Stereotactic Radio Surgery
What is SRS?
Stereotactic radio-surgery, or SRS, is a method for delivering radiation to brain tumours, which may be given in place of surgery. It is used to treat tumours that start in the brain as well as brain metastases (cancer that has spread to the brain from other parts of the body).
The technique uses advanced imaging technologies combined with sophisticated computer guidance to deliver a highly targeted and intense dose of photon radiation. The radiation conforms to the three-dimensional shape and size of a tumour, resulting in minimal exposure to the rest of the brain and fewer side effects than conventional radiation techniques.
Which patients are good candidates for SRS?
Stereotactic radio-surgery has become an increasingly common approach for patients who have smaller brain tumours. Other candidates for stereotactic radio-surgery also include those patients whose disease is not surgically accessible or is too advanced for neurosurgery, as well as those who cannot tolerate anaesthesia.
How is SRS given?
To deliver stereotactic radio-surgery, a radiation oncologist uses a computerised system to shape the radiation beam to match a three-dimensional outline of the tumour. This outline is generated by MRI and CT scans, which you will have before your procedure.
Radiation oncologists collaborate closely with medical physicists to design a treatment plan that allows the delivery of radiation that conforms to the dimensions of your tumour.
What are the benefits of SRS?
The technique allows the radiation to be delivered with greater precision to the cancerous tissue than other types of radiation therapy, sparing the surrounding healthy brain tissue from any significant dose. The system also controls the intensity of the beam so that no area gets too large a dose.
SRS helps avoids the risk of hemorrhage, infection, and anesthesia that come from surgery. It can be done as an outpatient treatment, and requires only minimal interruption of other treatments, such as chemotherapy. The results for SRS for brain metastases appear to be equivalent to the results for surgery to remove the tumor.
This single-day, high-dose treatment can also replace other types of radiation therapy that are delivered in lower daily doses for a longer period of time (usually several weeks).
How is the procedure performed?
Stereotactic Radio Surgery Using the Gamma Knife Gamma Knife radio-surgery involves four phases: placement of the head frame, imaging of the tumour location, computerised dose planning, and radiation delivery.
In the first phase, a nurse will place a small needle in your hand or arm to give you medications and contrast, if needed, for imaging. A neurosurgeon will use local anaesthesia to numb two spots on your forehead and two spots on the back of your head. A box-shaped head frame will be attached to your skull using specially designed pins to keep your head from moving within the frame until the treatment session is finished. This lightweight aluminium head frame is also a guiding device that makes sure the Gamma Knife beams are focused exactly where the treatment is needed.
Next, you will be taken to an imaging area where a magnetic resonance imaging (MRI) scan will be performed to show the exact location of the tumour in relation to the head frame. In some cases, a computed tomography (CT) scan may be performed instead of, or in addition to, an MRI scan.
If you are having treatment for an arteriovenous malformation, you may also have an angiogram. New developments in Gamma Knife software allow for pre-planning. Therefore, you may have your treatment planning MR images prior to the day of your treatment to improve the efficiency of the treatment process.
During the next phase, you will be able to relax for an hour or two while your treatment team identifies the tumor(s) for treatment and develops a treatment plan using special computer software to optimally irradiate the tumor and minimize dose to surrounding normal tissues.
Next, you will lie down on the Gamma Knife bed and your head frame will be fixed to the machine before beginning treatment. You will be made comfortable with a pillow or wedge-shaped sponge under your knees and a blanket over you. The treatment team will then go to the control area outside the treatment room to begin your treatment. You will be able to talk to your physician through a microphone in the helmet, and a camera will allow the team to see you at all times. The bed you are lying on will move backward into the Gamma Knife machine. You will not feel the treatment and the machine is very quiet.
Depending on the Gamma Knife model and the treatment plan, the whole treatment may be performed without interruption or it may be broken up into multiple smaller parts.
As soon as the treatment is finished, you will sit up and the head frame will be removed. In most cases, you should be able to go home soon afterward. Radiosurgery Using the Linear Accelerator Linear accelerator (LINAC) SRS is similar to the Gamma Knife procedure and its four phases: head frame placement, imaging, computerized dose planning and radiation delivery. LINAC technology is much more common than Gamma Knife technology and has been in practice for a similar length of time. Unlike the Gamma Knife, which remains motionless during the procedure, part of the LINAC machine (called a gantry) rotates around the patient delivering the radiation beams from different angles. Obtaining the MRI before frame placement is also a more routine pre-planning practice with LINAC-based SRS.
A CT with the frame in place is also commonly acquired. a robotic arm moves the compact LINAC around the patient under image-guidance.
This facility is not routinely available with us. If needed we use FFF capabilities of LINAC to deliver high doses.