Fig. 4.

a Acute DNA damage response 30 min post-irradiation. Histology sections of fluorescent γ-H2AX and corresponding DAPI (nuclei) stained for tumor (MDA-MB-231-BR) and normal brain are shown. Images were taken with a fluorescence microscope (100X objective). Scale bar = 50 μm. b Quantification of the intensity of γ-H2AX staining versus radiation dose 30 min after radiotherapy. Tumors are plotted in green and normal brain tissue are plotted in blue. In irradiated normal brain tissue, the γ-H2AX intensity had a linear trend (R² = 0.78, p < 0.001). In tumors, γ-H2AX did not continue to increase at the dose of 24 Gy even though the γ-H2AX intensity is significantly different between irradiated and un-irradiated sides (p < 0.0001). Error bar indicates standard error of the mean. c Residual DNA damage response 11 days post-irradiation. Scale bar = 50 μm. (d) Quantification of the intensity of γ-H2AX staining for the various radiation dose 11 days after radiotherapy. In normal brain, γ-H2AX intensities returned to the background level. In irradiated tumors, γ-H2AX intensity was higher than both the background level and tumors in the irradiated side. ** = p ≤ 0.01, *** = p ≤ 0.001, and error bar indicates standard error of the mean