Stereotactic Radiosurgery (SRS) in the management of Brain Tumors

What is stereotactic radiosurgery?

Stereotactic radiosurgery (SRS) is a highly precise form of radiation therapy initially developed to treat small brain tumors and functional abnormalities of the brain. Despite its name, SRS is a non-surgical procedure that delivers precisely-targeted radiation at much higher doses, in only a single or few treatments, as compared to traditional radiation therapy. This treatment is only possible due to the development of highly advanced radiation technologies that permit maximum dose delivery within the target while minimizing dose to the surrounding healthy tissue. The goal is to deliver doses that will destroy the tumor and achieve permanent local control.

How is it used?

Three-dimensional imaging, such as CT, MRI, and PET/CT is used to locate the tumor or abnormality within the body and define its exact size and shape. These images also guide the treatment planning—in which beams of radiation are designed to converge on the target area from different angles and planes—as well as the careful positioning of the patient for therapy sessions.

When is it used?

SRS is an important alternative to invasive surgery, especially for patients who are unable to undergo surgery and for tumors and abnormalities that are:

• Hard to reach
• Located close to vital organs/anatomic regions
• Chance of complications following surgery is high.

SRS is used to treat:

• Many types of brain tumors including:

• • Benign and Malignant
  • Primary and Metastatic
  • Single and Multiple
  • Residual Tumor Cells Following Surgery
  • Intracranial, Orbital and Base-of-Skull Tumors

• An arteriovenous malformation (AVMs), a tangle of expanded blood vessels that disrupts normal blood flow in the brain and sometimes bleeds.
• Other neurological conditions like trigeminal neuralgia (a nerve disorder in the face), tremor, etc.

How does it work?

SRS fundamentally works in the same way as other forms of radiation treatment. It does not actually remove the tumor; rather, it damages the DNA of tumor cells. As a result, these cells lose their ability to reproduce. Following treatment, benign tumors usually shrink over a period of 18 months to two years. Malignant and metastatic tumors may shrink more rapidly, even within a couple of months. When treated with SRS, arteriovenous malformations (AVMs) may begin to thicken and close off slowly over a period of several years following treatment. Many tumors will remain stable and inactive without any change. Since the aim is to prevent tumor growth, this is considered a success. In some tumors, like acoustic neuromas, a temporary enlargement may be observed following SRS due to an inflammatory response within the tumor tissue that overtime either stabilizes, or a subsequent tumor regression is observed called pseudoprogression.

Who will be involved in this procedure and who operates the equipment?

The treatment team is comprised of a number of specialized medical professionals, typically including a neurosurgeon, radiation oncologist, medical radiation physicist, radiologist, dosimetrist, radiation therapist, and radiation therapy nurse.

• The radiation oncologist or a neurosurgeon lead the treatment team and oversee the treatment; they outline the target(s) to be treated, decide on the appropriate radiation dose, approve the treatment plan, and interpret the results of radiological procedures.

• A neurologist or neuro-oncologist may participate with the radiation oncologist and neurosurgeon in the multidisciplinary team that considers various treatment options for individual cases and helps decide who may benefit from radiosurgery for lesions in the brain.

Radiosurgery Using the Linear Accelerator

Linear accelerator (LINAC) SRS is similar to the Gamma Knife procedure and its four phases: head frame placement, imaging, computerized dose planning and radiation delivery. LINAC technology is much more common than Gamma Knife technology and has been in practice for a similar length of time. Unlike the Gamma Knife, which remains motionless during the procedure, part of the LINAC machine (called a gantry) rotates around the patient delivering the radiation beams from different angles. Obtaining the MRI before frame placement is also a more routine pre-planning practice with LINAC-based SRS. A CT with the frame in place is also commonly acquired.

What are the side effects?

Side effects of radiation treatment include problems that occur as a result of the treatment itself as well as from radiation damage to healthy cells in the treatment area.

Radiation therapy can cause early side effects during or immediately after treatment and are typically gone within a few weeks. Late side effects can occur months or years later. Common early side effects of radiation therapy include tiredness or fatigue and skin problems. Skin in the treatment area may become more sensitive, red, irritated, or swollen. Other skin changes include dryness, itching, peeling and blistering.

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

• Hair loss in the treatment area
• Mouth problems and difficulty swallowing
• Eating and digestion problems
• Diarrhea
• Nausea and vomiting
• Headaches
• Soreness and swelling in the treatment area
• Urinary and bladder changes

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

Brain Changes, Spinal Cord Changes, Lung Changes, Kidney Changes, Colon and Rectal Changes, Infertility, Joint Changes, Lymphedema, Mouth Changes, Secondary Cancer and Fracture of Bones

There is a slight risk of developing cancer from radiation therapy. Following radiation treatment for cancer, you should be checked on a regular basis by your radiation oncologist for recurring and new cancers.

Dr. Dilip Dutta | Consultant Neuro-Onco Surgery | Narayana Superspeciality Hospital, Howrah