ESTRO 2024 - Abstract Book

S4773

Physics - Quality assurance and auditing

ESTRO 2024

References:

1. Mobius3D Commissioning Quick Start Guide. Varian Medical Systems, Inc.

2. Shepard, A.J. and Frigo, S.P., 2021. Characteristics and limitations of a secondary dose check software for VMAT plan calculation. Journal of Applied Clinical Medical Physics, 22(3), pp.216-223.

3. McDonald, D.G., Jacqmin, D.J., Mart, C.J., Koch, N.C., Peng, J.L., Ashenafi, M.S., Fugal, M.A. and Vanek, K.N., 2017. Validation of a modern second ‐ check dosimetry system using a novel verification phantom. Journal of Applied Clinical Medical Physics, 18(1), pp.170-177.

770

Proffered Paper

Vendor-independent validation of the MR-to-MV isocentre shift at two MRI-linacs

Hans Lynggaard Riis 1,2 , Adriaan Fietje 3 , Benny Clifford Buthler 1 , Anders Smedegaard Bertelsen 1 , Rasmus Lübeck Christiansen 1 , Kenni Højsgaard Engstrøm 1 , Adam Johansson 4,5 , David Tilly 4,5 , Carsten Brink 1,2 , Uffe Bernchou 1,2 1 Odense University Hospital, Department of Oncology, Odense, Denmark. 2 University of Southern Denmark, Department of Clinical Research, Odense, Denmark. 3 Elekta Instrument AB, Service Department, Stockholm, Sweden. 4 Uppsala University, Department of Immunology, Genetics and Pathology, Uppsala, Sweden. 5 Uppsala University Hospital, Medical Physics, Uppsala, Sweden

Purpose/Objective:

A safe clinical application of magnetic resonance imaging (MRI)-linacs involves frequent quality assurance (QA) on the relative location of the MRI scanner and the linac megavoltage (MV) isocentre. A relative translation that is not adequately accounted for could result in systematic mistreatment of all patients. For the 1.5 T MRI-linac, the vendor has provided a specialised phantom and software for evaluating the mutual positions of the two isocentres. Previous investigations indicate that the MR-to-MV isocentre shift applied in the treatment planning system (TPS) by the vendor results in dose delivery errors between 0.2 and 0.7 mm in the anterior posterior direction[1,2]. Therefore, the aim of this study was to create a vendor-independent method for relative isocentre shift QA.

Material/Methods:

Two 1.5 T Elekta Unity MRI-linacs were investigated using an in-house developed cylindrical water-filled ∅ 40 mm phantom with an insert consisting of a stick holding a zirconium oxide (ZrO 2 ) sphere of ∅ 8 mm, see figure 1. The left-