Unexpected vaginal bleeding is a concern for a woman at any stage of life.
Given your history of uterine cancer, undergoing a hysterectomy and radiation, and no mention of bleeding prior to the last couple months, I would suggest that you contact your physician as soon as possible.
Please describe your situation fully and ask to be seen.
Your physician will be able to perform an internal exam to better understand the source of this bleeding.
My response to your question, is yes, the bleeding you are describing is concerning and I would recommend seeking medical advice.