When Nancy Tarbell entered radiation oncology, almost no one in the room looked like her. She was in a field dominated by men and went on to help transform how children with cancer were treated-pioneering approaches that made radiation more precise and helping spare young patients from some of its lifelong consequences. Radiant is the story of what it takes to be a change maker and what it costs. Dr. Tarbell rose to the highest levels of academic medicine at Harvard Medical School while caring for children with devastating illnesses, mentoring generations of physicians, and opening doors for women coming behind her. At home, she was raising a family with her husband, Jay, navigating the tensions between ambition, caregiving, love, and loss. Honest about sacrifice, grief, and the invisible labor of building something fairer, Radiant asks a larger question: What endures? Dr. Tarbell's answer lies not only in the patients she treated or the institutions she changed, but in the people she lifted along the way.