About the treatment:

What is external beam 

radiation therapy?

■ It is a common cancer treatment

that uses high doses of radiation to

destroy cancer cells and shrink

tumors. 

■ A large machine aims radiation at

the cancer. The machine moves

around you without touching you.

■ It doesn’t hurt. 

■ It doesn’t make you radioactive.

■ It can’t be seen, felt, or smelled. 

How does treatment work?

■ At low doses, radiation is used as an

x-ray to take pictures inside your

body. In cancer treatment, higher

doses of radiation are used to

destroy cancer cells.

National Cancer Institute

U.S. DEPARTMENT

OF HEALTH AND

HUMAN SERVICES

National Institutes

of Health

Understanding Radiation Therapy

What To Know 

About External Beam Radiation Therapy

“My wife and I made a list of questions to 

ask my doctor. My doctor answered them 

and helped me understand my treatment. 

He also told me that the external beam radiation

therapy wouldn’t make me radioactive. I was

very happy to hear that. I’m glad I can still be

around my wife and children.”

turn page over

■ The radiation that destroys cancer

cells also injures nearby healthy

cells. This is why you may have

some side effects.

How long does treatment take?

■ The length of your treatment

depends on your type and stage 

of cancer.

■ Most treatments take 2 to 10 weeks.

■ Most people get treatment once a

day for 5 days in a row. Treatment

usually happens on Monday

through Friday. Sometimes, people

get treatment twice in 1 day.

■ Most treatment visits last for 

30 minutes to 1 hour. You will get

radiation for only 1 to 5 minutes,

but you may be in the treatment

room for 15 to 30 minutes. Your

visit may be longer if you have

other tests done.
Before treatment starts:

You will meet with a doctor or nurse before

your first treatment. He or she will tell you how

the treatment works and how it can help you.

You will also learn about any side effects to

expect. Be sure to ask any questions you have. 

Your first meeting:

■ You will get a checkup (physical exam).

You and your doctor will talk about your

health and medical history.

■ You might get tests, such as x-rays or 

CT scans.

Follow-up meeting: 

■ Your radiation therapist will put small

marks (tattoos or dots of colored ink) on

your skin. These marks show where to 

aim the radiation.

■ A body mold or mask might be made at

this meeting. It will help you stay still

during your treatment sessions.

Understanding Radiation Therapy: What To Know About External Beam Radiation Therapy

During your treatment:

■ You will probably lie down on a 

treatment table.

■ Your radiation therapist will be in the

next room to control the machine. He or

she will be able to see, hear, and talk with

you through a speaker at all times.

■ You will need to stay very still, but you

won’t have to hold your breath.

■ You may see lights pointed at you. They

are safe and show the therapist where to

aim the radiation.

When you go for treatment:

■ Don’t have powder, deodorant, Band-Aids®,

or jewelry near your treatment area.

■ Wear loose-fitting, comfortable clothes.

Ask your doctor or nurse about side

effects from this treatment.

The side effects you may have depend

on where you are getting radiation. 

There are fact sheets to help you learn

how to manage side effects.

Free Services To Learn More

National Cancer Institute

Cancer Information Service

Phone: 1-800-422-6237 

(1-800-4-CANCER)

TTY: 1-800-332-8615

Online: www.cancer.gov

Chat Online: www.cancer.gov/help

NIH Publication No. 10-6111

Reprinted April 2010