The first step in your treatment is the planning process, which may include CT, CAT (computerized tomography) and/or PET scans. These scans allow the radiation oncologist to determine the exact area to treat and the proper positioning of the treatment machines that will be used during the course of your radiation therapy.
Before CT simulation scans are done, immobilization devices may be made to assist the radiation therapists in accurately duplicating your exact treatment position each day. These immobilization devices may include masks that cover your face or other areas of your body during treatment, and/or something you lay in each day. The exact positioning device(s) used will be determined by the physician and depend on the area of your body that will be treated.
To determine the area to be treated, the physician will use images from a CT scanner. This process is "virtual simulation" or CT simulation. A CT scanner produces images that allow the study of virtually any portion of the body to pinpoint the location of a tumor for treatment planning purposes. Performing a CT scan is a painless procedure producing body pictures similar to a loaf of sliced bread; that is, each "slice" can be lifted out and looked at. Each scan produces a cross-sectional image of the part of the body under study. The CT technologist may take many CT images to show a tumor's exact shape and location. The physician will use the CT images to "simulate" your treatment by planning the treatment fields, position of the radiation beams, etc. in the treatment planning computer.
Another test you may be given is the PET scan or Positron Emission Tomography scan. The PET scan allows your doctors to determine exactly what tissues and organs need to be treated. Before your PET scan, you will be given an IV containing sugar and a small amount of radioactive tracer chemical called FDG. Cancer cells absorb high amounts of the sugar allowing the tracer to detect the location of the cancer cells. The special camera in the PET scan machine can spot the places where the sugar collects. A PET scan can be useful because it looks for cancer throughout the body.
Once you have been given the FDG tracer chemical, you will need to wait quietly in a dimly lit room for about 60 minutes. This time will allow the sugar and tracer chemical to work its way through your entire body. When you are ready to be scanned, you will be asked to lie on a flat table that will move through the PET scan machine, which looks like a giant donut. While you lie very still, the table will move you through the machine. The PET scanner will detect positively charged energy particles given off by the tracer chemical. You will not feel anything as you are being scanned and may leave as soon as the scan is complete.
After you have had your CT and/or PET scans, a technologist may draw special colored lines on your skin with ink. The semi-permanent lines drawn on your skin are used to outline your treatment fields and to make sure that you will be correctly positioned each time you receive a treatment. These lines are very important to your treatment team and should not be intentionally washed off until you have completed your entire course of therapy. The ink used to make these lines sometimes rubs off on your clothing and may be difficult to remove. You may want to wear a t-shirt between your outer clothes and your skin to prevent this from happening. A photograph will be taken of your lines and kept in your medical record to indicate where your treatments were given.