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Purpose: To evaluate the longitudinal change of intra-tumoral susceptibility signal (ITSS) on high-resolution SWI as an adjunctive imaging tool to evaluate treatment response of brain metastasis following stereotactic radiosurgery. This approach will allow further stratification of the patients and guide clinical decision making.

Methods: An IRB approved retrospective study included 63 brain metastatic lesions within 49 patients (33 females and 16 males) who have undergone stereotactic radiosurgery with at least one follow-up MRI and available clinical data. The average age was 63.17 years (±1.48, ranged from 34-83 years). The longitudinal change in ITSS was categorized into 3 groups; increased, stable and decreased. The treatment response of each lesion was evaluated according to the longitudinal change in size, enhancement and susceptibility at the baseline and follow-up MRIs. Chi-square test was used to compare differences in categorical variables. Receiver operating characteristics (ROC) curve was used to evaluate the accuracy of including longitudinal change in ITSS with size and enhancement pattern in determining the treatment response following SRS.

Results: Our results demonstrated higher sensitivity and specificity when including longitudinal change in ITSS with size and enhancement for the evaluation of the treatment response of brain metastatic lesions treated with SRS. There was statistically significant difference between the different ITSS and enhancement patterns at baseline and follow-up MRIs (Wilcoxon Signed Ranks Test (p = .000, and .003) respectively. The multiparametric analysis of the longitudinal change in size, contrast enhancement, and ITSS in the evaluation of treatment response in the follow-up MRIs, showed that the sensitivity and specificity significantly improved (AUC 0.953).

Conclusion: High resolution SWI can contribute as an imaging biomarker with supplemental information for monitoring treatment and predicting treatment response. High resolution SWI can complement the standard contrast enhanced T1 images to evaluate treatment response with a multiparametric MRI approach.