Razi Journal of Medical Sciences

Despite major progress in radiotherapy, exponential attenuation of initial photons due to the nature of their interaction with matter has remained as the most important challenge. Photons have no well-defined range and their doses are reduced exponentially. Therefore, tissues located before and after the tumors receive a significant dose. Today, new techniques based on proton and carbon charged particle beams have been developed in many radiotherapy centers around the world. These charged particles have a high density of ionization at the end of their ranges and most of their energy is released at the end of the path which appears as a peak with a sharp final descent called Bragg peak. Physical advantages for therapeutic purposes, such as well-defined range and the absence of exit dose have made charged particles as very good tool for delivering higher physical dose to the cancerous tissues while lower dose to surrounding healthy tissue. In addition to superior physical properties, the charged particles also possess favorable radiobiological properties which increase tumor control probability. However, some unwanted doses from secondary neutrons and photons found in areas far from the target tissue is an ongoing concern. Until the 1990s, treatment with proton beams was done only in research centers. Afterwards, hospital-based centers started using charged particles for clinical purposes. With increasing development of these centers, the overall cost of treatment is somewhat reduced and this trend is continuing with the construction of new centers