Fig. 1

The ranges in which 100%, 110%, and 50% of the prescribed dose (40 Gy) were administered are marked in yellow, red, and blue, respectively. The positional relationship between the tumor and organs at risk (OARs) is important because the dose restrictions to the stomach and small intestine (duodenum) are strict. a Pancreatic head tumor and large stomach. As the head of the pancreas may be far from the stomach, even a large stomach can be administered the prescribed dose to the planning target volume (PTV). However, the duodenum will be irradiated. b Pancreatic head tumor and small stomach. The stomach may be distant from the tumor, but the duodenum will be irradiated. c Pancreatic body tumor and large stomach. A large stomach may cause the stomach to stick to the pancreas, reducing tumor PTV coverage at the site of contact with the stomach. d Pancreatic body tumor and small stomach. As the area in contact with the pancreas is small and may be located far from the tumor, the prescribed dose can be prepared within the limits of those to the OARs