Segmentation of Brain Metastases Using Background Layer Statistics (BLAST)

Abstract

BACKGROUND AND PURPOSE: Accurate segmentation of brain metastases is important for treatment planning and evaluating response. The aim of this study was to assess the performance of a semiautomated algorithm for brain metastases segmentation using Background Layer Statistics (BLAST). MATERIALS AND METHODS:Nineteen patients with 48 parenchymal and dural brain metastases were included. Segmentation was performed by 4 neuroradiologists and 1 radiation oncologist. K-means clustering was used to identify normal gray and white matter (background layer) in a 2D parameter space of signal intensities from postcontrast T2 FLAIR and T1 MPRAGE sequences. The background layer was subtracted and operator-defined thresholds were applied in parameter space to segment brain metastases. The remaining voxels were back-projected to visualize segmentations in image space and evaluated by the operators. Segmentation performance was measured by calculating the Dice-Sørensen coefficient and Hausdorff distance using ground truth segmentations made by the investigators. Contours derived from the segmentations were evaluated for clinical acceptance using a 5-point Likert scale. RESULTS:The median Dice-Sørensen coefficient was 0.82 for all brain metastases and 0.9 for brain metastases of $10 mm. The median Hausdorff distance was 1.4 mm. Excellent interreader agreement for brain metastases volumes was found with an intraclass correlation coefficient ¼ 0.9978. The median segmentation time was 2.8 minutes/metastasis. Forty-five contours (94%) had a Likert score of 4 or 5, indicating that the contours were acceptable for treatment, requiring no changes or minor edits. CONCLUSIONS:We show accurate and reproducible segmentation of brain metastases using BLAST and demonstrate its potential as a tool for radiation planning and evaluating treatment response.ABBREVIATIONS: BL ¼ background layer; BLAST ¼ Background Layer Statistics; BM ¼ brain metastases; DL ¼ deep learning; DSC ¼ Dice-Sørensen coefficient; HD ¼ Hausdorff distance; ICC ¼ intraclass correlation coefficient; IQR ¼ interquartile range; SRS ¼ stereotactic radiosurgery; TH ¼ threshold B rain metastases (BM) are diagnosed in up to 40% of patients with metastatic cancer and usually imply a short survival. 1 However, recent advances in the treatment of BM, with, for