Targeted energy to stop or slow cancer.

Medical team operating computers

How radiation therapy works

Radiation therapy (also called radiotherapy) uses beams of intense energy to kill cancer cells or slow down their growth by damaging their DNA. Cancer cells with damaged DNA stop dividing or die, and they’re broken down by the body over a period of days or weeks. 

There are two main types of radiation therapy:

  • External radiation: Uses a machine outside the body and aims radiation toward the cancer.

  • Internal radiation: A radioactive substance is placed in or near the cancer by needles, catheters or other methods.

Preparing for treatment

We understand that undergoing radiation treatment for cancer can be difficult for you and your family. Our goal is to help you understand what to anticipate.

  • Visit with your radiation oncologist: Your first appointment is with the radiation oncologist, the doctor who oversees your treatment. You may be asked to undergo imaging and other diagnostic tests (such as blood tests and biopsies) to learn how to best treat your cancer.

  • Imaging: The radiation oncologist uses images to determine the exact size, shape and position of the area to be treated, known as the treatment site. Imaging may include X-rays, computed tomography (CT), magnetic resonance imaging (MRI) or positron emission tomography (PET) scans.

  • Treatment planning: To create a treatment plan, we determine the best technique and calculate the position, dose, and frequency of the treatment.

What to expect during treatment

Most people are treated on an outpatient basis every day (Monday–Friday) for up to six weeks. Legacy Cancer Institute also offers specialized therapies such as SBRT (stereotactic body radiation therapy), brachytherapy and Gamma Knife, each of which may take one to 10 treatments. 

When you receive radiation therapy, you lie on a couch under the machine. During the process, images of the treatment site are taken to verify accuracy. The treatment is painless, and you cannot see or feel radiation.

It’s important that you follow the treatment plan, because missed treatments may affect your success.

What happens next

Because radiation kills not only cancer cells but also nearby healthy ones, you may experience side effects, such as fatigue, nausea, skin changes and hair loss. Talk to your doctor about what types of side effects you might expect and how you can manage them.

A radiation oncologist is always available to answer questions or concerns about the treatment. To speak with the provider on-call, please call the radiation oncology department where you are receiving treatment.

Once you complete your treatment, you attend follow-up clinics for up to five years. These visits help you manage any side effects and monitor the disease.

Whenever possible, we work to stop cancer. But when we can’t, we can often control it for a better quality of life, often called palliative care.

Working together for you

Our cancer experts work together with a common goal: delivering the right care for you.


A range of specialists collaborate regularly in meetings called tumor boards to discuss the best plan for your care. Your treatment plan is made just for you, depending on your general health, your age, your particular cancer and its growth.

More support

You are not alone. Legacy offers support throughout your cancer journey, as well as care for your emotional, social and spiritual needs.

Nurse navigators
Legacy Cancer Healing Center 
Support groups and classes
Cancer rehabilitation 
Survivorship services

Meet our providers

Our cancer specialists work closely together to deliver the latest treatments based on your needs. Learn more about our radiation therapy team.

Find your location

Legacy Health has four locations for radiation therapy. Look for one close to your home.