Study protocol for a randomized controlled trial on a multimodal training curriculum for laparoscopic cholecystectomy - LapTrain - Friedrich, Mirco; Kowalewski, Karl-Friedrich; Proctor, Tanja; Garrow, Carly R.; Preukschas, Anas; Kenngott, Hannes Götz; Fischer, Lars; Müller, Beat P.; Nickel, Felix (International journal of surgery protocols, 2017)