1) Get away from toxins. Smoking, second-hand smoke, air pollution, animal products(contains environmental pollutents) and any other toxin which causes inflammation and promotes cancer.
2) Include antioxidants in your diet that can cross the blood brain barrier, like lutein and zeaxanthin, from whole foods like leafy greens. No antioxidant supplements because they have a bad record of promoting cancer.
Basically, eliminate source of inflammation and give your brain the nutrients it requires to heal itself.
The Gerson Therapy is well known for reversing Cancer, including astrocytoma. http://gerson.org/
Did you get your Vitamin D levels checked?