Duodenum

The first part of the small bowel, curving in a C-shape from the pylorus around the head of the pancreas to the duodenojejunal flexure. Its second part wraps directly around the pancreatic head, which is why it so often touches pancreatic targets.

The duodenum is the first part of the small intestine; bile and pancreatic juice enter it to digest food.

The duodenum is usually the dose-limiting organ for pancreas treatment and for tumors near the porta hepatis. Late toxicity includes ulceration, bleeding, stricture and perforation. In conventional plans, the volume above about 55 Gy is linked to late toxicity; in SBRT, limits are written as very small-volume maxima. Because it lies against the target, its limit often decides how much of the target can receive full dose.

In gynecologic treatment the duodenum matters when the para-aortic nodes are treated, because its third part crosses in front of the aorta near the top of the field. The V55 Gy <15 cc limit comes from a study of para-aortic IMRT in gynecologic cancer.

Jabbour 2014 traces its four parts:

• First part (about 5 cm): starts just below the pylorus, with the common bile duct, portal vein and IVC behind it.
• Second part (descending): attached to the head of the pancreas, to the right of L1–L3 and of the IVC.
• Third part: turns toward the midline at L3 and crosses to the left, in front of the aorta and IVC and behind the superior mesenteric artery and vein.
• Fourth part: rises to the left of L3 toward the pancreatic body and ends at the duodenojejunal junction (ligament of Treitz). The inferior mesenteric vein is a useful landmark for that junction.

Coronal views help, especially for the third part. In the consensus work the fourth part was often missed.

Timmerman 2022 (Tables 8–11, written for its SBRT dose tables): the entire duodenal wall and lumen from the pylorus to the duodenojejunal flexure.