Intensity-Modulated Radiation Therapy (IMRT) for Cancer

Cross section of skin showing high-dose radiation waves directed at tumor.

Intensity-modulated radiation therapy or IMRT is a form of radiation therapy used to treat cancer. This sheet tells you more about IMRT and what to expect. If you have more questions about the treatment, be sure to talk with your healthcare provider.

How IMRT works

With IMRT, a machine called a linear accelerator (linac) is used to deliver an exact amount (dose) of strong X-rays to a three-dimensional (3-D) shape of the tumor. This exact dose limits the amount of X-rays that the tissue around the tumor gets. This form of external radiation therapy is called "intensity modulated" because the strength or intensity of each beam can be controlled or modulated.

The X-ray beams are aimed at the tumor from different angles. Both the shape and the strength (intensity) of the X-ray beams can be changed to keep them focused exactly on the tumor. The treatment destroys as many cancer cells as possible while limiting the dose to nearby healthy cells and tissues.

Planning your treatment

IMRT is done by a radiation therapy team. This team can include a radiation oncologist, a radiation oncology nurse, a radiation therapist, a medical physicist, and a dosimetrist. Before your first session, you and your team will plan the details of your treatment. This planning process is called a simulation. During the simulation:

  • Computed tomography (CT) scans or other imaging tests are done. The scans are used to map out the exact sites in your body that will be treated.

  • Positioning devices might be made that will help hold your body still and in the same position for each treatment session. These can include molds, masks, rests, and cushions.

  • Temporary ink or dot tattoos might be placed on your body. These marks help the therapist line up the beams from the machine with your body for treatment.

Having IMRT treatments

IMRT is usually given once a day, 5 days a week. Each session takes about 10 to 30 minutes. But the time that you are actually getting the treatment is very short. Treatments may last several weeks. You and your team will discuss the schedule for your treatment in advance. Here’s what to expect before, during, and after each session:

  • You change into a patient gown. The radiation therapist positions you on the treatment table. You may lie on your back, stomach, or side. If positioning devices were made, they’re used at this time.

  • The therapist leaves the room and turns on the machine from outside. He or she watches you on a TV monitor or through a window. You and the therapist can speak and heart each other through an intercom.

  • Imaging methods, such as X-ray or other scans, might be used before each treatment to make sure that the beams from the machine are positions and lined up with your body correctly. 

  • The machine then turns around you in precise positions. It directs the radiation beams at the tumor. You’ll hear sounds from the machine, but you won’t feel anything and the machine won't touch you. Tell the radiation therapist about any problems you might have during treatment. The machine can be stopped at any time.

  • You can go home shortly after the treatment is finished. Your healthcare providers will let you know when to return for your next session. You are not "radioactive" and are not a risk to the people around you.

Possible side effects of IMRT

IMRT is more accurate than some other methods for giving radiation. But as with any form of radiation therapy, healthy cells and tissue around the tumor can also be affected by the treatment. This can lead to side effects. Side effects from IMRT are usually limited to the area getting the radiation. More common side effects can include:

  • Skin in the treatment area becoming red, irritated, or swollen

  • Skin dryness, itching, peeling or blistering

  • Hair loss in the treatment area (may be permanent)

  • Feeling tired

  • Eating or swallowing problems (especially if the radiation is aimed at the head or neck)

  • Nausea or vomiting (especially if the radiation is directed at the stomach)

  • Diarrhea (especially if the radiation is directed at the stomach) 

Most side effects go away over time after treatment ends. But some side effects may not happen until months or even years after the treatment. For example, radiation can increase your risk of getting another cancer in the treated area later on.

Your healthcare provider can tell you more about what side effects to expect and how to manage them. If needed, your healthcare provider may give you medicines to treat or control some side effects. Your healthcare team can also teach you ways to help cope with side effects.

Call the healthcare provider

Contact your healthcare provider if you have any of the following during treatment:

  • Fever of 100.4ºF (38ºC) or higher, or as directed by your healthcare provider

  • Tiredness that doesn't go away

  • Trouble concentrating

  • Trouble breathing or shortness of breath

  • Pain that doesn’t go away, especially if it’s in the same place

  • A new or unusual lump, bump, or swelling

  • Dizziness or lightheadedness

  • Unusual rashes, bruises, or bleeding

  • Uncontrolled nausea and vomiting

  • Diarrhea that doesn’t improve over time

  • Skin breakdown or severe pain due to skin irritation

  • Any new symptom, or one that causes concern

 Be sure you know what other problems you should watch for, and know how to get help any time, including after office hours, on weekends, and on holidays.