Biopsy of enlarging lesions after stereotactic radiosurgery for brain metastases frequently reveals radiation necrosis.

Background: Stereotactic radiosurgery (SRS) offers excellent local control for brain metastases (BM) with low rates of toxicity. Radiation necrosis (RN) may occur after treatment and is challenging to distinguish from local recurrence (LR). We evaluated enlarging brain lesions following SRS that were subsequently biopsied to differentiate RN versus LR.

Methods: This study reviewed patients receiving SRS for BM between 2008 and 2012 who underwent a biopsy for suspicion of RN versus LR on MRI. Data collection included demographics, radiation parameters, imaging findings, and post-biopsy pathology. Kaplan-Meier methods determined overall survival. Fisher's exact test assessed for association between lesion biopsy result and variables of interest.

Results: Thirty-four patients with 35 biopsied BM were included. Lesions were biopsied a median of 8.8 months after SRS. Most patients had primary lung cancer (11; 31.4%). Eleven (31.4%) biopsies were positive for LR and 24 (68.6%) showed RN only. Median overall survival was longer for patients with RN (31.0 mo) than for patients with LR (14.5 mo; P = 0.135). Time from SRS to biopsy was significantly different between RN and LR groups; 10 lesions (52.5%) biopsied ≤9 months after SRS showed LR, whereas 1 lesion (6.3%) biopsied >9 months after SRS showed LR (P = 0.004). For 16 (65.7%) lesions, management was changed or directed by the biopsy results.

Conclusions: Stereotactic biopsy for accessible enlarging lesions after SRS appears diagnostically valuable in patients with few lesions and changes clinical management. RN should be suspected in patients with an enlarging lesion more than 9 months post-SRS.