Impact of MRI resolution for Linac-based stereotactic radiosurgery

Abstract

ObjectiveMagnetic resonance imaging (MRI) is a standard imaging modality in intracranial stereotactic radiosurgery (SRS) for defining target volumes. However, wide disparities in MRI resolution exist, which could directly impact accuracy of target delineation. Here, sequences with various MRI resolution were acquired on phantoms to evaluate the effect on volume definition and dosimetric consequence for cranial SRS.Materials/MethodsFour T1-weighted MR sequences with increasing 3D resolution were compared, including two Spin Echo (SE) 2D acquisitions with 5mm and 3mm slice thickness (SE5mm, SE3mm) and two gradient echo 3D acquisitions (TFE, BRAVO). The voxel sizes were 0.4×0.4×5.0, 0.5×0.5×3.0, 0.9×0.9×1.25, and 0.4×0.4×0.5 mm3, respectively. Four phantoms with simulated lesions of different shape and volume (range, 0.53–25.0 cm3) were imaged, resulting in 16 total sets of MRIs. Four radiation oncologists provided contours on individual MR image set. All observer contours were compared with ground truth, defined on CT image according to the absolute dimensions of the target structure, using Dice similarity coefficient (DSC), Hausdorff distance (HD), mean distance-to-agreement (MDA), and the ratio between reconstructed and true volume (Ratiovol). For dosimetric consequence, SRS plans targeting observer volumes were created. The true Paddick conformity index (CIpaddicktrue), calculated with true target volume, was correlated with quality of observer volume.ResultsAll measures of observer contours improved as increasingly higher MRI resolution was provided from SE5mm to BRAVO. The improvement in DSC, HD and MDA was statistically significant (p<0.01). Dosimetrically, CIpaddicktrue strongly correlated with DSC of the planning observer volume (Pearson’s r=0.94, p<0.00001).ConclusionsSignificant improvement in target definition and reduced inter-observer variation was observed as the MRI resolution improved, which also improved the quality of SRS plans. Results imply that high resolution 3D MR sequences should be used to minimize potential errors in target definition, and multi-slice 2D sequences should be avoided.

Improvement of 2D cine image quality using 3D priors and cycle generative adversarial network for low field MRI‐guided radiation therapy

“…Our strategy, however, not only improves the spatial resolution, but maps the rich features, such as the contrast and the detailed intensity distribution, between the real clinical images. Intuitively, both the spatial resolution and image contrast information are important for target contouring 54,55 . The results of the ablation studies indicate that only histogram‐matching or denoising itself results in very limited improvement in the target auto‐contouring accuracy, and the other network designs such as the Enhancement‐only CycleGAN and DE CycleGAN render out inferior performance over the proposed sequential network design.…”

“…Intuitively, both the spatial resolution and image contrast information are important for target contouring. 54,55 The results of the ablation studies indicate that only histogram-matching or denoising itself results in very limited improvement in the target auto-contouring accuracy, and the other network designs such as the Enhancement-only CycleGAN and DE CycleGAN render out inferior performance over the proposed sequential network design. The target auto-contouring performance on the images generated by the Enhancement-only CycleGAN was the closest to that on the images generated by the sequential Denoising and Enhancement CycleGAN, indicating that the Enhancement module which focuses on mapping between the 3D and 2D image information contributes most to the image quality improvement.…”