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How does​​​​​​​​​​​​​​

radiotherapy work?

To understand how radiation works, it may help to know that normal cells grow and divide in a cycle. This happens in all cells and is happening all the time. The cell cycle is normally tightly controlled; however, this regulation may be lost in cells that are cancerous, leading to rapid cell division and uncontrolled growth.

Radiotherapy ​​​​​​​ damages the cell’s DNA ​​​​​​​ at the point during the cell cycle when the cell divides. Rapidly dividing cells are the most sensitive to radiation – so it destroys these cells first. This can hinder the cell cycle to prevent cell proliferation and tumour growth, however it can also affect the cells of normal tissues that are dividing at a slower rate. Radiotherapy is therefore commonly targeted only at cancer cells to reduce side effects.

How is it used in breast cancer and for which types?

Radiation is targeted at specific parts of the body and can be used alone or in combination with other treatments.
It is commonly given in early breast cancer but can also be given in later stages.

Radiotherapy in early breast cancer

  • In early stages of breast cancer, radiotherapy may be given to help shrink and destroy the tumour ​​​​​​​
  • Radiotherapy may be given with chemotherapy
  • Radiotherapy may be given before breast-conserving surgery to help make the tumour easier to remove
  • Radiotherapy may be given after surgery to help lower the risk of the cancer returning

 Radiotherapy in metastatic breast cancer

  • When the cancer has spread to other parts of the body, radiotherapy may be given to help shrink the tumour or relieve symptoms.

 For example:

  • External beam radiotherapy may be used where the
    cancer has spread to the bone

  • Whole brain radiotherapy may be used when the cancer
    has spread to the brain and surgery is not possible

How is radiotherapy given?

In breast cancer, radiotherapy  is commonly given by a machine that emits beams of radiation directly at the area where the tumour  is located (external beam radiation).

Various types of radiotherapy may be offered. These include whole breast radiotherapy or partial breast radiotherapy. Your doctor will talk to you about which method is most suited to your type of breast cancer.

The radiotherapy schedules for metastatic breast cancer are different from those you may have experienced already. If you need radiotherapy, you will have to visit the radiotherapy department at the hospital.

​​​​​​​You might have one treatment a day for a few days or over a couple of weeks. Each treatment is called a fraction and takes a few minutes.

What are the side effects of radiotherapy?

Radiotherapy can cause side effects. These may vary from person to person and will depend on the type of radiotherapy and target organs.
Talk to your doctor about the potential effects of radiotherapy and the best treatment options for you.

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The What’s Breast for Me? Campaign is funded by Pfizer Healthcare Ireland. Copyright © 2024 Pfizer Healthcare Ireland. All rights reserved. This site is intended for residents of the Republic of Ireland. The information provided on this site is intended for general information and education and is not intended to be a substitute for advice provided by a doctor or other qualified healthcare professional. All decisions regarding patient care must be made with a healthcare provider, considering the unique characteristics of the patients.


Date of preparation: January 2024