Relationship Between Evolution of Resting Energy Expenditure and Tumoral Response to Chemotherapy in Patients Suffering From Pancreas Cancer

Inclusion Criteria: * Pancreatic metastatic cancer * Patient older than 18 years * Initiation of a first line of chemotherapy by Folfirinox, or Gemcitabine or in combination with Nab-Paclitaxel. * At least one measurable target lesion * Patient signed consent for Energie-Pancreas study participation Exclusion Criteria: * Other concomitant cancer * Major general status alteration ( Performance status = 3 or 4 at inclusion) * Concomitant diseases explaining an altered general status or having an impact on energetic expenditure (i.e.chronic or severe infection, severe cardiac insufficiency, severe respiratory insufficiency, chronic inflammatory disease, recent surgery (\< 1 month), ongoing Healing, hyperthyroidism. * Smoker * Patient deprived of his liberty, under guardianship, curator. * Pregnant patient or breastfeeding * Claustrophobic patient