Optimal timing of initial surveillance MRI following treatment of brain metastases with stereotactic radiation: a comparison of six weeks versus standard twelve weeks

Summary: To elucidate whether short-term initial routine surveillance imaging following single-fraction stereotactic radiosurgery (SRS) or fractionated stereotactic radiosurgery (FSR) to brain metastases offers an advantage when compared to standard timeline. A retrospective analysis was performed on a cohort of patients with brain metastases treated with SRS or FSR at a single institution from 2017-2020, scheduled to undergo 6-week or 12-week initial surveillance MRI. The interval was based on the practice of different providers. Patients were grouped based on timing of MRI completion from the start of radiotherapy into 6-week or 12-week groups, using a threshold of less than or greater than 56 days, respectively. Outcome measures included detection of new or progressive lesions, presence of neurological symptoms, and whether imaging surveillance led to interventions including repeat short-interval MRI, additional radiation, surgical resection, addition of systemic therapy or enrollment in Hospice. Of 309 patients reviewed, 233 completed follow-up MRI scans, of whom 110 underwent 6-week MRI and 123 underwent 12-week MRI. Mean time to MRI was 42.8 days (SD 8 days) and 90.5 days (SD 23.9 days) (p 1 cm compared to the 12-week group (39% vs 23%, p = 0.02). Among patients with brain metastases treated with stereotactic radiation, patients undergoing 12-week initial surveillance MRI had a higher incidence of new or progressive disease compared to patients undergoing 6-week MRI, though not statistically significant. This translated to an increase in subsequent intervention observed following imaging at the 12-week time point. As the presence of neurological symptoms were similar between the groups, these data suggest that surveillance MRI at 12 weeks is acceptable and does not increase risk of development of a symptomatic metastasis relative to 6-week surveillance. Further studies may identify high-risk subgroups that would benefit from early surveillance. Emily Vonderhaar-Meister, MD, PhD (Presenting Author) - Johns Hopkins Hospital; Timothy Lin, MD, MBA (Co-Author) - MD Anderson Cancer Center; Anne Li, Student (Co-Author) - Johns Hopkins Undergraduate School; Kristin J. Redmond, MD (Co-Author) - Johns Hopkins University; Lawrence R. Kleinberg, MD (Co-Author) - Johns Hopkins University