Relationship between the consolidation to maximum tumor diameter ratio and outcomes following stereotactic body radiotherapy for stage I non-small-cell lung cancer

Purpose We investigated whether the ratio of the maximum diameter of consolidation to the maximum tumor diameter (consolidation/tumor ratio, CTR) predicted the outcomes of patients who received stereotactic body radiotherapy (SBRT) for non-small-cell lung cancer (NSCLC). Methods and materials Between 2005 and 2014, 237 patients with stage I NSCLC were treated with SBRT, receiving 48 Gy in 4 fractions. Of these patients, those who received pretreatment thin section computed tomography were selected for this analysis. The relationship between the CTR and outcomes (local control [LC], disease-free survival [DFS], and overall survival [OS]) was analyzed. Results One hundred and fifty-five patients were eligible. The median follow-up time was 34.7 months (range, 1.2–109.8). In the CTR < 0.5, CTR 0.5–<1, and CTR = 1 groups, 0, 2, and 12 patients experienced local recurrences, respectively. Three-year DFS and OS rates were 96.7% and 87.5% in the CTR < 0.5 group, 85.1% and 81.1% in the CTR 0.5–<1 group, and 63.3% and 70.1% in the CTR = 1 group, respectively. In multivariate analysis, CTR was the only significant predictor of DFS (P < 0.001). Conclusion The CTR effectively predicts DFS after SBRT in NSCLC patients.