Rates Of Radionecrosis In Re-Irradiation Of Brain Metastases Using Hypofractionated Stereotactic Radiotherapy

Abstract

Improved overall survival rates among brain metastases (BM) patients have led to higher rates of salvage re-irradiation in patients with local failure. Hypofractionated stereotactic regimens are an attractive option due to the possibility of lower rates of radionecrosis (RN). This study aims to determine the incidence and risk factors of RN following re-irradiation with hypofractionated stereotactic radiotherapy (hSRT) and compares the results to the incidence of RN following re-irradiation with single fraction SRS reported in literature. Retrospective chart review was conducted on patients from a single institution who received re-irradiation using hSRT to BMs that previously received stereotactic radiotherapy. Patients who received additional whole brain radiation (WBRT), prior to, or after stereotactic radiotherapy were included. Patient, tumor, treatment characteristics, and follow-up data were collected. MRI and pathology of any lesions resected post-radiotherapy were reviewed to assess for the development of RN and the response to treatment. RN was confirmed through MRI or by surgical resection. Associations between RN and target volume, as well as number of months between stereotactic treatments were examined using logistic regression. Association between RN and use of additional WBRT was examined using relative risk and chi-square tests. A total of 110 metastatic brain lesions in 90 patients received hSRT reirradiation between August 2010 and December 2019. 26.7% (n = 24) of patients also received additional WBRT. The most common histologies were breast (n = 31), NSCLC (n = 30), and melanoma (n = 29). The median volume of lesions was 12.25cc (IQR 4.97 – 25.07cc). The most common fractionation scheme was 25 Gy in 5 fractions (72 lesions). The incidence of local failure was 11.6% and 17.4% at 6 and 12 months, respectively. Incidence of symptomatic RN was 6.15% and 15% at 6 and 12 months, respectively. There was no statistically significant association between symptomatic RN at 12-months and radiation dose (p = 0.40), target volume (p = 0.96), use of additional WBRT (p = 0.74), or number of months between SRT (p = 0.99). The incidence of symptomatic RN following re-irradiation with hSRT is lower compared to re-irradiation with single fraction SRS as reported in literature. hSRT provides an alternative salvage option for treating local failure of BMs to reduce risk of RN while achieving local control.