LearningRadiology - Radiation Pneumonitis

Radiation Pneumonitis

Damage to lungs after radiation therapy
Usually requires at least 4500 rads
- Especially common if >6000 R given in 5-6 weeks
Occurs more often if there is concurrent or later chemotherapy
Pathologic phases
- Exudative phase = edema fluid + hyaline membranes
- Organizing phase
- Fibrotic phase = interstitial fibrosis
Time of onset
- Usually at least 6 weeks up to 6 months after treatment
Location
- Confined to radiation portal

Radiation portal (left) with subsequent radiation pneumonitis

· Acute Radiation Pneumonitis

o Occurs within 1-8 weeks after radiation therapy

o Pathology

§ Depletion of surfactant (1 week to 1 month later), plasma exudation, desquamation of alveolar + bronchial cells

o Usually asymptomatic

o When symptomatic

§ Nonproductive cough, shortness of breath, weakness, fever (insidious onset)

§ Acute respiratory failure (rare)

o Changes usually confined to radiation portal

o Patchy / confluent consolidation, may persist up to 1 month (exudative reaction)

§ Atelectasis + air bronchogram

§ Spontaneous pneumothorax (rare)

CT findings of acute radiation pneumonitis
- Homogeneous slight increase in attenuation (2-4 months after therapy)
- Patchy consolidation (1-12 months after therapy)
- Non-uniform discrete consolidation (most common; 3 months to 10 years after therapy)

Sequential transverse images through lung showing radiation pneumonitis in right lung

· Chronic Radiation Damage

o 9-12 months after radiation therapy

o Histology

§ Permanent damage of endothelial + type I alveolar cells

o May be associated with:

§ Thymic cyst

§ Calcified lymph nodes (in Hodgkin disease)

§ Pericarditis + effusion (within 3 years)

§ Severe loss of volume

§ Dense fibrous strands from hilum to periphery

§ Thickening of pleura

o CT findings

§ Solid consolidation (radiation fibrosis) + bronchiectasis (stabilized by 1 year after therapy)

Text from Dahnert, 4^th Edition