Proton therapy: the current status of the clinical evidences

Proton therapy has the potential advantages of better conformal planning and higher biological effect than photon therapy (X-ray) for targeting tumor tissues. While the energy of a photon passes through the target, the energy of a proton is deposited at a certain depth, which in turn is negligible beyond this stopping point (i.e., the "Bragg peak"). In addition, the proton beam has a 10% higher biological effect in the same dose than the photon beam. Recent technological advances have led to wide use of proton therapy in clinical practice. To date, more than 170,000 patients have received proton therapy. Although clinical experience with proton therapy is increasing now, only approximately 1% of all radiation therapy recipients receive proton therapy and prospective randomized studies involving large sample populations remain very limited yet. The aim of this review is to describe the physical and biological properties of proton therapy and discusses the clinical evidence supporting proton therapy in various disease sites.