At the Gamma Knife Center they like to be thorough. Before they perform radiosurgery on someone’s brain they do exhaustive tests to locate the problem. One of the problems they treat is called Cerebral Arteriovenous Malformation, AVM for short. An AVM happens when small blood vessels in the brain form a tangled mass. This mass can cause brain cells to die, it can start bleeding, and it often causes headaches and sometimes seizures.
Gamma Knife Radiosurgery (GKR) has become a good alternative to open brain surgery for these patients. A Gamma Knife isn’t really a knife, but a large machine that generates a highly concentrated beam of radiation that is used to specifically target a lesion in the brain.
While the treatment itself is quick and painless, the planning that goes into it is elaborate and takes a team of neurosurgeons and physicists. They must determine the exact location of the AVM, how big it is, and how much radiation to use without causing any unnecessary damage to healthy parts of the brain. To do this they have to take an image of the brain that visualizes the AVM.
Dr. Steven Isaacson from the Gamma Knife Center and his colleagues recommend doctors use not one but two imaging sources in planning for radiosurgery. They described their methods in the International Journal of Radiation Oncology Biology and Physics. They looked at ten cases of AVM that were treated at their center and compared the planning method used to the patient’s outcome. They concluded that the results of two tests in particular should be combined to best locate the AVM.
These tests are Magnetic Resonance Angiography (MRA) and Digital Subtraction Angiography (DSA). Both tests use Angiography, that is they rely on IV driven contrast dye to make the blood vessels in the brain more visible. In MRA, 3D images are taken using a Magnetic Resonance Imaging (MRI) machine. In DSA, 2D X-Rays are taken. When combined, these tests together form a more accurate picture of the size, shape and location of the AVM.
Dr. Isaacson and his colleagues emphasize that, though small, human error can also come into play when these tests are interpreted and therefore should be taken into account. At the Gamma Knife Center they use a mathematical formula that combines all these factors in planning for radiosurgery. A plan that is this in-depth, they report, increases the accuracy of the radiosurgical treatment and more importantly, patients do better.
To learn more, see the article, Incorporate Imaging Characteristic into an Arteriovenous Malformation Radiosurgery Plan Evaluation Model, in the April 2008 Issue of the International Journal of Radiation Oncology Biology and Physics
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