What to Know About Radiation Therapy for Brain Tumors
Radiation therapy uses high-energy radiation to kill cancer cells. Radiation therapy controls some types of brain tumors better than others. Radiation is often used with surgery or chemotherapy for brain tumor treatment.
Doctors give radiation treatment in one of these two ways:
From a machine outside the body called external beam radiation
From small radioactive pellets placed inside or near the area with cancer called brachytherapy, internal radiation, or interstitial therapy
Your doctor may give you both types of treatment.
Radiation can harm normal brain cells. To limit the damage, your doctor will focus high doses directly on the tumor. One way to do this is with 3-D conformal therapy (3DCRT). In this treatment, doctors use computers and computed tomography (CT) or magnetic resonance imaging (MRI) scans to match the radiation beams to the shape of the tumor from different angles. Intensity modulated radiation therapy (IMRT) is a similar technique that allows doctors to control the intensity of the radiation beams directed at different parts of the tumor. A newer technique, known as conformal proton beam therapy, focuses beams of protons (instead of X-rays) on the tumor. Protons are more likely to pass through normal tissues without damaging them, which may lead to fewer side effects. These types of radiation therapy are usually given over several weeks of treatment.
Another way to minimize damage is stereotactic radiosurgery (SRS). It can be used on small tumors. Once doctors know the size and location of the tumor, they give a high-energy dose of radiation to the tumor from many different angles. These types of radiation treatment are given as a one time dose or several doses over a few days. These are the two types of SRS:
Gamma knife radiation. Radiation beams (gamma rays) from a machine are focused at the tumor from hundreds of different angles at the same time.
Linear accelerator. Instead of delivering many beams at once, this machine moves around the head to deliver radiation to the tumor from different angles.
Your doctor may use SRS as the main treatment or as an additional treatment.
You'll have imaging tests to see if the cancer has spread to other parts of your brain and your spinal cord. If the cancer has spread, you may have radiation to your whole brain and spinal cord.
Brachytherapy involves inserting radioactive seeds or pellets directly into or near the tumor either through inserted tubes or during open craniotomy for surgery. The radiation they give off travels a very short distance, so it affects the tumor with very little effect on surrounding tissue. This technique may be used with external radiation to provide a high dose of radiation at the tumor site, while the external radiation treats nearby areas with a lower dose.
Potential side effects of radiation therapy for a brain tumor
Even though doctors try to be precise when giving radiation therapy, some normal cells are almost always exposed to the effects of radiation. This causes side effects.
Here are some of the possible side effects of radiation therapy for brain tumors:
Sometimes, dead brain tissue will form at the site of the radiation. This is called radiation necrosis. Most of the time, the mass of dead brain tissue contains both cancerous and healthy cells. Radiation necrosis can take anywhere from months to years to develop.
If you have problems from the mass from radiation necrosis, you may need to have it removed with surgery. Here are examples of some problems it may cause:
It's not always easy to tell the difference between radiation necrosis and cancer that has come back. A special brain scan, called a positron-emission tomography (PET) scan, can sometimes tell the difference between dead tissue and living cancer tissue. But often a biopsy is the only way to tell for sure.
Radiation can also affect your genes. As a result, after radiation, you have a small risk of getting a second cancer. This second cancer usually occurs many years later. Always talk to your radiation oncologist about the risks and benefits of radiation therapy to know your options.
Radiation therapy may also cause problems with your thyroid, hypothalamus, or pituitary glands. These will be monitored by your neuro-oncologist.