CNS Lymphoma post radiation hair growth

Hello! I am a Lymphoma survivor. I had 3 lesions in my brain, did chemo as well as radiation. During my chemo treatments,  my hair was growing back in between treatments but with radiation, I cannot say the same. I look like an elderly balding man. My hair is thin and I have major bald spots. I was told today to use Nioxin and was wondering if anyone here, who had radiation treatment on their head, has used this and if you had success. I threaten to just shave it off every other day and I am miserable over my lack luster hair. My fear is that the radiation killed my follicles and nothing will help.