Prior to receiving radiation therapy, measurements and a CT scan are performed to map the precise area to be treated. This preparation for therapy is called the “simulation” or “planning session.” The simulation will take longer than any other appointment—from 30 minutes to two hours. Because simulation does not involve any high-energy radiation, parents may be allowed to remain in the simulation room to help and comfort their child. Young or active children require sedation for the simulation.

During simulation, the radiation oncologist and technologist use a specialized x-ray machine or a CT scanner to outline the treatment area. They will adjust the table the child lies on, the angle of the machine, and the width of the x-ray beam needed to give the exact dosage in the proper place. Ink marks are placed on the immobilization device to ensure treatment accuracy. After the simulation, you and your child can go home while the radiation oncologist carefully evaluates the imaging and measurements to design the treatment field.