Extent of surrounding edema does not correlate with acute complications after radiosurgery for melanoma brain metastases.

To assess whether extent of surrounding edema correlates with acute adverse clinical outcomes within 3 months after stereotactic radiosurgery (SRS) for melanoma brain metastases (BM).Patients with melanoma BM treated with SRS were included in a single center retrospective analysis. A contrast-enhanced magnetic resonance image (MRI) brain was acquired on the day of treatment and used to calculate the volume of the largest lesion (the index BM) and total volume of all BM. Their corresponding volume of surrounding edema was defined based on the fluid attenuated inversion recovery (FLAIR) sequence. After SRS, MRI was performed every 3 months for at least 2 years if the patient remained well enough to do so. Adverse neurologic events after SRS were defined using common terminology criteria for adverse events (CTCAE) version 5.0. Multivariate regression analyses assessed for associations between BM size and edema at baseline with increasing edema and neurologic adverse events within 3 months after SRS.

Mean volume of the index BM reduced from 2.2 to 0.5 cm³ at 3 months after SRS (p = 0.03). Mean volume of edema surrounding the index BM was 6.4 cm³ at baseline, 10.2 cm³ at 3 months and 5.5 cm³ at 6 months. There were 7/43 (16%) patients that experienced an adverse neurological event within 3 months (attributable to any cause) and 4/43 (9%) were associated with an increase in BM edema. On univariate and multivariate analyses, there were no correlations between any baseline factors and volume of edema at 3 months. However, SRS dose delivered and systemic therapy use within 4 weeks of SRS both correlated with a reduction in edema surrounding the index BM.

A transient increase in mean volume of edema was apparent at 3 months after SRS. However, this resolved by 6 months and did not correlate with adverse events or dexamethasone requirement. Thus, the clinical significance is uncertain.