Stereotactic radiosurgery

Stereotactic radiosurgery (also known as radiosurgery) is a very precise form of non-surgical therapeutic radiology. Instead of requiring a conventional surgery or incisions, very focused beams of targeted radiation (gamma rays, X-rays or protons) are used to treat cancer tissues, metastatic brain tumors and small tumors.

How does stereotactic radiosurgery work?

Stereotactic radiosurgery works by delivering high doses of precisely-targeted radiation to cancer cells while avoiding the surrounding healthy tissue.

Rather than removing the tumor, radiosurgery cancer treatment changes the DNA of tumor cells to prevent them from reproducing and growing. Over time – usually a period of 18 months to 2 years – the tumor will shrink in size. Some tumors shrink rapidly over a few months, mainly malignant tumors and brain metastases. For blood vessel lesions, such as an arteriovenous malformation (AVM), the blood vessels close off over a period of several years after treatment.

Doctor sharing information with patient

Stereotactic radiation therapy relies on the following technologies:

  • 3D imaging techniques (CT, MRI or PET Scans) that determine the exact coordinates of the tumor in the body.
  • Image-guided radiation therapy (IGRT) which uses medical imaging techniques to confirm a tumor’s location before and sometimes during the procedure. This is mainly to improve the accuracy of the treatment.
  • Precisely-targeted gamma-ray or x-ray beams that converge on a tumor.
  • Positioning and immobilizing systems to keep the patient in the proper position during the procedure.

In some instances, more than one stereotactic radiosurgery treatment may be recommended. This is mainly for larger tumors that are not located within the brain or spine, as delivering radiation in multiple sessions can improve safety by allowing healthy tissue to heal between treatments.

Spreading out radiotherapy treatments is known as fractionated stereotactic radiosurgery, which typically encompasses 2-5 treatment sessions. This type of SRS treatment is mainly effective for treating lung, liver, adrenal and other soft tissue tumors.

What is stereotactic radiosurgery used for?

Stereotactic radiosurgery is an important surgical alternative, and is mainly recommended for patients who can’t undergo surgery. It is also used for tumors or abnormalities that may be hard to reach, close to vital organs or that can move within the body.

The following conditions are also treated by SRS:

  • An array of brain tumors, both non-cancerous (benign) and cancerous (malignant). These include meningioma, paraganglioma, hemangioblastoma and craniopharyngioma.
  • Arteriovenous malformations (AVMs), abnormally connected arteries and veins that can become tangled and can bleed or disrupt blood flow to the brain.
  • Acoustic neuroma, a noncancerous tumor in the balance and hearing nerve that can cause hearing loss, dizziness, loss of balance and facial paralysis.
  • Neurological conditions like trigeminal neuralgia, a facial nerve disorder.
  • Pituitary adenomas, benign tumors in the pituitary gland that can affect your hormone regulation.
  • Other cancers, such as those of the liver, lung and spine.
  • Tremors associated with Parkinson’s  Disease.

Other conditions. Research is ongoing about how SRS could treat other conditions, such as breast cancer, prostate cancer, epilepsy, melanoma and some psychological disorders. Further research is needed to confirm its effectiveness.

Neurosurgeons looking at brain images

The stereotactic radiotherapy procedure

How to prepare for the procedure

Stereotactic radiosurgery is usually performed on an outpatient basis, meaning you will not be required to stay in the hospital overnight. However, you should be prepared to spend up to half a day or longer at the facility. Your care team will inform you if you need someone to accompany you there, or to drive you home after.

Depending on your treatment, your radiation oncologist may ask you to fast before treatment, meaning you cannot eat or drink anything after midnight the night before you receive treatment. Consult with your doctor if you can continue taking medications and bring them with you the day of the procedure.

You should also tell your care team if you:

  • Are allergic to iodine or contrast material.
  • Are claustrophobic.
  • Have an artificial heart valve, brain aneurysm clips, chemotherapy ports, eye or ear implants, neurostimulators or a pacemaker.
  • Take diabetes medications.

What to expect during the procedure

Your radiosurgery treatment will be similar to having an x-ray, and will take between 1-4 hours.

You will not be able to feel, hear or see the x-rays during the procedure, unless you are having brain radiation therapy in which case you may see some flashes of light. You will also be equipped with a microphone to talk to your care team if you have any needs that should be addressed.

You should not have any pain during treatment. If you have discomfort from the head frame or back pain during the procedure, let your care team know so they can properly accommodate you.

After the procedure, when the head frame is removed you may have some minor bleeding from the pin sites, which will be bandaged and heal quickly. You might also have a headache which can be eased with medication.

In most cases, you will be able to resume all normal activities within one or two days.

Types of stereotactic radiosurgery

There are 3 types of stereotactic radiosurgery, each using different equipment
and radiation sources.

Cobalt60 systems (Gamma Knife radiosurgery)

Cobalt60 (Gamma Knife®) systems use cobalt as a source for gamma rays. The Gamma Knife® is not really a knife at all; instead, it uses 192 or 201 beams of highly-focused gamma rays to treat problems in and around the brain, such as brain tumors, AVMs and trigeminal neuralgia.

With Gamma Knife, many beams of gamma radiation join to focus on the lesion during treatment, providing a very intense dose of radiation in a safe way. Gamma Knife treatment generally includes these steps:

  1. Head frame placement. To keep the head from moving during treatment, a box-shaped frame is attached to the head with pins to fasten the frame to the skull. The head frame also is a guide to focus the gamma ray beams to the exact location of the problem.
  2. Tumor location imaging. Once the head frame is in place, the exact location of the lesion to be treated will be found using a CT scan or MRI scan.
  3. Radiation dose planning. After the CT scan or MRI has been done, the radiation therapy team will figure out the treatment plan. The results of the imaging scan, along with other information, will be used by a medical physicist to find the best treatment.
  4. Radiation treatment. After being positioned for the treatment, a type of helmet with many hundreds of holes in it is placed over the head frame. These holes help to focus the radiation beams on the target. The equipment stays in the same place throughout the treatment.  Treatment will last a few minutes up to a few hours. This depends on the type and location of the area being treated. Generally, only one treatment session is needed for a lesion.

Linear Accelerator (LINAC) systems

Linear accelerator (LINAC) systems use high-energy X-rays (photons), as opposed to gamma rays, to treat large tumors or other lesions outside of the brain. Some common types of LINAC systems include CyberKnife treatment, X-Knife, Novalis, and Peacock.

With LINAC systems, the machinery moves around the person during treatment, so LINAC systems can treat larger tumors and larger affected areas than the Gamma Knife. Areas other than the brain can be treated with a LINAC system as well. Treatment steps with a LINAC system are generally similar to the treatment steps used for the Gamma Knife, and can be done in a single session or multiple fractionated stereotactic radiotherapy sessions.

Proton beam therapy (heavy charged particle radiosurgery)

Proton beam therapy is a type of particle beam radiation therapy. Rather than using rays of radiation, like gamma rays or X-rays, particle beam therapy uses particles, like protons or neutrons.

Proton therapy is the most widely-used type of particle beam therapy. Proton beam therapy is useful in treating tumors or lesions that are small or have an irregular shape. The radiation dose can be more closely controlled with these systems. The proton beam can be controlled to allow it to deposit its energy almost completely in the tumor or lesion being treated. Other forms of radiation lose energy as they enter body tissues on their way to the tissue under treatment. Because the proton beam’s depth can be controlled precisely, there is less damage to normal tissues around the area being treated.

Proton beam therapy may be used for radiosurgery procedures, or when several smaller doses of radiation are given over a certain period of time. There are only a few facilities in North America that provide proton beam therapy.

Frequently asked questions (FAQs) about stereotactic radiosurgery

What are the side effects of stereotactic radiosurgery?

In general, side effects can occur from radiation damage to normal tissue, as well as a general reaction to radiation depending on the dosage you received and what part of your body was treated. Discuss with your doctor and nurse about any side effects you experience so they can help you properly manage them.

Side effects can start early – during or immediately after treatment – but typically clear up within a few weeks. Late side effects can occur months or years later.

Early side effects

Depending on the area being treated, early side effects may include:

  • Diarrhea.
  • Difficulty swallowing.
  • Fatigue.
  • Hair loss in the treatment area.
  • Headaches.
  • Nausea and vomiting.
  • Radiation necrosis, a rare but severe side effect that results in the permanent death of brain tissue.
  • Soreness and swelling in the treatment area.
  • Skin problems such as sensitivity, swelling, dryness or itching.
  • Trouble with eating and digestion.
  • Urinary and bladder changes.

Late side effects

Late side effects are rare. They tend to occur months or years following treatment, and they are often permanent. They include:

  • Brain changes.
  • Bone fractures.
  • Colorectal changes.
  • Infertility.
  • Joint changes.
  • Kidney changes.
  • Lung changes.
  • Lymphedema.
  • Mouth changes.
  • Secondary cancer.
  • Spinal cord changes.

There is a slight risk of developing secondary cancer from radiation therapy. Be sure to get checked regularly by your radiation oncologist for recurrent or new cancers.

How much does stereotactic radiosurgery cost?

If you have health insurance, radiosurgery procedures and the preparations before and after typically cost as low as $100 copay, or coinsurance of 20% or more up to $10,000 or the out of pocket maximum.

For patients without health insurance, stereotactic radiosurgery usually costs between $12,000 and $55,000. Discuss with your insurance and care team your expectations and how to pay for treatment if necessary.

Who will be part of my radiosurgery team?

Your treatment team at UCHealth will be made up of many specialized medical professionals and radiation oncologists. It will typically include:

  • A medical radiation physicist to ensure proper delivery of the right dose of radiation.
  • A neurologist to consider treatment options and if you may benefit from the procedure.
  • A physicist who will use a special software to calculate the radiation exposure and beam configuration as part of your treatment plan.
  • A radiation oncologist, who will outline the areas to treat, identify tissues at risk, decide the proper dose of radiation for the treatment plan, and interpret the results of your procedure. They may be led by a neurosurgeon.
  • A radiation therapist to position you properly and to operate the machinery as part of your treatment.
  • A radiologist who will interpret the imaging tests to help identify the treatment areas.
  • A stereotactic radiotherapy nurse to assess your needs and provide information before, during, and after treatment.


National Center for Biotechnology Information (NCBI): National Library of Medicine. Stereotactic Radiosurgery (

MedlinePlus: National Library of Medicine. Stereotactic radiosurgery – CyberKnife (

Radiological Society of North America (RSNA). Stereotactic Radiosurgery (SRS), Stereotactic Body Radiotherapy (SBRT) (