Quantitative Changes in Intratumoral Habitats on MRI Correlate With Pathologic Response in Early-stage ER/PR+ HER2− Breast Cancer Treated With Preoperative Stereotactic Ablative Body Radiotherapy

Objective To quantitatively evaluate intratumoral habitats on dynamic contrast-enhanced (DCE) breast MRI to predict pathologic breast cancer response to stereotactic ablative body radiotherapy (SABR). Methods Participants underwent SABR treatment (28.5 Gy x3), baseline and post-SABR MRI, and breast-conserving surgery for ER/PR+ HER2− breast cancer. MRI analysis was performed on DCE T1-weighted images. MRI voxels were assigned eight habitats based on high (H) or low (L) maximum enhancement and the sequentially numbered dynamic sequence of maximum enhancement (H1−4, L1−4). MRI response was analyzed by percent tumor volume remaining (%VR = volume post-SABR/volume pre-SABR), and percent habitat makeup (%HM of habitat X = habitat X voxels/total voxels in the segmented volume). These were correlated with percent tumor bed cellularity (%TC) for pathologic response. Results Sixteen patients completed the trial. The %TC ranged 20%–80%. MRI %VR demonstrated strong correlations with %TC (Pearson R = 0.7–0.89). Pre-SABR tumor %HMs differed significantly from whole breasts (P = 0.005 to Conclusion In patients undergoing preoperative SABR treatment for ER/PR+ HER2− breast cancer, quantitative MRI habitat analysis of %VR and %HM change correlates with pathologic response.