Radiation woes

My Dad began radiation treatments 12/16. He has non-small cell. Aside from the cancer, he is in good health. He has 1 ping pong size tumor in the right lung and 3 spots that are being radiated in the chest lymph nodes. (These 3 spots happen to be behind the espophagus so the beams go thru the espophagus). We just found out that the cancer has spread to his left hip so radiation will begin on the hip this week. He is to have 10 weeks of treatment. Chemo has not started yet but he will have this also. Here's the problem--he stays nauseous all the time. He kept vomiting and was unable to eat much the first 2 weeks of treament and lost 10 lbs. He would have the worst time of it right after the treatment when he got in the car to ride home. The doctor said it was "rare" to have this type of reaction to radiation and that some people are just allergic to it and he must be one of them. The doctor prescribed an anti-nausea drug several days ago and told him to take it 1 hour before the treatment. This has helped some because he isn't getting sick right after the treatments now but he still continues to stay nauseated all the time. It gets a little better after taking the medicine but he still can't eat much. Can anyone offer some insight on their own experiences with radiation? Several people at the cancer center who take radiation have told Dad that they don't have any problems with it. Then we've talked to friends who have relatives who have gone through it who say it's common. He's just beginning week 3 of radiation and is very discouraged that he is so sick already. The main thing he is able to eat now is popsicles and a little ice cream. We are worried about dehydration and how in the world he is going to get through 10 weeks of this.