There are 5 main steps in the treatment.

Step 1: Headpiece Frame Placement
A local anesthetic and mild sedative are given to prevent discomfort and relax patients while the headpiece frame is attached to the patient's head with four pins. Once in place, the frame is used to localize the target area and immobilize and position the patient's head during treatment with the Gamma Knife.

Step 2: Diagnostic Imaging
Patients then undergo an MRI to help physicians determine the precise location and size of the tumor or abnormality. Patients with AVM will also undergo an angiogram.

Step 3: Treatment Planning
Using the information obtained from diagnostic imaging, the Gamma Knife's computerized treatment-planning software develops a three-dimensional picture of the target lesion and the surrounding tissues. Radiation dosage and duration of treatment are then determined.

Step 4: Gamma Knife Procedure
Convergent X-ray beams of cobalt radiation are aimed at the targeted tumor or malformation. At the site of the tumor or abnormality, the separate beams converge delivering enough radiation to eradicate diseased tissue while sparing surrounding normal tissue. The Gamma Knife at Johns Hopkins has been designed and built with the most current robotics and computer technology to ensure accurate positioning. Treatment time ranges from approximately 15 minutes to a couple of hours depending on the nature of the diagnosis. It is non-invasive and painless, so patients remain awake during treatment. Specially trained staff, located in an adjoining room, maintain constant visual and voice contact with patients during treatment.

Step 5: Recovery
Most patients are treated on an outpatient basis. In some cases, an overnight stay in the hospital is required for observation and monitoring. The majority of patients resume normal activities within a few days. Patients will return to their personal physician for follow-up diagnostic tests to monitor and assess their progress.

For more technical and specific explanations in the steps involved, please read below.

Gamma Knife Surgery involves the "center of arc" principle in which the center of the target is the center of the circular arc rotation. This allows a 3D approach (otherwise known as a stereotactic approach to the brain). More will be discussed later about this principle.



The cross section view of the Gamma Knife below shows the large shielding ball, which contains radioactive cobalt pellets that provide the radiation delivered by the Gamma Knife. The total weight of the Gamma Knife ball alone is approximately 44,000 lbs.



The total weight of the radioactive pellets used for which 44,000 lbs of steel are required for adequate shielding is only 5 ounces. The half life of these pellets is 5 years approximately, meaning that in this time, the cobalt would lose half of its radioactivity.

The loading process is when the radioactive pellets of cobalt are placed within the Gamma Knife machine. It is a quite lengthy process that may take several days for completion. The loading device shown below weighs 16,000 lbs.



The beams of radiation of the Gamma Knife are seen converging upon the target, which may be a brain tumor, blood vessel disorder, or nerve. This principle is not only used for Gamma Knife, but also for open neurosurgery.



To better understand the principle, consider the following example. As sunlight is not strong enough to burn a hole in a paper, we take a magnifying glass and focus the sunlight beams onto a single spot, so that the focused energy can burn a hole in the paper. The same principle holds for Gamma Knife Surgery. Each individual gamma ray of energy, by itself, is too weak to cause much harm to a brain tumor. However, when 201 beams of radiation energy are gathered together, the focused target will receive an enormous amount of radiation.



The accuracy of the Gamma Knife is critical for the doctors and the patients. In the dose profile shown below, we see that even millimeters away from the center of the target where a great deal of radiation is received is only exposed to minimal amounts of radiation. Without this accuracy, the patient would get normal brain tissues damaged as well.



Down below is a picture of the helmet that the patient has to wear for the Gamma Knife Surgery. The helmet is critical as it holds the collimators, which shape the beams of radiation. Radiation would pass through these ports in the helmet, into the brain, then it would converge on the target.



Here is a close-up view of the collimators which are located in the helmets. They will shape the beams and block out all but a small portion (see the small holes) of the individual beams of the Gamma Knife, which allows the surgery to be as accurate as possible.



Also, the patient would have to wear the Leksell stereotactic frame for the surgery. The placement of the frame takes a several minutes,and depending upon the anesthetic used, many patients are not at all bothered by it, and sometimes, they don't even remember having it placed upon them.



Afterwards, the patient will go through diagnostic imaging prior to the actual surgery procedure. For example, in the diagram below, the patient is going through an MRI machine. This is done so that the surgery team can identify the target (a brain tumor, blood vessel malformation, etc) upon which the radiation will be focused. Usually, diagnostic imaging involved would be a CT or an MRI scan, or an angiography or a PET scan in some cases. Generally, the MRI scan shows the most favorable results, especially for a small brain tumor.



A CT scan may also be used when a patient cannot undergo an MRI scan (e.g. if a patient has a pacemaker). The diagram below shows a CT scan of the head with the Leksell frame already fixed to the patient's head. The surgery team would try to determine the coordinates of the target.



By using a software on the computer called the Gamma Knife Planning Station Software, the team can see the modeling and simulation of the treatment outcome, which would help in ensuring the safety of the treatment, as well as the accuracy.