Prostate Cancer External Beam Radiation: IMRT Beats 3D, Proton Beam
By Daniel J. DeNoon
WebMD Health News
Reviewed by Laura J. Martin, MD
April 16, 2012 -- The most popular form of radiation therapy for prostate cancer may also be the best, a new comparison study finds.
Nearly all men with prostatecancer who opt for external beam radiation get a treatment called intensity-modulated radiation therapy or IMRT. IMRT has almost entirely replaced another type of radiation treatment called 3D conformational therapy -- even though it's much more expensive, with little head-to-head evidence showing it works better.
And there's an even newer and even more expensive prostate cancer treatment: proton beam therapy. More and more medical centers are spending hundreds of millions of dollars to build new proton beam therapy centers.
Which treatment really offers a man the best chance of a prostate cancer cure with the fewest side effects? IMRT, according to Ronald C. Chen, MD, MPH, and colleagues at the University of North Carolina at Chapel Hill.
"For prostate cancer in this country, we have completely adopted IMRT," Chen tells WebMD. "I don't see anybody going back to 3D therapy. And thankfully, our study does show it is better in terms of cancer control and reducing long-term side effects. So IMRT is here to stay."
Chen's team didn't conduct a clinical trial. Instead, they compared results for similar Medicare patients who underwent IMRT, 3D conformational therapy, or proton beam therapy for prostate cancer. The data came from Medicare-linked records from the huge U.S. Surveillance Epidemiology and End Results (SEER) database.
The study analyzed data from 6,666 men treated with IMRT, 6,310 men treated with 3D conformational therapy, and 684 men treated with proton beam therapy.
- Men treated with IMRT were 19% less likely to need additional cancer treatment compared to men treated with 3D conformational therapy.
- Men treated with IMRT were 12% more likely to suffer erectile dysfunction than were men treated with 3D conformational therapy.
- Men treated with IMRT were 22% less likely to be diagnosed with hip fractures and 9% less likely to have gastrointestinal problems than were men treated with 3D conformational therapy.
- There was no difference in the need for additional cancer treatment between men treated with IMRT and those treated with proton beam therapy.
- Men treated with IMRT were 34% less likely to suffer gastrointestinal events than were men treated with proton beam therapy.
"The use of IMRT has skyrocketed in the past 10 years and it's good to see that this study affirms the use of IMRT to reduce side effects and to reduce the risk of additional therapy," Louis Potters, MD, chair of radiation medicine at North Shore University Hospital, Manhasset, N.Y., tells WebMD.
Potters, who was not involved in the Chen study, says that IMRT costs more than 3D radiation, and that the new findings "validate" the procedure.
Proton Beam Therapy vs. IMRT for Prostate Cancer
But what about proton beam therapy, which costs even more than IMRT -- but which did no better in the Chen study?
"This is not to say that at the end of the day, proton beam radiation is not right for prostate cancer," Potters says. "It's just we need to do additional study of it. And given the rate of construction of proton machines on a national level, the data should be more forthcoming to show whether it's worth the expense for prostate cancer."
Chen notes that doctors switched from 3D conformational therapy to IMRT even before there was hard data to show it might be better. As more and more medical centers build proton beam facilities, he suggests that doctors might again switch to the next new thing.
"We are saying, 'Wait a minute, let's compare outcomes before we jump to a new therapy,'" Chen says. "I don't think this study prevents a prostate cancer patient from choosing proton beam therapy. But it does tell him to ask his doctor about showing him data on whether protons are better."
Much of the data that is available contradicts the Chen study, says Nancy Mendenhall, MD, medical director of the University of Florida Proton Therapy Institute and associate chair of the university's department of radiation oncology.
Mendenhall says the Chen study fails to collect important data, such as the doses radiation patients received, exactly how well their tumors responded to treatment, and exactly which toxicities the patients suffered.
She says that studies from proton therapy centers find far lower rates of side effects than the Chen study did.
"There is discordance between what is in the published proton therapy medical literature and this study, for which there is no explanation," Mendenhall says. "There is so much we don't understand here. ... We don't have the data we need for disease control and morbidity."
Not included in the Chen study was another effective form of radiation therapy for prostate cancer: brachytherapy, the implantation of radioactive seeds.
Potters recommends brachytherapy to his patients. "From a comparative perspective, this remains one of the mainstay options for prostate cancer," he says.
But Chen says brachytherapy is appropriate only for patients with early prostate cancer.
"So brachytherapy is not a fair comparison with the others because it can only be given to a limited number of patients," he says.
The Chen study appears in the April 18 issue of the Journal of the American Medical Association.
SOURCES: Sheets, N.C. Journal of the American Medical Association, April 18, 2012. Louis Potters, MD, FACR, chair, Department of Radiation Medicine at North Shore University Hospital, Manhasset and Long Island Jewish Medical Center in New Hyde Park, N.Y. Nancy Mendenhall, MD, associate chair, department of radiation oncology, and medical director, Proton Therapy Institute, University of Florida. Ronald C. Chen, MD, MPH, assistant professor of radiation oncology, University of North Carolina at Chapel Hill.
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