PACS-Integrated Tools for Peritumoral Edema Volumetrics Provide Additional Information to RANO-BM-Based Assessment of Lung Cancer Brain Metastases after Stereotactic Radiotherapy: A Pilot Study

Simple Summary Peritumoral edema can contribute significantly to the development of neurological symptoms in patients with brain metastases (METS), but the quantification of edema has historically been challenging. PACS-based peritumoral edema volume measurement is feasible, and this study suggests that tracking edema volume may facilitate better prediction of treatment outcome. This need is highlighted in our study as over half of the METS studied do not show congruent changes when comparing peritumoral edema volume changes to changes in diameter measurements of contrast-enhancing lesions in longitudinal assessment. Additionally, our results indicate that changes in peritumoral edema volume can pre-date tumor core size changes and could help with early identification of lesions progressing after treatment. Availability of PACS-integrated segmentation tools will allow the incorporation of edema and tumor core volumetrics into treatment response assessment in clinical practice.Abstract Stereotactic radiotherapy (SRT) is the standard of care treatment for brain metastases (METS) today. Nevertheless, there is limited understanding of how posttreatment lesional volumetric changes may assist prediction of lesional outcome. This is partly due to the paucity of volumetric segmentation tools. Edema alone can cause significant clinical symptoms and, therefore, needs independent study along with standard measurements of contrast-enhancing tumors. In this study, we aimed to compare volumetric changes of edema to RANO-BM-based measurements of contrast-enhancing lesion size. Patients with NSCLC METS >= 10 mm on post-contrast T1-weighted image and treated with SRT had measurements for up to seven follow-up scans using a PACS-integrated tool segmenting the peritumoral FLAIR hyperintense volume. Two-dimensional contrast-enhancing and volumetric edema changes were compared by creating treatment response curves. Fifty NSCLC METS were included in the study. The initial median peritumoral edema volume post-SRT relative to pre-SRT baseline was 37% (IQR 8-114%). Most of the lesions with edema volume reduction post-SRT experienced no increase in edema during the study. In over 50% of METS, the pattern of edema volume change was different than the pattern of contrast-enhancing lesion change at different timepoints, which was defined as incongruent. Lesions demonstrating incongruence at the first follow-up were more likely to progress subsequently. Therefore, edema assessment of METS post-SRT provides critical additional information to RANO-BM.