Abstract
The unique acute effects of the large fractional doses that characterize stereotactic radiosurgery (SRS) or radiotherapy (SRT), specifically in terms of antitumor immune cellular processes, vascular damage, tumor necrosis, and apoptosis on brain metastasis have yet to be empirically demonstrated. The objective of this study is to provide the first in-human evaluation of the acute biological effects of SRS/SRT in resected brain metastasis. Tumor samples from patients who underwent dose-escalated preoperative SRT followed by resection with available non-irradiated primary tumor tissues were retrieved from our institutional biorepository. All primary tumors and irradiated metastases were evaluated for the following parameters: tumor necrosis, T-cells, natural killer cells, vessel density, vascular endothelial growth factor, and apoptotic factors. Twenty-two patients with irradiated and resected brain metastases and paired non-irradiated primary tumor samples met inclusion criteria. Patients underwent a median preoperative SRT dose of 18 Gy (Range: 15–20 Gy) in 1 fraction, with 3 patients receiving 27–30 Gy in 3–5 fractions, followed by resection within median interval of 67.8 h (R: 18.25–160.61 h). The rate of necrosis was significantly higher in irradiated brain metastases than non-irradiated primary tumors (p < 0.001). Decreases in all immunomodulatory cell populations were found in irradiated metastases compared to primary tumors: CD3 + (p = 0.003), CD4 + (p = 0.01), and CD8 + (p = 0.01). Pre-operative SRT is associated with acute effects such as increased tumor necrosis and differences in expression of immunomodulatory factors, an effect that does not appear to be time dependent, within the limited intervals explored within the context of this analysis.
Highlights
The unique acute effects of the large fractional doses that characterize stereotactic radiosurgery (SRS) or radiotherapy (SRT), in terms of antitumor immune cellular processes, vascular damage, tumor necrosis, and apoptosis on brain metastasis have yet to be empirically demonstrated
Our understanding of the biology of stereotactic radiotherapy (SRT) on brain metastasis and the effect of high fractional doses on immunomodulatory cell populations, endothelial cells and vascular networks, and DNA integrity is limited to preclinical s tudies[13] and anecdotal legacy reports[14], which have largely relied on obtaining tissue at much later time points
We hypothesized that metastasis treated with SRT would exhibit differences in tissue parameters associated with antitumor immune cellular processes, vascular damage, tumor necrosis, and apoptosis compared to non-irradiated primary tumors
Summary
The unique acute effects of the large fractional doses that characterize stereotactic radiosurgery (SRS) or radiotherapy (SRT), in terms of antitumor immune cellular processes, vascular damage, tumor necrosis, and apoptosis on brain metastasis have yet to be empirically demonstrated. Our understanding of the biology of stereotactic radiotherapy (SRT) on brain metastasis and the effect of high fractional doses on immunomodulatory cell populations, endothelial cells and vascular networks, and DNA integrity is limited to preclinical s tudies[13] and anecdotal legacy reports[14], which have largely relied on obtaining tissue at much later time points. Such reports suggest the presence of delayed histopathologic changes following SRS/SRT, but limited information exists regarding the occurrence of acute post-SRS/SRT effects. Given the variability in timing between SRT and surgery in our studied patient population, we hypothesized that some of these parameters might demonstrate dose or timing dependency
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