SU-E-T-632: Metrics for Comparing Dose Volume Histograms

The process of IMRT planning is an iterative inverse process, where a planner seeks to attain a desired dose distribution, specified for tumors and OARs, hence creating a plethora of competing constraints. However, the final product is rather the unpredictable outcome of a series of trial-and-error attempts at meeting these competing objectives. A key tool to inspect the quality of a plan is the DVH. We provide a set of metrics for unbiased DVH comparison.

The treatment of one prostate case was planned by seven planners, while imposing the same clinical objectives for PTV and OARs. The resulting seven DVHs were compared based on their deviation of from the ideal coverage, namely 100% of PTV receiving 100% of the dose. Our deviation function L measures the area between the ideal and realized DVH. A weight function W is used for dose dependency. We employ a set of Ws: constant, piece-wise linear, quadratic, normal and beta-distributional.

We show that the deviation of some planners are consistently higher than others for all eight Ws. Similarly, we observe that one of the planners consistently exhibits the lowest deviation, while another one is low for linear and quadratic Ws and worsen for the distributional functions independent of their slope and range. Further, the normal and beta-density function weights, as they primarily penalize the range of 95% < Dose < 105%, hence discriminating only deviations in the respective region.

The outcome of treatment planning is strongly related to the planning personal. The proposed set of DVH metrics allow for unbiased comparison, beyond the visual inspections. An optimized superposition of these metrics may yield a practical tool for daily treatment planning. Furthermore, these results exhibit the need for methods whose outcomes are independent of the planning personal.