The next step is a CT simulation appointment where your radiation oncologist will use a CT scan and possibly an MRI and/or PET scan to reconstruct the tumor and surrounding areas. This reconstruction enables him or her to plan accurate, precise dose targeting to the tumor while protecting the surrounding normal tissue. Once your personalized treatment plan is complete and before your first treatment, you will participate in a “dress rehearsal,” which ensures your positioning and dosage are accurate. Your physician will review every aspect of treatment during this time. If he or she gives approval, treatment may begin either the same day or the next.