Clinical meaning
Radiation pneumonitis develops 1-6 months after thoracic irradiation when ionizing radiation damages type I and type II pneumocytes and pulmonary capillary endothelial cells. Free radical-mediated DNA damage triggers apoptosis of alveolar lining cells, leading to surfactant depletion, increased capillary permeability, and alveolar edema. The inflammatory response involves macrophage and lymphocyte infiltration with release of pro-fibrotic cytokines (TGF-beta, TNF-alpha). Without treatment, the acute inflammatory phase progresses to irreversible radiation fibrosis within 6-24 months.
Exam relevance
Risk factors: - Radiation dose > 20 Gy to the lung - Large radiation field volume (V20 > 30%) - Concurrent chemotherapy (especially taxanes, gemcitabine) - Pre-existing lung disease (COPD, interstitial lung disease) - Previous thoracic irradiation - Withdrawal of corticosteroids during radiation - Older age
Diagnostics: - Chest X-ray or CT showing consolidation corresponding to the radiation field - Pulmonary function tests showing restrictive pattern with decreased DLCO - Pulse oximetry and ABG to assess oxygenation - CBC to rule out concurrent infection (neutropenia from chemoradiation) - Sputum cultures and blood cultures to exclude pneumonia - Correlation of imaging findings with radiation treatment fields