Robust optimization systems and methods are provided for intensity modulated proton therapy (IMPT) that may be deployed in a clinically practical way to enable users to control the balance between nominal plan quality and plan robustness in a user-defined way. The method may include a normalized dose interval volume histogram (NDIVH)-based robust optimization, where the normalized dose interval (NDI) is calculated for each voxel considering dose variations in the face of uncertainties. It is then used to create a NDIVH. The area under this NDIVH curve may then be used to quantify plan robustness. By using normalized dose interval volume constraints (NDIVC) to control the shape of the NDIVH curves, plan robustness may be adjusted. The tradeoff between nominal plan quality and plan robustness can be modified in a user-defined way by adjusting positions of the NDIVCs on the NDIVH curves.