Later, several studies explored the enhanced cytotoxicity of X-ray radiation when different modified GNPs were used [163-167]. Chitarani et al. reported that GNPs, with a diameter of 50 nm, showed the highest radio-sensitization enhancement factor (1.43 at 220 kVp) compared to GNPs of 14 and 74 nm (1.20 and 1.26, respectively) [168].