Traditional transrectal ultrasound (TRUS) is a technique used to help determine the stage of rectal cancer. All patients at Memorial Sloan-Kettering Cancer Center with rectal cancer have an ultrasound at the beginning of their treatment to accurately determine the depth of penetration (how deep into the rectal wall the tumor goes) and lymph node involvement of their tumor. This information helps determine the best way to treat the patient's disease. Three-dimensional TRUS (3-D TRUS) is a new form of ultrasound that gives us all of the information of traditional ultrasound in addition to being able to view the tumor in 3-dimensions. This image can be stored and analyzed to evaluate the tumor size and volume as well as determine the unique shape of the tumor. Chemoradiotherapy before surgery is considered standard of care for most rectal cancers.