Source:Practical Radiation Oncology
Author(s): Michael A. Garcia, Mekhail Anwar, Yao Yu, Sai Duriseti, Bryce Merritt, Jean Nakamura, Christopher Hess, Philip V. Theodosopoulos, Michael M. McDermott, Penny K. Sneed, Steve E. Braunstein
BackgroundA previous analysis showed that brain metastases treated with frameless stereotactic radiosurgery (SRS) planned with MRI >14 days before SRS had worse local control (LC). To evaluate if worse LC may be due to unaccounted interval metastasis growth and radiosurgical marginal miss, we quantified growth before SRS on pre-radiosurgical imaging.MethodsWe reviewed patients treated with fixed-frame SRS for brain metastases at our institution from 2010-2013 who had pretreatment diagnostic brain MRI and SRS-planning MRI scans available. Metastases were contoured on the pretreatment MRI and the day-of-treatment planning MRI for volumetric comparison. Growth rates were calculated. Serial volumetric contour expansions on the pretreatment MRI were used to determine the minimum margin necessary to encompass the entire metastasis on day of SRS. LC was estimated by Kaplan-Meier method.ResultsAmong 411 brain metastases in 165 patients, time between pretreatment and treatment MRI was associated with metastasis growth (p<0.001) with mean growth rate of 0.02 ml/day (95% CI 0.01-0.03), and 1.35-fold volume increase at 14 days. Time between MRI scans was associated with the amount of margin needed to target the entire brain metastasis volume on day of SRS (p<0.001), as were volume of metastasis on the pretreatment MRI (p<0.001) and melanoma histology (p<0.001). LC was not associated with growth rate among fixed-frame SRS patients.ConclusionTime between pretreatment MRI and SRS is associated with brain metastasis growth, but LC is not compromised when patients receive fixed-frame SRS with same-day MRI planning. Margins may be needed for metastases treated by frameless SRS to account for growth between planning MRI and SRS delivery.In this study we quantify brain metastasis growth over time by taking advantage of the availability of two pre-treatment MRI scans taken at two time points among patients treated with frame-fixed radiosurgery. We found metastasis growth is associated with time, initial metastasis size, melanoma histology, and concurrent chemotherapy. Performing serial margin expansions demonstrated factors that are associated with the amount of margin needed to target the entire metastasis on day of radiosurgery.
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