The present invention relates to a radiotherapy planning system (100) for determining a solution (101) corresponding to a fluence profile. The invention proposes to use a Pareto frontier navigator (140) to select the best plan from a set of various auto-planned solutions. An interactive graphical user interface (400) is provided to the planner to navigate among convex combinations of auto-planned solutions. This proposed Pareto plan navigation can be considered as a further optional refinement process, which can be applied to find the best plan in those cases where auto-generated solutions are not fully satisfying the planners requirements. The navigation tool (400) moves locally through a set of auto-generated plans and can potentially simplify the planners decision making process and reduce the whole planning time on complex clinical cases from several hours to minutes.
