Proliferation index Px = Nt / N0;
where Nt is the cell number at different post-irradiation times and N0 is the number at the time of plating. Cells were fixed with ice-cold 80% ethanol and stored at 4°C for at-least 24 h before analyzing the DNA content by flow cytometry. Ethanol fixed cells were washed twice with PBS and incubated with RNAase-A (cat# 10109142001, Sigma, USA) for 45 minutes at 37°C. Cellular DNA was stained with propidium iodide (25 µg/mL) (0.1 x 106 cells/100µL of PBS) and incubated in dark at room temperature for 30 minutes. PI-stained cells were then subjected to flow cytometry with CytoflexS (Beckman Coulter, California, USA). All the data was acquired with CytExpert software and was provided with a cytometer. Acquired data were analyzed with the FlowJo_10.4 version. The percentages of cells in G0/G1-, S-, and G2+M phases were determined, after filtering for doublets and aggregates using the inbuilt software.