**3. Staging and assessment**

**2. Anatomy**

28 Radiotherapy

**Figure 1.** Tumor invasion to chest wall.

**Figure 2.** Tumor over left main bronchus causing collapse of left upper lobe (red arrow).

Lungs are a paired structure that is separated into left and right by the mediastinum, which contains the tracheal, heart, esophagus, and lymph nodes. The left lung is divided into upper and lower lobe by oblique fissure, while the right lung is divided into three lobes (upper,

Lung cancers can arise from mucosa of the tracheobronchial tree or the alveolar lining cells of peripheral lung parenchyma. Tumor can spread locally within lung parenchyma or invading surrounding structures including mediastinum, major vessels, or chest wall (**Figure 1**). They can also spread along major airways causing obstruction, distal collapse, or atelectasis (**Figure 2**).

middle, and lower) by oblique and horizontal fissures.

All patients with suspected lung cancer should have computer tomography (CT) of thorax with intravenous contrast for proper staging. Histological proof from primary tumors can be obtained by bronchoscopy if centrally located or by image‐guided approach if peripherally located. For those patients planned for radical treatment, positron emission tomography (PET) scan is recom‐ mended to exclude any distant metastasis. Unanticipated metastasis may be detected in up to 10–20% cases. It is also more useful than CT in differentiating collapse or atelectasis from primary tumors (**Figure 4**). Any suspicious lymph nodes based on enlargement on CT or uptake in PET should be confirmed by needle technique (e.g., endoscopic ultrasound) or mediastinoscopy.

**Figure 4.** Use of PET in differentiating primary tumor with intense uptake (red arrow) from surrounding collapse or atetactasis (white arrow).
