Pre-treatment serum bicarbonate predicts for primary tumor control after stereotactic body radiation therapy in patients with localized non-small cell lung cancer

•Pre-treatment bicarbonate is associated with tumor recurrence after lung SBRT.•This remained after accounting for dose, T-stage, tumor volume, and histology.•Findings were validated in an independent cohort from three institutions. Tumor aggressiveness and hypoxia are linked to acidosis in the tumor microenvironment (TME). We hypothesized that low pre-treatment serum bicarbonate, potentially correlating with an acidic and hypoxic TME, predicts for poor outcomes after stereotactic body radiation therapy (SBRT) for non-small cell lung cancer (NSCLC). We included patients with localized NSCLC treated to a biologically effective dose (BED) ≥ 100 Gy, with available pre-treatment bicarbonate values within 3 months of treatment. We used receiver operating characteristic analysis to determine the bicarbonate concentration optimally predicting for primary tumor recurrence, and evaluated its association with recurrence and survival. We validated our findings in an independent cohort of patients from three collaborating institutions. A total of 110 patients and 114 tumors were included in the training cohort, with median follow-up of 15.0 months. Bicarbonate