Supplementary Material for: Gastrointestinal Bleeding after Particle Radiotherapy for Pancreatic Cancer

Introduction: Particle radiotherapy (PRT) is a new option for the treatment of unresectable pancreatic cancer (PC). While gastrointestinal bleeding (GIB) is a feared adverse event, real-world evidence in this setting is limited. Methods: We conducted a single-center retrospective study to evaluate the frequency and outcomes of GIB and to elucidate the risk factors for GIB after PRT for PC. Results: Thirty-four patients were included. Twenty-nine received PRT to the pancreatic primary, while five received PRT for metastases. Concurrent chemotherapy was given to 26 patients (76%). Eleven patients (32%) experienced acute GIB symptoms after PRT. Median time from PRT to GIB was 13.2 months. Endoscopic signs of hemorrhage were observed in eight patients (24%), and endoscopic hemostasis was performed in six (18%). Three cases presented with ruptured pseudoaneurysms, of which two were treated with transarterial embolization. Hemostasis was ultimately achieved in all cases, and no deaths occurred directly as a result of GIB. However, overall survival after GIB was short (median: 1.9 months). Median overall survival after PRT tended to be longer in bleeders than in non-bleeders (26.8 vs. 22.7 months, P = 0.03). Concurrent chemotherapy was associated with a lower risk of GIB in univariate analysis (P = 0.05). Conclusion: Gastrointestinal bleeding after particle radiotherapy may not be as rare as previously believed, particularly in the terminal stages of pancreatic cancer.