Pulmonary Magnetic Resonance-guided Online Adaptive Radiotherapy of Locally Advanced Non-Small Cell Lung Cancer

Inclusion Criteria: * Histologically-proven non-small cell lung cancer (NSCLC) * Stage III A - C according to the 8th edition of the Union for International Cancer Control (UICC) TNM classification * Indication for definitive thoracic chemoradiotherapy * Age ≥ 18 years * ECOG 0 - 2 * Adequate pulmonary function for chemoradiotherapy confirmed by a current pulmonary function test (≤ 6 weeks from treatment start) * Ability to lie still on the MR-linac table for at least one hour * Ability to hold one's breath for at least 20 seconds * Successful completion of an MR-guided treatment simulation * For women with childbearing potential: adequate contraception * Ability of the patient to understand character and individual consequences of the clinical trial * Written informed consent (must be available before enrolment in the trial) Exclusion Criteria: * Involvement of supraclavicular lymph nodes (supraclavicular N3) * Additional pulmonary lesions (T3 - 4 due to additional lesion in the same or another lobe) * Previous radiotherapy of the lung and mediastinum, if previous and current target volumes overlap * Patients who have not yet recovered from acute toxicities of prior therapies * Contraindications against performing MRI scans (e.g. pacemakers or other implants making MRI impossible) * Pregnant or lactating women * Participation in another competing clinical study or observation period of competing trials * Refusal of the patients to take part in the study