Understanding Radiation Therapy

Radiation therapy can help you in your fight against cancer. Radiation therapy uses high-energy X-rays or particles to kill cancer cells.

What is cancer?

Normally, cells in the body grow and divide the way they should. In some cases, cells change in abnormal ways. They then begin to grow and divide out of control. These are cancer cells. These cells multiply to form a lump called a tumor. Cancer cells can sometimes spread to other parts of the body, a process called metastasis.

How radiation therapy works

Radiation destroys cancer cells gradually, over time. The goal of therapy is to focus on and kill as many cancer cells as possible. Radiation can also damage or kill some of the normal cells that are closest to the tumor. But damaged normal cells are more likely to be able to repair themselves than cancer cells.


Microscopic view of normal cells and cancer cells.

Image showing a damaged normal cell and a dying cancer cell.

Image showing how radiation therapy works.

Image showing how radiation therapy works.

Types of radiation therapy

Different types of radiation therapy can be used to treat cancer.

External radiation 

With external radiation, a machine directs beams of high-energy X-rays or radioactive particles at the tumor. The goal of treatment is to kill all of the cancer cells, while affecting few normal cells. The machine can change position so the X-ray beams can enter your body from any angle. Newer types of external radiation therapy, such as 3-D conformal radiation therapy (3D-CRT), intensity modulated radiation therapy (IMRT). Stereotactic radiation therapy allows the radiation to be focused more precisely at the tumor. This can help spare nearby normal cells. 

Internal radiation (brachytherapy)

With internal radiation, one or more implants are placed in or around the cancer tumor. The implants put the radiation as close to the cancer as possible. This type of radiation travels only a short distance. This helps spare nearby normal cells. Implants can be temporary or permanent.

Systemic radiation therapy

Some types of radiation therapy are given as an injection of tiny particles into a vein (IV). The particles travel through the blood to reach tumors anywhere in the body. Once they get to where they are needed, they give off small amounts of radiation to kill the cancer cells.