A person have a esophageal cancer, why would the doctor insert a tube in the doudenum instead of the stomach?

is that because the stomach can reverse the food to the esphagos, and create a problem in breathing?

They place the tube in the duodenum for several reasons.
First, if the tube is past the stomach and in the duodenum, the feedings cannot be refluxed backwards into the esophagus which causes problems with aspiration pneumonia and reflux esophagitis to an already damaged esophagus Gastric feedings are harder to tolerate for the pt than j tube or other type feedings.
Secondly, if the tube is in the duodenum, it takes the stomach out of the digestion process and prevents nausea for a cancer pt who has already been unbelievably sick to their stomach.
Thirdly, the tube is in the duodenum to increase the likelihood the nutrients will be processed thru the small intestine and not thrown up before it gets there.
Radiation and chemotherapy make people increadibly sick sometimes, so the likelihood of tolerating g tube feedings are less if you take them into the stomach vs the duodenum.
I personally prefer jejunostomy feedings which are even lower in the intestinal track.
Prayers for you and your sick relative.
RN in Oncology for many years.

The duodenum of the small intestine is where a majority of absorption takes place. The stomach just basically breaks substances down so that they can be absorbed once they get into the small intestine.

A lot of the nutritional supplements for feeding tubes are made to go directly to the duodenum. Also, if it is esophageal cancer, that area should be as free of tubes as possible in case radiation treatment is ordered. There are many areas for placements of tubes and sometimes the only reason that a doctor uses a certain placement is the doc's personal preference.

The feeding tube should be in the duodenum to avoid aspiration into the lungs in case of vomiting. You are correct in that notion.

Typically these are placed through the abdominal wall and into position. A tube placed down the esophagus and into the stomach still has a chance of aspiration because the lower esophageal sphincter is not completely closed (because of the tube present).