ArticleJournal of applied clinical medical physics2026
Clinical implementation and performance evaluation of a motorized MR-compatible OCTAVIUS 4D system for SBRT patient-specific QA on a 1.5 T MR-LINAC.
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. Not yet cited in PubMed.
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Abstract
backgroundMagnetic resonance-guided radiotherapy using 1.5 T MR-LINAC systems introduces specific constraints for patient-specific quality assurance (PSQA), requiring MR-compatible dosimetric devices capable of accurate three-dimensional dose verification. While previous studies have characterized the dosimetric performance of MR-compatible detector arrays, the clinical implementation of rotational three-dimensional QA systems in MR-guided workflows remains insufficiently documented. PURPOSE: This study investigated the clinical implementation and practical performance of a motorized MR-conditional OCTAVIUS 4D system for stereotactic body radiotherapy (SBRT) PSQA on a 1.5 T MR-LINAC.
methodsThe MR-conditional OCTAVIUS 4D phantom equipped with a 1500 MR ionization chamber array was implemented for PSQA measurements on a Unity 1.5 T MR-LINAC (Elekta, Stockholm, Sweden). A total of 40 clinical step-and-shoot treatment plans were analyzed with an SBRT prescription. The system was evaluated in terms of three-dimensional dose reconstruction accuracy under clinically relevant off-axis condition, angular positioning consistency with the gantry positioning, and integration into clinical workflow. Measured dose distributions were compared with treatment planning system (TPS) calculations using a 3D gamma analysis with a local 2.5%/2.5 mm criterion and a 10% dose threshold. Independent angular measurements were additionally performed using a digital inclinometer.
resultsThe system demonstrated high agreement between measured and calculated dose distributions, with a mean gamma passing rate of 98.3% (local 2.5%/2.5 mm). All plans met institutional acceptance criteria (GPR ≥ 95%). Independent angular measurements demonstrated excellent agreement between gantry angle, phantom angle, and software-reported angle, with deviations below 0.6° and no systematic bias observed. No visible dependence of gamma passing rate on radial off-axis target positioning was observed within the investigated clinical range. The evaluated beam arrangements included irregular angular spacing and clockwise/counterclockwise gantry transitions during delivery, supporting effective synchronization between the OCTAVIUS 4D MR system and the Unity gantry under clinical step-and-shoot conditions.
conclusionsThe motorized MR-conditional OCTAVIUS 4D system demonstrated clinically feasible implementation for rotational three-dimensional PSQA for SBRT on a 1.5 T MR-LINAC. The system provided consistent dose reconstruction accuracy and reliable angular positioning under clinically relevant delivery conditions, supporting its integration into routine MR-guided radiotherapy QA workflows.
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