With emerge of MR-linear accelerator technology, the interest for MR-only radiotherapy is growing rapidly. This study evaluated the feasibility of using pseudo-CT generated from conventional Dixon-MR scans for treatment planning of lung cancer where dosimetric differences are expected to be high due to tissue inhomogeneity. A model-based method including spine was applied to generate synCT from whole-body Dixon-MR data. The plans for radiotherapy in lung cancer calculated on synCT images closely agreed with the doses computed on standard CT to within 1%. Further evaluation of the MR-based treatment planning in a large patient cohort is needed.