Proton beam therapy continues to generate significant interest — and controversy — in prostate cancer. 

About 45 cancer centers in the US offer proton therapy to treat a variety of cancers, including prostate cancer. Some facilities market proton therapy for prostate cancer as having “remarkable promise and advantages over conventional therapy” along with “unparalleled precision” over photon-based techniques, which can help patients avoid bowel and urinary complications. 

The technology, however, faces ongoing debate about its role in prostate cancer. Despite the buzz, there is no randomized evidence demonstrating that proton therapy is superior to the current standard of care: intensity-modulated radiation therapy (IMRT). 

The core question has become: Is proton therapy for prostate cancer worth it?

Some would argue that it is.

“I think men can go and seek definitive treatment when it’s appropriate with a radiation oncologist and know that, whether it’s proton therapy or IMRT, it’s an excellent treatment option” for intermediate- or low-risk localized prostate cancer, Sameer Keole, MD, a radiation oncologist at the Mayo Clinic in Phoenix, told Medscape Medical News in 2024.

Patients are also increasingly expressing interest in proton therapy, according to Jonathan Tward, MD, PhD, a radiation oncologist and prostate specialist at Huntsman Cancer Institute in Salt Lake City. In his experience, about 20% of men ask for proton therapy at their initial consult, often after reading about it online, talking with a friend, or seeing an ad on social media. 

But Tward and other experts are skeptical. 

“I have to dispel lots of myths with prostate cancer. Proton therapy is one of them,” Tward said. 

“We’ve had a proton machine for years, and I have not put a single prostate cancer patient on it because the weight of the evidence shows no clear benefit,” he said. 

IMRT is more widely available than proton therapy, and there’s a cost concern: Proton therapy costs substantially more than IMRT, and it’s not always covered by insurance in the US. 

“Is it oversold to some degree?” asked James Gray, MD, medical director at Tennessee Oncology Proton Center in Nashville. 

“Yes,” he said.

The Case for Proton Therapy

Proton therapy delivers radiation using proton beams rather than X-rays, which are used in IMRT.

The main advantage of proton therapy is its precision. Protons deposit most of their energy directly in the tumor with little spillover into surrounding tissue, explained Kenneth Rosenzweig, MD, a radiation oncologist at the Mount Sinai School of Medicine and a board member of the New York Proton Center in New York City.

This precision is critical when tumors are near structures such as the heart, brain stem, or spinal cord, particularly in children where radiation exposure can affect the growth of bones and developing tissues. Proton therapy is the preferred radiation technique for certain pediatric cancers, although evidence of a clear advantage over modern IMRT continues to evolve.

When the first proton center opened in Loma Linda, California in 1990, proton therapy made sense for targeting prostate tumors buried deep in the pelvis, given the limitations of radiation delivery with earlier techniques. 

But since then, newer approaches like IMRT that target lesions with beams tightly shaped to the tumor have gotten so precise that “we’ve kind of erased” much of the benefit proton therapy once had for prostate cancer, Tward said. 

No Clear Advantage

A large body of research has explored whether proton therapy can improve toxicity and long-term outcomes for various cancer indications. But a key question has persisted: Does proton therapy outperform IMRT in prostate cancer? 

To answer this, researchers conducted the phase 3 PARTIQoL trial — the largest randomized trial to directly compare proton therapy with IMRT in men with prostate cancer. The trial randomized 450 men with low- to intermediate-risk localized tumors equally to either treatment. 

The analysis found no meaningful difference between the two approaches. Progression-free survival was about 93% at 5 years with both techniques. Researchers observed no difference in bowel function, with men in both groups experiencing only small drops from baseline, as well as no significant differences in urinary, sexual, and hormonal side effects.

The case for protons over IMRT “fell apart” in PARTIQoL, Tward said. “It’s hard to even argue with it” since the trial was so well done.

Other experts, however, had a more positive take on the findings. “This is a tremendous study [that] really shows us we have two great options, with equal results across the board for both control rates and toxicity rates,” Keole said in 2024, following the study publication.

Some experts speculate that an advantage could emerge for proton therapy with longer follow-up or in higher-risk populations, such as men with more advanced disease or those requiring treatment of regional lymph nodes.

But Tward doubts that will happen. Adverse events in prostate cancer largely depend on how much of the rectum and bladder are exposed to the highest radiation dose. “Protons can’t keep that high dose off the bladder or rectum any better than IMRT. They’re both so good that it doesn’t make a difference,” he said. 

In its latest guidance, published in January 2026, the National Comprehensive Cancer Network (NCCN) came to a similar conclusion: “No clear evidence supports a benefit or decrement to proton therapy over IMRT for either treatment efficacy or long-term toxicity,” the group stated.

A Cost Problem

In 2014, the Institute for Clinical and Economic Review (ICER) evaluated the effectiveness of proton therapy to treat a variety of cancers and concluded it was not cost-effective for prostate cancer. 

These cost concerns have not changed. Several analyses suggest proton therapy for prostate cancer can cost about twice as much as IMRT, though estimates can vary widely by setting, treatment protocol, and payer.

In its 2026 guidelines, the NCCN acknowledged the “potential financial toxicity” for patients undergoing proton therapy for prostate cancer. The NCCN noted that the higher costs of proton therapy “should be considered when tumor control and side effects appear similar between photon and proton beam therapy for prostate cancer, especially if these charges are incurred by the patient.”

In Tennessee, Gray has seen men pay tens of thousands of dollars out-of-pocket when insurance coverage is limited or denied. Although Medicare and private insurers may cover proton therapy when deemed medically necessary, coverage is often conditional and may be denied when conventional radiation is considered sufficient.

Another important consideration: The costs of building proton centers and the technology itself. For instance, standalone, single‑room proton therapy machines can cost up to $50 million, compared with roughly $5 million for a standard IMRT linear accelerator. 

ICER’s former president, Steven Pearson, MD, said the high costs could in part explain the push he’s observed toward proton therapy for prostate cancer.

When ICER was writing its 2014 report, “we heard from clinicians at proton centers that to be financially successful, they couldn’t just do proton beam on very rare pediatric and neurology tumors,” Pearson said. “They had to bring through more common cancers in order to make the investment in proton beam centers financially viable.” 

Prostate cancer was the leading candidate, he said. 

Rosenzweig remembers this too: “A lot of the proton centers were based on prostate treatments. That was their model.” 

If proton therapy had prevailed in PARTIQoL, he added, “A lot of people would have been happy and said, ‘See, our advanced technology does have a benefit.’” 

Given the high cost of proton centers and the fact that more are being built, Pearson anticipates ongoing buzz around proton therapy for prostate cancer, even with the PARTIQoL results. 

“The human mind has some cocky reasons to not trust new information that contradicts what you want, especially when it is even unconsciously linked to your business model,” Pearson said. “It’s like a huge battleship. Turning it around is difficult.”

For now, Rosenzweig believes proton therapy should be reserved for specialized situations in prostate cancer, such as retreatment.

Gray, meanwhile, anticipates that “eventually, we’ll see some advantages” for higher-risk patients, but in the short term, he agrees with Rosenzweig. 

Most men with prostate cancer “probably don’t get any particular benefit from proton therapy and should get treatment with standard radiation because that’s the best we can do,” Gray said.

M. Alexander Otto is a physician assistant with a master’s degree in medical science and a journalism degree from Newhouse. He is an award-winning medical journalist who worked for several major news outlets before joining Medscape. Email: aotto@medscape.net.