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A component-wise commissioning and validation framework for non-transit electronic portal imaging device
Leyla Moghaddasi1,2, Mario Perez1, Maegan Stewart1,3
1Northern Sydney Cancer Centre, Royal North Shore Hospital, Sydney, New South Wales, Australia.
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.
