Hypoxic fraction determined with the regrowth delay assay

This study investigates the use of the regrowth delay assay for measurement of relative changes in hypoxic fraction after irradiation of the mouse RIF-1 tumor. After single local treatments ranging from 15-45 Gy, the time for growth delay to 3 times initial treatment volume increased linearly with dose for both unperturbed and clamped tumors. The slopes of the two growth delay versus dose curves were not statistically different, and the common slope indicated a D/sub o/ of 2.34 Gy. The horizontal dose difference between the two curves was 17.8 Gy with a 95% confidence interval of 14.7 to 20.9 Gy. This can be translated into 0.1% hypoxic cells (0.01 to 0.2%) Since these results are not inconsistent with the author's previous findings using the paired survival curve method (D/sub o/ = 2.54 Gy, HF = 1.1%), they have begun to evaluate the regrowth delay assay for determining changes with time in the hypoxic fraction after a fractionated schedule of 5 daily treatments of 5 Gy/day