Postoperative stereotactic radiosurgery for patients with resected brain metastases: a volumetric analysis.

Purpose: Postoperative stereotactic radiosurgery (SRS) is increasingly utilized following resection of brain metastases (BM); however, there are no volumetric data guiding dose selection. We performed a volumetric analysis to guide cavity SRS dosing for resected BM.Methods: 83 consecutive patients with gross total resection who underwent postoperative SRS to 90 cavities were identified. The 12 Gy isodose lines (V12_total) along with the volume of brain parenchyma receiving 12 Gy excluding cavity fluid, ventricular fluid, and calvarium (V12_parenchyma) were contoured. Local recurrence (LR) and radionecrosis (RN) were calculated using cumulative incidence rates. Multivariate analysis (MVA) and cutpoint analysis were conducted.Results: Median follow-up was 12.3 months; median dose was 16 Gy. 1- and 2-year cumulative incidence rates of LR were 7.9% and 11.0%. Radiation dose [hazard ratio (HR) 2.04, p = 0.002] was significantly associated with time to LR on MVA. 1- and 2-year cumulative incidence rates of RN were 2.6% and 5.5% respectively. MVA demonstrated increased risk of RN with a larger V12_parenchyma (HR 1.46, p = 0.0496). Cavities ≤ 10 cc showed a low 2-year RN risk (4.3%), but had a modest LR risk (13.9%). A radiation dose ≥ 18 Gy significantly improved LC (HR 4.79, p = 0.01).Conclusions: V12_parenchyma should be examined in postoperative SRS to assess RN risk. Cavities > 10 cc treated with 16 Gy achieved excellent LC and minimal RN at 2 years. Cavities ≤ 10 cc may be better treated with a dose ≥ 18 Gy to significantly improve LC given the low RN rate observed with 16 Gy. [ABSTRACT FROM AUTHOR]