RefleXion X1 planning
CT scans and structure sets used for VMAT CSI plan generation were imported to RefleXion X1 TPS for planning. The PTV_CSI target ranged between 48.1-49.3 cm and was the same for VMAT and X1 planning. All patients were planned on the RefleXion X1 v1.0.46 TPS using step-and-shoot IMRT technique with 6 MV FFF (energy, 2 cm jaws, accelerated proximal gradient based on FISTA algorithm and Collapsed Cone Convolution (CCC) superposition dose calculation algorithm, and a calculation grid of 2.1 mm. Plan isocenter was placed in the middle of the target. As plan dose normalization was not available in RefleXion X1 v1.0.46, each plan was optimized to allow for 95% of the PTV to receive the prescription dose (36 Gy in 20 fractions).