Your doctor has prescribed radiation therapy to treat your cancer. We hope the information provided here answers many of your questions about radiation treatment. Knowing what to expect can help put you at ease. As always, we are here to help in any way possible and answer your questions at any time.

Radiation therapy: what is it and how does it work?

Radiation therapy is a form of cancer treatment that uses radiation (strong beams of energy) to kill cancer cells or keep them from growing and dividing. Radiation therapy, including intensity modulated radiotherapy, may be used in conjunction with surgery or chemotherapy to treat cancer.

Through years of research and experience, doctors specializing in radiation therapy have determined the optimum doses for specific types of cancer that maximize effectiveness and minimize any harm to healthy tissues. The radiation oncologist will select the type of therapy best suited for your particular type of cancer.

Some of the types of radiotherapy include:

  • Interstitial Brachytherapy
  • Intracavitary Brachytherapy
  • Stereotactic Radiosurgery
  • Image Guided Radiation Therapy

Typically, radiation therapy involves small doses of radiation administered daily over a period of several days to several weeks.

External Radiation

External beam radiation therapy (EBRT) is the most common form of radiation therapy. A linear accelerator produces beams of high-energy radiation that are directed at the tumor. We can change the position of the machine to aim the beams at different angles.

External radiation therapy is usually given five days a week for one to eight weeks, depending on the disease. The daily treatment usually takes only a few minutes.

Internal Radiation (Brachytherapy)

In some instances, using internal radiation therapy, also called brachytherapy, is more effective than external radiation. Brachytherapy involves implanting a radioactive source or "seed" in or around a tumor. The source (and sometimes more than one) emits a high dose of radiation to a small area to kill cancer cells. Implants can be temporary or permanent.

What is simulation?

Before actual radiation therapy begins, a radiation therapist, under the supervision of a radiation oncologist, plans the details of the patient's therapy. This step is called simulation. It is important that patients are treated in exactly the same way each time so the correct amount of radiation is delivered to a precise area. Simulation is the treatment-planning step that customizes each individual's treatment.

The simulation procedure is performed in a room with special fluoroscopic X-ray equipment (that produces an X-ray movie) or CT scanner. These simulate the action of actual treatment machine, but without radiation. The therapist will use molds, masks, or blocks to make sure your alignment is correct and to help you lie still. Harmless laser light beams also help us accurately position our patients.

Measuring body contours allows us to use computerized treatment planning. Radiation beams are often directed from several different directions to optimize treatment.

Once all measurements are taken, we usually mark the skin to identify the precise area to be treated. Sometimes we use tiny permanent tattoos (small dots the size of a freckle). A contrast medium, taken by mouth or given intravenously, is sometimes needed to improve the contrast of a scan. Your radiation oncologist will discuss this or any other necessary procedures with you at the time of simulation.

The simulation procedure typically takes 30 minutes to about an hour. During this time, you will need to lie flat and still on a somewhat hard table.

The information we collect from the simulation is sent to radiation dosimetrists and physicists, who, under the supervision of the radiation oncologist, calculate appropriate settings for each individual patient.

What will happen on cancer treatment days?

Please check in with our receptionist when you arrive for your radiation treatment. Most patients are taken to a changing room and asked to change into a hospital gown. You then will be escorted to the treatment area. (Family and friends remain in the waiting area until you are finished with your treatment.)

Radiation treatments are typically given between 7 a.m. and 5 p.m., Monday through Friday. Your therapist will discuss future appointments on the day of your first treatment. Generally, treatments will be the same time each day.


The radiation therapist will take an X-ray (called a port film) on your first day of treatment, and another one every week or as needed. Port films verify that you are being positioned accurately during each treatment. Port films are not diagnostic and don't show your progress, but they are important in providing precise treatment. In some situations, ultrasound may be used instead of X-ray.

During Treatment

Once the therapist is certain you are positioned correctly, he or she will leave the room and start the radiation treatment. Video cameras and an intercom in the treatment room allow two-way communication between you and your therapist at all times. The radiation is "on" for only one or two minutes for each treatment field. During the treatment, you will need to lie as still as possible, breathe normally and relax. Your therapist will be in and out of the room to reposition the machine and change your position. The treatment machine will not touch you and you will feel nothing during treatment. Total treatment time can vary from a few to several minutes.

Once your radiation treatment is complete, your therapist will help you off the table and escort you back to the changing area or waiting room, and you can then be on your way to your normal activities.

What support services are available during cancer treatment?

To find out more about either of the following services, ask your nurse.

Social Worker

Our Radiation Oncology Department social worker is available during daytime hours to discuss any emotional issues or concerns about your treatment or your personal circumstances. The social worker also may be able to assist with housing and transportation problems, and can provide information about support groups that often prove valuable to our patients.

Integrative Medicine

Reflections, a special program offered free to all patients undergoing cancer treatment at Cleveland Clinic, is designed to help you manage stress and promote wellness.

What advanced radiation therapy programs, like image guided radiotherapy does Cleveland Clinic offer?

We offer image guided radiotherapy, gamma knife surgery, 3-D conformal radiation therapy, intensity-modulated radiation therapy, and are the only hospital in Ohio to offer.

Gamma Knife Radiosurgery

The Gamma Knife is considered by many to be the "gold standard" for radiation treatment for brain tumors or lesions. The Gamma Knife provides results comparable to or better than conventional surgery in many cases, without the need for a surgical incision or protracted recovery in the hospital.

  • Stereotactic Radiosurgery - Gamma Knife

3-D conformal radiation therapy

This technology uses CT scans and special computer software to help us create a three-dimensional computer model of the area to be treated. This allows us to more precisely target treatments at the tumor and spare surrounding normal tissue.

Intensity-modulated radiation therapy (IMRT)

Intensity modulated radiotherapy allows us to provide even more precise radiation therapy for our patients. With the help of sophisticated computer software, this multi-beam system can vary dose intensity and narrow in on diseased cells.

  • Intensity-modulated radiation therapy (IMRT)

Image guided radiotherapy (IGRT)

Especially useful for irregularly shaped tumors, our Novalis image guided radiotherapy system delivers high-precision radiation to a tumor, while sparing adjacent organs. Cleveland Clinic also is one of the first centers in the nation to use ultrasound-based image-guidance technology.

  • Image guided radiotherapy (IGRT)

Radiation Therapy - Types of Treatment

  • Learn More

Reviewed by a Cleveland Clinic medical professional.

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