In a finding likely to add fuel to the debate over

In a finding likely to add fuel to the debate over treatments for prostate cancer, proton-beam therapy provided no long-term benefit over traditional radiation despite far higher costs, according to a study of 30,000 Medicare beneficiaries published Thursday in the Journal of the National Cancer Institute.

Proton radiotherapy uses atomic particles to treat cancer rather than X-rays and theoretically can target tumors more precisely. But it requires a particle accelerator roughly the size of a football field that typically costs about $180 million.

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Proton-beam therapy is given at Massachusetts General Hospital.

Faith in the superiority of proton therapy by some has sparked an arms race among major medical centers. Ten proton accelerators are in operation in the U.S., and nine more are in development, including two by the Mayo Clinic and one by Memorial Sloan-Kettering Cancer Center and a consortium of other hospitals in New York City.

Ion Beam Applications IBAB.BT +3.60% of Belgium is the leading manufacturer. Others include Hitachi Ltd., 6501.TO -2.07% Varian Medical Systems Inc. VAR -0.67% and Mevion Medical Systems Inc.

Critics long have cited proton-beam therapy as a costly new technology with no proven advantage. Medicare pays over $32,000 per patient for proton therapy, compared with under $19,000 for radiation, according to the study.

Some 242,000 men in the U.S. are diagnosed with prostate cancer each year, and many oncologists and health-policy experts say the condition is overtreated. Most prostate cancers are slow-growing, so many men could avoid treatment and ultimately die of something else, experts say. But about 28,000 U.S. men die annually from aggressive prostate cancers that aren't treated in time, so most men opt to treat their cancers as a precaution, either with radiation or surgery.

Side effects of both can include incontinence and impotence, so researchers have sought potentially less-damaging therapies.

Proton-beam therapy has been the subject of heated debate among urologists, radiation oncologists and health-care cost analysts. The therapy isn't considered more effective than standard radiation, or surgery, at stopping the cancer. And the patient experience is about the same as with standard radiation: Patients typically have daily treatments, Monday through Friday, for approximately eight weeks. Each treatment is painless, and lasts about five minutes.

The main debate has been over side effects.

For the new study, researchers at Yale School of Medicine examined Medicare records of men aged 66 and over who had either proton therapy or intensity-modulated radiotherapy (IMRT)—the standard radiation for prostate cancer in recent years—in 2008 and 2009. The researchers found the incidence of problems with urinary function was slightly lower for proton radiotherapy at six months after treatment, but the difference disappeared by 12 months. There was no difference in the rate of other common side effects of radiation treatment for prostate cancer, including erectile dysfunction, hip fractures, gastrointestinal issues or musculoskeletal problems.

"It's not that proton radiation causes a lot of side effects," said James Yu, a radiation oncologist at Yale and the paper's lead author. "The takeaway point is that IMRT already had a low side-effect profile."

Another recent study, which asked men to rate their quality of life after various radiation treatments for prostate cancer, also found that proton beam conferred only a short-term benefit. After two to three months, the 94 men who underwent proton therapy had fewer gastrointestinal issues than the 153 who had IMRT or 123 who had an older form of radiation. But all three groups had very few GI issues after two years, according to the study presented last month at a meeting of the American Society for Radiation Oncology.

The findings put "the ball back in the court of the proton advocates to demonstrate that the benefit is there," said Dr. Yu.

Proponents of proton therapy say the beams can be programmed more precisely to the site of tumors and stop there, minimizing damage to surrounding tissue, whereas conventional X-rays deliver radiation to a wider swath of tissue.

"If the costs were the same, there would be no debate. Less radiation to healthy tissue is always better for the patient," said Leonard Arzt, executive director of the National Association for Proton Therapy, a nonprofit advocacy group.

He cited a study presented last month, led by M.D. Anderson Cancer Center, in which 1,090 men who had proton therapy reported virtually the same urinary and bowel function as 112 healthy men. The proton patients did report lower sexual function, but the authors said the two groups weren't comparable on that score given their ages and other factors.

Meantime, researchers at Massachusetts General Hospital and the University of Pennsylvania are enrolling patients in a randomized trial to directly compare proton therapy with IMRT for the first time. "Men need to know which is better, and cancer doctors need to be able to provide the evidence," said Justin Bekelman, a radiation oncology at Penn who is one of the principle investigators.

Write to Melinda Beck at HealthJournal@wsj.com