The goal of this clinical trial is to learn if inverted-Ω anastomosis after pancreatic head resection or mid-pancreatectomy works in benign or low-grade malignant tumor. It will also learn about the safety and feasibility of inverted-Ω anastomosis. The main questions it aims to answer are:
1. Does inverted-Ω anastomosis operate safely? (operative time, blood loss, transfusion and conversion rate)
2. What is the incidence and severity of postoperative complications in inverted -Ω anastomosis? What advantages does it have over conventional anastomosis methods such as roux-en-y？