Radiation Oncology Services
Lifespan Cancer Institute

Glossary of Medical Terms


The following medical terms are related to Gamma Knife treatment:

  • Arteriovenous malformations (AVMs): A tangling of minute blood vessels in the brain in which the blood from the arteries abnormally flows into the veins. The Gamma Knife treats this tangling, often referred to as the "nidus."
  • Cerebral arteriography or angiography: A procedure that enables blood vessels to be seen on film after the vessels have been injected with a substance that is visible to x-rays. The resulting films are called angiograms or arteriograms. This imaging technique gives more precise information than MRI or CT scans. Digital subtraction angiography (DSA) is the technique currently used.
  • Cobalt-60: The radioactive source (isotope) used in the Gamma Knife. Pellets of the isotope are enclosed in 201 small metal cylinders, which are mounted inside the Gamma Knife.
  • CT or CAT scan (computerized tomography): A method of examining body tissues such as the brain using x-rays, with the beam passing or scanning through a body part and a computer measuring the density of the organ being examined. It compiles an image or picture by computer analysis. CT scans are excellent for identifying bone structures and to detect a hemorrhage.
    More about CT scans
  • Collimator helmet: A half spherical, helmet-like device with small openings of different sizes through which the radiation passes into the brain during a Gamma Knife procedure. It is attached to the couch. The patient's skull is positioned in the helmet by the stereotactic head frame. There are four different helmets with different size portals (4, 8, 14 and 18 mm).
  • Gamma radiation: Similar to x-ray (photon radiation) but much more powerful. It is not a laser. Gamma radiation is invisible, cannot be felt and is able to penetrate deep through tissues. The radioactive source is Cobalt-60.
  • Magnetic resonance imaging (MRI): A scanning technique that uses a very powerful magnet to record, process and analyze the radio waves generated by body tissues during the exam. The result is a computer-generated image of the area scanned. MRI is excellent for scanning soft tissue structures. Contrast (gadolinium) is usually injected to make tumors show up better.
  • Radioactive source: The source that emits the radiation (gamma radiation in this case) by the process of radiation decay. Cobalt-60 is the radioactive source used in the Gamma Knife.
  • Stereotactic head frame: An aluminum frame that is secured to the patient's head after the patient receives local anesthesia. It is used to define the target location and secure the head in the Gamma Knife's collimator helmet.
  • Stereotactic radiosurgery: The highly precise delivery of a single, high dose of radiation to a small area in the brain. This is achieved by letting a large number of beams all focus simultaneously at this area. Gamma Knife is one type of stereotactic radiosurgery and was the first to be used in clinical applications.