Self-monitoring of Physical Activity After Hospital Discharge in Patients Who Have Undergone Gastrointestinal or Lung Cancer Surgery: Mixed Methods Feasibility Study 由 Marijke Elizabeth de Leeuwerk, Martine Botjes, Vincent van Vliet, Edwin Geleijn, Vincent de Groot, Erwin van Wegen, Marike van der Schaaf, Jurriaan Tuynman, Chris Dickhoff, Marike van der Leeden