Side effects during/soon after treatment (Early or ‘acute’ side effects)


Fatigue is quite common in the second half of treatment and tends to vary between patients. It may also persist for several weeks after treatment.


The other side effects of radiation therapy come from the structures and organs in and just next to where the radiation is being targeted. These side effects appear halfway through treatment and increase in severity toward the end of treatment. Due to the cumulative nature of these side effects they can peak in severity 7-10 days following treatment.

Skin reddening and irritation – The skin on the scalp may become red, dry and/or itchy. Usually the skin reaction is mild to moderate.

Loss of hair (alopecia) – Hair loss may be partial or total depending on the treatment. The hair loss can be temporary or permanent depending on the amount of radiation.

Cerebral oedema (swelling in the brain) – Radiation therapy can cause temporary inflammation around the brain tumour. This may cause headaches, nausea, vomiting and/or drowsiness. If these symptoms occur during treatment, corticosteroid medication may be used to treat these symptoms. Inflammation may also temporarily worsen pre-existing neurological symptoms.

Tinnitus (ringing in the ears) and hearing loss – These symptoms are uncommon during radiation treatment.

What can help reduce acute side effects?

Resting as needed can help with fatigue. Creams can be used on the scalp for skin reddening and irritation. Wigs can be used for temporary or permanent hair loss. If headaches, nausea and/or vomiting occur during treatment, corticosteroid medication may be used to reduce the swelling around the tumour, which usually improves symptoms. Pain medications and anti-nausea medications are prescribed if needed.

Early-delayed side effects (side effects occurring 1-6 months after treatment) 

Somnolence syndrome- this is uncommon but can occur 1-6 months following radiation treatment. Symptoms can include sleepiness, irritability, headaches, nausea, vomiting and loss of appetite. The symptoms usually resolve after a few weeks and corticosteroid medication may be used to treat symptoms.

Side effects well after treatment (Late or long-term side effects)


Neurocognitive effects include changes that can affect thinking, learning, processing or remembering information. Neurocognitive effects may also occur following surgery and/or chemotherapy.


If the tumour is located close to the following structures, uncommon side effects may occur.

Eye and optic nerves – Radiation can cause the lens of the eye to become cloudy (cataract). This can cause painless visual impairment years after treatment. Radiation changes to the retina may be asymptomatic or cause painless loss of vision, which can be partial or total. Radiation to the optic nerves can very rarely cause permanent visual loss.

Ear – Hearing loss and ringing in the ear (tinnitus) can develop progressively over a few years following treatment and is usually permanent.

Pituitary gland – Radiation may cause the pituitary gland to become underactive. Your doctor may recommend blood tests following treatment to monitor for this.

Brain necrosis (tissue death) – This is a rare event occurring after high doses of radiation. It tends to occur 1-3 years post treatment. Symptoms depend on the location of the necrosis. It can be a very serious complication that may require surgical treatment.

Radiation induced cancers – Second cancers occurring as a result of radiation therapy are an extremely rare side effect of radiation therapy.

What can be done to treat late side effects?

Changes in vision following radiation treatment should be assessed to determine the cause. If radiation results in a cataract, the lens can be replaced with a minor operation. Radiation effects to the retina or optic nerve are generally irreversible. It is important to prevent and treat other medical conditions that can contribute to eye problems (diabetes). Hearing aids may be beneficial for hearing loss. If the pituitary gland becomes underactive, hormone replacement is prescribed. Medications may be useful for some neurocognitive changes that occur after radiation treatment. There are medications under investigation that may be helpful in preventing neurocognitive effects from radiation.

You should discuss management of any side effects with your medical team.

Information and Guidance

Radiotherapy Treatment Process

Click below for a video that shows the external beam radiotherapy treatment process.