Stereotactic radiosurgery (SRS)

Overview

Stereotactic radiosurgery (SRS) is a precise medical procedure employed to address tumors and various medical conditions within the brain, neck, lungs, liver, spine, and other bodily regions. Unlike traditional surgery, SRS does not require incisions. Instead, it utilizes advanced 3D imaging techniques to focus radiation beams precisely on the affected area, minimizing harm to surrounding healthy tissue.

Similar to other radiation treatments, stereotactic radiosurgery functions by causing damage to the DNA of the targeted cells. Consequently, these affected cells lose their ability to replicate, leading to the reduction in tumor size.

Stereotactic radiosurgery for brain and spine conditions is typically completed in a single session. On the other hand, when addressing tumors in areas of the body outside the brain, the procedure may be referred to as either stereotactic body radiotherapy (SBRT) or stereotactic ablative radiotherapy (SABR). In such cases, treatment typically involves multiple sessions, usually ranging from three to five sessions, to effectively target the condition.

During stereotactic radiosurgery in the brain and various body regions, medical professionals utilize three distinct technologies to administer radiation:

• Linear accelerator (LINAC) machines: These machines employ X-rays (photons) to target and treat abnormalities in the brain and elsewhere in the body. LINAC machines are sometimes referred to by their manufacturer’s brand names, such as CyberKnife and TrueBeam. They can perform stereotactic radiosurgery (SRS) in either a single session or, for larger tumors, over a course of three to five sessions, known as fractionated stereotactic radiotherapy.
• Gamma Knife machines: Gamma Knife machines utilize 192 or 201 small beams of gamma rays to pinpoint and treat both cancerous and noncancerous brain abnormalities. These machines are less common compared to LINAC machines and are typically used for smaller to medium-sized tumors and lesions in the brain associated with various medical conditions.
• Proton beam therapy (charged particle radiosurgery): Proton beam therapy, the latest advancement in stereotactic radiosurgery, is available at a select number of research centers in the United States. However, the availability of centers offering proton beam therapy has significantly expanded in recent years. This technology can treat brain cancers either in a single session using stereotactic radiosurgery or, for body tumors, over multiple sessions using fractionated stereotactic radiotherapy.

Reasons for undergoing the procedure

As a less invasive and safer alternative to traditional brain surgery (neurosurgery), which necessitates incisions in the skin, skull, and membranes around the brain and brain tissue, stereotactic radiosurgery was invented about 50 years ago.

Since then, a wide range of neurological and other disorders have been treated with stereotactic radiosurgery, including:

• Brain tumor. Meningioma, paraganglioma, hemangioblastoma, and craniopharyngioma are just a few examples of the noncancerous (benign) and cancerous (malignant) brain tumors that can be treated using stereotactic radiosurgery, such as the Gamma Knife.
  Brain metastases, or malignancies that have spread from other regions of the body to the brain, may also be treated with SRS.
• Arteriovenous malformation (AVM). In your brain, AVMs are aberrant tangles of arteries and veins. Blood bypasses capillaries and travels directly from your arteries to veins in an AVM. AVMs can cause a stroke or bleeding (hemorrhage) by obstructing the blood’s natural flow.
  The AVM is eliminated using stereotactic radiosurgery, which also eventually causes the damaged blood vessels to close off.
• Trigeminal neuralgia. A chronic pain disorder known as trigeminal neuralgia affects one or both of the trigeminal nerves, which transmit sensory data from your brain to your forehead, face, and lower jaw. Extreme facial pain that feels like an electric shock is brought on by this nerve condition.
  To block these pain impulses, stereotactic radiosurgery is used to treat trigeminal neuralgia.
• Acoustic neuroma. Acoustic neuromas, alternatively referred to as vestibular schwannomas, are non-cancerous growths that form along the primary nerve responsible for both balance and hearing, extending from the inner ear to the brain. Hearing loss, vertigo, loss of balance, and ringing in the ears (tinnitus) can all result from the tumor pressing on the nerve. As the tumor expands, it may also exert pressure on the nerves that control facial feelings and movement.
  With a low risk of irreversible nerve injury, stereotactic radiosurgery may slow the growth or reduce the size of an acoustic neuroma.
• Pituitary tumors. Numerous issues can result from tumors of the pituitary gland, a bean-sized organ located near the base of the brain. Your body’s hormones, such as those that regulate your stress response, metabolism, growth, and sexual function, are controlled by the pituitary gland.
  Shrink the tumor and reduce the impairment of pituitary hormone control via radiosurgery.
• Tremors. Tremors brought on by functional neurological illnesses like Parkinson’s disease and essential tremor may be treated with stereotactic radiosurgery.
• Other cancers. Spinal, lung, and liver malignancies can all be treated using SRS.

Stereotactic radiosurgery may also be used to treat various diseases, such as eye melanoma, breast cancer, lung cancer, prostate cancer, epilepsy, and psychological problems like obsessive-compulsive disorder.

Risks

Since stereotactic radiosurgery doesn’t require any incisions, it’s often safer than open surgery. You run the danger of anesthetic, bleeding, and infection issues with standard surgery.

Early issues or adverse effects are typically transient. They may consist of:

• Fatigue. For the first few weeks following stereotactic radiosurgery, tiredness may develop.
• Swelling. Headache, nausea, and vomiting are signs and symptoms of brain swelling at or close to the treatment site. Corticosteroid pills, (anti-inflammatory drugs), may be prescribed by your doctor to treat any symptoms that may arise from such issues.
• Scalp and hair problems. At the locations where a device is fastened to your head during the treatment, your scalp may become red, itchy, or sensitive. Some people have a brief loss of hair.

Rarely, patients could have late adverse effects such as further neurological or brain issues months after treatment.

Before the procedure

Depending on the ailment and body area being treated, the preparation for stereotactic radiosurgery and stereotactic body radiotherapy may vary, but generally entails the following steps:

• Food and medications. The night before the surgery, avoid eating or drinking anything after midnight. Ask your doctor if you can continue to take your regular medications the night before or the morning of the surgery.
• Clothing and personal items. Put on relaxed, comfy attire. On the day of your surgery, refrain from wearing eyeglasses or contact lenses, jewelry, makeup, nail polish, wigs or hair piece, or dentures.
• Precautions regarding medications and allergies. If you use medications or injections to manage your diabetes, let your doctor know. Also, inform your doctor if you have allergies to iodine or shellfish, which are chemically related to the potential procedure dyes. And finally, notify your doctor if you have a pacemaker, prosthetic heart valve, aneurysm clips, neurostimulators, or stents put in your body.

When you arrive at the treatment facility, bring any medications you are presently taking with you and inquire about how to take them on the day of the operation.
The specific steps leading up to the treatment may differ based on the location of the treatment area and the type of radiation delivery equipment in use.

Preparation for Gamma Knife and LINAC stereotactic radiosurgery of the brain shares a high degree of similarity, with the exception of the initial step — the use of a head frame, which is not required for LINAC stereotactic radiosurgery. This preparation typically involves three key steps:

• Head frame placement: For Gamma Knife, a head frame is secured to your head. However, for LINAC stereotactic radiosurgery, a head frame is not required.
• Imaging: Following head frame placement (if applicable), brain imaging scans are conducted to precisely locate the tumor or abnormality in relation to the head frame. The choice of imaging scan depends on the specific condition being treated.
• Dose planning: The results from the brain imaging scans are input into a computerized planning system. This system assists the radiosurgery team in mapping out the areas to be treated, determining radiation dosages, and devising strategies to precisely focus the radiation beams on the targeted areas.

This planning phase typically takes about an hour or two. During this time, if you are undergoing LINAC stereotactic radiosurgery of the brain, you may be allowed to go home, with the treatment administered on a later date.

Preparation for stereotactic radiosurgery or radiotherapy for other parts of the body entails a series of steps, including:

• Marking: In some instances, specific SRS technologies may require the placement of a fiducial marker within or near the tumor. This procedure is typically conducted as an outpatient appointment before the SRS treatment. However, it is generally unnecessary for most CT-guided technologies.
• Simulation: A radiation oncologist will perform a simulation to ascertain the optimal positioning of your body to align it precisely with the radiation beams. Your body will be securely immobilized with the aid of a specialized device. It’s essential to inform your doctor if you have claustrophobia or any concerns.
• Planning: After immobilization, imaging scans are obtained, and you may be allowed to return home before proceeding to the next phase. Your treatment team will then utilize these imaging scans and specialized software to determine the most effective combination of radiation beams for precisely targeting your tumor or other abnormality.

During the procedure

The approach to anesthesia and patient interaction varies between children and adults undergoing stereotactic radiosurgery:

• Children: Typically, children are anesthetized for imaging tests and during the radiosurgery procedure.
• Adults: Adults are generally awake during the procedure, although they may receive a mild sedative to help them relax.

If Gamma Knife technology is used for treatment, the patient will lie on a bed that smoothly slides into the machine, with their head frame securely attached to the bed frame. The machine remains stationary, and the bed is adjusted within the machine. The duration of the procedure varies, typically lasting from under an hour to around four hours, depending on the size and shape of the target. For LINAC stereotactic radiosurgery of the brain, the treatment tends to be quicker.

In contrast to the Gamma Knife, the LINAC machine moves and rotates around the target during treatment to deliver radiation beams from different angles. The entire procedure typically lasts less than an hour.

During the treatment:

• You won’t feel the radiation.
• You can communicate with the medical team through a microphone.

After the procedure

Following the procedure, you should anticipate the following:

• If a head frame was utilized, it will be carefully removed. You might experience minor bleeding or tenderness at the pin sites.
• In the event of post-procedure symptoms like headaches, nausea, or vomiting, you will be provided with suitable medications to alleviate discomfort.
• After the procedure, you’ll be able to eat and drink as usual.

Outcome

Depending on the problem being treated, stereotactic radiosurgery’s therapeutic effect develops gradually:

• Benign tumors (including vestibular schwannoma). The tumor may shrink after stereotactic radiosurgery over the course of 18 months to 2 years, but the major objective of treatment for benign tumors is to stop any further tumor growth.
• Malignant tumors. Tumors that are cancerous (malignant) may shrink more quickly, frequently in a few months.
• Arteriovenous malformations (AVMs). The aberrant blood vessels of brain AVMs thicken and seal off as a result of the radiation therapy. It can take this process two years or longer.
• Trigeminal neuralgia. SRS causes a lesion that prevents pain signals from traveling along the trigeminal nerve. While it often takes several weeks, many people report feeling pain alleviation.

You’ll be given instructions on the proper follow-up assessments to evaluate your development.