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

摘要

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 (MADsubGlobal/sub). Local GD relative to the magnetic isocentre was assessed by MADsubLocal/sub. 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 MADsubGlobal/sub in 7T and 3T images ranged from 0.3 to 2.2?mm and 0.2–0.8?mm, respectively. MADsubLocal/sub increased with increasing distance from the isocentre, showed an anisotropic distribution, and was significantly larger in 7T MR sequences (MADsubLocal/sub?=?0.2–1.2?mm) than in 3T (MADsubLocal/sub?=?0.1–0.7?mm) (p??0.05). Significant differences in GD were detected between 7T images (p??0.001). However, maximum MADsubLocal/sub 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.