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Purpose: To investigate dose escalation for brain metastases (BM) subvolumes with low cerebral blood flow (CBF) using dose-painting technology based on MR 3D arterial spin labeling (3D-ASL) images.Methods: A total of 50 patients with single BM were selected for this study. CT and MR simulation images, including contrast-enhanced T1-weighted (T1W) images and CBF images, were obtained. The gross tumor volume (GTV) was determined by fusion of contrast-enhanced CT and T1W images, and this volume was divided into high- and low-perfusion areas according to the difference in CBF. Sub-volume with less than 25% of the maximum CBF was defined as hypoxic region GTVH which was settled for dose escalation. The planning target volume (PTV) and PTVH were calculated from the GTV and the GTVH, respectively. The PTVN was calculated by subtracting the PTVH from the PTV. Plan 1 was defined as the conventional plan with a prescription dose of 60 Gy for the PTV. Plan 2 and Plan 3, respectively, escalated the prescription dose for the PTVH to 72 Gy with and without the maximum dose constrained based on Plan 1. Dosimetric indices were compared among the three plans.Results: On average, the GTV volume was 34.53 cm3, and the GTVH volume was 16.95 cm3, accounting for 49.09% of the GTV. Compared to Plan 1, the D2%, D98% and Dmean values of the PTVH escalated by 20.50%, 19.32%, and 19.60%, respectively, in Plan 2 and by 24.05%, 6.77%, and 17.00%, respectively, in Plan 3 (all P<0.05). The doses administered in Plans 2 and 3 were 73.67±0.34 Gy and 72.37±0.61 Gy, respectively (both P<0.05). In Plans 2 and 3, respectively, the conformity index of PTVH was increased by 45.45% and 63.64%; meanwhile, the homogeneity index was sacrificed, increasing from 0.04 to 0.05 and 0.11 (all P<0.05). Plan 2 achieved better values of D98% and Dmean, as well as a smaller increase in the homogeneity index, than Plan 3. The doses received by organs at risk (OARs) did not significantly differ between the conventional plans and the boost plans (all P >0.05).Conclusions: Targeted dose escalation guided by the 3D-ASL-based CBF differences in BM effectively escalated the dose delivered to low-CBF subvolumes without increasing the dose to OARs. |
