Correlation Between Lower Lobe Dose Parameters and Radiation Pneumonitis in Definitive Radiation Therapy for Non-Small Cell Lung Cancer.

BACKGROUND: This study examined whether lobar-specific dose-volume histogram (DVH) parameters add predictive information for radiation pneumonitis (RP) beyond conventional whole-lung parameters in patients with non-small cell lung cancer (NSCLC) undergoing definitive radiotherapy. METHODS: We retrospectively analyzed 145 NSCLC patients treated between 2018 and 2023. Conventional whole-lung parameters, including V5%, V20%, and mean lung dose (MLD), lobar-specific parameters, including Low V20% (percentage of the bilateral lower lobes receiving ≥ 20 Gy), and clinical parameters were analyzed. The predictive performance of each parameter for Grade ≥ 2 RP was evaluated using receiver operating characteristic curve analysis. Associations with Grade ≥ 2 RP were assessed by Gray test and Fine-Gray competing risks regression. RESULTS: Grade ≥ 2 RP had an incidence of 41% (60/145) and showed significant associations with V20% (p = 0.005), MLD (p = 0.025), Low V5% (p = 0.006), and Low V20% (p = 0.003). In multivariate analysis, a high Brinkman Index (BI) (HR = 2.10, 95% CI: 1.27-3.48, p = 0.004) and high Low V20% (HR = 2.31, 95% CI: 1.12-4.74, p = 0.023) were independent predictors for Grade ≥ 2 RP. The correlation between V20% and Low V20% was moderate (r = 0.505), with minimal multicollinearity (variance inflation factor 1.34). CONCLUSION: Low V20% was independently associated with Grade ≥ 2 RP and may provide complementary information to conventional whole-lung DVH parameters and BI. This simple lobar-specific parameter may help refine pretreatment RP risk stratification, although external validation is required before its incorporation into individualized planning constraints.