FIG. 2.

Experimental timeline. At 8 weeks of age, groups of 12 bitransgenic CCSP-rtTA/Ki-ras mice were entered into the experiment. Half of the groups were given 500 μg/ml of doxycycline (DOX) in their drinking water; the other half were given normal drinking water. One week after initiating the DOX treatment, DOX or No DOX mice were lightly anesthetized and either sham-irradiated or irradiated once each week for 4 weeks with 5, 15 or 25 mGy of 100 kVp X rays from a clinical helical CT scanner. At 3, 6 and 9 months after the last weekly fraction, the lungs were imaged with CT (30 mGy/image) to noninvasively determine the size of the tumors. At 12 months of age the mice were euthanized, the lungs were excised, and the tumors were counted and sized.