Comparison of IMRT delivery techniques and helical Tomo Therapy using Pareto front evaluation

Abstract: Purpose: The purpose of this work was to explore the possibility to compare treatment-planning- and treatment-delivery systems for intensity modulated radiation therapy (IMRT) using an objective approach. The approach investigated was the Pareto front concept. An additional aim was to adequately compare three different IMRT treatment planning and delivery systemsMaterials and methods: In IMRT treatment planning the goal is to find an optimal compromise between organ at risk (OAR) sparing and target coverage. During the optimization process objectives are chosen for each OAR and for the planning target volume (PTV). For a Pareto optimal plan one objective cannot be improved without worsening another objective. This makes IMRT optimization suitable for Pareto front evaluation. A set of Pareto optimal plans form a Pareto front. By using Pareto front evaluation the influence of individual plans is suppressed and the whole range of plans with the chosen objectives can be evaluated at the same time. Pareto fronts from different treatment planning systems (TPSs) are expected to differ from each other. In this study, different head and neck cases were used. Several plans with varying importance concerning the sparing of a specific OAR were created for each case using different TPSs. The importance of the PTV coverage was held constant for all plans. The TPSs used in the study were Oncentra Masterplan (OMP) (Nucletron B.V.), Eclipse (Varian Medical Systems) and TomoTherapy (Tomotherapy inc.) planning system. A Pareto front was obtained for each TPS by plotting the average OAR dose as a function of underdosed volume of the PTV. The underdosed volume was defined as the relative volume that receives less than 95% of the prescribed dose. Each plan fulfilled the dose restrictions for OARs according to the clinical protocol used apart from the OAR chosen for the trade-off.Results: The TomoTherapy Pareto front is situated below both the OMP front and the Eclipse front indicating that for the same target coverage, the sparing of the parotid is always favourable for this technology. For low priority OAR sparing, however, the Eclipse and the TomoTherapy fronts exhibit almost equal target coverage. As the importance of the OAR increases the target coverage decreases faster for the Eclipse front compared to the TomoTherapy front and is approaching the same coverage as OMP.Conclusion: The results clearly indicate that the approach of using Pareto fronts for different systems is a feasible way to compare different methods and technologies for advanced radiotherapy. For the particular cases studied, TomoTherapy seems to be superior to OMP and Eclipse regarding target coverage and sparing of the parotid gland.