A component-wise commissioning and validation framework for non-transit electronic portal imaging device patient-specific quality assurance.

Abstract

Background and purpose The American Association of Physicists in Medicine Task Group 307 (AAPM TG-307) recommends validation of electronic portal imaging device (EPID) patient-specific quality assurance (PSQA), including verification of measured and calculated components. This study established a TG-307-aligned commissioning and benchmarking framework for non-transit EPID pre-treatment PSQA. Material and methods Fraction Zero Absolute Dose (FZAD) was commissioned on two TrueBeam linear accelerators equipped with amorphous silicon (aS) aS1000 and aS1200 EPIDs across flattened and flattening filter-free (FFF) photon beams (6MV/10MV) and two multi-leaf-collimator models. EPID performance was characterised for dose-rate linearity. Independent validation of measured and predicted dose components was performed using ion chamber, phantom-based, and treatment planning system dose planes in geometry replicating EPID configuration. System performance was benchmarked against Portal Dosimetry (PDIP) and phantom-based PSQA across >800 clinical fields. Error-detection sensitivity was evaluated using receiver operating characteristic (ROC) analysis of externally supplied audit plans. Results The aS1200 panel was linear across dose-rate and source-to-imager distance (SID) conditions, whereas the aS1000 exhibited saturation for FFF beams at shorter SIDs, with up to 5% under-response, with linearity restored at ≥150 cm SID. Independent component validation achieved mean gamma pass rates ≥97% (3%/2 mm). Bland-Altman analysis showed concordance within 95% limits of agreement, supporting equivalence in clinical decision-making. Sensitivity testing demonstrated discrimination at 2%/2 mm (area under ROC curve of 0.886), with improved detection compared to phantom-based PSQA at high specificity. Conclusions A TG-307-aligned framework enables component-level interpretability and actionable insight for tolerance definition and model optimisation of EPID PSQA.