I found that my voice pretty much disappeared toward the end of RT. I could whisper, that was about it. But it came back within, hmm, I'll say a month or so after treatment. Maybe a bit more. Do ask your docs about this but my first guess is that it's a normal response.

Oh and similar to Kevin's situation, my own voice deepened about two years out from treatment. Over the course of the second summer I gained 4 notes on the bottom. Now I can sing bass. Not that you'd want to hear me do so, of course.