Standardizing MRI Image Quality QA for Gamma Knife SRS and Fsrs across a Multicampus Radiation Medicine Network
Abstract
Purpose
Gamma Knife (GK) stereotactic radiosurgery (SRS) and fractionated SRS (fSRS) planning require high-fidelity MRI for accurate target delineation with minimal planning margins. This work evaluates MRI image quality across diagnostic MRI systems using GK scanning parameters and ACR phantom methods to support a standardized, centralized, vendor-independent QA workflow.
Methods
ACR MRI phantom scans were acquired on 1.5 T MRI systems across multiple campuses and vendors. Primary acquisitions used GK planning sequences and stereotactic parameters (1 mm slice thickness, 256×256 matrix, no overlap or angulation), including sequences T1 MPRAGE, T2, T2 FRFSE, and T2 FIESTA. At one site, an additional phantom scan was acquired using standard ACR parameters (5 mm slice thickness) to assess protocol dependence. Four ACR image-quality metrics were evaluated: high-contrast spatial resolution (HCSR), image intensity uniformity (IIU), percent signal ghosting (PSG), and low-contrast object detectability (LCOD).
Results
HCSR achieved 1.0 mm for most sequences, with one scanner resolving 0.9 mm. IIU met acceptance criteria for all scans and ranged from 0.8895–0.9600 for GK protocols; the ACR acquisition demonstrated IIU of 0.9586. PSG ranged from 0.090%–1.461% across GK protocols and remained below 2.5%, with the highest PSG in T2 FRFSE (1.461%). LCOD showed full detectability at higher contrast levels; at 1.4% contrast, most sequences resolved 10/10 spokes, while the T2 GK protocol resolved 9/10 spokes. PSG differed between GK protocols (T1 MPRAGE 0.384%; T2 0.714%) and the ACR acquisition (0.278%).
Conclusion
All MRI systems satisfied ACR acceptance thresholds under GK planning parameters, though sequence- and protocol-dependent variability was observed. Comparison of GK versus ACR acquisitions suggests protocol selection can affect low-contrast performance even within ACR limits. These findings support GK sequence-specific baselines and internal action limits, consistent with AAPM TG-178 and TG-284, to harmonize MRI performance across campuses for SRS/fSRS planning.