Dan, these next few months the trick will be just keeping the wieght you have on. When I started this (or)deal I weighed about 170, now down to 130-ish, and this is 3 months after finishing the last go-round of radiation/chemo. Wasn't on a PEG tube either time, and have been eating pretty much "normal" solid foods since beginning of June, from the second go-round. Or at least normal for me anyway.
As a supplement, even with eating my normal diet, I've also been doing ensure/Instant breakfast when I've got it available. They don't sell either around here, nor any other diet supplement, so I have to bring it in from HK in the case of Ensure, or have the Instant Breakfast shipped over from the U.S.
As Packer and Karen have said, you're body's going to use a lot of calories just to heal. Also, I imagine the radiation and Chemo are going to mess around with your system and metabolism, so just concentrate on maintining at this point. After these 3 months, it finally looks like I might be starting to gain, or at least not have as much trouble maintaining.
As a side note, I was going through some old clothes yesterday, getting rid of some suits that at one point fit tight. My wife was telling me to keep them, I'll be getting fatter... I put on the pants, and looked like the "after" picture on a weight loss advertisement. Good 4 inches too big the pants were. Out they went.