The purpose of this study is to find out if performing adaptive planning during the treatment anal cancer will decrease the dose of radiation to normal organs and decrease the side effects. In this study, subjects will have a daily adjustment (adaptation) of their radiation plan as the tumor changes during the radiation treatment. The radiation will be given as part the standard of care treatment with chemotherapy, known as chemo-RT (CRT). Are you Eligible? (Inclusion Criteria) To be considered for this study, you must: 1. Have invasive anal cancer confirmed with biopsy 2. Be greater than 18...
