Endoscopic submucosal dissection for early gastric cancer performed by supervised residents: assessment of feasibility and learning curve - Yamamoto, Shunsuke; Uedo, N.; Ishihara, R.; Kajimoto, N.; Ogiyama, H.; Fukushima, Y.; Yamamoto, Sachiko; Takeuchi, Y.; Higashino, K.; Iishi, H.; Tatsuta, M. (Endoscopy, 2009)