Like you I am more than a few years out from my radiation. If this were me, I would be looking to get an ultrasound, just to be sure. I am making the assumption that you get annual mammograms. So an ultrasound probably makes more sense. But this needs to be in a setting familiar with breast issues.
If there is something there they can order a biopsy and if there isn’t, you can go celebrate with an eased mind.
Do you have access to a doctor who would asses this?