An innovative hippocampal-sparing whole-brain radiotherapy planning approach via the Halcyon system: achieving lower hippocampal doses

Objective To evaluate the feasibility and dosimetric benefits of Halcyon-based coplanar dual-arc volumetric modulated arc therapy (VMAT) for hippocampal-avoidance whole brain radiotherapy (HA-WBRT). Methods Twenty-one HA-WBRT patients were replanned using dual-arc VMAT (collimator 23°/293°) on Halcyon and Truebeam. The planning target volume (PTV) was segmented into three substructures and optimized with different weight parameters. Dosimetric parameters of PTV, monitor units (MUs), does to organs-at-risk(OARs), hippocampal normal tissue complication probability (NTCP) and gamma passing rate were recorded. Results All plans met RTOG 0933 criteria. The Halcyon plans demonstrated significantly better homogeneity index (HI) and V 30Gy of the PTV (HI: 0.105 vs. 0.121, P <0.001; V 30Gy : 97.1% vs. 96.3%, P <0.001), alongside reduced hippocampal dose (D 100% : 626.8 vs. 695.0cGy; D mean : 850.0 vs. 898.4cGy; D max : 1348.1 vs. 1399.8 cGy; NTCP: 34.16% vs. 31.67%, P ≤ 0.001), OARs sparing improved for Lens D max (495.0 vs. 525.8cGy, P = 0.001), Optic nerves D max (3047.7 vs. 3077.6cGy, P = 0.006), and eyes D mean (927.1 vs. 937.9cGy, P = 0.009). The average gamma passing rates were higher for Halcyon than Truebeam (3%/2mm: 99.96% vs. 99.85; 2%/2mm: 99.83% vs. 99.49%). Conclusions Under the innovative planning approach, redefined hippocampal-sparing radiotherapy using Halcyon system, providing superior prescription dose coverage, improved OAR sparing, and reduced hippocampal NTCP.