Lung Abnormalities at Multimodality Imaging after Radiation Therapy for Non–Small Cell Lung Cancer

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Abstract
Three-dimensional (3D) conformal radiation therapy (CRT) and stereotactic body radiation therapy (SBRT) are designed to deliver the maximum therapeutic radiation dose to the tumor, allowing improved local disease control, while minimizing irradiation of surrounding normal structures. The complex configuration of the multiple beams that deliver the radiation dose to the tumor in 3D CRT and SBRT produces patterns of lung injury that differ in location and extent from those seen after conventional radiation therapy. Radiation-induced changes in lung tissue after 3D CRT and SBRT occur within the radiation portals. The imaging appearance of irradiated tissues varies according to the time elapsed after the completion of therapy, with acute-phase changes of radiation pneumonitis represented by ground-glass opacities and consolidation and with late-phase changes of radiation fibrosis manifesting as volume loss, consolidation, and traction bronchiectasis. Knowledge of treatment timelines and radiation field locations, as well as familiarity with the full spectrum of possible radiation-induced lung injuries after 3D CRT and SBRT, is important to correctly interpret the abnormalities that may be seen at computed tomography (CT). Differential diagnoses in this context might include infections, lymphangitic carcinomatosis, local recurrence of malignancy, and radiation-induced tumors. The integration of morphologic information obtained at CT with metabolic information obtained at positron emission tomography is helpful in distinguishing radiation-induced parenchymal abnormalities from residual, recurrent, and new cancers. Thus, multimodality follow-up imaging may lead to substantial changes in disease management.

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