In order for the doctor to design your treatment, the exact location of the tumor, including its size and position relative to the surrounding structures (organs, bones, tissues, etc.) must first be determined. This is done typically by taking a detailed 3-D scan of the tumor with a CT scan (computed tomography). Depending on the general location of the tumor, disease type and other factors, additional scans may be recommended, which could include an MRI, a PET scan or an ultrasound scan. With the help of these scans, your healthcare team can see details of the tumor from every possible angle.
These imaging scans serve as guides, not only to enable the doctor to design your treatment, but also to help the rest of the team direct the radiation delivery equipment when treatment is actually being administered. It is therefore very important that the position in which you are being scanned is reproduced at the time of treatment. Sometimes temporary skin marks or even tiny tattoos (about the size of a freckle) are made on your body to assist in maintaining your position, day after day. Depending on the location of the tumor, a body mold, a head mask or other device may be constructed to make it easier for you to remain in the same position during treatment.