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Radiation to the brain

There is always potential for some side effects to occur when radiation therapy is given to the brain. Many of these side effects are due to swelling of the brain (called cerebral edema). Side effects can develop shortly after treatment starts. Most side effects go away once treatment is over, but a few may continue or occur long after radiation therapy. High doses of radiation to the brain are more likely to cause long-term neurological (nervous system) problems. In children, the younger the child, the more sensitive the brain cells are to the effects of radiation.

In addition to the potential side effects of radiation therapy, there may also be soreness where the frame is attached to the head for stereotactic radiosurgery.

Cerebral edema

Cerebral edema is swelling of brain tissue. It is caused by large doses of radiation or by the tumour itself. Cerebral edema can develop quickly during treatment. It can cause an increase in intracranial pressure (ICP). Some of the symptoms of cerebral edema include:

  • headache
  • vision changes
  • nausea and vomiting
  • muscle weakness
  • changes in memory and concentration
  • seizures

Corticosteroids, such as prednisone or dexamethasone (Decadron, Dexasone), are often given to reduce swelling and relieve the symptoms of cerebral edema due to radiation therapy. Once corticosteroids are given, they cannot be stopped all at once, so the dose is gradually reduced over time.

It is important to report symptoms to the radiation therapy team. They will assess what is causing these side effects and decide if they need to stop treatment temporarily, adjust medications or use pain-relieving drugs.

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Seizures can sometimes occur when radiation therapy is given to the brain. Seizures are caused by abnormal electrical impulses in the brain. Some people have an aura, or an unusual feeling, before a seizure. Some seizures can be mild, while others cause more serious symptoms. Symptoms of seizures include:

  • unusual smells or tastes
  • visual changes or hallucinations
  • twitching or jerking of the muscles or limbs
  • biting the tongue
  • drooling
  • loss of bladder control
  • loss of consciousness (complete or momentary)
  • confusion

Anticonvulsants (antiseizure medicines) are given to manage seizures. The healthcare team will do regular blood tests to check the level of the anticonvulsant drug in the blood. If the levels are too low, there may not be enough drug in the body to effectively control seizures. Some anticonvulsants that are used to prevent and treat seizures include:

  • phenytoin (Dilantin)
  • carbamazepine (Tegretol)
  • valproic acid (Depakene, Epival)

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Skin reactions

If external beam radiation therapy is used, the scalp in the treatment area may become dry, itchy, red and tender. These side effects usually occur about 2–3 weeks after treatment starts and usually go away a few weeks after treatment ends. The radiation therapy team will give instructions for skin care. The scalp should be protected from the sun and cold by wearing a hat, turban or scarf. Follow the radiation therapy team’s advice about using sunscreen on the scalp.

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Thinning or loss of hair

Thinning of the hair or hair loss (alopecia) on the scalp can occur about 2–3 weeks into radiation therapy treatment because fast-growing hair follicles are sensitive to radiation. Hair loss occurs over the whole head if the entire brain is treated with external beam radiation therapy. If radiation is given to only part of the brain, hair loss or thinning occurs only in the area treated.

Hair loss may be temporary when lower doses of radiation are used. It is important to be gentle with the hair. Use a mild shampoo and a soft hairbrush, and let hair dry naturally. Hair often regrows 3–6 months after radiation therapy ends. Hair loss is more likely to be permanent with high doses of radiation.

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Somnolence syndrome

Somnolence syndrome is a group of symptoms that occur about 4–12 weeks after radiation is finished and can last for 2–8 weeks. Symptoms of somnolence syndrome include:

  • drowsiness
  • lethargy (lack of energy)
  • mild headache
  • low-grade fever
  • nausea and vomiting
  • loss of appetite
  • irritability
  • confusion
  • difficulty swallowing
  • difficulty speaking

The person with somnolence syndrome will want to sleep a lot. Symptoms usually go away on their own (without treatment) a few hours after they begin.

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Nausea and vomiting

Nausea and vomiting are not common side effects of radiation therapy to the brain, but they can occur. Nausea and vomiting may also occur due to swelling of the brain (cerebral edema). Nausea and vomiting may occur after 1–2 weeks of radiation therapy. These side effects can usually be managed with antinausea medication and usually go away after treatment is finished.

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Earaches or difficulty hearing

Earaches or difficulty hearing can happen if the ear is in the treatment area. These problems may be due to hardened earwax, irritation or damage to the middle or inner ear caused by radiation. Hearing difficulties should be reported to the radiation therapy team. Sometimes eardrops may be prescribed. The ear should be protected from exposure to the sun, wind and cold. Earaches and difficulty hearing usually go away on its own a few months after radiation therapy is done.

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Neurological changes

Neurological changes are often a late problem that can occur with radiation therapy to the brain. Neurological changes include:

  • changes in cognitive function, including concentration and reasoning
  • changes in emotions, including depression, irritability or mood swings
  • short-term or long-term memory loss
    • Short-term memory loss usually goes away about 2 months after radiation therapy is finished.
  • speech problems
  • balance and coordination problems

How radiation affects mental or emotional function is not really known.

A psychologist or neurologist may assess the person and suggest ways or medications to help cope with these changes. Cognitive rehabilitation may help a person regain or cope with changes in cognitive function.

Cranial nerve damage

Nerve damage can happen when radiation therapy damages any of the 12 pairs of cranial nerves. The cranial nerves are involved in seeing, eye movement, smelling, hearing, taste and balance. They affect sensation and control the muscles of the face, tongue, throat and shoulders. Damage to cranial nerves may cause:

  • vision changes
  • hearing problems
  • weakness of the face, tongue, neck or shoulder

The healthcare team will do a neurological examination to check nervous system function and detect changes in neurological function. These problems are more often a late effect of radiation therapy.

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Hormone deficiencies

Hormone deficiencies (low levels of hormones) are a late effect of radiation therapy. They can occur if the hypothalamus, pituitary gland or thyroid is damaged by radiation. These glands control the release of certain hormones, including:

  • sex hormones (such as estrogen, progesterone or testosterone)
    • Changes in the levels of sex hormones can lead to early or delayed puberty in children, menstrual changes in women and infertility in men or women.
  • growth hormone
    • If radiation to a child’s brain reduces the amount of growth hormone in the body, it will result in shortened stature, shortened limb length and diminished overall physical development.
  • thyroid hormone
    • Decreased thyroid hormone (hypothyroidism) results in fatigue, hair loss, brittle nails, dry skin, menstrual changes and lowered metabolism.
    • In children, low levels of thyroid hormone can cause slowed physical and mental development.
  • adrenal gland hormones
    • Lower amounts of adrenal gland hormones lead to water and electrolyte imbalances, muscle weakness, lowered ability to cope with stress and greater risk of infection.

These altered hormone levels often become long-term problems that need regular monitoring. Medications may be used to replace certain hormones.

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Radiation necrosis

Radiation necrosis (sometimes called brain necrosis) occurs when an area of dead tissue forms at the site of a brain tumour after radiation therapy. Radiation necrosis may occur as early as 6 months after radiation treatment, but symptoms usually occur 1–2 years after treatment is finished.

Symptoms of radiation necrosis are similar to increased intracranial pressure (ICP) and can include:

  • headache
  • drowsiness or somnolence syndrome
  • memory loss (short-term or long-term)
  • personality changes
  • seizures

Imaging tests, such as magnetic resonance imaging (MRI) or computed tomography (CT) scan, may be done to tell the difference between tumour recurrence and radiation necrosis. Sometimes a biopsy may need to be done to make a diagnosis. Radiation necrosis often gets worse over time.

Treatment options for radiation necrosis include:

  • corticosteroids to help control symptoms and reduce ICP
    • dexamethasone (Decadron, Dexasone) – most commonly used
    • prednisone
  • surgery to remove some of the dead tissue in the brain

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Radiation myelopathy

Radiation myelopathy is damage to the spinal cord caused by radiation therapy. The 2 types of radiation myelopathy are transient and late, or delayed.

Transient radiation myelopathy is characterized by Lhermitte’s sign, which is an electrical shock-like sensation in the neck, back or legs. It usually happens when the neck is bent forward. This side effect most often occurs 2–6 months after radiation therapy. It usually improves without treatment and is not linked with any long-term problems.

Late, or delayed, radiation myelopathy develops months or years after radiation therapy. It is characterized by weakness, not being able to feel temperature or loss of proprioception, which is the sense that deals with feelings of body position, posture, balance and motion. Late radiation myelopathy does not usually improve on its own and may lead to gradual paralysis.

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Reduced vertebrae growth

Radiation to the spinal cord can result in lowered or altered growth of the vertebrae (the bones of the spinal column) in the treatment area. Decreased vertebrae growth can lead to short stature, scoliosis and uneven bone and soft tissue growth. To lower the risk of scoliosis or other uneven bone and soft tissue development on either side of the vertebrae, the entire vertebra is treated with radiation rather than just one side.

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Leukoencephalopathy is a side effect that occurs more commonly after chemotherapy, but can also occur after radiation therapy to the brain. Leukoencephalopathy usually affects the white matter of the brain. The white matter contains nerve cells covered with myelin (a substance that acts like an insulator and speeds up nerve signals). With leukoencephalopathy, the myelin sheaths (called demyelination) in the treated area and surrounding tissue are destroyed.

Leukoencephalopathy is a late effect of radiation therapy to the brain and can be permanent. Symptoms include:

  • lethargy (lack of energy)
  • ataxia (inability to coordinate movements)
  • numbness
  • muscles spasms
  • muscle weakness or paralysis
  • seizures

An MRI may be done to diagnose leukoencephalopathy.

Treatment options for leukoencephalopathy include:

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Heart problems

Radiation therapy to the spinal cord in the chest area can damage the heart. If chemotherapy is given with the radiation, these side effects are more common and can be more severe. Symptoms such as fever, shortness of breath, difficulty breathing, swelling of the arms or legs or chest pain should be reported to a doctor as soon as possible.

Heart problems due to radiation therapy usually develop many years after radiation therapy. They often last a long time and are chronic problems. People who have had radiation to the heart area have an increased risk of premature coronary artery disease, heart attack, heart valve problems and scarring of the heart muscle.

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Bowel problems

In rare cases, radiation to the spinal cord that passes through the lower abdomen could cause diarrhea and radiation enteritis.

Diarrhea may begin 2–3 weeks into radiation therapy. Abdominal cramping may occur with the diarrhea.

Radiation enteritis is irritation and inflammation of the large and small intestines. It occurs during or after radiation therapy to the spinal cord in the abdominal area. It can occur when radiation therapy is first given and up to 8 weeks after (called acute enteritis). Sometimes it occurs several months to years after (called chronic enteritis).

Diarrhea and radiation enteritis should be reported to the radiation therapy team.

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Any steroid hormone that acts as an anti-inflammatory by reducing swelling and lowering the body’s immune response (the immune system’s reaction to the presence of foreign substances).

Corticosteroids are made by the adrenal gland. They can also be produced in the lab.


A substance that regulates specific body functions, such as metabolism, growth and reproduction.

Natural hormones are produced by glands. Artificial or synthetic hormones can be made in the lab.

magnetic resonance imaging (MRI)

An imaging technique that uses a magnetic field to produce pictures of areas inside the body. A contrast medium may be injected into the body to make structures and organs show up clearly on the image.

Doctors use MRI to make detailed images of organs and tissues in the body.

Also called nuclear magnetic resonance imaging (NMRI).

computed tomography (CT) scan

An imaging technique that uses a computer to put a series of x-ray images together to create a 3-dimensional picture of organs, tissues, bones and blood vessels inside the body. A contrast medium may be injected to make organs and structures show up clearly on the x-ray images.

The image produced is called a CT scan.

Also called computerized axial tomography (CAT) scan.


Treatment that uses physical means, such as special exercises, activities and massage.

Physiotherapy may be used to treat pain, disease or injury. It is given by a specially trained healthcare professional called a physiotherapist.

Also called physical therapy.

occupational therapy

Treatment that helps people develop, maintain or recover the ability to carry out the activities of daily living. It includes first assessing a person’s needs along with their home and work or school environments and then recommending changes or adaptive devices to help them in their daily life.

Occupational therapy may be used to help people return to their activities of daily living after cancer treatment. It is given by a trained healthcare professional called a occupational therapist.


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