After the initial consultation and decision to use radiation treatment, the next session is usually a planning session, which is called a simulation. Simulation is used to determine the radiation treatment fields and most of the treatment planning. Of all the visits to the radiation oncology facility, the simulation session may actually take the most time.
The CT simulator does not deliver radiation treatment, but instead allows the radiation oncologist and technologists to see the area to be treated. Images are obtained and transferred to the planning system where a virtual 3D image of the patient is created, and the treatment delivery plan is developed.
For the simulation session, temporary marks are made on your skin with markers to identify the treatment areas. The room is periodically darkened while the treatment fields are being set. Alignment is critical during simulation and is facilitated by lasers mounted on the wall and ceiling. Special individually constructed immobilization devices may be used to help achieve this alignment. While you may see red lines of light, the low energy lasers are for alignment purposes only and you will not feel burning or anything else from the laser light.
Once the aspects of the treatment fields are set, the technologist will take special simulation X-rays representing the treatment fields. In most centers, the patient is given multiple “tattoos,” which mark the treatment fields and replace the marks previously made with magic markers. These tattoos are not elaborate and consist of no more than pinpricks followed by ink, appearing like a small freckle. Tattoos enable the radiation technologists to set up the treatment fields each day with precision, while allowing you to wash and bathe without worrying about obscuring the marks that indicate where treatment will be delivered.
Sometimes several simulation sessions are necessary in order to optimize treatment and are often performed prior to planned “boost” or “reduced field” treatments as part of the overall treatment plan.
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