Radiation for Prostate Cancer: Intensity Modulated Radiation Therapy versus Proton Beam

Abstract

To the Editor: This opposing views article highlights some of the fundamental differences in how radiation oncologists view the burgeoning (but not new) application of proton beam therapy (PBT) to treat prostate cancer. Hoppe et al articulate the respective arguments of the so-called proton and photon “camps” that have emerged within our specialty. These camps predictably fall along the lines of whether one practices at a center with PBT, and the financial differences between the 2 technologies are the key driver of the debate. Frankly none of us would be arguing against a product or device that delivers less unwanted radiation while maintaining (if not increasing) dose to the targetdif the cost is comparable to the alternatives. But it is different with prostate cancer. Excellent and affordable alternatives do exist, including brachytherapy, which is cheaper and more conformal than PBT and intensity modulated radiation therapy (IMRT). Those who use PBT should ask the important clinical questions, test them, and be given the time and resources to do so. Those who use only photon based techniques should, in turn, support these efforts, recognizing that IMRT was not held to the same standard when it was widely adopted over older and cheaper conventional techniques. Rather than recapitulating conflicting interpretations of the same methodologically flawed study, 1,2 as is done here, the radiation oncology community could look to patient level data on prospectively collected toxicity and quality of life outcomes for a disease as prevalent as prostate cancer. 3 In the spirit of incorporating patient reported outcomes Hoppe and Bryant suggest that the retrospectively observed 6% to 8% difference in bowel quality of life as measured by EPIC (Expanded Prostate Cancer Index Composite) is not only statistically significant, but also clinically relevant. 4 Sandler references the currently open randomized trial of IMRT vs proton therapy in prostate cancer, which has a primary end point of 2-year patient reported bowel quality of life (using EPIC). While this study will examine whether the retrospectively observed difference in bowel quality of life is statistically significant in a phase III setting, will it answer the question of whether it is clinically meaningful? If we do not see a difference for this specific end point, the trial will be negative. But will we truly feel that we answered the question of which is better? The media and payers certainly will, and frankly in many cases they have already decided that cheaper is better, period. The tide against PBT due to its generally greater costs is a foregone conclusion in many parts of the country but we have not afforded it the opportunity to prove itself. The institutional studies that have been reported to date generally all used passive scatter technique, an increasingly outdated and suboptimal form of proton beam delivery. We need to compare the “best” PBT techniques (ie pencil beam scanning) to the best IMRT. This comparison will require patience as centers work to responsibly deploy such capabilities. 5 While time is a rare luxury in the world of “do more with less,” it is necessary if we really want to test the various hypotheses described by the authors. Although there is multidirectional pressure to produce and report trial results quickly, doing so in prostate cancer can give a limited view of a disease with a long natural history involving patients who are at risk for late toxicities and relapses. As Sandler notes, the proton debate in prostate cancer carries great economic importance. But the comparative effectiveness challenges inherent to prostate cancer hopefully will not translate to a general disregard of PBT for other cancers. As a genitourinary radiation oncologist who uses PBT and photon based IMRT, I would like us to focus our efforts on investigating the promise of