SU-E-T-604: Inter Planner Dosimetric Variations in IMRT

To study inter-planner variations in IMRT dosimetry with identical dose prescription in IMRT optimization for estimation of quality of treatment plans by using dose volume histogram (DVH).

Five treatment planners: p1, p2, p3, p4 and p5 with Eclipse TPS and Varian accelerator were chosen. The 3D data sets including PTV and OAR of a prostate case was sent with instructions for beam orientations, energy and dose-volume constraints. Each planner performed the treatment planning process with inhomogeneity corrections by using the same dose constraints. DVH and isodose distributions were compared to examine the inter-planner variations.

There were large variations in the IMRT plans reflected by the DVH among the planners even with identical dose constraints in IMRT optimization. Clinically constraint#1 (D95-V95) dose criteria could be considered as the most important one. Two planners did not meet the criteria, whereas planner 4 met all of the dose criteria for PTV and OARs. The inter-planner variations in PTV as large as 20% were found in this study. Every time optimization is performed even with the same constraints, the DVH output was significantly different due to the differences in constraint weights.

There exists a significant inter planner variation for all cases studied indicating that even for the same constraints the outcome cannot be guaranteed to be identical due to cost function convergence. It seems feasible to control the over-dosage for all planners. However we see large deviations in plans with respect to different constraints. Planner 4 met all the dose criteria for PTV and OARs indicating that it is possible to plan and meet all the dose criteria. This approach could be used as gold standard.