The simulation and treatment planning appointment, which takes about one hour, is required to properly plan your radiation therapy. To be most effective, radiation therapy must be aimed precisely at the same target each time treatment is given. The process of measuring your body and marking your skin to help safely direct the beams of radiation is called simulation.
Images are taken to determine the precise area to be treated. We do this with the help of a machine called an Acuity Simulator, which simulates the treatment machine, and a CT scanner. Neither the simulator nor the CT scanner delivers the radiation treatment. During simulation, your radiation oncologist and therapist position you on the simulation machine in the exact position you will be in during actual treatment. . Because positioning is so important for your treatment, you may have a custom mold, mask or headrest made. These immobilization devices help you remain in the same position during the entire treatment. Depending on the area treated, your physician may request that you receive IV contrast or barium to drink. Contrast is used to highlight organs so that they can be seen on X-ray or CT images. When imaging is complete, the therapist will either place a temporary mark on your skin and cover it with protective tape or give you small permanent tattoos (very small black dots). These marks are sometimes placed on your customized immobilization device. The marks will be used to position you each day for your radiation treatments. When this appointment is complete, you will be given another appointment to begin your course of treatment, usually one to two weeks after the simulation.
Images obtained from the simulator and CT are transferred to a sophisticated treatment-planning computer system where a virtual three-dimensional image is created and the treatment delivery plan is developed. This step takes place even though you are not in the radiation oncology department. The planning team (radiation oncologist, dosimetrists, and medical physicists) then custom designs the best treatment plan for you. This process can take anywhere from a couple of days to two weeks depending on the complexity of the plan. After reviewing all of your information and your treatment plan, your doctor will write a prescription that outlines exactly how much radiation you will receive and what parts of your body will receive the radiation. The final step in the simulation and planning process is the verification simulation. This can be done on the Acuity Simulator or on the treatment machine. If temporary marks were used, they will be replaced with tattoos. Each patient is different and each treatment plan is unique – verification of all treatment parameters ensures that you are ready to start your treatment.
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