Before beginning radiation, you will have what is called a "simulation" to plan your radiation. During the simulation, you will be flat on your back on a computed tomography (CT) table and a soft plastic mask will be made to help hold your head still during treatment. This is the position you will be in when you receive radiation treatment. You will then have a CT scan, which will make computerized images to help plan your treatment. This should take about 15 minutes.