Brain metastases resection cavity radio—surgery based on T2-weighted MRI: technique assessment

Purpose: Stereotactic radiosurgery (SRS) is commonly performed after surgical resection of brain metastases to reduce the chance of local tumor recurrence while maintaining cognitive function. Target delineation in these cases is typically based off T1-weighted post-gadolinium MRI (T1Gd). In this study, we report outcomes for patients having postoperative SRS in which the planning target volume (PTV) was based on T2-weighted MRI (T2W). Methods: Sixty-two consecutive patients having single-fraction SRS after brain metastases resection were retrospectively reviewed. Excluded were patients with prior whole brain radiation therapy, multiple resection cavities, and small cell pathologies. Results: The median time from surgery to SRS was 11 days; 26 patients (42%) had SRS ≤ 7 days. The median PTV was 8.0 cm³; the median margin dose was 18 Gy. The crude rates of local tumor control (LC), leptomeningeal disease (LMD), distant brain recurrence (DBR), and radiation necrosis (RN) were 85%, 19%, 37%, and 2%, respectively. The 1-year LC, LMD, DBR, and RN rates were 88%, 25%, 36%, and 0%, respectively. No tumor or dosimetric factor was associated with LC. Sub-total tumor resection was a risk factor for LMD (HR 5.11, P = 0.003), whereas patients with multiple brain metastases had a greater risk of DBR (HR 2.88, P = 0.01). The median PTV was smaller compared to the median PTV based off the consensus guidelines utilizing T1Gd MRI (8.0 cm³ vs. 9.1 cm³, P = 0.004). Conclusion: T2W MRI provided accurate resection cavity delineation even in the early postoperative period and was associated with decreased PTV compared to T1Gd MRI in the majority of cases.