Characterizing geometrical accuracy in clinically optimised 7T and 3T magnetic resonance images for high-precision radiation treatment of brain tumours

Jurgen Peerlings; Inge Compter; Fiere Janssen; Christopher J Wiggins; Alida A Postma; Felix M Mottaghy; Philippe Lambin; Aswin L Hoffmann

doi:10.1016/j.phro.2018.12.001

Characterizing geometrical accuracy in clinically optimised 7T and 3T magnetic resonance images for high-precision radiation treatment of brain tumours

Phys Imaging Radiat Oncol. 2019 Jan 3:9:35-42. doi: 10.1016/j.phro.2018.12.001. eCollection 2019 Jan.

Authors

Jurgen Peerlings^{1

2}, Inge Compter¹, Fiere Janssen¹, Christopher J Wiggins³, Alida A Postma², Felix M Mottaghy^{2

4}, Philippe Lambin¹, Aswin L Hoffmann^{1

5

6

7}

Affiliations

¹ Department of Radiation Oncology (MAASTRO), GROW - School for Oncology and Developmental Biology, Maastricht University Medical Centre+, Maastricht, The Netherlands.
² Department of Radiology and Nuclear Medicine, Maastricht University Medical Centre+, Maastricht, The Netherlands.
³ Scannexus BV, Maastricht, The Netherlands.
⁴ Department of Nuclear Medicine, University Hospital RWTH Aachen University, Aachen, Germany.
⁵ Institute of Radiooncology, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany.
⁶ OncoRay National Center for Radiation Research in Oncology, Dresden, Germany.
⁷ Department of Radiotherapy, University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany.

Abstract

Background and purpose: In neuro-oncology, high spatial accuracy is needed for clinically acceptable high-precision radiation treatment planning (RTP). In this study, the clinical applicability of anatomically optimised 7-Tesla (7T) MR images for reliable RTP is assessed with respect to standard clinical imaging modalities.

Materials and methods: System- and phantom-related geometrical distortion (GD) were quantified on clinically-relevant MR sequences at 7T and 3T, and on CT images using a dedicated anthropomorphic head phantom incorporating a 3D grid-structure, creating 436 points-of-interest. Global GD was assessed by mean absolute deviation (MAD_Global). Local GD relative to the magnetic isocentre was assessed by MAD_Local. Using 3D displacement vectors of individual points-of-interest, GD maps were created. For clinically acceptable radiotherapy, 7T images need to meet the criteria for accurate dose delivery (GD < 1 mm) and present comparable GD as tolerated in clinically standard 3T MR/CT-based RTP.

Results: MAD_Global in 7T and 3T images ranged from 0.3 to 2.2 mm and 0.2-0.8 mm, respectively. MAD_Local increased with increasing distance from the isocentre, showed an anisotropic distribution, and was significantly larger in 7T MR sequences (MAD_Local = 0.2-1.2 mm) than in 3T (MAD_Local = 0.1-0.7 mm) (p < 0.05). Significant differences in GD were detected between 7T images (p < 0.001). However, maximum MAD_Local remained ≤1 mm within 68.7 mm diameter spherical volume. No significant differences in GD were found between 7T and 3T protocols near the isocentre.

Conclusions: System- and phantom-related GD remained ≤1 mm in central brain regions, suggesting that 7T MR images could be implemented in radiotherapy with clinically acceptable spatial accuracy and equally tolerated GD as in 3T MR/CT-based RTP. For peripheral regions, GD should be incorporated in safety margins for treatment uncertainties. Moreover, the effects of sequence-related factors on GD needs further investigation to obtain RTP-specific MR protocols.

Keywords: Anthropomorphic phantom; Diametric spherical volume; Geometrical distortion; Neuro-oncology; Radiation treatment planning; Ultra-high field MRI.