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Background/Aim: To identify predictors of adverse gastrointestinal (GI) events related to stereotactic body radiation therapy (SBRT) for liver tumors. Patients and Methods: We retrospectively analyzed 56 patients who underwent SBRT for liver tumors at our institution between 2016 and 2021. The a/ß ratio of the GI tract (stomach, duodenum, and large intestine) was assumed to be 3 Gy in the Linear-Quadratic model (LQ model). The dose to the GI tract, that is, the biologically effective dose 3 (BED3) was converted to a 2 Gy equivalent dose (Gy2/3=2 Gy equivalent dose, a/ß=3). Using this 2 Gy equivalent dose, predictors of adverse GI events of Grade 2 or higher were investigated. Results: The median observation period was 10 months (0-40 months) and median age was 77 years (range=29-93 years). Forty-three of the 56 patients had hepatocellular carcinoma and the other 13 had metastatic liver tumors. Tumors were irradiated with 30-54 Gy/5-18 fractions of planning target volume D95% prescription (80% isodose). Eight of the 56 patients had Grade 2 or higher adverse GI events. By univariate analysis, GI D1cc, Dmax, V20, V25, V30, and V35 were all significant predictors of Grade 2 or higher adverse GI events. Among these, gastrointestinal V35 was the most significant predictor of Grade 2 or higher adverse GI events. Conclusion: For SBRT of liver tumors, GI V35 was the best predictor of Grade 2 or higher adverse GI events. [ABSTRACT FROM AUTHOR]