Stereotactic Body Radiotherapy (SBRT) With Biologically Equivalent Dose > 150 Gy is Associated With Improved Local Control in Patients With Squamous but not Non-Squamous Cell Carcinoma of the Lung: A Multi-Institutional Analysis

Purpose/Objective(s) Recent studies suggest improved local control (LC) of early-stage non-small cell lung cancer (NSCLC) treated with SBRT regimens with biologically equivalent dose (BED10) > 150 Gy. It is unclear if this association is histology dependent. Multiple groups have shown lower LC rates after SBRT for squamous cell carcinoma (SCC), compared to non-SCC NSCLC. We compared LC between BEDlow and BEDhigh SBRT schemes, stratified by histology. Materials/Methods As part of an IRB approved collaborative, we retrospectively analyzed 684 patients with cT1-2, cN0, cM0 NSCLC, treated with definitive SBRT to a minimum BED of 100 Gy at five international centers. Patients were grouped into SCC and non-SCC, then divided into BEDhigh (BED10 ≥150 Gy) or BEDlow (BED10 Results Of 684 eligible tumors, 457 were non-SCC and 227 SCC. Median follow-up was 30 months. Of non-SCC patients, 262 (57%) were BEDlow and 195 (43%) BEDhigh. Of SCC patients, 144 (63%) were BEDlow and 83 (37%) BEDhigh. BEDhigh SBRT included those treated with 54 Gy in 3 fractions (54/3). BEDlow included 60/5, 50/5, 48/4, or 60/8. Baseline characteristics, including T-stage and max tumor dimension, were similar between BED groups after matching. MVA including T-stage, tumor grade, and tumor location, showed BEDlow regimens were associated with higher rates of local failure for SCC (HR 9.8, 95% CI 1.9-25.1, P = 0.007), but not for non-SCC (HR 1.2, 95% CI 0.6-2.5, P = 0.6). Three-year LC rates for BEDlow and BEDhigh were 70% and 97%, respectively for SCC, and 91% and 92%, respectively, for non-SCC. Similarly, there were higher rates of failure with BEDlow PTVmean (3 yr LC 94 vs 69%, MVA HR 6.4, 95% CI 1.9-22.2, P = 0.003) and BEDlow GTVmean (3 yr LC 87 vs 68%, MVA HR 7.6, 95% CI 2.7-21.6, P = 0.001) in SCC patients. In non-SCC patients, LC was similar between BED groups for PTVmean (3 yr LC 92% vs 93%, MVA HR 1.1, 95% CI 0.5-2.8, P = 0.8) and GTVmean (3 yr LC 94 vs 90%, MVA HR 0.8, 95% CI 0.3-2.6, P = 0.8). There was a trend of worse survival in BEDlow SCC patients (MVA HR 1.3, 95% CI 0.9-1.9, P = 0.1), but survival was similar in non-SCC patients (MVA HR 1.02, 95% CI 0.8-1.3, P = 0.9). There were no differences in regional recurrence or distant metastases between BED groups in either histology. Conclusion This multi-institutional analysis shows improved LC in early-stage SCC NSCLC treated with SBRT regimens with BED10 > 150 Gy. No difference was observed in LC between BED groups for non-SCC patients. Our results suggest BEDhigh SBRT should be strongly considered for early-stage non-central SCC NSCLC.