To quantify motion based variation of the target volume of the primary tumor over the course of chemoradiotherapy in esophageal cancer patients, and to use this information to calculate appropriate PTV (planning target volume) margins according to the margins recipe for patients receiving trimodality (neoadjuvant chemoradiation and surgery) or definitive chemoradiation in order to personalize radiation treatment, resulting in either better target coverage or a reduction in normal tissue radiation exposure.

A single center prospective observational study will be performed in esophageal cancer patients. This study registers motion of the esophageal tumor, using 4D planning CT scans and repeated 4D CBCT scanning. Motion of fiducial markers inserted into the esophageal wall, will be used as a surrogate for tumor motion in the limited image quality of CBCT scans.

Patients planned for trimodality treatment will additionally be imaged by serial 4D Pet CT and MRI in week 0 (before start chemoradiotherapy), week 3 (during chemoradiotherapy) and week 10 (just prior to surgery) to observe (early) signs of tumor response.

Patients planned for definitive chemoradiation will not receive extra MRI imaging during treatment because of the inability to correlate this imaging with pathological response.

Inclusion Criteria:

1. Histologic evidence of invasive adenocarcinoma or squamous cell cancer of the esophagus
2. Patient eligible for trimodality treatment (chemoradiotherapy and surgery) or definitive chemoradiotherapy
3. T3N0M0 or T1-4N1-3M0. Patients with M1 disease solely on the basis of supraclavicular metastasis and not a junction tumor as primary are eligible. (AJCC 7th edition,).
4. WHO performance status ≤2 (WHO scale)
5. Clinically operable for R0 resection in the opinion of an experienced upper gastrointestinal or thoracic surgeon for patients planned for trimodality
6. Tumor localization at least 2cm from the upper esophageal sphincter and invading no more than 5cm into gastric cardia
7. Age ≥ 18 years
8. Written informed consent before endoscopy or EUS

Exclusion criteria:

1. Prior treatment with thoracic surgery or thoracic radiotherapy
2. Pregnancy
3. Severe cardiopulmonary restriction

• Histologic evidence of invasive adenocarcinoma or squamous cell cancer of the esophagus
• Patient eligible for trimodality treatment (chemoradiotherapy and surgery) or definitive chemoradiotherapy

data of two clinic trials will be joined for MRI scans