RADI-11. Evaluating the Tissue Effects of Dose-escalated Pre-operative Stereotactic Radiotherapy for Resectable Brain Metastasis

Abstract Background Although the classic radiobiologic principles of radiotherapy are well understood, unique effects large fractional does that characterize stereotactic (SRT), specifically in terms antitumor immune cellular processes, vascular damage, tumor necrosis, and apoptosis on brain metastasis have yet to be adequately demonstrated. The objective this study is provide first in-human evaluation biological SRT resected metastasis. Methods All paired primary tumors metastases for patients who underwent dose-escalated preoperative followed by resection were evaluated necrosis using hematoxylin-eosin staining. T cells (CD3+, CD4+, CD8+), natural killer (CD56+), vessel density (CD31+), apoptotic factors (caspase-3) determined immunohistochemical analysis. Results Fifteen with from solid received a median dose 18 Gy (range: 15–18 Gy) 1 fraction, 2 receiving 27–30 3–5 fractions, within interval 90 hours (Range: 17.1–260 hours). rate was found significantly higher irradiated than non-irradiated samples (mean difference: 30.47, SD: 29.28, p=0.001). A decrease all immunomodulatory cell populations metastasis: CD3 difference -19.4, 31.7, p=0.03), CD4 (-10.0, 20, p=0.01), CD8 (-17.4, 22.1, p=0.008). While had numerically lower CD 31+, 56+, caspase-3 scores, not statistically significant. Time surgery no effect these parameters. Conclusions There complex interplay between tumor-associated radiobiological tissue. time associated increased differences may multifactorial, including concurrent corticosteroids or immunosuppressive SRT.