Conformal proton beam radiation therapy for prostate cancer: concepts and clinical results

In contrast to x-rays, protons have a low entrance dose, a well-defined high-dose plateau (“Bragg peak”), and no exit dose beyond the target tissue. These properties make them ideal for treating localized cancers in areas surrounded by doselimiting normal structures. Their routine use required the creation of dedicated medical treatment centers which have only been in existence since the early 1990s. Protons have been successfully used in dose-escalation studies of organ-confined prostate cancer, with a recently published prospective randomized trial demonstrating an approximately 25% improvement in biochemical disease-free survival in the high-dose (79.2 Gy) arm, without a significant increase in moderate-to-severe treatment-related morbidity. Long-term treatment results from nonrandomized trials also demonstrate biochemical disease-free rates equivalent to other forms of therapy with minimal morbidity. Impending technical advances in proton beam treatment delivery (active beam scanning) will further enhance the dosimetric advantages of this unique form of radiation therapy.