Low Accrual

The investigators will be using the combination of FDG-PET and multiparametric MRI in pre- and post-adjuvant chemoradiation therapy in order to attempt to predict pathologic response on surgical resection.

Inclusion Criteria:

• A diagnosis of histopathologically confirmed rectal adenocarcinoma.
• Locally advanced disease as determined by ERUS or pelvic MRI. Endoscopy reports should clearly state both the T and N stage.
• Patients with cT2N1-3M0 or cT2-4NxM0 will be considered eligible for participation.
• Age ≥18.
• Ability to understand a written informed consent document and the willingness to sign it.
• Tumor must be determined to be surgically resectable. Surgical resection is planned to take place at Univeristy of California, San Francisco (UCSF).
• Neoadjuvant chemoradiation prior to resection is planned..
• Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1 or 2.

Exclusion Criteria:

• ERUS tumor state of T1.
• Radiographic evidence of metastatic disease
• Weight in excess of limitations of the scanner or girth that prohibits entry into the bore of the PET/CT scanner due to size.
• Any medical condition which impairs the ability to lie flat and without movement for 15 minutes (e.g. cough, severe arthritis, etc.)
• Prior receipt of any therapy, including local excision, radiation or chemotherapy, for the diagnosed rectal adenocarcinoma.
• Prior history of pelvic radiation.
• Uncontrolled hyperglycemia (defined as inability to achieve a glucose of <250 mg/dL at time of fluorodeoxyglucose (FDG) injection).
• Impaired renal function (CKD 4 or 5: estimated glomerular filtration rate (eGFR) < 30 mLs/min), which is a contraindication to gadolinium containing contrast.
• Known allergy to gadolinium containing contrast agents.
• Contraindication to use of fluoropyrimidines as a radiosensitizing agent.
• Pregnancy or nursing. Women of child bearing potential must have a negative serum or urine pregnancy test (minimum sensitivity 25 IU/L or equivalent units of HCG) within 72 hours prior to randomization. This is because of the potential teratogenic effects of the involved imaging modalities, radiation, and chemotherapy.

20 patients with newly diagnosed rectal adenocarcinoma