Proton Beam Therapy

Proton beam therapy exploits subatomic particles with mass rather than x-rays to deliver radiation dose. It has gained increasing interest primarily due to its advantageous physical property. When passing through tissue, a proton deposits increasing dose slowly until reaching a sharp increase (Bragg peak) at its maximum depth of penetration, eliminating the exit dose seen with photons. Initial studies in prostate cancer, used a lower energy proton beam applied as a conformal perineal boost after initial photon therapy. In the early 1990s, the first hospital-based facility was established with higher energy protons, allowing prostate treatment with the now traditional, opposed lateral beam arrangement. Several single institutions, population database, and other nonrandomized, retrospective, comparative effectiveness analyzes have been reported since, but there is no randomized evidence comparing protons to other curative prostate cancer therapies. As proton therapy becomes increasingly available at a number of centers, there is a call for high-level evidence to support its use in the setting of increased cost.