Radiotherapy of the brain (fractionated)
Radiotherapy 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. Radiotherapy uses low dose beams to treat the tumor and a margin of normal cells surrounding the target area to prevent recurrence. The type and amount of radiation that you receive is carefully calculated during a number of therapy sessions. Over time, the abnormal cells die and the tumor may shrink. Normal healthy cells can also be damaged by radiation, but are able to repair themselves more easily. The goal of radiotherapy is to maximize the damage to abnormal cells and minimize the exposure to normal cells.
What is fractionated radiotherapy?
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.
Radiotherapy is split into a number of treatments called fractions that are given over several weeks. Delivering a fraction of the total radiation dose allows normal cells time to repair themselves between treatments. It also reduces side effects. Fractions are usually given five days a week with a rest over the weekend. Therapy sessions often take less than an hour.
The radiation beams come from a machine called a linear accelerator. The beams are precisely shaped to match the tumor and are aimed from a variety of directions by rotating the machine around the patient (Fig. 1). There are several types of machines, but they all do the same things:
- Precisely locate the target (tumor, lesion)
- Hold the target still
- Accurately aim the radiation beam
- Shape the radiation beam to the target
- Deliver a specific radiation dose
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.
What's the difference?
Delivers radiation at lower doses, over multiple times, and to larger areas. Treats a “margin” of tissue around malignant tumors.
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.
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 radiotherapy if you have a:
- Malignant tumor: glioma, glioblastoma, astrocytoma, lymphoma
- Benign tumor: acoustic neuroma, pituitary adenoma, meningioma, craniopharyngioma, glomus tumor
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?
Your first appointment is a consultation with a radiation oncologist. 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.
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.
Step 1: create face mask
The next appointment is to have a custom-made stereotactic mask to fit your face exactly. It will be used during each 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.
Step 2: simulation
Once the facemask is created you will undergo imaging scans, called a CT simulation, to carefully plan your radiation treatment. Reflective balls are placed on the facemask and worn during the CT scans (Fig. 3). These markers appear on the scan and help pinpoint the exact three-dimensional coordinates of the target within the brain. It may be necessary to obtain a new MRI scan.
After the scan, the facemask is removed and you may go home. The doctors continue with step 3 (treatment planning), and the patient returns within a week or so to begin treatment.
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 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
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.
What happens during treatment?
About a week after the simulation you will return to the center for your first treatment. The nurse or radiation therapist will escort you to a holding room, where you may need to change into a gown.
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.
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. 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.
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.
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.
What happens after treatment?
After treatment the therapist releases the mask from the table so you can get up. 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.
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 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.
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.
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.
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?
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.
Some patients experience memory loss and difficulty concentrating after radiotherapy. Typically this occurs when large areas of the brain are treated with radiation. The simple explanation for this decline is that radiotherapy 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 all radiotherapy sessions are done, 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."
Figure 6. For slow growing tumors like acoustic neuromas, radiation causes gradual shrinkage with time.
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 malignant tumors, results vary depending on the size, location, and type of tumor. Talk to your doctor about your specific prognosis.
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.
1. McKenzie JT, Guarnaschelli JN, Vagal AS, Warnick RE, Breneman JC. Hypofractionated stereotactic radiotherapy for unifocal and multifocal recurrence of malignant gliomas. J Neurooncol. 2013 Jul;113(3):403-9.
benign: not cancerous.
chemotherapy: treatment with toxic chemicals (e.g., anticancer drugs).
fractionated: delivering the radiation dose over multiple sessions.
lesion: a general term that refers to any change in tissue, such as a tumor, blood clot, malformation, infection, or scar tissue.
linear accelerator: a machine that creates a high-energy radiation beam, using electricity to form a stream of fast-moving subatomic particles; also called a LINAC.
metastatic: a cancerous tumor that has spread from its original source.
radiation necrosis: death of healthy tissue caused by the delivery of radiation to kill tumor cells.
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 other abnormality of the body.
reviewed by > John Breneman, MD, Ronald Warnick, MD
Mayfield Certified Health Info materials are written and developed by the Mayfield Clinic in association with the University of Cincinnati Neuroscience Institute. This information is not intended to replace the medical advice of your health care provider.