Proton therapy for prostate cancer
Although this is the most common use of proton therapy, controversy remains
Part 2 in a series
Part 2 in a series. The last issue of “CancerScope” discussed the research advances and financial challenges of proton therapy treatment. This issue will focus on the use of proton therapy to treat prostate cancer and the many questions about the treatment that medical research has not yet answered.
The majority of patients who undergo proton therapy are those with prostate cancer. The goal of proton therapy in these cases is not to have better disease control than standard radiation but to avoid long-term side effects, including the development of a second malignancy.
With x-rays, a low dose can spread through the entire pelvis, which can affect the rectum and bladder, notes James D. Cox, MD, head of the division of radiation oncology at The University of Texas M.D. Anderson Cancer Center in Houston, Texas. Although M. D. Anderson Cancer Center and other medical centers are examining quality-of-life studies for proton therapy and prostate cancer, clinical results concerning the therapy's effectiveness in reducing second malignancies after 5 to 15 years are not yet available.
Many patients with prostate cancer are savvy medical consumers who are self-referred and have heard about proton therapy through word-of-mouth. Groups for these patients were started at both Loma Linda University in Loma Linda, California (called Brotherhood of the Balloon, because a balloon is used to immobilize the prostate) and The University of Texas M. D. Anderson Cancer Center (called Proton Pals).
“They are really convinced,” Dr. Cox says. “Patients I personally have followed don't even have fatigue, but of course that's not very scientific. I couldn't possibly convince someone who's a skeptic.”
Research Still Inconclusive
Articles and letters to the editor in the Journal of Clinical Oncology (JCO) and other journals have called attention to the need for randomized clinical trials comparing proton therapy with conventional x-ray therapy, saying the promised clinical outcomes of proton therapy have not been demonstrated by such studies. Dr. Cox and Michael Goitein, PhD, professor emeritus of radiation oncology at Harvard Medical School in Boston. Massachusetts, responded with a JCO editorial arguing the advantages of proton therapy in terms of dose distribution and minimization of healthy tissue damage.1
“It is primarily for this reason that the practitioners of proton beam therapy have found it ethically unacceptable to conduct randomized clinical trials (RCT5) comparing protons with x-rays. Such comparison would not meet a central requirement for performing RCTs, namely that there be equipose between the arms of the trial,” they noted in the editorial.
However, in response to the editorial, a group of physicians from the University of Pennsylvania School of Medicine in Philadelphia, Pennsylvania, noted that randomized studies comparing protons versus photons can and should be performed.2
The majority of proton therapy patients are men with prostate cancer, many of whom have heard through research and word-of-mouth about the therapy's purported benefits.
Researchers do not yet have clinical data regarding whether proton therapy for prostate cancer reduces second malignancies and other long-term side effects after 5 to 15 years.
Some physicians call for randomized clinical trials comparing proton therapy with standard radiation therapy, but others say they do not feel comfortable conducting such trials.
Although proton therapy is usually covered by insurance companies, patients and physicians often have to appeal.
Still more types of targeted radiation therapies are already being offered, including pencil beam proton therapy and carbon ions.
“The enormous expenditures to build a proton center at the moment mean that during the next 5 to 10 years, there will be a relatively small number of facilities that have proton beam therapy,” the editorial stated. “The rest of the radiotherapeutic community will be interested in outcomes to see if they really need to obtain such technology. It is likely that well-designed clinical trials that randomly assign proton beam therapy to patients would be supported by the National Cancer Institute and possibly third- party payers themselves. To accrue the required numbers for such studies would probably require a concerted effort from virtually all the centers where proton beam therapy is available.”
Allan Pollack, MD, PhD, chair of radiation oncology at the University of Miami Miller School of Medicine in Miami, Florida, notes that in the past, many new technologies such as intensity-modulated radiation therapy were introduced without rigorous testing, and they usually translated into patient benefit. But those times have changed, and proton therapy presents new challenges.
“It's important that studies be done related to defining the role of protons for different sites,” he says, noting that the Obama administration is considering cost/benefit ratios when grappling with how new technology is introduced.
“Proton therapy is generally covered by insurance companies, although patients and treatment centers usually have to appeal,” Dr. Cox says. He adds that the cost differential for proton versus conventional radiation treatment is not as large as some people assume. The Medicare reimbursement rate for the most high-tech conventional radiation treatment for prostate cancer is approximately $30,000, whereas the rate for radical prostatectomy is $35,000. For proton therapy, it's $40,000, he says.
The Future of Proton Therapy
On the horizon, Dr. Cox and colleagues are working on a newer version of proton therapy called “pencil beam”: in which protons are actually painted into the size and shape of the tumor, which allows even greater precision and less damage to surrounding tissue. Still other centers in Japan and Europe have built facilities that are using carbon ions to generate more targeted, localized radiation—at double the cost of proton therapy.