| What is a Gamma Knife? The Gamma Knife
is not a knife, but a highly sophisticated technology that can be used
to replace some conventional neurosurgical procedures.
The body of the Gamma Knife is a shielded container in which 201
sources of Cobalt 60 that are constantly emitting narrow beams of gamma
radiation. These individual beams converge at a central point that is
fixed (fixed isocenter). The patient wears a lightweight head holder
(frame) similar to a 'halo' often associated with head immobilization
seen in neck injuries. The frame is placed on the patient's head using
local anesthetic. At the beginning of a treatment session, the patient
lies on a sliding couch and the head frame is attached to a collimator
helmet which adds additional focus to the beams of radiation.
Computer-driven motors on the helmet position the patient's head so that
the target for treatment will lie at the focus of the beams of
radiation. The actual treatment occurs when the shielding doors of the
Gamma Knife have opened and the couch moves toward the Gamma Knife so
that the collimator helmet docks with the radiation source in the Gamma
Knife unit. At this point the beams of radiation are aligned with the
openings in the collimator helmet so that radiation can pass. The dose
of radiation is determined by the time spent in the docked position and
by the size of the openings in the collimator helmet. During a treatment
session, several different locations in a lesion can be targeted; the
couch will move out of the treating position, cutting off delivery of
radiation, the computer-driven motors will adjust the head position, and
then the couch will move back into the treating position, as many times
as are necessary to complete the planned treatment.
By holding the head immobile and delivering radiation via immobile
sources, the Gamma Knife avoids errors which may be introduced by other
radiation delivery devices which use a mobile radiation source. This
allows precise targeting (within a few tenths of a millimeter).
The Gamma Knife is faster and more precise than other radiosurgical
tools that are currently available. The Gamma Knife procedure can treat
brain lesions with enough radiation to destroy them even in the most
critical, difficult-to-access areas of the brain and yet spare healthy
normal brain tissue. Referred to as "surgery without a scalpel," the
Gamma Knife procedure does not require the surgeon to make an incision
in the scalp, nor an opening in the skull.
Back to questions |
