What Causes Constant Choking And Vomiting While Going Through Chemotherapy And Radiation?

I hope so a friend has gone through chemo & radiation & next week will be 6 week check up. but he was eating today & its like the food is caught below his throat & when he tries to drink anything he starts throwing it back up, he says he feels like he is drowning. could the food be caught & not going down? If so what should we do?