Postoperative Radiotherapy for Locally Advanced NSCLC: Implications for Shifting to Conformal, High-Risk Fields

Abstract Background To examine the effect of radiotherapy field size on survival outcomes and patterns of recurrence in patients treated with postoperative radiotherapy (PORT) for non-small cell lung cancer (NSCLC). Methods We retrospectively reviewed the records of 216 patients with T1-4 N1-2 NSCLC following surgery and PORT using whole mediastinum (WM) or high-risk (HR) nodal fields from 1998 to 2015. Survival rates were calculated using the Kaplan-Meier method. Univariate and multivariable analyses were conducted using Cox proportional hazards modeling for outcomes and logistic regression analysis for treatment toxicities. Results Median follow-up was 28 months (interquartile range [IQR] 13-75 months) and 38 months (IQR 19-73 months) for WM (n=131) and HR (n=84) groups, respectively. Overall survival (OS) was not significantly different between groups (median OS: HR 49 vs. WM 32 months; P=0.08). There was no difference in progression-free survival (PFS), freedom from locoregional recurrence (LRR), or freedom from distant metastasis (P>0.2 for all). Field size was not associated with OS, PFS, or LRR (P>0.40 for all). LRR rates were 20% for HR and 26% for WM groups (P=0.30). There was no significant difference in patterns of initial site of LRR between groups (P>0.1). WM fields (OR 3.73, P=0.001) and concurrent chemotherapy (OR 3.62, P=0.001) were associated with grade ≥2 toxicity. Conclusions Locoregional control and survival rates were similar between PORT groups; an improved toxicity profile was observed in the HR group. Results from an ongoing prospective randomized clinical trial will provide further insight into the consequences of high-risk PORT fields.