OA24.07 The Impact of Population Heterogeneity on the Efficacy of SBRT to the Lung

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Stereotactic Body Radiation Therapy (SBRT) is the standard of care for medically inoperable patients with early-stage non-small cell lung cancer (NSCLC). However, NSCLC is comprised of several histological subtypes and the impact of this heterogeneity on SBRT treatments has yet to be established. We analyzed 740 early-stage NSCLC patients treated definitively with SBRT from 2003 through 2015. We calculated cumulative incidence curves using the competing risk method and identified predictors of local failure using Fine and Gray regression. Overall, 72 patients had a local failure with a cumulative incidence of local failure at three years of 11.8%. On univariate analysis, squamous histology, younger age, fewer medical comorbidities, higher BMI, higher PET SUV, central tumors and lower radiation dose were associated with an increased risk of local failure. On multivariable analysis, squamous histology (HR 2.4 p = 0.008) was the strongest predictor of local failure. Patients with squamous cancers fail SBRT at a significantly higher rate than those with adenocarcinomas or NSCLC-not otherwise specified, with three-year cumulative incidences of local failure of 18.9% (95% CI= 12.7-25.1%), 8.7% (95% CI= 4.6-12.8%), 4.1% (95% CI= 0-9.6%), respectively. Our results demonstrate an increased rate of local failure after SBRT in patients with squamous cell carcinoma. Standard approaches for radiotherapy that demonstrate efficacy for a population may not achieve optimal results for individual patients. Establishing the differential dose-responses of SBRT across histological groups is likely to improve efficacy and inform ongoing and future studies that aim to expand indications for SBRT.