I finished 4 cycles of chemo on the 16th feb. Started radiotherapy a month ago and after one week noticed my voice was sounding a bit fried. I'm a singer and its the kind of sound Britney Spears make...
Remember with chemo your good old cells are changing to good new cells and just like a baby you have to get your voice back in to its vocal range and train it. Try not to over stress it and perhaps choose songs with less of a vocal range. Little by little it will return as good as before but it will take time.