Due To Chemo And Radiation, For The Past 8 Weeks,my

Due to chemo and radiation, for the past 8 weeks,my husband hasn't been able to eat solid foods. Severe nausea. Mostly dry heaving. How long can this go on? They want to start weening him off the TPN because It causes nausea but since they started that his nausea is worse. Just the word FOOD makes him gag.
Thank you,