Radiation exposure less than 12 weeks typically causes which lung condition?

• A. Pulmonary fibrosis
• B. Hypersensitivity pneumonitis
• C. Pneumonitis
• D. Pneumoconiosis

Answer: (C)

Radiation injury to the lungs in the short term triggers an inflammatory response. When exposure occurs and symptoms appear within weeks (less than about 12 weeks), this inflammatory stage is called pneumonitis. It reflects acute inflammation and edema in the lung tissue after radiation. If the inflammatory phase doesn’t resolve, it can later progress to scarring and fibrosis, but the immediate, under-12-week effect is pneumonitis. Pulmonary fibrosis is a later, chronic change, hypersensitivity pneumonitis is an immune reaction to inhaled antigens, and pneumoconiosis is related to dust exposure—none are tied to the radiation timing in the way pneumonitis is.