I had cisplatin and radiation for tonsillar cancer, and I lost my voice for about 2 or 3 months. I could croak a few words here and there, but mostly I just whispered. Sorry to say, but your husband's condition will worsen until about 2 or 3 weeks after he's finished with the radiation, and then he will start to improve. It's frustrating, but tell him to hang in there. He'll get better, just not quite as soon as he wants to.
Best wishes,
Mike