Stereotactic body radiotherapy
Stereotactic radiosurgery (SRS) is a type of radiotherapy. When it's performed on the body rather than the brain, this procedure is sometimes called stereotactic body radiotherapy (SBRT) or stereotactic ablative radiotherapy (SABR).
The procedure uses many precisely focused radiation beams to treat tumors and other problems all over the body. SBRT is used to treat tumors in the lungs, spine, liver, neck, lymph node or other soft tissues.
Because there's no incision, SBRT isn't a traditional type of surgery. Instead, SBRT uses 3D imaging to target high doses of radiation to the affected area. This means there's very little damage to the surrounding healthy tissue. Like other forms of radiation, stereotactic radiosurgery works by damaging the DNA of the targeted cells. Then, the affected cells can't reproduce, which causes tumors to shrink.
Body radiotherapy usually involves between one to five sessions.
Types of stereotactic radiosurgery
Doctors use two types of technology to deliver radiation during stereotactic radiosurgery.
- Linear accelerator (LINAC) machines use X-rays (photons) to treat cancerous and noncancerous abnormalities in the brain and other parts of the body. LINAC machines are also known by the brand name of the manufacturer, such as CyberKnife and TrueBeam. These machines can perform SRS in a single session or over two to five sessions for larger tumors (fractionated stereotactic radiotherapy).
- Proton beam (charged particle) is the newest type of stereotactic radiotherapy and is available in only a few research centers in the U.S., although the number of centers offering proton beam therapy has greatly increased in the last few years. It can use fractionated stereotactic radiotherapy to treat body tumors over several sessions. Proton beam SBRT may be used to treat tumors in parts of the body that have previously received radiation therapy, or those that are near critical organs.
How it works
All types of stereotactic radiosurgery and radiotherapy work in a similar manner.
The specialized equipment focuses beams of radiation on a tumor or other target. Each beam has very little effect on the tissue it passes through, but a targeted dose of radiation is delivered to the site where all the beams intersect.
The high dose of radiation delivered to the affected area causes tumors to shrink and blood vessels to close off over time following treatment, robbing the tumor of its blood supply.
The precision of stereotactic radiosurgery means there's minimal damage to the healthy surrounding tissues. In most cases, radiotherapy has a lower risk of side effects compared with other types of traditional surgery or radiation therapy.
Why it's done
Around 50 years ago, stereotactic radiosurgery was pioneered as a less invasive and safer alternative to standard brain surgery (neurosurgery), which requires incisions in the skin, skull, membranes surrounding the brain and brain tissue.
Since then, the use of SRS has expanded widely to treat a variety of neurological and other conditions. SBRT may be used to treat cancers of the liver, lung, abdomen, lymph nodes and spine.
Stereotactic radiosurgery doesn't involve surgical incisions, so it's generally less risky than traditional surgery. In traditional surgery, you may have risks of complications with anesthesia, bleeding and infection.
Early complications or side effects are usually temporary. They may include:
- Fatigue. Tiredness and fatigue may occur for the first few days after SBRT.
- Swelling. Swelling at or near the treatment site can cause signs and symptoms such as a temporary increase in pain. Your doctor may prescribe anti-inflammatory medications (corticosteroid medications) to prevent such problems or to treat symptoms if they appear.
- Nausea or vomiting. Some patients may experience temporary nausea or vomiting if the radiated tumor is near the bowel or liver.
Rarely, people may experience late side effects, months after treatment, although this varies for each body site. Your physician will discuss potential risks more thoroughly with you. These may include:
- Weakened bones that may break
- Changes affecting the bowel
- Changes in the lungs
- Changes in the spinal cord
- Developing a new cancer (secondary cancer)
- Swollen arms and legs (lymphedema)
How you prepare
Preparation for SRS and SBRT may vary depending on the condition and body area being treated but usually involves the following steps:
Food and medications
- You may be asked not to eat or drink anything after midnight the night before the procedure.
- Talk to your doctor about whether you can take your regular medications the night before or morning of the procedure.
Clothing and personal items
Wear comfortable, loosefitting clothing.
Avoid wearing the following items during SRS of the spine:
- Contact lenses
- Nail polish
- Wigs or hairpieces
Precautions regarding medications and allergies
Tell your doctor if you:
- Have implanted medical devices in your body, such as a pacemaker, artificial heart valve, aneurysm clips, neurostimulators or stents.
- Bring any medications you are currently taking with you to the treatment center and ask about what you should do about taking your medications on the day of the procedure.
What you can expect
Stereotactic body radiotherapy is most commonly delivered as an outpatient and takes between 20 to 60 minutes for each treatment. While not common, your doctor will advise you if a family member or friend will need to accompany you for the treatment.
Stereotactic body radiotherapy machines use many precisely focused radiation beams to treat tumors and other problems all over the body.
Linear accelerator (LINAC) machines use X-rays (photons) to treat cancerous and noncancerous abnormalities in the brain and other parts of the body.
Before the procedure
Preparation for stereotactic radiosurgery of the body involves several steps, including:
- Marking. Some technologies require the placement of a small metal marker (fiducial marker) in or near the tumor in certain cases. The fiducial marker is about the size of a grain of rice. The marker is usually in a cylinder, coil or sphere shape and is often made out of gold. The marking procedure is usually done as an outpatient procedure prior to SRS treatment. But this step is not needed for most CT-guided technologies.
Simulation. A radiation oncologist will conduct a simulation. This step determines the best placement of your body to align it with the radiation beams. Your body will be held very tightly and still by an immobilization device. Tell your doctor if you have claustrophobia.
After you are immobilized, imaging scans will be taken. Your doctor might perform a 4DCT to capture information about how your tumor moves when you are breathing. A 4DCT is most often used on tumors located in the liver or lungs. After the scans, you'll probably be sent home before the next stage. Sometimes, holding your breath for 10-30 seconds at a time during treatment may be required to reduce movement of the tumor.
- Planning. Using the imaging scans and specialized software, your treatment team will determine the best combination of radiation beams to target your tumor or other abnormality.
During the procedure
Children are often anesthetized for the imaging tests and during the radiosurgery. Adults are usually awake, but in rare instances, you might be given a mild sedative to help you relax if you're feeling very anxious.
The LINAC machine moves and rotates around the target during treatment to deliver radiation beams from different angles. The treatment takes less than 30 minutes to an hour.
Having SBRT is kind of like having an X-ray. During the procedure:
- You won't feel the radiation.
- You'll be able to talk with the doctors via a microphone.
LINAC stereotactic radiosurgery preparation
Prior to LINAC stereotactic radiosurgery or stereotactic body radiotherapy, Mayo Clinic radiation therapists create a customized immobilization device. The patient lies on a base filled with small beads that conform to the body with the aid of a vacuum. A plastic sheet is placed over the body and base to hold the patient in place and minimize movement during the procedure.
After the procedure
After the procedure, you can expect the following:
- If you experience symptoms such as a temporary increase in pain or nausea you'll receive appropriate medications.
- You'll be able to eat and drink after the procedure.
- Usually, you'll go home the same day.
- You can usually get back to normal activities within one to two days.
The treatment effect of stereotactic radiosurgery occurs gradually, depending on the condition being treated:
- Benign tumors (including vestibular schwannoma). Following stereotactic radiosurgery, the tumor may shrink over a period of 18 months to two years, but the main goal of treatment for benign tumors is to prevent any future tumor growth.
- Malignant tumors. Cancerous (malignant) tumors may shrink more rapidly, often within a few months.
You'll receive instructions on appropriate follow-up exams to monitor your progress.
Liver tumor before and after SBRT
Tumor in the liver before (left) and after (right) stereotactic body radiotherapy.