After patients arrive at the Gamma Knife Center they are given a mild sedative (children are often completely anesthetized). Shortly after that time, a box-shaped head frame is attached to the head with four screws (two in front and two in back). The key to the gamma-knife's precision lies in this box-shaped frame. The frame serves two purposes: 1. It holds the patient's head perfectly still when radiation is given. 2. The frame acts as a reference point in determining exactly where the beams of radiation should converge.
The four spots on the scalp where the screws enter are numbed first with injections containing an anesthetic similar to that used by dentists. Hair will not be shaved, but it may be tied back into a ponytail if it is long. The head-frame is lightweight, so patients are able to move their head around after the frame is attached to the skull.
Once the head-frame is attached, an imaging scan (MRI or CT) is performed to locate the exact area inside the skull that needs treatment. Even though a scan may have been done before, these scans must be repeated with the head-frame in place.
A transparent plastic box is attached to the head-frame for the imaging scans. This box has special material in it that acts as localizer when the physicians plan the necessary radiation configuration used for treatment.
After the imaging scans are taken, it may take an hour or more for the targeting plan to be computed. During this waiting period, patients are taken to an area in the Gamma Knife Center where they can relax.
When it is time for the treatment, the patient is asked to lie down in the radiation machine so that the patient's head is put into a helmet. The helmet attaches to the head-frame, which keeps the head perfectly still. This type of setup ensures that there is no head movement. The lack of head movement allows the radiation beams to converge on the target and not on the healthy tissue surrounding the target area(s).
The helmet does not cover the face and the radiation is not felt by the patient. There is no noise during the treatment.
The number of minutes that each radiation dose lasts is determined during the dose planning. Treatment may include multiple doses. Sometimes, more than one type of helmet and head position is used to deliver the radiation.
The head-frame stays on the head through the entire procedure. When the frame is removed, the places on the scalp where the screws entered may be a little tender, but the pin sites typically do not scar. Some patients may have a headache or feel nauseated for a few hours after the procedure.