Brain metastasis growth on preradiosurgical magnetic resonance imaging

A previous analysis showed that brain metastases that are treated with frameless stereotactic radiation surgery (SRS) and planned with magnetic resonance imaging (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 preradiosurgical imaging.

We reviewed data from patients who were treated with fixed-frame SRS for brain metastases at our institution between 2010 and 2013 and had pretreatment diagnostic brain MRI and SRS-planning MRI scans available. Metastases were contoured on the pretreatment MRI scan and the day-of-treatment planning MRI scan for volumetric comparison. Growth rates were calculated. Serial volumetric contour expansions on the pretreatment MRI scans were used to determine the minimum margin necessary to encompass the entire metastasis on day of the SRS. LC was estimated by Kaplan-Meier method.

Among 411 brain metastases in 165 patients, the time between pretreatment and treatment MRI was associated with metastasis growth (P < .001) with a mean growth rate of 0.02 ml/day (95% confidence interval, 0.01-0.03) and a 1.35-fold volume increase at 14 days. Time between MRI scans was associated with the amount of margin that was needed to target the entire brain metastasis volume on the day of the SRS (P < .001), as were volume of metastasis on the pre-treatment MRI (P < .001) and melanoma histology (P < .001). LC was not associated with growth rate among patients who underwent fixed-frame SRS.

Time 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 that are treated with frameless SRS to account for growth between the planning MRI and SRS delivery.

In this study, we quantify brain metastasis growth over time by taking advantage of the availability of 2 pretreatment magnetic resonance imaging scans taken at 2 time points among patients treated with frame-fixed radiation surgery. We found that 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 that is needed to target the entire metastasis on the day of radiation surgery.