Dosimetric analysis of upper gastrointestinal ulcer after carbon-ion radiotherapy for pancreatic cancer

Purpose: The aim of this study was to clarify the incidence, clinical risk factors, and dose-volume relationship of upper gastrointestinal (GI) ulcer after carbon-ion radiotherapy (C-ion RT) for pancreatic cancer. Materials and methods: Fifty-eight pancreatic cancer patients were treated with C-ion RT from April 2014 to December 2015. The total dose was 55.2 Gy (RBE) in 12 fractions. D-2cm3 of GI tracts were restricted under 46 Gy (RBE); RBE-weighted absorbed dose. The association between dosimetric parameters (V10-50, D-max, D-1cm3, D-2cm3) and GI ulcer was examined using Spearman's correlation. The incidence of GI ulcer was compared between the two groups divided by the cutoff value. Results: Twelve patients (21%) experienced gastric ulcer including only one (2%) grade 3 ulcer. There was no grade 4/5 toxicity or duodenal ulcer. V10-30 was significantly associated with gastric ulcer. The 1-year estimated risk of gastric ulcer for the determined cutoff values were 51% vs. 10% (V-10, >= 102 cm(3) or less), 42% vs. 9% (V-20, >= 24 cm(3) or less), 34% vs. 4% (V-30, >= 6 cm(3) or less). Conclusions: The incidence of GI ulcer after C-ion RT was very low with the dose constraint of D-2cm3 <46 Gy (RBE). To further minimize the risk of GI ulcer, V10-30 should also be reduced. (C) 2016 Elsevier Ireland Ltd. All rights reserved.