Contralateral tissue sparing in lymph node-positive breast cancer radiotherapy with VMAT technique

Abstract The objective of this study was to modify volumetric modulated arc therapy (VMAT) design for breast irradiation with axillary lymph node involvement to enhance normal tissue sparing while maintaining good planning target volume (PTV) coverage. Four VMAT plans were generated retrospectively for 10 patients with breast cancer for comparison. First, 2 partial arcs with an avoidance sector (Pavoid) for the lung and the heart were created. Second, a split-arc design with 2 partial arcs was used, changing the collimator angle by splitting the arcs in the middle, resulting in 4 partial arcs (Psplit). Third, the arc angles in the Psplit were modified to emphasize tangential directions, corresponding to the avoidance sector in Pavoid, resulting in 2 lateral and 2 anterior partial arcs. Furthermore, a fifth arc was added to ensure the coverage of axillary lymph nodes (Ptang). Fourth, one of the anterior arcs was removed to limit the number of arcs during treatment (Ptang-1). PTV coverage was the highest in Psplit with a V90%(PTV) of 98.4 ± 0.6%. Also the dose homogeneity and conformity were the best ( p