It costs about $48,000 - at least twice as much as other prostate radiation treatments. Hospitals are rushing to build proton centers, and nine are operating now - sites include Philadelphia, Boston, Chicago, Houston, Jacksonville, Fla., and Loma Linda, Calif. Promoters often contend it is less likely to cause complications.
"There's no clear evidence that proton therapy is better" for prostate cancer, and the new results suggest it may cause more complications, said Ronald Chen, a radiation specialist at the University of North Carolina, Chapel Hill.
He led the study and will give results at a medical meeting in San Francisco later this week. They were discussed Tuesday in a telephone news conference sponsored by the American Society of Clinical Oncology and two other cancer groups.
Proton therapy uses proton particles instead of X-rays. In theory, it targets radiation more directly to tumors and spares healthy tissue, which should lead to fewer side effects. Its value is established for treating eye and certain pediatric tumors. But it often is marketed for prostate cancer, a far more common condition.
Researchers checked Medicare records on more than 12,000 men treated for early-stage prostate cancers from 2002 through 2007. Follow-up information was available for four years on average.
The federal Agency for Healthcare Research and Quality paid for the study, which included researchers from the National Cancer Institute. The government also is paying for a definitive study to compare proton therapy with other types.
It "clearly is a promising therapy," but it has not yet shown an advantage for treating prostate cancer, said Jason Efstathiou of Massachusetts General Hospital, who will lead the new study.
Early results from patients at his hospital suggests there are fewer complications in the first six months after proton therapy, but "maybe this is a short-term advantage" that disappears or does not occur at every hospital using it, he said.
Only a rigorous study will tell. It starts this summer and will give results in three to five years.