How can you regain appetite after radiation treatment?

Patience, time. The effects of radiation therapy take time to resolve. Appetite is one that may take some time and may be slowed in recovery by other continuing medical problems and medicines. The cancer that caused the need for radiation may also cause loss of appetite as can depression and other medical illnesses.
Low dose steroids. Radiation especially when given to the abdomen or esophageal region can markedly reduce appetite. It can also be related to the lesion that was treated. Two approaches are used. The first is to give steroids which may increase apetite. The second is employing progestational agents like megace (megestrol) which will enhance apetite.