Assistant professor of radiation oncology Dr. Nathan Lee prepares an African lion named Tsavo for cancer treatment at the University of Tennessee’s Veterinary Medical Center in Knoxville, Tenn. The 11-year-old big cat is undergoing radiation treatment for a large tumor near its mouth. This was the fourth, and last, of Tsavo’s radiation treatments. At his first visit, the tumor measured 10 centimeters — about the size of an orange. At this one, it measured about 6 centimeters, smaller than a lime. With any luck, the radiation has killed the cancer’s DNA so that the tumor will continue to shrink over the next four weeks. If not, Tsavo will have surgery to remove it.