- On the first 10 patients, we will perform approximately 5CT simulations throughout the course of their therapy. On each simulation, the initial treatment plan will be re-run. The dose-volume data from target and normal tissues will then be re-analyzed. From this analysis we will be better able to determine the size of margins needed to account for organ motion and changes such as varying amounts of gas in the bowel and fluid in the bladder. To the best of our knowledge, no such analyses have been published.