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Dosimetric Comparison of Multi-Criteria Optimization and Direct Machine Parameters Optimization Generated VMAT Plans for Head and Neck
Z Fellows*, S Chen , M Guerrero , J Snider , S Mossahebi , K Spaeth , N Lamichhane , University of Maryland School of Medicine, Baltimore, MD
Presentations
SU-I-GPD-T-445 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: Directly correlating the objectives with weights to optimize a desired dose distribution during treatment planning is generally lacking. Multi-criteria optimization (MCO) introduces vector function fluence based objectives where explicit weights are avoided. The planning system thus creates Pareto solutions that can be utilized to navigate the impact and tradeoffs between all clinical goals and organ constraints in real time. The purpose of our work is to compare previously direct machine parameters optimized (DMPO) set of objectives and constraints for head and neck cancer (HN) to MCO VMAT plans.
Methods: Seven HN patients planned with 2 coplanar arcs with DMPO VMAT technique were randomly selected. Prescription doses for primary PTVs were 50.4Gy for 4 patients and 54Gy for 3 patients in 1.8Gy per fraction. The PTVs ranged from 612 to 999 cc. The MCO plans were retrospectively generated with a universal set of standardized constraints and objectives that were used clinically. Both plans were blindly presented to an MD for final review. Finally, DMPO and MCO based plans were evaluated using dose-volume constraints for target conformity (CI), homogeneity (HI) and critical structures.
Results: The differences between PTV HI for MCO and DMPO based VMAT plans were not statistically significant; ranging from 1.03 to 1.11. The target conformity for both techniques were identical. For all patients, the critical structure maximum doses such as cord, brainstem, mandible, cochlea’s were satisfactory with both techniques. For both parotids, MCO generated significantly lesser average doses as compared to DMPO (P≤0.05). Although all critical structures constraints were met with both techniques, low dose portion of the DVH for most of the critical structures were much lower for MCO plans as compared to DMPO.
Conclusion: MCO HN VMAT plans obtained with standardized objectives and constraints generated plans similar to DMPO with better low dose conformity
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