Abstract: Objective To identify dosimetric predictors for the development of gastrointestinal toxicity in patients with pancreatic adenocarcinoma treated with TOMO radiotherapy.Methods From January 2014 to January 2015,we analysed the medical records of 68 pancreatic cancer patients who received helical tomotherapy from Air Force General Hospital.The stomach and duodenum were contoured separately to determine their dose volume histogram(DVH)parameters.Chi-square test was employed to analyze the count data.Spearman correlation analysis was used to analyze the relationship between occurrence of gastrointestinal toxicity and clinical and physical factors.Logistic regression models was performed to identify risk factors associated with gastrointestinal toxicity.Results The median follow-up was 9 months(4~16months).18 patients experienced grade II acute gastrointestinal toxicity,1 patient experienced grade Ⅲ acute gastrointestinal toxicity,whereas 17 patients experienced grade II late gastrointestinal toxicity,1 patient experienced grade Ⅲ late gastrointestinal toxicity.On UVA,the volume,Dmean,D1,D3,D5,D10,V5 to V40,and V5′ to V45′ of duodenum were significantly associated with Grade Ⅱ or higher gastrointestinal toxicity(P＜0.05).The MVA,V45′ of duodenum was independent predictor for grade Ⅱ or higher gastrointestinal toxicity(P＜0.05).The ROC analysis also showed that V45′ of 0.5cm3 was the optimal threshold to predict for gastrointestinal toxicity for the entire cohort.Conclusion V45′ of duodenum is of greater importance in the judgment of occurrence of hypofractioned radiation-induced gastrointestinal toxicity.

Key words: Pancreatic cancer, Gastrointestinal toxicity, Helical tomotherapy, Hypofractioned radiation