Evaluation of a novel software application for magnetic resonance distortion correction in cranial stereotactic radiosurgery

This study aimed to validate a novel commercially available software for correcting spatial distortion in cranial magnetic resonance (MR) images. This software has been used to assess the dosimetric impact of MR distortion in stereotactic radiosurgery (SRS) treatments of vestibular schwannomas (VSs). Five MR datasets were intentionally distorted. Each distorted MR dataset was corrected using the Cranial Distortion software, obtaining a new corrected MR dataset (MRcorr). The accuracy of the correction was quantified by calculating the target registration error (TRE) for 6 anatomical landmarks identified in the co-registered MRcorr and planning computed tomography (pCT) images. Nine VS cases were included to investigate the impact of the MR distortion in SRS plans. Each SRS plan was calculated on the pCT (1 x 1 x 1 mm(3) voxel) with the target and organs at risk (OARs) delineated using the planning MR dataset. This MR dataset was then corrected (MRcorr) using the Cranial Distortion software. Geometrical agreement between the original target and the corresponding corrected target was assessed using several metrics: MacDonald criteria, mean distance to agreement (MDA), and Dice similarity coefficient (DSC). Target coverage (D99%) and maximum doses (D2%) to ipsilateral cochlea and brainstem resulting on the MRcorr dataset were compared with the original values. TRE values (0.6 mm +/- 0.3 mm) and differences found in Macdonald criteria (0.3 mm +/- 0.4 mm and 0.3 mm +/- 1 0.3 mm) and MDA (0.8 mm +/- 0.2 mm) were mostly within the voxel size dimension of the pCT scan (1 x 1 x 1 mm(3)). High similarity (DSC > 0.7) between the original and corrected targets was found. Small dose differences for the original and corrected structures were found: 0.1 Gy +/- 0.1 Gy for target D99%, 0.2 Gy +/- 10.3 Gy for cochlea D2%, and 0.1 Gy +/- 0.1 Gy for brainstem D2%. Our study shows that Distortion Correction software can be a helpful tool to detect and adequately correct brain MR distortions. However, a negligible dosimetric impact of MR distortion has been detected in our clinical practice. (C) 2018 American Association of Medical Dosimetrists. Published by Elsevier B.V. All rights reserved.