Room: Exhibit Hall
Purpose: To evaluate the planning and delivery performance of the Halcyonâ„¢ V2 for the treatment of multiple small cranial targets with a single-isocenter as compared to the Halcyonâ„¢ V1 and noncoplanar Multi-Aperture Dynamic Conformal Arc (DCA).
Methods: 10 patients were retrospectively studied, each with 6-10 targets with volumes from 0.11 to 8.57cc. VMAT plans were created for the Halcyonâ„¢ V1 (1cm leaf width) and Halcyonâ„¢ V2 (dual-layer modulation with 0.5cm effective resolution) and compared with the clinical noncoplanar DCA plan generated with Truebeam HDMLC. All Halcyonâ„¢ plans were coplanar due to machine limitation. Conformity Index (CI), gradient index (GI), V12Gy, V6Gy, V3Gy, and brain mean dose were compared. Additionally, the platform efficiency was compared analyzing optimization time, delivery time, and total MU.
Results: Halcyonâ„¢ V2 showed improved CI compared to V1 for targets with a diameter <1cm, and performed similarly in almost all parameters. Compared to the DCA plan, Halcyonâ„¢ V2 exhibited a superior CI for targets >1cm in diameter but an inferior CI for smaller targets. The DCA plan exhibited a superior GI for all targets. V12Gy, V3Gy, and brain mean dose were similar. All plans met clinical constraints for critical structures. Halcyonâ„¢ VMAT optimization took twice as long as Truebeam VMAT plans. The total required MUs were approximately 7500 and 12000 MU for the DCA and Halcyonâ„¢ plans, respectively, with an estimated delivery time of approximately 15 minutes for each considering dose rate and couch rotation time.
Conclusion: Halcyonâ„¢ V2 improved dose conformity for small targets (<1cm) compared to V1, and achieved better CI for large targets using VMAT compared to DCA. GI for Halcyonâ„¢ is inferior to DCA, likely due to the coplanar limitation. Overall, the planning performance of the Halcyonâ„¢ V2 system is clinically acceptable for targets > 0.7cm.