Outcomes following Definitive Single Fraction Stereotactic Radiosurgery for Larger Brain Metastases

Abstract

Limited data is available addressing the effectiveness of single fraction stereotactic radiosurgery (SRS) as a definitive treatment, without surgical resection, for larger brain metastases (LBM; largest diameter >2cm). We report the outcomes of patients treated for LBM with SRS at a single institution. We queried a prospectively maintained registry of 2059 BM treated with SRS between 2006 and 2017 to identify 280 LBMs. We analyzed demographics and treatment details descriptively. For survival analyses, we used the Kaplan-Meier method, with survival calculated from the date of LBM treatment (per lesion analyses). We performed univariate analyses using log-rank tests, and multivariate analyses with Cox regression models. We identified 255 patients with a median 1 LBM (range 1-3). Median largest diameter was 2.52 cm (range 2.01-4.64 cm); 56 LBM were >3 but <4 cm and 9 were >4 cm. Eighty-one percent of patients had an ECOG <2 and 75% of lesions had peritumoral edema. Prior to SRS for LBM(s), 15% underwent resection of other BM, 13% received SRS for smaller lesions, and 62% of patients received systemic therapy. Mean prescribed dose was 17 Gy (range 10-24 Gy) and target minimum dose 15.1 Gy (range 5.7-21.2 Gy). During SRS for LBM, 27% had concomitant lesions (<2 cm) treated with SRS and 53% had measurable extracranial disease. Median overall survival was 10 months (range 1-98 months). At a median follow up of 7 months (range 1-95 months), 63 lesions (22%) had failed locally (LF), with 24 of 63 (8% of all lesions) exhibiting synchronous intracranial distant failure. Local control (LC) for LBM was 88%, 76%, and 55% at 6-months, 1-year and 2-years, respectively. The median time to LF was 7 months (range 1 to 61 months). No disease (site of primary, size/ volume of LBM, concomitant disease, prior radiation) or treatment (prescribed dose, minimum/ maximum target dose, conformity indices) related factors tested were significantly associated with LF on univariate analysis. Radionecrosis (RN) developed in 39 lesions, with 1-year and 2-year rates of 18%, and 28%, respectively. Prescription dose, use of steroids during SRS, and V12 Gy were not associated with the rate of RN. Treatment details and LC rates according to selected variables are summarised in Table 1. Single fraction radiosurgery for LBM is associated with relatively poor rates of local control and relatively high rates of RN. Use of hypofractionated radiosurgery to deliver higher biologically effective doses more safely may expand the therapeutic index and result in improved outcomes.Abstract MO_24_2690; Table 1Factor1-year actuarial LCp valueLocation Supratentorial (223) Cerebellum (42) Brainstem (15)75% 75% 91%0.85Primary (three most common) Lung (106) Breast (60) Melanoma (34)69% 82% 65%0.18Prescribed dose 15 Gy or less (119) > 15 Gy-20 Gy (105) > 20 Gy (56)74% 75% 82%0.36Target volume 4 cc or less (119) More than 4 cc (161)78% 74%0.21 Open table in a new tab