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

PurposePostoperative 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.Methods83 consecutive patients with gross total resection who underwent postoperative SRS to 90 cavities were identified. The 12Gy isodose lines (V12(total)) along with the volume of brain parenchyma receiving 12Gy 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.ResultsMedian follow-up was 12.3months; median dose was 16Gy. 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). Cavities10cc showed a low 2-year RN risk (4.3%), but had a modest LR risk (13.9%). A radiation dose18Gy significantly improved LC (HR 4.79, p=0.01).ConclusionsV12(parenchyma) should be examined in postoperative SRS to assess RN risk. Cavities>10cc treated with 16Gy achieved excellent LC and minimal RN at 2years. Cavities10cc may be better treated with a dose18Gy to significantly improve LC given the low RN rate observed with 16Gy.