WIth IMRT plans the variety of possible dose distributions is quite large. Typically if a physician does not like an IMRT plan they will request a plan to be re-run. This requires the planner to input new constraints and objectives and a new plan to be run from the beginning of the optimization process. This is a time consuming process. An MCO (Multi Criteria Optimization) approach allows planners and physicians to visualize the the tradeoff between obtaining the required dose to the target volumes while reducing the dose to the OAR's. MCO treatment planning is based on a set of Pareto optimized plans. Pareto surface navigation puts the interactive exploration of dosimetric objectives at the planners and physicians fingertips. For a given plan it is considered optimal if it satisfies all the constraints and none of the objectives can be improved without worsening at least one of the other objectives. In other words the MCO plan cannot be improved in any one objective without worsening another objective. Instead of just creating one plan the ASTROID TPS creates a database of plans that satisfies the treatment planning goals.

Constraints are non-negotiable, the highest priority. They are chosen to limit the range of the Pareto surface. If the constraints are too tight there may be no reasonable feasible plans. If the constraints are too loose there may too many solutions to approximate. Objectives are negotiable, they do not have a hard level that must be obtained. The number objectives chosen should be so that all the relevant trade offs will be demonstrated.

After the constraints have been entered the user may start the Feasibility calculation by clicking calculate in the Feasibility block. The Feasibility calculation is based solely on the constraints entered. The Feasibility calculation will be run to let the user know if there is a feasible plan possible. Using a narrow range of constraints may improve the optimizer performance. The Feasibility calculation may be an iterative processes in order to get an appropriate plan. In other words the user may need to enter a constraint, check the feasibility, then progressively drop the constraint and check the feasibility until the plan is no longer feasible. The user should start by obtaining a feasible plan utilizing the target constraints then add OAR constraints.

The user needs to be aware of the constraints being set on Fraction Group level versus the Plan level. It is possible to have a constraint set in the Fraction Group level so that the whole dose to an OAR is given on one day and not on another. This could happen when there are two Fraction Groups and the OAR dose is not split between the two.

The Objectives as stated before are negotiable. The user can put Objectives on Targets and OAR's. The user can choose to put Objectives on structures that they wish to try to guide the dose to or from. The Objectives will guide the MCO. Objectives may be added all at once. There is no need to place them in any particular order as the MCO will work at finding all solutions so that one objective cannot be improved without worsening another objective. As the MCO is trying to find multiple solutions this can be a lengthy process. The MCO takes into consideration the size of the calculation grid, the number of objectives, the number of beams as well as the number of spots. The smaller the calculation grid the longer the MCO will take to find a solution. The larger the number of objectives, beams and spots the longer the optimization process will take.

Once the user has all the Objectives entered as well as a Feasible plan they can start the MCO by clicking the calculate option in the Navigation block.

Discuss how to check progress (put in later when progress widget done)

Screen shots Absolute vs relative color wash isoline etc Everything on right hand side for dose controls

screen shots & explanations of sliders meaning of each item on the slider Explain save button on sliders reset button on sliders