dose is created at the center point where the beams converge. At the periphery of this sphere, the dose of radiation falls rapidly from 80% to 20% of the maximum dose level within distances as narrow as 0.2 mm. Any normal tissue through which a single beam passes to reach the center point receives less than 0.5% of the dose level where all 201 beams converge. Treatment plans are developed that take advantage of these properties so that normal or radiation-sensitive structures are spared from receiving unacceptable levels of radiation.
Will a patient be radioactive after Gamma Knife treatment?
No. Exposure to Gamma Knife radiation cannot make a person (or anything else) radioactive.
Can the Gamma Knife treat sites outside the head?
No. Sometimes it may be possible (based on the proportions of a patient's head) to treat a region as low as the second cervical vertebra below the patient's skull. This permits treatment of indications such as glomus tumors and some lower brainstem arteriovenous malformations and tumors.
For other sites in the body such as the spinal cord, St. Joseph's Hospital and Medical Center's Department of Radiation Oncology operates an Accuray CyberKnife--a linear accelerator mounted on a precision robot arm that uses treatment-beam geometry very similar to the Gamma Knife.
For more information, please call 1-800-315-0980 or 602-406-6075.