ArticleJournal of applied clinical medical physics2026
The geometric accuracy of off-axis targets in stereotactic body radiotherapy treatments across three linear accelerators.
Article in Journal of applied clinical medical physics, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 1 paper.
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1 citing paper in PubMed.
- The geometric accuracy of off-axis targets in stereotactic body radiotherapy treatments across three linear accelerators.Journal of applied clinical medical physics · 2026Article
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2 authors.
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Abstract
purposeThis study quantifies isocenter and off-axis geometric uncertainties using MultiMet Winston-Lutz (WL) tests to optimize gross tumour volume (GTV)-to-PTV (planning target volume) margin for single isocenter multiple target (SIMT) stereotactic body radiotherapy (SBRT) across three linear accelerators. METHODS AND MATERIALS: Geometric inaccuracies were quantified for Trilogy (HD-MLC, 6 MV SRS), TrueBeam (Millennium MLC), and TrueBeam STx (HD-MLC, 6-degrees-of-freedom (6DoF) couch) using a Sun Nuclear MultiMet-WL cube containing six tungsten carbide markers arranged along the superior-inferior axis. The electronic portal imaging device (EPID) images acquired at four cardinal gantry angles with varied collimator/couch rotations were analyzed using MultiMet-WL software (v2.1) to measure 3D (Δ) displacements for all the LINACs. The required GTV-to-PTV margins were calculated using a modified van Herk formula (2.5Σ+1.64σ), incorporating measured 3D displacements for isocenter and off-axis targets.
resultsThe TrueBeam STx (HD-MLC/6DoF) demonstrated superior geometric accuracy, maintaining ≤0.5 mm isocenter precision and ≤0.59 mm off-axis targeting (3-7 cm). The Trilogy exceeded TG-142 tolerances (1.06 ± 0.59 to 1.09 ± 0.57 mm) at all targets, requiring 4 mm uniform margins, while the TrueBeam (MMLC) showed optimal variations (isocenter: 0.68 ± 0.34 mm; superior off-axis: 0.74 ± 0.36 mm). Both TrueBeam platforms achieved sub-millimeter accuracy but demonstrated direction dependency for off-axis targets, requiring 2-3 mm anisotropic margins. Notably, isotropic margins introduced up to 11% delineation errors for off-axis targets due to these machine-specific geometric variations, highlighting the imperative for platform-specific margin protocols in SIMT SBRT.
conclusionThis study demonstrates that routine analysis of MultiMet WL testing is an essential tool for the spatial accuracy of the LINAC to establish machine-specific PTV margin expansion in SIMT-SBRT, particularly for targets where rotational errors dominate.
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