Stereotactic radiosurgery is a technique for delivering high dose radiation in a very precise manner to a specific region of the brain. It is a commonly used technique for treating benign and malignant brain tumors, as well as vascular malformations (abnormal blood vessels that are prone to bleeding without treatment). When SRS is used, the target receives a very high dose, but the surrounding brain receives a minimal amount of radiation. The entire process is noninvasive. The likelihood of serious long-term side effects with SRS is typically low and recovery periods are often short.
Because the brain does not move (as do the lungs, for example) and the skull serves as a stable gauge for the location of the tumor, the clinical team is able to deliver high doses of tightly focused radiation beams with pinpoint precision to treat tiny tumors. Many patients can be treated in a single radiation session. Patients with large tumors sometimes require a lower dose of radiation given over multiple treatment days, a technique called stereotactic radiotherapy (SRT).
SRS requires immobilization with a customized external mask that is molded to the contours of the face and head. The use of pre-treatment CT and MRI scans and special stereoscopic x-rays allows for a highly targeted radiation plan without the need for a head frame or pins attached to the skull, which were techniques needed in the past. SRS has revolutionized the way we treat many patients with brain tumors, and in certain scenarios it can improve patient survival.
A significant percentage of patients we treat with SRS have brain metastases. In patients with 1-4 brain metastases, SRS is generally favored over whole brain radiation, a technique that treats the entirety of the brain. Yet in patients with more than 4 brain metastases, whole brain radiation is considered more standard. Our radiation oncologists have designed a clinical trial to test the effectiveness of whole brain radiation against SRS in patients with 5-15 brain metastases. If successful, this may be the first trial to assess whether patients with 5-15 brain metastases can be safely treated with SRS.
Our radiation oncologists and physicists have also developed a technique called one-isocenter, multi-target volumetric modulated arc therapy to treat many targets in the brain in one session. Historically, if a patient had multiple tumors in the brain, radiation had to be delivered to each tumor in sequence, causing treatment to last many hours. Using this new technique, multiple tumors can be treated in 15-30 minutes.
We have also implemented a patient-tracking system called optical surface monitoring system (OSMS), which monitors patient motion in real-time. If the patient were to somehow move outside of the 1mm tolerance threshold, the treatment stops until patient motion has ceased. This new system helps increase the precision of the treatment and will hopefully lead to better patient outcomes.
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