Rationale: Accurate staging of lung cancer is important because it directs treatment and determines prognosis. The development of Stereotactic Ablative Radiotherapy (SABR), has revolutionized radiation therapy for early stage lung cancer and results demonstrate similar outcomes in comparison to surgical resection of the lung tumor. The staging work-up program for patients with a potentially resectable Non-Small-Cell Lung Cancer (NSCLC) includes at least a computed tomography (CT) scan of the chest and integrated Positron Emission Tomography - Computed Tomography (PET/CT) scans, and when indicated, invasive mediastinal staging. However, patients who are treated with SABR do not routinely undergo the same nodal staging work-up as do surgical candidates. As both surgery and SABR appear to achieve comparable rates of local and regional tumor control, it appears only logical to perform a similar staging work-up in all patients with early stage lung cancer who will be treated with either of the two curative local modalities. In the past, a lack of invasive nodal sampling before SABR was considered acceptable as invasive surgical staging (mediastinoscopy) was widely considered the preferred procedure. However, with minimally invasive and safe endosonography procedures now available, improved pre-treatment staging has become possible for patient groups who are eligible for SABR, including those with significant comorbidities.

Hypothesis: Complete endosonographic (combined endobronchial and esophageal) staging of hilar and mediastinal lymph nodes in patients with (suspected) non-small cell lung cancer (NSCLC) will result in change of loco-regional nodal status in 20% of patients, in comparison to staging by PET-CT alone.

Study population: Patients with either established or suspected early-stage NSCLC who are medically inoperable, or who refuse surgery but are potential candidates for SABR with curative intent (provided no intrathoracic metastases are present). Patients will undergo a single scope complete mediastinal and hilar staging procedure (combined EndoBronchial UltraSound (EBUS) and Transesophageal Endoscopic Ultrasound with EBUS scope (EUS-B)).

Inclusion Criteria:

• Proven, or highly suspected, non-small cell lung cancer (NSCLC)
• Absence of distant metastases based on PET-CT
• Stereotactic ablative radiotherapy (SABR) with curative intent is contemplated
• One of the following features based on PET-CT:
• Centrally located clinical T1-T2 N0 tumor
• Peripheral located clinical T2 N0 tumor
• Suspicion of N1- N2 disease based on either size (short axis > 10mm CT) or FDG uptake
• Non-FDG avid primary lung tumor and lymph nodes

Exclusion Criteria:

• Medically operable patients with a resectable lung tumor (unless SABR is the explicit preference of the patients or treating physicians preference).
• Bulky nodal disease based on PET-CT
• Contra-indications for endosonography and / or bronchoscopy
• Pregnancy
• Age under 18
• No informed consent

Patients with either established or suspected early-stage NSCLC who are medically inoperable, or who refuse surgery but are potential candidates for stereotactic ablative radiotherapy (SABR) with curative intent (provided no intrathoracic metastases are present)