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Intensity-Modulated Radiation Therapy (IMRT) for Cancer

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

Radiation therapy is often used as a treatment against cancer. IMRT is a form of radiation therapy. Depending on your treatment goals, IMRT may be used to help treat your cancer. This sheet tells you more about IMRT and what to expect. If you have more questions about the treatment, be sure to talk to your healthcare provider.

How IMRT works

With IMRT, a machine called a linear accelerator (linac) is used to deliver a precise dose of radiation to a tumor while limiting the dose to surrounding normal tissue. The radiation is aimed at the tumor from different angles, and both the shape and the strength (intensity) of the radiation beams can be changed to keep the radiation focused on the tumor. The treatment destroys as many cancer cells as possible while limiting the dose of radiation to nearby healthy cells and tissues.

Planning your treatment

IMRT is performed by a radiation therapy team. This team can include healthcare providers called 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. It takes one or more visits. During the simulation:

  • 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 with radiation.

  • Positioning devices might be made that will help hold your body 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 align the beams from the linac with your body for treatment.

Having IMRT treatments

IMRT is usually given once a day, 5 days a week. The course of the treatment may last several weeks, depending on why you are having it. You and your team will discuss the schedule for your treatment in advance. Each treatment session takes about 10 to 30 minutes. 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 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 linac from outside. He or she watches you on a TV monitor. You and the therapist speak through an intercom.

  • Imaging methods, such as X-ray or CT scans, might be used before each treatment to confirm accurate positioning and alignment of the linac with your body. This is known as image guided radiation therapy (IGRT). 

  • The machine then rotates 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.

  • You can go home shortly after the treatment is finished. Your healthcare providers will let you know when to return for your next session.

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

  • 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 soon after treatment ends. But some side effects do 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, medicines can be prescribed to treat 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

  • Ongoing fatigue

  • Trouble concentrating

  • Trouble breathing

  • 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

© 2000-2018 The StayWell Company, LLC. 800 Township Line Road, Yardley, PA 19067. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.