One-Shot Automated Constancy Testing of Halcyon Kv Planar Imaging with Phantom Metrics and Entrance-Dose Tracking
Abstract
Purpose
To develop and clinically evaluate an automated, objective monthly constancy-testing workflow for Halcyon kV planar imaging using a single service-mode acquisition of a PTW NORMI 4 FLU phantom combined with an external entrance-dose measurement (PTW CONNY II), aligned with AAPM recommendations for accelerator imaging QA implementation and imaging-dose management (TG-142/TG-198/TG-75) and using a geometry–image-quality–dose constancy concept (TG-179).
Methods
Monthly kV XI images were acquired in service mode (125 kV, 20 mA, 20 ms, 1×1 binning; system-reported dose 0.036 mGy). A Python pipeline imports the XIM image, performs rigid registration to a baseline, applies fixed ROIs, and automatically extracts: (i) spatial resolution from the line-pair test pattern (limiting resolution, lp/mm); (ii) gray-scale/dynamic range from the step wedge by verifying visibility and separation across all 17 steps; (iii) geometric constancy from predefined distance measurements; and (iv) entrance dose using CONNY II positioned in front of the phantom. The submitted overview figure documents the ROIs and measurement geometry (line, arc, and distance overlays). Results are exported as a standardized PDF and appended to date-sorted CSV and Excel (XLSX) logs for trending.
Results
Over >6 months of monthly measurements, the automated analysis consistently detected all 17 step-wedge levels and reported limiting spatial resolution of 1.2–1.4 lp/mm. Measured entrance dose differed by 0–11% relative to the system-reported value. Geometric distance metrics remained stable over time with no systematic drift.
Conclusion
A single Halcyon kV service-mode acquisition enables fully automated, observer-independent extraction of key imaging-QA parameters (resolution, gray-scale/dynamic range, geometry, and dose) with standardized reporting and longitudinal trend tracking.