Dosimetric performance of the Elekta Unity MR-linac system: 2D and 3D dosimetry in anthropomorphic inhomogeneous geometry.

Dosimetric performance of the Elekta Unity MR-linac system: 2D and 3D dosimetry in anthropomorphic inhomogeneous geometry. Phys Med Biol. 2019 Oct 30;: Authors: Pappas E, Kalaitzakis G, Boursianis T, Zoros E, Zourari K, Pappas EP, Makris DN, Seimenis I, Efstathopoulos EP, Maris TG Abstract Following the clinical introduction of the Elekta Unity MR-linac, there is an urgent need for development of dosimetry protocols and tools, not affected by the presence of magnetic field. This work presents a benchmarking methodology comprising 2D/3D passive dosimetry and involving on-couch adaptive treatment planning, a unique step in MR-linac workflows. Two identical commercially available 3D-printed head phantoms (featuring realistic bone anatomy and MR/CT contrast) were employed. One phantom incorporated a film dosimetry insert, while the second was filled with polymer gel. Gel dose-response characteristics were evaluated under the Unity irradiation and read-out conditions, using vials and a cubic container filled with gel from the same batch. Treatment plan for the head phantoms involved a hypothetical large C-shape brain lesion, partly surrounding the brainstem. An IMRT step-and-shoot 7-beam plan was employed. Pre-treatment on-couch MR-images were acquired in order for the treatment planning system to calculate the virtual couch shifts and perform adaptive planning. Absolute 2D and relative 3D measurements were compared against calculations r...
Source: Physics in Medicine and Biology - Category: Physics Authors: Tags: Phys Med Biol Source Type: research