How Does Radiotherapy Work?

Radiotherapy is one of the main treatments for cancer. It can be used alone or in combination with other treatments and draws on the properties of ionizing radiation to fight cancer.

Radiotherapy involves the local application of rays, or “ionizing radiation”, which cause major damage to DNA. Since cancer cells cannot repair this damage as effectively as healthy cells, they are unable to multiply and/or they die. This same mechanism causes the side effects of the treatment: when a tumor is irradiated, certain cells in the surrounding healthy tissue can become damaged, even when the tumor is targeted precisely. This is particularly damaging in important organs such as the heart, or when the patient is a child and their body is therefore still developing.

Radiotherapy may be applied for curative purposes, i.e. to treat the patient, or for palliative reasons, such as to relieve the patient in the case of painful bone metastases. It is sometimes used alone, for example to treat certain brain or lung tumors that cannot be removed surgically. It is also regularly used in combination with surgery and drug treatments (particularly chemotherapy). Radiotherapy often helps to avoid mutilating surgical operations, for example in breast, rectal, or ENT cancers.


There are several different types of radiotherapy

  • External radiotherapy is the most common form and uses particle accelerators to deliver electrons, photons, or (in the case of proton therapy) protons.
  • Brachytherapy involves putting radioactive sources in contact with or inside tumors. Since the radiation comes from inside the body, the treatment is more targeted.


copyright: Département de Radiothérapie / Institut Curie