Abstract
This study presents a comparative dosimetric and efficiency analysis of volumetric modulated arc therapy (VMAT) for large planning target volumes (PTVs) (≥1000 cm³), contrasting plans from a flattening filter-free (FFF) Halcyon system with a conventional flattened filter (FF) Clinac iX. Retrospective plans for 11 rectal cancer patients were evaluated for key dosimetric parameters, monitor unit (MU) requirements, and treatment times. While all plans achieved comparable PTV coverage, FF plans demonstrated marginally superior dose homogeneity. Conversely, Halcyon's FFF plans yielded superior organ-at-risk (OAR) sparing, demonstrating a statistically significant reduction in mean OAR doses. Despite necessitating a substantial MU increase, the 3-arc VMAT treatment time was reduced by approximately 62% versus the conventional FF platform. In conclusion, for large-volume PTVs, Halcyon-based FFF VMAT offers equivalent target coverage with enhanced OAR sparing and markedly accelerated delivery, establishing it as a highly efficient and clinically valuable modality.