Room: Stars at Night Ballroom 1
Purpose: In the treatment of breast cancer with extensive nodal involvement, VMAT has demonstrated dosimetric advantages over 3D techniques. Multi-criteria optimization (MCO) within RaystationÂ® v8a allows users to navigate many Pareto-optimal plans and has been reported for several treatment sites but never for comprehensive breast plans. We sought to (1) determine the dosimetric quality of MCO plans compared to clinical plans and (2) assess the robustness of MCO and clinical plans to maximum residual CBCT mismatch from planning CT as a first step towards incorporating robustness into the planning process.
Methods: For eleven randomly selected comprehensive breast patients, using the clinical beam arrangement, MCO plans were generated with a standard set of objectives and constraints. After the navigated plan was converted to deliverable and post-processed to correct for plan degradation, MCO plans were compared to clinical plans per our institutional clinical goals. Using a RaystationÂ® v8a feature, evaluation CT datasets were deformed to reflect residual mismatch between daily CBCTs and planning CTs. The plan doses were calculated on the deformed CTs and robustness was evaluated in terms of CTV coverage.
Results: MCO plans were favorable dosimetrically to clinical plans, having improved coverage (D99%) of the total and individual IMN CTVs (p<0.04, Wilcoxon Rank-Sum). No significant difference was found for other metrics (PTV coverage, heart and lung avoidance). Considering robustness, CTV coverage was degraded in both MCO and clinical plans with an average difference from original plans of 5%. MCO plans, however, retained significantly more coverage (D99%) of the total and IMN CTVs (Wilcoxon Rank-Sum, p<0.05).
Conclusion: MCO plans are comparable to clinically delivered plans. Both MCO and clinical plans showed expected degradation of CTV coverage when applied to deformed CTs. MCO plans were slightly more robust and may be further improved with the incorporation of robustness into the planning process.