Proton Therapy for Prostate Cancer

Last Modified: August 30, 2008

Dear OncoLink "Ask The Experts,"

I am seriously considering Proton Therapy for my recently diagnosed Prostate cancer. I am 55 years old, my Gleason Score is 6 (3+3), and my PSA is 4.5. The information I have been reading everywhere is very vague regarding side effects. Terms like "minimal" side effects or "largely spares surrounding healthy tissue from potentially damaging effects" do not help! What about the numbers? What's the percent of patients who have changes in potency?

James M. Metz, MD, Editor-in-Chief of OncoLink and Assistant Professor of Radiation Oncology at the Hospital of the University of Pennsylvania, responds:

You are having a problem finding these numbers because they really do not exist yet. To date, there are no prospective randomized trials comparing proton therapy for prostate cancer to other treatments such as radical prostatectomy, IMRT, and standard 3D conformal radiation to understand the actual rates of tumor control and toxicity. Much of the discussion regarding reduced toxicity comes from the better dose distributions that protons can achieve compared to conventional radiation therapy. These dose distributions represent how well dose conforms to the target and how well it stays off of the normal organs, and are reflected in the radiation treatment plan. Because the dose is distributed more to the target and less to normal surrounding tissues, the natural expectation is that there will be less toxicity because less normal tissue is exposed to radiation. Most reports to date on proton therapy have been single institution retrospective studies. It is the sense from these institutions that there is an improvement in toxicity, but without randomized trials, it is difficult to say there is definitive proof. As proton therapy expands, there are more opportunities for these types of studies to be completed. In fact, as we move forward with our proton therapy center at the University of Pennsylvania which is currently under construction, we are committed to treating patients on clinical trials so that these important questions are answered.