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Intensity-Modulated Radiation Therapy (IMRT) for Cancer

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 cure your cancer. Or, it may be used to help relieve pain and other symptoms caused by your cancer. This sheet tells you more about IMRT and what to expect. If you have further questions about the treatment, be sure to talk to your doctor.

How IMRT Works

High doses of radiation waves are directed at a tumor.

With IMRT, detailed imaging studies are used to find the precise location of a cancer tumor. Then a machine called a linear accelerator (linac) is used to direct high doses of radiation (high-energy X-rays) at the tumor. This is done at different angles and intensity levels based on the tumor’s size, shape, and location. The treatment destroys as many cancer cells as possible while sparing healthy cells and tissues. This helps shrink the size of the tumor.

Planning Your Treatment

IMRT is performed by a radiation therapy team. This team can include a radiation doctor, nurse, therapist, physicist, and 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 are 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 are 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, five days a week. The course of the treatment may last 2-8 weeks. You and your team will discuss the schedule for your treatment in advance. Each treatment session takes about 10-30 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, are used to confirm accurate positioning and alignment of the linac with your body.

  • 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 doctor or nurse will let you know when to return for your next session.

Possible Side Effects of IMRT

IMRT is more accurate than 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, such as fatigue and skin changes. Most side effects go away soon after treatment ends. But some side effects do not occur until months or even years after the treatment. The type of side effects you have and how severe they are will depend on the amount of radiation received and the part of your body being treated. Your doctor 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 health care team can also teach you ways to help cope with side effects.

Call the Doctor If You Have Any of the Following During Treatment:

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

Online Medical Reviewer: de la Cruz, Marlene, RN
Online Medical Reviewer: Lee, John W., MD
Online Medical Reviewer: Zlotecki, Robert A., MD, PhD, Radiation Oncology
Date Last Reviewed: 8/31/2012
© 2000-2015 The StayWell Company, LLC. 780 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.
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