Radiosurgery of the brain - stereotactic

updated > 04.14.2014
reviewed by > John Breneman, MD and Ron Warnick, MD

Overview

Radiosurgery is a form of radiation therapy that uses high-energy rays to destroy tumors and other diseases of the brain. Radiation works by damaging the DNA inside cells and makes them unable to divide and grow. Beams of radiation are aimed at the brain by a machine outside your body. Radiosurgery uses very high dose beams meant to kill all the cells in the target area. The beams are extremely focused and accurate to avoid damaging normal healthy cells. It is often given in a one-time therapy completed in a single day or it can be broken into 2 to 5 treatments given over a week (hypo-fractionated). Radiosurgery may be used as an alternative to open brain surgery, which requires an incision in the skull to reach the brain.

What is stereotactic radiosurgery?

The benefits of radiation are not immediate but occur with time. Aggressive tumors, whose cells divide rapidly, tend to respond quickly to radiation. Over time, the abnormal cells die and the tumor may shrink. Benign tumors, whose cells divide slowly, may take several months to a year to show an effect.

In radiosurgery, pinpoint accuracy is critical so that the lethal dose is applied only to the target itself and not to surrounding healthy tissue or critical structures (Fig. 1). To achieve the razor-sharp precision, computer image-guided technology is used to plan and carry out the procedure. The method of targeting an object by taking all three dimensions into account is called stereotaxis.

Radiosurgery may be given as a one-day session or split into a few treatments that are given over several days. Delivering a fraction of the total radiation dose allows normal cells time to repair themselves between treatments. It may also reduce side effects.

 

 

Consultations

Precision Radiotherapy offers high-precision radiotherapy and radiosurgery for tumors and other abnormalities in the brain and throughout the body. Our three radiation technologies allow us to match precise treatment to your specific tumor or lesion.

A partnership of the Mayfield Clinic, University Radiation Oncology, and UC Health, Precision Radiotherapy's nationally recognized physicians are available for consultation, usually within a few days of your call. If you would like a consultation, contact us at info@precisionradiotherapy.com, or call 513-475-7777.

Various machines can deliver radiosurgery, including a linear accelerator, Gamma Knife, or particle accelerator. Each technology has important differences, but they all do the same things:

1. Precisely locate the target (tumor, lesion)
2. Hold the target still
3. Accurately aim the radiation beam
4. Shape the radiation beam to the target
5. Deliver a specific radiation dose

Doctors may advise radiosurgery as a standalone treatment or in combination with surgery, chemotherapy or immunotherapy. Radiation may be given before surgery to shrink a tumor or AVM or after surgery to stop the growth of tumor cells that remain. If eliminating the tumor is not possible, radiation can be used to relieve pain, seizures, or other symptoms. This is called palliative care.

What's the difference?

RadioTHERAPY
5-33 fractions
Delivers radiation at lower doses, over multiple times, and to larger areas. Treats a “margin” of tissue around malignant tumors.
RadioSURGERY
1-5 fractions
Delivers radiation at very high doses, a few times, to a small area. Benefit is its rapid fall-off giving a less dose to normal cells.

 

Linear accelerator(LINAC)

Aims a single beam multiple times by moving around patient. It can fractionate treatments using a facemask for positioning.

Gamma Knife

Aims 198 beams all at once while machine is stationary. It moves patient into center of beams using a head frame inside a helmet.

Figure 1. Radiotherapy shapes the radiation beam to match the outline of the tumor and includes a margin of normal brain to prevent recurrence. The beams come from many angles with the cone focused on the tumor. The red ring shows the high dose and each outer ring represents lower and lower doses.

Doctors may advise radiotherapy as a standalone treatment or in combination with surgery, chemotherapy or immunotherapy. Radiation may be given before surgery to shrink the tumor or after surgery to stop the growth of tumor cells that remain. If eliminating the tumor is not possible, radiation can be used to relieve pain, seizures, or other symptoms. This is called palliative care.

Who is a candidate?

You may undergo radiosurgery if you have a:

  • Benign tumor: acoustic neuroma, pituitary adenoma, meningioma, craniopharyngioma, glomus tumor
  • Metastatic tumor: lung, breast, or other cancer that spread to the brain
  • Arteriovenous malformation (AVM)
  • Cavernoma
  • Trigeminal neuralgia
  • Epilepsy
  • Essential tremor

Who performs the procedure?

Radiation oncologists are doctors who have special training in treating cancer and other diseases with radiation. Their role is to evaluate the patient and determine the treatment plan, also called the prescription. The radiation oncologist works with a team that includes a surgeon, medical physicist, dosimetrist, radiation therapist, and oncology nurse. The surgeon and radiation oncologist decide what techniques to use to deliver the prescribed dose. The physicist and the dosimetrist then make detailed calculations and set up the equipment. The radiation therapists position you on the machine and deliver the treatments. The nurse provides care and helps you manage any side effects.

What happens before treatment?

Consultation
Your first appointment is a consultation with a radiation oncologist or neurosurgeon. He or she will perform a physical exam and reconfirm your diagnosis based on the imaging studies (CT, MRI) and pathology reports. They will discuss with you the best type of radiation treatment for your particular tumor or lesion, explain the treatment process, and describe possible side effects. Once you've decided to go ahead with treatment, you will sign consent forms.

What happens next varies depending if treatment involves a facemask or a head frame. A facemask and imaging (Steps 1-3) are done a week prior to treatment. If a head frame is used, all steps occur in one day.

What happens during treatment?

On the day of treatment, arrive at the center and check in with the receptionist. You may bring a friend or a relative with you for company. Please arrange for a family member or friend to drive you home after the treatment.

Depending on the target's size and location, either a facemask or head frame will be used to hold your head completely still during treatment.


Figure 2. A thermoplastic mask is custom-fit to the contours of your face. The front and back pieces of mesh are secured to a U-shaped frame that attaches to the treatment table to hold the head still.

Video: Creating the Radiosurgery Mask | Stereotactic Mask

Step 1: facemask or frame attachment
A stereotactic mask is custom-made to fit your face exactly. It will be used during the treatment session to hold your head perfectly still. You will lie with your head on a cradle of mesh stretched between a U-shaped frame. Next, strips of stretchy plastic are placed across your forehead, under your nose, and over your chin. You will be asked to bite a small piece of plastic with your front teeth. Next, thermoplastic mesh is dipped into a water bath, making the mesh very flexible. The mesh is placed over the face and allowed to conform (Fig. 2). You will be able to easily breathe. Cold mitts help the mesh cool and harden. Creation of the mask takes about 30 minutes.

Occasionally, it is necessary to use a stereotactic frame attached to your head with small pins. While you are seated, the frame is temporarily positioned on your head with Velcro straps. The four pin sites are cleaned and injected with local anesthesia. You may receive a light sedative to minimize discomfort. You may feel some pressure as the pins are tightened. Placement of the head frame takes about 30 minutes.

Step 2: imaging
Next you will undergo imaging scans while wearing the facemask or head frame. Reflective balls are placed on the facemask and worn during the CT scan (Fig. 3). These markers appear on the scan and help pinpoint the exact three-dimensional coordinates of the target in the brain. It may be necessary to obtain a new MRI scan.

After the scan, you are taken to a private room and given a light snack while the doctors plan the radiation prescription for later the same day. Your family and friends may keep you company. If you had a head frame attached, it remains in place.

Step 3: treatment planning
Information about the tumor's location, size, and closeness to critical structures is gathered by the CT or MRI scan. Advanced computer software uses the scans to create a 3D view of your anatomy and the tumor (Fig. 4). Using the software, the radiation oncologist, surgeon, dosimetrist, and physicist work as a team to determine the:

  • appropriate radiation dose
  • number and angle of treatment beams
  • size and shape of the beams to exactly match the tumor or target

Figure 3. Reflective balls are placed on the facemask prior to CT scanning. Markers are seen on the CT scan and help pinpoint the exact coordinates of the tumor or lesion.

Step 4: position the patient
Once the radiation machine is calibrated and prepared for your specific treatment plan, you will lie on the table. The mask is placed over your face and secured to the table. If you had a head frame, it is secured to the treatment table.

Alignment lasers and x-rays help the therapist position you correctly. Stereoscopic x-rays are taken and compared to the treatment plan. Any misalignments are corrected before treatment.

 

Step 5: deliver the radiation
The therapist leaves the room and operates the machine from the control room. The team watches you through video monitors and speaks to you over an intercom. The machine and treatment table move every so often to deliver radiation beams from one or more directions (Fig. 5).

The machine is large and makes a humming noise as it moves around your head. Its size and motion may be intimidating at first. It may pass close to your body, but it will not touch you. You do not have to hold your breath—just breathe normally. Treatment may take 30 minutes or longer, depending on the number of targets.

Each beam alone is not strong enough to damage the healthy cells it passes through on the way to the target. But at the center where all of the beams meet, the energy dose is strong enough to destroy the abnormal cells.


Figure 4. The computer creates a 3D view of your anatomy. A treatment plan determines the number and angle of beams, the size and shape of the radiation beams, and the radiation dose.

What happens after treatment?

After treatment the therapist releases the facemask or frame from the table so you can get up. If multiple treatments are planned, the facemask is stored at the center for your next session. You will return each day at your scheduled time to repeat steps 4 and 5 until all fractions of the complete dose are delivered. You may be prescribed medication for a few days or weeks after treatment.

If you had a head frame, the pins and frame are removed. You may have oozing from the pin sites and a mild headache. You may then gather your belongings and go home. Follow these instructions for care of the pin sites:

1. If you have discomfort or tenderness around the pin sites, Tylenol may help.
2. Steri-strips or bandaids may be placed over the pin sites. Remove them the next day.
3. Swelling may occur around the pin sites for the first few days. Keep your head elevated and apply an ice pack to the area.
4. Call the doctor if you have a fever greater than 101 degrees or have any drainage, separation, or sign of infection at the pin sites.


Figure 5.  The facemask is secured to the treatment table and holds the patient's head perfectly still and positioned in the treatment field. The machine rotates around the patient, aiming radiation beams at the tumor.

Recovery and prevention

Side effects of radiation vary, depending on the tumor type, total radiation dose, size of the fractions, length of therapy, and amount of healthy tissue in the target area. Some side effects are temporary and some may be permanent. Ask your doctor about specific side effects you may experience. General side effects may include:

Fatigue
Fatigue is common. You may feel more tired than usual for a few weeks following treatment. In addition to fighting the tumor cells, your body is repairing the normal cells that may have been damaged by the radiation. Fatigue can continue for weeks or months after treatment stops. Save your energy for important obligations and allow others to assist with chores or errands. Make sure you get plenty of sleep, take a nap after treatment, and eat a balanced diet. Some patients may need to increase their caloric and protein intake because their bodies are working hard to repair itself. Some may notice a lack of appetite and a loss of taste.

Exercise and/or stretching can also help you to combat fatigue. A short, brisk walk can be rejuvenating and can give you a boost.

Skin irritation
The skin in the area where the radiation beams pass through may become slightly red and dry. This will go away after treatment stops. To prevent irritation, use mild soap when bathing. Apply lotion daily, immediately after a shower, to those areas exposed to radiation. It is important to monitor your skin throughout the entire course of radiotherapy. Left untreated, skin irritation can lead to a small infection.

Hair loss
You may experience hair loss in the treated area about 2 weeks after treatment begins. Hair will often grow back after treatment stops, though in some cases the regrowth may be incomplete. To prevent further hair loss, use a mild shampoo (not harsh or fragranced) when bathing. Soft hairbrushes and low heat while blow-drying will also help prevent further damage to your hair. Wearing a wig, hat, or scarf may protect your head from the sun. Apply sunscreen to skin that has been exposed to radiation. These areas tend to sunburn easily.

Swelling (edema)
Radiation causes cells to die. The body's natural response to cell death or injury is swelling. Edema is extra fluid, or swelling, within the tissues of the brain. If brain swelling occurs, it can cause headaches, weakness, seizures, confusion, or speech difficulty. It may also worsen the symptoms that were present before treatment. If you start to feel uncomfortable with headaches or any other symptoms, discuss this with your radiation oncologist. Steroid medication (dexamethasone or methylprednisolone) may be given to reduce brain swelling and fluid within the tumor. Steroids should always be taken with food to protect your stomach and prevent nausea. Steroids can also affect the normal bacteria in your mouth and cause a yeast infection called thrush – whitish patches on the tongue. Do not abruptly stop taking steroids. A tapering schedule is required to avoid withdrawal.

What are the risks?

Radiation necrosis
Uncommonly, the radiation dose can cause the tumor tissue to become necrotic. Dead or necrotic tissue can become toxic to surrounding normal tissue, and swelling may occur. Radiation necrosis can happen anytime, but it most often occurs 6 to 12 months after radiotherapy. On an MRI scan, radiation necrosis can look similar to a recurrent tumor. A positron emission tomography (PET) scan or other imaging test may be done to tell between active tumor and radiation necrosis. However, sometimes these tests are not definitive. Treatment for radiation necrosis may include:

  • Medicines that promote blood vessel formation called pentoxifylline (Trental) and Vitamin E.
  • Hyperbaric oxygen therapy. Just as wounds need air to heal, damaged brain tissue may need a high stream of oxygen to repair itself.
  • A drug called bevacizumab (Avastin) may be given if swelling persists.
  • In some cases, radiation necrosis can progress and cause compressive symptoms similar to those of a tumor. Surgery may be needed to remove the necrotic tissue

Cognitive problems
Some patients experience memory loss and difficulty concentrating after radiosurgery. Typically this occurs when large areas of the brain are treated with radiation. The simple explanation for this decline is that radiation has the potential to injure good brain cells as well as bad tumor cells. Clinical trials are being conducted to investigate why this happens and what can be done to prevent or treat it. Some patients may benefit from seeing a neuropsychologist, who can evaluate thinking and memory problems and give tips for improvement.

What are the results?

After radiosurgery, MRI scans will be taken periodically so that your doctors can look for signs of response. Several months may pass before the effects of treatment are visible. Some tumors may be completely eliminated with radiation. For others the goal is to stop or halt the growth. In some cases the tumor may not shrink, but still be considered “controlled.”

For benign tumors, the goal is to stop or control the tumor's growth. About 40% of patients with an acoustic neuroma or meningioma show tumor shrinkage after radiosurgery, while about 40% of tumors remain the same (Fig. 6). Fewer than 20% of these tumors continue to grow. Facial nerve and/or trigeminal nerve problems develop in about 3% of patients with an acoustic neuroma.

For metastatic tumors, the goal of shrinking or stopping the tumor's growth is achieved in the majority of patients (Fig. 7).

For malignant tumors, results vary depending on the size, location, and type of tumor. Talk to your doctor about your specific prognosis.

For AVMs, the goal is to thicken the vessel walls and create clots that will close off the blood supply. It may take up to 3 years for an AVM to completely close. Results are related to the size and flow rate of the AVM. Small AVMs (<3 cm) have an 80% success rate. Larger AVMs (>5 cm) may require multiple radiosurgery treatments spaced several years apart.


Figure 6.  For slow growing tumors like acoustic neuromas, radiation causes gradual shrinkage with time.

 


Figure 7.  For fast growing tumors like a metastatic lung cancer, radiation causes rapid shrinkage (3 months).

Sources & links

If you have questions, please contact the Precision Radiotherapy Center, a partnership of Mayfield Clinic and University Radiation Oncology, at 513-475-7777.

Links
www.cancer.gov
www.irsa.org
www.abta.org

Glossary

benign: not cancerous.
fractionated: delivering the radiation dose over multiple sessions.
malignant: cancerous.
metastatic: a cancerous tumor that has spread from its original source.
stereotactic: a precise method for locating structures within the body through the use of 3-dimensional coordinates.
target: the area where radiation beams are aimed; usually a tumor, malformation, or body area.