Radiation-induced lung injury patterns and the misdiagnosis after SBRT of lung cancer

Purpose: To analyze radiation-induced lung injury (RIL) after stereotactic body radiotherapy (SBRT) of lung cancer and the subsequent clinical problems. Methods: 106 lung cancer patients treated with SBRT were included, their computed tomography (CT) scans were reviewed. Late injury pattern was classified by Koening's, radiologist' diagnosis reports for RIL was reviewed. Logistic regression was used to analyze the predictive model of injury pattern, which was also validated by ROC curve. Results: Radiographic late injury within at least 6 months after SBRT was concluded. The majority of late RIL was mass-like pattern, not the modified conventional pattern. 36.8% patients showed acute injury, which trend to occur late lung injury earlier than patients who were not found acute injury (p = 0.0185). 24.5% RIL cases were misdiagnosed to tumor progression by radiologists. Most misdiagnosis occurred among mass-like pattern. Per fraction dose (p < 0.0001), prescription isodose line (p = 0.027) and age (p = 0.089) trend to associate with the occurrence of mass-like injury pattern. Nomogram was established based on these parameters, ROC curve showed that area under the ROC curve (AUC) of the nomogram was 0.767 (95% CI = 0.677-0.857), which was better than any factors along. Conclusion: SBRT for lung cancer patients was safe, the majority of late RIL was mass-like pattern. This injury was difficult to be distinguished from tumor progression, which leaded to misdiagnosis of 24.5% patients receiving SBRT. A nomogram based on age, per fraction dose and the prescription isodose line may assist the diagnosis in clinical practice.