This is pretty normal but if it continues frequently then he should get checked out. Tube feedings can be hard to tolerate and can cause nausea. Just remember whatever comes out must get put back in. Since he just finished rads only 2 weeks ago he probably is still feeling pretty lousy. His intake daily must hit the minimums of 2500 calories and 48-64 oz of water to help him with his recovery. If you can get him to push more and hit 3000 or even 3500 calories it can only help his body to recover faster.

Usually feedings that are too fast or thick will cause the throwing up and nausea. If he is doing pump feedings then slow down the rate. If doing gravity or the push methods, slow them down and add more water. Have him sit still and upright for at least 30 minutes (preferably an hour) after a feeding. This should help his stomach to settle and help ease the nausea.

Hang in there, the worst is almost behind you. Only about another week or so and he will slowly begin to feel a little better. Dont be surprised if the recovery takes many months, its a long road but Im sure with you helping he will do great.

Best wishes!