Objective: This study aimed to quantitatively analyze changes in blood perfusion in brain metastases (BMs), normal brain areas, and peritumor edema areas during radiotherapy (RT) using three-dimensional arterial spin labeling (3D-ASL) in BMs patients. The associations between perfusion changes in the three brain regions and RT dose gradients need to be established to provide a reference for individualized RT for BMs patients. Methods: MR-simulated location images of 26 BMs patients before and after RT were collected (including enhanced T1W images and perfusion maps of 3D-ASL; BMs tumor target areas were identified using enhanced T1W images and perfusion information was obtained from 3D-ASL). The high signal areas of BMs on contrast-enhanced T1W images, normal brain areas, and peritumor edema areas were defined as regions of interest (ROIs). The changes and correlation of the mean maximum cross-sectional area and mean maximum cerebral blood flow (CBF) in BMs tumor target areas before and after RT were assessed. Changes in CBF values in the three ROIs under different dose gradients were analyzed. Results: The mean maximum cross-sectional area and CBF values of BMs decreased by 26.46% and 29.64%, respectively, after RT (both P<0.05). The decreasing CBF rates in BMs at 30-40, 40-50, and >50 Gy dose gradients were 33.75%, 24.61%, and 27.55%, respectively (all P<0.05). In normal brain areas, under dose gradients of 0-10, 10-20, 20-30, 30-40, 40-50, and >50 Gy, the decreasing CBF rates after RT were 7.65%, 11.12%, 18.42%, 20.23%, 19.79%, and 17.89%, respectively (all P<0.05). The decreasing CBF rates in peritumor edema areas increased as dose gradients increased after RT. The perfusion changes in BMs after RT were more notable than those in normal brain areas and peritumor edema areas. Conclusions: Thus, 3D-ASL can objectively reflect changes in perfusion in BMs, normal brain areas, and peritumor edema areas. Based on changes in CBF, it is recommended to control the dose administered to normal brain areas to <30 Gy, whereas high doses

Objective:To evaluate the feasibility of magnetic resonance (MR) perfusion imaging for sub-region segmentation of brain metastases (BMs), and to provide reference for individualized radiotherapy based on blood flow perfusion heterogeneity in BMs patients.Methods:96 BMs patients were selected, including 55 patients with necrosis and 41 without necrosis. Each patient was scanned with CT simulation and MR simulation before radiotherapy. MIM Maestro 6.8.8 software was used to delineate the gross tumor volume (GTV) and necrosis GTV (GTV N) from enhanced T 1W images and T 2 Propeller images, respectively, and the solid GTV (GTV S) was obtained by the subtraction of the two. Then, the cerebral blood flow map of three dimensional arterial spin labeling (3D-ASL) was employed to determine the high perfused GTV (GTV H) and low perfused GTV (GTV L). The volume and proportion of sub-regions were counted and compared between two groups and the correlation of each sub-region was analyzed. Results:The volume of GTV in the necrosis and non-necrosis groups was 19.56 and 7.34 cm 3, respectively. Besides, the AUC of the ROC between GTV volume and necrosis was 0.749. In the necrosis group, the ratio of GTV N, GTV S, GTV H and GTV L to GTV was 20.47%, 79.53%, 33.03% and 46.50%, respectively (all P<0.05). Among them, the r value between GTV S and GTV was 0.963, 0.849 for GTV L and GTV, and 0.840 for GTV L and GTV S, significantly higher than 0.683 for GTV H and GTV and 0.764 for GTV H and GTV S (all P<0.05). In the non-necrosis group, the ratio of GTV H to GTV was higher than that in the necrosis group (58.95% vs. 33.03%, P<0.05). In addition, the ratio of GTV L to GTV was slightly lower than that in the necrosis group (41.05% vs. 46.50%, P>0.05). The r value between GTV H and GTV was 0.776, significantly higher than 0.574 between GTV L and GTV ( P<0.05). Conclusion:MR-3D-ASL can quantitatively analyze the heterogeneous blood perfusion of BMs, which could guide the sub-region segmentation and local dose escalation of tumors.