Can Chemotherapy For Breast Cancer Affect Carotid Artery?

I am a 64 year old female with few risk factors other than stress. Four years ago I was diagnosed with breast cancer, went through chemo, radiation and took Herceptin. I just had a carotid artery ultrasound and was told i have the arteries of a 79 year old woman. That is very scary news. I have a healthy diet, do yoga and walk regularly. Can this be from my cancer treatment? Can I reverse this situation?