Inside a cavernous hall at the Swiss-French border, the air hums with high voltage and possibility. From his perch on the wraparound observation deck, physicist Walter Wuensch surveys a multimillion-dollar array of accelerating cavities, klystrons, modulators, and pulse compressors—hardware being readied to drive a new generation of linear particle accelerators.

Wuensch has spent decades working with these machines to crack the deepest mysteries of the universe. Now he and his colleagues are aiming at a new target: cancer. Here at CERN (the European Organization for Nuclear Research) and other particle-physics labs, scientists and engineers are applying the tools of fundamental physics to develop a technique called FLASH radiotherapy that offers a radical and counterintuitive vision for treating the disease.

CERN researcher Walter Wuensch says the particle physics lab’s work on FLASH radiotherapy is “generating a lot of excitement.”CERN

Radiation therapy has been a cornerstone of cancer treatment since…