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 (V_10–50, 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. V_10–30 was significantly associated with gastric ulcer. The 1-year estimated risk of gastric ulcer for the determined cutoff values were 51% vs. 10% (V₁₀, ⩾102 cm³ or less), 42% vs. 9% (V₂₀, ⩾24 cm³ or less), 34% vs. 4% (V₃₀, ⩾6 cm³ 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, V_10–30 should also be reduced.