Learning curve of a modified technique of peroral endoscopic myotomy (POEM) – analysis of safety and efficacy in 9 consecutive patients with follow-up - Dolak, W; Kamogawa-Schifter, Y; Sieghart, W; Schoeniger-Hekele, M; Tribl, B; Trauner, M (Zeitschrift für Gastroenterologie, 2019)