Your Radiation Therapy Simulation

This is a time in your life when things can seem out of your control. The information on this page will help you know what to expect during your treatment, because knowledge and confidence are powerful tools to help you refocus and move forward.

What is Simulation?

Simulation is a process by which the radiation treatment fields are defined, filmed and marked on your skin. The simulator is a large-bore CT scanner used to contour your body. The CT scan itself is not used as a diagnostic scan; rather, it is used to contour the shape of your body and visualize structures. Since people come in all shapes and sizes, very specific patient measurements need to be obtained.

The images are then sent to our staff members in the physics department who, with the doctors, decide the arrangement of the radiation beams and make a customized plan especially for you. Special care is taken to make the patient’s position as comfortable as possible while ensuring the patient’s body positioning can be re-created exactly the same on a day-to-day basis.


You will probably encounter the following members of the radiation therapy team during your simulation:

  • Your physician/radiation oncologist is in charge of your simulation
  • A different physician from the radiation oncology group might occasionally assist with or complete a simulation; this should not cause you any distress because the physicians meet and review cases frequently, and they always work in collaboration with the primary radiation oncologist
  • The radiation therapist is trained and certified in the radiation therapy profession; he or she is qualified to participate in simulation and administer daily treatments under the direction of your radiation oncologist  
  • The oncology nurse is a registered nurse whose specialty is caring for the needs and concerns of oncology patients, particularly those receiving radiation therapy
  • The medical physicist specializes in the principles of radiation physics; He or she is responsible for maintaining the therapy equipment and overseeing the treatment planning process
  • The medical dosimetrist is responsible for performing dose calculations and developing treatment plans in conjunction with the physician and physicist

Positioning on the Table

How you are positioned on the treatment table depends on the area of your body receiving treatment. We might want you to lie on your stomach, on your side or flat on your back. Your head could be elevated or turned to one side. You might begin your treatment course in one position and later have it modified.

Unfortunately, both the simulation table and the treatment table are very hard and very flat. This is done purposely to ensure that your position, relative to the table, is exactly the same during the entire course of treatment. The simulation team will do their best to find a suitable, comfortable position for you. We have special immobilization aids to help you maintain your position, including:

  • Breast boards
  • Molded face masks
  • Foam sponges
  • Specially designed headrests
  • Acrylic molds
  • Foam body molds
  • Plaster casts

Your particular setup might not require any of these special supports or it might require a combination of several. It is very dependent upon the treatment site, your position and your ability to remain in that position for a ceratin amount of time. Don’t hesitate to let the therapist know if you're still unable to maintain your position.

We try to anticipate which simulations require fabrication of these supports so we can correctly estimate the amount of time you need to allow for your appointment.

Try to Relax

We realize that everyone can be nervous and apprehensive at this time. For both simulation and treatment, we want you to try to relax. There is no need to hold your breath during the CT scan, so breathe normally. The overall procedure can vary in length from thirty minutes to one hour.

You will be monitored throughout your simulation. A viewing window is above our outer control console and an intercom system is mounted into the unit, so we'll be able to see and hear you at all times.

What to Wear

Wear clothing that is comfortable and easy to remove. We will provide you with a hospital gown.

Jewelry will need to be removed prior to the simulation so that it doesn’t appear on the scans. We recommend leaving your jewelry at home.

We’ll ask you to leave the markings on your skin until treatment is completed. These markings might rub off slightly onto your clothing, especially during warm summer months, so consider wearing old clothing and underwear when you come for your appointment.

No Eating Limitations

There are no dietary restrictions prior to your simulation. You may eat and drink as usual.


In order for us to better visualize certain organs or various other sites in or around the treatment area, we sometimes need to administer contrast material (radiographic dye) during simulation. The contrast might be given intravenously (with a needle through the vein), orally or through a catheter inserted by the nurse or therapist. This contrast procedure would be done for the simulation only, not for daily treatment.

Marking the Fields

The therapist will take a few preliminary measurements and the physician (or the therapist) might mark a rough “sketch” of the area onto your skin with ink. The simulation team will then leave the room, and a series of events will begin, including:

  • The room lights might go on and off
  • A red laser lights might appear
  • All kinds of sounds and noises will be audible
  • Your table will move into the CT scanner

The table supporting your body will slide through a large “doughnut hole” in the CT scanner machine. There is plenty of room, so you shouldn’t feel too enclosed or claustrophobic.

Try not to be nervous. Remember, even though you’re alone in the room, you can be seen and heard the entire time.


Can you imagine if everyone you knew was the same size and shape? How boring life would be! Instead -- because everybody (and every body) is unique -- your personal radiation therapy "prescription" will be customized especially for you based on your body’s size, shape, measurements and information from the CT scan.

Your measurements might be taken by the therapist alone, or in conjunction with the dosimetrist (the person who calculates the radiation therapy dosage and develops the treatment plan with your physician).

Skin Marking / Tattoos

During your simulation appointment, we’ll draw very small marks or make tiny tattoos on your skin. Do not remove these marks. They need to remain visible on your skin throughout the course of your treatment so that we can precisely align the treatment lasers in exactly the same position at every appointment.

To create a tattoo, the therapist will prick the surface of your skin with a very thin needle. Then, an extremely small amount of ink will be injected into this pricked area. The result will be barely noticeable, and will look more like a freckle than a tattoo.

Emergency Cases

Like most hospital departments, we sometimes need to accommodate unexpected emergencies, which can disrupt the day’s schedule. Should we need to delay your appointment, we will explain the reason and then work as quickly as possible to remedy the situation.

Appointment Times

Some patients need their radiation treatments to be on specific days or at specific times. No matter the reason -- whether it’s your work schedule, a traffic concern, a child-care issue or something else -- we will do our best to accommodate you and your busy schedule.


We’ll take two photos of you on the day of your simulation. A photo of your face will be taken for future identification purposes.

A second photo (or set of photos) will be taken to help us remember how your body needs to be positioned on the treatment table. This is especially helpful if we have immobilization items propping you up, or when the treatment therapist is not the same therapist who performed your simulation, Both photos remain a part of your confidential treatment record.

When will my treatment begin?

Many patients assume their treatment will begin the day after simulation, but this is usually not the case. There will be a delay while our radiation therapy team customizes a cancer treatment plan especially for you. After your plan is determined, the calculations are then independently re-checked for accuracy.

Your course of treatment can last up to eight weeks, during which time we continuously monitor you and your body for any type of change. If a change occurs to your body -- such as weight loss or weigh gain -- that would require new calculations, it might be necessary to schedule a return visit to the simulator on short notice.

Don’t be shy!

Our goal is to make you knowledgeable about your radiation therapy, and comfortable enough to ask questions. If you have a question or concern about what is happening around you at any time during your many visits, don’t hesitate to ask us.