VMAT CSI planning
VMAT CSI plans were generated on Eclipse v15.6 (Varian Medical Systems, Palo Alto, CA) using 6 MV energy beams, Photon Optimization (PO) algorithm, Analytical Anisotropic Algorithm (AAA) dose calculation, and a calculation grid of 2.5 mm. Two full arcs were used to treat the brain and a single arc was used to treat the spine, with an overlap of at least 2 cm between the brain and spine fields. Brain and Spine isocenters were placed such that there was only longitudinal shift between them. Auto-feathering was enabled during optimization to create smooth dose gradients in the overlapping areas between fields. The spine arcs used avoidance sectors to limit dose entering through the arms. VMAT CSI plans were normalized at 95% PTV coverage by the prescription dose of 36 Gy.