A radiation planning system includes a predictor-corrector optimizer unit which computes a predicted dose based on a collection of control points with a current approximate dose, each control point with a corresponding set of leaf positions, and determines an additional control point with a corresponding set of leaf positions based on a difference of the predicted fluence and the current approximate fluence through a least cost or shortest path in a layered graph structure of realizable leaf positions. Tools are described to help a planner to evaluate the effect of parameter changes to the current plan based on an identified zone of influence. The planner interactively views the current plan based on a visualization of the plan objectives and correlations between the objectives.