Behavioral activation for depression in patients with advanced cancer: study protocol for a multicenter randomized controlled trial oleh Takatoshi Hirayama, Yuko Ogawa, Asao Ogawa, Emi Igarashi, Saaya Soejima, Kotone Hata, Yusuke Utsumi, Yuki Mashiko, Kyoka Ogata, Ayako Kayano, Yuko Yanai, Shin-ichi Suzuki