An anesthetic is applied (local anesthetic for adults and general anesthetic for children), and the patient is fitted with a stereotactic frame. This is a measuring guide that helps the Gamma Knife team accurately position the patient. Next, imaging studies such as MRI, CT scan, or angiography are performed to allow the physicians to precisely localize the tumor or vascular malformation. The tumors or vascular malformations can be targeted accurately to prevent injury to surrounding tissue.

Using 3-D computer imaging, the Gamma Knife team develops a radiation dose plan. The patient is then placed on the Gamma Knife bed and the frame is attached to the collimator helmet. The helmet contains 201 evenly distributed portals through which radiation beams will be directed. Individually, the beams are small and harmless. Only at the precise point where they intersect are they powerful enough to affect the targeted abnormality.

Next, the bed slides the patient headfirst into the Gamma Knife cavity, a heavily shielded globe containing the radiation source. The Gamma Knife team uses a video camera to monitor the patient from an adjacent room, and communicates with the patient through a two-way intercom. The Gamma Knife treatment begins, and the patient typically feels no pain or minimal discomfort, from the frame. The treatment itself is painless.