Lung Injury after Precision Radiotherapy: Temporal Evolution, Potential Pitfalls, and Complications

High-precision radiation therapy (HPRT) techniques, including stereotactic body radiation therapy, intensity-modulated radiation therapy, and proton therapy, have significantly improved tumor targeting in lung cancer while minimizing damage to surrounding lung tissue. Despite these advances, radiation-induced lung injury (RILI) remains a common complication, manifesting as acute pneumonitis and chronic fibrosis. Compared with conventional radiation therapy, HPRT is associated with a delayed onset and more localized manifestations of RILI. Pneumonitis typically occurs around 3 months following completion of radiation therapy, whereas fibrosis usually begins after 9 months and can evolve for up to 4 years. Radiologic patterns of RILI after HPRT are often confined to the radiated lung volume and can mimic tumor recurrence, with appearances ranging from masslike to scarlike opacities. Accurate interpretation of these findings is critical to avoid misdiagnosis and unnecessary interventions. The authors outline the temporal evolution and imaging characteristics of RILI following HPRT; highlight potential diagnostic pitfalls; and discuss complications such as local recurrence of malignancy, organizing pneumonia, radiation recall pneumonitis, and in situ pulmonary artery thrombosis. Understanding the distinct radiologic features and timelines of RILI is essential for differentiating posttreatment changes from recurrent malignancy, guiding appropriate follow-up, and optimizing patient outcomes. ^©RSNA, 2026.