Upper Arm Humerus Pain?

Hi everyone it's been a while since I posted I hope everyone's doing well.

My mom's been doing radiation and only has about 7 sessions left. During radiation she started to develop pain in her upper right arm (non cancer side). We waited for it to go away but it hasn't and it's been about 3 weeks. From what she describes it it's pain in her upper humerus not quite at the joint that's constant as long as she moves her arm (if she sits still she doesn't feel it). She says it's not very painful at all and very dull unless she lifts or moves her arm in certain ways. We can rule out pain from surgery/node dissection as it's in the non affected side. She also isn't taking tamoxifen or an AI (she's due to start tamoxifen after radiation). So therefore I brought it up to her medical oncologist and she said not to worry and it was likely a rotator cuff issue. Also brought it up to her radiation oncologist and he said it may be due to positioning during radiation but neither can really give a clear answer.

Of course my mind goes to cancer in the humerus even when I'm aware it can be many other things, so I guess we should wait till radiation is done and see if it improves. I thought I should post nonetheless in case anyone has any insight. Should we try and ask for a bone scan? She did have a clear PET/CT in March but I've heard lobular likes to not show up on those.

Thanks so much for listening!