The purpose of this pilot study is to develop a more advanced software program that will collect, compare and analyze tumor images for evaluation. Another purpose of this study is to learn if a new radio-tracer for tumor imaging called 3'-deoxy-3'(18) F-fluorothymidine (FLT) can improve the evaluation of tumors during a PET/CT scan. This new type of image tracking is meant to improve the visualization of tumor active and size.

• The following are standard medical procedures that are part of regular cancer care that the participant would probably have done even if they did not join the study: Chemotherapy; physical examination; pregnancy test (if applicable); diagnostic FDG-PET/CT scan before and after treatment to evaluate disease.
• The following diagnostic procedures are being done specifically because of this study: Three FLT-PET/CT scans before, during and after treatment and one FDG PET/CT scan during treatment.
• Participants will be in this research study for approximately 12-14 weeks.

Inclusion Criteria:

• Histologically or cytologically confirmed adenocarcinoma of the esophagus or gastroesophageal junction. Biopsy or cytology of the primary tumor, or of involved regional lymph nodes, is acceptable.
• Tumors must be TNM stage T2-4, N0-1, M0 as determined by pretreatment endoscopic ultrasound. T1 tumors are eligible if they are T1, N1, M0. Regional thoracic lymph node involvement is permitted.
• Disease must be clinically limited to the esophagus or gastroesophageal junction. If the tumor extends below the gastroesophageal junction into the proximal stomach, 50% of the tumor must involve the distal esophagus or gastroesophageal junction. Adenocarcinomas of the distal esophagus would therefore include tumors of the gastroesophageal junction which involve equally both the distal esophagus and proximal stomach, or Siewert type II. Tumor much be surgically resectable and have a minimum length of 2cm.
• Patients must be judged by their oncologist to be a candidate for combined modality therapy with chemotherapy consisting of oxaliplatin with protracted infusion 5-FU and concurrent radiation.
• FDG PET/CT performed off-site must be available for review by the Overall PI in DICOM format and has been performed within one month of study entry
• 18 years of age or older
• ECOG Performance Status 0-1
• Laboratory values as outlined in the protocol

Exclusion Criteria:

• No prior chemotherapy or radiotherapy is permitted. Patients must be at least 4 weeks since major surgery, or must have recovered from the effects of minor surgery.
• No prior malignancies (other than basal cell or squamous cell carcinoma of the skin, in situ cervical carcinoma, or superficial transitional cell bladder carcinoma) are permitted unless diagnosed and/or treated 3 years or longer before registration and without evidence of recurrence.
• Patients with the following tumor characteristics are not eligible: TIS (in situ carcinoma); tumors determined to be T1N0 following endoscopic ultrasound; supraclavicular (for distal tumors) or celiac (for proximal tumors) lymph node involvement, as determined by EUS, CT scan, or PET scan, unless this is proven to be a false positive by an appropriate biopsy; cervical esophageal tumors, or gastric cancers with minor involvement of the gastroesophageal junction or distal esophagus; no patients with tracheoesophageal fistulas
• Patients with evidence of metastatic disease
• No poorly controlled diabetes despite attempts to improve glucose control by fasting duration and adjustment of medications
• Pregnant and breast feeding women are excluded
• HIV-positive individuals on combination antiretroviral therapy are ineligible