If you have prostate cancer, should you consider proton beam therapy? Dr. Jack Mostwin, Medical Editor of the Johns Hopkins Prostate Bulletin, offers his insights.
Q. Even though I have been told that the radical prostatectomy offers the best chance for a cure of my prostate cancer, I am put off by potential side effects from the surgery, erectile dysfunction in particular. At my prostate cancer support meeting last night, I spoke with a man who traveled to California last year to have his prostate cancer treated with proton beam radiation. Not only did he not suffer any side effects, but his doctor told him that he is cured of his prostate cancer. Is there any good evidence that this therapy is something I should consider as a viable treatment option?
From a Prostate Bulletin subscriber in Lake Havasu City, AZ
A. There are only a few centers offering proton beam radiotherapy in the United States: Loma Linda University in California pioneered the application of the technique to prostate cancer, and Harvard University has used it for neurosurgical problems as well as prostate cancer. Other proton beam centers in the United States include The Proton Therapy Center at the University of Texas M.D. Anderson Cancer Center in Houston, TX; the Midwest Proton Radiotherapy Institute in Bloomington, IN; and the University of Florida Proton Therapy Institute in Jacksonville, FL.
More precision is claimed for this form of beam than other forms. Because of reduced scatter of the proton beam, a higher dosage of radiation can be administered in a precise way to the tumor or targeted structure. Higher conformal beam radiation doses are thought to be more effective against cancer, and the reduced scatter of the proton beam will also reduce local side effects and reduce the possibilities of local recurrence.
I spoke to my friend and colleague, Dr. Theodore DeWeese, before completing the answer to this question. Dr. DeWeese is the director of Radiation Oncology at Hopkins, with extensive clinical and experimental work in radiation and prostate cancer. He had just returned from a meeting at which he discussed the very issues brought up in your question. Here are some of the things we discussed.
In the September 14, 2005 issue of the Journal of the American Medical Association, researchers from the Massachusetts General Hospital in Boston (Harvard System) reported on two groups of 393 (total) prostate cancer patients treated with conventional (70.2 Gy, pronounced “Gray”) or higher dose (79.2 Gy) therapy delivered by photon (a quantum of electromagnetic energy) and proton beam therapy. Five years after treatment, the proportion of men free of PSA recurrence was 61.4% after conventional therapy, 80.4% for high-dose therapy. The researchers did not report any difference on overall death rate from prostate cancer, and the difference in side effects was minimal.
However, rectal toxicity in higher-grade tumors undergoing high dose therapy was 17%, much higher than standard IMRT (intensity-modulated radiation therapy). The most recent studies comparing proton beam to IMRT have suggested comparable responses, but the questions about greater rectal toxicity in proton beam therapy leave some concerns still to be addressed.
