Contact   |    Careers   |    Employees   |    Physicians

Radiation Oncology




Radiation Oncology - Radiation Therapy Simulation: What to Expect

Your diagnosis is confirmed. You’ve had more tests and seen more doctors than you care to remember. You’ve heard all the options for treatment. You’ve chosen to proceed with radiation therapy at the Radiation Oncology Department of Sibley's Cancer Center in Washington DC. Now what? Where do we go from here? The information that follows will answer those questions.

What is Simulation?

Simulation is a process by which the radiation treatment fields are defined, filmed and marked out on your skin. The simulator is actually a large bore CT scanner that is used to contour your body. The images are then sent to the physics department who, with the doctors, arrange the radiation beams and make a customized plan. It is here that special care is taken to make the patient’s position as comfortable as possible while ensuring reproducibility on a day-to-day basis. Since people come in all shapes and sizes, very specific patient measurements need to be obtained.
Treatment unit parameters are finalized and recorded. All setup information is documented to make your treatment record complete. It is an integral part of the planning process. The CT scan itself is not used as a diagnostic scan but instead used to contour the shape of your body and visualize structures. The physician can then arrange the beams and make a plan using a computer system.


The following are members of the radiation therapy team you may encounter during your simulation:
Physician—your radiation oncologist. He or she is in charge of your simulation. On rare occasions a different physician from the radiation oncology group may be asked to help with, or complete a simulation. Rest assured, the physicians meet and review cases often and always work in collaboration with the primary radiation oncologist. The radiation oncologist will direct the therapist in the simulator.

Radiation Therapist—a person trained and certified in the radiation therapy profession. He or she is qualified to participate in simulation and administer daily treatments.

Oncology Nurse—registered nurse whose specialty is the needs and concerns of oncology patients, particularly those receiving radiation therapy.

Medical Physicist—a person who specializes in the principles of radiation physics. He or she is responsible for maintaining all therapy equipment as well as overseeing the treatment planning process.

Medical Dosimetrist—the person responsible for performing dose calculations as well as developing treatment plans in conjunction with the physician and physicist.

What to Wear

Since we will be marking the skin surface, it is necessary that we expose the treatment site. In addition, clothing worn adjacent to that area may have to be removed as well. The reason for this is reproducibility. Having a shirt rumpled underneath you, or snugly fitting pantyhose around your waist, may change your position slightly from day to day. We can easily avoid this problem by simply having you change into a gown.
It is a good idea to leave jewelry at home, particularly if the simulation is to be the head, neck, or chest region. Earrings and necklaces will only have to be removed prior to the simulation as some jewelry items appear on the scans.
Choose clothing that is comfortable and easy to remove. Skin markings can usually be removed at the end of the session but occasionally we request that a patient leave them on until treatment commences. These markings may rub off slightly onto your clothing, especially during warm summer months, so consider wearing old clothing and underwear when you come for your appointment.

How to Prepare

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


The simulation team will do its best to find a suitable, comfortable position for you. We regret that both the simulation and treatment tables 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 position chosen will be dependent upon the area treated. We may want you to lie on your stomach, on your side, or flat on your back. Your head may be elevated or perhaps turned to one side. We might even start out in one position only to find after a short time that we need to try a different one. We have special aids to assist you in maintaining your position. Please let the therapist know if you feel you are unable to maintain a position.
We realize that everyone is nervous and apprehensive at this time. For both simulation and treatment we want you to try to relax. Breathe normally. There is no need to hold your breath during the CT scan. The overall procedure can vary in length, anywhere from thirty minutes to one hour.
You will be monitored at all times. A viewing window is located above our outer control console and an intercom system is mounted into the unit should the need arise for you to speak with the therapist.


Immobilization means "to prevent movement or to keep in place." We use immobilization devices that do just that. They are treatment aids that are pre-made, or that we construct, to help you in maintaining the desired treatment position throughout the entire course of therapy. Some of these aids, to name a few, are:
  • Tape (simple masking, paper or silk tape)
  • Foam sponges
  • Specially designed headrests
  • Acrylic molds
  • Foam body molds
  • Plaster casts
Keep in mind that your particular setup may not require any special accessories or it may require a combination of items. It is very dependent upon treatment site, position, and the ability of the patient to sustain a position for a limited amount of time. We try to anticipate which simulations will require fabrication of such devices so that we correctly estimate the amount of time you will need to allow for your appointment.


In order to better visualize anatomic sites in or around the treatment area, we sometimes find it necessary to administer contrast material (radiographic dye) during simulation. Contrast can be given intravenously, that is, with a needle through the vein, orally, or through a catheter inserted by the nurse or therapist. Identifying certain organs is much easier when they can be referenced to other structures highlighted with contrast. This procedure would be done for simulation only, not for daily treatment, and requires no special preparation prior to your appointment.

Marking the Fields

A few preliminary measurements are taken by the therapist. A rough "sketch" of the area may be marked on your skin by the physician and/or the therapist using wire markers and marking directly on the skin with ink. The simulation team will then leave the room (remember, you can be seen and heard at all times). Then a series of things may happen. They are:
  • Room lights may go on and off
  • Red laser lights may appear
  • The table will move into the scanner
  • All kinds of noises will be audible
The CT scanner is a large hole in a machine that your body will pass through. There is plenty of room and you should not feel enclosed or claustrophobic.


Wouldn’t it be nice if all people were the same size and shape? How easy our job would be! But since we’re not, this is the time that your specific measurements must be obtained for calculations. For each patient, the physician writes out a radiation therapy "prescription," a written directive to follow. In order to carry this out, we must combine treatment field information with data taken as to your body shape and size. This data may be taken by the therapist alone, or in conjunction with a dosimetrist. Using the CT scan, the physician will contour the areas needed, and while you are at home, a plan is generated.


In most cases, we do not require that markings drawn on your skin be left on throughout the course of treatment. You will be able to remove them at the end of your simulation session. This is because a few tiny permanent marks, or tattoos, are put on the skin at the simulation’s completion. Critical setup points are chosen for tattoo sites. The therapist, using a very small needle, will prick just the skin surface and insert an extremely small amount of ink into this area. The result looks much like a tiny freckle. By aligning the tattoos with precise lasers in the treatment room, the therapist will be able to reproduce fields accurately and quickly every day. This also avoids the problem of marks smearing or smudging which could require a re-simulation to verify setup.
Occasionally, we may request that a patient retrain his or her skin markings during treatment. If so, your treatment therapist will remark the area as needed. Please do not attempt to do so yourself.


Photographs are taken on the day of simulation for two reasons: as chart documentation, and as a treatment set-up aid. A facial picture is taken for identification purposes and kept in your permanent treatment record. Each day before treatment you will also be asked your name and birth date for triple verification.
Photographs of the treatment and setup fields will be taken. If an unusual configuration of immobilization items is being used, a photo to document this is helpful. Since the treatment therapist is not present at the time of simulation, using photos in conjunction with tattoos make daily setup easier. The same is true for the dosimetrist. Sometimes viewing a field on the patient, via photograph, can answer questions that arise during the calculation process. These photos are necessary and they remain a confidential part of your treatment record.
Special Considerations

The following are a few topics worth noting:

Like most hospital departments, we sometimes see patients who, for medical reasons, must be simulated on an emergency basis. This means squeezing them into an already full schedule. We try to do this with the least amount of inconvenience for those patients being simulated that day, but delays occasionally occur. Should this happen, we certainly will inform you of the reason for the delay and work as quickly as possible to remedy the situation.
Many patients assume that their treatment will begin the day after simulation. This may not occur for two reasons, the first being treatment planning. After simulation all the necessary calculations not only have to be completed but also independently checked. This usually takes approximately one week. Secondly, the daily treatment schedule is an extremely busy one. Most times a patient must complete his or her course of therapy before another patient can begin in that time slot. Some patients are very specific as to what treatment time they need, whether due to traffic concerns, work schedules, or daycare problems. Whatever the reason, we know it’s important to you, and we will do our best to work with you in choosing the most convenient treatment time possible. The short delay between simulation and treatment in no way compromises the outcome of your therapy. These factors are considered by the radiation therapy team when planning your specific course of treatment.
Since the course of treatment can run from two to eight weeks, we constantly monitor each patient’s setup in a number of ways. If a change occurs, it may be necessary to schedule a return visit to the simulator on short notice. An example of this might be a weight gain or loss that would require new calculations. In order to interrupt your treatment schedule as little as possible, a simulation check that same day or the following morning may be appropriate. Again, this is routine and does not suggest a change in your health status. It simply means that we’re doing our job in providing the best care we know how. It’s important that we stay aware of all patient changes.
Our goal is to make every patient as knowledgeable about the radiation therapy process as possible and comfortable enough to ask questions. If, at any time during your many visits with us, you are unsure as to what is happening around you, please do not hesitate to ask. At a time in your life when things are seemingly out of your control, knowing what to expect can be a powerful tool in becoming refocused and moving onward. 
© Copyright 2014 Sibley Memorial Hospital