The purpose of this study is to perform prospective data analysis on tumor response in terms of local tumor control after 2 years, potential acute and late toxicity and survival in patients with non-metastatic, non-small-cell lung cancer treated by radiotherapy that are medically inoperable due to coexisting comorbidities or that refuse surgery. SBRT regimens used will be 4 fractions of 12 Gy or 3 fractions of 17 Gy depending on tumor location in a risk-adapted approach.

Inclusion Criteria:

1. Stage T1,T2,T3N0M0 NSCLC, histological confirmation either by biopsy or cytology
2. Maximal tumor diameter of 6 cm
3. Only T3 lesions based upon thoracic wall involvement, only 1 lesion
4. Informed consent is required
5. Life expectancy of at least 6 months
6. Age >/= 18 y.
7. Karnofsky score ≥ 70 or ECOG score ≤ 2
8. Inoperable patients or patients refusing surgery
9. Patients with measurable lesion (according to RECIST criteria)

Exclusion Criteria:

1. Diagnosis of small cell lung cancer
2. Lymph node involvement
3. Prior radiotherapy to the chest and/or mediastinum
4. No chemotherapy and/or targeted treatment within 3 months before SBRT
5. Pregnant or lactating women
6. Known allergy for CT contrast
7. No FDG-PET
8. Mental condition rendering the patient unable to understand the nature, scope, and possible consequences of the study.
9. Patient unlikely to comply with protocol, i.e., uncooperative attitude, inability to return for follow-up visits, extreme degradation of lung function tests and patients not likely to complete the study.