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

Abstract

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.

Keywords: %LAA; Low attenuation area; Predictive factor; Radiation-induced lung toxicity; SBRT.