Part 2 of six posts today about proton beam therapy. To start from the top, click here.
MD of Missouri on head-to-head comparisons
...I would suggest that, while proton beam therapy is excellent, so is brachytherapy (radioactive seed implants) done by an expert. I would welcome a head-to-head comparison between the two. I would bet that brachytherapy would be proven to provide similar excellent outcomes.
I suspect you may be right, MD. The bulk of the research suggests that, at least in terms of controlling the spread of localized prostate cancer, there are a variety of relatively good treatment options, including brachytherapy, external beam radiation, prostatectomy, and even watchful waiting. (A caveat: Doctors tell me that accurately comparing rates of side effects for these various treatments tends to be difficult. That's because many of the existing studies use slightly different criteria and that getting men to forthrightly report problems—particularly those related to sexual or urinary functioning—can be challenging given the sensitivity of the topic.) Nevertheless, there is relatively reliable preliminary evidence that suggests protons might cause somewhat lower rates of side effects.
I'm glad you mentioned the issue of "head-to-head comparisons." There's a very active debate going on among radiation oncologists over this very topic. Since there's a lack of randomized trials that directly compare proton beam therapy to, say, prostatectomy or brachytherapy, it's hard for doctors to say definitively whether protons are superior. Some radiation oncologists suggest that such studies can and should be done. Others disagree, arguing that such trials would be difficult to carry out because the technology advances so quickly—making studies outdated before they're even finished—and because getting patients to participate would be nearly impossible, if not unethical.
It's hard to predict whether randomized trials comparing proton beam therapy with other prostate treatments will ever be done. Some doctors say they already have plans to conduct such trials and will start soon, while others say openly that they expect such trials will never be completed.
(A note on study lingo: A randomized trial would require that patients agree to enter a trial in which they would be randomly assigned a treatment rather than choosing the one they prefer. This theoretically eliminates bias that might creep into men's assessment of side effects, as well as bias doctors might have in selecting particular patients for particular treatments.)