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ABSTRACT
There is a growing interest in the use of proton therapy for the treatment of many cancers. With its unique dose-distribution properties, proton therapy has the potential to improve the therapeutic ratio of prostate radiation by allowing for an increase in dose without a substantial increase in side effects. While much evidence supports this notion in the context of many oncologic sites, only limited clinical data have compared protons to photons in prostate cancer. Therefore, the increasing enthusiasm for the use of protons in prostate cancer has aroused considerable concern. Some have questioned its ability to limit morbidity, and others have questioned its value relative to the cost. In addition, theoretical concerns have been raised about a potential additional risk for secondary malignancies. In this article, we review the current status of the evidence supporting the use of protons in prostate cancer and discuss the active controversies that surround this modality.
External-beam radiation is a highly effective curative treatment option for men with localized prostate cancer. [1,2] Over the past several decades, efforts have been made to improve the "therapeutic ratio" of radiation by increasing dose to improve cure rates without causing a substantial increase in side effects. Due to its potential to create superior dose distributions, proton therapy is considered by many to be the best available form of external radiation therapy. Here we will critically examine the evidence supporting the use of protons in the treatment of prostate cancer.
Theoretical Advantages and Disadvantages of Protons
Photon beams deposit their dose continuously as they traverse tissue so that the volume in the beam's path beyond the primary target also receives a measurable amount of falloff dose. Proton beams, on the other hand, deposit a large share of their dose in the "Bragg peak" over a relatively short distance close to the end of the particle's track in tissue. Beyond the Bragg peak, the position of which is determined by the beam energy, protons deliver almost no additional exit dose. This property has allowed proton beams to effectively spare critical structures that are located very close to the target, and thus, this modality has been used successfully in the treatment of certain optic tumors, central nervous system tumors, base-of-skull diseases, and pediatric...