During the study, you will have additional CT scans that will be performed on a special scanner in the radiation treatment room. You also will have additional CT scans twice a week during the 5 weeks of radiation treatment. The first 12 participants enrolled will receive the standard radiation therapy taking into account the maximum possible movements of the bladder. No adjustments will be made according to the results of the additional CT scans. The next 12 participants may have their radiation therapy adjusted according to the CT scans in an effort to target less of the normal tissue without missing cancer tissue. To reduce movement of your bladder due to different amounts of fluid in your bladder, you will be asked to drink 3 glasses of water before treatment and to come for treatment with a full bladder.