Two different approaches for mixed neutron-gamma-radiation fields are investigated in this project. The main goal is to enable 3D dose calculation for the fission based fast neutron therapy (FNT) unit MEDAPP located at the research reactor FRM 2 run by the TUM in Garching. While the investigated pencil beam kernels enable time efficient planning on patient CT data, the considered Monte Carlo dose calculation approach provides higher flexibility in both handling different material compositions in the dose calculation and investigation of different (biological) optimization approaches.