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


Fatigue is common in the second half of treatment and is very variable between patients. Fatigue may persist for several weeks after treatment.


All other side effects of radiation therapy come from the structures/organs in and just next to where the radiation is being targeted.

Skin reddening and irritation – The skin can become increasingly red and itchy during treatment. Sometimes there can be skin peeling most commonly occurring under the breast or in the lower armpit due to rubbing of the skin in these areas. The peak of the reaction occurs 7-14 days after the treatment finishes. Occasionally there may be aches and pains in the breast or chest wall, but pain medications are rarely required.

Loss of hair (alopecia) – Hair in the armpit may fall out during or after radiation treatment. If hair loss occurs, it may be permanent.

What can help reduce acute side effects?

Resting as needed can help with fatigue. During treatment your Radiation Oncology team will provide advice on creams and dressings based on the degree of your skin reaction. Special creams can be used for itchy skin and if pain develops in the breast, pain medications can be prescribed.

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

Inflammation of the lung (pneumonitis) – This is an uncommon side effect occurring after breast irradiation. It can occur 6 weeks to 6 months following treatment. Symptoms most commonly include a dry cough and shortness of breath. Short-term corticosteroid medication are rarely needed to improve symptoms.

Breast Swelling – mild swelling can occur after treatment. The swelling can take several months after treatment to resolve.

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

Late side effects may occur a few months to years after treatment. They are more rare than early side effects. Depending on the problem, it may occur only once and then resolve or may be more persistent over the long term or may come and go over time.

Skin changes – If permanent skin changes occur after radiation treatment they are usually minimal. Occasionally the skin can be a little lighter or darker in the regions that have received radiation. Tiny blood vessels under the skin may become swollen and more prominent (telangiectasias) over time. Increased firmness in the breast may also occur with variable changes in appearance or shape compared to the other breast.

Rib fracture – Radiation can weaken the ribs located underneath the treated breast or chest wall, which can increase the risk of a fracture. This risk of rib fracture is 1%.

Lung scarring (fibrosis) – This may occur in the small amount of lung that receives radiation just under the breast and chest wall. The scarring may be visible on a chest x-ray but is not expected to cause symptoms.

Heart – If the left breast or chest wall is being treated, there is a low risk of damage to the heart and a small increased risk of heart disease. Radiation treatment techniques (deep inspiration breath hold) are now being used more commonly to reduce the amount of radiation to the heart to as low as possible.

Swelling of the arm (lymphoedema) – The risk of developing lymphoedema is approximately 5% if the lymph nodes located above the collar bone and/or armpit are treated. If lymphoedema occurs, it is usually mild to moderate but can rarely be severe.

Damage to the nerves that control the arm and hand (brachial plexopathy) – This is an extremely rare side effect that may occur if the lymph nodes above the collar bone and/or armpit are treated. Symptoms may include pain, numbness and weakness in the arm and hand.

Radiation induced cancers – Any exposure to radiation increases the risk of a second cancer developing in that area, usually decades later. This risk is not entirely attributable to radiation received as part of your treatment. All X-rays and scans received over your lifetime contribute to this risk, as does unavoidable exposure to environmental radiation. The risk of a cancer being caused by radiation therapy is in the order of 0.5 – 1% at 10 years.

What can be done to treat late side effects?

If the glands above the collar bone and/or armpit are treated and lymphoedema occurs, advice from a specialist nurse is required. Management may include exercises, compression garments and massage therapy. To minimise the risk of developing heart problems after radiation it is important to lead a healthy lifestyle and prevent or treat medical conditions that can increase the risk of heart problems.


Information and Guidance

Radiotherapy Treatment Process

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