Prognostic Value of Radiation Pneumonitis After Stereotactic Body Radiotherapy: Effect of Pulmonary Emphysema Quantitated Using CT Images

Background The aim of this study was to determine the prognostic factors of radiation pneumonitis (RP) after stereotactic body radiotherapy (SBRT). Patients and Methods A total of 50 patients (36 male and 14 female) were treated with SBRT for 42 primary lung cancers and 8 metastatic lung cancers. SBRT was performed with 48 Gy in 4 fractions to the isocenter or with 40 Gy in 4 fractions covering 95% of the planning target volume. Percentage of low attenuation area (%LAA) was defined as percentage of the lung area with attenuation of −860 Hounsfield units (HU) or lower (%LAA-860) or of −960 HU or lower (%LAA-960). The dosimetric parameter of V 20 Gy , which means percentage volume of the lung receiving 20 Gy or more, was recalculated. RP was assessed using Common Terminology Criteria for Adverse Events version 4.0. Results The median follow-up period was 39.0 months (range, 7.2-94.5 months). RP of Grade 0, Grade 1, and Grade 2 to 3 was diagnosed in 11, 29, and 10 patients, respectively. Multivariate analyses (MVA) for Grade 1 showed that higher %LAA-860 and higher %LAA-960 were significantly associated with a lower rate of Grade 1 RP. MVA for Grade 2 to 3 showed that lower Brinkman index and lower lung V 20 Gy were significantly associated with a lower rate of Grade 2 to 3 RP, and, in contrast, %LAA-860 and %LAA-960 had no association with Grade 2 to 3 RP. Conclusion This result suggests that high %LAA is associated with radiological changes (Grade 1) but that %LAA has no correlation with Grade 2 to 3 RP because symptomatic RP might also be affected by other factors.