Radiation is energy that moves through space. Radiation can be given off naturally, like from sunshine and, in low doses, from the earth and rocks.

Radiation can also be produced artificially by machines. In lower doses, it is used for things like x-rays, to take pictures of the inside of your body.

Radiation therapy to treat cancer uses much higher doses of radiation to destroy cancer cells. It damages the cancer cells over and over again. The cancer cells don’t have time to repair themselves between daily treatments so eventually they die.

How radiation therapy works

Radiation therapy works by destroying cancer cells and damaging a cancer cell’s DNA so that it stops dividing and growing. Radiation therapy can shrink a tumour or completely destroy it. It is most effective on cells that grow and divide quickly. Cancer cells tend to divide more quickly than most normal cells. This makes them more likely to be affected by the radiation (be radiosensitive) than normal cells.

Even though cancer cells and normal cells react differently to radiation, it’s very hard to destroy cancer cells without damaging some normal cells too. Damage to normal cells causes side effects. Normal cells are often able to recover better from radiation damage than cancer cells. The goal of radiation therapy is to give enough radiation to destroy cancer cells in your body but not so much that normal cells can’t recover.

How radiation therapy is used

Radiation therapy may be used alone to treat cancer or with other treatments such as surgery or chemotherapy. It may be used before surgery to shrink a tumour or after surgery to destroy any cancer cells that remain and to prevent the cancer from coming back. Radiation therapy may also be used to relieve symptoms, improve quality of life and extend life for people living with advanced cancer (called palliative radiation therapy).

External radiation therapy (also called external beam radiation therapy) is the most common type of radiation therapy used to treat cancer. A machine directs a beam of radiation at a cancerous tumour in the body. There are different types of external radiation therapy.

Internal radiation therapy puts radioactive substances into the body, such as directly into the tumour or into an area of the body, to kill the cancer cells. There are different types of internal radiation therapy.