JohnAdler

In 2025, John Adler walked into the National Inventors Hall of Fame ceremony in Washington, D.C., and took a seat beside the inventors of GPS, the artificial heart valve, and the fiber optic cable. He was there for the CyberKnife - a robotic radiosurgery system he built at Stanford in the late 1980s that has since treated more than two million people worldwide. He then flew home to San Carlos, California, sat back down at his desk, and kept building.

That particular detail - the returning to work - tells you more about Adler than the Hall of Fame citation does. He founded Accuray in 1992 to commercialize CyberKnife, watched it go public on NASDAQ, and walked away from executive leadership to co-found a medical journal. Then in 2014, at an age when most inventors are content to collect the royalties, he founded ZAP Surgical Systems and started solving a problem the CyberKnife had left unsolved: most of the world still couldn't afford to use it.

The problem Adler kept returning to was access. The CyberKnife was a marvel of precision engineering - it delivered radiation from hundreds of angles, guided by real-time imaging, without bolting a frame to the patient's skull. But to use it, hospitals needed a radiation vault: a room with walls several feet of reinforced concrete, costing $3 million or more to construct before a single patient walked through the door. That constraint kept the technology out of community hospitals, outpatient clinics, and virtually every healthcare system in the developing world.

The ZAP-X was built to remove that constraint entirely. It is a self-shielded gyroscopic radiosurgery platform - the machine contains its own shielding, meaning it can be installed in a standard office suite without vault construction. The beam delivery system is gyroscopic: the radiation source arcs around the patient's head in a spherical pattern, approaching the tumor from thousands of unique angles while sparing surrounding tissue. The system received FDA clearance in September 2017. Today it operates at more than 30 sites globally, and in mid-2025 it crossed the milestone of 5,000 patients treated.

From Hazardville to the Karolinska

Adler grew up in Hazardville, Connecticut - a name that did nothing to diminish his ambitions - where he played Little League baseball and earned the Eagle Scout rank before heading to Harvard College to study biochemistry. He graduated in 1976, finished Harvard Medical School in 1980, and spent seven years in neurosurgical residency at Massachusetts General Hospital and Brigham and Women's Hospital.

The decisive turn came in 1986, when he traveled to Stockholm for a radiosurgery fellowship at the Karolinska Institute under Professor Lars Leksell - the Swedish neurosurgeon who had invented the Gamma Knife decades earlier. Leksell's philosophy was simple and radical: in the brain especially, surgery should be made noninvasive. Adler absorbed this principle and began asking what it would take to extend it further - to treat tumors anywhere in the brain, without the rigid frame Leksell's own device required, without bolting hardware to the skull.

Back at Stanford in 1987 as a new Assistant Professor, Adler began the collaboration that would produce the CyberKnife: pairing with computer scientists, roboticists, and radiation physicists to build a system that could track a tumor in real time using imaging, and deliver radiation with a robotic arm that followed the target wherever it moved. The patent was filed in 1990. Accuray was founded in 1992. The first clinical treatment happened at Stanford in 1994. The device that Leksell's student built would eventually rival - and in some markets surpass - the Gamma Knife that Leksell himself had invented.

The reluctant entrepreneur who kept founding companies

Stanford's 2018 profile of Adler called him "the reluctant entrepreneur." It is an accurate description - and a strange one for someone who has now co-founded three category-defining organizations. The CyberKnife led to Accuray (now NASDAQ: ARAY). The frustration with academic publishing led to Cureus in 2009, an open-access peer-reviewed medical journal that combined traditional editorial review with crowd-sourced expert evaluation, designed to give practicing clinicians a publication venue that the major journals chronically denied them. Springer Nature acquired Cureus in 2022.

The frustration with global access to radiosurgery led to ZAP Surgical. After closing a $78 million Series E round in November 2024 - bringing total funding to $159 million - ZAP Surgical is now deploying ZAP-X internationally. Recent installations include Institut Gustave Roussy in Paris, one of the world's leading cancer centers. In early 2025, ZAP Surgical announced a landmark clinical collaboration in Beijing: using the ZAP-X platform for radiomodulation therapy targeting treatment-resistant depression at Beijing Anding Hospital and the Chinese PLA General Hospital - an entirely new clinical application for a device designed around brain tumor treatment.

That goal - four million patients annually - is the number Adler returns to in interviews when asked what he is building toward. Global current radiosurgery volume is a fraction of that. Reaching it requires putting the technology in places where it does not currently exist, which requires the economics to work at a price point traditional vault-based systems cannot reach. The ZAP-X is the argument that the economics can work.

The scope of that ambition is characteristic. Adler's career is not a series of incrementally larger bets - it is a series of problems identified at the frontier of what medicine can do, followed by multi-year engineering collaborations to solve them. The pattern holds from the CyberKnife to Cureus to ZAP-X: find the constraint, build around it, hand it to the world, and find the next constraint.

He holds the Dorothy and TK Chan Professor of Neurosurgery Emeritus title at Stanford - awarded in 2007, a recognition that the institution where he spent his career building things is still willing to claim him as one of their own. He has published more than 300 peer-reviewed articles. He holds more than 20 US patents. He was recognized by the American Radium Society with its Janeway Medal for Lifetime Achievement in 2022. He grew up in a town called Hazardville.