The RESPECT study is intended to prospectively assess the impact of PET/CT on the delineation of target volumes and to estimate the proportion of recurrences that could possibly be prevented by the use of PET/CT-based target volume, instead of CT-based. Patients will recieve radiotherapy using CT-based planning, but a PET/CT-based treatment plan will also be made. CT-based and PET/CT-based target volumes will be compared after treatment has been completed. If a locoregional recurrence takes place, the localisation will be compared to the CT-based and PET/CT based clinical target volumes (CTVs). If the local recurrence is located outside the CT-CTV but inside the PET/CT-CTV, the recurrence could possibly have been prevented with PET/CT-based radiotherapy.

This is a prospective cohort study testing the hypothesis that in a proportion of patients, locoregional recurrence, observed at 6, 12 or 18 months after treatment, can be prevented if PET/CT-based treatment planning was used instead of CT-based treatment planning alone.

Patients eligible for the study will undergo definitive radiotherapy with or without concomitant chemotherapy with planning-CT based target volumes, either or not followed by surgery.

A planning-PET/CT will be made for research purposes only, and will be blinded for the treating physicians. This planning-PET/CT will not be used for actual treatment planning.

In case of neoadjuvant chemoradiation the response on this therapy will be analysed at pathologic evaluation of the esophageal specimen.

Routine follow up will be carried out every 6 months, using CT. In case of no locoregional recurrence and/or metastases, patients will be followed up to 18 months for study evaluation.

In case of distant metastases, patients will be censored if locoregional recurrence is excluded. When indicated, palliative treatment will be given.

In case of (suspicion of) locoregional recurrence, PET/CT-based recurrence analysis should be carried out with comparison and co-registration of CT-based and PET/CT-based target volumes.

Inclusion Criteria:- Histologically proven adenocarcinoma or squamous cell carcinoma of the esophagus or GEJ

• Locally curable disease without distant metastases (M1b is excluded) (TNM clinical classification UICC 7th edition)
• Planned for high dose radiotherapy with or without chemotherapy with or without surgery
• Age ≥ 18 years;
• WHO performance status 0-2
• informed consent must be given according to ICH/EU GCP, and national/local regulations

Exclusion Criteria:- previous or concurrent malignancies (except basal cell carcinoma of the skin or in situ carcinoma of the cervix or superficial bladder cancer (pTa)) in the past five years

• Previous treatment
• Evidence of serious active infections
• any psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule

Patients with histologically proven esophageal carcinoma who are planned for curative high dose radiotherapy with or without chemotherapy, with or without surgery.