Hypoxic fractions in the experimental groups at day 8 assessed from pimonidazole immunohistochemistry of tumor tissue sections. Group mean and SEM are shown, with n = 8 per group. 3.5 mg/kg PL-DXR was administered 24 hours prior to RT. RT was delivered at a dose of 2 Gy/day for 5 consecutive days. Hypoxia was induced by clamping the tumor-bearing leg 5 minutes prior to and during RT. A significant difference (p < 0.05) to the control group is indicated with # (A). Representative images of pimonidazole-stained sections of an untreated tumor (B), and an irradiated tumor (C), respectively.