I would guess that any change in your speech will be only temporary due to sores in your mouth caused by the radiation. At the end of my rad/chemo, just when I was ready to celebrate, I lost my voice, which happens to some people, and was reduced to a very soft whisper for about two weeks. There are many posts here on how to survive the rigors of radiation, and you can ask questions as you go along. Here is one tip. Before I lost my sense of taste all together, the chemo gave me an annoying metallic taste in my mouth which I found was relieved by sucking on honey lemon cough drops. Radiation is no picnic, but you can get through it. I am convinced that while I had great surgeons, it was the rad that saved my life and I would do it again in a minute. Keep that thought in mind and it may help you, as it did me. And let us know how you are faring. There are lots of us here to help you.