Roadblock after roadblock

That’s how Dr. Billy W. Loo Jr. describes Stanford Medicine’s pursuit of proton therapy. The hospital, in the heart of Silicon Valley, chased the technology for years, but projects kept stalling. By 2016, it came closest to building a proton and carbon ion facility on Palo Alto VA land, with federal approvals in hand. Rising construction costs and a tech-driven real estate boom, however, shelved the project.

Simply put, proton therapy centers are enormous. Loo notes that a single large accelerator — the most expensive component — often feeds several treatment rooms, each with a gantry that rotates around the patient. The structure alone can rise three stories, with a footprint that can stretch to the size of a football field and more with the addition of clinical infrastructure. “You can imagine, given our location, what the building costs would be,” Loo quips.

One breakthrough came from startup Leo Cancer Care, which reimagined both the physics and the footprint. Rather than rotating a massive gantry around a patient lying flat, Leo’s system keeps the beam fixed while the patient sits upright and rotates. Combined with a compact accelerator from Mevion Medical Systems, “another major breakthrough,” Loo says, the required space drops from 29,000 square feet to roughly 1,700, a reduction of more than 90%. In the end, Stanford brought Mevion and Leo together, integrating the compact accelerator with the upright positioning system.

The reduced footprint let Stanford fit the system into an existing X-ray vault, fully integrating proton therapy into the cancer center. “Typically, bringing in proton therapy means building across town,” Loo says. “You separate facilities, need new nursing rooms and CT scanners, and split your staff. With this system, it’s fully integrated.”

March marks the start of patient treatments at Stanford. “We’re just getting started with proton therapy,” he says.

How proton therapy works
Unlike X-rays, which deposit radiation along their entire path through the body, protons stop at a specific depth. The result: reduced exposure to surrounding healthy tissue, an advantage particularly relevant for pediatric cancers and tumors near critical structures such as the brain and spinal cord.

Loo highlights a recent Lancet phase III trial led by Dr. Steven Frank at MD Anderson Cancer Center, showing five-year survival of 91% with proton therapy versus 81% for conventional radiation, and fewer long-term side effects in head and neck cancer patients. The key distinction, he notes, is how the treatment delivers radiation: unlike X-rays, which pass through tissue and affect everything along the path, protons stop at a specific depth, sparing surrounding healthy tissue.

Loo says this is especially critical for children, who “are particularly susceptible to the collateral effects of radiotherapy because their tissues are growing.” Any scenario where incidental doses reach surrounding tissue can have lasting effects, he adds.

Dr. Benjamin Durkee, medical director of the University of Wisconsin (UW) Health Proton Therapy Program at Eastpark Medical Center, notes that for select patients — especially children — investing in tissue-sparing technology is justified.

Not that proton therapy replaces conventional radiation. “Ninety-nine percent of our cancer patients are treated with X-rays, and that works very well,” Durkee says.

Dr. Shannon MacDonald, senior medical director at Southwest Florida Proton in Estero, highlights the importance of quality of life. With patients living longer, minimizing long-term side effects — particularly for younger patients — has become a critical measure of success. “Proton therapy’s ability to spare healthy tissues and organs allows patients to live a better life after cancer treatment,” she says.

That benefit, however, comes at a steep cost, Loo cautions. Proton machines are larger and more expensive than conventional radiotherapy equipment, and construction costs push the price even higher. By contrast, traditional radiotherapy is highly cost-effective, accounting for roughly 3% of total cancer care costs, while cancer drugs can approach 20%. “People don’t realize that,” Loo says. “Radiotherapy is a really tiny slice of the pie.”

The U.S. houses roughly 45 proton centers, leaving many patients more than a four-hour drive away. “Even here in the heart of Silicon Valley, it used to be an eight-hour trip to the nearest proton center — until now,” Loo adds.

MacDonald says Florida is also closing that gap. Southwest Florida Proton in Estero delivered its first treatment on December 30, 2025, becoming the first proton center on Florida’s west coast. The facility started with prostate cancer but quickly expanded to pediatric tumors, brain and skull base tumors, breast cancers, and head and neck cancers. Physicians across the region and beyond are now referring patients with a wide range of cancers, MacDonald says.

It’s welcome news for Florida patients, she says, but much of the U.S. remains a proton therapy treatment desert; particularly the West Coast, where the nearest center can be hours or even states away. “No one in this country should have to relocate for a month or two to access a treatment that could improve their outcomes,” she maintains.

To Durkee, the situation is more nuanced. Access to care is a nationwide challenge, he says, and getting top treatment often requires travel. “Proton therapy is no different.”

Still, cost and insurance coverage remain the biggest barriers, even as momentum builds.

Building the case
MacDonald says proton therapy’s reimbursement woes are easing as evidence shows it can reduce treatment complications. Once lacking in scientific evidence, the therapy is now supported for select patient populations, prompting a shift among insurers. “In recent years, more insurers have come to realize that proton therapy is indeed a treatment with the best outcomes for many patients.”

“Yes, it costs more than traditional radiation therapy,” MacDonald concedes. “But for certain patients, proton therapy provides superior results with fewer side effects and better long-term results.”

Better long-term outcomes for patients, yes, but not always for the finances of proton centers, Durkee adds. “On the business side, it’s not a clear money-winner. Some institutions end up in Chapter 11 despite various financing arrangements.” He urges facilities to assess how proton therapy fits into their overall strategy before investing.

UW, for its part, is testing a hybrid approach: one accelerator powers both a traditional gantry and the upright Marie by Leo Cancer Care, letting clinicians compare efficiency, patient comfort, and dosimetry. Like Stanford, the upright system treats patients in a movable chair, Durkee says, which could improve comfort, better align certain organs, and lower costs. The first patients are expected this spring.

“When we go to meetings nationally and internationally, people want to know which approach to invest in,” Durkee says. “We’ll be the only center in the world with both in-house, and we’ll be able to compare them head-to-head.”

One challenge, Durkee says, will be keeping the equipment running. “Our goal is 99% uptime. If it goes down, treatments would be delayed, and that’s costly and disruptive to patients.” For those awaiting proton therapy, even a brief interruption matters. To prevent that, UW has tasked two on-site engineers with keeping the beam precisely tuned and the system running smoothly.

Maintenance is reshaping how centers design proton therapy systems, Loo says. He argues that modular setups like Stanford’s offer a practical edge over massive, centralized builds.

“Every machine eventually needs upgrades or replacement,” he explains. In traditional facilities, downtime can halt everything. Modular systems allow centers to upgrade or replace one treatment machine at a time, instead of shutting down an entire multiroom facility. Loo says it keeps patient care moving in a way that feels “much more organic,” calling it “the new paradigm.”

Scaling up: The next frontier
The goal, Loo says, is not only to make proton therapy accessible, scalable, and integrated, but also to advance its clinical benefits. “From the start, we wanted to push the envelope and advance the field at Stanford,” he adds.

Removing the gantry and rotating patients more flexibly opens new possibilities, Loo explains. It allows more beam angles and greater control over dose distribution. “Think of a helix, not just an arc,” he says. Treatments can cover a longer area, giving clinicians more ways to sculpt the dose; something conventional therapy couldn’t achieve.

“Stanford is doing something really cool, and we’re also doing something really cool too: bringing the footprint down,” Durkee says. “That saves money for payers and makes protons more accessible nationally and internationally.”

MacDonald cautions that globally, the proton therapy sector still has a long way to go. Many countries — including Canada and Australia, both known for strong healthcare systems — still lack an operating proton center.

The U.S., however, shows no signs of slowing down. More than 100 proton therapy centers are expected to be under construction or under contract by 2030, Durkee projects — a sign of growing confidence in the technology. Hospitals increasingly view proton therapy not as a distant, high-cost outlier, but as part of a broader cancer strategy.

That growth comes with a caveat. “With that kind of expansion in a field that demands deep expertise, staffing shortages and knowledge gaps are inevitable,” Durkee says. “How do you hire enough physicians, physicists, dosimetrists, and therapists who actually know how to run it? It’s not like conventional radiation.”

It’s another roadblock proton therapy advocates hope the industry will overcome in its quest to deliver better patient outcomes. The challenge now isn’t whether the technology works, but how quickly — and wisely — it can scale.

Ensuring that expertise, maintenance, and infrastructure keep pace with expansion will determine whether patients truly benefit from proton therapy’s promise.