Though it may seem counterintuitive, delivering ultrafast, high-intensity doses of radiation to tumors can actually reduce the toxicity to surrounding healthy cells, while still directing a potent anti-cancer effect towards the target. Scientists have documented this perplexing phenomenon—dubbed the FLASH radiotherapy effect—in both cell lines and animal models, but they have yet to confirm how or why it works. A new experimental platform that uses X-rays to investigate the FLASH effect brings science a step closer to clarifying its underlying mechanisms, laying the foundation for major strides in the field of radiation oncology.