2. What is Stereotactic Radiosurgery?
• Stereotactic radio surgery is a non-surgical technique used to selectively
destroy abnormalities within the brain.
• Using a machine called the gamma knife, 201 sources of cobalt 60 are
focused to small point (isocentre).
• Ranging from 4-18mm in diameter.
• This tiny area provides very high dose of radiation which is used to irradiate a
focal point within the brain with sub-milimetre accuracy.
3. What is a Gamma Knife?
• Gamma knife is a treatment unit designed specially
for intracranial radiosurgery.
• The gamma knife is a stereotactic radio surgical
instrument which can deliver a single, high dose of
precisely focused radiation with pinpoint accuracy
to any part of the brain
• The gamma knife was developed in Sweden in 1968 for the
treatment of brain disorder.
• Neurosurgeon Dr. Lars Leksell developed the gamma knife after
years of searching for a non-evasive way to treat functional disorders
of the brain.
• The gamma knife wasn’t introduced into the United States until
• There are now over 200 gamma knife centres worldwide.
5. Why Choose Gamma Knife?
• It is the latest advancement in noninvasive radiosurgery treatment of tumors
and abnormalities in the brain.
• Gamma Knife radiosurgery results in minimal damage to healthy tissues
surrounding the target.
• Low risk of side e
• Gamma knife radiosurgery is often a safer option than is traditional brain
• One time therapy completed in a single day.
6. Why Choose Gamma Knife?
• It removes the physical trauma and the majority of risks
associated with conventional surgery.
• It may be use an alternative to standard neurosurgical
operations or as an adjunctive therapy in the treatment.
• No surgical incision is required.
7. Components of Gamma Knife
• A radiation unit with an upper hemispherical
shield (central body).
• Lower half of hemisphere as a shielding door.
• An operating table & sliding cradle.
• A set of 4 helmets providing circular beam
with diameters 4, 8, 14, 18mm of isocentre.
• A Control unit.
• Planning computer system. Gamma Knife Helmet
8. What can be treated with Gamma Knife Stereotactic Radiosurgery?
• Brain Metastases
• Pituitary Adenoma
• Central Neurocytoma
• Nasopharyngeal Carcinoma
• Selected Gliomas
• Other Skull Base tumors
10. Factors Considered for Gamma Knife
• General medical conditions.
• Location and size of the brain
• Previous treatments.
11. Gamma knife Procedure
• Begins with placement of this head frame
-by a neurosurgeon - local anesthetic
• four screws are used to tightly secure a rigid metal frame to
the patient’s skull.
• the patient is brought to the CT scanner and fixed to the
scanning table in a supine position.
• A CT scan is acquired for treatment planning, and the patient
is then released from the table and awaits treatment.
12. Gamma Knife Procedure
Ct Scans ,MRI and angiograpies are used cumulatively to procedure a 3D computer
image of the brain in which the oncology team can highlight the area to be treated,
and formulate a dose traetment plan.
Angiography CT SCAN MRI
13. Steps of Gamma Knife Planning
•Acquired image transferred to TPS
•Co-ordinates of target are recognised by computer with help of
•Target volume de
ned by drawing margin to lesion
•Dose level that would ideally cover entire target volume selected
•Maximum dose to tumor is set
•Target volume is covered with shots, each application of radiation is referred to as
•Shot produces isocenter that can be de
ned as active radiation
14. • No. Of shots required to deliver dose to entire tumour volume
is determined by size, geometry and location of tumor
• Usually more than one shot / isocenter is required to treat a
tumor because of smaller
eld size and
xed beam geometry.
• Optimisation of parameters no. of shot, shot sizes, shot
location, shot weight, collimator helmet, plugging pattern.
Steps of Gamma Knife Planning
15. Steps of Gamma Knife Planning
• The intensity of each shot and its weight depends on how long
the involved collimator remains open.
• Shot position de
ned relative to stereotactic frame by X,Y & Z
co-ordinate position so that target is precisely at the isocenter of
• Once the treatment plan is completed, plan is exported via
network to console computer
16. Gamma knife - SRS treatment planning
• The treatment planning process begins as a cooperative
effort between neurosurgeon, radiation oncologist, and
17. Gamma knife - SRS treatment planning
• When complete, radiation dose delivery is planned by placing one or more
isocenters. Each isocenter represents a point at which all of the beams will
converge for a certain amount of time.
• The result is a high radiation dose around the isocenter with a sharp falloff in
the surrounding tissue.
• Spherical lesions require a single isocenter ,while irregular shapes require
multiple isocenters adjacent to one another to conform to the desired shape.
18. Gamma knife - SRS treatment planning
prescribed dose- four isocenters are used in this plan.
19. Gamma knife - SRS treatment planning
• When planning is complete, the patient is placed supine
on the Gamma Knife table and the head frame is fixed to
• The patient is then monitored from outside the room
while treatment is given, usually 30 to 90 minutes.
20. How It Works / Gamma Knife Procedure
• Gamma Knife radio surgery works in the same manner as
other types of therapeutic radiation.It destroys the DNA
of tumor cells causing them to be unable to reproduce
21. Gamma Knife Procedure
Before treatment starts, the patients put on an IV and given intravenous
to prevent dehydration because the patient cannot eat drink until the traetment
The patient may get local or generalized anesthesia.
• If a localized anesthesia is used, the patient may also be given a
sedative through the IV in order to minimize movement during the
22. Gamma Knife Procedure
After the anesthesia,the patient in
tted with a steriotactic
frame.The frame is used as a measuring guide that helps to
accurately position the patient.
23. Gamma Knife Procedure
Once correctly positioned on the gamma knife bed, the
stereotactic frame is attached to a collimator helmet.
Stereotactic Frame Collimator Helmet
24. Gamma Knife Procedure
The patient is slid into the
gamma knife cavity which is like
a heavily shielded globe canting
the radiation source.
26. Gamma Knife Procedure
• 201 Cobalt gamma ray beam
sources are arrayed in a hemisphere
and it aimed through a collimator to
a common focal point.
• The patient head is positioned within
the gamma knife so that the tumor is
in the focal point of the gamma rays.
27. Effectiveness of treatment
• The gamma knife is accurate to within 0.3mm.
• Usually only 1 treatment is needed.
• Because of continued advances since its development in
1968,gamma knife presently has an overall success rate of
28. Side Effect of Treatment
• Swelling of the brain
• Vision Changes (rarely)