Vitamin pill artifact. The GTV (green), the duodenum (orange), and the stomach (pink) were well visualized for the purposes of localization and adaptive reoptimization but only after the patient drank water to float the iron-containing pill to move the artifact away from the area of interest. The constraint isodose line (40 Gy, in blue) is seen to be well away from the artifact, as well.GTV: gross tumor volume