Stereotactic Radiation (SBRT / Radiosurgery / SRS)

Stereotactic radiation therapy is a type of external beam radiation that delivers radiation to a tumor from many different angles. This kills the cancer cells or stops them from dividing and spreading. Stereotactic radiation therapy may also be called stereotactic ablative radiotherapy (SABR).

How is stereotactic radiation therapy different than standard radiation therapy?

Stereotactic radiation uses fewer treatment days or “fractions” of radiation compared to standard radiation. A fraction is when the full dose of radiation is split into several smaller doses and given over days or weeks. Even though there are fewer fractions being used, the dose of radiation is much higher for each fraction.

Many different angles are used to focus the radiation at one small point. These beams combine to deliver high doses of radiation to a specific area, while sparing as much normal tissue as possible. This can lower the risk of side effects.

Who can have stereotactic radiation therapy?

Treatment with stereotactic radiation depends on:

• Cancer type.
• Size, shape, and location of the tumor.

This type of treatment is used for small tumors (less than 5 cm) that are well-defined, and easily seen on imaging (like CT or MRI). Stereotactic radiation may not be used if your tumor is close to or touching your airways, heart, or other critical structures.

What are the types of stereotactic radiation therapy?

There are two types of stereotactic radiation therapy:

• Stereotactic radiosurgery (SRS).
• Stereotactic body radiation therapy (SBRT).

Stereotactic Radiosurgery (SRS)

• Stereotactic radiosurgery (SRS) is not surgery. There is no incision (cut in the skin).
• SRS is used mostly used for small tumors in the brain.
• Often, only one fraction of radiation is given.
• Before starting SRS, you will have an MRI to help plan your treatment. The 3D images from the MRI will give your care team a detailed picture of your tumor.
• Your head will need to remain still during treatment. This is done by using a custom immobilization mask or another similar device.
• Your SRS treatment plan may include providers from neurosurgery and radiation oncology.

Stereotactic body radiation therapy (SBRT)

• SBRT is delivered in one to five fractions and is used for tumors within your body, not including the brain or spine.
• SBRT is used mostly for small tumors in the body. They can be found in the chest, abdomen (belly), or pelvis. This may be done if you are not able to have surgery. Examples of these cancers are:
  • Some cancers that start in or spread to the lung (lung metastases).
  • Some prostate cancers.
  • Some pancreatic cancers.
  • Cancers that start in or spread to the liver (liver metastases).
• SBRT can use either photons or protons.
• Before starting SBRT, you will have a CT or MRI to help plan your treatment. The 3D images from the CT or MRI will give your care team a detailed picture of your tumor.
• Metal markers called “fiducial markers” may be placed in or near your tumor. These markers help track the tumor during treatment. They are put into place using needles that are guided by ultrasound and will stay in your body forever.
• You may also need to have small ink tattoos placed on your skin. These help with positioning and alignment (lining up) of your body during treatment.
• Your body may need to be held in place (immobilized) using special devices to keep you from moving. You may need respiratory gating such as a compression belt or deep inspiration breath hold (DIBH) during treatment. This helps reduce motion and keep the tumor in the same position.

What can I expect after having stereotactic radiation therapy?

You may have side effects during or after SBRT or SRS. The type and severity of side effects depend on where your tumor is, the dose of radiation given, and how many treatments (fractions) you have received. Since only a small area of your body is exposed to radiation, there tend to be fewer side effects with SBRT as compared to standard radiation therapy. These side effects are often temporary. There may also be some side effects that happen later, weeks or months after you finish SBRT.

Be sure to talk with your healthcare provider about which kind of radiation you will be getting. Your team will talk to you about your options, as well as possible side effects of treatment. Call your provider right away with any new or worsening symptoms, even if it has been weeks or months since treatment ended.