Having pain 12 years later is unusual after Radiation. Did it start suddenly? As a radiation oncologist I will tell you don't just accept the explanation it is "from Radiation" from another doctor. See a radiation oncologist and undergo a workup. If you had an ER/PR positive tumor it could be coming back even at this late stage. Had one recur at 22 years before. Put her back on Tamoxifen and she went into remission and passed due to other causes. You at the very least need some tests and see a pain doctor if a correctable problem is not found.