ArticleJournal of applied clinical medical physics2025
Application of a model-based water-equivalent EPID image conversion algorithm for linac beam QA.
Article in Journal of applied clinical medical physics, 2025. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 3 papers.
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3 citing papers in PubMed.
- A component-wise commissioning and validation framework for non-transit electronic portal imaging device patient-specific quality assurance.Physics and imaging in radiation oncology · 2026Article
- Sensitivity and concordance study of an open source EPID-based linear accelerator test suite.Journal of applied clinical medical physics · 2026Article
- Application of a model-based water-equivalent EPID image conversion algorithm for linac beam QA.Journal of applied clinical medical physics · 2025Article
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2 authors.
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Abstract
purposeThe nonwater-equivalent energy response of electronic portal imaging devices (EPIDs) is a major obstacle to using them for linear accelerator (linac) beam parameter verification. In this study, we propose an EPID-based machine quality assurance (QA) application that uses a model-based radiation transport algorithm to convert EPID-measured images into water-equivalent dose distributions that can be used to assess beam flatness and symmetry.
methodsAn in-house developed, model-based radiation transport algorithm was used to estimate the incident beam fluence from measured EPID images and convert it into either 3D dose distributions in a virtual water tank or 2D water-equivalent dose distributions in a virtual ion chamber array. The conversion algorithm was validated using independent measurements in a scanning water tank and a reference ion chamber array under symmetric and also intentionally detuned (i.e., asymmetric) beam conditions.
resultsFor symmetric fields, EPID-reconstructed percentage depth dose distributions (PDDs) agreed with water tank measurements to within 1% beyond the first 10 mm of depth. Beam profile comparisons showed differences within 1% in low dose-gradient regions. For all symmetric and intentionally asymmetric fields, beam flatness and symmetry derived from reconstructed images agreed with reference measurements to within 0.2% and 0.3%, respectively. The model demonstrated high sensitivity to the controlled beam asymmetries and steering distortions, with EPID-reconstructed metrics closely matching reference water-equivalent measurements and significantly outperforming metrics derived from raw EPID images.
conclusionsThe proposed model-based algorithm enables accurate conversion of EPID images into water-equivalent dose distributions, facilitating accurate determination of beam flatness and symmetry. This application addresses some limitations of the previously proposed EPID-based linac QA techniques, which are limited to nonwater-equivalent constancy checks, and supports the use of EPIDs as robust dosimetry tools for linac radiation beam parameter verification.
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