Early Imaging Characteristics Associated with Development of Future Brain Metastases in Patients Undergoing Stereotactic Radiosurgery

Abstract

<h3>Purpose/Objective(s)</h3> Brain MRIs are carefully reviewed during the process of stereotactic radiosurgery (SRS) planning to select targets with radiographic characteristics typical of brain metastases (BM). Some BMs, especially ones that are small, dural-based, appear similar to blood vessels or resemble microinfarcts, are difficult to definitively identify and may go untreated initially, only to become apparent on future imaging. We hypothesized that in patients receiving multiple courses of SRS, retrospective review of the initial planning MRI would reveal early evidence of lesions that would subsequently develop into metastases requiring SRS. <h3>Materials/Methods</h3> Patients undergoing two or more courses of SRS to BMs within a 6-month interval between 2016 and 2018 were included in this single-institution, retrospective study. Exclusion criteria included small cell histology or previous whole-brain radiation therapy. Brain MRIs from the initial treatment course were reviewed for the presence of a contrast enhancing lesion at the same location as a lesion treated in a subsequent course of SRS, which was classified as a "retrospectively identified metastasis" or RIM. <h3>Results</h3> Of the 683 patients who underwent 923 courses of SRS within the study period, 98 patients met inclusion criteria. There were 120 repeat courses of SRS, with 345 treated metastases in the subsequent course, 128 of which were RIMs. 48% were within 5mm of the dura: 12% were abutting blood vessels: 8% became symptomatic. 23% of subsequent courses consisted of metastases that were all identified as RIMs. <h3>Conclusion</h3> Radiographic evidence of lesions requiring future treatment was occasionally present on brain MRIs from prior SRS treatments. RIMs are typically small, often abut blood vessels and/or the dura, and rarely become symptomatic. In some patients undergoing SRS, RIMs alone were treated, suggesting that enhanced detection of RIMs could reduce the need for additional courses of SRS.