Figure 5. Comparison of fold increases of percent ORO-stained aortic area over sham-irradiated controls between high (x rays) and low dose-rate (gamma rays) groups.

Assuming a quality factor of 1 for x rays and gamma rays, a high radiation dose (6 Gy) would be equally efficient in enhancement of atherogenesis at both high and low dose rate. In contrast, a moderate dose (0.3 Gy) could significantly enhance atherogenesis only when delivered acutely (P = 0.0143, acute versus sham irradiated). When comparing fold increases, mice receiving 0.3 Gy acutely have enhanced atherogenesis compared with mice receiving the same dose as a chronic exposure (P = 0.0298).