What is it?
Stereotactic radiosurgery (SRS) is a specialized radiation procedure in which the radiation is delivered in one dose. The primary advantage of this procedure is that patient movement is minimized, via the use of a stereotactic head frame which is attached to the skull. This allows for us to be much more accurate in our treatment delivery.
The word “stereotactic” implies the use of a 3-dimensional coordinate system to more accurately deliver the radiation. “Radiosurgery” implies the use of a single high dose of radiation, in an attempt to ablate the radiation target. Despite the word “surgery” being a component of the word “radiosurgery,” there is no surgical intervention. As described in the section on fractionated radiation, therapeutic radiation uses high energy photons to treat the tumor. The mechanism by which a single high dose of radiation treats the tumor is not fully understood, but perhaps high doses cause the tumor cells and neighboring blood vessels to undergo a coordinated series of events leading to cell death, termed “apoptosis.”
What machine delivers the radiation?
The University of Rochester uses a linear accelerator (LINAC) based system, specifically the Novalis Shaped Beam Radiosurgery platform which uses BrainLAB planning. The Novalis LINAC allows us to modify the shape of each radiation beam, so as to provide better shaping of the radiation dose distribution. There are other SRS systems which are well publicized, including the Gamma knife and Cyberknife. While each system has its unique attributes, they all accomplish the same result. The University of Rochester has been performing SRS for over decade, and has used the Novalis Shaped Beam Radiosurgery system since 2000. The University of Rochester also has a Varian Trilogy and tomotherapy machines, which have the capability of SRS.
What is its goal?
The goal of SRS to kill the cancer cells (or the cells comprising a benign tumor) while minimizing the risk of damage to the surrounding tissues. The ultimate goal is to prevent further growth of a tumor, and in some cases regression of the tumor. For patients with trigeminal neuralgia, in which there is no tumor present, the goal of radiation is to achieve pain control.
How is it done?
The SRS procedure is a joint effort by the radiation oncologist and neurosurgeon. There are many other people who are involved in the procedure as well, including radiation physicists, radiology technicians, radiation therapist technicians (RTT) and nurses. SRS is generally an all day procedure.
A specialized MRI scan is performed in the days prior to SRS, or on the morning of SRS. The morning of the SRS, the neurosurgery team places a head frame on the patient. A CT scan is then performed with the head frame attached to the CT table. The radiation oncologist and neurosurgeon use the MRI and CT scans to pinpoint where the radiation dose should go, and determine what critical areas of the brain need to spared from higher doses of radiation. With the help of physicists (with PhD or MS level of training), a plan is generated in which multiple radiation beams are aligned to hit the radiation target. A way in which to visualize this is to imagine many spotlights fixed onto one spot. After a plan is generated, the physicists perform quality assurance on the LINAC to assure accuracy of < 0.6 mm.
In the late afternoon, the radiation is delivered. The radiation oncologist and physicist align the patient on the treatment table, with the assistance of LASER beams directed at a localizer frame which is attached to the stereotactic head frame. Once the patient is accurately aligned, the treatment is delivered. During treatment, the radiation therapist will move the patient and adjust the settings on the LINAC several times, so as to align the different radiation beams. The total time that the patient is on the treatment table is from 20 minutes to an hour, depending on the complexity of the treatment and the number of lesions being treated.
What is the success rate?
The success at controlling the tumor depends on many factors, including what type of tumor is being treated, where the tumor is located and what other treatments (such as surgery or chemotherapy) are given. Your doctor can discuss this in much more detail with you since every patient’s case is unique. Despite being able to tell a patient the odds of success, no physician can tell a patient with certainty whether or not radiation will be successful for that patient.
What are the risks?
Most patients tolerate the SRS quite well. Occasionally patients experience mild headache, nausea, or numbness on the scalp. Hair loss on the scalp is uncommon, but can occur in small patches. Symptoms from tumor swelling can occur; most patients receive a dose of steroids prior to the procedure which minimizes this risk. Seizure can also occur; most patients receive a dose of anti-seizure medication which minimizes this risk. While radiation can impact vision, strength and sensation, every attempt is made to minimize these risks. The risk of symptomatic necrosis- a form of tissue breakdown from radiation exposure – is low. The risk of radiation causing a cancer years or decades later is also low.
How long will I stay in the hospital?
Most patients stay overnight and are discharged the next morning.