Hi @Lynnym
I don't sing professionally but have some singing training and have a degree in music (Arts). I've had the AC chemo then the paclitaxel then 6 weeks of radiotherapy. I finished the radio about 10 days ago. I've started on the hormone therapy now...I sang for my radiotherapy team and waiting room after my last treatment ("I'm on my way" The Proclaimers). I've found the biggest effect on my voice so far is the fatigue, it's starting to get slightly better now. I've also noticed that I have less power in my upper register (I'm an alto) and think perhaps that might be the hormone therapy, although I had a bit of that before I had my first injection of goserelin. Could be fatigue related too..Definitely discuss your concerns with your treating team as @arpie suggested.
The good news is that as a trained singer if you're having left sided radiation using dibh (deep inhalation breath holding) you will ace it and have no issues with holding your breath during the radiation. As a singer you're well used to controlling your breath, I had no issues with it either but others struggle apparently.
Best wishes for your treatment, it's a long haul but you will get through it!