Stereotactic Radiation (SBRT / Radiosurgery / SRS): The Basics

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What is stereotactic radiation therapy?

Stereotactic radiation therapy is a type of external beam radiation. Beams of radiation from a machine are directed at a tumor in the body. These beams use high energy x-rays to damage the DNA of cells. This kills the cancer cells or stops them from reproducing. 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 a number of smaller doses given over days or weeks. In stereotactic radiation, there are fewer fractions but the dose of radiation is much higher with each fraction. Many different angles are used to focus the radiation beams at one small point, like a magnifying glass. These beams combine to deliver high doses of radiation to a very specific area. This delivers powerful radiation to the cancer cells, while sparing as much normal tissue as possible.

Who can have stereotactic radiation therapy?

Treatment with stereotactic radiation depends on: 

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

This type of radiation works best with tumors that are very small, well-defined, and easily seen on imaging (like CT or MRI). It may not be safe if a tumor is close to or touching another organ in your body. 

What are the types of stereotactic radiation therapy?

There are two types of stereotactic radiation therapy: 

  1. Stereotactic radiosurgery (SRS).
  2. 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 for small tumors in the brain. 
  • Often, only one fraction of radiation is given. 
  • Before starting SRS, you will have an MRI to map out your tumor. The 3D images from this MRI provide a precise picture of your tumor. 
  • Your head may need to be held in place (immobilized.) This can be done with a mesh covering or other device.
  • Your SRS treatment plan will involve providers from both neurosurgery and radiation oncology. 

Stereotactic body radiation therapy (SBRT)

  • SBRT delivers one to five stereotactic radiation treatments to tumors within the 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. They cannot be removed with surgery or treated with conventional radiation therapy. Examples of these cancers are:
    • Some lung cancers.
    • Cancers that started somewhere else in the body and spread to the lung (lung metastases).
    • 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 map out your tumor. The 3D images from this CT or MRI will help your treatment team get a precise picture of your tumor.
  • Metal markers called “fiducial markers” may need to be placed in your tumor. These markers help track the tumor during treatment. Fiducial markers remain permanently in the body and are placed during a procedure similar to a biopsy. An Interventional Radiologist in the Radiology Department often does this procedure.
  • 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) with a special device to keep you from moving during planning and treatment. Your radiation team may also use a compression belt or may teach you how to hold your breath at certain times during treatment so that the tumor stays in the same position as much as possible.

What can I expect after having stereotactic radiation therapy?

You may have some side effects during or after SBRT. The type and severity of side effects depend on many things, like:

  • Where your tumor is.
  • The dose of radiation given.
  • How many treatments (fractions) you have. 

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. Side effects may include:

  • Fatigue.
  • Swelling of the area being treated.
  • Nausea and/or vomiting if the treatment area is near the belly or liver.

There may also be some side effects that happen later, weeks or months after you finish SBRT. These may include:

  • Skin and hair changes: These can happen 4-6 weeks after you finish treatment. You may notice pink or tan skin around the area that was treated. You may lose some or all of the hair in the area that was treated.
  • Cough or rib pain: These can happen months after treatment if your lungs were treated with SBRT. Call your provider right away with any new or worsening shortness of breath.
  • Weakened bones.
  • Swollen arms and legs (lymphedema).

Be sure to talk with your providers 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.

Referencias

American Society for Radiation Oncology (ASCO). (2020). Stereotactic Radiation Therapy: Patient Brochure. Retrieved from https://www.rtanswers.org/RTAnswers/media/RTAnswers/patient%20materials/PDFs/Stereotactic.pdf 

Andrews DW, Scott CB, Sperduto PW, et al. Whole brain radiation therapy with or without stereotactic radiosurgery boost for patients with one to three brain metastases: phase III results of the RTOG 9508 randomised trial. Lancet. 2004 May 22;363(9422):1665-72.

Goodman, C. R., M. Zainib, M. Arshad, D. Cutright, H. Beydoun, M. M. Dominello, P. Mohindra, N. P. Amin, C. B. Simone, and T. J. Kruser. "Stereotactic Body Radiation Therapy to Multiple Sites of Intrathoracic Disease: A Multi-Institutional Analysis." International Journal of Radiation Oncology• Biology• Physics 102, no. 3 (2018): e683. 

Rusthoven KE, Kavanagh BD, Cardenes H, et al. Multi-institutional phase I/II trial of stereotactic body radiation therapy for liver metastases. J Clin Oncol 2009; 27:1572.

Rusthoven KE, Kavanagh BD, Burri SH, et al. Multi-institutional phase I/II trial of stereotactic body radiation therapy for lung metastases. J Clin Oncol 2009; 27:1579.

Timmerman R, Paulus R, Galvin J, et al. Stereotactic body radiation therapy for inoperable early stage lung cancer. JAMA 2010; 303:1070.

Wang XS, Rhines LD, Shiu AS, et al. Stereotactic body radiation therapy for management of spinal metastases in patients without spinal cord compression: a phase 1-2 trial. Lancet Oncol 2012; 13:395.

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