PET/MRI as a Predictor of Response to Pre-op Chemoradiation in Resectable Rectal Cancer: a Pilot Study

Inclusion Criteria: * Low-lying, low- to moderate-risk pathologically-confirmed rectal cancer (stage uT3n) or uT1-3N+ * Negative workup for distant disease * \> 18 years of age * Pre-treatment workup completed including: * history and physical * CT or MRI of the abdomen and pelvis * endoscopic tumor evaluation (biopsy, blood work to assess CEA and hematopoietic, renal and liver function) * if female of child-bearing age, negative pregnancy test * Recommendation to undergo preoperative concurrent chemoradiation, as determined by the treating physician * Informed consent reviewed and signed Exclusion Criteria: * Not deemed a candidate for preoperative chemoradiation for medical reasons, such as uncontrolled infection (including HIV), uncontrolled diabetes mellitus or cardiac disease * Hemoglobin ≤ 10.0 g/dL (transfusion allowed to achieve or maintain levels) * ANC ≤ 1,500/cubic mm³ * Platelet count ≤ 100,000/mm³ * ALT and AST ≥ 2.5 times upper level of normal (ULN) * Alkaline phosphatase ≥ 2.5 times ULN * Total bilirubin ≥ 1.5 times ULN * Creatinine clearance \< 50 mL/min * Creatinine ≥ 1.5 times ULN * Not deemed a candidate for concurrent preoperative chemoradiation for social reasons, such as psychiatric illness * Not deemed a surgical candidate * Currently active second malignancy, except non-melanoma skin cancer, non-invasive bladder cancer, low risk adenocarcinoma of the prostate and carcinoma in situ of the cervix * Previous pelvic radiation therapy * History of severe reaction to gadolinium * Inability to tolerate MRI (e.g., inability to lie flat for \> 1 hour) * Presence of a pacemaker, intracranial aneurysm clip, bladder stimulator, cochlear implant or metal near eyes * Body Mass Index (BMI) \> 35 * Pregnant or lactating female