Inclusion Criteria:

1. Age ≥ 18 year-old

2. Clinical status:

   1. Primary lung tumour T1-T2 N0, confirmed histologically by bronchoscopic examination, or meeting the criteria set out in the Aura 2026 and ASTRO guidelines for the indication of stereotactic radiotherapy (tumor growth of at least 2 mm between two CT scans performed 3 months apart, metabolic hyper-intensity on PET, and no pathological evidence), OR
   2. Metachronous oligometastatic disease: isolated mediastinal or non-central pulmonary lymph node recurrence occurring sometimes after initial cancer treatments for an initially localised, locally advanced or oligometastatic cancer that has been treated OR
   3. Synchronous oligometastatic disease: all metastatic sites and the primary tumour must be amenable to local debulking treatment following systemic treatment. Systemic treatment (chemotherapy or targeted therapy) must not be administered concurrently with radiotherapy OR
   4. Metachronous oligoprogression: isolated metastatic recurrence in the mediastinal or ultra-central lung lymph nodes, with the primary tumour and metastatic sites under control (no change observed on two consecutive imaging scans and a complete metabolic response on PET) and not requiring continued treatment with chemotherapy or targeted therapy to ensure disease control (hormone therapy is, however, permitted)

3. Patient unsuitable for surgery, and treatment with stereotactic RT validated by multidisciplinary tumor board (including the radiation oncologist and medical physician)

4. Ultracentral lesion defined by a GTV less than 1 cm of the PBT (proximal bronchial trachea, including the main bronchi, trachea and intermediate bronchi), oesophagus, or pericardum

5. ECOG performance status ≤2 (for all patients)

6. Patient covered by a health insurance system

7. Patient agreed to take part in the study, and signed an informed consent form

8. Use of a method of contraception (for female patients of childbearing age)

Exclusion Criteria:

1. Tumour with intrabronchial or intratracheal invasion identified by fibroscopy, bronchoscopy or localisation MRI
2. Prior RT overlapping the intended treatment field
3. Patients with oligoprogression requiring continued systemic treatment during RT
4. Uncontrolled intercurrent diseases
5. Contraindication to radiotherapy due to a comorbidity such as pulmonary fibrosis or scleroderma
6. Respiratory contraindications (FEV1 < 20%)
7. Need of oncologic systemic treatment during RT
8. Contraindication to MRI (e.g. severe claustrophobia unmanageable)
9. Pregnancy or breastfeeding patient
10. Patient under guardianship or curatorship