Physician-physicist partnership built first U.S. medical accelerator

Physicists at Stanford in the 1940s were consumed with the task of building a linear accelerator that would allow them to discover the mysteries of elusive atomic structures. But when Henry Kaplan, MD, became chair of the Department of Radiology in 1948, he thought that such technology might have another huge application: treating cancer with tumor-killing radiation.

A particle accelerator—which can be linear or circular—uses electric fields to propel charged particles to great energies. By slamming accelerated electrons into a target made of heavy metal, high-energy X-ray beams result, which Kaplan dreamed of harnessing to reach tumors deep in the body while sparing superficial tissue.

At the "100 years of radiology" symposium Saturday, participants will discuss, among other subjects, the unusual collaborations it took to make Kaplan's dream a reality.

Kaplan was not the only physician who saw the medical potential for linear accelerators, but he realized that he needed to work with physicists to pull it off. That was a big reason he chose to come to Stanford and shortly after he arrived, he began working with physics professor Edward Ginzton, PhD.

Together, the two scientists developed the first medical linear accelerator in the western hemisphere (the world's first was in London four years earlier. It was installed at Stanford-Lane hospital in San Francisco. The X-rays generated by this groundbreaking linear accelerator—which could be more accurately focused and could penetrate deeper than earlier radiation-generating machines—were first used in January 1956 to treat a boy suffering from a cancer of the eye, retinoblastoma.

After 16 years of patient treatments, the original accelerator was retired in 1972 and now resides at the Smithsonian Institution.

Today, Kaplan's insight works to the benefit of thousands of cancer patients worldwide who undergo radiation therapy generated by these machines. Almost a half-century after Kaplan treated the first patient with his linear accelerator, the medical center has six linear accelerators in use.

Scientists at Stanford continue to push the boundaries of the uses for newer versions of these machines. A specially designed linear accelerator called the Cyberknife was co-developed at Stanford and first used for patient therapy in 1994. It's a step forward in that it continually tracks tumors during treatment and zeros in accurately on targets smaller than 1 millimeter.

"The stride that this technology has made is that it opens up the feasibility of clinicians being able to deliver bigger doses in a shorter amount of time," said Diana Ho, the administrative director of Radiation Oncology Services. "Linear accelerators are not in real time. You have to image a patient ahead of time and hope they don't move or even breathe too much during treatment."

With real-time devices such as the Cyberknife and the new Trilogy accelerator, it is safe to give more radiation because doctors can better hit the intended target. Stanford currently has a number of clinical trials in progress investigating real-time radiotherapy for cancers. mcr