Perfusion CT as a Predictor of Treatment Response in Patients With Rectal Cancer

Inclusion Criteria:

* Patients with suspected or biopsy-proven, locally advanced rectal cancer will be eligible for enrollment.
* Patients must be 18 years or older. Patients must not be pregnant and, if of child-bearing age, must take precautions not to become pregnant.
* No life expectancy restrictions.
* ECOG and Karnofsky Performance Status will not be employed.
* Patients with renal failure are ineligible for this study (GFR must be \> 60)
* Ability to understand and willingness to sign a written informed consent document.

Exclusion Criteria:

* Patients who have undergone prior treatment for rectal cancer are ineligible for enrollment.
* No restrictions regarding use of other investigational agents.
* Patients with severe contrast allergy are ineligible.
* Patients who are pregnant or are trying to become pregnant are excluded from this study.
* Patients who are cancer survivors or HIV-positive will not be excluded.