Evaluating the Efficacy and Safety of 48-Week Low-Dose Dienogest Administration in Patients With Dysmenorrhea Caused by Endometriosis: Protocol for a Randomized, Open-Label, Parallel-Group Trial - Kyoko Kikuno; Ryuta Asada; Takuma Ishihara; Yoshimasa Bomoto; Saki Murase; Yoko Ueda; Tomomi Shiga; Yoh Hayasaki; Tatsuro Furui; Satoko Matsuzaki; Masahiko Takemura; Kazutoshi Matsunami; et al. (JMIR Research Protocols)