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Proton therapy vs. external beam radiation for prostate cancer

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Eric Shinohara, MD, MSCI
Last Modified: August 7, 2008

Dear OncoLink "Ask The Experts,"
I am presently on hormonal therapy to shrink an enlarged prostate gland. Treatment plan is to follow with external beam radiation. I also have approval for treatment at the Loma Linda proton treatment center. Does data show conclusively that the proton treatment is a superior method to the external beam? Any commentary would be appreciated.  

Eric Shinohara, MD, MSCI Radiation Oncology Section Editor for OncoLink responds;

There are a number of proton therapy centers, such as those at Harvard and Loma Linda, that have been treating men with prostate cancer for several years and have published their results. The data from the majority of these studies suggest that there is reduced toxicity with proton therapy compared with historical data from men treated with photon based radiation therapy (3D conformal or IMRT). Loma Linda University reports fewer complications with higher numbers of patients being disease free by PSA blood test. Harvard randomized a small number of men to either proton or photon therapy and found that protons were "not significantly inferior" to X-rays, although the planning and delivery of the proton therapy for this study was fairly primitive by today’s standards.

Unfortunately, there have not been any large randomized trials which have compared proton with photon radiation. However, there have been a number of studies which have investigated whether protons can be used to escalate the dose of radiation given to the prostate. The largest of these studies, a combined study done by Harvard and Loma Linda, found that protons could be used, in addition to photon based therapy, to boost the prostate to higher doses safely. They also found that the higher doses appeared to be more effective than the lower doses of radiation. While this study was not a direct comparison of protons and photons it does suggest that higher prostate doses (which have been associated with better tumor control in other studies as well) can be safely delivered with proton therapy. Currently there are numerous ongoing studies to escalate the dose of radiation using protons that may, theoretically, improve survival in the future. Go wherever you feel most comfortable. There isn't a wrong answer, as current convention external beam treatment offers very good tumor control and is generally very well tolerated.