2618 - Risk of Radiation Necrosis after Stereotactic Radiosurgery with and without Immune Checkpoint Inhibition in Patients with NSCLC Brain Metastases in Eloquent Locations

A. Thomas¹, M. Arshad², A. P. Sivananthan³, R. R. Katipally³, T. Pathmarajah⁴, P. P. Connell⁵, S. J. Chmura⁶, A. Juloori³, S. P. Pitroda³, and M. C. Korpics³; ¹University of Chicago, Chicago, IL, United States, ²Department of Radiation Oncology, Wayne State University School of Medicine, Detroit, MI, ³Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL, ⁴University of Chicago, Chicago, IL, ⁵Department of Radiation and Cellular Oncology, University of Chicago Medical Center, Chicago, IL, ⁶Department of Medicine, University of North Carolina, Chapel Hill, NC

Purpose/Objective(s): There is growing interest in combined stereotactic radiosurgery (SRS) with immune checkpoint inhibitors (ICI). Given the potential for significant clinical neurologic deterioration with injury to eloquent areas, understanding the impact of modern systemic therapy on risk of RN in eloquent locations is critical. In this exploratory analysis, we aimed to evaluate if SRS to brain metastases with concurrent immunotherapy increases the risk of RN in patients with NSCLC. We hypothesized that SRS and concurrent ICI are associated with a higher rate of RN in eloquent brain areas compared to metastases treated without concurrent ICI. Materials/

Methods: We retrospectively reviewed patients with NSCLC with brain metastases treated from 2015-2020 with SRS. Treatment was delivered using linac-based SRS at a single institution. Metastases were classified as eloquent or non-eloquent as per the Spetzler-Martin grading system. Diagnosis of RN was determined on review of radiologic and clinical findings. Concurrent ICI was defined as immunotherapy within 30 days prior, during, or following SRS. Analysis for RN was conducted on a metastasis-level basis. RN proportion rates between concurrent/non-concurrent ICI was evaluated using chi-square statistics in both eloquent and non-eloquent brain regions.
Results: 148 patients treated with SRS to 388 brain metastases were included with median age of 61 years and median follow up of 14 months. Most metastases were treated to 20 Gy in 1 fraction (72%) or 27 Gy in 3 fractions (18%). Concurrent ICI was used in 27% of patients with 48% receiving ICI prior to SRS. Of the metastases treated, 364 (94%) were classified as non-eloquent of which 27% were treated with concurrent ICI. The risk of RN was 8.99% and 9.28% for metastases treated without and with concurrent ICI, respectively for the non-eloquent brain metastases (p= 0.93). 29% of eloquent metastases were treated with concurrent ICI. The risk of RN for eloquent brain metastases was 17.65% vs 14.29% without vs with concurrent ICI (p = 0.84). The difference in RN incidence for metastases within eloquent locations and non-eloquent locations was not statistically significant (16.7% vs. 9.1%, p = 0.22)
Conclusion: Our findings demonstrate that SRS to eloquent brain metastases in combination with ICI is safe in patients with NSCLC. SRS, single or multi-fraction, with concurrent ICI is not associated with a higher risk of RN in either eloquent or non-eloquent brain regions among patients treated for NSCLC. Prospective studies are needed to validate these findings and to evaluate if these results can be generalized to other malignancies.