The risk of radiation necrosis following stereotactic radiosurgery with concurrent systemic therapies.

To investigate late toxicity among patients with newly-diagnosed brain metastases undergoing stereotactic radiosurgery (SRS) with concurrent systemic therapies with or without whole-brain radiation therapy (WBRT). Patients with newly-diagnosed brain metastasis who underwent SRS at a single tertiary-care institution from 1997 to 2015 were eligible for inclusion. The class and timing of all systemic therapies were collected for each patient. The primary outcome was the cumulative incidence of radiographic radiation necrosis (RN). Multivariable competing risks regression was used to adjust for confounding. During the study period, 1650 patients presented with 2843 intracranial metastases. Among these, 445 patients (27%) were treated with SRS and concurrent systemic therapy. Radiographic RN developed following treatment of 222 (8%) lesions, 120 (54%) of which were symptomatic. The 12-month cumulative incidences of RN among lesions treated with and without concurrent therapies were 6.6 and 5.3%, respectively (p = 0.14). Concurrent systemic therapy was associated with a significantly increased rate of RN among lesions treated with upfront SRS and WBRT (8.7 vs. 3.7%, p = 0.04). In particular, concurrent targeted therapies significantly increased the 12-month cumulative incidence of RN (8.8 vs. 5.3%, p < 0.01). Among these therapies, significantly increased rates of RN were observed with VEGFR tyrosine kinase inhibitors (TKIs) (14.3 vs. 6.6%, p = 0.04) and EGFR TKIs (15.6 vs. 6.0%, p = 0.04). Most classes of systemic therapies may be safely delivered concurrently with SRS in the management of newly-diagnosed brain metastases. However, the rate of radiographic RN is significantly increased with the addition of concurrent systemic therapies to SRS and WBRT.