Characterization of high-resolution detector response for stereotactic patient-specific QA across different TPS-linac...

This study aimed to characterize the response and inter-system consistency of a high-resolution myQA SRS detector used for patient-specific quality assurance (PSQA) across different configurations of treatment planning system and linear accelerator (TPS-linac). A total of 20 clinically approved stereotactic radiosurgery / stereotactic body radiotherapy (SRS/SBRT) cases were included in a paired-study design to eliminate patient-specific anatomical bias. Each case was re-optimized on both Monaco-Versa HD (Agility 160 MLC) and Eclipse-TrueBeam STx (HD120 MLC) platforms, resulting in 40 unique plans. Doses from all plans were measured using the myQA SRS detector, with TrueBeam-based plans additionally verified via an electronic portal imaging device (EPID) for comparative detector analysis. Gamma passing rates (GPRs) (2%/1 mm to 3%/2 mm) and plan complexity metrics, including monitor units (MUs), segment number, and Modulation Factor (MF), were evaluated using non-parametric statistics. For the myQA SRS, mean GPRs ranged from 85.1% to 95.5% for Monaco and 80.6% to 92.9% for Eclipse, with no statistically significant differences observed between platforms (p > 0.05). Spearman's analysis confirmed that plan complexity did not correlate with QA outcomes (p > 0.05), indicating that the detector's response remains independent of modulation levels within clinical ranges. Comparative analysis between myQA SRS and EPID revealed systematic detector-dependent differences that became more pronounced at wider gamma criteria. Isolated low-passing outlier cases, associated with very small targets in steep dose-gradient regions, were observed for both detectors and were analyzed separately. Overall, the myQA SRS detector demonstrated high inter-system consistency, and appears to be a robust tool for PSQA of highly modulated stereotactic plans. The findings suggest that PSQA outcomes are more influenced by system-specific modelling and detector characteristics than by plan complexity alone.