Can my 18 year old brother get custody of me?

I'm 15 years old. My birthday is January 15, 1999. My brother is 18 years old. My mother and I have always butted heads. She gave temporary custody of me to my grandma and aunt when I was 13 because I was too much for her. I just recently moved back in with her on November 2, 2014 (without my favor) and since I've lived with her, I've ran away twice due to her physical and mental abuse. I was caught shoplifting because I needed things that I didn't want to go back to her house to get because I was and still am afraid of her abuse. I know that if my older brother would try to get guardianship of me, my mother would take it to court because she knows I dislike her, her drug habit, her illegal activities going on in her home and her abuse. She knows I do not want to live with her. But my brother is 18, has a steady job, his own apartment and can support me with legal help (as in food stamps) just like my mother can. I believe it's in my own interest and my mother's interest to sign over guardianship to my brother because he keeps my head on straight. He wants me to live with him because he knows what it's like to deal with my mother. She has kicked him out of the house since he was 13 years old. My mother makes me depressed. I've harmed myself because of her, she brings out the worst in me. My daddy isn't in the picture so my brother is my best option because I fear I'll continue to harm myself if I don't get out fast.