Conebeam CT-based Online Adaptive Radio-Therapy for Esophageal Cancer (ARTEC)

Inclusion Criteria: * Written informed consent * Histologically confirmed diagnosis of AC (Adenocarcinoma) or SCC (squamos cell carcinoma) of the thoracic esophagus or gastroesophageal junction (Siewert I-II) * Patients with cT2-4b cN0 cM0 or cTany cN+ cM0 or any patient with early stage EC ineligible for upfront surgery * Age \>= 18 years old * Karnofsky Performance Status (KPS) \>= 70 or ECOG (Eastern Cooperative Oncology Group) 0 - 1 * Absence of any psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule; those conditions should be discussed with patients before registration in the trial Exclusion Criteria: * Cervical esophageal cancers (15-18 cm from the incisors) * Definitive clinical or radiologic evidence of metastatic disease * Any active malignancy within 2 years of study registration that may alter the course of esophageal cancer treatment * Prior thoracic radiotherapy that would result in overlap of radiation therapy fields * Induction chemotherapy for the current malignancy prior to RCHT is allowed if last dose is no more than 90 days and no less than 10 days prior to registration * Pregnant and/or breast-feeding females