What is it?
Stereotactic Radiosurgery (SRS) is a radiation technique that uses precise patient positioning and extremely accurate radiation delivery to treat brain lesions in one or up to five treatments. At Duke, SRS is delivered by a Novalis TX® or Varian TrueBeam STX linear accelerator. These machines have state-of-the-art technology, which allows your Radiation Oncologist to give treatment with great precision, speed and patient comfort.
Stereotactic Body Radiotherapy (SBRT) uses the same precise techniques to treat tumors outside of the brain. This is most often used for small tumors in the lung, liver or spine.
What does it treat?
SRS is used to treat many types of brain tumors. The use of SRS is limited by the size of tumors, which generally need to be less than 5 cm in maximum diameter (about 2 inches). Larger lesions up to approximately 3 cm (about 1 ¼ inches diameter) can often be treated in a single session, while larger tumors may require five, lower dose treatments. Treatable tumor types include metastatic lesions (meaning a brain tumor which develops as the result of spread from another primary site), such as breast, lung, melanoma or renal cell cancer. More recently, SRS has been used to treat malignant gliomas, such as glioblastoma (GBM) and anaplastic astrocytoma, that have recurred after previous treatment with surgery, radiation therapy and chemotherapy.
SRS can also effectively treat small, non-malignant tumors, such as meningiomas, acoustic neuromas (also known as vestibular schwannomas) and glomus tumors. SRS is used to treat other brain abnormalities, including arteriovenous malformation (AVM) and trigeminal neuralgia (severe facial pain originating from the trigeminal nerve).
SBRT is used to treat metastatic tumors in the spine, lung, liver, abdominal or pelvis areas. There are limitations to using SBRT including the size and number of lesions. Early stage lung cancer can be treated with SBRT alone instead of undergoing lung surgery. Most often SBRT requires 3-5 treatments, but can be completed in one session if the lesion is small enough.
What is the benefit?
At the time of the consultation visit with your Radiation Oncologist, the specific benefits of SRS vs. any other treatment options will be discussed in detail. In general, SRS for metastatic lesions is very well tolerated with few expected side effects. Since SRS can be completed in a short period of time, it allows the patient to move on quickly to other recommended treatments such as surgery or chemotherapy. For recurrent gliomas, the best option for safely delivering a second course of radiation therapy is using this highly precise SRS technique.
Patients with non-malignant tumors will generally see a neurosurgeon to discuss the benefits of surgery vs. SRS. SRS can be used alone to treat a small tumor, or can be used together with surgery or whole-brain radiotherapy, depending on individual patient needs.
Treatment for AVM is often complicated and may include a combination of surgery, embolization and SRS. Your Radiation Oncologist will collaborate with your vascular neurosurgeon to determine the best treatment plan.
Treatment for trigeminal neuralgia is also complex sometimes requiring other procedures, such as surgery or nerve injections. SRS can still be done following any of these procedures. Successful treatment with SRS can reduce or alleviate facial pain, allowing patients to take significantly less pain medication.
SBRT for an early stage lung cancer can be more effective than standard daily, six week radiation therapy, with potentially fewer side effects. Also, SBRT for metastatic lesions can be used instead of surgery with fewer side effects, or when standard radiation therapy is not the best treatment option.
How often does a patient need it?
SRS can be completed in a relatively short timeframe. Every patient will have an initial consultation visit with a Radiation Oncologist specializing in their diagnosis. Once SRS is agreed upon, one or two planning procedures will need to be done at your next visit. First, a customized plastic-mesh face mask will be made, which will maintain your head in the correct position for treatment planning and subsequent delivery. The face mask is made by warming plastic mesh to make it pliable, which is then placed behind your head and over your face, covering the forehead to the upper lip. If requested prior to this procedure, oral medicine for relaxation or discomfort is available. You must lie still on your back for 40 minutes while the mask cools to conform to the shape of your head. During this time, you will easily be able to breathe and see through the mesh. A CT scan is obtained while you are wearing the mask, taking about 5 more minutes before the procedure is complete. This CT scan will be used to accurately position your head during the SRS treatment. In addition, a new MRI scan may be needed for the SRS planning even if you recently had one completed elsewhere. This MRI is also performed in our department and will require an injection of dye. The SRS treatment is usually ready to be performed in about 4 working days after the planning procedures are done. For larger tumors, SRS may need to be done daily for 5 treatments.
SRS for treatment of trigeminal neuralgia requires a different method of head immobilization. Instead of the plastic-mesh face mask, a light-weight metal stereotactic frame is used. After injecting a local anesthetic into the scalp and ensuring that the area is numb, the head frame is attached to the patient’s skull with four pins. A Neurosurgeon performs this procedure in the radiation Oncology clinic, with the aid of a Radiation Oncologist. Patients may initially feel pressure, similar to a tight headband, for five to ten minutes after the frame is placed. While discomfort is usually very slight after that time, anxiety and pain medications are available to you if needed. The frame is placed early in the morning and is followed shortly by a CT scan. An MRI scan is also used to plan the treatment, but this scan is performed one or more days before the day of SRS. The SRS procedure requires careful and precise planning and generally is ready to be performed by early afternoon. While you are wearing the head frame, you will be in a comfortable waiting area equipped with lounge chairs, TV, and accommodation for one visitor. This area is monitored by our nursing staff. The head frame is removed as soon as the SRS procedure is done.
SBRT requires another type of immobilization device. This device would either be a foam-based mold or a cradle made via a vacuum. A CT scan is also performed while the patient is in the treatment device to begin the radiation planning. The first treatment will be scheduled in approximately one week.
How long does the treatment last?
SRS and SBRT treatments are outpatient procedures that take about 45 minutes to complete for one lesion, and somewhat longer for more than one lesion. The majority of the treatment time involves assuring your position is perfectly aligned before each x-ray beam is given. Your radiation therapist will keep you informed about your progress throughout the treatment process. Discharge instructions will be given to you at the SRS completion, including when to return for a checkup and MRI scan. You are free to travel home after the procedure. However, you may be asked to spend the night if you are returning on an airplane.
What are the side effects?
Side effects from a SRS or SBRT procedure vary depending on the location, size, and number of lesions that are treated. During the consultation appointment, any potential side effects will be discussed in detail with you by your Radiation Oncologist. Also, you will be given contact information for your Oncologist and Nurse Practitioner, who are available to answer any further questions or concerns.
Who performs Radiosurgery?
All radiosurgery procedures are performed by a multidisciplinary team consisting of a Radiation Oncologist, radiation physicist, radiation therapists, radiosurgery-specific treatment planners and, depending on the site of the body to be treated, a Neurosurgeon, Neurotologist or Thoracic Oncologist. Duke physicians, physicists, planners and therapists are actively involved in radiosurgery clinical trials, teaching, technology assessment and development of quality assurance systems.
Karen Allen, MSN, ANP-BC