Volumetric analysis of radiographic changes after stereotactic radiosurgery for treatment of non-responding brain metastases.

Abstract

Purpose: Stereotactic radiosurgery (SRS) effectively treats brain metastases, yet some lesions ultimately require post-SRS surgery due to local failure. We examined whether the use of volumetric changes in FLAIR hyperintensity and/or necrosis in conjunction with enhancing volumetric changes after Gamma Knife SRS correlate with pathological outcome at subsequent surgery.

Methods: We queried our institutional database for patients who received first-time SRS for a single brain metastasis and later underwent surgical resection of the same lesion. Tumor volumes were measured manually before SRS and at 6 weeks, 3 months, and 6 months post-treatment. FLAIR:enhancing (FER) and enhancing:necrotic ratios were analyzed. Linear mixed-effects models assessed variables influencing volume trajectories; Pearson correlation examined associations with pathological outcome.

Results: Thirty-six patients met inclusion criteria. Mean enhancing volume changed - 28.5%, - 25.8%, and - 18.9% from baseline at 6 weeks, 3 months, and 6 months, respectively. Mean FLAIR volume changed - 16.9%, - 22.2%, and - 2.4% at the same intervals. Percent changes in FLAIR and enhancing volume correlated significantly at 6 weeks (p = 0.004) and 3 months (p < 0.001). FER trended differently between RN and recurrent tumor with patients who developed radiation necrosis (RN) having significantly lower FLAIR volumes at 6 weeks compared to those with recurrent tumor. Baseline lesion size, FLAIR volume, FER (all p < 0.001), primary cancer type, and sex (both p = 0.02) influenced FLAIR trajectories.

Conclusions: Perilesional edema and enhancement trajectories after SRS are variable but may help distinguish RN from recurrent tumor, particularly at early follow-up. Incorporation of automated edema volumetry should be considered in routine post-SRS surveillance.