Dosimetric Comparison of Volumetric Modulated Arc Therapy Treatment Plans using Pareto and Constrained Modes of Optimization with Monaco Treatment Planning System for Left Breast Cancer with Breast Conserving Surgery

Introduction: Volumetric Modulated Arc Therapy (VMAT) is an advanced method of radiation therapy with increased flexibility in intensity modulation. The study aims to compare the dosimetric outcomes of VMAT treatment plans generated using Pareto and Constrained modes of optimization for left breast cancer with breast-conserving surgery (BCS). Material and Methods: We carried out a retrospective study of twenty female patients who underwent BCS for left breast cancer. VMAT treatment plans were generated using two optimization modes, Pareto and Constrained, on the Monaco (version 5.11.03) treatment planning system (TPS), with a single arc of 6MV x-ray photon beam from Elekta Versa HD linear accelerator (linac). The prescribed dose was 42.56 Gray (Gy) in 16 fractions to the PTV. Dosimetric parameters, such as the target volume coverage, organs at risk (OARs) doses, homogeneity index (HI), as well as conformity index (CI), were studied and compared between the two modes of optimization using the Wilcoxon signed-rank test (Jamovi 2.3.26). Results: The study showed that the Pareto mode of optimization within VMAT gave superior outcomes, with increased coverage of the target and comparable OAR doses. However, there is a slight increase in the volume receiving 107% of the prescribed dose (V107), maximum dose (Dmax) within the target volume, and monitor units (MU); the HI and CI show excellent performance. Conclusion: This study suggests that Pareto mode optimization in VMAT is a preferable and superior approach for left breast cancer patients undergoing BCS.