Evaluation of energy deposition and secondary particle production in proton therapy of brain using a slab head phantom

Aim: Evaluation of energy deposition of protons in human brain and calculation of the secondary neutrons and photons produced by protons in proton therapy.

Background: Radiation therapy is one of the main methods of treating localized cancer tumors. The use of high energy proton beam in radiotherapy was proposed almost 60 years ago. In recent years, there has been a revival of interest in this subject in the context of radiation therapy. High energy protons suffer little angular deflection and have a well-defined penetration range, with a sharp increase in the energy loss at the end of their trajectories, namely the Bragg peak.

Materials and methods: A slab head phantom was used for the purpose of simulating proton therapy in brain tissue. In this study simulation was carried out using the Monte Carlo MCNPX code.

Results: By using mono energetic proton pencil beams, energy depositions in tissues, especially inside the brain, as well as estimating the neutron and photon production as a result of proton interactions in the body, together with their energy spectra, were calculated or obtained. The amount of energy escaped from the head by secondary neutrons and photons was determined.

Conclusions: It was found that for high energy proton beams the amount of escaped energy by neutrons is almost 10 times larger than that by photons. We estimated that at 110 MeV beam energy, the overall proton energy "leaked" from the head by secondary photons and neutrons to be around 1%.