Rainbow IMRT and Volumetric Imaging for Anterior Mesenteric Targets.

Mesenteric masses can considerably shift positions between fractions of radiation therapy (RT). With image-guided RT, we can adapt our treatment delivery daily to target the mass while avoiding surrounding structures. We report the case of a highly-mobile mesenteric mass which required adaptive planning from a traditional "butterfly" intensity modulated radiation therapy (IMRT) plan to an anterior "rainbow" beam arrangement to permit shifting of the isocenter without compromising target coverage or increasing dose to organs-at-risk.