Stereotactic Therapies - Treatment

Operating on the brain is always delicate and can be cause for concern. Depending on the position of the tumor or abnormality, neurosurgeons may be reluctant to cut through a patient’s skull. They may be afraid of damaging healthy brain tissue while performing surgery to remove a malignant tumor.

Stereotactic therapy is a non-invasive treatment in which high-dose radiation beams are delivered to a tumor or lesion in a concentrated, extremely precise manner. Many beams of radiation – often more than 100 – are directed at the tumor from different directions. Each of these many beams is relatively weak and therefore causes very little damage when entering the patient’s body.

However, when all the beams converge at the target, their cumulative effect adds up to an extremely potent dose aimed at destroying the target cells with great precision. They spare the surrounding tissue, and minimize damage to otherwise healthy cells. Typically, a single, high-dose application of radiation is delivered to the tumor instead of many smaller doses as is the case in conventional radiation treatment.

Stereotactic therapies are administered as the primary mode of therapy, or can be used in conjunction with conventional surgery to treat remaining cancer cells.

CyberKnife

UT Southwestern is one of only five institutions in the United States to offer its patients stereotactic therapy with the Accuray CyberKnife® Robotic Radiosurgery System. The CyberKnife delivers painless, non-invasive treatment utilizing high doses of precisely targeted radiation to destroy tumors or lesions within the body, while minimizing radiation to surrounding healthy tissue.

The CyberKnife system features tracking software and a linear accelerator mounted on a robotic arm.  The robotic arm is coupled with two orthogonal X-ray imaging cameras, used to locate the position of the tumor. The flexibility of this robotic arm makes it possible to treat certain areas of the body that cannot be treated by other conventional radiotherapy techniques, such as the spine and spinal cord.

At UT Southwestern, CyberKnife stereotactic radiotherapy is most commonly used to treat primary or metastatic brain tumors, which are those that have spread to the brain from other parts of the body. It is also the therapy of choice for treating other tumors of the head and neck, base of skull and cervical spine. Researchers at UT Southwestern are developing investigational protocols for treatment in other body sites such as the pancreas and prostate.

In many cases, patients with tumors undergoing treatment today with the CyberKnife system were previously considered to be untreatable with surgery or conventional radiation therapy.

Before Your Therapy

Before receiving CyberKnife stereotactic radiotherapy on an outpatient basis, you will be scheduled to receive an initial consultation with the radiation oncologist and neurosurgeon. During this visit, you will undergo a CT imaging scan. The CT scan is an X-ray in which a three-dimensional image of the tumor site is constructed by a computer. This 3-D image lets the physicians see all sides of the tumor and allows them to plan for the radiation beams to be precisely focused on the unique shape of the tumor or lesion.

Once the CT scan has been completed, the physicians and medical physicists will use the computerized planning system to create the treatment plan. This usually takes one day or less.

What to Expect During the Procedure

You will return for your first treatment the next day. The number of treatments required depends on the location, size and shape of the tumor. Each treatment lasts between 30 and 90 minutes. Typically, only two to five daily sessions are required.  You will lie comfortably on the procedure table without anesthesia while the robotic arm moves to treat all areas of the tumor.

Compared to other radiosurgical treatments, the CyberKnife system will allow you to recover immediately, given the low risk of complications and damage to healthy tissue.

After Your Therapy

CyberKnife radiotherapy treatment will not have immediate results. Your progress will be monitored through follow-up imaging exams, and many weeks or months may pass before the effects of the treatment become apparent.

Gamma Knife

Gamma Knife® stereotactic radiotherapy is a non-invasive method for treating brain disorders. It works by delivering a single, high dose of radiation to a small and critically located intra-cranial tumor through the patient’s skull.

The extreme precision of Elekta Leksell Gamma Knife® system makes it possible to administer a high radiation dose to the diseased area, minimizing the risk of damaging healthy tissue.

Gamma Knife® radiotherapy has many advantages. The risk of complications, as compared to open surgery, is less, and it is a gentler form of treatment for the patient. Gamma Knife® radiotherapy can normally be performed in a day, and the convalescence time is extremely short.

Gamma-knife stereotactic radiotherapy is most commonly used for:

Brain tumors. The procedure is useful in the management of both benign and malignant brain tumors, especially metastatic tumors originating elsewhere in the body that have migrated to the brain. Radiosurgery often can treat tumors located in areas of the brain so difficult to access that they may have been termed inoperable.
 
Arteriovenous malformations (AVMs). AVMs are abnormal collections of blood vessels where arteries and veins are connecting directly, instead of through a network of capillaries. When located in the brain, these abnormalities can cause severe bleeding, headaches or seizures. While many of these lesions can be removed with a scalpel, radiosurgery is frequently a better treatment with less risk of neurologic injury.

Trigeminal neuralgia. This nerve disorder causes disabling facial pain that feels like an electric shock. Gamma-knife surgery can create a lesion on the nerve, blocking its pain signals. Radiosurgery for trigeminal neuralgia is typically performed for older patients or for patients with recurrent pain after other operations.

Acoustic neuromas. These non-cancerous tumors, also called schwannomas, develop on the nerve that affects balance and hearing. Radiosurgery can effectively control the growth of these tumors with a lower risk of deafness or loss of facial movement, compared to conventional surgery.

Pituitary tumors. Tumors of the pea-sized "master gland," which is located deep within the brain, can cause a variety of problems because the pituitary controls the thyroid, adrenal and reproductive glands. Gamma-knife surgery is effective at stopping the abnormal hormone secretion that can occur from these tumors.

Before Your Therapy

Do not eat or drink anything after midnight the night before the procedure. However, you can take your regular medications with a sip of water. You will not be allowed to wear jewelry, eyeglasses, contact lenses, dentures or wigs during the procedure.

What to Expect During the Procedure

The key to the gamma-knife's precision lies in the box-shaped frame that is attached to your head with four screws. In addition to holding your head perfectly still during the procedure, the head-frame also acts as a reference point in determining exactly where the beams of radiation should converge. You will typically be awake, although you may take a mild sedative to help you relax.

The four spots on your scalp where the screws enter first are numbed with injections containing an anesthetic similar to that used by dentists. Your hair will not be shaved, but it may be tied back into a ponytail if it is long. The head-frame is lightweight, so you will be able to move your head around after the frame is attached to your skull.

Once the head-frame is attached, you'll undergo CT imaging scans to locate the exact area inside your skull that needs treatment. Even though you may have had similar scans before, these scans must be repeated with the head-frame in place.

A transparent plastic localizer is attached to the head-frame for the CT scans. This localizer acts as a landmark used in the planning computations.

After you finish the imaging scans, it may take an hour or more for the targeting plan to be computed. During this waiting period, you will be taken to a room where you can relax and watch television or read, if you want. When it is time for the treatment, you'll lie down and put your head into a helmet. The helmet attaches to your head-frame, which keeps your head perfectly still so the radiation beams will converge on their target and not on the healthy tissue surrounding it.

The helmet will not cover your face. You will not feel the radiation nor hear any noise during the treatment.

The number of minutes that each radiation dose lasts is determined during the dose planning. Treatment usually includes multiple doses. Sometimes, more than one type of helmet and head position is used to deliver the radiation.

The head-frame stays on your head throughout the entire procedure. When the head-frame is removed, the places on your scalp where the screws entered may be a little tender, but they typically don't scar. You may have a headache or feel nauseated for a few hours after the procedure.

After Your Therapy
Gamma-knife radiotherapy will not have immediate results. Your progress will be monitored through follow-up imaging exams, and many weeks or months may pass before the effects of the treatment become apparent.