Clinical applications of the Halcyon O-ring linear accelerator in radiation therapy: a systematic review of treatment efficacy, workflow efficiency, and imaging integration.

Abstract

Background and purposeThe Varian Halcyon is an O-ring gantry linear accelerator designed to streamline radiotherapy delivery through automated workflow and integrated image guidance. This systematic review evaluated its clinical applications across treatment efficacy, workflow efficiency, and imaging integration.MethodsA PRISMA-based systematic review was conducted using Scopus, PubMed, and Web of Science Core Collection through August 4, 2026. Studies were included if they evaluated patient treatments delivered on or planned with Halcyon and provided clinically transferable evidence across at least two predefined domains. Fifty studies met the eligibility criteria.ResultsHalcyon generally achieved clinically acceptable target coverage and organ-at-risk sparing across diverse applications. Shorter delivery-related times were frequently reported, particularly for routine coplanar VMAT, although workflow advantages were less consistent for stereotactic, multi-isocenter, craniospinal, and total-body treatments. Integrated kV-CBCT and MV-CBCT supported daily setup verification, treatment monitoring, and dose assessment. Newer CBCT technologies demonstrated improved image quality, Hounsfield Unit fidelity, and technical feasibility for contouring and dose recalculation. However, the evidence was dominated by planning studies, retrospective analyses, technical validation, and surrogate endpoints. Advantages were less consistent when noncoplanar geometry, steep dose gradients, rotational correction, repeated imaging, or large or elongated targets were required.ConclusionHalcyon appears most useful when acceptable plan quality, efficient delivery, and integrated image guidance align within a standardized coplanar workflow. Its advantages are context-dependent, and platform selection should reflect the clinical indication and complete treatment workflow rather than assumed universal superiority.